CLINICAL-DIAGNOSIS AND INSTRUMENTED MEASU REMENT OF ANTERIOR KNEE LAXITY - A COMPARATIVE-STUDY OF THE LACHMAN TEST, KT1000 KNEE LIGAMENT ARTHROMETER AND THE SONOGRAPHIC LACHMAN TEST

We reviewed 45 patients on average 14.7 years after surgery for ruptur e of the anterior cruciate ligament. The aim of the study was to compa re the reliability of the Lachman test to evaluation of knee laxity wi th the KT 1000 arthrometer and the ultrasound-assisted Lachman test. F orty-five knees were examined with the Lachman test: 12 knees showed n o sign of instability; 20 had a + positive Lachman test with a hard en d point; 6 with a + positive test had no end point and were rated as u nstable; a ++ Lachman test was found in 7 knees. With the KT 1000 Arth rometer 44 knees were examined: 30 knees were graded as stable accordi ng to the criteria of Daniel; 14 knees were unstable. We used the ultr asound-guided Lachman test in 44 knees. Taking only the side-to-side d ifference into account, 37 knees were stable and 7 unstable. According to Gruber, a single translation great er than 4 mm is also a sign of instability. Therefore, 12 knees were unstable, although 6 of these kn ees were rated as stable, taking the side-to-side difference into acco unt. Comparing the two instrument measurements, all knees with ultraso und-rated instability on the basis of side-to-side measurements were a lso rated as unstable with the KT 1000 arthrometer. Only half of the k nees rated as unstable because of a single translation greater than 4 mm with the ultrasound technique were rated as unstable with the KT 10 00 arthrometer. Our results show that the accuracy of the Lachman test is as good as the instrument evaluation if the end point is taken int o consideration. A positive Lachman test indicating anterior knee laxi ty is one where the soft end point is as described by Torg et al. Both instrument measurements are accurate in indicating anterior knee laxi ty, but only if they are used by an experienced examiner. Using the si de-to-side measurements, the sensitivity of the KT 1000 arthrometer is higher. If only single translations greater than 4 mm without a signi ficant side-to-side difference with the ultrasound technique are inter preted as anterior knee instability, then some knees will be rated as unstable, although both the clinical and KT 1000 arthrometer examinati ons prove them to be stable. We believe that only a side-to-side diffe rence with the instrument technique should be interpreted as knee laxi ty. Borderline positive measurements should only be used together with the clinical findings. Both instrument measurements can help to impro ve the quality of the clinical examination if the examiners are inexpe rienced. If instrument measurements are required, we believe that the ultrasound technique is easy and cheap to perform. Nevertheless, we be lieve that instrument measurements of anterior knee laxity are not nec essary if a thorough clinical examination is performed, taking the end point of the Lachman test into consideration.