Reliability of a new computerized equinometer based on Silfverskiöld test to measure gastrocnemius tightness

BACKGROUND: Several tools exist to measure tightness of the gastrocnemius muscles; however, few of them are reliable enough to be used routinely in the clinic. The primary objective of this study was to evaluate the intra- and inter-rater reliability of a new equinometer. The secondary objective was to determine the load to apply on the plantar surface of the metatarsal heads to achieve the highest reliability when measuring gastrocnemius tightness. METHODS: The equinometer consisted of a goniometer and an electronic dynamometer, hooked up to a computer. Three raters carried out three trials of passive dorsiflexion by applying controlled pressure to the metatarsal heads of both ankles in 29 healthy subjects under two experimental conditions: knee extended (KE) and knee flexed at 30 degrees (KF). The equinometer continuously recorded the ankle dorsiflexion values (in °) corresponding to each 1 N interval of plantar pressure between 4 N and 20 N. The intra- and inter-rater reliability of the ankle dorsiflexion were evaluated through the intra-class correlation (ICC) coefficients in each of the pressure intervals. RESULTS: The intra-rater ICC in KE and KF was between 0.84 and 0.98. The inter-rater ICC in KE and KF was between 0.59 and 0.92. The pressure interval between 14 N and 15 N had the highest intra-rater (ICC = 1) and inter-rater reliability (0.87≤ICC≤0.99). A more refined analysis of this interval found that a load of 14.5 N yielded the best reliability. CONCLUSIONS: This compact equinometer has excellent intra-rater reliability and moderate to good inter-rater reliability. Since this reliability is optimal in the 14–15 N range, this load should be used going forward in clinical practice, especially when aiming to define a pathological threshold for tightness of the gastrocnemius muscles.