The effect of intraoperative isometric measurement on the outcome of anterior cruciate ligament reconstruction: a clinical analysis.

The concept of isometry is based on the measurement of displacement between potential femoral and tibial anterior cruciate ligament (ACL) graft attachment sites while the knee is taken through a range of motion. To evaluate the clinical benefit of intraoperative isometry measurements in ACL reconstruction, we prospectively compared 59 patients (58% acute) in whom isometry was tested (group I) with 35 patients (77% acute) in whom isometry was not tested (group II). All patients underwent arthroscopically assisted ACL reconstruction using autogenous bone-patella tendon-bone graft and interference screw fixation, and were followed-up for a minimum of 24 months (mean, 30 months). With 88% follow-up, no significant differences were found in objective testing, which included the pivot shift test, the Lachman test, KT-1000 arthrometer measurements, and range of motion. A significant difference was found between the two groups when Lysholm scores (P = .04) and Tegner Scores (P = .02) were compared, with group II having higher scores. In addition, one of 15 visual analog scales, "gives way," showed a significant difference between the two groups (P = .01). On a scale of 1 to 10 with 1 being "no giving way" and 10 being "very frequent giving way", group I had an average of 1.68 and group II had an average of 0.58. These differences were related to the greater percentage of chronic cases in group I. Analysis of only those patients with acute injuries from each group showed no significant differences in any objective or subjective measurement. Group I had an overall failure rate of 13%, and group II had a failure rate of 6.7% (chi 2 = .848). These results indicate that, in the hands of a surgeon experienced in ACL reconstruction, intraoperative assessment of isometry has little effect on the clinical outcome.