Association between abductor hallucis abductory force and navicular drop index, a predictive correlational study

The role of intrinsic muscles of the foot in the medial longitudinal arch mechanism was investigated in several recent studies. It is determined that the abductor hallucis muscle (AHM) has an important role in dynamic support of the arch. Objective of our preliminary study was to establish a relationship between the navicular drop index (NDI) and the AHM abduction force. A single group exploratory design was used. The participants were 127 athletes aged 8-16 years (m/f 74/53; 11.99 ± 2.11 years; 156.21 cm ± 15.51 cm; 47.61 kg ± 13.96 kg; 2-5 training h/week), examined at a regular sport medical checkup. Abductor hallucis force was measured by a digital Algometer FPX 25/220, which is a newly developed approach that should be properly assessed in further studies to establish standardization and qualification of the algometer for this specific use. Navicular drop test has been performed as originally developed by Brody. Data were analyzed using Student's t-test, Mann-Whitney U test, contingency coefficients and logistic regression. Average NDI was found to be significantly different comparing the group with positive abduction force and the group that cannot perform the active abduction. Logistic regression indicated that the variable representing impossible active abduction was significantly associated with NDI. Preliminary results showed that there was a strong relationship between the hallux active abduction force and NDI in young athletes: the higher abduction force correlates to lower NDI. To determine clinical relevance of our investigation, further study is planned in which hallux active abduction force and NDI would be compared and correlated pre- and postspecific strengthening program.