Importance and challenges of measuring intrinsic foot muscle strength

Abstract

BackgroundIntrinsic foot muscle weakness has been implicated in a range of foot deformities and disorders. However, to establish a relationship between intrinsic muscle weakness and foot pathology, an objective measure of intrinsic muscle strength is needed. The aim of this review was to provide an overview of the anatomy and role of intrinsic foot muscles, implications of intrinsic weakness and evaluate the different methods used to measure intrinsic foot muscle strength.MethodLiterature was sourced from database searches of MEDLINE, PubMed, SCOPUS, Cochrane Library, PEDro and CINAHL up to June 2012.ResultsThere is no widely accepted method of measuring intrinsic foot muscle strength. Methods to estimate toe flexor muscle strength include the paper grip test, plantar pressure, toe dynamometry, and the intrinsic positive test. Hand-held dynamometry has excellent interrater and intrarater reliability and limits toe curling, which is an action hypothesised to activate extrinsic toe flexor muscles. However, it is unclear whether any method can actually isolate intrinsic muscle strength. Also most methods measure only toe flexor strength and other actions such as toe extension and abduction have not been adequately assessed. Indirect methods to investigate intrinsic muscle structure and performance include CT, ultrasonography, MRI, EMG, and muscle biopsy. Indirect methods often discriminate between intrinsic and extrinsic muscles, but lack the ability to measure muscle force.ConclusionsThere are many challenges to accurately measure intrinsic muscle strength in isolation. Most studies have measured toe flexor strength as a surrogate measure of intrinsic muscle strength. Hand-held dynamometry appears to be a promising method of estimating intrinsic muscle strength. However, the contribution of extrinsic muscles cannot be excluded from toe flexor strength measurement. Future research should clarify the relative contribution of intrinsic and extrinsic muscles during intrinsic foot muscle strength testing.

Intrinsic Foot Muscle Activation During Specific Exercises: A T2 Time Magnetic Resonance Imaging Study

“…The authors 24 also found a longer time to peak T2 signal intensity in elderly participants (157.1 6 109.9 seconds) than in younger ones (95.1 6 77.6 seconds), suggesting that age may influence T2 peaks and the time to return to baseline. Heat mapping through T2 percentage-activation change has shown 25 varying activation levels in the medial gastrocnemius (13.3% 6 1.3%), lateral gastrocnemius (7.8% 6 1.2%), and soleus (6.3% 6 2.1%) after unilateral heel raises, which are comparable to the percentage increases in the intrinsic plantar foot muscles in our study. Emerging evidence has shown that for T2, higher-intensity exercises result in a quicker rate of change 26 as well as a larger overall increase 21 when compared with lower-intensity exercises.…”

The potential of ultrasonography in the evaluation of foot orthotics therapy

“…The reliability of different ultrasound based measurements was reported in the literature: intra and inter-rater reliability of dynamic compression of the heel pad [38]; dorso-plantar thickness, medio-lateral width and CSA of AbdH [39], thickness and CSA of FHB, FDB, flexor hallucis longus (FHL), quadratus plantae (QP), AbdM, quadratus plantae (PER); thickness of tibialis anterior (TA) and PF [9,28]; fascicle length and pennation angle of MG and TA [40], hypoechoic rims around tendons, joint spaces, erosions, cartilage thickness [10]. However, ultrasonography remains a highly operator-dependent technique [9].…”

“…However, ultrasonography remains a highly operator-dependent technique [9]. Seen from the perspective of tissue stress theory, there are not at this moment a large number of articles which have used ultrasound methods for evaluating the effectiveness of foot orthotics.…”

“…Modelling the force production in striated (skeletal) muscle embraces different specific parameters related to the muscle's architecture (physiological cross-sectional area, volume, fibre pennation angle and length) and physical and mechanical properties of the tissue (density, elasticity). Collectively, these should be considered when surgical or conservative treatment events are necessary [9,[49][50][51].…”

“…According to the literature, there are numerous difficulties to evaluate internal stresses in the foot structure, no specific technologies being yet feasible at a clinical level for this purpose [6], while a better understanding of the musculoskeletal injuries and their relationship with foot orthotic therapy is not possible in the absence of the predictive models [7]. Ultrasonography (US) is easily accessible as an imagistic technique and frequently used in clinical practice [8][9][10]. It is largely used for the detection of abnormal echostructures and echogenicities in different tissues including the diabetic foot: muscles, osteo-tendinous structures, subcutaneous layer, and integument [11], which are consistent with the first step of tissue stress theory.…”