Alignment and soft tissue (ligament) balance are two variables that are under the control of a surgeon during replacement arthroplasty of the knee. Mobile bearing medial unicompartmental knee replacements have traditionally advocated sizing the prosthesis based on soft tissue balance while accepting the natural alignment of the knee, while fixed bearing prosthesis have tended to correct alignment to a pre planned value, while meticulously avoiding overcorrection. The dynamic loading parameters like peak adduction moment (PKAM) and angular adduction Impulse (Add Imp) have been studied extensively as proxies for medial compartment loading. In this investigation we tried to answer the question whether correcting static alignment, which is the only alignment variable under the control of the surgeon actually translates into improvement in dynamic loading during gait. We investigated the effect of correction of static alignment parameter Hip Knee Ankle (HKA) angle and dynamic alignment parameter in coronal plane, Mean Adduction angle (MAA) on 1st Peak Knee Adduction Moment (PKAM) and Angular Adduction Impulse (Add Imp) following medial unicompartmental knee replacements. Twenty four knees (20 patients) underwent instrumented gait analysis (BTS Milan, 12 cameras and single Kistler force platform measuring at 100 Hz) before and after medial uni compartmental knee replacement. The alignment was measured using long leg alignment views, to assess Hip Knee Ankle (HKA) angle. Coronal plane kinetics namely 1st Peak Knee Adduction Moment (PKAM) and angular adduction impulse (Add Imp)- which is the moment time integral of the adduction moment curve were calculated to assess medial compartment loading. Single and multiple regression analyses were done to assess the effect of static alignment parameters (HKA angle) and dynamic coronal plane alignment parameters (Mean Adduction Angle – MAA) on PKAM and Add Imp.Background
Methods
The aim of this study was to evaluate the functional and clinical outcome following medial patello-femoral ligament reconstruction using autogenous hamstring tendon grafts for patellar instability. Over a 4 year period the senior author operated on 35 patients for lateral instability of the patella. The predominant initiating event was a sporting injury. Each patient had either failed conservative management including physiotherapy, or failed surgical management including tibial tuberosity transfer. Post-operatively, all patients were allowed full flexion and extension. Sporting activity was restricted until 4-6 months post-operatively. Patients were evaluated clinically and functionally. The Fulkerson score was utilised pre- and post-operatively. The minimum follow-up was 6 months, the mean follow-up was 20 months. There were 18 males and 17 females. The mean age was 24.6 years. The mean pre-operative Fulkerson score was 59.3 (range 6-100). The mean post-operative Fulkerson score was 83.6 (range 25-100), the mean improvement was 24.3. 24 patients returned to sporting activities. The main complications were one patient with a patella fracture that was stabilised with internal fixation, one patient requiring exploration and reinforcing the ligament which had attenuated. Both patients finally had a good clinical outcome. Our study has shown that symptomatic lateral instability of the patella can be effectively treated with a medial patello-femoral ligament reconstruction and result in overall good clinical and functional outcome. We would recommend this technique.
