Intrinsic foot muscle size can be measured reliably in weight bearing using ultrasound imaging

Abstract

Background:The intrinsic foot muscles (IFMs) are important contributors to optimal foot function. While assessment of IFM morphology using ultrasound imaging in non-weight bearing has been established, this does not evaluate the foot in its primary functional position of weight bearing.Research Question: Is ultrasound imaging a reliable and clinically feasible method of measuring IFM morphology in weight bearing, do these measures differ to those from nonweight bearing and are they associated with participant characteristics?Methods: Ultrasound images were obtained by a single rater from twenty-four healthy participants on two occasions, one week apart. Images were taken in weight bearing (bilateral stance) and non-weight bearing (seated). Cross-sectional area and dorsoplantar thickness of the abductor hallucis muscle, and dorsoplantar thickness of the muscles of the first interstitium were measured from acquired images. A second rater also acquired images at the first session.Participant characteristics included age, height, weight, sex, foot posture and foot mobility. Results: Measurements of IFM morphology demonstrated high reliability within and betweentest sessions, as well as between raters (ICCs > 0.8). Our findings suggest that changes of 10-18% could be considered to exceed measurement error. Larger IFM size was related to larger body size (taller, heavier), foot posture (longer foot, higher arch, wider midfoot) and male sex.Significance: This study is the first to describe a reliable and clinically feasible method of measuring IFM morphology in weight bearing. These measurements could be used in future studies to assess IFM morphology in patient populations and to evaluate the effect of intervention. Body size and foot posture explained between 20 and 41% of the variance in measurements and should be considered when comparing IFM morphology between individuals. The establishment of reliable measurements in weight bearing provides a crucial step towards the future evaluation of IFM function using ultrasound imaging.3

Ultrasound Imaging Is Reliable for Tibialis Posterior Size Measurements

“…As far as we know, this is the first study to report a reliable method for measuring the TP CSA using US. Our ICC scores were similar to or higher than those reported for other lower extremity muscles, which ranged from 0.57 to 0.99 15,26,29,30,34–36 . The SEM and LoA were also comparable to or lower than those seen in other studies 26,29,30 .…”

“…Our ICC scores were similar to or higher than those reported for other lower extremity muscles, which ranged from 0.57 to 0.99 15,26,29,30,34–36 . The SEM and LoA were also comparable to or lower than those seen in other studies 26,29,30 . For thickness measurements, our LoA ranged from 5.8% to 9.7%, whereas other researchers saw a range of 9% to 18% for foot and leg muscles 26,29 .…”

“…For the CSA, we saw even lower LoA (4.6%–7.4%), which were lower than the 8% to 30% found in previous studies 26,29 . Only a couple of previous studies presented SEMs: one was in weight‐bearing intrinsic foot muscles, showing scores ranging from 0.03 to 0.17, 30 and the other was performed in our research group 25 . Our range of 0.03 to 0.07 compares favorably.…”

“…Ultrasound imaging of superficial leg and foot muscles may provide the foundation for a robust TP measurement technique. Several studies have shown good to excellent reliability (intraclass correlation coefficients [ICCs], 0.57–0.99) of US imaging in many of the lower leg muscles, including tibialis anterior, flexor digitorum longus, flexor hallucis longus, fibularis longus, fibularis brevis, and medial gastrocnemius 14,26–30 . Most of these studies measured the CSA of lower leg muscles at 50% of the distance from the knee joint line to the inferior tip of the malleolus 14,26,29 .…”

Muscle Quality Assessment by Ultrasound Imaging of the Intrinsic Foot Muscles in Individuals with and without Plantar Fasciitis: A Case–Control Study

“…In regard to foot disorders, such as pes pannus, Angin et al reported an increase in the thickness of the plantar fascia in patients with this foot condition, with overpronation being an associated risk factor for PF or Achilles tendinopathy pathologies [ 19 ]. Several authors support the use of USI for the assessment of the IFMs, considering its quick examination procedure, relatively cheap cost and portable features, which make it a suitable tool for clinicians and physical therapy researchers [ 20 ]. Recently, there has been exponential growth in the use of USI for the analysis of muscle quality due to its applicability.…”