The Toe-spread-out Exercise in Patients With Hallux Valgus and Without the Deformity

The study design was based on an interventional model (clinical trial). The participants were assigned to two research groups (A - with diagnosis of hallux valgus and B- without the deformity) that received therapeutic intervention of the TSO exercise performed unilaterally. The unexercised feet could have caused a synergistic effect and falsified the results, thus the unexercised feet were excluded from the control group. Nevertheless, a small control group which did not undergo any hallux therapy was created to check if any changes in analysed parameters are actually related to the intervention. These control group patients were examined twice at an interval of 14 days.

The hallux deformities were assessed on the basis of X-ray images taken in weight-bearing conditions, in a standing position in the anterior-posterior projection. On all X-rays the hallux valgus angles (HVA) and the first intermetatarsal angles (FIA) were designated and measured by one radiologist.

Additionally, each patient with hallux valgus was assessed according to the Hallux Metatarsophalangeal-Interphalangeal scale (HMP-IP scale) developed by the AOFAS (American Orthopaedic Foot and Ankle Society).

The effects of the exercises were assessed using a comparison of the outcomes of two examinations: before and after therapy (research group A and B). For this purpose, a surface electromyographic examination (sEMG) recorded from the abductor hallucis (AbdH) muscle was performed. The following parameters of electromyography were analysed in three phases of TSO exercise: amplitude and frequency pattern. Additionally, the motor fibres of the tibial nerve and the sensory fibres of the sural nerve function in electroneurographic examination (ENG) and range of motion of hallux using goniometer were assessed.

The sEMG recorded from the AbdH muscle and the ENG were performed with the use of the KeyPoint System (Medtronic A/S, Skovlunde, Denmark) and appropriate to the type of neurophysiological studies and set of electrodes (surface electrodes, bipolar stimulating electrode, and grounding electrode).

For the analysis of the bioelectrical activity of the AbdH the standard disposable Ag/AgCl surface electrodes with an active surface of 5mm2 were applied. The active electrode (cathode) was located on the belly muscle and the reference electrode (anode) was attached 3 cm distally from the active electrode. For the purpose of the sEMG examinations, the time base on 80ms/D and sensitivity of the recording of 0.5mV/D were set. 10kHz upper and 20Hz lower filters of the recorder amplifier were used.

The sEMG recordings were performed during three phases of the TSO exercise. The following parameters were analysed: amplitude of motor unit action potential (MUAP) measured in mV, and the frequency pattern of the MUAP recruitment of AbdH muscle activity. The sEMG tests with maintaining each phase of the TSO exercise were performed three times in order to obtain more objective results. The first test was treated as a training trial. The other two were taken into account to assess the amplitude and the frequency pattern. Only the trial with the highest amplitude and the most interference pattern was analysed as the result of the most effective recruitment of the MUAPs. The minimal and maximal amplitude values were automatically measured by the KeyPoint System after the marking of the MUAP amplitude peaks. An 'on-line' evaluation of the frequency of the MUAP recruitment during a maximal muscle contraction was a subjective visual assessment made by one experienced neurophysiologist. It was based on the following classification patterns presented by Buchthal et al. and by Stalberg and Falck: interference, intermediate, poor, and straight.

In the ENG the following parameters of the CMAP (compound muscle action potential) from the tibial nerve and of the SNAP (sensory nerve action potential) from the sural nerve were analysed: amplitude (measured from a negative inflection to the baseline in mV or in µV), latency (measured in ms) and conduction velocity (measured in m/s). During the ENG the time base on 5ms/D and sensitivity of the recordings on 2mV/D were set. 10Hz upper and 10kHz lower filters of the recorder amplifier were used. In order to record the compound muscle action potentials (CMAP) evoked from the AbdH muscle, the same location of surface electrodes as in the EMG was used. The electrical stimulation of the tibial nerve was applied in two points: below the medial malleolus and in the popliteal fossa. The ground electrode was located in the plantar part of the foot. Single rectangular stimuli with duration of 0.2ms were delivered via bipolar electrode at 1Hz frequency while their intensity ranged from 30mA to the value evoking the supramaximal CMAP. For recordings of SNAP from the sural nerve antidromic and repetitive electrical stimulation with an intensity of 20 mA was required. Recording electrodes were placed near the lateral malleolus while the stimulation point was 15 cm proximally at the external border of the Achilles tendon.

A clinical examination with the use of a goniometer was performed in the supine position of the patient. The investigator measured the range of the motion of the plantar and dorsal flexion in the first metatarsophalangeal joint and plantar flexion in the hallux interphalangeal joint.