Pseudo-patella baja: a minor yet frequent complication of total knee arthroplasty.

PURPOSE: One of the complications in total knee arthroplasty (TKA) is pseudo-patella baja (PPB). PPB is present when there is no shortening of the patellar tendon, but the joint line is elevated. The purpose of this study is to investigate the incidence of PPB after TKA and its clinical effects.

METHODS

A case series of 158 patients undergoing TKA surgery between 1999 and 2012 at the 2nd Department of Orthopaedics and Traumatology, Pisa were retrospectively reviewed. Surgeries were performed by three senior surgeons, using the same surgical procedure for the implantation of a cemented posterior stabilized prosthesis. Lateral radiographs at 30° knee flexion were evaluated and the presence of PPB defined as modified Blackburne-Peel Index (mBPI) of < 0.54. All the patients were clinically evaluated using the Knee Society Score (KSS) and the Western Ontario and McMaster Universities Osteoarthritis Index score (WOMAC). Anterior knee pain was evaluated by visual analogue scale (VAS) and range of motion (ROM) was assessed through clinical examination.

RESULTS

The cohort group consisted of 158 patients, 109 (69.0%) female and 49 (31.0%) male. Median age at time of surgery was 74 years (range 36-87) and median follow-up was 66 months (range 12-163 months). Bilateral TKA surgery was performed in 50 patients, resulting in a total of 208 implants for investigation. On radiological evaluation, 139 (66.8%) showed no abnormalities (no joint line elevation and no patellar tendon shortening) and 55 (26.4%) presented joint line elevation with absence of patellar tendon shortening (PPB). No significant differences were found between the groups in terms of the KSS, WOMAC score, VAS or ROM.

CONCLUSION

Post TKA PPB is a relatively common complication. Careful preoperative planning, adequate soft tissue release, optimal cutting of bone components, on the femoral side in particular, and the use of thin polyethylene inserts can help to avoid this complication.

LEVEL OF EVIDENCE: IV.