Reliability of ultrasound measures of intrinsic foot motor function
Creators: name: Fraser, John J.
name: Hertel, Jay
Publisher: name: F1000Research
Year: 2017

description: Purpose/Hypothesis: The intrinsic foot muscles (IFM) play an important role in the shaping of the foot,<sup>1,2</sup> force attenuation,<sup>1,3</sup> and force transmission<sup>1,3</sup> during propulsion. Currently, clinically accessible assessment of IFM function and size has been limited to the IFM test<sup>4</sup> and resting ultrasound (US) imaging measures.<sup>5</sup> Reliability has yet to be established for innovative measures of IFM function under US imaging during dynamic activity. The purpose of this study was to establish test-retest reliability of US measures of IFM size and motor function.<br>Subjects: Data from 24 healthy, recreationally active individuals ages 18-50 with no history of ankle or foot sprain or fracture were included (12 males, 12 females; mean age 21.5±4.8 years; BMI 23.5±2.9 ).<br><br>Materials/Methods: Participants were imaged on two separate days by a physical therapist with 14-years clinical experience and 2-months experience using US imaging. Washout period between test sessions was 3-10 days. US cross section area (CSA, cm<sup>2</sup>) and thickness (cm) of the right (RT) and left (LT) abductor hallucis (AbdH), flexor digitorum brevis (FDB), and flexor hallucis brevis (FHB) were measured at rest and during active contraction, while resisted, and while performing toe spread, isolated hallux extension, and lesser toe extension exercises. Contracted measures were normalized to resting values and reported as activation ratios.  Reliability was assessed with intraclass coefficients (ICC, formula 2,<i>k</i>), with &gt;.75 interpreted as being excellent, .40-.75 as fair to good, and &lt;.40 as poor.<sup>6</sup><br><br>Results: Reliability of resting US measures of AbdH CSA (Baseline RT=2.66±.64cm<sup>2 </sup>LT=2.63±.57cm<sup>2</sup>, Final RT=2.66±.60cm<sup>2</sup> LT=2.67±.54cm<sup>2</sup>, ICC=.97-.98) and thickness (Baseline RT=1.25±.20cm LT=1.26±.19cm, Final RT=1.28±.21cm LT=1.25±.21cm, ICC=.88-.91), FDB CSA (Baseline RT=1.87±.52cm<sup>2 </sup>LT=1.81±.44cm<sup>2</sup>,Final RT=1.77±.46cm<sup>2</sup> LT=1.80±.42cm<sup>2</sup>, ICC=.93-.91) and thickness(Baseline RT=0.84±.19cm LT=0.80±.15cm, Final RT=0.81±.16cm LT=0.76±.14cm, ICC=.87-.89),  QP CSA (Baseline RT=1.47±.59cm<sup>2 </sup>LT=1.40±.51cm<sup>2</sup>, Final RT=1.47±.61cm<sup>2</sup> LT=1.47±.58cm<sup>2</sup>, ICC=.97-.98) and thickness (Baseline RT=0.91±.18cm LT=0.91±.15cm, Final RT=0.90±.17cm LT=0.94±.18cm, ICC=.90-.92), and FDB CSA (Baseline RT=3.00±.69cm<sup>2 </sup>LT=2.99±.85cm<sup>2</sup>,Final RT=2.97±.68cm<sup>2</sup> LT=2.97±.83cm<sup>2</sup>, ICC=.95-.98) and thickness (Baseline RT=1.42±.22cm LT=1.38±.18cm, Final RT=1.38±.19cm LT=1.38±.19cm, ICC=.76-.83) were excellent. During function, the AbdH and FDB had good to excellent (ICC=.61-.86) reliability for bilateral active and resisted CSA measures. Reliability of active, resisted and toe exercise CSA measures was excellent (ICC=.81-.99) and good to excellent (ICC=.66-.93) for thickness measures.<br><br>Conclusion: US measures of IFM function were found to have good to excellent reliability.<br>Clinical Relevance: These measures may have utility in patient care and clinical research and should be considered as a potential outcome measure.<br> <br>References<br><br>1.         Kelly LA, Cresswell AG, Racinais S, Whiteley R, Lichtwark G. Intrinsic foot muscles have the capacity to control deformation of the longitudinal arch. <i>J R Soc Interface R Soc</i>. 2014;11(93):20131188. doi:10.1098/rsif.2013.1188.<br>2.         Mulligan EP, Cook PG. Effect of plantar intrinsic muscle training on medial longitudinal arch morphology and dynamic function. <i>Man Ther</i>. 2013;18(5):425-430. doi:10.1016/j.math.2013.02.007.<br>3.         Zelik KE, La Scaleia V, Ivanenko YP, Lacquaniti F. Coordination of intrinsic and extrinsic foot muscles during walking. <i>Eur J Appl Physiol</i>. 2015;115(4):691-701. doi:10.1007/s00421-014-3056-x.<br>4.         Jam B. <i>Evaluation and Retraining of the Intrinsic Foot Muscles for Pain Syndromes Related to Abnormal Control of Pronation</i>. Advanced Physical Therapy Education Institute; 2006. http://goo.gl/zDGrDJ. Accessed March 13, 2015.<br>5.         Mickle KJ, Nester CJ, Crofts G, Steele JR. Reliability of ultrasound to measure morphology of the toe flexor muscles. <i>J Foot Ankle Res</i>. 2013;6(1):1–6.<br>6.         Fleiss JL. <i>Design and Analysis of Clinical Experiments</i>. John Wiley &amp; Sons; 2011.