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Biomechanical and Anatomical Assessment After Knee Hyperextension Injury

Stefan Fornalski, MD^*, Michelle H. McGarry, MS^*, Rick P. Csintalan, MD, Donald C. Fithian, MD and Thay Q. Lee, PhD^*,

From the ^* Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System, Long Beach, California, and the University of California Irvine, Irvine, California, Kaiser Permanente, Orange County, California, and Kaiser Permanente, San Diego, California

Address correspondence to Thay Q. Lee, PhD, Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (09/151), 5901 East 7th Street, Long Beach, CA 90822 (e-mail: tqlee{at}med.va.gov or tqlee{at}uci.edu).

Background: Knee hyperextension can be a serious and disabling injury in both the athletic and general patient population. Understanding the pathoanatomy and pathomechanics is critical for accurate surgical soft tissue reconstructions.

Purpose: To quantify the effects of knee hyperextension injury on knee laxity in a human cadaveric model and to qualitatively assess the anatomical injury pattern through surgical dissection.

Study Design: Descriptive laboratory study.

Methods: Six fresh-frozen cadaveric knees were rigidly mounted on a custom knee testing system that simulates clinical laxity tests. The knee laxity measurements consisted of anterior-posterior laxity, internal-external rotational laxity, and varus-valgus laxity using a custom testing setup and a Microscribe 3DLX system. The laxity data were collected at both 30° and 90° of knee flexion for the intact specimens and then after 15° and 30° hyperextension injury. After biomechanical assessment, a detailed dissection was performed to document the injured structures in the knee. Repeated-measures analysis of variance with a Tukey post hoc test (P < .05) was used for statistical comparison.

Results: The results from this study suggest progressive damage to translational and rotational knee soft-tissue restraints with increasing knee hyperextension. Knee hyperextension to 30° caused the most significant increase in anterior-posterior and rotational laxity. Anatomical dissections showed a general injury pattern to the posterolateral corner, partial femoral anterior cruciate ligament avulsion in 4 of 6 specimens, and no gross posterior cruciate ligament injuries.

Conclusion: Injuries to the posterolateral corner of the knee can result from isolated knee hyperextension.

Clinical Relevance: The clinician should be aware of the potential for posterolateral corner injuries with isolated knee hyperextension. This will allow early surgical planning and primary surgical repair.

Key Words: knee hyperextension • knee laxity • posterolateral corner • cadaveric study