A comparison of muscle strength testing for great toe extension

Although extensor hallucis longus (EHL) strength has been identified as a primary predictor of L5 nerve root radiculopathy and deep peroneal nerve palsy, assessment of EHL strength is commonly overlooked. This is mainly due to the lack of an objective and accurate method for evaluation, since manual muscle testing (MMT) has not been well utilized. A study of the reliability of evaluating MMT in various toe positions was performed.

To determine the reliability and validity of MMT for great toe extension, 40 normal volunteers (80 toes) with good muscle strength were recruited. Each subject was examined with MMT at the MTP joint (MTPp) and IP joint with various positions of the MTP joint (maximal extension: IPp-e, neutral position: IPp-n, maximal flexion: IPp-f) by two examiners. Inter-observer reproducibility was calculated for each MMT by κ values. Correlations between the great toe length and great toe extensor strength in each position, and between the angle in maximal extension of the MTP and great toe extensor strength in each position were examined using Spearman's correlation test.

Great toe extensor strength was highly maintained in MTP measurement. Correct detections in each position (MTPp, IPp-e, IPp-n, IPp-f) were 96.3 and 96.3; 45.0 and 32.5%; 53.8 and 33.8%; and 50.0 and 61.5% for the first and second observer, respectively. The inter-observer variability for great toe extensor strength was highly maintained in MTP measurement (κ values = 1.00). The κ value of each position was 0.69, 0.35, and 0.28 for IPp-e, IPp-n, and IPp-f, respectively. There were no correlations between great toe length or angle in extension of the MTP and great toe extensor strength in each position.

This study demonstrated that MTPp was much superior to the IP joint in the MMT procedure for great toe extension.