In patients with anterior cruciate ligament (ACL) tears, anterior laxity can be measured using stress radiographs or more recently introduced electronic measurement devices.

The GNRB^® arthrometer offers a radiation-free method of measuring anterior knee laxity whose diagnostic value is identical to that of Telos^® or Lerat stress radiographs.

One hundred and fifty-seven patients (40 years [18–69]) scheduled for knee arthroscopy were evaluated using the GNRB^® and two series of stress radiographs of both knees, one obtained using a 250-N Telos^® device and the other using the technique described by Lerat (posterior translation of the femur/tibia under a 9-kg loading device). Arthroscopic evaluation of the ACL served as the reference standard for assessing the diagnostic performance of the radiological and instrumental laxity measurements.

Under arthroscopic examination, the ACL was normal in 50.3%; “healed to roof of the notch” (partial tear) in 9.6%, “posterolateral bundle preserved” (partial tear) in 7.0%, “healed to the posterior cruciate ligament” (PCL) in 17.8%, and “empty notch” (complete tear) in 15.3%. In partial ACL tears, no significant differences in anterior laxity were found across the three measurement techniques. Telos^® and GNRB^® laxities were greater in the complete-tear group than in the normal-ACL, partial-tear, and healed-to-PCL groups. With the Lerat technique, the only significant differences were between the complete-tear group and the normal-ACL and partial-tear groups. Telos^® and GNRB^® showed similar diagnostic performance (sensitivity>62%, specificity>75%), whereas the Lerat technique lacked sensitivity (sensitivity=43.2%, specificity=82.7%) at 3mm.

Diagnostic performance was lower in our study than in earlier reports. The GNRB^® performed as well as Telos^®. The non-irradiating nature of GNRB^® assessments allows repeated measurements for therapeutic or diagnostic purposes.

Level III, prospective case-control study.