Progressive lateral femoral condyle lengthening in total knee arthroplasty produces dose-dependent increases in patellofemoral joint loading and alters patellar tracking.

PURPOSE: To examine the biomechanical effects of progressive lateral femoral condyle lengthening on patellofemoral joint (PFJ) kinematics and kinetics following total knee arthroplasty (TKA), and to determine whether lateral condyle distalisation produces measurable, dose-dependent alterations in PFJ loading and patellar tracking. METHODS: Eight fresh-frozen cadaveric knees were implanted with a cruciate-retaining TKA and tested in four states: Native (unresurfaced), Neutral (resurfaced to native thickness), medium (+2.5 mm distalisation) and Maximum (+4.5 mm distalisation). PFJ kinematics were recorded during passive flexion and simulated stair descent using optical tracking. PFJ kinetics were measured using calibrated thin-film pressure sensors (Neutral, Medium, Maximum). RESULTS: Progressive lateral condyle distalisation produced a significant, dose-dependent increase in PFJ reaction force during both passive flexion (Neutral: 55.98 ± 32.33 N; Maximum: 76.30 ± 46.19 N; p = 0.006) and stair descent (Neutral: 42.19 ± 28.84 N; Maximum: 55.72 ± 28.02 N; p = 0.006). Medial and lateral facet loads increased with distalisation. Kinematically, significant increases in anterior patellar translation and external rotation were observed in all resurfaced conditions compared with the native state (p < 0.05, Holm-corrected). Medial-lateral translation, superior-inferior translation, patellar flexion and valgus-varus rotation were not significantly affected. CONCLUSION: Lateral femoral condyle lengthening in TKA increases PFJ reaction forces and alters patellar tracking in a dose-dependent manner. These findings highlight lateral condyle distalisation as a modifiable surgical factor with important implications for femoral component preparation and alignment philosophy in TKA. LEVEL OF EVIDENCE: Level IV, controlled laboratory study.