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Relationship between the pivot shift and Lachman tests: a cadaver study
Keith L Markolf1, Steven R Jackson, David R McAllister
1Biomechanics Research Section, Department of Orthopaedic Surgery, University of California at Los Angeles Rehabilitation Center, 1000 Veteran Avenue, Room 21-67, Los Angeles, CA 90095-1759, USA. kmarkolf@mednet.ucla.edu
The injured-normal difference in laxity may predict pivot shift changes after anterior cruciate ligament (ACL) reconstruction. Insufficient graft tensioning can reduce laxity without improving pivot shift outcomes.
Area of Science:
- Orthopedic Surgery
- Biomechanics
- Sports Medicine
Background:
- The Lachman and pivot shift tests are standard clinical assessments for anterior cruciate ligament (ACL) integrity.
- Limited experimental research has explored the biomechanical relationship between these two crucial tests.
Purpose of the Study:
- To investigate the biomechanical correlations between the Lachman and pivot shift tests in knees with anterior cruciate ligament deficiency and after reconstruction.
- To evaluate how knee laxity and pivot shift magnitude relate under various ACL graft conditions.
Main Methods:
- Measured knee kinematics and anteroposterior laxities in 17 knees across intact, ACL-deficient, and reconstructed states.
- Simulated pivot shift testing and analyzed laxity-pivot shift relationships with unfixed and progressively loosened ACL grafts.
Main Results:
- Weak linear correlation between pivot shift magnitude and absolute laxity in ACL-deficient knees.
- Improved correlation (r²=0.53-0.73) between changes in pivot shift and anteroposterior laxity when grafts were tensioned to match intact knee laxities.
- Progressive graft loosening showed an initial linear increase in pivot shift, followed by a plateau.
Conclusions:
- Absolute knee laxity alone may not reliably predict pivot shift magnitude.
- The difference in laxity between the injured and normal knee (injured-normal difference) shows potential as a clinical predictor for the injured-normal difference in pivot shift.
- Inadequate anterior cruciate ligament graft tensioning can decrease anterior laxity but may not significantly alter pivot shift evaluation.
