Comparative reproducibility of TELOS™ and GNRB® for instrumental measurement of anterior tibial translation in normal knees

BackgroundTELOS™ is among the reference tools for the instrumental measurement of anterior tibial translation during the initial work-up and follow-up of patients with injuries to the anterior cruciate ligament (ACL). GRNB® is a non-irradiating but recently developed tool for which only limited data are available.HypothesisThe GRNB® offers better reproducibility than TELOS™ for measuring anterior tibial translation without rotation in normal knees.Material and methodsWe retrospectively evaluated instrumental laxity measurements in normal knees. Data were available for 60 TELOS™ measurements (9 kg load) and 57 GNRB® measurements (89 N and 134 N loads). For each instrument, we compared the absolute variation in anterior tibial translation between two measurements performed 6 months apart. For each GNRB® measurement, patellar pressure was recorded.ResultsNo significant differences were found between mean (± SD) variations in translation between the two instruments. A greater than 2.5 mm variation between the two measurements was significantly more common with TELOS™ than with GRNB® (P < 0.05, Chi2 test). GRNB® translation values did not correlate with patellar pressure.DiscussionThe GNRB® device offers greater reproducibility than TELOS™ when used to quantitate anterior tibial translation. The limited sample size may have prevented the detection of a significant difference between mean values. In addition, disadvantages of the TELOS™ include radiation exposure of the patient, operator-dependency of measurements made on the radiographs, and absence of a biofeedback system to limit hamstring contraction. GNRB® does have hamstring contraction biofeedback control but uses another parameter, namely, patellar pressure, for which the optimal value is unknown. Quadriceps and hamstring co-contraction induced by excessive patellar pressure may influence anterior tibial translation. The optimal patellar pressure value needs to be determined.Level of evidenceIV, retrospective study.