Preoperative instrumented testing of anterior and posterior knee laxity

Abstract

A prospective study was performed on 50 patients who were thought or suspected to have cruciate ligament tears. Each patient had a clinical examination preoper atively and under anesthesia and instrumented exami nation using the MedMetric KT-1000 arthrometer, Stry ker knee laxity tester, and Genucom knee analysis. The diagnosis was confirmed by arthrotomy or arthroscopy. Thirty had acute knee injuries (within 2 weeks), 9 had subacute (2 weeks to 3 months), and 11 had chronic injuries. The surgical findings demonstrated that five had other maladies, but no cruciate ligament tears. Two had a partial ACL tear, and the remaining 43 patients had at least one cruciate tear. The preoperative clinical examination for cruciate lig ament integrity was completely correct in 92%, correct but incomplete in 6%, and incorrect in 2%. Examination under anesthesia was correct in 98%, the KT-1000 was correct in 75% (involved knee minus noninvolved knee was ≥3 mm laxity equal to ACL tear), the Stryker was correct in 75%, and Genucom in 70%. The average laxity of those with ACL tears was 4.4 mm with the KT- 1000, 4.6 mm with the Stryker, and 2.0 mm with the Genucom. The methods of testing with the Stryker and the KT- 1000 are similar and the laxity recorded in patients with a torn ACL were almost identical. However, the KT- 1000 can be used to identify the quadriceps neutral position and therefore more accurately determine PCL instability. The Genucom has the most versatility, but the laxity recorded in patients with a torn ACL was significantly lower than the other devices. It had the poorest correlation with the clinical Lachman test. This study suggests that clinical examination by an experienced examiner is the most accurate way to determine cruciate ligament integrity. However, instru mented testing was beneficial. In many cases, confi dence in clinical diagnosis was improved by instru mented confirmation.