Anterior knee laxity measurement: Comparison of passive stress radiographs Telos® and "Lerat", and GNRB® arthrometer

Introduction: In patients with anterior cruciate ligament (ACL) tears, anterior laxity can be measured using stress radiographs or more recently introduced electronic measurement devices. Hypothesis: The GNRB (R) arthrometer offers a radiation-free method of measuring anterior knee laxity whose diagnostic value is identical to that of Telos (R) or Lerat stress radiographs. Patients and methods: One hundred and fifty-seven patients (40 years [18-69]) scheduled for knee arthroscopy were evaluated using the GNRB (R) and two series of stress radiographs of both knees, one obtained using a 250-N Telos (R) 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. Results: 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 (R) and GNRB (R) 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 (R) and GNRB (R) showed similar diagnostic performance (sensitivity > 62%, specificity > 75%), whereas the Lerat technique lacked sensitivity (sensitivity = 43.2%, specificity = 82.7%) at 3 mm. Discussion: Diagnostic performance was lower in our study than in earlier reports. The GNRB (R) performed as well as Telos (R). The non-irradiating nature of GNRB (R) assessments allows repeated measurements for therapeutic or diagnostic purposes.