Do Patients With Functional Hallux Limitus Have a Low-Lying or Bulky FHL Muscle Belly?

Functional hallux limitus (FHLim) refers to a limitation of hallux dorsiflexion when the first metatarsal head is under load, whereas physiologic dorsiflexion is measured in the unloaded condition. Limited excursion of the flexor hallucis longus (FHL) in the retrotalar pulley has been identified as a possible cause of FHLim. A low-lying or bulky FHL muscle belly could be the cause of this limitation. However, to date, there are no published data regarding the association between clinical and anatomical findings. The purpose of this anatomical study is to correlate the presence of FHLim and objective morphologic findings through magnetic resonance imaging (MRI).

Twenty-six patients (27 feet) were included in this observational study. They were divided into 2 groups, based on positive and negative Stretch Tests. In both groups, we measured on MRI the distance from the most inferior part of the FHL muscle belly and the retrotalar pulley as well as the cross-sectional area of the muscle belly 20, 30, and 40 mm proximal to the retrotalar pulley.

Eighteen patients had a positive Stretch Test and 9 patients had a negative Stretch Test. The mean distance between the most inferior part of the FHL muscle belly and the retrotalar pulley was 6.0 ± 6.4 mm for the positive group and 11.8 ± 9.4 mm for the negative group (P = .039). The mean cross section of the muscle measured at 20, 30, and 40 mm from the pulley were 190 ± 90, 300 ± 112, and 395 ± 123 mm² for the positive group and 98 ± 44, 206 ± 72, and 294 ± 61mm² for the negative group (P values .005, .019, and .017).

Based on these findings, we can conclude that patients with FHLim do have a low-lying FHL muscle belly causing limited excursion in the retrotalar pulley. However, the mean volume of the muscle belly was comparable in both groups, and therefore bulkiness was not found to be a contributing factor.

Level III, observational study.