The role of morphology and function of intrinsic foot muscles in young handball players with chronic ankle instability

Strong evidence shows the importance of intrinsic foot muscles (IFMs) in balance and foot and ankle biomechanics; despite this, not much research has been published regarding the role of IFMs on chronic ankle instability. The aim of the study was to compare IFMs morphology and function between young handball players with and without chronic ankle instability. The secondary objective was to assess the association between the morphology or function of the IFMs and the foot morphology. Cross-sectional case-control study. A sample of 100 young handball players were recruited and divided into athletes with chronic ankle instability (case group, n = 50) and without (control group, n = 50). Main outcome measures: morphology and function of abductor hallucis, abductor digiti minimi, flexor hallucis brevis, flexor digitorum brevis and quadratus plantae, which were assessed with ultrasound examination at rest and in active contraction. Foot Posture Index-6 was used to analyze foot morphology. Significant differences were only found in the abductor hallucis morphology (case group CSA 2.14cm2, control group CSA 1.84cm2, p 0.013) and in the flexor hallucis brevis morphology (case group thickness 1.31 cm, control group thickness 1.41 cm, p 0.005). A significant but weak positive correlation was found between foot morphology and abductor hallucis function (r = 0.32, p = 0.025). Between-groups differences were only found in abductor hallucis and flexor hallucis brevis morphology; no differences were found in the rest of IFMs morphology and function outcomes. A significant positive association was only found between foot morphology and AbH function in young athletes with CAI.