Increased Tibial Translation After Partial Sectioning of the Anterior Cruciate Ligament

We measured changes in anterior translation of the tibia with sequential sectioning of the bundles of the anterior cruciate ligament and correlated these changes with the clinical examination. Six fresh cadav eric lower extremities were examined by three experi enced knee surgeons in a masked fashion with the anterior cruciate ligament intact and after 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 demon strated progressive increases in anterior translation with incremental sectioning of the anterior cruciate lig ament. However, significant ( P < 0.05) increases in translation were found only after sectioning both the posterolateral bundle and half of the anteromedial bun dle and after complete sectioning of the anterior cruci ate ligament. The examiners were accurate in their interpretation of the status of the anterior cruciate lig ament in 89% of the intact specimens and 80% of completely sectioned ligaments. Only 11 % of the ex aminations correctly diagnosed the anterior cruciate ligament as partially cut when the posterolateral bundle was sectioned. A soft end point to the Lachman exam ination was noted only after cutting at least 75% of the ligament, but was not always present. Clinical evalua tion is accurate in defining intact and completely sec tioned anterior cruciate ligaments. However, it is un able to differentiate a sectioned posterolateral bundle from an intact anterior cruciate ligament, or a 75% sectioned ligament from a completely sectioned liga ment. The clinical diagnosis of a partial tear of the anterior cruciate ligament is more likely to represent a complete or "functionally complete" tear.