Biomechanical and anatomical assessment after knee hyperextension injury

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.

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.

Descriptive laboratory study.

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 degrees and 90 degrees of knee flexion for the intact specimens and then after 15 degrees and 30 degrees 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.

The results from this study suggest progressive damage to translational and rotational knee soft-tissue restraints with increasing knee hyperextension. Knee hyperextension to 30 degrees 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.

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

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.