Anterior Knee Laxity and Loss of Extension After Anterior Cruciate Ligament Injury

This study was performed to examine the relation ship between knee extension loss and the length of time after injury. We also wanted to compare anterior laxity in anterior cruciate ligament-injured knees in the early and late stages of injury. Loss of knee extension was measured in 81 patients with anterior cruciate ligament injury using lateral radiography with the injured leg relaxed and elevated. Extension loss was defined as the difference in maximal exten sion angle between the injured and uninjured knees. Average loss of extension was 3.6° in the 17 knees in which the anterior cruciate ligament had been torn 3 weeks or less before examination (the acute injury group) and 0.6° in the 64 knees in which the anterior cruciate ligament had been torn more than 3 weeks before examination (the chronic injury group). The extension loss in the acutely injured knees was sig nificantly greater compared with that in the uninjured knees and in the chronically injured knees. Arthro metric measurements using the KT-1000 arthrom eter were reliable to diagnose an acute tear. There was no correlation between the degree of extension loss and arthrometric anterior knee laxity measure ments. In 12 patients, the initial extension deficit in the early stage of injury significantly resolved with time, and manual maximum arthrometric measure ments of anterior knee laxity improved spontane ously with time.