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

Abstract

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(®) arthrometer offers a radiation-free method of measuring anterior knee laxity whose diagnostic value is identical to that of Telos(®) 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(®) 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.

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(®) 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.

Discussion: 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 of evidence: Level III, prospective case-control study.