Conventional fluoroscopes are routinely used to analyze human skeletal joints during motions such as deep knee bends. Such diagnostics are used to characterize pre and post operative arthoplasty results, particularly in association with total joint replacement procedures. The pseudo-stationary conditions imposed by the fixed fluoroscope limit the diagnostic procedures to much less than natural skeletal motion and load conditions, thus diminishing the 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 essentially a mobile robot that can acquire real-time x-ray records of hip, knee, or ankle joint motion while the patient walks normally within a laboratory floor area. It is anticipated that the TFS will provide clearer and more representative x-ray images.

The robotic mechanization includes an untethered and omni-directional mobile platform that follows the patient as he/she walks, including negotiating stairs or ramps.

In addition to following the patient, additional control devices track the joint motions that occur relative to the patient’s body, e.g., knee joint vertical and anterior/posterior relative motion. The technical features of the TFS will be described, and test results related to the commissioning of the TFS for clinical trials will be presented. Initial clinical test results will be provided.

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.

Introduction: Although use of modular femoral components in revision hip arthroplasty is widely accepted, many still question the need for modular versatility in primary THA. The purpose of our study was to examine in a large cohort the percentage of hips in which femoral component version was changed to optimize stability or avoid prosthetic impingement of the THA construct. We hypothesized that the percentage of hips needing version change in routine primary THA would be low.

Methods: This prospective study analyzed 1000 consecutive primary THAs using a modular S-ROM (DePuy) stem performed by 3 surgeons at 3 institutions all via a posterior approach. Mean patient age at surgery was 57.5 years; 51.6% were male. The difference in version between the femoral sleeve placed anatomically and the femoral stem was recorded intra-operatively.

Results: Femoral component version was changed in 47.9% of hips. Logistic regression analysis showed no correlation between the likelihood of changing stem version and patient age (p=0.87), gender (p=0.23), diagnosis (p=0.54), or surgeon (p=0.27). 10 hips (1%) experienced early dislocation (within 3 months post-op). With the numbers available, there was a slight trend of lower dislocation rate in hips where stem version was changed (0.6%) versus those in which it was not (1.5%, p=0.16, chi squared).

Conclusion: The incidence of femoral version change in routine primary THA was much higher than expected. It was difficult to predict the need to alter version based on clinical variables including diagnosis. Thus, we conclude it may be advantageous to routinely use a stem that allows variable version as it is not possible to pre-operatively determine when changing version will be required. In addition, we surmise our low dislocation rate compared to historical controls of THA performed using a posterior approach was aided by the ability to adjust version in almost half of our patients.

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.

Introduction: Common failure modes of revision total knee arthroplasty (TKA) include aseptic component loosening and damage to constraining mechanisms which are often required in revision TKA. Mobile-bearing (MB) revision TKA components have been developed in hopes of lessening these failure mechanisms. Our objective was to evaluate the early clinical outcomes for the use of MB in revision TKA with a minimum 2-year follow-up and to evaluate bearing complications.

Methods: Retrospective clinical and radiographic evaluation of 84 MB revision TKAs with minimum 2-year follow-up was performed. Revision TKAs were performed using PFC Sigma and LCS revision rotating platform implants (Depuy, Warsaw, IN).

Indications for revision include aseptic loosening (31 knees), instability (30 knees), failed unicompartmental knee replacement (8 knees), infection reimplantation (7 knees), arthrofibrosis (3 knees), chronic hemarthrosis (3 knees), failed patellofemoral replacements (1 knees), and nonunion of a supracondylar femur fracture (1 knee).

Results: At a mean follow-up of 3.7 years, the average Knee Society clinical and function scores had increased from 50.3 points preoperatively to 89.1 points and from 49.3 points to 80.1 points, respectively. Average motion improved from 99.8° preoperatively to 116.5° postoperatively. Radiographic review demonstrated excellent fixation with no evidence of component loosening upon latest follow-up. No cases of bearing instability were observed.

Conclusion: This evaluation of 84 MB revision TKAs has demonstrated favorable early results at a mean follow-up of 3.7 years with no occurrence of bearing instability. Longer follow-up is required to evaluate for potential advantages of reducing polyethylene wear, lessening fixation stresses, and protection of constraining mechanisms.

Introduction: Patellar crepitus (PC) has been reported in 13% of cruciatesubstituting total knee arthroplasty (TKA) patients resulting from synovial tissue impingement within the femoral component intercondylar box (IB). Patient factors, component design, and technical errors have been implicated in PC. We compared primary TKA patients with PC requiring surgery against matched controls to identify significant variables.

Methods: The databases of 2 institutions were reviewed to identify patients requiring surgery for PC. A control group matched for age, sex, and BMI was identified.

Patient charts and radiographs were reviewed. Statistical analysis was performed.

Significant variables associated with patient anatomy, implant size and alignment were subsequently investigated in a computational model to evaluate tendofemoral contact.

Results: Between 2002 and 2008, over 4000 primary TKAs were performed using the Press Fit Condylar Sigma (DePuy, Warsaw, Indiana) TKA. Of these, 59 knees developed PC requiring surgery. The mean time to presentation was 10.9 months. The incidence of PC correlated with greater number of previous surgeries (1.18 vs. 0.44, p= 0.002), decreased patellar button size (35.7 vs. 37.1mm, p=0.003), shorter patellar tendon length (54.5 vs. 57.9mm, p=0.01), and increase in posterior femoral condylar offset (1.27mm vs. 0.17mm, p=0.022). Using a patellar component of 32 or 35mm significantly increased the risk of PC compared to the use of a 38 or 41mm component (p< 0.01, RR=1.61, OR 2.63). Modeling results demonstrated decreased patellar tendon length created increased tendofemoral contact near the IB, while larger buttons increased separation between the tendon and the box edge.

Conclusion: Shortened patellar tendon length and use of smaller patellar components may expose the quadriceps tendon to increased irritation as it traverses across the femoral component IB. Increasing posterior femoral offset may increase quadriceps tendon tension, further risking synovial tissue impingement within the IB.

INTRODUCTION: Many orthopaedic device companies now offer a high flexion (HF) choice within their knee Arthroplasty portfolios. Early published results are mixed between standard (STD) and HF knee devices despite claims of increased flexion with the HF offerings. The purpose of this randomized, controlled, simultaneous, bilateral study was to compare two coronally conforming rotating platform devices to determine if flexion differences were attributed to implant design.

METHODS: Ninety-three subjects underwent simultaneous bilateral TKA across 8 centers. The HF device was randomly assigned to one side and the contralateral leg received the STD device. Average age was 61 years, 99% were diagnosed with osteoarthritis, 66% were females, average BMI was 32 and range of motion was measured by subjective expectations versus satisfaction.

RESULTS: The HF design had statistically better single leg active flexion (SLAF) 12 months after surgery compared to the STD. Consistent with Gupta et. al, in a subgroup with pre-op flexion < 120 degrees in both knees, the HF device was statistically superior in passive flexion, ROM, and SLAF by between 1.8 and 4.5 degrees at 6 months, 12 months, and longitudinally over all postoperative intervals using raw degrees, improvement from pre-op, and adjusting for potentially confounding variables. 57% of subjects preferred their HF knee 6 months postoperatively, although there was no difference in preference at 12 months.

DISCUSSION: The simultaneous bilateral design of this study necessitates that subjects act as their own control eliminating most confounding variables. Gains in postoperative flexion, although small, were superior in the HF TKA group and were greater in those subjects with less than 120 degrees of preoperative flexion, suggesting the ideal candidate for a HF TKA is one with lesser preoperative flexion.

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: Understanding the forces across the human lower extremity joint is of considerable interest to the clinician. In the past, telemetric hip implants have been used to determine the forces across the hip joint, but the forces at the knee joint remain unvalidated. Recently, video fluoroscopy has been utilized to accurately determine the in vivo kinematics of human joints during various activities. The objective of this study was to predict muscle and joint forces from a mathematical model utilizing fluoroscopy as the input motion data.

Methods: Initially, two subjects (one with a total knee and a second with a total hip arthroplasty) were asked to perform normal gait and a deep knee bend while under fluoroscopic surveillance. A fully automated computer model-fitting algorithm was employed to convert the two dimensional (2D) fluoroscopic videos to 3D, and the in vivo motion of the implanted joint was determined. The kinematic data then served as input to a mathematical model in which the relative motions of the segments and the interaction forces between the foot and the ground were also treated as input data. The predicted forces for the implanted joint, quadriceps muscles and patellar ligament were plotted with respect to time, percent gait cycle and knee flexion angle.

Results: The resultant force at the implanted knee joint ranged from 2.0 to 3.5 times body weight (BS) during gait, depending on walking speed and walking motion. A forward leaning pattern resulted in significantly higher knee joint forces. During a deep knee bend, the knee joint forces could rise as high as 3.5 BW. The resultant forces at the implanted hip joint ranged from 2.0 to 4.0 BW, depending on the activity (greater during deep knee bend), walking speed, walking motion and the incidence of hip separation. The patellofemoral forces were minimal during walking (< 0.5 BW), but increased significantly with greater knee flexion to a maximum of 3.5 BW. The quadriceps muscle and patellar ligament forces were similar during gait (1.0 BW), but the quadriceps force was 40% greater in deep knee flexion.

Discussion: The present study has determined that the predicted hip joint forces are similar to telemetrically derived joint forces at the hip joint. Both knee, hip and muscle forces were greater in deep flexion compared to gait. A sensitivity analysis determined that the model is extremely sensitive to patellar ligament and patella motion. Altering the kinematics of the patella and patellar ligament could increase the knee joint forces by 1.0 BW.

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 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: 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: 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.

Introduction: Proximal bone resorption is a common problem after total hip arthroplasty. This has been attributed to stress shielding and has been reported to be more pronounced for cemented than for uncemented implants.

Aim: To investigate the cortical strain distribution of a new proximal “fit and fill” cementless, titanium, femoral, hip prosthesis based on the SROM design.

Methods: Strain gauges were mounted on five fresh-frozen cadaveric and five saw-bone femora and checked against a template for the prosthesis. The strain gauges were placed at four levels on the anterior, posterior, medial and lateral cortices corresponding to the Gruen zones. Two extra strain gauges were placed on the proximal posteromedial cortex. Loading was applied to the intact and reconstructed femora in the ISO 7206–4 orientation and single legged stance in an MTS servo-hydraulic testing machine. Data were analysed using analysis of variance.

Results: The strain distributions following reconstruction and multi-axis loading (ISO 7206–4 orientation) approximated the strains in an intact femur in the diaphysis. The proximal posteromedial cortical strains were approximately 50% of those of the intact femur.

Conclusions: The strains observed in the proximal femur following reconstruction in the present study are considerably higher than most others reported in the literature. A number of factors may contribute to the high proximal strains observed. This study has illustrated that geometric design and material selection along with surgical technique may allow for greater loading to proximal bone and enhance the long term integrity of this type of implant.

Bone loss options in revision total knee replacement include prevention (earlier revision before extensive osteolysis, tedious prosthesis removal), prosthetic substitution, and bone grafting. Massive bone loss options include arthrodesis, custom total knee replacement, amputation, or revision with structural allograft-prosthesis composites. Advantages of structural allografts include their biologic potential, versatility (shape to fit host defects), relative cost effectiveness, potential for bone stock restoration, and the potential for ligamentous reattachment. Potential disadvantages include the risk of disease transmission and graft nonunion, malunion, collapse, or resorption. Extensive preoperative planning is required to rule out infection as well as properly select both the type and size of allograft and prosthetic implant. Fresh frozen allograft specimens are most commonly selected due to superior strength. Implant designs with diaphyseal-engaging stems and increased prosthetic constraint are often required. Extensive surgical exposure is often needed including proximal quadricepsplasty or tibial tubercle osteotomy in some cases. Both the host site and allograft require meticulous preparation both to maximise surface contact between host and allograft as well as mechanical interlock of the allograft with the host. Allograft fixation must be rigid to allow for incorporation. Diaphyseal-engaging stems, screws, and/or plates are often required to obtain this. The favoured method of fixation is cementing the prosthesis to the allograft with the addition of diaphyseal- engaging stems into the host medullary canal. Equivalent results have been obtained with either cemented or press-fit stems. Ligamentous reattachment to the allograft is more successful when done via a bone block technique. Wound closure difficulties may be encountered, particularly in the tibial region. Relaxing incision techniques as well as rotational muscle flaps are occasionally necessary to obtain soft tissue closure without excessive tension. Short-term results have shown union rates at greater than 90% when rigid fixation is obtained. In the author’s series of 32 cases, 86% good to excellent results were obtained at an average follow- up period of 50 months. More common complications include instability and graft collapse. Use of more constrained prostheses with long intramedullary stems will lessen these complications.

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.