Evaluation of knee instability in acute ligamentous injuries

The stability on clinical examination (CE) and examination under anaesthesia (EUA) was evaluated in 350 consecutive acute knee injuries. Valgus instability in knees with a medial collateral tear was observed on CE in 62 and on EUA in 67 cases (p less than 0.05). The anterior drawer sign was positive in 55 patients on CE and in 110 patients on EUA (p less than 0.0001), the corresponding figures for the Lachman test were 66 and 126 respectively (p less than 0.0001). The pivot shift-test was positive in 13 cases on CE and in 87 under anaesthesia (p less than 0.0001). Fresh total tears of the anterior cruciate ligament (confirmed at arthrotomy, n = 79) were detected by the Lachman test in 48 per cent on CE and in 96 per cent on EUA. Of the nine fresh, total tears of the posterior cruciate ligament three were disclosed by the posterior drawer test on CE and all nine on EUA. Anteromedial rotatory instability was observed on CE in 10 patients and on EUA in 47 (p less than 0.0001). In these patients 41 medial collateral tears, 23 posteromedial capsular tears, 21 medial meniscus and 40 anterior cruciate lesions were found. On CE only one anterolateral rotatory instability was found, whereas EUA disclosed 9 cases. Posteromedial rotatory instability was not confirmed on CE, though on EUA four cases were found. CE and EUA detected 2 and 3 posterolateral instabilities respectively. In conclusion, the use of EUA with an adequate mode of stability evaluation in acute knee injuries is strongly advocated. Clinical examination is considered highly unreliable with many false negative findings.