Patellar Tracking in Total Knee Arthroplasty-Influence on Clinical and Functional Outcome.

Anterior knee pain is a common problem after primary total knee arthroplasty (TKA). The aim of this study was to find parameters in patellar positioning which influence the clinical and functional outcome after TKA. Included were 59 patients who underwent TKA, of which three patients were treated bilaterally (n = 62 included knees). In a periodical follow-up of up to 5 years, each patient had to answer three questionnaires (HSS, WOMAC, SF-36) and underwent three radiographies of the knee (including merchant view) and a clinical examination, including Range Of Motion (ROM). All radiographs were evaluated by a single observer blinded to clinical data, who collected multiple parameters of sagittal and axial patellar alignment including newly developed methods for measuring patellar shift and tilt. Depending on the measurement results, three groups were built for each parameter and the influence on the outcome was determined. A lateral patellar tilt of more than 4° resulted in lower scores for both the HSS and WOMAC. The rarely investigated patellar facet angle showed a significantly inferior clinical and functional outcome in late follow-up of >24 months if lower than 142°, possibly due to progressive osteosclerotic changes of the patella caused by increased contact stress with corresponding patellar morphology. No significant difference was found for all other parameters. The newly developed method for measuring patellar shift has proven to be a valuable and easy instrument in the postoperative setting.