Aims We rotated the tibial tray, of a fixed and mobile bearing, total knee arthroplasty and studied the effects on the patellofemoral and tibiofemoral joints, when the arthroplasty was placed through a range of movement

Method and results A specially designed jig allowed us to put the knee arthroplasty under 100N of compression using a single pulley system. We rotated the tibial platform in isolation, in 5° increments of external rotation. At each position, the arthroplasty was put through 90° of flexion. We studied the PFC fixed bearing prosthesis and the LCS, PCL substituting rotating platform pros-thesis manufactured by Johnson & Johnson. We used a translucent custom femoral component for each type. This allowed us to observe dye at the femoral component articulations, recording the results using digital photography.

The mobile bearing prosthesis was surprisingly more sensitive to tibial tray external rotation. It suffered antero-lateral and posteromedial point loading on the polyethylene tray from 5–15° of tray rotation. Further increase caused the medial femoral component to lift off the polyethylene tray at 25° of rotation resulting in lateral femoral component loading. Simultaneously, there was lateral patella facet loading with medial facet lift off at the patellofemoral joint. The fixed bearing prosthesis did not experience impingement until 10° of rotation. At 25° of external tray rotation, there was posteromedial and antero-lateral point loading on the polyethylene but no lift off. The patellofemoral joint showed superior pole loading of the patella button but no medial/lateral loading.

Conclusion External tibial tray rotation caused polyethylene point loading in a knee arthroplasty. This would increase wear debris generation and aseptic loosening rates. Tray rotation does not improve patellofemoral tracking. We advise neutral alignment of the tibial tray to the femoral prosthesis. The mobile bearing prosthesis was more sensitive because the polyethylene tray could not rotate to confer the optimum tibiofemoral alignment.

We wanted to know if a mobile bearing Total Knee Arthroplasty was able to cope with rotation of the tibial tray about the femoral prosthesis, by studying the tibio-femoral and patello-femoral joints.

This was a kinematic study that used a mobile bearing TKA mounted on a jig that allowed rotation of the tibial tray. The TKA was moved through a 90° range of flexion and we used photography to record the effects at the tibio-femoral and patello-femoral joints. We found that with a fixed tibia, increasing the degree of external rotation increased the degree of medial femoral condyle lift off from the polyethylene insert which was complete at 25° of tibial tray external rotation. The lift off increased with the degree of flexion. The patello-femoral joint remained congruent. If the rotated tibial tray was mounted on a tibia that was allowed to freely rotate, it led to congruity at the tibio-femoral joint. Now we found that there was medial facet impingement and lateral facet lift off of the patella button in extension and flexion.

We concluded that this mobile bearing prosthesis did not cope well with rotation of the tibial tray. The relatively low congruency at the tibio-femoral articulation meant that there was a reduced “driving force” at the tibio-femoral joint resulting in less than adequate rotation of the mobile polyethylene insert. We feel that the tibial tray must be placed in neutral to the femoral prosthesis and failure to do so will result in abnormal polyethylene loading that would increase wear and may culminate in early prosthesis revision.

Twenty four operations were reviewed in 23 patients to show a modified Roux-Goldthwait operation would improve the symptoms of chronic patella instability. This retrospective study used a questionnaire to record symptoms before and after surgery. The examination assessed joint hypermobility, patella tracking and stability, the Q and valgus angles of the knee. Apprehension test and assessment of patella tilt was also assessed. All patients underwent radiographic assessment. Twenty of 23 patients were improved by this procedure. Patella subluxation was reduced by 22%. Patella dislocation was reduced by 86%. The 3 unsuccessful cases had generalised joint laxity and may have been improved by the addition of a medial reefing procedure. There were no cases of tibial tuberosity numbness post operatively, patella tilt or failure of the transposed tendon. We showed that this procedure is effective, regardless of x-ray signs. We did observe a subjective increase in patellofemoral pain post operatively.

Review of 133 cases of Anterior Cruciate Ligament (ACL) reconstruction, showed 91 cases had been arthroscoped twice. The incidence of meniscus pathology, at first arthroscopy was 71% and this fell to 63% at the second arthroscopy and reconstruction. 21% of recurrent tears were in previously undamaged menisci. The medial meniscus, was the most commonly damaged meniscus, at the time of the first arthroscopy. The incidence of lateral and bilateral meniscus pathology increased in the time period awaiting ACL reconstruction. The mean time between the two arthroscopies were 27 months. Damaged menisci continued to tear over the time period between first and second arthroscopies or new pathology occurred. The paper concludes that if ACL reconstruction is performed by a mini open technique then it should be re-arthroscoped immediately before the ACL reconstruction. This is essential to avoid missing meniscus pathology, even in previously arthroscoped knees.