INCREASED TIBIAL TRANSLATION AFTER PARTIAL SECTIONING OF THE ANTERIORCRUCIATE LIGAMENT - THE POSTEROLATERAL BUNDLE

We measured changes in anterior translation of the tibia with sequenti al sectioning of the bundles of the anterior cruciate ligament and cor related these changes with the clinical examination. Six fresh cadaver ic lower extremities were examined by three experienced knee surgeons in a masked fashion with the anterior cruciate ligament intact and aft er sectioning of the posterolateral bundle, the posterolateral bundle and 50% of the anteromedial bundle, and the entire ligament. Lachman, anterior drawer, and lateral pivot shift tests were performed. Both KT -1000 arthrometer testing (30 pounds) and biplanar radiography demonst rated progressive increases in anterior translation with incremental s ectioning of the anterior cruciate ligament. However, significant (P < 0.05) increases in translation were found only after sectioning both the posterolateral bundle and half of the anteromedial bundle and afte r complete sectioning of the anterior cruciate ligament. The examiners were accurate in their interpretation of the status of the anterior c ruciate ligament in 89% of the intact specimens and 80% of completely sectioned ligaments. Only 11% of the examinations correctly diagnosed the anterior cruciate ligament as partially cut when the posterolatera l bundle was sectioned. A soft end point to the Lachman examination wa s noted only after cutting at least 75% of the ligament, but was not a lways present. Clinical evaluation is accurate in defining intact and completely sectioned anterior cruciate ligaments. However, it is unabl e to differentiate a sectioned posterolateral bundle from an intact an terior cruciate ligament, or a 75% sectioned ligament from a completel y sectioned ligament. The clinical diagnosis of a partial tear of the anterior cruciate ligament is more likely to represent a complete or ' 'functionally complete'' tear.