There is great contemporary interest to provide treatments for knees with medial or medial plus patellofemoral arthritis that allow retention of the cruciate ligaments and the natural lateral compartment. Options for bicompartmental arthroplasty include custom implants, discrete compartmental implants and monoblock off-the-shelf implants. Each approach has potential benefits. The monoblock approach has the potential to provide a cost-efficient off-the-shelf solution with relatively simple surgical instrumentation and procedure. The purpose of this study was to determine if monoblock bicompartmental knee arthroplasty shows evidence of retained cruciate ligament function and clinical performance more similar to unicompartmental arthroplasty than total knee arthroplasty.

Nine females and one male patient were enrolled in this IRB approved study. Each subject received unilateral bicompartmental knee arthroplasty an average of 2.6 years (2.0 to 3.6 years) prior to this study. Subjects averaged 65 years (58–72 years) and 28 BMI (25–31) at the time of surgery. Mean outcome scores at the time of study were 97/95 for the Knee Society knee/function score, 16.4 Oxford score, 6.5 UCLA Activity score and 137 degrees range of motion. Subjects were observed using dynamic fluoroscopy during lunge, kneeling and step-up/down activities. Subjects also received CT scans of the knee in order to create bone/implant composite shape models. Model-image registration techniques were used to determine 3D knee kinematics (Figure 1). Knee angles were quantified using a flexion-abduction-rotation Cardan sequence and condylar translations were determined from the lowest point on the condyle with respect to the transverse plane of the tibial segment.

Maximum knee flexion during lunge and kneeling activities averaged 112°±8° and 125°±7°, respectively. Tibial internal rotation averaged 10°±6° and 12°±10° for the lunge and kneeling activities. For both deeply flexed postures, the medial condyle was 1 mm anterior to the AP center of the tibia while the lateral condyle was 11 mm and 13 mm posterior to the tibial center. For the step-up/down activity, tibial internal rotation increased an average of 2° from 5° to 75° flexion, but was quite variable (Figure 2). Medial condylar translations averaged 4 mm posterior from 5° to 25° flexion, followed by 6 mm anterior translation from 25° to 80° flexion (Figure 3). All knees showed posterior condylar translation from extension to early flexion.

An important potential benefit to any bicompartmental arthroplasty treatments is retention of the cruciate ligaments and maintenance of more natural knee function. The knees in this study showed excellent or good clinical outcomes and functional scores, and relatively activity high levels. There was no evidence of so-called paradoxical anterior femoral translation during early flexion, indicating retained integrity of the natural AP stabilizing structures. Weight-bearing deep flexion during lunge and kneeling activities was comparable to previously reported unicompartmental and well-performing total knee arthroplasty subjects. Kinematics were quite variable between subjects.

Monoblock bicompartmental arthroplasty appears to permit functional retention of the cruciate ligaments, consistent with functionally stable knees. Further efforts should focus on the specific surgical placement of off-the-shelf bicompartmental implants to optimize knee function and provide consistent knee mechanics.

INTRODUCTION

In patients with neural disorders such as cerebral palsy, three-dimensional marker-based motion analysis has evolved to become a well standardized procedure with a large impact on the clinical decision-making process. On the other hand, in knee arthroplasty research, motion analysis has been little used as a standard tool for objective evaluation of knee joint function. Furthermore, in the available literature, applied methodologies are diverse, resulting in inconsistent findings [1]. Therefore we developed and evaluated a new motion analysis framework to enable standardized quantitative assessment of knee joint function.

Introduction: In contrast to fixed-bearing total knee replacements (TKRs), mobile-bearing TKRs allow for unconstrained kinematics while providing a high congruency between the femoral component and polyethylene inlay. The concept of a mobile-bearing TKR is based on the mobility of the inlay. It has been suggested that inlay mobility may decrease due to the in-growth of fibrous tissue (Lemaire 1998). Previous studies report a loss of inlay mobility between 0% and 50% at an average follow-up time between 1.5 and 6 years postop (Bradley et al. 1987, Stiehl et al. 1997, Hartfort et al. 2001). However these studies are retrospective and do not define a threshold for inlay mobility.

Methods: In this prospective study, 61 mobile-bearing TKRs (SAL, Zimmer) in 60 patients were followed up 3, 12, 24 and 60 months post-op. The implant design allows for 6–9 mm (size dependent) inlay translation in the anteroposterior direction while the rotation is not constrained. A complete 60 month follow-up of 40 patients was available. At each follow-up the knees were X-rayed at 0, 30, 60 and maximal flexion. Using the 4 X-rays from each follow-up, digital image analysis was performed to compute inlay translation and rotation. An inlay was classified as mobile, if it translated more than 1 mm or rotated more than 5. Group means where compared using one-way ANOVA with a significance level of 5%.

Results: No significant change in average inlay translation and rotation with time was found. The average inlay translation was 2.5 mm (s.d. 1.8 mm) at 3 months postop, 3.0 mm (s.d. 1.8 mm) at 1 year post-op, 3.1 mm (s.d. 1.9 mm) at 2 years post-op, and 3.1 mm (s.d. 2.0 mm) at 5 years post-op. The average inlay rotation was 6.6 (s.d. 3.4) at 3 months post-op, 6.7 (s.d. 4.0) at 1 year post-op, 7.9 (s.d. 3.9) at 2 years post-op, and 8.3 (s.d. 4.1) at 5 years post-op. At all follow-ups, the inlay was classified as mobile in at least 90% of the cases. The patterns of inlay motion were observed to be repeatable for the individual knee joints but varied substantially between subjects.

Conclusion: In 40 mobile-bearing TKRs that were prospectively examined 3, 12, 24, and 60 months post-op, no significant change in average inlay motion or percentage of mobile inlays was found. The results do not support the hypothesis that inlay mobility is reduced due to in-growth of fibrous tissue. Mobile-bearing TKRs allow the kinematics to follow the knee specific soft tissue constraints.

Aims: Purpose of this retrospective study was to evaluate changes of pressure distribution during walking and joint movement after clubfootoperation. Methods: For this analysis the VICON 512 motion system including 12 cameras and 2 KISTLER force plates were used. Pressure distribution under both feet during gait was measured by a pressure sensitive plate (EMED NOVEL pressure plate). Muscle activity of the lateral and medial gastrocnemicus, anterior tibialis and longer peroneal muscles was registered by surface EMG using BIOVISION. The sampling rate of the motion analysis system was set at 120 Hz. Data acquisition of force and EMG signals were performed at 1080 Hz. The kinematic analysis of the human body was represented by a 7-segment model consisting of feet, lower legs, upper legs and pelvis. A set of 16 markers were used to identify the body segments. Results: 20 children with a mean age of 12 years underwent a quantitative 3-dimensional kinematic and kinetic gait analysis. Regarding to gait pattern a wide range from normal to equinal was found. Measurement of the pressure distribution during walking showed maximum pressure at different foot regions. There were only a few children with “normal” gait pattern. The striking gait pattern was combined with higher dorsalflexion in the ankle joint, missing extension and higher flexion in the knee joint. A lower extension in the hip joint was also found. Conclusions: A wide range of gait pattern was found during 3-dimensional analysis after clubfoot-operation by using the Imhaeuser method. Reasons could be the rehabilitation after operation and different daily activities of life. Work in progress is still the comparison with other methods.

Aims: The purpose of this study was to determine the intra-subject repeatability of the motion pattern of the PE inlay in a mobile-bearing total knee replacement (TKR) with respect to the post-op time. Methods: 75 mobile-bearing TKRs in 73 patients were included in this prospective study. Sagittal radiographs at 0°, 30°, 60° and maximum flexion were taken 3, 12, and 24 months post-op. On each X-ray, the AP position and the rotation of the PE inlay with respect to the tibial baseplate were determined based on a 2D algorithm. The accuracy of the method was ± 0.2 mm for the AP position and ± 1.7° for the angle of rotation. To classify the repeatability, the mean AP and rotation motion with respect to the flexion angle for each patient was computed and the overall standard deviation (STD) of all measurements with respect to the mean curves was calculated. The repeatability was defined as ‘excellent’ if the STD in the AP direction was less than 0.5 mm and the STD in rotation was less than 2.5°. It was defined as ‘good’ if the STD in the AP direction was less than 1 mm and the STD in rotation was less than 5°. Results: 19 of 75 knees (25%) showed an excellent repeatability and 33 of 75 knees (44%) displayed a good repeatability of the PE motion. Motion patterns were more repeatable between the 12 and 24 month results than between the 3 and 12 month results. Conclusions: The majority of the mobile-bearing knees exhibited a repeatable, patient specific motion pattern of the PE inlay. The fact that the repeatability was higher between 12 and 24 months may be attributed to a more stable state after rehabilitation. Mobile-bearing knees support patient specific motion in contrary to constrained fixed bearing knees.