Introduction

The patella experiences large forces and variable kinematic patterns throughout flexion which could influence function and patient satisfaction after a total knee arthroplasty (TKA). Therefore, the objective of this study is to analyze in vivo patellar mechanism forces and kinematics throughout flexion to determine influencing factors that may lead to patient dissatisfaction.

Introduction

Many groups consider passive flexion to be a good indicator of postoperative success, to the point where this outcome directly influences certain outcome scores such as Knee Society Scores (KSS). However, it is alternatively believed that normal-like kinematics result in better TKA outcomes, and previous fluoroscopy studies have demonstrated that there are many parameters that affect weight-bearing range-of-motion. The objective of this study to investigate the correlations between patient-reported outcomes, passive flexion, and weight-bearing knee kinematics.

Introduction

Although surgical remedies tend to be the long-term solutions for patients with osteoarthritis (OA), many alternatives exist that offer the potential to slow progression, alleviate pain, and/or restore function. One such option is the unloader OA knee brace. The objective of this study was to assess the in vivo medial joint space narrowing with and without the brace during weight-bearing portion of gait.

Background

While posterior cruciate retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bi-cruciate retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. Various fluoroscopic studies have focused on determination of kinematics but haven't defined differentiators that affect motion patterns. This research study assesses the importance of the cruciate ligaments and femoral geometry for Bi-Cruciate Retaining (BCR) and Posterior Cruciate Retaining (PCR) TKAs having the same femoral component, compared to the normal knee.

Introduction

A common goal of total knee arthroplasty (TKA) is to restore normal knee kinematics. While substantial data is available on TKA kinematics, information regarding non-implanted knee kinematics is less well studied especially in larger patient populations. The objectives of this study were to determine normal femorotibial kinematics in a large number of non-implanted knees and to investigate parameters that yield higher knee flexion with weight-bearing activities.

Introduction

Current methodologies for designing and validating existing THA systems can be expensive and time-consuming. A validated mathematical model provides an alternative solution with immediate predictions of contact mechanics and an understanding of potential adverse effects. The objective of this study is to demonstrate the value of a validated forward solution mathematical model of the hip that can offer kinematic results similar to fluoroscopy and forces similar to telemetric implants.

Introduction

Forward solution joint models (FSMs) can be powerful tools, leading to fast and cost-efficient simulation revealing in vivo mechanics that can be used to predict implant longevity. Unlike most joint analysis methods, mathematical modeling allows for nearly instantaneous evaluations, yielding more rapid surgical technique and implant design iterations as well as earlier insight into the follow-up outcomes used to better assess potential success. The current knee FSM has been developed to analyze both the kinematics and kinetics of commercial TKA designs as well as novel implant designs.

Introduction

Conventional hip radiographs allow surgeons, during preoperative planning, to make important decisions. Size and location of implants are routinely measured by overlaying schematics of the implanted components onto preoperative radiographs. Most currently available planning tools are in two-dimensions (2D), using X-ray images and 2D templates of the implants. Determination of the ideal component size requires two radiographic views of the femur: the anterior-posterior (AP) and the lateral direction. The surgeon uses this information to determine component sizes. Even though this approach has been used for many years leading to very good results, this manual process potentially carries multiple shortcomings. The biggest issue with the AP X-ray image is the fact that it is 2D in nature while the measurement's objective is to obtain three-dimensional (3D) parameters.

Introduction

Traditionally, conventional radiographs of the hip are used to assist surgeons during the preoperative planning process, and these processes generally involve two-dimensional X-ray images with implant templates. Unfortunately, while this technique has been used for many years, it is very manual and can lead to inaccurate fits, such as “good” fits in the frontal view but misalignment in the sagittal view. In order to overcome such shortcomings, it is necessary to fully describe the morphology of the femur in three dimensions, therefore allowing the surgeon to successfully view and fit the components from all possible angles.

Introduction

Untreated hip osteoarthritis is a debilitating condition leading to pain, bone deformation, and limited range of motion. Unfortunately, studies have not been conducted under in vivo conditions to determine progressive kinematics variations to a hip joint from normal to pre-operative and post-operative THA conditions. Therefore, the objective was this study was to quantify normal and degenerative hip kinematics, compared to post-operative hip kinematics.

Introduction

Numerous fluoroscopic studies have been conducted to investigate kinematic variabilities of total knee arthroplasty (TKA). In those studies, subjects having a posterior stabilized (PS) TKA experience greater weightbearing knee flexion and posterior femoral rollback of the lateral condyle. In those same studies, subjects did experience a high incidence of variable medial condyle motion and reverse axial rotation, especially occurring when the cam engaged the post. More recently, a PS TKA was designed to accommodate both gender and ethnicity. Therefore, the objective of this study was to assess in vivo kinematics for subjects having this TKA type to determine if subjects having this PS TKA experienced more optimal knee kinematics.

Introduction

Obtaining accurate anatomical landmarks may lead to a better morphologic understanding, but this is challenging due to the variation of bony geometries. A manual approach, non-ideal for surgeons or engineers, requires a CT or MRI scan, and landmarks must be chosen based on the 3D representation of the scanned data. Ideally, anatomical landmarking is achieved using either a statistical shape model or template matching. Statistical modeling approaches require multitude of training data to capture population variation. Prediction of anatomical landmarks through template matching techniques has also been extensively investigated. These techniques are based on the minimization or maximization of an objective or cost function. As is the nature of non-rigid algorithms, these techniques can fail in the local maxima if the template and new bone models have noise or outliers. Therefore, a combination of rigid and non-rigid registration techniques is needed, in order to obtain accurate anatomical landmarks and improve the prediction process.

Introduction

Previous research defines the existence of a “safe zone” (SZ) pertaining to acetabular cup implantation during total hip arthroplasty (THA). It is believed that if the cup is implanted at 40°±10° inclination and 15°±10° anteversion, risk of dislocation is reduced. However, recent studies have documented that even when the acetabular cup is placed within the SZ, high incidence dislocation and instability remains due to the combination of patient-specific configuration, cup diameter, head size, and surgical approach. The SZ only investigates the angular orientation of the cup, ignoring translational location. Translational location of the cup can cause a mismatch between anatomical hip center and implanted cup center, which has not been widely explored.

Summary

The mathematical model has proven to be highly accurate in measuring leg length before and after surgery to determine how leg length effects hip joint mechanics.

Introduction

Many fluoroscopic studies on total knee arthroplasty (TKA) have identified kinematic variabilities compared to the normal knee, with many subjects experiencing paradoxical motion patterns. The intent of this study was to investigate the results of a newly designed PCR TKA to determine kinematic variabilities and assess these kinematic patterns with those previously documented for the normal knee.

Introduction

Diagnosis of osteoarthritis relies primarily on image-based analyses. X-ray, CT, and MRI can be used to evaluate various features associated with OA including joint space narrowing, deformity, articular cartilage integrity, and other joint parameters. While effective, these exams are costly, may expose the patient to ionizing radiation, and are often conducted under passive, non-weightbearing conditions. A supplemental form of analysis utilizing vibroarthrographic (VAG) signals provides an alternative that is safer and more cost-effective for the patient. The objective of this study is to correlate the kinematic patterns of normal, diseased (pre-operative), and implanted (post-operative) hip subjects to their VAG signals that were collected and to more specifically, determine if a correlation exists between femoral head center displacement and vibration signal features.

Background

Although early TKA designs were symmetrical, during the past two decades TKA have been designed to include asymmetry, pertaining to either the trochlear groove, femoral condylar shapes or the tibial component. More recently, a new TKA was designed to include symmetry in all areas of the design, in the hopes of reducing design and inventory costs.

Introduction

At present, orthopaedic surgeons utilize either CT, MRI or X-ray for imaging a joint. Unfortunately, CT and MRI are quite expensive, non weight-bearing and the orthopaedic surgeon does not receive revenue for these procedures. Although x-rays are cheaper, similar to CT scans, patients incur radiation. Also, all three of these imaging modalities are static. More recently, a new ultrasound technology has been developed that will allow a surgeon to image their patients in 3D. The objective of this study is to highlight the new opportunity for orthopaedic surgeons to use 3D ultrasound as alternative to CT, MRI and X-rays.

During the preoperative examination, surgeons determine whether a patient, with a degenerative hip, is a candidate for total hip arthroplasty (THA). Although research studies have been conducted to investigate in vivo kinematics of degenerative hips using fluoroscopy, surgeons do not have assessment tools they can use in their practice to further understand patient assessment. Ideally, if a surgeon could have a theoretical tool that efficiently allows for predictive post-operative assessment after virtual surgery and implantation, they would have a better understanding of joint conditions before surgery.

The objectives of this study were (1) to use a validated forward solution hip model to theoretically predict the in vivo kinematics of degenerative hip joints, gaining a better understanding joint conditions leading to THA and (2) compare the predicted kinematic patterns with those derived using fluoroscopy for each subject.

A theoretical model, previously evaluated using THA kinematics and telemetry, was used for this study, incorporating numerous muscles and ligaments, including the quadriceps, hamstring, gluteus, iliopsoas, tensor fasciae latae, an adductor muscle groups, and hip capsular ligaments. Ten subjects having a pre-operative degenerative hip were asked to perform gait while under surveillance using a mobile fluoroscopy unit. The hip joint kinematics for ten subjects were initially assessed using in vivo fluoroscopy, and then compared to the predicted kinematics determined using the model. Further evaluations were then conducted varying implanted component position to assess variability.

The fluoroscopic evaluation revealed that 33% of the degenerative hips experienced abnormal hip kinematics known as “hip separation” where the femoral head slides within the acetabulum, resulting in a decrease in contact area. Interestingly, the mathematical model produced similar kinematic profiles, where the femoral head was sliding within the acetabulum (Figure 1).

During swing phase, it was determined that this femoral head sliding (FHS) is caused by hip capsular laxity resulting in reducing joint tension. At the point of maximum velocity of the foot, the momentum of the lower leg becomes too great for capsule to properly constrain the hip, leading to the femoral component pistoning outwards.

During stance phase, kinematics of degenerative hips were similar to kinematics of a THA subject with mal-positioning of the acetabular cup. Further evaluation revealed that if the cup was placed at a position other than its native, anatomical center, abnormal forces and torques acting within the joint lead to the femoral component sliding within the acetabular cup. It was hypothesized that in degenerative hips, similar to THA, the altered center of rotation is a leading influence of FHS (Figure 2).

The theoretical model has now been validated for subjects having a THA and degenerative subjects. The model has successfully derived kinematic patterns similar to subjects evaluated using fluoroscopy. The results in this study revealed that altering the native joint center is the most influential factor leading to FHS, or more commonly known as hip separation. A new module for the mathematical model is being implemented to simulate virtual surgery so that the surgery can pre- operatively plan and then simulate post-operative results.

Introduction

Many fluoroscopic studies on total knee arthroplasty (TKA) have identified kinematic variabilities compared to the normal knee, with many subjects experiencing paradoxical motion patterns. The intent of this research study was to investigate the results of customized-individual-made (CIM) and off-the-shelf (OTS) PS and PCR TKA to determine kinematic variabilities and to assess these kinematic patterns with those previously documented for the normal knee.

Currently, hip implant designs are evaluated experimentally using mechanical simulators or cadavers, and total hip arthroplasty (THA) postoperative outcomes are evaluated clinically using long-term follow-up. However, these evaluation techniques can be both costly and time-consuming. Neither can provide an assessment of post-operative results at the onset of implant development. More recently, a forward-solution mathematical model was developed that functions as theoretical joint simulator, providing instant feedback to designers and surgeons alike. This model has been validated by comparing the model predictions with kinematic results from fluoroscopy for both implanted and non-implanted hips and kinetics from a telemetric hip. The model allows surgical technique modifications and implant component placement under in vivo conditions.

The objective of this study was to further expand the capabilities of the model to function as an intraoperative virtual surgical tool (Figure 1). This new module allows the surgeon to simulate surgery, then predict, compare, and optimize postoperative THA outcomes based on component placement, sizing choices, reaming and cutting locations, and surgical methods.

This virtual surgery tool simulates the quadriceps, hamstring, gluteus, iliopsoas, tensor fasciae latae, and an adductor muscle groups, as well as the hip capsular ligament groups. The model can simulate resecting, weakening, loosening, or tightening of soft tissues based on surgical techniques. Additionally, the model can analyze a variety of activities, including gait and deep flexion activities.

Initially, the virtual surgery module offers theoretical surgery tools that allow surgeons to alter surgical alignments, component designs, offsets, as well as reaming and cutting simulations. The virtual model incorporates a built-in CT scan bone database which will assist in determining muscle and ligament attachment sites as well as bony landmarks. The virtual model can be used to assist in the placement of both the femoral component and the acetabular cup (Figure 2).

Moreover, once the surgeon has decided on the placements of the components, they can use the simulation capabilities to run virtual human body maneuvers based on the chosen parameters. The simulations will reveal force, contact stress, and motion predictions of the hip joint (Figure 3). The surgeon can then choose to modify the positions accordingly or proceed with the surgery.

This new virtual surgical tool will allow surgeons to gain a better understanding of possible post-operative outcomes under pre-operative conditions or intra-operatively. Simulations using the virtual surgery model has revealed that improper component placement may lead to non-ideal post-operative function, which has been simulated using the model. Further evaluation is ongoing so that this new module can reveal more information pre-operatively, allowing a surgeon to gain ample information before surgery, especially with difficult and revision cases.

Introduction

Hip osteoarthritis can be debilitating, often leading to pain, poor kinematics and limiting range of motion. While the in vivo kinematics of a total hip arthroplasty (THA) are well documented, there is limited information pertaining to the kinematics of native, non-arthritic (normal) hips and degenerative hips requiring a THA.

The objective of this study is to evaluate and compare the in vivo kinematics of the normal hip with pre-operative, degenerative hips and post-operative THA.

Introduction

Previous fluoroscopic studies of total knee arthroplasty (TKA) have revealed significant kinematic differences compared to the normal knee. Often, subjects having a TKA experienced kinematic patterns opposite of the normal knee. Therefore, the objective of this study was to determine the in vivo kinematics of subjects implanted with either a customized-individual-made (CIM) or the traditional (OTS) PS TKA to determine if customization offers a distinct advantage to the patient.

Background

The overall goal of total knee arthroplasty (TKA) is to facilitate the restoration of native function following late stage osteoarthritis and for this reason it is important to develop a thorough understanding of the mechanics of a normal healthy knee.

While there are several methods for assessing TKA mechanics, these methods have limitations that make them prohibitive to both replicating physiological systems and evaluating non-implanted knees. These limitations can be circumvented through the development of mathematical models that use anatomical and physiological inputs to computationally simulate joint mechanics. This can be done in an inverse or forward manner to solve for either joint forces or motions respectively. The purpose of this study is to evaluate one such forward model and determine the accuracy of the predicted motions using fluoroscopy.

Background

In vivo fluoroscopic studies have proven that femoral head sliding and separation from within the acetabular cup during gait frequently occur for subjects implanted with a total hip arthroplasty. It is hypothesized that these atypical kinematic patterns are due to component malalignments that yield uncharacteristically higher forces on the hip joint that are not present in the native hip. This in vivo joint instability can lead to edge loading, increased stresses, and premature wear on the acetabular component.

Background

Extensive research has previously been conducted analyzing the biomechanical effects of rotational changes (i.e. version and inclination) of the acetabular cup. Many sources, citing diverse dislocation statistics, encourage surgeons to strive for various “safe zones” during the THA operation. However, minimal research has been conducted, especially under in vivo conditions, to assess the consequences of cup translational shifting (i.e. offsets, medial and superior reaming, etc.). While it is often the practice to medialize the acetabular cup intraoperatively, there is still a lack of information regarding the biomechanical consequences of such cup medializations and medial/superior malpositionings.

Background

Previous in vivo fluoroscopic studies have documented that subjects having a PS TKA experience a more posterior condylar contact position at full extension, a high incidence of reverse axial rotation and mid flexion instability. More recently, a PS TKA was designed with a Gradually Reducing Radius (Gradius) curved condylar geometry to offer patients greater mid flexion stability while reducing the incidence of reverse axial rotation and maintaining posterior condylar rollback. Therefore, the objective of this study was to assess the in vivo kinematics for subjects implanted with a Gradius curved condylar geometry to determine if these subjects experience an advantage over previously designed TKA.

Introduction

Historically, knee implants have been designed using average patient anatomy and despite excellent implant survivorship, patient satisfaction is not consistently achieved. One possibility for this dissatisfaction relates to the individual patient anatomic variability. To reduce this inter-patient variability, recent advances in imaging and manufacturing have allowed for the implementation of patient specific posterior cruciate retaining (PCR) total knee arthroplasty (TKA). These implants are individually made based on a patient's femoral and tibial anatomy determined from a pre-operative CT scan. Although in-vitro studies have demonstrated promising results, there are few studies evaluating these implants in vivo. The objective of this study was to determine the in vivo kinematics for subjects having a customized, individually made(CIM) knee implant or one of several traditional, off-the-shelf (OTS) TKA designs.

Background

The Bi-Cruciate Stabilized (BCS) total knee arthroplasty (TKA) incorporates two cam-post mechanisms in order to replicate the functionality and stability provided by the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) in the native knee. Recently (2012), a second generation BCS design has introduced femur and tibial bearing modifications that are intended to delay lateral femoral condyle rollback and encourage more stable positioning of the medial femoral condyle to more closely replicate normal knee kinematics. The purpose of this study was to compare the kinematics of this TKA to the normal knee during a weight bearing flexion activity.

Background

Currently, hip implant designs are evaluated experimentally using mechanical simulators or cadavers, and total hip arthroplasty (THA) postoperative outcomes are evaluated clinically using long-term follow-up. However, these evaluation techniques can be both costly and time-consuming. Fortunately, forward solution mathematical models can function as theoretical joint simulators, providing instant feedback to designers and surgeons alike. Recently, a validated forward solution model of the hip has been developed that can theoretically simulate new implant designs and surgical technique modifications under in vivo conditions.

Introduction

The Bi-Cruciate Stabilized (BCS) total knee arthroplasty (TKA) incorporates two cam-post mechanisms to reproduce the functionality and stability provided by the anterior cruciate ligament and posterior cruciate ligament in the native knee. The anterior cam-post mechanism provides stability in full extension and early flexion (≤20°) while the posterior cam-post mechanism prevents anterior sliding of the femur during deeper flexion (≥60°). Recently (2012), a second generation BCS design introduced more normal shapes to the femur and tibial bearing geometries that provides delayed lateral femoral condyle rollback and encourages more stable positioning of the medial femoral condyle. The purpose of this study was to compare the in vivo kinematics exhibited by the two generations during weight bearing flexion.

Background

While not common in the native hip, occurrences of femoral head separation from the acetabular cup during gait are well documented after total hip arthroplasty. Although the effects of this phenomenon are not well understood, we hypothesize that these atypical kinematics are due to component misalignments that yield uncharacteristic forces on the hip joint that are not present in the native hip.

Introduction

Recently, a mobile-fluoroscopy unit was developed which can capture subjects performing unconstrained motions, more accurately replicating everyday demands that patients place on their TKA. The objective of this study was to analyze normal knee and various TKA while subjects perform both traditional and more challenging activities while under surveillance of a mobile fluoroscopy unit.

Introduction

Currently, knee and hip implants are evaluated experimentally using mechanical simulators or clinically using long-term follow-up. Unfortunately, it is not practical to mechanically evaluate all patient and surgical variables and predict the viability of implant success and/or performance. More recently, a validated mathematical model has been developed that can theoretically simulate new implant designs under in vivo conditions to predict joint forces kinematics and performance. Therefore, the objective of this study was to use a validated forward solution model (FSM) to evaluate new and existing implant designs, predicting mechanics of the hip and knee joints.

Previously more femoral rollback has been reported in posterior-stabilized implants, but so far the kinematic change after post-cam engagement has been still unknown. The tri-condylar implants were developed to fit a life style requiring frequent deep flexion activities, which have the ball and socket third condyle as post-cam mechanism. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during deep knee flexion.

The tri-condylar implant analyzed in the current study is the Bi-Surface Knee System developed by Kyocera Medical (Osaka, Japan). Seventeen knees implanted with a tri-condylar implant were analyzed using 3D to 2D registration approach. Each patient was asked to perform a weight-bearing deep knee bend from full extension to maximum flexion under fluoroscopic surveillance. During this activity, individual fluoroscopic video frames were digitized at 10°increments of knee flexion. A distance of less than 1 mm initially was considered to signify the ball and socket contact. The translation rate as well as the amount of translation of medial and lateral AP contact points and the axial rotation was compared before and after the ball and socket joint contact.

The average angle of ball and socket joint contact were 64.7° (SD = 8.7), in which no separation was observed after initial contact. The medial contact position stayed from full extension to ball and socket joint contact and then moved posteriorly with knee flexion. The lateral contact position showed posterior translation from full extension to ball and socket joint contact, and then greater posterior translation after contact (Figure 1). Translation and translation rate of contact positions were significantly greater at both condyles after ball and socket joint contact. The femoral component rotated externally from full extension to ball and socket joint contact, and then remained after ball and socket joint contact (Figure 2). There was no statistical significance in the angular rotation between ball and socket joint contact and maximum flexion. Translation of angular rotation was significantly greater before ball and socket joint contact, however, there was no significance in translation rate before and after ball and socket joint contact.

The ball and socket joint was proved to induce posterior rollback intensively. In terms of axial rotation, the ball and socket joint did not induce reverse rotation, but had slightly negative effects after contact. The ball and socket provided enough functions as a posterior stabilizing post-cam mechanism and did not prevent axial rotation.

Mathematical modeling provides an efficient and easily reproducible method for the determination of joint forces under in vivo conditions. The need for these new modeling methodologies is needed in the lumbar spine, where an understanding of the loading environment is limited. Few studies using telemetry and pressure sensors have directly measured forces borne by the spine; however, only a very small number of subjects have been studied and experimental conditions were not ideal for giving total forces acting in the spine. As a result, alternative approaches for investigating the lumbar spine across different clinical pathologies are essential. Therefore, the objective of this study was to develop of an inverse dynamic mathematical model for theoretically deriving in-vivo contact forces as well as musculotendon forces in patients having healthy, symptomatic, pathological and post-operative conditions of the lumbar spine.

Fluoroscopy and 3D-to-2D image registration were used to obtain kinematic data for patients performing flexion-extension of the lumbar spine. This data served as input into the multi-body, mathematical model. Other inputs included patient-specific bone geometries, recreated from CT, and ground reaction forces. Vertebral bones were represented as rigid bodies, while massless frames symbolized the lower body, torso and abdominal wall (Figure 1). In addition, ligaments were selected and modeled as linear spring elements, along with relevant muscle groups. The muscles were divided into individual fascicles and solved for using a pseudo-inverse algorithm which enabled for decoupling of the derived resultant torques defining the desired kinetic trajectory for the muscles.

The largest average contact forces in the model for healthy, symptomatic, pathological, and post-operative lumbar spine conditions occurred at maximum flexion at L4L5 level and were predicted to be 2.47 BW, 2.33 BW, 3.08 BW, and 1.60 BW, respectively. The FE rotation associated with these theoretical force values was 43.0° in healthy, 40.5° in symptomatic, 44.4° in pathological, and 22.8° in post-operative patients. The smallest forces occurred as patients approached the upright, standing position, followed by slight increases in the contact force at full extension. The theoretically derived muscle forces exhibited similar contributory force profiles in the intact spine (healthy, symptomatic, and pathologic); however, surgically implanted spines experienced an increase in the contribution of the external oblique muscles accompanied with decreased slope gradients in the muscle force profiles (Figure 2).

These altered force patterns may be associated with the decrease in the predicted contact forces in post-operative patients. In addition, the decreased slope gradients in surgically implanted patients corresponds with the observed difficulty of performing the prescribed motion, possibly due to improper muscle firing, thereby leading to slower motion cycles and less ranges-of-motion. On the contrary, patients having an intact spine performed the activity at a faster speed and to greater ranges-of-motion, which corresponds with the higher contact forces derived in the model. In conclusion, this research study presented the development of a mathematical modeling approach utilizing patient-specific data to generate theoretical in-vivo joint forces. This may serve to help progress the understanding for the kinetic characteristics of the native and surgically implanted lumbar spine.

INTRODUCTION:

Stationary fluoroscopy has been a viable resource for determining in vivo knee kinematics, but limitations have restricted the use of this technology. Patients can only perform certain normal daily living activities while using stationary fluoroscopy and must conduct the activities at speeds that are slower than normal to avoid ghosting of the images. More recently, a Mobile Tracking Fluoroscopic (MTF) unit has been developed that can track patients in real-time as he/she performs various activities at normal speeds (Figure 1). Therefore, the objective of this study was to compare in vivo kinematics for patient's evaluated using stationary and mobile fluoroscopy to determine potential advantages and disadvantages for use of these technologies.

INTRODUCTION:

Previous modalities such as static x-rays, MRI scans, CT scans and fluoroscopy have been used to diagnosis both soft-tissue clinical conditions and bone abnormalities. Each of these diagnostic tools has definite strengths, but each has significant weaknesses. The objective of this study is to introduce two new diagnostic, ultrasound and sound/vibration sensing, techniques that could be utilized by orthopaedic surgeons to diagnose injuries, defects and other clinical conditions that may not be detected using the previous mentioned modalities.

Introduction

The low-cost, no-harm conditions associated with vibroarthography, the study of listening to the vibrations and sound patterns of interaction at the human joints, has made this method a promising tool for diagnosing joint pathologies. This current study focuses on the knee joint and aims to synchronize computational models with vibroarthographic signals via a comprehensive graphical user interface (GUI) to find correlations between kinematics, vibration signals, and joint pathologies. This GUI is the first of its kind to synchronize computational models with vibroarthographic signals and gives researchers a new advantage of analyzing kinematics, vibration signals, and pathologies simultaneously in an easy-to-use software environment.

INTRODUCTION

In-vivo data pertaining to the actual cam-post engagement mechanism in PS and Bi-Cruciate Stabilized (BCS) knees is still very limited. Therefore, the objective of this study was to determine the cam-post mechanism interaction under in-vivo, weight-bearing conditions for subjects implanted with either a Rotating Platform (RP) PS TKA, a Fixed Bearing (FB) PS TKA or a FB BCS TKA.

Introduction

While fluoroscopic techniques have been widely utilized to study in vivo kinematic behavior of total knee arthroplasties, determination of the contact forces of large population sizes has proven a challenge to the biomedical engineering community. This investigation utilizes computational modeling to predict these forces and validates these with independent telemetric data for multiple patients, implants, and activities.

Introduction

Previous fluoroscopy studies have been conducted on numerous primary-type TKA, but minimal in vivo data has been documented for subjects implanted with revision TKA. If a subject requires a revision TKA, most often the ligament structures at the knee are compromised and stability of the joint is of great concern. In this present study, subjects implanted with a fixed or mobile bearing TC3 TKA are analyzed to determine if either provides the patient with a significant kinematic advantage.

Introduction

Electromyography (EMG) is the best known method in obtaining in vivo muscle activation signals during dynamic activities, and this study focuses on comparing the EMG signals of the quadriceps muscles for different TKA designs and normal knees during maximum weight bearing flexion. It is hypothesized that the activation levels will be higher for the TKA groups than the normal group.

Orthopaedic companies spend years and millions of dollars developing and verifying new total knee arthroplasty (TKA) designs. Recently, computational models have been used in the hopes of increasing the efficiency of the design process. The most popular predictive models simulate a cadaveric rig. Simulations of these rigs, although useful, do not predict in vivo behavior. Therefore, in this current study, the development of a physiological forward solution, or predictive, rigid body model of the knee is described.

The models simulate a non-weight bearing extension activity or a weight-bearing deep knee bend (DKB) activity. They solve for both joint forces and kinematics simultaneously and were developed from the ground up. The models are rigid body and use Kane's dynamical equations. The model began with a simple two dimensional non-weight bearing extension activity model of the tibiofemoral joint. Step by step the model was expanded. Quadriceps and hamstring muscles were added to drive the motion. Ligaments were added represented by multiple non-linear spring elements. The model was expanded to three-dimensions (3D) allowing out of plane motions and calculation of medial and lateral condylar forces. The patella was added as its own body allowing for simulation of the patellofemoral joint. The model was then converted to a weight bearing deep knee bend activity. A pelvis and trunk were added and muscles were given physiological origin and insertion points. A modified proportional-integral-derivative (PID) controller was implemented to control the rate of flexion and also to assist in joint stability by adjusting the force in individual quadriceps muscles. A method for representing articulating geometry was developed. Once the deep knee bend model was fully developed (Figure 1) it was converted back to a non-weight bearing extension model (Figure 2) resulting in simulations of a normal knee performing a weight bearing and non-weight bearing activity. The tibiofemoral kinematic results were compared to in vivo kinematics obtained from a fluoroscopy study of five normal subjects. Parameters from the CT models of one of these subjects (Subject 3) were used in the model.

The model kinematics behave as the normal knee does in vivo. The kinetic results were within reasonable ranges with a maximum total quadriceps force of 0.86 BW and 4.73 BW for extension and DKB simulations, respectively (Figure 3 and Figure 4). The maximum total tibiofemoral forces were 1.26 BW and 3.70 BW for extension and DKB, respectively. The relationship between the quadriceps force, patella ligament force and patellofemoral forces are consistent with how the extensor mechanism behaves (Figure 3 and Figure 4). The patellofemoral forces are low between 0 and 20 degrees flexion and the patella ligament and quadriceps forces are close in magnitude from 0 to around 70 degrees flexion when the patellofemoral forces increase and the quadriceps forces increase relative to the patella ligament force. The model allows for virtual implantation of TKA geometry and after kinematic and kinetic validation from in vivo TKA data can be used to predict the behavior of TKA in vivo.

Introduction

Previous fluoroscopic studies compared total knee arthroplasty (TKA) kinematics to normal knees. It was our hypothesis that comparing TKA directly to its non-replaced controlateral knee may provide more realistic kinematics information. Using fluoroscopic analysis, we aimed to compare knee flexion angles, femoral roll-back, patellar tracking and internal and external rotation of the tibia.

INTRODUCTION

Multiple video fluoroscopic analyses have been performed to determine the in vivo kinematic patterns of total knee arthroplasty (TKA) and non implanted knees. Unfortunately, many of these studies were not correlated with bearing surface forces and possible failure modes that could be detected with a sound sensor. Therefore, the objective of the present study was to conduct a comparative analysis of the kinematic data derived for all subjects having a TKA who were analyzed over the past seventeen years at our laboratory and to determine how these patterns correlate with bearing surface forces and joint sound.

Commercial C-arm fluoroscopes are routinely used to analyze human skeletal joints during motions such as deep knee bends, or chair rises. Such diagnostics are used to characterize pre and post operative arthoplasty results, particularly in association with total joint replacement procedures. Stationary fluoroscopes restrict the patient motion and load conditions, thus diminishing the diagnostic utility of the results. A new class of fluoroscopy has been developed in which a robotic mechanization is used to allow selected joints to be x-rayed while the human subjects perform natural motions such as walking. The tracking fluoroscope system (TFS) is a mobile robot that acquires real-time x-ray records of hip, knee, or ankle joint motion while the patient walks normally. Because the fluoroscope line of sight dynamically tracks the joint of interest, the TFS provides clearer and contained joint images.

The technical features of the TFS will be reviewed, recent development testing summarized, and the results of preliminary patient trials presented.

INTRODUCTION

Posterior stabilized (PS) total knee arthroplasty (TKA) provides posterior stability with the use of a cam-post mechanism which performs the function of the posterior cruciate ligament. The tibial post engages with the femoral cam, prevents the femur from sliding anteriorly and provides the posterior femoral rollback necessary for achieving deep flexion of the knee. However, these designs do not substitute the resection of the anterior cruciate ligament. In order to overcome this deficit, other TKA designs have been recently introduced to provide dual support, with the help of dual cam-post engagement mechanism. Various studies conducted on the PS TKA have suggested that the cam-post mechanism does not engage as designed, resulting in tibial post wear and increased stresses resulting in backside wear of the polyethylene insert component. Also, the in vivo data pertaining to the actual cam-post engagement mechanism in bi-cruciate stabilized knees is still very limited. Therefore, the objective of this study was to determine the cam-post mechanism interaction under in vivo, weight bearing conditions for subjects implanted with either a Rotating Platform (RP) Posterior Stabilized (PS) TKA or a bi-cruciate stabilizing TKA (BCS).

INTRODUCTION

Knee simulators are being used to evaluate wear. The current international standards have been developed from clinical investigations of the normal knee [1, 2] or from a single TKA patient [3, 4]. However, the forces and motions in a TKA patient differ from a normal knee and, furthermore, the resulting kinematic outcomes after TKA will depend on the design of the device [5]. Consequently, these standard tests may not recreate in-vivo conditions; therefore, the goal of this study was to perform a novel wear simulation using design-specific inputs that have been derived from fluoroscopic images of a deep knee bend.

INTRODUCTION

Telemetric implants have provided us with invaluable data as to the in vivo forces occurring in implanted knee joints. However, only a few of them exists. The knee is one of the most studied joints in the human body and various mathematical knee models have been used in the past to predict forces. However, these simulation studies have also been carried out on a small group of patients limiting their general usefulness in understanding overall trends of knee behavior. Therefore, it is the purpose of this research to study the implant forces experienced by a large group of patients so as to have a better understanding of the overall magnitudes and their variability with knee flexion.

INTRODUCTION

Total shoulder arthroplasty (TSA) implants are used to restore function to individuals whose shoulder motions are impaired by osteoarthritis. To improve TSA implant designs, it is crucial to understand the kinematics of healthy, osteoarthritic (OA), and post-TSA shoulders. Hence, this study will determine in vivo kinematic trends of the glenohumeral joints of healthy, OA, and post-TSA shoulders.

Anterior knee pain is one of the most frequently reported musculoskeletal complaints in all age groups. However, patient's complaints are often nonspecific, leading to difficulty in properly diagnosing the condition. One of the causes of pain is the degeneration of the articular cartilage. As the cartilage deteriorates, its ability to distribute the joint reaction forces decreases and the stresses may exceed the pain threshold. Unfortunately, the assessment of the cartilage condition is often limited to a detailed interview with the patient, careful physical examination and x-ray imaging. The X-ray screening may reveal bone degeneration, but does not carry sufficient information of the soft tissues' conditions. More advanced imaging tools such as MRI or CT are available, but these are expensive, time consuming and are only suitable for detection of advanced arthritis. Arthroscopic surgery is often the only reliable option, however due to its semi-invasive nature, it cannot be considered as a practical diagnostic tool. However, as the articular cartilage degenerates, the surfaces become rougher, they produce higher vibrations than smooth surfaces due to higher friction during the interaction. Therefore, it was proposed to detect vibrations non-invasively using accelerometers, and evaluate the signals for their potential diagnostic applications.

Vibration data was collected for 75 subjects; 23 healthy and 52 subjects suffering from knee arthritis. The study was approved by the IRB and an Informed Consent was obtained prior to data collection. Five accelerometers were attached to skin around the knee joint (at the patella, medial and lateral femoral condyles, tibial tuberosity and medial tibial plateau). Each subject performed 5 activities; (1) flexion-extension, (2) deep knee bend, (3) chair rising, (4) stair climbing and (5) stair descent. The vibration and motion components of the signals were separated by a high pass filter. Next, 33 parameters of the signals were calculated and evaluated for their discrimination effectiveness (Figure 1). Finally the pattern recognition method based on Baysian classification theorem was used for classify each signal to either healthy or arthritic group, assuming equal prior probabilities.

The variance and mean of the vibration signals were significantly higher in the arthritic group (p=2.8e-7 and p=3.7e-14, respectively), which confirms the general hypothesis that the vibration magnitudes increase as the cartilage degenerates. Other signal features providing good discrimination included the 99^th quantile, the integral of the vibration signal envelope, and the product of the signal envelope and the activity duration. The pattern classification yielded excellent results with the success rate of up to 92.2% using only 2 features, up to 94.8% using 3 (Figure 2), and 96.1% using 4 features.

The current study proved that the vibrations can be studied non-invasively using a low-cost technology. The results confirmed the hypothesis that the degeneration of the cartilage increases the vibration of the articulating bones. The classification rate obtained in the study is very encouraging, providing over 96% accuracy. The presented technology has certainly a potential of being used as an additional screening methodology enhancing the assessment of the articular cartilage condition.

Introduction

Achieving high flexion after total knee arthroplasty is very important for patients in Asian countries where deep flexion activities are an important part of daily life. The Bi-Surface Total Knee System (Japan Medical Material, Kyoto, Japan), which has a unique ball-and-socket mechanism in the mid-posterior portion of the femoral and tibial components, was designed to improve deep knee flexion and long-term durability after total knee arthroplasty (Figure 1). The purpose of this study was to determine the in vivo three dimensional kinematics of Bi-Surface Total Knee System in order to evaluate and analyze the performance of this system with other conventional TKA designs currently available in the market today.

Introduction

Numerous studies have been conducted to investigate the kinematics of the lumbar spine, and while many have documented its intricacies, few have analyzed the complex coupled out-of-plane rotations inherent in the low back. Some studies have suggested a possible relationship between patients having low back pain (LBP) or degenerative conditions in the lumbar region and various degrees of restricted, excessive, or poorly-controlled lumbar motion. Conversely, others in the orthopedic community maintain there has been no distinct correlation found between spinal mobility and clinical symptoms. The objective of this study was to evaluate both the in-plane and coupled out-of-plane rotational magnitudes about all three motion axes in both symptomatic and asymptomatic patients.

Recent fluoroscopic analyses evaluating the kinematic function of TKAs have demonstrated significant variability among patients with identical implant designs, suggesting surgical technique also influences function. To help explain these kinematic variations, we used intraoperative compartment pressure sensors to assess balancing at trial reduction and ROM then correlated these intraoperative findings with patients’ postoperative kinematics, assessed using video fluoroscopy.

This study involved 16 patients implanted with a posterior cruciate-sacrificing LCS TKA using a balanced gap technique. After releases in extension, the femur was rotated the appropriate amount to create a rectangular flexion gap relative to the cut tibial surface. As the knee was taken through a ROM from 0–120°, the sensors (placed on the tibial insert trial) dynamically measured the magnitude and location of compartment pressures throughout the ROM. Six to nine months postoperatively, all patients performed successive weight-bearing deep knee bends to maximum flexion under fluoroscopic surveillance. Each patient’s femoro-tibial contact positions and liftoff values were compared to their respective intraoperative compartment pressure findings to establish correlations.

Fluoroscopic results correlated closely with intraoperative compartment pressures and balance data. Three of the 16 patients had condylar liftoff: two patients experienced liftoff in flexion and one in extension (medial). The patient who experienced medial liftoff in extension had decreased medial compartment pressure and a slight valgus malalignment (7° of anatomic alignment). Two of the 13 patients without liftoff had abnormal compartment pressures in extension. In both cases, mechanical axis alignment resulted in loading of the lax compartment with weight-bearing. The other 11 patients had normal compartment pressures in extension and no condylar liftoff. One of these patients had slight valgus (7°) and another slight varus malalignment (4°), but both had normal compartment pressures. Despite good compartment balance, average tibiofemoral rotation was inadequate; three of 16 patients experienced opposite axial rotation with flexion. Extensive ligament release did not always result in equal compartment pressure magnitudes and distributions; compartment balance was influenced by the nature of the release.

These data suggest that liftoff may require both a compartment pressure imbalance and abnormal alignment that together exacerbate the laxity with physiologic loading. Previous kinematic studies of LCS knees have shown that the balanced gap technique produces wellbalanced compartment pressures, resulting in TKAs with little lift-off and very good translational and rotational characteristics. Therefore, while a given implant design may have inherent kinematic tendencies, surgical technique may significantly impact kinematic performance. To optimize implant kinematics and subsequent TKA function and longevity, it may be important for surgeons to accurately balance the flexion and extension gaps. Characteristic compartment pressure patterns and distributions for various ligament releases may shed some light on less than optimal rotational kinematic performance.

Subjects having a posterior cruciate ligament sacrificing (PCLS) mobile bearing TKA seem to experience less translation during gait, but often achieve less weight-bearing flexion. More recently, posterior stabilisation has been added to PCLS mobile bearing TKA, hoping to increase flexion. Therefore, the objective of this multi-center study was to determine the in vivo kinematics for subjects implanted with a mobile bearing PS TKA that attempts to maintain high contact area.

Subjects with 10 TKA from 2 surgeons were asked to perform maximum weight-bearing flexion (deep knee bend (DKB)) and gait while under fluoroscopic surveillance. During weight bearing flexion, the 3-D kinematics of the TKA were determined by analyzing fluoroscopic images in the sagittal plane at 30 degree increments. Fluoroscopic images taken in the frontal plane from four increments during the stance phase of gait were analyzed.

The average weight-bearing flexion was 116 degrees and the average medial and lateral anteriorposterior (AP) translation was posterior with −1.9 mm and −5.4 mm, respectively, from full extension to maximum weight-bearing flexion.

The average femorotibial axial rotation from full extension to maximum weight-bearing flexion was 3.9 degrees. During the stance phase of treadmill gait, patients experienced 0.8 mm (0.1 mm to 2.3 mm, SD=0.8 mm) of “pure” mediolateral translation of the femur relative to the tibia. The femorotibial axial rotation was 4.6 degrees from heel-strike to toe-off (Table 3).

The posterior femoral rollback and axial rotation patterns were similar to the normal knee, albeit experiencing less overall motion. More noticeably, subjects in this study experienced a significantly greater weight-bearing flexion than previous subjects analyzed with a mobile bearing PCLS TKA and more reproducible “fan-like” patterns, where the lateral condyle rolled greater posteriorly than the medial condyle.

All over the world, obesity rates are on the rise. Medical complications and increased health risks are often associated with being overweight or obese, but a thorough understanding of in vivo motions for obese, overweight and normal weight subjects does not exist. Therefore, the objective of this study was to compare knee kinematics in TKA subjects by body mass index (BMI).

In vivo knee kinematics were determined for 253 TKA subjects during a Deep Knee Bend (DKB) from full extension to maximum flexion using a 3D to 2D image registration technique. Each of these subjects was then classified into one of three BMI categories: obese (BMI greater than or equal to 30), overweight (BMI greater than or equal to 25 and less than 30) and normal weight (BMI less than 25 and greater than or equal to 18.5). Subjects were provided by 11 surgeons using ten different TKA devices. All subjects were deemed clinically successful.

On average, weight bearing range of motion (ROM) for the obese (n=79), overweight (n=113) and normal weight (n=61) groups were 107.7° (range: 74° to 136°, standard deviation (σ) =14.9°), 109.6° (60° to 150°, σ=17.5°) and 114.1° (72° to 147°, σ=14.4), respectively. ROM of 90° or less was seen in 16.5% of the obese subjects, 14.2% of the overweigh subjects and 6.6% of the normal weight subjects. ROM of 125° or more was seen in 15.2% of the obese subjects, 16.8% of the overweight subjects and 23.0% of the normal weight subjects.

From full extension to maximum flexion the obese, overweight and normal weight groups averaged 8.65° (−5.14° to 22.51°, σ=6.22°), 7.58° (−2.85° to 24.72°, σ=5.71°) and 5.72° (−4.84° to 19.43°, σ=5.65°) of axial rotation. Axial rotation of 3° or less was seen in 20.25% of the obese subjects, 23.01% of the overweight subjects and 39.34% of the normal weight subjects. Axial rotation of greater than 9° was seen in 51.90% of the obese subjects, 35.40% of the overweight subjects and 26.23% of the normal weight subjects. Opposite axial rotation was seen in 8.86% of the subjects in the obese group, 9.73% of the overweight group and 9.84% of the normal weight group.

On average, from full extension to maximum flexion, the medial condyle for the obese, overweight and normal weight groups experienced −5.44mm (−22.20mm to 8.04mm, σ=7.9mm), −6.30mm (−25.22mm to 5.35mm, σ=7.36mm) and −4.78mm (−20.79mm to 5.49mm, σ=6.68mm) of posterior femoral rollback (PFR), respectively. The obese, overweight and normal weight groups averaged −12.66 mm (−34.57mm to 0.34mm, σ=9.32mm), −12.38mm (−36.72mm to 1.83mm, σ=10.33mm) and −9.39 mm (−34.55mm to 0.35mm, σ=8.98mm) of lateral PFR, respectively.

Condylar lift-off of greater than 1mm was seen in 16.46% of obese subjects, 10.62% of overweight subjects and 11.48% of normal weight subjects.

Various statistical differences were seen across the groups. The normal weight subjects had significantly higher ROM that the obese subjects (p=0.0184), while there was no difference seen between the normal weight and overweight groups or the overweight and obese groups. The obese and the overweight groups had significantly more axial rotation than the normal weight group from 0° to 90°, 0° to maximum flexion, 30° to 90°, 30° to maximum flexion and 60° to 90°. There were a significantly higher number of cases of condylar lift-off for obese subjects when compared to both normal weight and overweight groups.

It can be concluded that body mass index does play a factor in TKA kinematics.

In vivo kinematic analyses of total hip arthroplasty (THA) have determined femoral head separation from the medial aspect of the acetabular component can occur. Various bearing materials are currently used in THA today. The objective of this study was to determine if differences in the incidence and magnitude of femoral head separation exist among various bearing surfaces for THA during different weight-bearing activities.

205 clinically successful subjects implanted with either metal-on-metal (MOM), metalon-polyethylene (MOP), ceramic-on-ceramic (COC) or ceramic-on-polyethylene (COP) materials were analyzed using video-fluoroscopy. Each patient performed either gait on a treadmill or an abduction-adduction activity. The fluoroscopic information was then analyzed using a computer aided 3D model fitting technique to determine the incidence and magnitude of hip separation. Additional variables analyzed included femoral head diameter, follow-up duration, and type of surgical approach utilized.

Less separation was noted with increasing femoral head diameter during abductionadduction.

Increased separation was observed during gait as follow-up duration increased. Hip separation was greater during gait when a posterolateral surgical approach was used but was greater in abduction-adduction if a antero-lateral approach was selected. The incidence and magnitude of hip separation during gait was least in subjects with COC THA and least with COC and MOM THA when analyzed during abduction-adduction.

It’s been proposed that THA patients are subject to femoral head separation due to alterations in the soft tissue supporting structures during THA that affect constraint of the joint.

The current analysis demonstrates lower magnitudes and incidence of THA separation occur when hard-on-hard bearing surfaces are selected and can vary based on femoral head diameter, follow-up duration, and surgical approach used. Potential detrimental effects resulting from THA separation include premature polyethylene wear, component loosening (secondary to impulse loading conditions) and hip instability.

Previous in vivo studies pertaining to THA performance have focused on the analysis of gait. Unfortunately, higher demand activities have not yet been analyzed. Therefore, the objective of the present study was to determine the in vivo kinematics for THA patients, using fluoroscopy, while they performed four higher demand activities.

The 3D in vivo kinematics of 10 THA patients were analyzed during the following activities: pivoting (PI), tying a shoe (SHOE), sitting down (SDOWN) and standing up (SUP) with and without the aid of handrails. Patients were matched for age, height, weight, body mass index, diagnosis and femoral head diameter to control for confounding variables possibly having influence on the hip performance and kinematics of the various activities.

The largest amount, incidence and variation of separation (femoral head sliding in the acetabular cup) were achieved during the PI with 1.5mm (SD 1.1) and 9 of 10 (90%) subjects experiencing separation. For the SHOE, SDOWN and SUP activities the average separation values were 1.1, 1.2 and 0.7mm, respectively. Femoral head separation was observed in 8 of 10 subjects (80%) during SHOE, in 9 (90%) during SDOWN, and in only one of 6 (60%) during SUP.

In this present study, subjects demonstrated hip separation during the high demand subjects, which could be a concern because these same activities are subjected to higher bearing surface forces. Also, the presence of hip separation leads to reduced contact area between the femoral head and the acetabular cup, possibly leading to higher contact stresses.

Low back pain (LBP) in the region of the lumbar spine is a significant problem among individuals, and efforts focused on treating both the symptoms and causes of LBP have proven to be difficult. Aside from conservative treatments, the predominant surgical approach for treating degenerative spine conditions has been to fuse the vertebral bodies at the symptomatic level. Even today, surgical fusion and its effect on adjacent levels are still not fully understood. Therefore, the objective of this study was to use fluoroscopy and mathematical modeling techniques to identify the in vivo kinematics and kinetics in subjects having either a normal, degenerative or fused condition of the lumbar spine.

Twenty-five subjects (ten normal, ten degenerative, and five fusion) were evaluated under fluoroscopic surveillance while performing flexion/extension of the lumbar spine. Subjects within the normal and degenerative groups were analyzed only once, while subjects from the fusion group were analyzed both pre-operatively and at a minimum of six months post-operative. The fusion group consisted of three subjects symptomatic at L4/L5, with the remaining two subjects symptomatic at L5/S1. In vivo kinematics data were derived using a 3D-to-2D model fitting algorithm and served as input into a 3D mathematical model of the lumbar spine. The parametric, inverse dynamics mathematical model was created to allow for the determination of the bearing surface contact and muscle forces at each level of the lumbar spine.

Three-dimensional kinematics analyses revealed that subjects classified as having a normal lumbar spine experienced a more uniform motion pattern compared to those observed in the degenerative and fusion groups. Alternatively, the degenerative and fusion subjects demonstrated a more coupled motion pattern in order to perform in plane flexion/extension. Compared to the normal group, rotations in the sagital plane decreased by an average of 28% at the pathological level in the degenerative group, while in the fusion group segmental motions slightly increased at the adjacent levels. Results from the mathematical model also revealed higher out-of-plane forces and increased loading at symptomatic and adjacent levels in both the degenerative and fused groups compared to forces observed in the normal spine.

The abnormal motion patterns, which result from decreased or loss of motion at pathological levels in the degenerative and fusion groups, are believed to result in higher resultant forces in the spine. This may be subjecting the intervertebral discs to increased stresses, and as a consequence may be linked to more rapid degeneration at levels where the abnormal kinematics are occurring.

Many nonoperative techniques exist to alleviate pain in unicompartmental osteoarthritic knees including physical therapy, heel wedges and off-loading knee braces [1]. Arthritic knee braces are particularly effective since they can be used on a regular basis at home, work, etc. Previous knee brace studies focused on their ability to stabilize anterior cruciate ligament (ACL) deficient knees. A standard technique for analyzing brace effectiveness is the use of an athrometer to look at the range-of-motion. Although this is helpful, it is more useful to use X-ray or fluoroscopy techniques to analyze the in vivo 3-D conditions of the femur and tibia. One method for doing this is Roentgen Steroephotogrammetric Analysis, which uses a calibration object and two static X-rays to perform 3-D registration of the femur and tibia. This technique is limited to static and typically non-weight bearing analysis.

We have analyzed five patients with moderate to severe osteoarthritis in both step up and step down activities with two different knee braces and also without a knee brace. Fluoroscopy of the five patients performing these activities was obtained as well as a CT scan of the knee joint for each patient. 3-D models of the femur and tibia were obtained from manual segmentation and overlaid to the fluoroscopy images using a novel 3-D to 2-D registration method [2]. This allowed analysis of 3-D in vivo weight bearing conditions. This work builds off of an analysis where 15 patients were analyzed in vivo during gait with and without knee braces [3].

All five patients experienced substantially less pain when performing the step up and step down activities with a knee brace versus without a knee brace. It should be noted that none of the five patients were obese, which can limit brace effectiveness. Preliminary results show that medial condyle separation was increased by 1.4–1.6 mm when using a knee brace versus not using a knee brace during the heel-strike and 33% phases of step up and step down activities. Also, the condylar separation angle was reduced by an average of 1.5–2.5°. Finally, consistently less condylar separation was seen during step down versus step up activities (0.5–1 mm), which can be attributed to a greater initial impact force on the knee joint during step down versus step up activities.

Previous fluoroscopic analyses of Total Hip Arthroplasty (THA) determined that the femoral head slides within the acetabular cup, leading to separation of certain aspects of the articular geometries. Although separation has been well documented, it has not been correlated to clinical complications or a more indepth understanding of the cause and effect. Surgical technique is one of the important clinical factors when considering THA procedures, and it is hypothesized, that it could affect the magnitude and occurrence of femoral head separation (sliding) in THAs. Hence, the objective of this study was to determine and compare in-vivo THA kinematics for subjects implanted with a THA using two different surgical approaches.

Thirty seven subjects, each implanted with one of two types of THA were analysed under in vivo, weight-bearing conditions using video fluoroscopy while performing a sit-to-stand activity. Ten subjects were implanted by Surgeon 1 using a long incision postero-lateral approach (G1); while a further 10 subjects were implanted by the same surgeon using a short incision posterolateral approach (G2). The remaining 17 subjects were implanted using the anterolateral approach; 10 by Surgeon 2 (G3) and seven by Surgeon 3 (G4). All patients with excellent clinical results, without pain or functional deficits were invited to participate in the study (HHS > 90). 3D kinematics of the hip joint was determined, with the help of a previously published 2D-to-3D registration technique. From a completely seated position to the standing position, four frames of the fluoroscopy video were analysed.

Subjects in all groups experienced some degree of femoral head separation at all increments of the sit-to-stand activity that were analysed. The magnitude and frequency of separation greater than 1.0mm varied between each surgeon group, between incision types, between incision lengths and between the two types of THA that were analysed. The average maximum separation was 1.3, 1.1, 1.3 and 1.4mm for G1, G2, G3 and G4 respectively. Though there was no difference in the average maximum separation values for the 4 groups, the maimum separation varied significantly. While the maximum separation in G2 was 1.8mm, the maximum separation in G4 was 3.0mm. G1 and G3 had maximum separation values of 2.3mm and 2.4mm respectively.

This study suggests that there may be a correlation between incision lengths and surgical approach with femoral head separation in THAs. The maximum separation that was seen among all groups was a subject with a traditional long incision, while the short incision group had less incidence of separation. Results from this study may give researchers and implant developers a better understanding of kinematics around the hip joint and how they vary with respect to different surgical techniques. Further analysis is being conducted on the subjects before definitive conclusions can be made.

This research is to relate functional outcomes to kinematics in high flexion CR and PS total knees by using the Total Knee Function Questionnaire in patients who had previously undergone kinematic analyses.

Patients were identified who had primary total knee arthroplasty and had undergone kinematic analyses using fluoroscopy. The Total Knee Function Questionnaire was sent to these patients, and data was obtained for 14 CR knees (NexGen CR-Flex, Zimmer) and for 13 PS knees (Legacy LPS-Flex, Zimmer). The questionnaire evaluates baseline activities of daily living, advanced activities, and recreational activities and exercises.

CR patients reported higher satisfaction and that their knees felt more “normal” than PS patients. Some baseline activity scores were significantly higher for CR than for PS knees.

Limitations in baseline activities were related to kinematic constraints, including flexion, lateral and medial anterior-posterior (A-P) translations, and tibiofemoral axial rotation. Kinematic data were related to difficulty data for advanced and recreational activities of kneeling, squatting, gardening, and stretching.

Comparisons between kinematic data and patient feedback on knee function provided unique information about differences between CR and PS high flexion implants. CR patients had better function than PS patients in walking on even ground or uphill or sitting. CR patients had higher activity scores for recreational than for advanced activities, while activity scores for the PS patients were similar between these activities. Kinematic variables that affected function for some activities included extremes of flexion, A-P translations of lateral and medial condyles, and axial rotation intervals.

Previosuly, Komistek et al. have shown that the kinematics of the patellofemoral joint is altered after a TKA surgery. Specifically the implanted patella experiences significantly less rotation than the natural patella. Also, in early flexion, the patellofemoral contact positions differed significantly between implanted and non-implanted patellae. It was also found that some of TKA subjects experience patellofemoral separation. These kinematical differences may lead to adverse mechanical conditions and increase fatigue or cause loosening of the implant components. This study’s objective was to determine the three-dimensional patellofemoral kinematics and correlate it with the in vivo sound (vibrations) detected using accelerometers for subjects having a TKA and a non-implanted knee under in vivo, weight bearing conditions. The correlation of the knee mechanical conditions with the vibration data may indicate new parameters that may be used to diagnose the condition of the articular cartilage or implant components.

Fifteen subjects (average age 71.8 ±7.4years) having one implanted knee (mobile bearing Hi-Flex PS) and the healthy contralateral knee, performed

deep knee bend to maximum flexion,

Three miniature, piezoelectric, three-axial accelerometers were attached to the patella and femoral epicondyle. The study was approved by the Institutional Review Board and informed consent was obtained from all subjects. The sensors detected the vibration magnitudes and frequencies of the articulating patellofemoral joint surfaces. The signals were amplified and low-pass filtered at 5 kHz by a signal conditioner. The 3D tibiofemoral and patellofemoral kinematics were derived for both knees using a previously published 3D-to-2D registration technique. The 3D bone models were recovered from CT scans, while implant models were obtained from the manufacturer. The patellofemoral rotations were described using the Grood and Suntay convention. The kinematics and sound data were synchronized and recorded under fluoroscopic surveillance, for 10 patients. Then a subset of seven subjects having a TKA was re-analyzed for their contralateral (non-implanted) knee. The vibration signal was then converted to audible sound and correlated with the 3D kinematics.

On average, the subjects achieved more flexion with their TKA (103.4°±15.9°) than with their contralateral knee (96.3°±18.3°). The patellofemoral kinematics varied between the TKA and nonimplanted patella groups; the resurfaced patella experienced less flexion, less medial rotation and less tilt than the contralateral patella. The patellar flexion results were consistent with previously reported literature for both TKA and non-implanted patellae. Also, the resurfaced patellae contacted the femur more proximally than healthy patellae. Audible signals were found for both groups of subjects. The frequency analysis demonstrated that specific frequencies were in similar range for both groups, but the magnitudes and variations were different for the TKA and contralateral knees.

This study correlated 3D patellofemoral kinematics with sound under in vivo conditions for three different activities. Variable audible signals were detected for TKA and non-implanted knees. Vibration magnitude and frequency identification, under in vivo conditions, for TKA may lead to a better understanding of wear and failure modes with respect to the patellofemoral mechanics, more specifically, the patellar insert. Currently this initial study is being expanded to degenerated knee joints and failed TKAs for possible applications of the vibration analysis to the early diagnosis of knee arthritis, detection of implant loosening or wear and monitoring of implant osteointegration progress.

Previous in vivo studies have not documented if ethnicity or gender influence knee kinematics for the healthy knee joint. Other measurements, such as hip-knee-ankle alignment have been previously shown to be significantly different between females and males, as well as Japanese and Caucasian populations in the young healthy knee [1]. Differences in knee kinematics in high flexion positions may relate to both etiology of osteoarthritis and success in knee replacement designs. Although differences in knee anatomy have been identified, their significance in knee function has not yet been clarified. Therefore, the objective of this study was to determine the 3D, in vivo normal knee kinematics for various subjects from different gender and ethnic backgrounds, and to identify significant differences, if any, between populations.

The 3D, in vivo, weight bearing normal knee kinematics was determined for 79 healthy subjects, including 48 Caucasians, 24 Japanese, 42 males, and 37 females. Each participant performed deep knee bend activity from a standing (full extension) to squatting to a lunge motion, until maximum knee flexion was reached. The study was approved by the Institutional Review Board and informed consent form was obtained from all subjects. The 3D bone models, created by segmentation from MR images, were used to recreate the 3D knee kinematics using the previously described fluoroscopic and 3D-to-2D registration techniques (Fig. 1) [2,3]. Tibiofemoral rotations were described using the ISB recommended Grood and Suntay convention [4,5]. Anterior-posterior translations of the centers of the posterior femoral condyles were normalized due to significantly different anthropometry in the subjects. Anterior cruciate ligament (ACL) laxity was also measured using a KT-1000 device for 72 of these subjects. Statistical analysis was performed using the Student’s t-test, set at the 95% confidence interval.

Most subjects achieved very high flexion, however substantial variability occurred in all groups. Range of motion (ROM) varied from 117° to 177°, while average external rotation was 31°± 9.9° for all subjects. Japanese and female subjects achieved greater ROM than Caucasian (p=0.048) and male (p=0.014) subjects. From full extension to 140° of flexion (which 87% of subjects achieved), few significant differences between any of the populations were observed. At deeper flexion, the external rotation was higher for female than for male subjects, however not statistically significant (p=0.0564 at 155°). Also at deep flexion, the adduction was significantly higher for female subjects. The translations of the lateral condyle were very similar between respective groups, but at deep flexion, the medial condyle remained significantly more anterior for females, leading to greater axial rotation and ROM. As ACL laxity increased, flexion/extension ROM significantly increased (r2=0.184, p< 0.001). In addition, ACL laxity was also higher for females (6.8 mm) compared to males (5.6 mm, p=0.011), as well as Japanese (7.5 mm) compared to Caucasian (5.6 mm, p=0.0002) subjects.

High variability and ROM in knee kinematics were similar to those seen in previous studies of healthy subjects during a deep knee bending activity [6]. Subjects in this study achieved much greater axial rotation and ROM than previously analyzed TKA patients. A relationship was found between greater axial rotation and increased ROM, and may be related in part to increased ACL laxity in the knee. Significant differences in ROM and laxity were identified between genders and ethnic groups. Also the medial condyle remaining significantly more anterior for females than for males in deep flexion may explain higher external rotation and consequently higher flexion experienced by women. However, understanding the causes for variability within each group may be the key to improved implant design.

Purpose of the study: Changes in prosthetic design to adapt to knee flexion greater than 120 degrees can modify the bone-prosthesis fixation and also displace the femorotibial contact. The purpose of this study was to analyze mid-term results in a consecutive series of 186 arthroplasties and to examine the femorotibial kinematics in vivo.

Material and methods: A posterior stabilized cemented prosthesis with a plateau with motion limited to rotation was used. Design changes concerned: lengthening of the posterior femoral condyle, scooping out the poly-ethylene anteriorly with reorientation and change in the height of the posterior stabilization stem. The same technique was used for all patients who followed the same rehabilitation protocol. Mean age was 69 years (range 22–87). All patients were evaluated clinically with the IKS score and radiologically on the anterioposterior and lateral images. An in vivo analysis of the femorotibial kinematics in the weight bearing condition was also performed in 20 patients under fluoroscopic control with automatic 3D modelization.

Results: Mean follow-up was 40 months (range 2–5 years). Mean IKS function score improved from 34 preoperatively to 96 at last follow-up. The knee score improved from 53 on average to 91 at last follow-up. The mean flexion was 115° (range 45–135°) preop-eratively and 120° (115–145°) at last follow-up. One implant was removed for infection and arthrolysis was performed for one case of stiff joint. Radiographically: the mean postoperative femorotibial alignment was 179° (178–181°), the mean tibial slope 3.8° (0–10°°, the mean patellar height (0.8° (0.56–1°), and the mean elevation of the joint space (4.5 mm. There were two cases of progressive lucent lines in the tibial zone which were stable at last follow-up. All patients analyzed showed a mean posterior displacement of the femorotibial point of contact of 9.7 mm at flexion.

Discussion and conclusion: Changes in prosthesis design to adapt to greater range of flexion do not appear to have a negative effect at mid-term on implant fixation. The clinical flexion ranges obtained were encourageing and the correlation with kinematic results show that the degree of preoperative flexion remains a determining factor for the postoperative outcome. Posterior displacement of the femoro-tibial point of contact, observed in all patients examined fluoroscopically, certainly contributed to the good postoperative flexion.

Considerable differences in kinematics between different designs of knee prostheses and compared to the natural knee have been seen in vivo. Most noticeably, lift off of the femoral condyles from the tibial insert has been observed in many patients. The aim of this study was to simulate lateral femoral condylar lift off in vitro and to compare the wear of fixed bearing knee prostheses with and without lift off.

Twelve PFC Sigma cruciate retaining fixed bearing knees (DePuy, Leeds, UK) were tested using six station simulators (Prosim, Manchester, UK). The kinematic input conditions were femoral axis loading (maximum 2.6 kN), flexion-extension (0–58°), internal/external rotation (±5°) and anterior/posterior displacement (0–5 mm). Six knees were tested under these standard conditions for 4 million cycles. Six knees were tested under these conditions with the addition of lateral femoral condylar lift off, for 5 million cycles. The lubricant used was 25% newborn calf serum. Wear of the inserts was determined gravimetrically.

Under the standard kinematic conditions the mean wear rate with 95% confidence limits was 8.8 ± 4.8 mm 3/million cycles. When femoral condylar lift off was simulated the mean wear rate increased to 16.4 ± 2.9mm 3/million cycles, which was statistically significantly higher (p < 0.01, Students t-test). The wear patterns on the femoral articulating surface of all the inserts showed more burnishing wear on the medial condyle than the lateral. However, in the simulation of lift off the medial condyle was more aggressively worn with evidence of adhesion and surface defects.

The presence of lateral femoral condylar lift off accelerated the wear of PFC Sigma cruciate retaining fixed bearing knees. The lateral lift off produced uneven loading of the bearing, resulting in elevated contact stresses and hence more wear damage to the medial side of the insert. The implications of condylar lift off include increased wear of the polyethylene and possible osteolysis.

Introduction: In vivo fluoroscopic studies have shown considerable differences in kinematics between different designs of knee prostheses and compared to the natural knee. Most noticeably, lift off of the femoral condyles from the tibial insert has been observed in many patients (Dennis et al, 2003). The aim of this study was to simulate lateral femoral condylar lift off in vitro and to compare the wear of fixed bearing knee prostheses with and without lift off.

Materials and Methods: 12 PFC Sigma cruciate retaining fixed bearing knees (DePuy, Leeds, UK) were tested. The 10 mm thick inserts were manufactured from GUR1020 UHMWPE and gamma irradiated in a vacuum. The inserts snap fitted into titanium alloy tibial trays, and articulated against Co-Cr-Mo alloy femoral components. The testing was carried out on six station simulators (Prosim, Manchester, UK). Femoral axis loading (maximum 2.6 kN) and the flex-ion-extension profile (0–58°) were adopted from ISO 14243 (1999). The internal/external rotation was ± 5° and anterior/ posterior displacement 0–5 mm. Six of the knees were tested under these standard conditions for 4 million cycles. A further six knees were tested under these conditions with the addition of lateral femoral condylar lift off, for 5 million cycles. The lift off was achieved by introducing an adduction moment to the tibial carriage, producing a separation of approximately 1 mm during the swing phase of the simulator cycle. The simulator was run at 1 Hz and the lubricant used was 25% newborn calf serum. Wear was determined gravimetrically, using unloaded soak controls to adjust for moisture uptake. Statistical analysis was performed using Students t-test (p < 0.05).

Results: Under the standard kinematic conditions the mean wear rate with 95% confidence limits was 8.8 ± 4.8 mm3/million cycles. When femoral condylar lift off was simulated the mean wear rate increased to 16.2 ± 2.9 mm3/million cycles, which was statistically significantly higher (p < 0.01). The wear patterns on the femoral articulating surface of all the inserts showed more burnishing wear on the medial condyle than the lateral. However, in the simulation of lift off the medial condyle was even more aggressively worn with evidence of adhesion and surface defects.

Discussion: The presence of lateral femoral condylar lift off resulted in a higher wear rate on the medial compartment of the PFC Sigma fixed bearing knee. This could be due to elevated contact stresses as the lateral lift off produced uneven loading of the bearing. Further, additional medial/lateral sliding of the medial condyle whilst it remained in contact may have accelerated the wear by cross shearing of the polyethylene in the medial/lateral direction. This direction is weakened when the polyethylene is preferentially molecularly orientated by sliding in the flexion-extension axis. The implications of condylar lift off include premature wear of the polyethylene and possible component loosening.

Introduction: Deep flexion may affect both femorotibial contact pattern and patellofemoral interface. The objective of this study was to conduct the first in vivo kinematic analysis that determines the 3D motions of the femorotibial and patellofemoral joints, simultaneously from full extension into deep flexion.

Methods: Three-dimensional femorotibial and patello-femoral kinematics were evaluated during a deep knee bend using fluoroscopy for five subjects having a normal knee, five having an ACL-deficient knee and 20 subjects having a TKA designed for deep flexion.

Results: The average weight-bearing range-of-motion was 125 degrees, significantly higher than in previous studies. On average, subjects experienced 4.9o of normal axial rotation and only three subjects experienced an opposite rotation pattern. On average, subjects experienced −9.7 mm of posterior femoral rollback (PFR) and all subjects experienced at least −4.4 mm of PFR. These subjects experienced less patellofemoral translation than the normal knee, but the average motion was similar in pattern to the normal knee. On average, the subjects having a TKA experienced patella tilt angles that were similar to the normal knee.

Discussion: It is assumed that femorotibial kinematics can play a major role in patellofemoral kinematics. Altering the patella motion and/or the patellar ligament rotation could lead to much higher forces at the patel-lofemoral interface. In this study, these subjects experienced kinematic patterns that were very similar to the normal knee and it can be deducted that forces acting on the patella were not significantly increased for TKA subjects compared with the normal subjects.

Introduction: Previous in vivo kinematic studies have assessed total knee arthroplasty (TKA) motion under weight-bearing conditions. This in vivo study analyzed and compared posterior cruciate retaining (PCR) and posterior stabilized (PS) kinematics under passive and weight-bearing conditions in subjects implanted with both a PCR and PS TKA.

Methods: Eighteen subjects were implanted with a PCR and a PS TKA, by a single surgeon using a similar surgical technique. Both implant designs had similar condylar geometry. Femorotibial contact positions for all 18 subjects (PCR and PS), implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject,while under fluoroscopic surveillance, performed a weight-bearing deep knee bend and a passive, nonweight-bearing flexion. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and femoral condylar lift-off were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: Under passive and weight-bearing conditions, the PCR TKA experienced more paradoxical anterior translation than the PS TKA. Under passive, non weight-bearing conditions, the PS TKA, on average, experienced 3.5 mm of posterior femoral rollback, compared to only 0.6 mm for the PCR TKA. Under weight-bearing conditions, the PS TKA experienced only 0.6 mm of posterior femoral rollback, compared to 0.9 mm for the PCR TKA. The maximum anterior slide was 10.0 mm for the PCR TKA and only 2.7 mm for the PS TKA. There was greater variability in both the PCR and PS anteroposterior data. Subjects having a PCR TKA experienced more normal axial rotation patterns. Sixteen of 18 PCR TKA experienced a normal axial rotation pattern under weight-bearing conditions, while only 9/18 PS TKA experienced a normal pattern. Nonweight-bearing, passive axial rotation patterns were more abnormal for both groups than the weight-bearing patterns. The greatest difference between passive and weight-bearing conditions occurred in the condylar lift-off data. Under passive conditions, both TKA groups experienced significantly greater magnitude and incidence of condylar lift-off. The maximum amount of condylar lift-off under passive conditions was 5.0 mm for the PCR TKA and 6.4 mm for the PS TKA.

Discussion: This is the first in vivo kinematic study to assess a comparison between PCR and PS TKA implanted by the same surgeon in the same patient. Subjects in this study experienced more abnormal kinematic patterns, especially condylar lift-off, when tested under passive, nonweight-bearing conditions. Subjects having a PS TKA experienced less variability in their kinematic data, but PCR TKA, on average, experienced more normal axial rotation and less condylar lift-off.

Introduction: Previously, in vivo kinematic studies have determined that posterior stabilized (PS) TKA experienced posterior femoral rollback during deep flexion, while posterior cruciate retaining (PCR) experience a paradoxical anterior slide during both gait and deep flexion. The objective of this present study was to analyze the in vivo kinematics for subjects implanted with a PS mobile bearing TKA to determine if there are any distinct advantages.

Methods: Femorotibial contact positions for ten subjects having a mobile bearing PS TKA, implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject,while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion and normal gait. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and condylar lift-off were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: During a deep knee bend, subjects having the Sigma PS rotating platform experienced minimal motion of their medial condyle and posterior femoral rollback of their lateral condyle. On average, the subjects experienced −2.3 mm of posterior femoral rollback (PFR) of their lateral condyle. Nine of ten subjects experienced PFR of their lateral condyle. During gait, on average, subjects experienced minimal motion of their medial (0.8 mm) and lateral condyles (−0.4 mm) from heel-strike to toe-off. During a deep knee bend all ten subjects experienced normal axial rotation (average = 4.0°). During gait, 6/10 subjects experienced normal axial rotation, while four subjects experienced less than 0.8 degrees of reverse rotation. Only 1/10 of the subjects experienced greater than 1.0 mm of condylar lift-off during gait or a deep knee bend.

Discussion: Subject in this study experienced normal kinematic patterns during gait and a deep knee bend. Only one subject experienced greater than 1.0 mm of condylar lift-off, during a deep knee bend and gait. At the present time, it is uncertain if the excellent kinematic patterns for the subjects in this study were related to the chosen surgeon, surgical technique or implant design. If implant design was an influencing factor, subjects requiring a TKA may receive benefit from having a PS mobile bearing type TKA.

Introduction: Previously, in vivo kinematic studies have determined the in vivo kinematics of the femur relative to the metal base-plate. These kinematic studies have reported posterior femoral rollback in posterior stabilized (PS) TKA designs, but the actual time of cam/post engagement was not determined. The objective of this present study was to determine, under in vivo conditions, the time of cam/post engagement and the kinematics of the femur relative to the polyethylene insert.

Methods: Femorotibial contact positions for twenty subjects having a PS TKA, implanted by two single surgeons, were analyzed using video fluoroscopy. Ten subjects were implanted with a PS TKA that is designed for early cam/post engagement (PSE) and ten subjects with a PS TKA designed for later cam/post engagement (PSL). Each subject, while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion. Video images were downloaded to a workstation computer and analyzed at ten-degree increments of knee flexion. Femorotibial contact paths for the medial and lateral condyles, axial rotation and condylar lift-off were then determined using a computer automated model-fitting technique.

Results: Subjects implanted with the PSE TKA experienced, on average, the cam engaging the post at 48° (10 to 80°). Subjects having the PSL TKA experienced more consistent results and did experience engagement in deep flexion (Average 75°). Subjects having the PSE TKA experienced, on average, −5.5 mm (1.5 to −9.3) of posterior femoral rollback (PFR), while subjects having the PSL TKA experienced only −2.6 mm (8.5 to −9.0) of PFR. Subjects having the PSE TKA experienced more normal axial rotation patterns. Nine subjects having the PSE TKA experienced condylar lift-off (maximum = 1.9 mm), while only 4/10 having the PSL TKA experienced condylar lift-off (maximum = 2.7 mm).

Discussion: This is the first study to determine the in vivo contact position of the cam/post mechanism. Subjects having a PSE TKA experienced earlier cam/post engagement than subjects having the PSL TKA. Some subjects did not experience any cam/post engagement throughout knee flexion. Subjects having the PSE TKA experienced more PFR and better axial rotation patterns, but subjects having a PSL TKA experienced lesser incidence of condylar lift-off. Results from this study suggest that there may be an advantage to early cam/post engagement, which leads to more normal axial rotation patterns caused by the medial condyle moving in the anterior direction as the lateral condyle rolls in the posterior direction.

Introduction: Previous in vivo kinematic analyses of the hip joint have determined that femoral head separation from the medial aspect of the acetabular component occurs in metal-on-polyethylene THA. The present study analyzes subjects having either an alumina-on-alumina (AOA),alumina-on-polyethylene (AOP),metal-on-metal (MOM) or metal-on-polyethylene (MOP) THA during gait to determine if the incidence of hip joint separation varies based on articular surface material.

Methods: Forty subjects were analyzed in vivo using video fluoroscopy. Ten subjects had a AOA THA, ten an AOP THA, ten a MOM THA, and ten having a MOP THA. All THA subjects were implanted by two surgeons and were judged clinically successful (Harris hip scores > 90.0). Each subject performed normal gait on a treadmill and an abduction/adduction leg lift maneuver while under fluoroscopic surveillance. The two-dimensional (2D) fluoroscopic videos were converted into 3D using a computer automated model-fitting technique. Each implant was analyzed at varying flexion angles to assess the incidence of hip joint separation.

Results: During gait and the abduction/adduction leg lift, no separation was observed in subjects having an AOA THA or in subjects having a MOM THA. Similar to our previous studies pertaining to subjects having a THA with a polyethylene acetabular insert, all ten subjects having a MOP THA and 6/10 subjects having an AOP THA experienced hip joint separation. The maximum amount of separation was 7.4 mm for a subject having an AOP THA and 3.1 mm for a subject having a MOP THA.

Discussion: This study shows femoral head separation from the medial aspect of the acetabular component can occur in the presence of a polyethylene liner. The femoral head often remains in contact with the liner, hinging superolaterally. Potential detrimental effects resulting from hip joint separation include premature polyethylene wear, component loosening (secondary to impulse loading conditions) and hip instability. Wear may be enhanced due to creation of multidirectional wear vectors or excessive loads due to eccentric femoral head pivoting. The absence of separation observed in AOA and MOM THA designs may be related to increased wettability of these materials and tighter radial tolerances resulting in a cohesive lubrication film. This data may be of value in hip simulation studies to better duplicate wear patterns observed in retrieval analyses and assist in the understanding of the lubrication regime and wear rates in AOA and MOM designs, allowing for the synthesis of prosthetic components that minimize wear and optimize kinematics.

Introduction: Previously, in vivo kinematic studies have determined that axial rotation patterns are quite variable between implant type and specific subjects. Previously, kinematic studies have determined that subjects having a mobile bearing TKA experience axial rotation, but it was unknown as to whether the bearing was rotating. Therefore, the objective of this present study was to analyze the in vivo kinematics for subjects having a mobile bearing prosthesis to determine if the polyethylene rotates relative to the femoral and/or the tibial components.

Methods: Femorotibial contact positions for ten subjects having a mobile bearing TKA, implanted by a single surgeon, were analyzed using video fluoroscopy. Each subject, while under fluoroscopic surveillance, performed a weight-bearing deep knee bend to maximum flexion. Video images were downloaded to a workstation computer and analyzed at varying degrees of knee flexion. Each polyethylene component had four metallic beads, inserted at known positions. Using a 3D model-fitting process, the femoral, tibial and polyethylene insert components were overlaid onto the fluoroscopic images. Initially, the polyethylene insert was made transparent, but the computer would overlay the four metal beads. Then, the polyethylene insert was made viewable and analyzed relative to the metal femoral and tibial components.

Results: All of the subjects experienced polyethylene bearing rotation relative to the metal tibial component and minimal rotation relative to the metal femoral component. On average, relative to the metal tibial component, the subjects experienced 4.7° (2.1 to 7.9°) of polyethylene bearing rotation. The subjects experienced a similar amount of metal femoral component rotation, relative to the metal tibial component. On average, the subjects experienced 4.0° (−0.7 to 10.0°) of rotation of the metal femoral component relative to the metal tibial component. Therefore, on average, subjects experienced only 0.7° of rotation for the metal femoral component relative to the polyethylene bearing. Also, on average, from full extension to 90° of knee flexion the subjects experienced −2.9 mm of posterior femoral rollback of their lateral condyle and –0.4 mm of their medial condyle.

Discussion: This is the firs study to determine the in vivo rotation of the polyethylene bearing for subjects having a mobile bearing TKA. The results from this study determined that the polyethylene bearing is rotating relative to the metal tibial component, but not relative to the metal femoral component. Therefore, as the metal femoral component axially rotates the polyethylene bearing is rotating a similar amount in the same direction. Since bearing rotation does occur under in vivo conditions, subjects implanted with a mobile bearing prosthesis may be subjected to lesser amounts of contact stresses, which may be beneficial to them.

Introduction: The goal of this study was to determine the difference between weight-bearing and non weight-bearing range of motion (ROM) for Japanese subjects having either a fixed or mobile bearing TKA with either a resurfaced (RP) or unresurfaced (UP) patella.

Methods: Forty subjects were evaluated using video fluoroscopy. Twenty subjects had a fixed bearing posterior cruciate retaining (PCR) TKA (10 RP, 10 UP) and twenty subjects had a mobile bearing (MB) TKA (10 RP, 10 UP). Under weight-bearing conditions, each subject performed successive deep knee bends to maximum flexion. Then, under passive, non weight-bearing conditions the subjects stood on one leg and passively flexed their knee to maximum flexion. Each trial was recorded and analyzed digitally. The angle between the femoral and tibial longitudinal axes was subtracted from 180o to obtain the amount of flexion.A single surgeon control was used. The average age of the subjects was 66.4, 78.1, 70.3, and 71.1 for subjects having PCR RP, PCR UP, MB RP, and MB UP, respectively. All total knee subjects were judged excellent clinically with HSS scores > 90 points. None complained of pain during testing.

Results: The preoperative ROM for the implanted knee groups was 115, 122, 110, and 120 degrees for subjects having a PCR RP, PCR UP, MB RP, and MB UP, respectively. The average passive ROM was 106 (90–131) and 108 (72–128) degrees for subjects having a PCR RP and PCR UP, respectively. Subjects having a MB TKA experienced greater passive ROM, 120 degrees for both the MB RP (105–136o) and MB UP (105–167o). Under weight-bearing conditions, ROM decreased for all groups, with the average ROM of 101 (90–125), 108 (86–128), 109 (92–134), and 114 (94–142) degrees for subjects having a PCR RP, PCR UP, MB RP, and MB UP, respectively. The greatest amount of ROM occurred for a subject having a MB UP, 167o during passive ROM and 142o during a weight-bearing ROM.

Discussion: Subjects in this study having a MB TKA experienced greater ROM for all of the compared four parameters. Subjects having a MB RP experienced greater passive (120 vs. 106) and weight-bearing (109 vs. 101) ROM compared to the PCR RP group. Similarly, subjects having a MB UP experienced greater passive (120 vs. 108) and weight-bearing (114 vs. 108) ROM compared to the PCR UP group. Interestingly, subjects having an UP TKA experienced greater ROM compared to subjects having a RP TKA. The results from this study may suggest that a mobile bearing TKA may lead to greater ROM for the Japanese populations, where achieving deep flexion is essential for normal daily activities.

Introduction: Recently, many different mobile bearing TKA designs are being implanted throughout the world. Also,fluoroscopy has been used to evaluate variousTKA under in vivo conditions to determine the kinematics. The objective of this study was to utilize a randomized prospective study to evaluate the kinematic patterns, for Japanese subjects implanted with two different mobile bearing TKA.

Methods: Twenty Japanese subjects were entered into a prospective study. Ten subjects were implanted with a mobile bearing TKA, which is free to rotate around the longitudinal axis of the tibia (MB1). The other ten subjects were implanted with a mobile bearing TKA that allows for unrestricted translation and rotation (MB2). Femorotibial contact positions were analyzed using video fluoroscopy. Each subject, while under fluoroscopic surveillance, was asked to perform gait. Video images were downloaded to a workstation computer and analyzed at varying degrees of gait stance. Femorotibial contact paths for the medial and lateral condyles were then determined using a computer automated model-fitting technique. Femorotibial contact anterior to the tibial midline in the sagittal plane was denoted as positive and contact posterior was denoted as negative.

Results: During gait, on average, subjects implanted with MB1 experienced minimal A/P translation of either condyle. Also, all subjects having MB1 experienced similar motion patterns throughout the stance phase of gait. Axial rotation was evident in these subjects, as one condyle would move in the anterior direction, a similar amount to the other condyle moving posterior. On average, subjects implanted with MB2 experienced both translation and rotation. The amount of translation for subjects with MB2 was greater than subjects with MB1. The kinematic patterns for subjects having MB2 were also more variable than subjects having MB1. Axial rotation was also evident for subjects having MB1.

Discussion: This study has shown that the kinematic patterns for subjects having two different mobile bearing TKA designs differed considerably. Subjects implanted with a mobile bearing TKA that only allows for free rotation, experienced minimal A/P motion and significant axial rotation (MB1). Subjects implanted with a mobile bearing TKA that allows for free translation and rotation did experience both types of motions (MB2). There was minimal variability in the kinematic patterns for subjects implanted with MB1, while subjects implanted with MB2 experienced more variable kinematic patterns.

Introduction: Understanding the in vivo motions of human joints has become increasingly important. Researchers have used in vitro (cadavers), non-invasive (gait labs), and in vivo (RSA, fluoroscopy) approaches to assess human knee motion. The objective of this study was to use fluoroscopy and computer tomography (CT) to accurately determine the 3D, in vivo, weight-bearing kinematics of normal knees.

Methods: Five normal knees clinically assessed as having no pain or ligamentous laxity were analyzed. Using CT scanning, slices were obtained six inches proximal to the joint line on the femur and six inches of the proximal tibia. Three-dimensional CAD models of each subject’s femur, tibia and patella were recreated from the 3D bone density data. Each subject was then asked to perform five weight-bearing activities while under fluoroscopic surveillance: (1) deep knee bend, (2) normal gait, (3) chair rise, (4) chair sit, and (5) stair descent. The computer-generated 3D models of each subject’s femur and tibiaon (> 1

The objective of this present study was to determine the in vivo kinematic patterns for subjects implanted with a patellofemoral arthroplasty (PFA).

Twenty subjects, all having a PFA, were studied (< 2 years post-op) under fluoroscopic surveillance to determine patellofemoral contact positions, sagittal plane, and medial/lateral translation using a skyline view.

The patellofemoral contact patterns for each subject having a PFA was highly variable, 11.9 mm of translation. The average amount of patella rotation during the full flexion cycle was 26.3 degrees, while one subject experienced 48.6 degrees. The average amount of medial/lateral translation was 3.8 mm (5 > 5 mm). Five subjects experienced grater than 5 mm of motion.

This was the first study to ever determine the in vivo kinematics for subjects having a PFA and the in vivo medial/lateral translation patterns of the patellofemoral joint. Subjects in this study experienced high variability and some abnormal rotational patterns. Most of the subjects who underwent PFA in this study had a previous history of subluxed or dislocated patella which affects the normal patella tracking, especially regarding tilting and translation. This tracking may also be directly affected by patellofemoral conformity, a consequence of femoral implant design. Finally, after PFA the patello-tibial tilt angle is influenced by the anteroposterior positioning of the femoral component.

The results of this very first in vivo kinematic study may play an important role, not only for design consideration of patellofemoral replacement but also for surgical technique in order to obtain optimal implant positioning.

The objective of the present study was to analyse kinematics of subjects having a UKA during stance phase of gait, where the ACL was intact at the time of the operative procedure.

Femorotibial contact positions for nineteen subjects (15 medial UKA (MUA); 14 lateral UKA (LUA); HSS > 90, post-op > 3 yrs) were analysed using video fluoroscopy.

During stance-phase of gait, on average, subjects having a medial UKA experienced 0.8 mm of anterior motion (7.7 to – 2.3 mm), while subjects having a lateral UKA experienced −0.4 mm (0.9 to – 2.1 mm) of posterior femoral rollback (PFR). Eight of 15 subjects having a medial UKA and two out of four lateral UKA experienced PFR. Eight of 15 subjects having a medial UKA experienced normal axial rotation (average = 0.9 degrees) and one out of four subjects having a lateral UKA experienced normal axial rotation (average = −6.0 degrees).

High variability in the kinematic data for subjects experiencing an anterior slide and opposite axial rotation suggests that these subjects had an ACL that was not functioning properly and was unable to provide an anterior constraint force with the necessary magnitude to thrust the femur in the anterior direction at full extension. Progressive laxity of the ACL may occur over time, and at least in part, lead to premature polyethylene wear occasionally seen in UKA. Our results support the findings of other studies that the ACL plays a significant role in maintaining satisfactory knee kinematics, which may also, in part, contribute to UKA longevity.

The objective of this present study is to conduct a comparative analysis of the kinematic data derived for all subjects having a TKA who were analysed over the past eight years at our laboratory.

Femorotibial contact positions for 705 subjects having either a fixed bearing PCR or PS TKA or mobile bearing TKA were analysed in three-dimensions using video fluoroscopy.

During a deep knee bend, all PS TKA types subjects experienced a medial pivot motion, averaging −3.8 of lateral condyle posterior femoral rollback (PFR), respectively. Subjects having a fixed bearing PCR TKA experienced only −0.7 mm of lateral condyle PFR and an anterior slide of 1.6 mm for the medial condyle. Twenty-nine percent of the PCR TKA analysed had a lateral pivot and 71% experienced a medial pivot. Subjects having a mobile bearing TKA experienced −2.8 mm of lateral condyle PFR and 0.4 mm of medial condyle anterior slide. Fifty-one percent of the moble bearing implants experienced a medial pivot and 43% experienced a lateral pivot. During gait, PS and PCR fixed bearing TKA types experienced similar kinematic patterns. Subjects having a mobile bearing TKA experienced minimal motion, probably due to the mobile bearing TKA having greater sagittal conformity and had the lowest standard deviation.

There was great variability in the data comparing various TKA designs. Subjects in this multicentre analysis predominantly experienced a medial pivot motion, although certain TKA designs did demonstrate a lateral pivot motion.

Purpose: Cinematic studies after total knee arthroplasty without an anterior cruciate ligament demonstrate abnormal behaviour compared with the normal knee. The purpose of this cinematic analysis was to examine the knee behaviour after implantation of single-compartment prostheses with an intact anterior cruciate ligament.

Material and methods: The femorotibial contact points were analysed by videofluoroscopy in 20 patients executing a complete weight-bearing extension to flexion movement. These patients had medial (n=16) or lateral (n=4) single-compartment implants. The clinical result in all patients was considered to be very good with a mean HSS score of 97.9 points at a mean 56 months postoperatively. The femorotibial contact points were determined using an automatic computerised adaptation-modelling system. An anterior contact on the medial tibial line in the sagittal plane was positive and a posterior contact was negative. The rotation axis in the craniopodal direction was measured between the anteroposterior longitudinal axis of the femoral component and the fixed axis of the tibial component.

Results: The mean position of the contact point for medial single-compartment prostheses was −90.8 mm in complete extension, −1.4 mm at 30° flexion, −2.4 mm at 60°, and −1.7 mm at 90°. Mean position of the contact point for lateral single-compartment prostheses was −4.0 mm at complete extension, −7.9 mm at 30° flexion, −5.7 mm at 60° and −5/7 mm at 90°. Seven patients with a medial implant and two patients with a lateral implant exhibited paradoxical anterior translation of the femur during flexion. On the average, patients with a medial implant had normal 3.3° axial rotation at 90°; axial rotation was 11.2° for patients with a lateral implant.

Discussion and conclusion: Cinematic analysis of the normal knee has demonstrated anterior femorotibial contact in extension and 14.2 mm posterior rolling of the femoral component during flexion. After total knee arthroplasty without preservation of the anterior cruciate ligament, the rolling movement is limited or absent and a paradoxical anterior translation can be observed. In the present study, the first reported on single-compartment implants, demonstrates that movement is similar to that in the normal knee but with major interindividual variability. A posterior contact at extension and a paradoxical anterior translation can also be observed. This suggests progressive development of anterior cruciate ligament laxity over time, which can at least in part explain the premature polyethylene wear observed after implantation of single-compartment knee implants.