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.
Shoulder dislocations account for 50 % of all dislocations, of which 98% are anterior dislocations. Different techniques have been described in literature with variable success, which depends upon type of dislocation, technique used and muscle relaxation. A retrospective review of data of all shoulder dislocations presented to accident and emergency department over a one-year period was undertaken. Over a 1-year period total of 52 patients presented with mean age of 41 years. Closed reduction was attempted in all patients by accident and emergency department using various techniques and combination of analgesia. Unsuccessful reductions and those with associated fractures were referred to orthopaedics department. This group had closed reduction utilising Sahas zero position technique in accident and emergency department. Post reduction all patients had two views of radiograph to confirm reduction and poly-sling for 2–3 weeks.Purpose
Method
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. A wear simulation was developed using fluoroscopic data from a pool of eighteen TKA patients performing a deep knee bend. All patients had a Sigma CR Fixed Bearing implant (DePuy) and were well functioning (Knee Society Score > 90). A single patient was selected that represented the typical motions, which was characterized by early rollback followed by anterior motion with an overall modest internal tibial rotation (Figure 1). The relative motion between the femoral and tibial components was transformed to match the coordinate system of an AMTI knee wear simulator [6] and a compressive load input was derived using inverse dynamics [7]. The resulting force and motions (Figure 2) were then applied in a wear simulation with 5 MRad crosslinked and remelted polyethylene for 3 Mcyc at 1 Hz. Components were carefully positioned and each joint (n=3) was tested in 25% bovine calf serum (Hyclone Laboratories), which was recirculated at 37±2°C [3]. Serum was supplemented with sodium azide and EDTA. Wear was quantified gravimetrically every 0.5 Mcyc using a digital balance (XP250, Mettler-Toledo) with load soak compensation.INTRODUCTION
METHODS
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. The patients were selected from a large database of over 3000 knees for which kinematic analysis had previously been carried out using fluoroscopy. The criteria used for selection was that the patients had a successful knee implant (HSS >90) and were able to perform a weight bearing deep knee bend of at least 110 degrees. The patients were randomly chosen without any other restrictions. The kinetic analysis was carried on a cohort of over 100 patients using a previously published inverse dynamic rigid body model. This model, which has been validated using telemetric data, is capable of predicting the contact forces on the medial and lateral condyles of the knee. Analysis was carried out till 130 degrees of flexion to remove any effect of thigh calf contact that the model does not incorporate. 20 normal knees were also included for comparison.INTRODUCTION
METHODS
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. In vivo shoulder kinematics were determined pre and post-operatively for five unilateral TSA subjects with one healthy and a contralateral OA glenohumeral joint. Fluoroscopic examinations were performed for all three shoulder categories (healthy, OA, and post-TSA) for each subject shoulder abduction and external rotation. Then, three-dimensional (3D) models of the left and right scapula and humerus were constructed using CT scans. For post-operative shoulders, 3D computer-aided design models of the implants were obtained. Next, the 3D glenohumeral joint kinematics were determined using a previously published 3D to 2D registration technique. After determining kinematics, relative Euler rotation angles between the humerus and scapula were calculated in MATLAB® to determine range of motion (ROM) and kinematic profiles for all three shoulder categories. The ROMs for each category were compared using paired t-tests for each exercise. Also, the location of the contact point of the humerus on the glenoid was found. This allowed the vertical translation from the most superior to most inferior contact point (SI contact range) to be calculated as well as the horizontal translation from the most anterior to most posterior contact point (AP contact range). The SI and AP contact ranges for all shoulder categories were compared using paired t-tests for each exercise.INTRODUCTION
Methods
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. Ten healthy, 10 LBP, and 10 degenerative patients were CT scanned and evaluated under fluoroscopic surveillance while performing flexion/extension of the lumbar spine. Three-dimensional, patient-specific bone models were created and registered to fluoroscopic images using a 3D-to-2D model fitting algorithm. Introduction
Methods
There is increasing application of bone morphogenetic proteins
(BMPs) owing to their role in promoting fracture healing and bone
fusion. However, an optimal delivery system has yet to be identified.
The aims of this study were to synthesise bioactive BMP-2, combine
it with a novel α-tricalcium phosphate/poly(D,L-lactide-co-glycolide)
(α-TCP/PLGA) nanocomposite and study its release from the composite. BMP-2 was synthesised using an Objectives
Methods
The annual incidence of fractures in the UK is almost 4%. Bone grafting procedures and segmental bone transport have been employed for bone tissue regeneration. However, their limited availability, donor site morbidity and increased cost mean that there is still a large requirement for alternative methods and there is considerable research into regeneration using bone morphogenetic proteins (BMPs). The aims of this study are to synthesise and combine BMP-2 with a novel nanocomposite and study its release. BMP-2 was synthesised using an E. coli expression system and purified. C2C12 cells were used to test its bioactivity using an alkaline phosphatase (ALP) assay. The modified solution evaporation method was used to fabricate 30% a-TCP/PLGA nanocomposite and it was characterized using SEM, TEM, TGA, XRD, EDX and particle size analysis. The release pattern of adsorbed BMP-2 was studied using an ELISA assay.Introduction
Materials and Methods
A literature review of bone graft substitutes for spinal fusion was undertaken from peer reviewed journals to form a basis for guidelines on their clinical use. A PubMed search of peer reviewed journals between Jan 1960 and Dec 2009 for clinical trials of bone graft substitutes in spinal fusion was performed. Emphasis was placed on RCTs. Small and duplicated RCTs were excluded. If no RCTs were available the next best clinical evidence was assessed. Data were extracted for fusion rates and complications. Of 929 potential spinal fusion studies, 7 RCTs met the inclusion criteria for BMP-2, 3 for BMP-7, 2 for Tricalcium Phosphate and 1 for Tricalcium Phosphate/Hydroxyapatite (TCP/HA). No clinical RCTs were found for Demineralised Bone Matrix (DBM), Calcium Sulphate or Calcium Silicate. There is strong evidence that BMP-2 with TCP/HA achieves similar or higher spinal fusion rates than autograft alone. BMP-7 achieved similar results to autograft. 3 RCTs support the use of TCP or TCP/HA and autograft as a graft extender with similar results to autograft alone. The best clinical evidence to support the use of DBMs are case control studies. The osteoinductive potential of DBM appears to be very low however. There are no clinical studies to support the use of Calcium Silicate. The current literature supports the use of BMP-2 with HA/TCP as a graft substitute. TCP or HA/TCP with Autograft is supported as a graft extender. There is not enough clinical evidence to support other bone graft substitutes. This study did not require ethics approval and no financial support was received.
Radial head fractures with fragment displacement should be reduced and fixed, when classified as Mason II type injuries. We describe a method of arthroscopic fixation which is performed as a day case trauma surgery, and compare the results with a more traditional fixation approach, in a case controlled manner. We prospectively reviewed six Mason II radial head fractures which were treated using an arthroscopic reduction and fixation technique. The technique allows the fracture to be mobilised, reduced, and anatomically fixed using headless screws. All arthroscopic surgeries were conducted as day-cases. We retrospectively collected age and sex matched cases of open reduction and fixation of Mason II fractures using headless screws. The arthroscopic cases required less analgesia, shorter hospital admissions, and had fewer complications. The averaged final range of follow-up, at 1 year post-operation was 15 to 140 degrees in the arthroscopic group and 35 to 120 degrees in the open group. The Mayo Elbow Performance Score was 95/100 and 90/100 respectively. No acute complications were noted in the arthroscopic group, and a radial nerve neuropraxia [n=1], superficial wound infection [n=1], and loose screw [n=1]. Two patients of the arthroscopic group required secondary motion gaining operations [n=1 arthroscopic anterior capsulectomy for a fixed flexion contracture of 35 degrees, and n=1 loss of supination requiring and arthroscopic radial scar excision]. Three patients in the open group required secondary surgery [n=2 arthroscopic anterior capsulectomy for fixed flexion deformities, and n=1 arthroscopic anterior capsulectomy for fixed flexion deformities, and n=1 arthroscopic radial head excision for prominent screws, loss of forearm rotation, and radiocapitellar arthrosis pain]. The technique of arthroscopic fixation of Mason II radial head fractures appears to be valid, with respect to anatomical restoration of the fracture, minimal hospital admission, reduction in analgesia requirement, fewer complications, and a decreased need for secondary surgery.
At present, long-term follow-up studies are used to assess the performance and longevity of an implant, but the downside is that designers must wait 5–10 years before they receive this feedback. Therefore, the objective of this study was to develop a theoretical simulator that will allow for prediction of kinematic patterns based on implant shape and prediction of implant longevity based on the implant’s ability to adapt to in vivo conditions. A model of the normal lower leg, including muscles and all ligament structures, was developed using Kane’s theory of dynamics. All muscles and ligaments were modeled as distributed loads and included wrapping points to follow the true path of soft-tissue structures. Currently, two activities are available to the user: leg extension and deep flexion. 3D shapes, pertaining to the implant designs are input to the model. A validation of the model was conducted using an initial force prediction for each muscle. The predicted kinematics were compared to a library of in vivo kinematics from over 2000 knees obtained using fluoroscopy and a 3-D model fitting technique. If the kinematic patterns from the model were incorrect, an optimization feedback algorithm induced a change in the muscle force. This process continued until the proper muscle force profiles were determined. Then, using muscle forces which achieve observed motion in TKA previously implanted and analyzed, evaluation of various new implant designs could be assessed. Altering designs or constraints in TKA lead to quite different kinematic profiles, even when the same muscle force profiles are used. Further research needs to be conducted using more design profiles before multiple implant designs could be evaluated and compared.
An institution of the authors (Center for Musculoskeletal Research) and one author (DAD) have received funding from DePuy, Inc. (Warsaw, IN). Each author certifies that his or her institution has approved the reporting of these cases, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. This work was performed at Center for Musculoskeletal Research, University of Tennessee, Knoxville, TN and the Rocky Mountain Musculoskeletal Research Laboratory, Denver, CO.
To identify radiological patterns of compression (POC) of the spinal cord To develop a surgical protocol based on POC and determine its efficacy. To identify parameters predicting outcome of surgery
Pattern I – predominant one/two level compression in normal/narrow canal Pattern II – anterior &
posterior compression at one/ two levels (pincer cord) Pattern III – Three or more levels of predominant anterior compression with a normal canal Pattern III(A) – Pattern III in a patient with multiple medical co-morbidities Pattern IV – Three/more levels of anterior compression in narrow canal +/− posterior compression (beaded cord) Pattern IV(A) – Pattern IV with one/two level severe compression amongst the multiple anterior compressions. Mean follow-up was 3 yrs (2–8). ACDF was performed for patterns I, II &
III and posterior decompression for pattern IV and III(A). For pattern IV(A), a two stage primary posterior decompression followed by targeted ACDF at the site of maximal compression was performed. The clinical outcome was measured by modified JOA (mJOA) score, Hirayabashi Recovery Rate (HRR) and functional outcome by modified Neck Disability Index (NDI).
At present, contact stress analyses of TKA involve in vitro experimental testing. The objective of this project was to develop a parametric mathematical model that determines in vivo contact stresses for subjects implanted with a TKA, under in vivo, dynamic conditions. It is hypothesized that the results from this model will be more representative of in vivo conditions, thus leading to more accurate prediction of TKA bearing surface stresses. In vivo kinematics were determined for ten subjects implanted with a posterior stabilized TKA during gait and a deep knee bend under fluoroscopic surveillance. Three-dimensional contact positions, determined between the femoral component and the polyethylene insert, were entered into a complicated mathematical model to determine bearing surface forces. In vivo kinematics and kinetics were entered into a deformation model to predict in vivo contact areas between the medial and lateral condyles and tibial insert. The orientation of the femoral and tibial components, the predicted in vivo contact areas, and vectoral information of soft-tissue derived from MRI images were then entered into a mathematical model that predicted in vivo contact stresses between the femoral component and the tibial insert. This is the first computational model that utilizes fluoroscopy, MRI, deformation characteristics and Kane’s theory of Dynamics to predict in vivo contact stresses. Although previous models have not been validated, this model was validated by comparing the predicted foot/ ground force with the experimentally derived force. This study demonstrates that patellar motion influences forces throughout the lower extremity. The in vivo contact stress values predicted in this initial study were less than the yield strength of polyethylene.
The objective of this study was to determine the location of polyethylene post position and/or axis of polyethylene (PE) bearing rotation in order to maximize the rotational freedom of the PE bearing in a posterior-stabilized mobile-bearing TKA. Kinematic data obtained in a previous study involving subjects implanted with the PFC Sigma RP (PS) was used in two mathematical models to determine the optimal configuration of the implant’s features. An inverse dynamics mathematical model used the kinematic input to calculate interactive forces between the implant components. The second mathematical model used the femur-polyethylene and polyethylene-tibial plate interactive forces in a forward solution giving the amount of polyethylene bearing rotation. Researchers altered the location of cam/post interaction and/or bearing rotation to determine the criteria for optimal bearing rotation. During flexion, the maximum femur-polyethylene contact force calculated by the inverse model was 1.9 x BW, at maximum flexion. Maximum quadriceps, patello-femoral, and patellar ligament forces were approx. 2.9 x BW, 2.8 x BW, and 1.5 x BW at maximum flexion, respectively. We determined that the sample group experienced an average maximum bearing rotation of approximately 3.5°. Maximum bearing rotation reached approx 12.5° (10°–15°) with a 5mm lateral shift in cam/post engagement. Bearing rotation reached approximately 17.5° (15°–20°) by shifting the bearing axis 5mm posterior to that of the current design. Shifting the cam/post mechanism or bearing axis by greater than 5mm in any direction produced undesirable results. The mathematical models used in this study were verified by comparing kinematic results obtained from a 3-D model-fitting program whereby models are matched to their respective silhouettes in a 2-D fluoroscopic image. Results from this study show that the rotational freedom of the PE bearing can be optimized by shifting its axis of rotation posterior to its present location.
We have evaluated retrospectively the relationship of bony injuries seen on 106 consecutive MR scans in elderly patients of a mean age of 81.4 years (67 to 101) who were unable to bear weight after a low-energy injury. There were no visible fractures on plain radiographs of the hip but eight patients (7.5%) had fractures of the pubic ramus. In 43 patients (40.5%) MRI revealed a fracture of the femoral neck and in 26 (24.5%) there was a fracture of a pubic ramus. In 17 patients (16%) MRI showed an occult sacral fracture and all of these had a fracture of the pubic ramus. No patient with a fracture of the femoral neck had an associated fracture of the pelvic ring or
