Functional hallux limitus (Fhl) is a loss of 1st metatarsophalangeal joint extension during the second half of the single-support phase, when the weight-bearing foot is in maximal dorsiflexion, with important consequences during gait. Our objectives were to evaluate the functional results in the sagittal plane biomechanics following the endoscopic release of the Flexor Hallucis Longus (FHL) tendon at the retrotalar pulley, by assessing the kinematics and kinetics of the foot using a multi-segment model.

A prospective cohort of 20 patients with FHL was analyzed before and after surgical treatment and compared with 10 healthy subjects comprising the control group. A complete orthopaedic clinical examination was performed. Foot posture was determined with the Foot Posture Index and function before and after surgery was measured with the AOFAS Ankle-Hindfoot and AOFAS Midfoot validated scales. The multi-segment model consisted of Gait and joint angles’ analysis with the use of inertial sensors, plantar pressure analysis and surface electromyography analysis with the use of EMG. Pressure parameters, e.g., peak pressure, maximum force, time of occurrence, and contact time in different foot sub-regions and duration of activation, normalized EMG amplitude, and frequency content of selected muscles of shank were calculated.

Results showed an alteration of the gait pattern in the sagittal plane by increasing the flexion moment at the knee and ankle. A diminished dorsal flexion of the great toe at push-off, explaining the failure of the windlass mechanism, was also evident. An alteration of the plantar pressure distribution along the stance phase was associated to a mistimed supination to pronation motion, necessary to gain instability before heel-strike and push-off.

FHL causes a sagittal plane blockade, which is usually present at the retrotalar pulley and causes an asynchronic and mistimed gait that changes the biomechanics of the lower limb, especially the foot. Range of motion at the 1st metatarsophalangeal (1MTPJ) joint, ankle and knee joints are comparable to control group values, indicating the restoration of gait biomechanics following the endoscopic release of the FHL. Even though not statistically significant, the existent changes in the angular velocity values of the lower limb, especially below the knee, illustrate the involvement of a delayed muscular activation which is a time dependent factor.

Endoscopic FHL release is a safe and promising treatment alternative for 1MTPJ pathologies that restores normal gait and minimizes the occurrence of associated degenerative sequelae. Further studies including larger cohort groups are warranted.