Patellar obliquity causes altered patellofemoral biomechanics in total knee replacement: An in vitro study

Abstract

Purpose: Patellofemoral joint (PFJ) complications are a common cause of dissatisfaction and revision after total knee arthroplasty (TKA). Asymmetric patellar resections may alter PFJ biomechanics. This study investigated the effects of patellar obliquity on PFJ kinematics and contact forces in a cadaveric model. Methods: Eleven fresh-frozen cadaveric knees (mean age 71.2 years) were resurfaced under three conditions: neutral thickness, medial-thick oblique (+2 mm) and lateral-thick oblique (+2 mm). A six-degree-of-freedom robotic system simulated passive flexion (0°–90°) and stair descent (10°–60°). Kinematics were measured with optical tracking; PFJ forces were recorded using a calibrated three-zone sensor (C1–C3). Kruskal–Wallis tests with Bonferroni-adjusted post hoc comparisons were applied (α = 0.05). Results: During passive flexion, medial-thick oblique produced greater medialization than native and lateral-thick (p = 0.013 and p = 0.009, respectively) and increased internal rotation versus native (p < 0.001). Central ridge pressure (C2) was higher in medial-thick versus lateral-thick (0.80 ± 0.54 V vs. 0.52 ± 0.44 V; p = 0.0189). Composite PFJ force (Newtons) did not differ between groups (p = 0.9126). During stair descent, medial-thick oblique showed greater medialization than native and lateral-thick (p = 0.017 and p = 0.039) and increased internal rotation versus native (p < 0.001). C2 was higher in medial-thick than neutral (0.77 ± 0.49 V vs. 0.50 ± 0.49 V; p = 0.0106) and lateral-thick (0.45 ± 0.42 V; p = 0.0169). Composite force again showed no between-group difference (p = 0.3186). Conclusion: Patellar obliquity alters PFJ tracking and regional loading—even without increasing total joint force—with a medial-thick oblique patella consistently elevating central ridge pressures. Prioritizing symmetric patellar resection may help avoid maltracking and focal overload that predispose to PFJ-related symptoms following TKA. Level of Evidence: Level IV, controlled laboratory study.