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A modified test for patellar instability: the biomechanical basis.

Suzanne M Tanner·William P Garth·Ramona Soileau·Jack E Lemons
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Abstract

OBJECTIVE: (1) Determine if displacement of the patella in a distal lateral direction results in a more sensitive method to show deficiency of the medial patellofemoral ligament (MPFL), the primary restraint to lateral patellar dislocation, than the traditional patellar apprehension test in a direct lateral direction. (2) Determine objective criteria for defining a positive patellar instability test rather than subjective evaluation of apprehension. DESIGN: In vitro biomechanical study. SPECIMENS: Ten above-the-knee amputation specimens. MAIN OUTCOME MEASURES: Force-displacement curves with direct lateral patellar displacement were compared with curves with distal lateral patellar displacement before and after sectioning the MPFL. RESULTS: After dividing the MPFL, average terminal restraining force to distal lateral patellar displacement declined by 53% (P=0.024), but force declined only by 30% (P=0.09) with lateral displacement. The greatest difference in terminal slope (eg, end point) was with the MPFL intact with lateral displacement compared with distal lateral displacement with the ligament divided (P=8.67x10(-5)). The terminal slope declined after ligament division with lateral (P=0.07) and distal lateral patellar displacement (P=0.09). CONCLUSION: Displacement of the patella in a distal lateral direction is a more sensitive maneuver to detect disruption of the MPFL, the primary soft tissue restraint, than with traditional lateral displacement. With the knee flexed 30 degrees and patella displaced 2 cm, objective criteria for a positive patellar instability test include greater ease of patellar translation and a softer end point compared with a normal, contralateral knee.

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AdultAgedAged, 80 and overBiomechanical PhenomenaCadaverHumansIn Vitro TechniquesJoint DislocationsJoint InstabilityLigaments, ArticularMiddle AgedPatellaPhysical ExaminationRange of Motion, ArticularJournal Article

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Suzanne M Tanner, William P Garth, Ramona Soileau, Jack E Lemons. 2003. A modified test for patellar instability: the biomechanical basis.. https://doi.org/10.1097/00042752-200311000-00001

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