Highlights
- •Femoral torsion has a significant impact on the patellofemoral joint.
- •Increased internal femoral torsion produces a lateralizing force on the patella.
- •20° internal torsion and an intact medial patellofemoral ligament can be a risk factor for patellar instability.
- •10° internal torsion and a torn medial patellofemoral ligament can be a risk factor for patellar instability.
Abstract
Background
Increased internal femoral torsion is regarded as a risk factor for patellar instability.
Biomechanical investigations confirming this hypothesis are missing.
Methods
Eight fresh-frozen cadaver knees were tested on a specially designed simulator. Patellar
motion and patellofemoral pressure were evaluated for 0°, 10°, and 20° of increased
internal and external femoral torsion with native and with transected medial patellofemoral
ligaments used to simulate patellar instability. A regression analysis was used for
statistical analysis.
Findings
In native medial patellofemoral ligaments, there were no significant changes in mean
or peak pressures for any torsional states (P ≥ 0.07). At 20° increased internal femoral torsion, there was a significant center of
force shift towards the lateral side (P = 0.01). Patellar shift was directed laterally at low knee flexion angles up to 30°.
Lateral patellar tilt increased significantly at 10° and 20° of increased internal
femoral torsion (P ≤ 0.004). In transected medial patellofemoral ligaments, mean pressure (P ≤ 0.005) and peak pressure (P ≤ 0.02) decreased significantly for all torsional states. There was a significantly
greater lateral center of force shift with increased internal femoral torsion (P ≤ 0.04). Lateral patellar tilt increased significantly (P < 0.001). Patellar shift did not change significantly with increased internal femoral
torsion (P ≥ 0.30).
Interpretation
In a native medial patellofemoral ligament, 20° of increased internal femoral torsion
can be regarded as a significant risk factor for patellar instability. With an insufficient
medial patellofemoral ligament, 10° of increased internal femoral torsion already
represents a significant risk factor.
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Article info
Publication history
Published online: June 10, 2017
Accepted:
June 8,
2017
Received:
September 11,
2016
Identification
Copyright
© 2017 Elsevier Ltd. All rights reserved.
