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Related Experiment Videos

A modified test for patellar instability: the biomechanical basis.

Suzanne M Tanner1, William P Garth, Ramona Soileau

  • 1Gundersen Lutheran Sports Medicine, Onalaska, WI 54650, USA. smtanner@gundluth.org

Clinical Journal of Sport Medicine : Official Journal of the Canadian Academy of Sport Medicine
|November 11, 2003
PubMed
Summary

Distal lateral patellar displacement is more sensitive for detecting medial patellofemoral ligament (MPFL) tears than traditional lateral displacement. This study establishes objective criteria for diagnosing patellar instability, improving upon subjective apprehension tests.

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Area of Science:

  • Orthopedic biomechanics
  • Knee joint kinematics
  • Soft tissue injury assessment

Background:

  • The medial patellofemoral ligament (MPFL) is crucial for stabilizing the patella against lateral dislocation.
  • Current diagnostic methods for MPFL deficiency, such as the apprehension test, rely on subjective patient feedback.
  • Objective biomechanical assessments are needed to quantify patellar instability and ligamentous integrity.

Purpose of the Study:

  • To compare the sensitivity of distal lateral patellar displacement versus traditional lateral displacement in detecting medial patellofemoral ligament (MPFL) deficiency.
  • To establish objective criteria for diagnosing patellar instability, moving beyond subjective apprehension.

Main Methods:

  • An in vitro biomechanical study was conducted using ten above-the-knee amputation specimens.

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  • Force-displacement curves were generated for direct lateral and distal lateral patellar displacement.
  • These measurements were compared before and after sectioning the MPFL to simulate injury.

    • Main Results:

    • Dividing the MPFL resulted in a 53% decline in terminal restraining force with distal lateral displacement (P=0.024), versus a 30% decline with lateral displacement (P=0.09).
    • The most significant difference in terminal slope occurred when comparing the intact MPFL with lateral displacement to the divided MPFL with distal lateral displacement (P=8.67x10(-5)).
    • Terminal slope reduction after MPFL division was observed in both lateral (P=0.07) and distal lateral (P=0.09) displacement tests.

    Conclusions:

    • Distal lateral patellar displacement is a more sensitive diagnostic maneuver for MPFL disruption than traditional lateral displacement.
    • Objective criteria for positive patellar instability include increased patellar translation and a softer endpoint at 30 degrees knee flexion and 2 cm displacement, compared to the contralateral knee.