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

Background: TELOS(TM) 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(R) is a non-irradiating but recently developed tool for which only limited data are available. Hypothesis: The GRNB(R) offers better reproducibility than TELOS(TM) for measuring anterior tibial translation without rotation in normal knees. Material and methods: We retrospectively evaluated instrumental laxity measurements in normal knees. Data were available for 60 TELOS(TM) measurements (9 kg load) and 57 GNRB(R) 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(R) measurement, patellar pressure was recorded. Results: No 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(TM) than with GRNB(R) (P < 0.05, Chi(2) test). GRNB(R) translation values did not correlate with patellar pressure. Discussion: The GNRB(R) device offers greater reproducibility than TELOS(TM) 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(TM) 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(R) 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. (C) 2015 Elsevier Masson SAS. All rights reserved.