QUANTIFICATION OF GASTROCNEMIUS MUSCLES TIGHTNESS WITH PASSIVE ANKLE DORSIFLEXION MEASUREMENT: A RELIABLE APPROACH

L. Martinez¹, M. Lalevée², J. Beldame³, M. L'Hermette⁴, H. Brunel⁵, F. Dujardin², F. Billuart¹

¹IFMK Saint Michel- Université Paris-Saclay, Paris, France, ²Centre Hospitalier Universitaire de Rouen, Service de Chirurgie Orthopédique et Traumatologique, Rouen, France, ³Clinique Mégival, Saint-Aubin-sur-Scie, France, ⁴University of Rouen Normandy, Research Center for Sports and Athletic Activities Transformations, Rouen, France, ⁵IFMK Saint Michel, Paris, France

Background: Limited passive ankle dorsiflexion contributes to decompensation of foot and ankle pathologies and may be caused by tightness of the Parallel Elastic Component (PEC) of gastrocnemius muscles. Its diagnosis and treatment appear to be crucial. Equinometers help to measure this tightness but few of them are reliable enough to be used routinely in the clinic.

Purpose: We designed an equinometer to measure the passive ankle dorsiflexion and to quantify the load applied to the foot, thus reflecting the force-length relationship of the PEC. The main objective of this study was to evaluate the intra- and inter-rater reliability of this new equinometer. The secondary objective was to determine the optimal amount of load to apply on the foot to achieve the highest reliability.

Methods: Ethics approval was obtained on 02/18/2021. 29 healthy volunteers (24.60±3.29-year-old) were enrolled in the study. The equinometer consisted of a goniometer and an electronic dynamometer, hooked up to a computer. Three experimented raters (R1, R2, R3) carried out three trials of passive dorsiflexion by applying controlled pressure to the metatarsal heads of both foot under two conditions: Knee Extended (KE) and Knee Flexed at 30° (KF). The equinometer continuously recorded the dorsiflexion values (in °) corresponding to each 1N interval of plantar pressure between 4N and 20N. The intra- and inter-rater reliability was evaluated with intraclass correlation coefficients (ICC) for each load interval and for both experimental conditions. The loading interval where the ICC was the best was then refined in 0.1N increments.

Results: The lowest intra-rater ICC (0.84) was found in the 4–5N interval in the KE condition. Conversely, the highest intra-rater ICC (0.99) were in the intervals with higher applied forces, up to a certain point beyond which the reliability decreased. The 14–15N interval had the ICC closest to 1 for each rater (ICC with KE = 0.97 for R1, 0.96 for R2 and 0.98 for R3; ICC with KF = 0.98 for R1, 0.99 for R2 and 0.96 for R3). The inter-rater ICC showed low agreement between the raters, especially for the lower force levels. The ICCs were higher in the KF. The 14–15N interval had the highest ICC both in the KE and KF conditions. For the inter-rater ICC, the highest values were achieved in KF. An applied load of 14.5N had the highest inter-rater and intra-rater ICC values.

Conclusions: This equinometer has excellent intra-rater reliability, a moderate to good inter-rater reliability and reflects the force-length relationship of the PEC classically observed on a passive muscle. The interval between 14 and 15N is the most reliable for clinical use.

Implications: Quantifying the tightness of the PEC of gastrocnemius muscles by measuring ankle dorsiflexion has a genuine clinical application. In this context, the purpose of this study was above all to validate this new equinometer. This is an essential prerequisite for the use of this tool in clinical practice and for research purposes, especially when aiming to define a pathological threshold for tightness of the PEC of gastrocnemius.

Funding acknowledgements: No funding was received for this study

Keywords:
Gastrocnemius tightness
Equinometer
Reliability study

Topics:
Orthopaedics
Musculoskeletal: lower limb

Did this work require ethics approval? Yes

Institution: Hôpital Hôtel Dieu Paris

Committee: Comité de Protection des Personnes

Ethics number: IORG0009918