Reliability of ultrasound to measure morphology of the toe flexor muscles

Mechanical drivers of intrinsic foot muscle for maximum toe flexor strength in upright standing across different body size

This study aimed to evaluate maximum toe flexor strength, foot arch height, intrinsic toe flexor muscle size and foot arch stiffness among individuals with different body sizes, and to compare these variables between sitting and standing positions. Maximum toe flexor strength in sitting and standing, and intrinsic foot muscle thicknesses (flexor hallucis brevis: FHB, flexor digitorum brevis: FDB, abductor hallucis: AH and quadratus plantae: QP), were measured using a toe grip dynamometer and a B-mode ultrasound in healthy young men. FHB was thicker than AH, FDB and QP, AH was thicker than FDB and QP, and no significant difference was found between FDB and QP. Toe flexor strength was correlated with FHB and AH, and foot arch height was correlated with FHB. Toe flexor strength was greater in standing than in sitting. Stepwise multiple regression analysis identified FHB and AH as determinants of toe flexor strength in standing, and the relative muscle strength values per body weight in standing were determined by QP, foot arch index and foot arch stiffness. Overweight individuals had a decreased rate of increase in relative toe flexor strength compared to normal individuals. These results suggest that a large muscle thickness of intrinsic foot muscle a key contributor to toe flexor strength. Moreover, toe flexor muscle in upright standing could have the potential to generate force independently of intrinsic foot muscle size, but obese individuals who chronically put weight on their feet might impair the force amplification mechanism in upright standing.

A Literature Review of the Morphological Variability in the Intrinsic Muscles of the Foot: Traps Awaiting Clinicians during Ultrasound

Purpose: Like other muscular compartments of the human body, the intrinsic muscles of the foot present considerable morphological variability. The aim of this review was to present variations that can potentially cause problems during surgery but might be detected during an ultrasound examination. Materials and methods: PubMed was searched for relevant articles. The identified papers were listed, and citation tracking was performed. Results: Even though lower limb structure is well studied, the variations associated with the intrinsic muscles of the foot and their related ultrasound examination are not. Conclusions: The muscles and tendons of the foot demonstrate similar degrees of variance as other regions of the human body; however, this subject is not as widely covered in the literature. Further ultrasound studies are needed to build awareness of morphological variability in this region, as the findings could prevent misdiagnosis.

Effects of Rehabilitative Exercise and Neuromuscular Electrical Stimulation on Muscle Morphology and Dynamic Balance in Individuals with Chronic Ankle Instability

Background and Objectives: Muscle atrophy caused by chronic ankle instability (CAI) can incur muscle weakness, altered movement patterns, and increased risk of injury. Previous studies have investigated the effects of rehabilitative exercises and neuromuscular electrical stimulation (NMES) on characteristics in CAI individuals, but few studies have examined their effects on foot and ankle muscle morphology. This study aimed to determine the effects of rehabilitative exercises and NMES on muscle morphology and dynamic balance in individuals with CAI. Materials and Methods: Participants with CAI (n = 47) were randomly divided into control (CG), rehabilitative exercise (REG), NMES (NG), and rehabilitative exercise and NMES combined (RNG) groups. The six-week intervention program consisting of rehabilitative exercises and NMES was applied to groups excluding CG. Muscle morphology and dynamic balance were evaluated using a portable wireless diagnostic ultrasound device and dynamic balance tests. For statistical analysis, an effect size with 95% confidence interval was calculated to assess mean differences according to intervention. Results: After six weeks, significant increases in morphology and dynamic balance were observed for all muscles except flexor hallucis longus (p > 0.05) in the intervention groups except for CG. However, no significant changes were observed in the CG (p > 0.05). Conclusions: These findings suggest that intervention programs may help prevent muscle atrophy and improve balance in CAI individuals.

Reliability of muscle thickness and muscle echo intensity evaluation of the posterior medial tibia in long-distance athletes using an ultrasound imaging device

OBJECTIVE

We aimed to verify the reliability of muscle thickness and luminance evaluation of the deep leg muscles using an ultrasound device.

DESIGN

Cohort study.

SETTING

Track and field, Participants: high school track and field long distance athletes (N = 10, female: 50.0%, age = 16.0 ± 2.8 years, BMI = 18.2 ± 2.3 kg/m2) PARTICIPANTS: This study included Japanese high school track and long-distance field athletes.

MAIN OUTCOME MEASURES

The thickness and echo intensity of tibialis posterior, flexor digitorum longus, and soleus muscles in the posterior medial tibia were clarified.

RESULTS

The echo intensity evaluation of the tibialis posterior muscle showed an additive error.

CONCLUSION

The study suggested that the results could be clinically applied clinically, except for the evaluation of echo intensity of the posterior tibialis muscle.

Effects of technological running shoes versus barefoot running on the intrinsic foot muscles, ankle mobility, and dynamic control: a novel cross-sectional research

BACKGROUND

Technological running shoes have become increasingly popular, leading to improvements in performance. However, their long-term effects on foot musculature and joint mobility have not been thoroughly studied.

OBJECTIVE

To compare the activation of the intrinsic foot muscles between runners wearing technological footwear and barefoot runners. Secondary objectives included assessing ankle dorsiflexion (DF) range of motion (ROM) and dynamic postural control in both groups.

METHODS

A cross-sectional study was conducted involving 22 technological footwear runners and 22 barefoot runners. Ultrasonography was used to measure the thickness of the plantar fascia (PF) and the quadratus plantae (QP), abductor digiti minimus (ADM), abductor hallucis (AH), and flexor hallucis longus (FHL) muscles. Ankle mobility and dynamic postural control were also recorded.

RESULTS

Ultrasonography measurements showed statistically significant differences for PF thickness (mean difference [MD]: -0.10 cm; 95% CI: -0.13, -0.05 cm), QP cross-sectional area (CSA) (MD: -0.45 cm2; 95% CI: -0.77, -0.12 cm2), ADM CSA (MD: -0.49 cm2; 95% CI: -0.70, -0.17 cm2), and FHL thickness (MD: 0.82 cm; 95% CI: 0.53, 1.09 cm), with all measurements being lower in the group wearing technological footwear compared to the barefoot runners. Ankle DF ROM was also significantly greater for the barefoot runners (MD: -5.1°; 95% CI: -8.6, -1.7°).

CONCLUSIONS

These findings suggest potential implications for the foot musculature and ankle mobility in runners using technological footwear.

Age-Related Reduction of Foot Intrinsic Muscle Function and the Relationship with Postural Stability in Old Adults

Introduction

The risk of falls among the elderly significantly increases, which has become a serious public health concern. Falls can not only lead to serious complications such as fractures and brain injuries but also limit their mobility function, reducing quality of life. Foot intrinsic muscles (FIMs) are an essential part of foot core stability even overall postural stability. This study aimed to investigate the effects of aging on the function of FIMs and to explore the influence of FIMs on postural control in the elderly.

Materials and Methods

56 healthy old participants (60-75 years) and 57 healthy young participants (18-29 years) joined this study. An ergoFet dynamometer was used to determine foot muscle strength (Doming, T1, T23 and T2345), and ankle muscle strength (plantarflexion and dorsiflexion). The morphology of FIMs and extrinsic foot muscle was determined using a Doppler ultrasound system, whereas the postural stability was assessed through Limits of Stability test. Independent samples t-test was used to determine the differences in strength and morphological parameters and Spearman correlation analysis was used to determine whether an association existed between muscle strength and postural stability parameters in the elderly.

Results

Compared with young adults, foot muscle strength and ankle muscle strength (Doming, T1, T23, T2345, dorsiflexion, and plantarflexion, all p <0.05) and the morphology of foot muscles (all p <0.05) were significantly reduced in the elderly. The strength of FIMs and the limit of stability (r = 0.302-0.424, all p <0.05) were significantly correlated in the elderly.

Conclusion

Compared with young adults, the weakness of strength as well as the morphological decline of the intrinsic and extrinsic foot muscles were found in the elderly. In addition, a correlation was observed between FIM's strength and postural stability in the elderly, suggesting their potential role in posture stability.

Minimalist school shoes improve intrinsic foot muscle size, strength, and arch integrity among primary school students

Minimalist walking shoes have been shown to improve foot muscle size and strength in active adults, but not in our previous study involving children, which could relate to the more structured footwear used in our study. Hence, this study examined the effects of true minimalists on intrinsic foot muscle size and strength, foot arch integrity, and physical function among primary school children. After a baseline assessment, 30 primary school students aged between 9 and 12 were given a pair of minimalist shoes (minimalist index = 92%) as their regular school shoes for two school terms, followed by a re-assessment. Seventeen of the 30 participants in the minimalist group completed the study. Compared to the control group, the minimalist group showed significantly increased cross-sectional area of abductor hallucis (p = 0.047, Cohen's d = 0.57) and flexor digitorum brevis (p = 0.037, Cohen's d = 0.80), increased strength of the hallux (p = 0.015, Cohen's d = 0.76) and lesser toes (p = 0.014, Cohen's d = 0.66), greater arch height (p = 0.020, Cohen's d = 0.52) and standing long jump distance (p = 0.001, Cohen's d = 9.79). The control group exhibited improved standing long jump performance only (p = 0.020, Cohen's d = 10.70). Minimalist shoes worn daily to school promote intrinsic foot muscle size and strength, and improve foot arch integrity among primary school students.

Reconsidering the nomenclature of the flexor digiti minimi muscles: a proposed solution to ambiguity in anatomical description

Background

The nomenclature surrounding the 'flexor digiti minimi brevis' muscle prompts deliberation concerning its accuracy and potential variations. Addressing this uncertainty entails expunging the term 'brevis' from nomenclature references to the muscle, opting instead for the term 'flexor digiti minimi.' This nomenclatural adjustment currently being advocated raises inquiries about the necessity for descriptors denoting the muscle's specific placement along the upper or lower extremities. This study was conducted with a dual objective: to illuminate this topic and consolidate existing research on this issue.

Main body of the abstract

Research encompassing the terms 'flexor digiti minimi' OR 'flexor digiti minimi brevis' was screened within this field. The inclusion criteria involved original articles, case reports, case series, relevant books, and book chapters. Excluded from this review were articles mentioning 'flexor digiti minimi' and 'digiti minimi' that were unrelated to the subject, as well as poster presentations, proceedings, conference materials, abstracts, and atlases.

Short conclusion

In summary, changing the name of the muscle enhances anatomical understanding, promotes clarity and precision in communication, facilitates research efforts, and helps prevent confusion in medical education and clinical practice. These benefits highlight the importance of revising nomenclature to reflect anatomical accuracy and improve healthcare outcomes. It also promotes consistency in studies and allows for more meaningful comparisons across studies, ultimately advancing our understanding of anatomical variations and their clinical significance. Furthermore, it allows for more effective teaching and learning experiences, enabling medical practitioners to make accurate diagnoses, develop effective treatment strategies.

Effect of Neuromuscular Electrostimulation With Blood Flow Restriction on Acute Muscle Swelling of the Abductor Hallucis

CONTEXT

Plantar intrinsic foot muscle strength training is difficult to master to a degree sufficient to elicit muscle hypertrophy in most individuals. It is possible that combining neuromuscular electrostimulation (NMES) and blood flow restriction (BFR) can elicit plantar intrinsic foot muscle hypertrophy regardless of the individual's technique. This study aimed to determine the effects of NMES training with BFR on acute muscle swelling in the abductor hallucis.

DESIGN

Randomized, controlled, single-blind trial design.

METHODS

Forty-eight participants were randomly allocated to the NMES + BFR, NMES, or Sham NMES + BFR groups. All participants received abductor hallucis NMES for 15 minutes. Participants in the NMES + BFR and Sham NMES + BFR groups received NMES with BFR. The intensity of NMES was the sensory threshold in the Sham NMES + BFR group. The cross-sectional area of the abductor hallucis was measured pretraining and posttraining using ultrasonography by a single investigator blinded to the participants' allocations.

RESULTS

After 15 minutes of training, the cross-sectional area of the abductor hallucis was significantly increased in the NMES + BFR (P < .001) and the Sham NMES + BFR (P = .004) groups. Moreover, the rate of increase was significantly higher in the NMES + BFR group than in the NMES or the Sham NMES + BFR groups (P < .001 and P = .001, respectively).

CONCLUSIONS

Since it is possible that the amount of muscle swelling immediately after training correlates with muscle hypertrophy when training is continued, the results of this study suggest that NMES training with BFR is a training method that can be expected to produce plantar intrinsic foot muscle hypertrophy. Further studies are needed to confirm the long-term effects of NMES training with BFR.

Morphological and mechanical characteristics of the intrinsic and extrinsic foot muscles under loading in individuals with flat feet

BACKGROUND

The intrinsic and extrinsic foot softtissue structures that apply force and support the medial longitudinal arch (MLA) have been implicated in the development of flat feet. However, the relationship between the changes in MLA height under increasing load and the morphological and mechanical properties of individual intrinsic and extrinsic foot soft tissue structures is not fully understood.

RESEARCH QUESTION

To examine the morphological and mechanical characteristics of the foot soft tissue structures in flat feet when subjected to loading.

METHODS

This study consisted of two studies focusing on the extrinsic foot muscles (10 normal feet/11 flat feet) and intrinsic foot muscles (14 normal feet/13 flat feet). Images of the extrinsic and intrinsic foot muscles and plantar fascia (PF) under 10%, 50%, and 90% body weight conditions were obtained using ultrasound-based shear-wave elastography.

RESULTS

The cross-sectional area (CSA) of the peroneus brevis was larger in the flat-foot group than in the normal-foot group under all loading conditions. The CSAs of the intrinsic foot muscles (abductor hallucis, flexor digitorum brevis, and quadratus plantae) and thickness of the PF in the flat-foot group decreased significantly with increasing load. As for mechanical characteristics, the stiffness of the flexor digitorum longus and abductor hallucis was higher in the flat-foot group than in the normal group under high loading conditions. In addition, flat feet with greater flexibility tended to exhibit a greater decrease in PF thickness and smaller increase in stiffness.

SIGNIFICANCE

Excessive stretching of the intrinsic foot muscles and PF occurs in flat feet, and excessive contraction of the flexor digitorum longus may counteract the excessive lowering of the foot arch. Therefore, it is necessary to promote the contraction of the intrinsic foot musculature in feet with greater flexibility of the MLA during loading.

Unique case study: Impact of single-session neuromuscular biofeedback on motor unit properties following 12 days of Achilles tendon surgical repair

We explored the first evidence of a single-session neuromuscular biofeedback effect on motor unit properties, neuromuscular activation, and the Achilles tendon (AT) length 12 days after undergoing AT surgical repair. We hypothesized that immediate neuromuscular biofeedback enhances motor unit properties and activation without causing AT lengthening. After 12 days AT surgical repair, Medial Gastrocnemius (MG) motor unit decomposition was performed on a 58-year-old male before and after a neuromuscular biofeedback intervention (surface electromyography (sEMG) and ultrasonography), involving unressited plantar flexion. The analysis included motor unit population properties, sEMG amplitude, force paradigm, and AT length. There were increased MG motor unit recruitment, peak and average firing rate, coefficient of variation, and sEMG amplitude, and decreased recruitment and derecruitment threshold in the repaired AT limb. The non-injured limb increased the motor unit recruitment, and decreased the coefficient of variation, peak and average firing rate, inter-pulse interval, derecruitment threshold and sEMG amplitude. The AT length experienced -0.4 and 0.3 cm changes in the repaired AT and non-injured limb, respectively. This single-session neuromuscular biofeedback 12 days after AT surgery shows evidence of enhanced motor unit properties and activation without signs of AT lengthening when unresisted plantar flexion is performed in the repaired AT limb.

Evaluation of the activities of the intrinsic and extrinsic muscles of the foot during toe flexion with or without interphalangeal joint flexion using ultrasound shear wave elastography

The intrinsic muscles of the foot are important to maintain the arch of the foot and to participate in sports activities. Using ultrasound shear wave elastography, we investigated the effect of different toe flexion methods on the activity of the intrinsic and extrinsic muscles of the foot. The study included 15 healthy adults who performed toe flexion under 2 conditions: with interphalangeal (IP) joint flexion and without IP joint flexion. The applied load during flexion was 500 g. Muscle stiffness was measured in the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis, quadratus plantae, flexor hallucis longus, and flexor digitorum longus muscles using ultrasound shear wave elastography. Muscle stiffness was statistically compared with IP flexion and without IP flexion (P < 0.05). The stiffness of the abductor hallucis (P < 0.0005), flexor hallucis brevis (P = 0.022), and flexor digitorum brevis muscles (P < 0.0005) was significantly greater without IP flexion than with IP flexion. In contrast, the muscle stiffness of the flexor hallucis longus (P = 0.001) and the flexor digitorum longus (P = 0.004) was significantly greater during with IP flexion than without IP flexion. This study shows that the abductor hallucis, flexor hallucis brevis, flexor digitorum brevis muscles are more active during toe flexion without IP flexion. These results suggest that the toe flexion method is important for more effective training of the intrinsic muscles of the foot.

Current evidence regarding 2D ultrasonography monitoring of intrinsic foot muscle properties: A systematic review

Background

Ultrasonography can discriminate between intrinsic and extrinsic foot muscle properties and has therefore gained considerable popularity as an indirect strength evaluation. However, an overview on the use of ultrasound for assessing intrinsic foot musculature (IFM) is currently lacking.

Research question

What is the current evidence regarding (1) 2D ultrasonography protocols and its reliability? (2) Reference values for cross-sectional area and dorso-plantar thickness evaluation in asymptomatic and symptomatic persons?

Methods

The PRISMA guidelines were used to conduct this systematic review. Eight databases (PubMed, Embase, Web of Science, Cochrane Library, Scopus, CINAHL, SPORTDiscus and EuropePMC) were searched up to November 1, 2021. Studies reporting quantitative 2D ultrasound findings of the intrinsic foot muscles with no limitation to sex, BMI, ethnicity or physical activity were included. Studies were assessed for methodological quality using the Downs and Black checklist.

Results

Fifty-three studies were retained. Protocols showed an overall good to great reliability, suggesting limits of agreement between 8 and 30% of relative muscle size with minimal detectable changes varying from 0.10 to 0.29 cm² for cross-sectional area and 0.03-0.23 cm for thickness. Reference values are proposed for both cross-sectional area and thickness measurements of the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis and quadratus plantae in asymptomatic persons. This could not be performed in the symptomatic studies due to a limited number of relevant studies addressing the symptomatic population, therefore a clinical overview is outlined. Clinically, IFM properties have been studied in ten distinct pathological conditions, predominantly pointing towards decreased muscle properties of the abductor hallucis.

Significance

We provide a clear and comprehensive overview of the literature regarding 2D ultrasonography of the IFM, making the available evidence more accessible to decision makers and researchers.

Activation Capacity of the Intrinsic Musculature of the Foot in Handball Athletes with Chronic Ankle Instability

Chronic ankle instability (CAI) is a common pathology in handball. The role of the intrinsic musculature of the foot in these players in relation to proprioception and stability has not been stablished. The objective of this study was to compare the ultrasound morphology of the heel fat pad of the foot in professional handball players to CAI in healthy players and establish relationships between CAI and physical and psychological variables. The study has been a descriptive observational case-control study in which 20 professional handball male players over 18 years of age were divided into 8 cases (CAI) and 12 controls (healthy). An ultrasound evaluation, the thickness and/or cross-sectional area at rest and the contraction measurement of the Abductor Digiti Minimi, Abductor Hallucis, Flexor Digitorum Brevis and Quadratus Plantae muscles were analyzed. Moreover, the compressibility index of the heel fat pad and the activation of the abdominal wall musculature (ultrasound), the flexion strength of the hallux and lesser toes (dynamometry), the foot functionality (Bristol Foot Score (BFS) questionnaire) and the psychological variables (self-reported questionnaires) were measured. There were no significant differences between the activation capacity values of the foot muscles of healthy and CAI athletes. Significant differences were found between groups regarding the BFS score (p = 0.007), d = 1.404), and significant correlations were also found between hallux flexion strength and lesser toes flexion strength in the total sample. Although there were no differences between the two groups, the identification of the activation pattern of these muscles in handball athletes is essential to the improvement of performance and preventing injuries such as CAI.

Validity of ultrasound imaging for intrinsic foot muscle cross-sectional area measurements demonstrated by strong agreement with MRI

PURPOSE

Intrinsic foot muscles maintain foot structural integrity and contribute to functional movement, posture and balance. Thus, assessing intrinsic foot muscle size and strength are important. Magnetic resonance imaging (MRI) has been shown to accurately image the individual muscles but is costly and time consuming. Ultrasound (US) imaging may provide an alternative that is less costly and more readily available. The purpose of this study was to investigate the validity and intratester reliability of US imaging in measuring intrinsic foot muscle size in comparison to MRI.

METHODS

US and MRI were employed to measure the intrinsic foot muscle size involving 35 participants (females = 13; males = 22). The scanned intrinsic foot muscles included the flexor hallucis brevis (FHB), abductor hallucis (ABDH), flexor digitorum brevis (FDB), quadratus plantae (QP) and abductor digiti minimi (ADM). Pearson product correlation (r), intraclass correlation coefficients (ICC), standard error of the measurement (SEm) and minimal detectable difference (MDD) were calculated.

RESULTS

High correlations were detected between the US and MRI cross-sectional area (CSA) measurements (r = .971 to 0.995). Test reliability was excellent for both MRI and US (ICC = 0.994 to 0.999). Limits of agreement between MRI and US measurements from ranged from 5.7 to 12.2% of muscle size. SEm values for US ranged from 0.026 to 0.044 cm2, while the SEm for MRI ranged from 0.018 to 0.023 cm2. MDD values for US ranged from 0.073 to 0.122 cm2, while MRI ranged from 0.045 to 0.064 cm2.

CONCLUSIONS

US appears to be a valid and reliable alternative to MRI when measuring intrinsic foot muscle CSA. While US is less costly and more readily available, the MRI results were shown to be slightly more precise.

The long-term effects of wearing moderate minimalist shoes on a child's foot strength, muscle structure and balance: A randomised controlled trial

BACKGROUND

From retrospective research, it is believed that children who predominantly spend their time shod have poorer foot strength and performance than those who are predominantly barefoot. Children's foot motion has been shown to be adversely affected by standard school shoes; however, the long-term effect of moderate minimalist shoes on foot strength, muscle structure and balance in children is unknown.

RESEARCH QUESTION

Does wearing moderate minimalist shoes, compared to stiff shoes, benefit a child's foot strength, muscle structure and performance over time?

METHODS

Seventy healthy children (9-12 yr) were randomly assigned to wear standard (control), or minimalist shoes (experimental) at school, for nine months. Cross-sectional areas (CSA) of Abductor Hallucis (AH) and Flexor Digitorum Brevis (FDB) muscles, and toe flexor strength (TFS) of hallux and lesser toes separately, were primary outcome measures. Single leg balance (SLB), Y-balance test (YBT) and standing long jump (SLJ) were secondary outcome measures. Pre- and post-intervention measurements were analysed for between group differences with ANCOVA.

RESULTS

Minimalist shoes resulted in moderate but statistically non-significant increases in muscle CSA (AH η²_p =.04, FDB η²_p =.05) and TFS (hallux η²_p =.05, lesser toes η²_p =.04). Significant moderate to large improvements in YBT in the experimental group were found in the postero-medial (P = .04, η²_p =.07) and postero-lateral (P = .01, η²_p =.10) directions. YBT (anterior, postero-medial and postero-lateral) was correlated with hallux TFS (R =.29,.27 and.33 respectively), lesser toes TFS (R =.28,.35 and.38 respectively) and SLJ (R =.30,.39 and.57 respectively). CSA of FDB was correlated with SLJ (R =.34) and SLB (R =.42).

SIGNIFICANCE

Wearing moderate minimalist shoes long-term improves balance in children. TFS is correlated with better balance and SLJ. Moderate minimalist school shoes are recommended for children.

Intra-assessor reliability and measurement error of ultrasound measures for foot muscle morphology in older adults using a tablet-based ultrasound machine

Background

To gain insight into the role of plantar intrinsic foot muscles in fall-related gait parameters in older adults, it is fundamental to assess foot muscles separately. Ultrasonography is considered a promising instrument to quantify the strength capacity of individual muscles by assessing their morphology. The main goal of this study was to investigate the intra-assessor reliability and measurement error for ultrasound measures for the morphology of selected foot muscles and the plantar fascia in older adults using a tablet-based device. The secondary aim was to compare the measurement error between older and younger adults and between two different ultrasound machines.

Methods

Ultrasound images of selected foot muscles and the plantar fascia were collected in younger and older adults by a single operator, intensively trained in scanning the foot muscles, on two occasions, 1–8 days apart, using a tablet-based and a mainframe system. The intra-assessor reliability and standard error of measurement for the cross-sectional area and/or thickness were assessed by analysis of variance. The error variance was statistically compared across age groups and machines.

Results

Eighteen physically active older adults (mean age 73.8 (SD: 4.9) years) and ten younger adults (mean age 21.9 (SD: 1.8) years) participated in the study. In older adults, the standard error of measurement ranged from 2.8 to 11.9%. The ICC ranged from 0.57 to 0.97, but was excellent in most cases. The error variance for six morphology measures was statistically smaller in younger adults, but was small in older adults as well. When different error variances were observed across machines, overall, the tablet-based device showed superior repeatability.

Conclusions

This intra-assessor reliability study showed that a tablet-based ultrasound machine can be reliably used to assess the morphology of selected foot muscles in older adults, with the exception of plantar fascia thickness. Although the measurement errors were sometimes smaller in younger adults, they seem adequate in older adults to detect group mean hypertrophy as a response to training. A tablet-based ultrasound device seems to be a reliable alternative to a mainframe system. This advocates its use when foot muscle morphology in older adults is of interest.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13047-022-00510-1.

Comparison of foot posture and foot muscle morphology between lifesaver athletes and healthy adults

This study aimed to compare the foot muscle morphology and foot posture between healthy adults and lifesavers in sandy beach sports. The participants included 15 lifesaver athletes and 15 healthy adults. Using a non-contact three-dimensional foot measurement device, the foot length, width, and arch height of the right foot were measured while standing and sitting without back support, and the transverse arch length ratio and arch height index were subsequently calculated. Muscle cross-sectional area was measured using an ultrasound imaging device. Muscle cross-sectional areas, arch height, foot width, arch height index, and transverse arch length ratio were larger in the lifesaver than in the healthy adult group. Lifesavers had higher arches and more developed intrinsic and extrinsic muscles than healthy adults. Performing physical activity while barefoot on sandy beaches may effectively develop the foot intrinsic and extrinsic muscles and raise the arch.

Reliability of musculoskeletal ultrasonography for peri-ankle muscles in subjects with unilateral chronic ankle instability

BACKGROUND

Ankle sprain is a common problem among active people and athletes. It causes reduces their activity of daily living and quality of life. Because of the impaired muscle strength and neuromuscular and postural control, it seems that the morphological criteria of peri-ankle muscles are changed.

OBJECTIVE

This study aimed to develop a reliable method for measuring tibialis anterior (TA) and peroneus longus (PL) muscles in the injured and intact side of lower limbs in people with unilateral chronic ankle instability (CAI).

STUDY DESIGN

Cross-sectional study.

METHOD

This study was intra-tester reliability by ultrasound imaging to measure ultrasonography characteristics contains thickness, width, fiber length, pennation angle, and cross-sectional area (CSA) of TA, and PL in both limbs of 25 subjects at three separate times. Intra-class correlation coefficients (ICC), limits of agreement (LOA), standard error of measurement (SEM), and minimal detectable change (MDC) were calculated to analyzed relative and absolute intra-tester reliability, respectively.

RESULTS

The present study showed good to excellent relative reliability for both injured and intact sides (ICC 0.88-0.98), less proportional measurement error (β coefficient of LOA≈ 0), and suitable absolute reliability.

CONCLUSION

Musculoskeletal ultrasonography is a reliable method for the measurement of peri-ankle muscle morphology such as thickness, width, CSA, fiber length, and pennation angle.

Ultrasonic evaluation of muscle functional recovery following free functioning gracilis transfer, a preliminary study

BACKGROUND

Ultrasonic measurement has not been utilized to assess the functional recovery of transplanted muscle. This study aimed to investigate the feasibility of using B-ultrasound measurement to assess muscle recovery following free functioning gracilis transfer.

METHODS

From January 2009 to January 2014, 35 patients receiving free functioning gracilis transfer to treat total brachial plexus injury were enrolled. B-ultrasound was adopted to determine the cross-sectional area (CSA) of transplanted gracilis muscle at rest and contraction state. The ratio of pre- to post-transplant CSA value at rest state was defined as muscle bulk ratio (MBR). The ratio of CSA value at contraction state to rest state was defined as contraction ratio (CR).

RESULTS

Patients with muscle strength M ≥ 4 had significantly higher CR1 (post-transplant), CR2 (pre-transplant), and range of motion (ROM, joint mobility) than those with muscle strength M < 4. The CR1 > CR2 group had significantly higher CR1, muscle strength, and ROM than the CR1 ≤ CR2 group. The MBR > 1 group had significantly higher muscle strength than the MBR ≤ 1 group. CR1 value was highly correlated with muscle strength and with ROM. CR2 value was moderately correlated with muscle strength and ROM. Multivariate linear regression analysis showed that a higher CR1/CR2 value was associated with a higher muscle strength and joint mobility. The CR1 > CR2 group had better muscle strength and ROM than the CR1 ≤ CR2 groups.

CONCLUSION

B-ultrasound measurement can quantitatively reflect muscle strength following gracilis transfer, and CR value could be a potential indicator for functional recovery of the transplanted gracilis muscle.

LEVEL OF EVIDENCE

Prognostic studies, Level II.

Ultrasound Imaging Is Reliable for Tibialis Posterior Size Measurements

OBJECTIVES

The tibialis posterior (TP) is a vital muscle for controlling the medial longitudinal arch of the foot during weight-bearing activities. Dysfunction of this muscle is associated with a variety of pathologic conditions; thus, it is important to reliably assess its morphologic characteristics. Ultrasound (US) has been used to assess characteristics of TP tendons but not the muscle cross-sectional area (CSA). The purpose of this study was to establish a reliable US technique to measure the TP CSA and thickness.

METHODS

Twenty-three healthy volunteers participated. We evaluated the CSA and thickness at 4 measurement locations (anterior and posterior views at both 30% and 50% of the shank length).

RESULTS

The participants included 12 female and 11 male volunteers (mean age ± SD, 31.23 ± 14.93 years). Excellent reliability was seen for the CSA and thickness at all locations (intraclass correlation coefficients, 0.988-0.998). Limits of agreement (LoA) and standard errors of the measurement (SEMs) were slightly lower at the 30% locations (LoA at 30%, 4.6-9.2; LoA at 50%, 6.4-9.7; SEM at 30%, 0.03-0.05; SEM at 50%, 0.04-0.07). Strong correlations were seen between anterior and posterior measurements of the CSA (30%, r = 0.99; P < .0001; 50%, r = 0.94; P < .0001) and thickness (30%, r = 0.98; P < .0001; 50%, r = 0.95; P = .0001).

CONCLUSIONS

Based on these results, the TP can be measured accurately with US at any of the tested locations. Due to the ease of collection and the quality of the data, we recommend the anterior view at 30% of the shank length to measure the CSA. The ability to assess muscle size of the TP will aid in a variety of medical and research applications.

The effect of a 12-week custom foot orthotic intervention on muscle size and muscle activity of the intrinsic foot muscle of young adults during gait termination

BACKGROUND

The tissue stress theory is commonly used to prescribe foot orthoses, however the mechanisms of foot orthoses are not understood well. The effect foot orthotics have on the plantar intrinsic muscles remains unclear. The study was designed to assess changes in muscle size and activity of the intrinsic muscles of individuals with pes planus after wearing custom-made foot orthotics for 12-weeks.

METHODS

Eighteen young adults with pes planus were allocated by stratified sampling into the orthotic group (n = 9) or control group (n = 9). Ultrasonography measured the cross-sectional area of the flexor digitorum brevis, abductor digiti minimi, and abductor hallucis at baseline, 6 and 12-weeks. Subsequently, participants completed an unexpected gait termination protocol (12 of 50 trials unexpected) and average electromyography magnitude was recorded.

FINDINGS

After 12-weeks the orthotic group cross-sectional area significantly decreased by 9.6% (P < .001) for the flexor digitorum brevis, 17.1% for abductor digiti minimi (P < .001) and 17.4% for abductor hallucis (P < .001). There were no significant differences of muscle activity magnitude for the intrinsic muscles.

INTERPRETATION

The short-term use of custom-made foot orthoses created a decrease in muscle size of the flexor digitorium brevis, abductor digiti minimi and abductor hallucis plantar intrinsic muscles but had no effect on muscle activity. Clinically, these results help to understand the adaptations that are created when foot orthoses are supporting a pes planus foot structure when reducing plantar pressures. These findings may help enhance the prescription of foot orthoses by adding a strength program to prevent disuse atrophy of these muscles.

Use of Cine Loops and Structural Landmarks in Ultrasound Image Processing Improves Reliability and Reduces Error in the Assessment of Foot and Leg Muscles

OBJECTIVES

Foot and leg muscle strength and size are crucial to proper function. It is important to assess these characteristics reliably. Our primary objective was to compare the measurement of still images to cine loops. The secondary purpose was to determine interoperator and intraoperator reliability between operators of different experience levels using video clips and internal and external landmarks.

METHODS

Twelve healthy volunteers participated in our study. Internal (navicular tuberosity) and external (lateral leg length at 30% and 50% from the knee joint line) landmarks were used. Two operators each captured and later measured still and cine loop images of selected foot and leg muscles.

RESULTS

The 12 participants included 8 male and 4 female volunteers (mean age ± SD, 23.5 ± 1.9 years). Good to excellent intraoperator and interoperator reliability was seen (intraclass correlation coefficient range of 0.946-0.998). The use of cine loops improved the intraclass correlation coefficients for both intraoperator and interoperator reliability (0.5%-4% increases). The use of cine loops decreased the intraoperator standard error of the measurement and limits of agreement of the novice operator (decreases of 45%-73% and 24%-51%, respectively), and these became comparable to those of experienced operators using still images. The interoperator standard errors of the measurement dropped by 42% to 53%, whereas the limits of agreement dropped by 27% to 40%. No substantial changes were noted in the tibialis anterior across reliability metrics.

CONCLUSIONS

Improved protocols that take advantage of using internal bony landmarks and cine loops during both the image-gathering and measurement processes improve the reliability of research examining muscle size changes in the lower leg or foot associated with muscle changes due to exercise, injury, disuse, or disease.

Foot exercise plus education versus wait and see for the treatment of plantar heel pain (FEET trial): a protocol for a feasibility study

Background

Plantar heel pain (PHP) is present in a wide range of individuals and creates significant burden to quality of life and participation in physical activity. The high recurrence rates and persistence of PHP suggests current management options may not address all potentially modifiable factors associated with the condition. Reports of intrinsic foot muscle (IFM) atrophy in individuals with PHP, together with biomechanical evidence of their important contribution to optimal foot function, suggests that an intervention focused on IFM training may be beneficial in managing PHP. We will test the feasibility of a prospective, assessor-blinded, parallel-group, randomised clinical trial that compares foot exercise plus education to brief advice in individuals with PHP.

Methods

Twenty participants with PHP will be randomly allocated to one of two groups for a 12-week intervention period: (i) foot exercise plus education, or (ii) brief advice. The foot exercise plus education group will attend eight sessions with a physiotherapist and receive detailed education on self-management strategies as well as a progressive exercise program for the IFMs. The brief advice group will attend one session with a physiotherapist and receive brief information about self-management strategies and reassurance. Outcome measures will be obtained at baseline and the primary end-point of 12 weeks. Primary outcomes will be the feasibility of conducting a full-scale randomised clinical trial (RCT), and the credibility and acceptability of the foot exercise plus education intervention. Secondary outcomes will explore treatment effects, which will consist of pain, physical function, physical activity level, pain self-efficacy, perceived treatment effect, magnetic resonance and ultrasound image measurement of IFM morphology, ultrasound imaging measurement of plantar fascia thickness, IFM motor performance, foot posture, foot mobility, ankle dorsiflexion range of motion, toe flexor and plantar flexor strength/endurance.

Discussion

To reduce the burden of PHP on individuals and society, there is a need to establish effective treatments that are feasible and accepted by patients and health professionals. This trial will be the first to evaluate the feasibility of conducting a full-scale RCT, as well as the credibility, acceptability, and treatment effects, of education and foot exercise for PHP. The findings of this study will inform the development of a full-scale RCT.

Trial registration

The trial protocol was prospectively registered with the Australia and New Zealand Clinical Trial Registry (ACTRN12619000987167) on 11th July 2019.

Navicular drop is negatively associated with flexor hallucis brevis thickness in community-dwelling older adults

BACKGROUND

Flatfoot is characterized as a lower longitudinal arch and is a common foot deformity in older adults. Foot intrinsic muscle dysfunction has been considered as one of the factors for a lower medial longitudinal arch. The objective of this study was to investigate the association of the navicular drop with the thickness of foot intrinsic muscles in older adults.

RESEARCH QUESTION

Which intrinsic muscle contributes most to support the medial longitudinal arch in older adults?

METHODS

We studied 88 community-dwelling older adults (mean age 74.2 ± 6.2 years). We measured the navicular height, the calcaneus inclination, and hallux valgus angle on the right foot in the sitting and standing positions using a 3D foot scanner. Then, we calculated the navicular drop and changes in the calcaneus inclination from the sitting to the standing position. The muscle thickness of the flexor hallucis brevis (FHB), flexor digitorum brevis (FDB), and abductor hallucis (AbH) was measured on the right foot using Bmode ultrasonography.

RESULTS

Multiple regression analysis demonstrated that FHB thickness was significantly associated with navicular height in the standing positions (β = 8.568, P = 0.016) as well as navicular drop (β = -9.495, P = 0.037) after adjusting for age, sex, height, weight, and hallux valgus angle. There was no association with FDB or AbH. The thickness of any intrinsic muscle was not associated with the calcaneus inclination or changes in the calcaneus inclination.

SIGNIFICANCE

Our data suggest that FHB plays an important role in preventing navicular drop and that intrinsic muscles likely do not contribute to the rearfoot angle in older adults.

Does Function Determine the Structure? Changes in Flexor Hallucis Longus Muscle and the Associated Performance Related to Dance Modality: A Cross-Sectional Study

Background and Objectives: Flexor hallucis longus pathology is one of the most common conditions of the ankle and foot in dancers, due to the high demand of dance movements performed in an extreme plantar flexion and dorsiflexion range of motion. The objectives of this study were to determine the bilateral differences between the thickness and cross-sectional area of the flexor hallucis longus muscle in dancers, to establish possible differences between dance modalities, and to analyze whether there is a correlation between ultrasonographic parameters or performance variables and the dance modality. Material and Methods: A sample of 50 (29 classical and 21 contemporary) full-time pre-professional female dancers were included in the study. The thickness and cross-sectional area of the flexor hallucis longus muscle were evaluated for both limbs using ultrasound imaging. The range of movement of the first metatarsophalangeal joint was measured using functional extension with maximal ankle plantarflexion, balance was measured in a unilateral stance with the heel raised, endurance was evaluated through a modified heel rise fatigue test, and a counter movement jump to assess the vertical jump performance was measured bilaterally. Results: There were no significant differences recorded between the dominant and non-dominant limbs for each variable, within both groups. Contemporary dancers showed a greater thickness and cross-sectional area of the flexor hallucis longus muscle than classical dancers. However, classical dancers showed an increase of balance, endurance, range of movement of the first metatarsophalangeal joint, and counter movement jump with respect to contemporary dancers. Conclusion: Bilateral symmetry was identified in all variables for both groups. The size and performance of the flexor hallucis longus muscle may be influenced by the specific nature of dance modality.

Comparison of foot kinematics and the morphology of intrinsic musculature of the foot using a foot-type classification based on function

[Purpose] The purpose of this study was to investigate a correlation between the morphology of the intrinsic musculature of the foot and foot kinematics during gait using a foot type classification based on the windlass function. [Participants and Methods] We examined 67 feet of 35 healthy participants in this study. We collected three-dimensional foot kinematic data during gait from the Oxford Foot Model and assessed the morphology of the flexor digitorum brevis, abductor hallucis, adductor halluces (oblique head), and abductor digiti minimi muscles using B-mode ultrasound. Using the Foot Posture Index (six-item version), we divided static foot postures into two groups: normal arch and flatfoot. Subsequently, we compared foot kinematics and the morphology of the intrinsic musculature among the four groups using the analysis of variance with the Bonferroni test. [Results] Foot kinematics of the flatfoot-adduction type during gait significantly differed from that of the normal arch-abduction type. The abductor digiti minimi of the flatfoot-adduction type was significantly thinner than that of the normal arch-abduction type. [Conclusion] There may be some variations in flatfoot, and the flatfoot-abduction type might not be a risk factor for overuse injuries.

Ultrasound imaging features of the Achilles tendon in dancers. Is there a correlation between the imaging and clinical findings? A cross-sectional study

OBJECTIVES

To analyze the prevalence of tendon pathology and performance associated in pre-professional classic dancers with no history of Achilles tendon (AT) pain.

DESIGN

A cross-sectional study was conducted.

PARTICIPANTS

Twenty-nine classic ballet dancers without AT pain (58 tendons) were recruited. The tendons were classified (normal, abnormal) using ultrasound imaging (USI). Cross-sectional area (CSA) and thickness of flexor hallucis longus (FHL) muscle were measured using USI. Range of movement (ROM) of the first metatarsophalangeal join, balance test, endurance test and vertical jump were measured (bilaterally) as performance variables.

RESULTS

More than a half (62%) of the participants had at least one abnormal tendon, with 45% of the dancers in the abnormal group having bilateral abnormalities. Dancers with AT pathology had significantly more years of dancing and number of weekly pointe hours than those with no pathology on US imaging. No significant differences between the groups were identified for the rest of the variables. Dancing years were moderately correlated with AT thickness.

CONCLUSIONS

Asymptomatic classic dancers had a high incidence of tendon pathology. Increased dancing years was associated with pathology in the AT. Nevertheless, these abnormalities may not affect dance performance.

Direct muscle electrical stimulation as a method for the in vivo assessment of force production in m. abductor hallucis

In vivo assessment of the force-generating capacity of m. abductor hallucis (AbH) is problematic due to its combined abduction-flexion action and the inability of some individuals to voluntarily activate the muscle. This study investigated direct muscle electrical stimulation as a method to assess isometric force production in AbH about the 1st metatarsal phalangeal joint (1MPJ) at different muscle-tendon lengths, with the aim of identifying an optimal angle for force production. A 7 s stimulation train was delivered at 20 Hz pulse frequency and sub-maximal (150% motor threshold) intensity to the AbH of the left foot in 16 participants whilst seated, and with the Hallux suspended from a force transducer in 0°,5°,10°,15° and 20° 1MPJ dorsal flexion. Reflective markers positioned on the foot and force transducer were tracked with 5 optical cameras to continuously record the force profile and calculate the external 1MPJ joint flexion moment at each joint configuration. A parabolic relationship was found between AbH force production and 1MPJ configuration. The highest 1MPJ joint moments induced by electrical stimulation were found between 10° and 15° of Hallux dorsal flexion. However, the joint angle (p < 0.001; η² = 0.86) changed significantly across all but one 1MPJ configurations tested during the stimulation-evoked contraction, resulting in a significant change in the corresponding external moment arm (p < 0.001; η² = 0.83). Therefore, the changes in joint geometry during contraction should be accounted for to prevent an underestimation of the resulting joint moment. We conclude that direct muscle electrical stimulation combined with dynamometry offers a robust method for standardised assessment of AbH sub-maximal isometric force production.

Early-Stage Diabetic Neuropathy Reduces Foot Strength and Intrinsic but Not Extrinsic Foot Muscle Size

BACKGROUND

Tracking progression of diabetic peripheral polyneuropathy (DPN) is usually focused on sensory nerves and subjective testing methods. Recent studies have suggested that distal muscle atrophy may precede sensation loss. Methods to objectively measure distal muscle size and strength are needed to help understand how neuropathy affects muscle function.

PURPOSE

To evaluate individual intrinsic and extrinsic foot muscle sizes and functional foot strength in participants with DPN.

METHODS

Thirty individuals participated in this cross-sectional study (15 DPN and 15 matched controls). Sizes of 10 separate muscles of the lower leg and foot were measured using ultrasound imaging. Functional foot strength was also quantified using custom great toe and lateral toe flexion tests along with a doming test. Muscle size and strength metrics were compared between groups using ANOVAs and paired t-tests (α = 0.05). Correlations between strength and relevant muscle sizes were also evaluated.

RESULTS

The sizes of all four intrinsic foot muscles were smaller in individuals with DPN (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (p ≤ 0.03), while only one (toe extensor) of the six extrinsic muscles was smaller (r ≤ 0.80) with several corresponding intrinsic muscle sizes. The doming strength test did not show any difference between groups and was moderately correlated with one muscle size (r ≤ 0.80) with several corresponding intrinsic muscle sizes. The doming strength test did not show any difference between groups and was moderately correlated with one muscle size (.

CONCLUSION

Diabetic peripheral polyneuropathy affects intrinsic muscles before extrinsics. Ultrasound imaging of individual muscles and functional toe flexion tests can be used clinically to monitor DPN progression and foot function. Participants need to be trained in the doming test before a relationship can be established between this test and DPN foot function. Future studies should include muscle quality measurements to better understand characteristics of affected muscles.

Effects of a 6-week intrinsic foot muscle exercise program on the functions of intrinsic foot muscle and dynamic balance in patients with chronic ankle instability

We aimed to evaluate the effects of a 6-week intrinsic foot muscle exercise program on the activation of intrinsic foot muscle movement and dynamic balance in adults with chronic ankle stability. A total of 30 adults with chronic ankle instability were recruited. The participants were randomly assigned to a group performing intrinsic foot muscle exercises and a control group doing no exercises. We measured the activation rate and dynamic balance of the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and quadratus plantae before and after the intervention. We found that the activation rate and dynamic balance significantly increased in all intrinsic foot muscles in the experimental group. These results suggest that intrinsic foot muscle exercise for patients with chronic ankle stability is an effective treatment for improving the functions and balance ability of the intrinsic foot muscles.

Morphological and mechanical properties of plantar fascia and intrinsic foot muscles in individuals with and without flat foot

PURPOSE

Many musculoskeletal disorders are associated with over-pronated foot and decreased medial longitudinal arch (MLA) height. Foot intrinsic muscles and plantar fascia (PF) are the primary structures that support MLA. An important reason for the over-pronated foot and the reduction in the MLA height may be the morphological characteristics of the foot intrinsic muscles and PF as well as changes in their mechanical properties. The aim of the present study is to investigate the morphologic structure and mechanical properties of PF, flexor hallucis brevis (FHB), flexor digitorum brevis (FDB), and abductor hallucis (AbH) muscles in individuals with flat foot and to compare the results with those of healthy individuals.

METHODS

The study included 80 participants, 40 with flat foot and 40 with normal foot posture. The foot posture of the participants was assessed using the Foot Posture Index. PF, FHB, FDB, and AbH thickness and stiffness were measured with an ultrasonography device using a linear ultrasonography probe.

RESULTS

Individuals with flat foot had higher AbH thickness compared to individuals with normal foot posture ( p < 0.001), whereas both groups were similar in terms of PF ( p = 0.188), FHB ( p = 0.627), and FDB ( p = 0.212) thickness. Stiffness values of the assessed tissues were similar in both groups ( p > 0.05).

CONCLUSION

AbH thickness was higher in individuals with flat foot; however, PF, FHB, and FDB thickness were similar in both groups. In addition, our results suggest that foot posture is not related to the stiffness of the assessed tissues.

Intra- and Interobserver Reliability of Size Measurement of Morton Neuromas on Sonography

OBJECTIVES

Sonography is often used for analysis of Morton neuromas, but the measurement reliability is unknown. The aim of this study was to determine the intra- and interobserver reliability and precision of sonographic measurement of Morton neuromas.

METHODS

Three observers with different levels of sonography experience (observer A, expert; observer B, intermediate; observer C, beginner) performed repeated measurements of the size of Morton's neuroma in 20 patients. Intraclass correlation coefficient and limit of agreement were used to evaluate reliability and measurement precision.

RESULTS

The intraclass correlation coefficient for intraobserver reliability was 0.80, 0.71, and 0.43 (limit of agreement, 20%, 18%, and 47%) in observers A, B, and C, respectively. The intraclass correlation coefficient for interobserver reliability was 0.72, 0.38, and 0.38 (limit of agreement, 25%, 36%, and 35%) between observers A/B, A/C, and B/C, respectively.

CONCLUSIONS

The intra- and interobserver reliability values for sonographic measurement of Morton neuroma size were dependent on observer experience. Experienced observers had higher reliability, while observers who were less familiar with sonography showed moderate to low reliability.

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

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 non-weight 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 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 between test 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.

The effect of running on foot muscles and bones: A systematic review

Despite the widespread evidence of running as a health-preserving exercise, little is known concerning its effect on the foot musculature and bones. While running may influence anatomical foot adaptation, it remains unclear to what extent these adaptations occur. The aim of this paper is to provide a systematic review of the studies that investigated the effects of running and the adaptations that occur in foot muscles and bones. The search was performed following the PRISMA guidelines. Relevant keywords were used for the search through PubMed/MEDLINE, Scopus and SPORTDiscus. The methodological quality of intervention studies was assessed using the Downs and Black checklist. For cross-sectional studies, the Newcastle-Ottawa scale was used. Sixteen studies were found meeting the inclusion criteria. In general, the included studies were deemed to be of moderate methodological quality. Although results of relevant literature are limited and somewhat contradictory, the outcome suggests that running may increase foot muscle volume, muscle cross-sectional area and bone density, but this seems to depend on training volume and experience. Future studies conducted in this area should aim for a standard way of reporting foot muscle/bone characteristics. Also, herein, suggestions for future research are provided.

A protocol to prospectively assess risk factors for medial tibial stress syndrome in distance runners

Background

Medial tibial stress syndrome (MTSS) is a lower leg injury with a reported incidence rate of up to 35% in active individuals. Although numerous prospective studies have tried to identify risk factors for developing MTSS, managing the syndrome remains difficult. One risk factor yet to be extensively explored in MTSS development is reduced lower leg girth. Further investigation of reduced lower leg girth is required due to the important role lower leg musculature plays in attenuating ground reaction forces during the gait cycle. Therefore, the primary aim of this study is to ascertain whether lower leg muscle morphology and function contribute to the development of MTSS. Our ultimate aim is to identify potential risk factors for MTSS that can be targeted in future studies to better manage the injury or, preferably, prevent individuals developing MTSS.

Methods

This study will be prospective in design and will recruit asymptomatic distance runners. All participants will be tested at base line and participants will have their training data longitudinally tracked over the following 12 months to assess any individuals who develop MTSS symptoms. At base line, outcome measures will include bilateral measures of lower limb anthropometry; cross sectional area (CSA) and thickness of the tibialis anterior, peroneals, flexor digitorum longus, flexor hallucis longus and thickness of soleus, medial and lateral head of gastrocnemius. Tibial bone speed of sound, ankle dorsiflexion range of motion, strength of the six previously described muscles, foot alignment and ankle plantar flexor endurance will also be assessed. Participants will also complete a treadmill running protocol where three-dimensional kinematics, plantar pressure distribution and electromyography data will be collected.

Discussion

This study will aim to identify characteristics of individuals who develop MTSS and, in turn, identify modifiable risk factors that can be targeted to prevent individuals developing this injury.

Characteristics of lower leg and foot muscle thicknesses in sprinters: Does greater foot muscles contribute to sprint performance?

The present study aimed to determine the differences in thicknesses of the lower leg and foot muscles between sprinters and non-sprinters and to examine the relationship between these muscle thicknesses and sprint performance in sprinters. Twenty-six well-trained sprinters and 26 body size-matched non-sprinters participated in this study. Total 9 muscle thicknesses of bilateral lower leg and foot muscles in participants were measured using ultrasonography. Regarding the lower leg muscles, thicknesses of the tibialis anterior, gastrocnemius medial, and gastrocnemius lateral were measured. Regarding the foot muscles, thicknesses of the flexor digitorum longus, flexor hallucis longus, peroneal longus and brevis, abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis were measured. Most muscle thicknesses were significantly larger in sprinters than in non-sprinters. The differences in mean thicknesses of both legs between the two groups were greater in the foot muscles, where it ranged from 10.2% to 17.1%, than in the lower leg muscles, where it ranged from -0.9% to 9.4%. Among foot muscles, the thickness of only the abductor hallucis was positively correlated with the personal best 100-m sprint time in sprinters (r = 0.419, P = 0.033), indicating that a greater abductor hallucis may be a negative factor for superior sprint performance. These findings suggest that although the foot muscles in addition to the lower leg muscles are more developed in sprinters than in non-sprinters, these muscle sizes may not contribute to achieve superior sprint performance.

Evaluation of the activities of the medial and lateral heads of quadratus plantae in flexion movements of the lateral four toes using ultrasound real-time tissue elastography

Quadratus plantae (QP), one of the plantar intrinsic foot muscles, assist plantarflexion of the lesser toes. QP has medial and lateral muscle heads with different anatomical structures. The two heads of this muscle may have different roles in foot function. Ultrasound real-time tissue elastography (RTE) measurements have allowed quantitative assessment of deep-layer muscle elasticity. The purpose of this study was to determine the activity of the QP in flexion movements of the lateral four toes using RTE. Thirteen healthy subjects performed maximal voluntary contractions using a hand-held dynamometer with external belt fixation for each toe flexion movement. The elasticity of the muscles were measured using RTE during rest and flexion of each toe. The strain ratio of the muscle to that in an acoustic coupler was calculated as an index of muscle elasticity. Higher strain ratio values imply lower elasticity. The strain ratio of the medial head of QP for second toe flexion (0.10±0.11) was significantly stiffer than at rest (0.34±0.33). The strain ratios of the lateral head of QP for flexion of the second (0.32±0.19), third (0.41±0.37), fourth (0.33±0.26), and fifth (0.45±0.39) toes were significantly stiffer than at rest (1.02±0.68). These results suggest that the medial head of QP has a role in assisting second-toe flexion, and the lateral head has a role in assisting flexion of all four lateral toes.

Reliability and correlates of cross-sectional area of abductor hallucis and the medial belly of the flexor hallucis brevis measured by ultrasound

Background

Weakness of the intrinsic foot muscles is thought to produce deformity, disability and pain. Assessing intrinsic foot muscles in isolation is a challenge; however ultrasound might provide a solution. The aims of this study were to assess the reproducibility of assessing the size of abductor halluces (AbH) and the medial belly of flexor hallucis brevis (FHBM) muscles, and identify their relationship with toe strength, foot morphology and balance.

Methods

Twenty one participants aged 26–64 years were measured on two occasions for muscle cross-sectional area using a Siemens Acuson X300 Ultrasound System with 5-13 MHz linear array transducer. Great toe flexor strength was measured by pedobarography, the paper grip test and hand-held dynamometry. Foot morphology was assessed by foot length, truncated foot length, Foot Posture Index (FPI) and dorsal arch height. Balance was measured by the maximal step test. Intra-class correlation coefficients (ICC_3,1) were used to evaluate intra-rater reliability. Pearson’s correlation coefficients were performed to assess associations between muscle size and strength, morphology and balance measures. To account for the influence of physical body size, partial correlations were also performed controlling for truncated foot length.

Results

Intra-rater reliability was excellent for AbH (ICC_3,1 = 0.97) and FHBM (ICC_3,1 = 0.96). Significant associations were found between cross-sectional area of AbH and great toe flexion force measured standing by pedobarography (r = .623, p = .003),), arch height measured sitting (r = .597, p = .004) and standing (r = .590, p = .005), foot length (r = .582, p = 006), truncated foot length (r = .580, p = .006), balance (r = .443, p = .044), weight (r = .662, p = .001), height (r = .559, p = .008), and BMI (r = .502, p = .020). Significant associations were found between cross-sectional area of FHBM and FPI (r = .544, p = .011), truncated foot length (r = .483, p = .027) and foot length (r = .451, p = .040). Significant partial associations were found between AbH and great toe flexion force in standing by pedobarography (r = .562, p = .012) and FHBM and the FPI (r = .631, p = .003).

Conclusions

Measuring the cross-sectional area of AbH and FHBM with ultrasound is reproducible. Measures of strength, morphology and balance appear to relate more to the size of AbH than FHBM. After controlling for physical body size, cross-sectional area of AbH remained a significant correlate of great toe flexor strength and might be a useful biomarker to measure early therapeutic response to exercise.

Relationship between transverse arch height and foot muscles evaluated by ultrasound imaging device

[Purpose] Few studies on the transverse arch (TA) in the forefoot have been conducted. The forefoot is where pains occur most frequently and is related to walking and balance; hence, paying attention to TA is vital. However, the relationship between TA and foot muscles has not been investigated. Therefore, this study aims to investigate muscles related to TA. [Subjects and Methods] Nineteen healthy young males were included. Measurements of their feet, excluding one foot with recent foot pain (n=37), were obtained. The height of TA (TAH) was measured in two ways: during 10% and 90% loading of body weight. The cross-sectional area and thickness of five muscles were measured: flexor digitorum longus, peroneus longus and brevis, flexor hallucis brevis, flexor digitorum brevis (FDB) and abductor hallucis (ABH). All measurements were performed with an ultrasound device. [Results] FDB and ABH were correlated with TAH during 10% and 90% loading after removing the effect of body mass index and age. The greater FDB and ABH, the higher TAH. [Conclusion] As FDB becomes larger, the second, third and fourth metatarsal heads are raised more. Furthermore, the height of the first metatarsal head is lowered by a larger ABH. These mechanisms may increase TAH.

Morphology of the Toe Flexor Muscles in Older Adults With Toe Deformities

OBJECTIVE

It has been suggested that atrophied or weak toe flexor muscles are associated with the formation of toe deformities, but there is little evidence to support this theory. This study aimed to determine whether the size of the toe flexor muscles differed in older adults with and without toe deformities.

METHODS

Forty-four older adults (>60 years) were recruited for the study. Each participant had their feet assessed for the presence of hallux valgus or lesser toe deformities. Intrinsic and extrinsic toe flexor muscles were imaged with an ultrasound system using a standardized protocol. Assessor-blinded measurements of muscle thickness and cross-sectional area were taken using Image J software.

RESULTS

Participants with lesser toe deformities (n = 20) were found to have significantly smaller quadratus plantae (P = 0.003), flexor digitorum brevis (P = 0.013), abductor hallucis (P = 0.004), and flexor hallucis brevis (P = 0.005) muscles than the participants without any toe deformities (n = 19). Female participants with hallux valgus (n = 10) were found to have significantly smaller abductor hallucis (P = 0.048) and flexor hallucis brevis (P = 0.013) muscles than the female participants without any toe deformities (n = 10; P < 0.05).

CONCLUSION

This is the first study to use ultrasound to investigate the size of the toe flexor muscles in older adults with hallux valgus and lesser toe deformities compared to otherwise healthy older adults. The sizes of the abductor hallucis and flexor hallucis brevis muscles were decreased in participants with hallux valgus, whereas the quadratus plantae, flexor digitorum brevis, abductor hallucis, and flexor hallucis brevis muscles were smaller in the participants with lesser toe deformities.

Contributions of foot muscles and plantar fascia morphology to foot posture

BACKGROUND

The plantar foot muscles and plantar fascia differ between different foot postures. However, how each individual plantar structure contribute to foot posture has not been explored. The purpose of this study was to investigate the associations between static foot posture and morphology of plantar foot muscles and plantar fascia and thus the contributions of these structures to static foot posture.

METHODS

A total of 111 participants were recruited, 43 were classified as having pes planus and 68 as having normal foot posture using Foot Posture Index assessment tool. Images from the flexor digitorum longus (FDL), flexor hallucis longus (FHL), peroneus longus and brevis (PER), flexor hallucis brevis (FHB), flexor digitorum brevis (FDB) and abductor hallucis (AbH) muscles, and the calcaneal (PF1), middle (PF2) and metatarsal (PF3) regions of the plantar fascia were obtained using a Venue 40 ultrasound system with a 5-13 MHz transducer.

RESULTS

In order of decreasing contribution, PF3 > FHB > FHL > PER > FDB were all associated with FPI and able to explain 69% of the change in FPI scores. PF3 was the highest contributor explaining 52% of increases in FPI score. Decreased thickness was associated with increased FPI score. Smaller cross sectional area (CSA) in FHB and PER muscles explained 20% and 8% of increase in FPI score. Larger CSA of FDB and FHL muscles explained 4% and 14% increase in FPI score respectively.

CONCLUSION

The medial plantar structures and the plantar fascia appear to be the major contributors to static foot posture. Elucidating the individual contribution of multiple muscles of the foot could provide insight about their role in the foot posture.

Can breast characteristics predict upper torso musculoskeletal pain?

BACKGROUND

Several studies have associated a large breast size with an increased prevalence and severity of musculoskeletal pain, particularly pain in the upper torso. Despite this evidence, no research has explored whether breast size or related characteristics are risk factors for upper torso musculoskeletal pain.

METHODS

A backward multiple regression analysis was performed to identify whether characteristics of the breasts and upper torso, as well as physical factors known to be associated with musculoskeletal pain, could predict musculoskeletal pain among a cohort of 378 Australian women aged 18 years and over who had a wide range of breast sizes.

FINDINGS

The model identified that breast volume, age and nipple-to-nipple distance predicted 23% of the variance in upper torso musculoskeletal pain reported by the participants.

INTERPRETATION

Women with a larger breast volume, lower age and a greater nipple-to-nipple distance were predicted to report a higher upper torso musculoskeletal pain score.

Foot strength and stiffness are related to footwear use in a comparison of minimally- vs. conventionally-shod populations

The longitudinal arch (LA) helps stiffen the foot during walking, but many people in developed countries suffer from flat foot, a condition characterized by reduced LA stiffness that can impair gait. Studies have found this condition is rare in people who are habitually barefoot or wear minimal shoes compared to people who wear conventional modern shoes, but the basis for this difference remains unknown. Here we test the hypothesis that the use of shoes with features that restrict foot motion (e.g. arch supports, toe boxes) is associated with weaker foot muscles and reduced foot stiffness. We collected data from minimally-shod men from northwestern Mexico and men from urban/suburban areas in the United States who wear ‘conventional’ shoes. We measured dynamic LA stiffness during walking using kinematic and kinetic data, and the cross-sectional areas of three intrinsic foot muscles using ultrasound. Compared to conventionally-shod individuals, minimally-shod individuals had higher and stiffer LAs, and larger abductor hallucis and abductor digiti minimi muscles. Additionally, abductor hallucis size was positively associated with LA stiffness during walking. Our results suggest that use of conventional modern shoes is associated with weaker intrinsic foot muscles that may predispose individuals to reduced foot stiffness and potentially flat foot.

Morphological characteristics and variations of the human quadratus plantae muscle

The quadratus plantae (QP) is a highly variable structure. A number of partly inexact descriptions of this entity have been provided in textbooks of anatomy. Although several authors have examined the QP, its exact site of origin and type of insertion have hitherto not been specified. The aim of this study has been to provide detailed qualitative and quantitative data about the number of heads, points of origin, and type of insertion of the QP. The QP in both feet of 50 formalin-fixed specimens of body donors (25 men and women) were analyzed by gross anatomical dissection. It was composed of one (34%), two (57%) or three heads (9%). The latter condition was observed only in men. The lateral head was absent in 31 feet, and the medial head only in one right foot of a man. The medial head arose, amongst others, in 100% of the examined cases from the medial calcaneal surface, in 93% from the long plantar ligament and in 80% from the plantar calcaneocuboid ligament. The lateral head arose, amongst others, from the long plantar ligament in 90%, and from the lateral process of the calcaneal tuberosity in 64% of the examined feet. The type of insertion was always a mixture of at least two of three types; i.e. muscular (84%), tendinous (89%) and aponeurotic (45%). As additional findings, the flexor digitorum accessorius longus (FDAL) and the peroneocalcaneus internus (PCI) were observed in 12% of all individuals and in 20% of men. The present investigation revealed that the QP may be classified according to the number of heads, but no classification can be given for its points of origin or type of insertion. The present data are mandatory for anatomical and surgical practice and will hopefully lead to further imaging and biomechanical studies.