Ultrasound evaluation of gravity induced anterior drawer following anterior cruciate ligament lesion.

Ultrasound is not so far a standard procedure to visualize the anterior drawer following anterior cruciate ligament (ACL) lesions. This is because the described techniques are either technically difficult or depend on the experience of the performer and are not standardized. The purpose of this prospective analysis on ACL intact, ACL deficient and ACL reconstructed knees was to compare the diagnostic accuracy of prone ultrasonographic Lachman testing with KT-1000 measurements in the same study population. Our technique is based on a prone position of the patient. The thigh lies on the table surface such that the patella has no contact. The lower leg is placed on a roll in the ankle area and flexed to 30 degrees . The transducer (5 MHz) is positioned over the medial aspect of the popliteal fossa to visualize the femoral condyle as well as the tibial head. Under ultrasound control the lower leg is manually lifted as far the thigh stays in contact with the surface defining the start position. The lower leg is then released and drawn by gravity into the anterior drawer position, the final position. The distance between the posterior tangent from the medial femoral condyle to the medial tibial plateau was registered by three independent ultrasound measurements of the injured knee. The uninvolved opposite knee served as an internal control. The same procedure was done using a KT-1000 device (89 and 133 Newton and manual maximum force). The patients were split into two groups: acute injury (A), and (B) 6 months following ACL repair with a patellar tendon graft. All patients then underwent arthroscopy. In group A with acute ACL lesions the anterior drawer resulted in 14.1 mm (+/- 3.5) and was significantly (P < 0.001) different from the contralateral knee (7.7 mm +/- 2.9). The KT 1000 showed a comparable difference with 14.4 mm (+/- 3.9) for the injured knee and 8.3 mm (+/- 3.4) for the uninjured (P < 0.001). Sonometrically, group B patients showed no clear difference between the repaired (9.9 mm +/- 2.7) knee and its control (8.1 mm +/- 2.5). This was found for the KT-1000 results as well. The results derived from the ultrasound evaluation of the anterior drawer correlated well with those from the KT-1000 (r = 0.46). Based on a minimum intra-individual difference of 5 mm in the ultrasound measured anterior drawer, the sensitivity of the test in group A resulted in 0.96, and the specificity in 0.98. The described technique is reproducible, painless and easy to perform in order to evaluate acute ACL tears using any commercially available ultrasound device. The reproducibility is similar to the KT-1000 device. We recommend this technique for use in cases of acute ACL tears as well as in the follow-up of ACL repair.