Pseudo-patella baja after total knee arthroplasty: Radiological evaluation and clinical repercussion

Abstract

Background: Anterior knee pain is an important complication after total knee arthroplasty (TKA). One possible contributor is the elevation of the joint line, known as pseudo-patella baja (PPB). Limited research has been conducted regarding this condition impacting TKA management. This study aims to evaluate the incidence, identify possible related factors and assess PPB clinical repercussions.

Methods: A total of 813 consecutive TKAs were retrospectively reviewed. Patients were submitted to the same surgical procedure and information regarding TKA characteristics was collected. Lateral postoperative knee radiographs were analyzed using the modified Insall-Salvati Ratio and the Blackburne-Peel Index. A clinical evaluation was conducted on 112 knees where the Oxford Knee and Kujala Scores were applied. Range of motion was evaluated, and knee pain was assessed using the numeric pain rating scale, in addition to analgesic consumption.

Results: A cohort of 612 knees was analyzed, of which 64 knees developed PPB (10.5% incidence). Statistically significant differences were found for advance components sizes (femoral P = 0.026 and tibial P < 0.001), polyethylene thickness (P < 0.001) and patients' height (P = 0.022) with smaller implant sizes, greater insert thicknesses and lower height showing an association with PPB. The PPB group had a significantly lower median Kujala score (P = 0.011), higher frequency of flexion contracture and of anterior knee pain (P = 0.039).

Conclusion: PPB has a clinical relevance that should not be overlooked. Its prevention through the recreation of the natural position of the joint line and correct choice of implant sizes and polyethylene thickness is of major importance and should always be considered.

Keywords: Anterior knee pain; Complications; Joint line elevation; Pseudo-patella baja; Radiographic measurement; Total knee arthroplasty.