Evaluation of the medial longitudinal arch: a comparison between the dynamic plantar pressure measurement system and radiographic analysis

Objectives: The measurement of the medial longitudinal arch (MLA) of the foot is a controversial issue in orthopedics. Several methods have been developed to define and determine the MLA, but none of them are universally accepted. The purpose of this study was to compare some statically obtained radiographic angles with the dynamic plantar pressure distribution measurement system for the evaluation of the MLA in healthy individuals. Methods: A total of 95 subjects (72 females, 23 males; mean age 37.8 years; range 11 to 85 years) were retrospectively evaluated. All the subjects were referred to the pedobarography laboratory for varying causes, had foot radiographies, and were evaluated as having normal feet. On standard lateral weight-bearing radiographs of the foot, the lateral talocalcaneal angle, talo-first metatarsal angle, talohorizontal angle, and calcaneal pitch angle were measured. The plantar pressure distribution was measured by the EMED-SF system. To evaluate the MLA, the arch index method was used. The arch index was calculated by the ratio of the pressure area of the midfoot to the sum of the forefoot, midfoot, and the hindfoot areas. Correlations between the radiographic angles and the arch index were analyzed by the Pearson correlation test. Results: The mean values of the lateral talocalcaneal angle, tab-first metatarsal angle, talohorizontal angle, and calcaneal pitch angle were 43.2, 7.2, 29.5, and 41 degrees, respectively. The mean value of the arch index was 0.12 (range 0.04 to 0.17). There was no significant correlation between the arch index and gender (r=-0.10, p>0.05). The tab-first metatarsal (r=0.38) and talohorizontal (r=0.19) angles were found to be in significant correlation with the arch index (p<0.05), whereas the talocalcaneal (r=-0.16) and calcaneal pitch (r=-0.10) angles did not show correlation with the arch index (p>0.05). Conclusion: The arch index method is a simple and reproducible pedobarographic measurement for the evaluation of the MLA. However, the angles measured on statically obtained radiographs and showing correlations with the arch index may give similar results concerning the MLA. Both static and dynamic methods can be utilized in the evaluation of the MLA.