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BackgroundSuccessful component alignment is a major metric of success in total knee arthroplasty. Component translational placement, however, is less well reported despite being shown to affect patient outcomes. CT scans and planar X-rays are routinely used to report alignment but do not report measurements as precisely or accurately as modern navigation systems can deliver, or with reference to the pre-operative anatomy.MethodsA method is presented here that utilises a CT scan obtained for pre-operative planning and a post-operative CT scan for analysis to recreate a computation model of the knee with patient-specific axes. This model is then used to determine the post-operative component position in 3D space.ResultsTwo subjects were investigated for reproducibility producing 12 sets of results. The maximum error using this technique was 0.9° ± 0.6° in rotation and 0.5 mm ± 0.3 mm in translation. Eleven subjects were investigated for reliability producing 22 sets of results. The intra-class correlation coefficient for each of the three axes of rotation and three primary resection planes was > 0.93 indicating excellent reliability.ConclusionsRoutine use of this analysis will allow surgeons and engineers to better understand the effect of component alignment as well as the placement on outcome.

The modularity of femoral head and femoral stem provides many benefits to surgeons. However, case-reports have shown failure in large head Metal-on-Metal hip replacement due to trunnionosis. The exact causes of trunnionosis are not yet identified but the additional interface at the modular joint seems to be a contributing factor. In this study, a three dimensional non-linear finite element model was created to analyse the effects of head size and trunnion design on the micromotion at the head-neck interface. Four different metal head sizes and two trunnions designs and materials were used in the model. The femoral heads were assembled onto the trunnions with 7kN axial force and one cycle of gait load was applied to the head after assembly. The study showed that the micromotion was substantially increased in femoral head larger than 36mm. Trunnions material has greater effect on micromotion than trunnion design, particularly with the larger head sizes. The stability at the modular junction is important. Our findings suggest that there is a limit of assembly force to maintain enough stability on the joint; beyond this limit; the maximum micromotion will not be affected.

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ability of TKA patients to return to sports and the tolerance of sports activities on the mid term survivorship of the prosthesis. Methods: From January 2001 to January 2008, 500 patients received a posterior cruciate ligament-substituting mobile bearing TKA. Clinical and radiological outcomes were assessed at baseline and postoperatively using the Knee Society (KS) Knee and Function and activity by the University of California at Los Angeles (UCLA) scale. Results: Mean age at surgery was 70.6 years (range,40-91). Osteoarthritis predominated (91.8%). Mean follow-up was 7.5 years (5-13) including 123 knees (21%) followed more than 10 years.At 3 months after surgery, 215 patients (43%) enjoyed outdoor activities such as hiking, cycling, fishing, golf, hunting and horse-riding. At last follow-up, 145 patients were not concerned by physical activities; 355 patients (71%) could perform regular physical activities, with a mean UCLA rating of 7.3AE1/10 (5 to 10). 133 patients (26%) could perform sport activities at a level equal or greater than 8/10 on the UCLA rating score. In 96 of these 133 knees (72%), the patient had more than one sports activity (total ¼ 233 itemized activities). In 103 of these 133 cases, UCLA rating was 9/10 (backpacking, dancing, cross country skiing, aerobics, rollerblade running, horseriding or jumping-show or heavy farm labor), and in 30, 10/10 (tennis, marathon, downhill skiing, alpine glacier hiking, parasailing). Kaplan-Meier 13-year survivorship with revision for aseptic loosening as end-point was 99.4% (95% CI, 99.8-100). On the 3 loosenings occuring during this period, none occured on patients with intense physical activity. All 3 were on patients with moderate activities. Conclusion:This study reports that return to an intense physical activity is possible after this Mobile bearing Total Knee Arthroplasty and does not compromise the midterm survivorship of the implant.