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Objectives and questions: Recurrent patellofemoral instability (PFI) is strongly associated with altered positioning of the tuberositas tibiae (TT), patella alta and femoral rotational deformities. While surgical realignment aims to restore physiological tracking, the biomechanical consequences of these predisposing factors on patellofemoral (PF) kinematics and joint loading remain insufficiently quantified, and reported correction thresholds remain largely inconsistent. We therefore determined how alterations in TT positioning and FR influence PF force magnitude and flexion-angle dependency.

Material and methods: Four fresh-frozen cadaveric knees were mounted in a dynamic knee simulator. A specimen-specific patellar implant was integrated using 3D-printed molds reproducing individual retropatellar geometry. The implant measured shear forces in three orthogonal planes (frontal, sagittal, transverse) along the anteroposterior (Fy), longitudinal (Fz), and mediolateral (Fx) axes. Following Fulkerson-type osteotomy, the TT was refixed with a custom T-plate allowing reproducible 5-mm repositioning. Proximalization and distalization were simulated up to 10 mm, medialization and lateralization up to 25 mm, and femoral rotation up to 40° in 10° increments of internal and external rotation. Quadriceps muscle bellies were loaded according to physiological force distribution. Standardized flexion–extension cycles were performed for each condition, and resultant PF force (F_res) was recorded continuously. Linear mixed-effects models were appliedand dose–response relationships were analyzed using mixed-effects regression.

Results: Across four specimens, telemetric measurements demonstrated a consistent mid-flexion peak at 40–50° independent of TT alignment. Proximalization simulating patella alta significantly increased PF loading without altering peak angle. Mean flexion forces increased by +71.8 N (5 mm) and +63.0 N (10 mm) (both p < .001). During extension, forces increased dose-dependently (+74.0 N at 5 mm; +136.5 N at 10 mm; both p < .001), with 10 mm exceeding 5 mm (p < .001). Peak forces reached 412 N in flexion and 352 N in extension. Load augmentation was primarily driven by increased anteroposterior shear (Fy). Despite increased mediolateral force components, lateralization did not result in a statistically significant increase in PF loading. Femoral internal rotation significantly increased mediolateral Fx during flexion (20°: +11.6 N; 40°: +28.9 N; both p < .001) and across the full cycle (40°: +19.0 N, p < .001). In contrast to TT malposition, Fx peaks occurred later at 65–75° flexion.

Discussion and conclusions: Alterations in TT positioning and FR significantly modify PF force magnitude without shifting the characteristic mid-flexion loading zone. Patella alta markedly increases shear-dominant loading, whereas internal FR ≥ 20° alters mediolateral force components. These findings provide quantitative insight into alignment-dependent PF biomechanics and may help refine surgical correction thresholds in treatment of PFI.