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Background: Clinicians and researchers are beginning to pay attention to the importance of the intrinsic foot muscles (IFMs). Among IFMs, the abductor hallucis (AbH) is associated with foot disorders. However, so far no method for assessing the strength of the AbH has been established. In addition, previous studies have shown increased IFM activity in the plantarflexed position of the ankle. Therefore, this study tests the hypothesis that a correlation will be found between the cross-sectional area (CSA) of the AbH and the flexion torque and that the first metatarsophalangeal (MTP) joint would be stronger in the plantarflexed (PF) position of the ankle joint than in the neutral (N) position., Methods: Eight male and 8 female patients (16 lower limbs) were included in this study to measure the CSA of IFM and the extrinsic foot muscles of the lower leg. Furthermore, the flexion torque of the first MTP joint was measured using a handheld dynamometer at the N and PF positions of the ankle joint. Correlation analysis was performed to examine the relationship between the CSA of each muscle and the flexion torque of the first MTP joint in the N and PF positions., Results: In the N position, a correlation was found between the flexion torque of the first MTP joint and the CSA of the AbH ( r  = 0.818), flexor hallucis brevis ( r  = 0.730), and flexor hallucis longus ( r  = 0.726). In the PF position, a correlation was found between the flexion torque of the first MTP joint and the CSA of the AbH ( r  = 0.863) and flexor hallucis brevis ( r  = 0.680). ( P  < .05)., Conclusion: Overall, this study suggested that by measuring flexion torque of the first MTP joint in the PF position, AbH strength can be estimated without using any expensive equipment., Level of Evidence: Level V, mechanism-baced reasoning., Competing Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article. Disclosure forms for all authors are available online., (© The Author(s) 2024.)

There is growing evidence to support a role for the abductor hallucis (AH) in standing balance control; however, functional properties of the muscle that may provide more insight into AH's specific contribution to upright posture have yet to be characterized. This study was conducted to quantify functional neuromechanical properties of the AH and correlate the measures with standing balance variables. We quantified strength and voluntary activation during maximal voluntary isometric contractions of the great toe abductor in nine (3 females and 6 males) healthy, young participants. During electrically evoked twitch and tetanic contractions, we measured great toe abduction peak force and constructed a force-frequency curve. We also evaluated peak abduction force, contraction time (CT), half-relaxation time (HRT), rate of force development (RFD), and relaxation rate (RR) from twitch contractions evoked using doublet stimuli. Strength, VA, CT, HRT, RFD, and RR were correlated to centre of pressure standard deviation (COP SD) and velocity (COP VEL) variables of the traditional COP trace and its rambling and trembling components during single-legged stance. AH twitch properties (e.g., CT: 169.8 ± 32.3 ms; HRT: 124.1 ± 29.2 ms) and force-frequency curve were similar to other slow contractile muscles. Contractile speed related negatively with COP VEL, suggesting AH may be appropriate for slow, prolonged tasks such as ongoing postural balance control. Correlation coefficient outcomes for all variables were similar between rambling and trembling components. Our results provide further evidence for the importance of AH neuromechanical function for standing balance control, at least during a challenging single-legged posture., Competing Interests: The authors declare there are no competing interests.

Background: Assessment of neuromuscular dysfunction following a lateral ankle sprain during running typically focuses on the activities of the extrinsic foot muscles. Although the interaction between intrinsic and extrinsic foot muscles has been reported, there are no studies on the activities of intrinsic foot muscles in individuals with chronic ankle instability and ankle sprain copers., Research Question: Do copers and individuals with chronic ankle instability (CAI) have different abductor hallucis activity?, Methods: This study included 11 controls, 11 copers, and 16 CAI participants. A wireless surface electromyography system was applied to the abductor hallucis, peroneus longus, tibialis anterior, and medial gastrocnemius muscles. Running was performed on a treadmill (speed of 3.5 m/s). The stance phase is divided into four functional phases. The muscle activities during these phases were calculated using the root mean square standardized by the root mean square during static standing with a double-leg stance., Results: Abductor hallucis activity was significantly lower during most phases in the coper and control groups than in the CAI group (P < 0.05). There were no differences in the extrinsic foot muscles among the groups (P > 0.05)., Significance: Simultaneous investigations of muscle activity in the abductor hallucis and extrinsic foot muscles identified neuromuscular dysfunction after ankle sprains. Increased activity of the abductor hallucis may be associated with recurrent ankle sprains., Competing Interests: Declaration of Competing Interest The authors have no conflicts of interest to declare., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Normal alignment of the foot is important because the feet support the body's weight. The intrinsic muscles of the foot mainly maintain the alignment and movement of the foot, whereas the abductor hallucis (AbdH) aligns the first metatarsophalangeal joint and maintains the medial longitudinal arch., Objective: This study was conducted to investigate the muscle activity of the AbdH and hallux valgus (HV) angle during three different foot exercises., Methods: Participants included 15 subjects aged 20-24 years with mild HV. All subjects performed three different foot exercises in random order: short foot exercise (SF), toe spread out exercise (TSO), and TSO with a pressure bio-feedback unit (TSOP). The muscle activity of the AbdH and the HV angle were measured during each foot exercise using surface electromyography and X-ray and then compared using one-way repeated-measures analysis of variance, followed by Bonferroni adjustment., Results: AbdH muscle activity differed significantly among SF, TSO, and TSOP. AbdH muscle activity was greater in TSOP (89.60%) than in SF (19.99%) and TSO (60.96%) (p= 0.006). The HV angle was significantly smaller in TSOP (15.72∘) than in SF (18.85∘) and TSO (16.81∘) (p= 0.001)., Conclusions: TSOP can be recommended as an effective AbdH strengthening exercise in subjects with mild HV.

Purpose: Intraoperative muscle motor evoked potentials (m-MEPs) are widely used in spinal surgery with the aim of identifying a damage to spinal cord at a reversible stage. Generally, lower limb m-MEPs are recorded from abductor hallucis [AH] and the tibialis anterior [TA]. The purpose of this work is to study an unselected population by recording the m-MEPs from TA, AH and extensor digitorum brevis (EDB), with the aim of identifying the most adjustable and stable muscles responses intraoperatively., Methods: Transcranially electrically induced m-MEPs were intraoperative recorded in a total of 107 surgical procedures. m-MEPs were recorded by a needle electrode placed in the muscle from TA, AH and EDB muscles in the lower extremities., Results: Overall monitorability (i.e., at least 1 Lower Limb m-MEP recordable) was 100/107 (93.5%). In the remaining 100 surgeries in 3 cases, the only muscle that could be recorded at baseline was one AH, and in other 2 the EDB. Persistence (i.e., the recordability of m-MEP from baseline to the end of surgery) was 88.7% for TA, 89.8% for AH and 93.8% for EDB., Conclusion: In our series, EDB m-MEPs have demonstrated a recordability superior to TA and a stability similar to AH. The explanations may be different and range from changes in the excitability of the cortical motor neuron to the different sensitivity to ischemia of the spinal motor neuron. EDB can be used alternatively or can be added to TA and AH as a target muscle of the lower limb in spinal surgery., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Electrophysiological studies in nonhuman primates reported the existence of strong corticospinal output from the primary motor cortex to distal compared with proximal hindlimb muscles. The extent to which corticospinal output differs across muscles in the leg in humans remains poorly understood. Using transcranial magnetic stimulation over the leg representation of the primary motor cortex, we constructed motor evoked potential (MEP) recruitment curves to measure the resting motor threshold (RMT), maximum MEP amplitude (MEP-max), and slope in the biceps femoris, rectus femoris, tibialis anterior, soleus, and a foot muscle (i.e., abductor hallucis) in intact humans. We found that the RMT was lower and the MEP-max and slope were larger in the abductor hallucis compared with most other muscles tested. In contrast, the RMT was higher and the MEP-max and slope were lower in the biceps femoris compared to all other muscles tested. Corticospinal responses in the rectus femoris, tibialis anterior, and soleus were in between those obtained from other leg muscles, with the soleus having a higher RMT and lower MEP-max and slope than the rectus femoris and tibialis anterior. To examine the origin of increases in corticospinal excitability in the abductor hallucis, we compared short-interval intracortical inhibition (SICI) and F -waves between the abductor hallucis and tibialis anterior. SICI was similar across muscles while the F -wave amplitude was larger in the abductor hallucis compared with the tibialis anterior. These results support a nonuniform distribution of corticospinal output to leg muscles, highlighting that increases in corticospinal excitability in a foot muscle could be related to a spinal origin. NEW & NOTEWORTHY We provide evidence on how corticospinal output differs across muscles in the leg in intact humans. We found that corticospinal responses were larger in a distal intrinsic foot muscle and were smaller in the biceps femoris compared to all other muscles in the leg. Increases in corticospinal excitability to an intrinsic foot muscle could have a spinal origin.

Purpose: It was aimed to reveal whether the positions and dimensions of the extrinsic and intrinsic muscle tendons related to the hallux around the first metatarsal bone are affected by the severity of hallux valgus (HV) and whether tendon positional changes and tendon sizes affect each other., Methods: In formalin-fixed 46 feet, three HV angle subgroups (normal, mild, and moderate/severe) were defined. Width, thickness, and cross-sectional area (CSA) of tendons of the extensor hallucis longus (EHL) and brevis (EHB), abductor hallucis (AH), and flexor hallucis longus (FHL) were measured. On the clock model created in coronal plane, positional variations of each tendon were determined., Results: In the moderate/severe HV group, thickness and CSA of the EHB, width and CSA of the AH were smaller, compared to mild HV. Width and CSA of the FHL were smaller in moderate/severe HV than in the normal. Regardless of HV, the width and CSA of the FHL were greater in cases where the FHL was located more lateral, and the width of both FHL and AT were greater in cases where AH located was more plantar., Conclusion: The smaller tendon size of two intrinsic (one plantar and one dorsal) and one extrinsic muscle in the moderate/severe HV group indicates that changes in the tendons are evident in cases of high severity of HV but not in cases of mild HV. Accordingly, the changes do not appear to be due to a factor limited to only one aspect of the foot. It is recommended to consider the possible biomechanical effects of AH, FHL, and EHB tendon dimensional weakness in surgical planning in moderate/severe HV cases., (© 2022. The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature.)

Introduction: Peripheral nerve stimulation can modulate the excitability of corticospinal pathways of muscles in the upper and lower limbs. Further, the pattern of peripheral nerve stimulation (continuous vs. intermittent) may be an important factor determining the modulation of this corticospinal excitability. The pelvic floor muscles (PFM) are crucial for maintaining urinary continence in humans, and share spinal segmental innervation with the tibial nerve. We explored the idea of whether the neuromodulatory effects of tibial nerve stimulation (TibNS) could induce effects on somatic pathways to the PFM. We evaluated the effects of two patterns of stimulation (intermittent vs. continuous) on corticospinal excitability of the PFM compared to its effect on the abductor hallucis (AH) muscle (which is directly innervated by the tibial nerve). We hypothesized that intermittent TibNS would increase, while continuous stimulation would decrease, the excitability of both AH and PFM., Methods: Twenty able-bodied adults (20-33 years of age) enrolled in this study. TibNS was delivered either intermittently (1 ms pulses delivered at 30Hz with an on:off duty cycle of 600:400 ms, for 60 min), or continuously (1 ms pulses delivered at 30Hz for 36 min) just above the motor threshold of the AH. We randomized the order of the stimulation pattern and tested them on separate days. We used surface electromyography (EMG) to record motor-evoked responses (MEP) in the PFM and AH following transcranial magnetic stimulation (TMS). We generated stimulus-response (SR) curves to quantify the changes in peak-to-peak MEP amplitude relative to TMS intensity to assess changes in corticospinal excitability pre- and post-stimulation., Results and Conclusion: We found that TibNS increased corticospinal excitability only to AH, with no effects in PFM. There was no difference in responses to continuous vs. intermittent stimulation. Our results indicate a lack of effect of TibNS on descending somatic pathways to the PFM, but further investigation is required to explore other stimulation parameters and whether neuromodulatory effects may be spinal in origin., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Eginyan, Zhou, Williams and Lam.)

Background: Hallux valgus (HV), which is one of the most common musculoskeletal abnormalities of the foot, is defined as the medial deviation of the first metatarsophalangeal (MTP) joint and the lateral deviation of the great toe., Objects: This study aimed to investigate the immediate effects of a manual stretching maneuver (MSM) in subjects with HV., Methods: Twenty-five subjects with a total of 25 feet with mild HV participated in the study. The MSM, consisting of global stretching of the foot and toes, traction of the hallux, local stretching for hallux, and mobilization of the MTP joint of the hallux. The HV angle between the line of the first metatarsal bone and the proximal phalanx were measured using a goniometer. The cross-sectional area (CSA) of the AbdH was measured using ultrasonography. Zebris FDM was used to measure the static plantar pressure and the movement of the center of pressure (COP) standing on one foot. The dependent variables before and after treatment were compared using paired t-tests. The significance level was set at .05., Results: The HV angle significantly decreased from 20.25° to 16.96°. The CSA of the AbdH significantly increased from 14.00 mm 2 to 16.11 mm 2 . The peak pressure on the hallux and 1st, 2nd and 3rd metatarsals increased significantly. The contact area and total pressure on the hallux significantly increased. The sway of the COP on the length of the minor axis and velocity significantly decreased., Conclusion: This study suggests that the MSM can be effective in decreasing the HV angle in subjects with mild HV. However, further longitudinal clinical studies are required to investigate the long-term effects of the MSM in subjects with HV., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Background: The morphology of foot muscles that support the medial longitudinal arch differs between normal and pronated feet. The degree to which the difference depends on the severity of the pronated foot deformity is unclear. In the clinical setting, however, to reduce the pronated deformity, muscle-strengthening exercises are performed., Research Question: Does a relationship exist between foot muscle morphology and severity of the pronated foot deformity and foot kinematics during gait?, Methods: Using the six-item foot posture index (FPI-6), 26 study participants were assessed for their foot posture and divided into two groups of 13 participants each based on the FPI-6 score: pronated foot group (with a score of 6-9) and highly pronated foot group (with a score of 10-12). Select foot muscles were scanned with ultrasonography, and muscle thicknesses were measured. The following were the muscles of interest: abductor hallucis, flexor hallucis brevis and longus, flexor digitorum brevis and longus, and peroneus longus. Foot kinematic data during gait was collected using a three-dimensional motion capture system as a dynamic navicular drop., Results: No between-group differences were noted for muscle thickness and dynamic navicular drop. However, the abductor hallucis and flexor hallucis brevis thicknesses were correlated with the dynamic navicular drop, but not with the severity of the pronated foot deformity., Significance: In individuals with pronated foot deformity, more developed abductor hallucis and flexor hallucis brevis muscles may reduce the dynamic navicular drop that represents the degree of medial longitudinal arch deformation during the stance phase of gait., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Objective: This study examines and compares excitability characteristics of tibialis anterior (TA) and abductor hallucis (AH) transcranial motor evoked potentials (tcMEP) during anterior cervical decompression and fusion (ACDF) surgery., Methods: Electrophysiological and clinical data of 89 patients who underwent ACDF procedure were retrospectively reviewed. TcMEP data of TA and AH muscles from 178 limbs were analyzed for availability, robustness and stability during the procedure., Results: TA tcMEP was available at 83% whereas AH tcMEP was available at 99% of the monitored lower limbs at preposition baseline. Availability of both TA and AH tcMEP was demonstrated in 147/178 limbs. The baseline amplitude of AH tcMEP was significantly greater than that of TA tcMEP recorded from the same limb (744.6 ± 54.0 and 326.9 ± 33.3 µV, respectively). Simultaneous deterioration of TA and AH tcMEP data was demonstrated in 10/147 limbs. Deterioration of either TA or AH tcMEP data accompanied by unchanged tcMEP data from the other lower limb muscle was noted in 32/147 compared to 1/147 limbs, respectively. The deteriorated TA and AH tcMEP data returned to baseline before closing at incidence of 17% compared to 46%, respectively. No new lower extremity (LE) neurological deficit was presented postoperatively in any patient., Conclusions: AH tcMEP is a more reliable candidate than TA tcMEP for intraoperative LE monitoring in ACDF procedure., Significance: The excitability differentials in LE tcMEP in ACDF is a variable that need to be considered while interpreting intraoperative neurophysiological data., (© 2020 International Federation of Clinical Neurophysiology. Published by Elsevier B.V.)

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; η 2  = 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; η 2  = 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., Competing Interests: Declaration of Competing Interest No conflicts of interest are declared by the authors., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Lateralising calcaneal osteotomy for pes cavus is generally regarded to be harder to shift than a medialising calcaneal osteotomy for pes planus. The aim of our study was to determine the structures which restrain a lateral shift., Methods: Lateralising calcaneal osteotomy was performed on four soft-embalmed cadavers via a standard lateral approach and the lateral calcaneal shift was measured before and after the release of flexor retinaculum. Further exploratory dissection around the osteotomy site revealed the abductor hallucis muscle to be the main restraint to the lateral shift of the calcaneus. Subsequently, lateralising calcaneal osteotomy was performed on another four cadavers and the abductor hallucis muscle fascia as well as the plantar fascia was released. The lateral shift was measured before and after the fascia release, and compared with the results achieved following the flexor retinaculum release in the first four cadavers., Results: Lateralising calcaneal osteotomy alone resulted in an average of 4.5-mm lateral shift in the first four cadaveric specimens. Releasing the flexor retinaculum led to a further 3-mm increase of lateral shift on average. In the next four cadaveric specimens, lateralising calcaneal osteotomy alone resulted in an average of 5.5-mm lateral shift. Release of abductor hallucis muscle fascia and the plantar fascia in these four specimens increased the lateral shift by an additional 7 mm on average. Hence, release of abductor hallucis muscle fascia resulted in an extra 4-mm shift on average compared with what is achieved with flexor retinaculum release., Conclusions: Abductor hallucis muscle fascia was discovered to be one of the main structures limiting the lateral shift in lateralising calcaneal osteotomy. Release of fascia over this muscle as well as the plantar fascia should help in improving lateral shift. Further experimental and clinical research is necessary to confirm the findings of this pilot study., Competing Interests: Conflict of interestThe authors declare that they have no conflict of interest., (© Indian Orthopaedics Association 2020.)

The aim of the current study was to evaluate the effectiveness of intraoperative neuromonitoring (INM) as an adjunct in performing tarsal tunnel decompression surgery. We reviewed 38 patients who met inclusion criteria. INM was used to measure the voltage of the abductor hallucis and digiti quinti muscles both before and after decompression. Observed changes intraoperatively were acute and within minutes of the decompression performed by the surgeon. Patient outcomes were ascertained from clinical findings and classified as excellent, fair, or poor. Patient outcomes and the voltage change were measured and assessed for association, and statistically significant differences were found between outcome groups. Of the 38 patients, 29 (76%) had excellent outcomes, with a mean change in microvolts of 2088.28 ± 1172.44 (684%) (p = .0004) and 2173.24 ± 1228.39 (742%) (p = .0014) for abductor hallucis and abductor digiti quinti, respectively. The study supports INM as a useful adjunct in performing tarsal tunnel decompression., (Copyright © 2019 the American College of Foot and Ankle Surgeons. Published by Elsevier Inc. All rights reserved.)

Purpose: To evaluate the characteristics of brain-evoked muscle action potential [Br(E)-MsEP] waveforms of lower limb muscles in thoracic spine surgery., Methods: The subjects were 159 patients who underwent thoracic spine surgery with intraoperative Br(E)-MsEP monitoring from January 2009 to December 2015, using a total of 2226 muscles in the extremities. The waveform derivation rate for each lower extremity muscle was examined at baseline and intraoperatively. Data were interpreted based on the preoperative motor status., Results: The preoperative ambulatory and non-ambulatory rates were 38% (60/159, McCormick grades I and II) and 62% (99/159, grades III-V), respectively. Eleven cases (all non-ambulatory) had undetectable baseline waveforms in all muscles, and in 19 cases (12%) a baseline waveform could only be derived from the abductor hallucis (AH). The waveform derivation rate in all lower limb muscles was significantly higher in ambulatory cases (p < 0.05), and the rates for the AH were the highest in both groups (p < 0.05). Postoperative paralysis occurred in 31 cases (19%). A decrease in intraoperative amplitude of ≥ 70% from baseline occurred in 54 cases and had sensitivity of 100% and specificity of 82% for prediction of postoperative motor deficit., Conclusions: This is the first study of Br(E)-MsEP waveforms for each lower limb muscle based on preoperative ambulatory status. Detection of waveforms from distal muscles was still possible in a case with preoperative motor deficit, and the AH had an especially high derivation rate, even in cases with preoperative muscle weakness. Collectively, the results support use of Br(E)-MsEP monitoring using the AH in the lower extremities.

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., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background: The short foot (SF) exercise is a strengthening exercise for the intrinsic foot muscles that is difficult to master., Objective: To examine the effect of three different electromyographic (EMG) biofeedback methods on learning the SF exercise., Methods: Thirty-six healthy subjects were randomly allocated to the control group (CTG), EMG-controlled electrical stimulation group (ESG), visual EMG biofeedback group (VSG), and combination EMG-controlled electrical stimulation with visual EMG biofeedback group (CBG). The CTG practiced the SF exercise for 5 minutes using the conventional method. The other groups each used the EMG biofeedback method and the conventional method. The EMG activity of the abductor hallucis (ABH), the medial longitudinal arch (MLA) angle, and the foot length during the SF exercise were measured before and after 5 minutes of practice., Results: The EMG activity of the ABH in the VSG and CBG was significantly higher than that before practice. There were no intergroup differences in MLA morphology., Conclusions: These results suggest that visual EMG biofeedback is an effective method of increasing the EMG activity of the ABH during the SF exercise in a short practice time.

Introduction: This study performed motor unit number estimation (MUNE) of the abductor hallucis (AH) muscle from 16 healthy control participants on the basis of the compound muscle action potential (CMAP) scan., Methods: Muscle responses to electrical stimuli ranging from subthreshold to supramaximal intensity were recorded, and MUNE was determined from a model of the responses (MScanFit program)., Results: The average CMAP amplitude and MUNE of the AH for the right and left sides combined were 19.6 ± 0.75 mV and 127 ± 5 (mean ± SE), respectively., Discussion: Findings of the study provide useful information about the motor unit number of the AH. Muscle Nerve 58: 735-737, 2018., (© 2018 Wiley Periodicals, Inc.)

Background: Intraoperative neuromonitoring using motor evoked potentials (MEP) satisfactorily detects motor tract integrity changes during spinal surgery. However, monitoring is affected by "anesthetic fade," in which the stimulation threshold increases because the waveform amplitude decreases with the accumulation of propofol. Therefore, the purpose of this study was to clarify the effect of anesthetic fade on transcranial MEPs by investigating the time-dependent changes of amplitude during spinal deformity surgeries., Methods: We retrospectively reviewed medical records of 142 spinal deformity patients (66 patients with idiopathic scoliosis, 28 with adult spinal deformities, 19 with neuromuscular scoliosis, 17 with syndromic scoliosis, and 12 with congenital scoliosis). The average age was 28 years (range, 5 to 81 years). MEPs were recorded bilaterally from the abductor digiti minimi (ADM) and abductor hallucis (AH) muscles during spinal deformity surgeries. The Wilcoxon signed-rank test was used to investigate the time-dependent changes of amplitude after propofol infusion to evaluate anesthetic fade effects., Results: The average time to baseline from initial propofol infusion was 113 min (range, 45 to 182 min). In the ADM, the amplitude was 52% at 1 h after initial propofol infusion, 102% at 2 h, 105% at 3 h, 101% at 4 h, 86% at 5 h, and 81% at 6 h. Compared to the 2-h time point, MEP decreased significantly by 16% at 5 h (P < 0.0005) and by 21% at 6 h (P < 0.05). In the AH, the amplitude was 49% at 1 h after initial infusion of propofol, 102% at 2 h, 102% at 3 h, 92% at 4 h, 71% at 5 h, and 63% at 6 h. Compared to the 2-h time point, MEP decreased significantly by 10% at 4 h (P < 0.005), by 31% at 5 h (P < 0.0000005), and by 39% at 6 h (P < 0.05)., Conclusions: MEP amplitude significantly decreased in the upper limbs at 5 and 6 h and in the lower limbs at 4, 5, and 6 h after the initial infusion of propofol, respectively. The influence of anesthetic fade could influence false positive MEPs during long spinal surgeries.

Objective: To investigate the effectiveness of modified free medial plantar flap with preserved abductor hallucis for repairing cicatricial contracture deformity of palm., Methods: Between January 2012 and July 2017, a modified free medial plantar flap with preserved abductor hallucis was used to repair 9 cases of cicatricial contracture deformity at the palm. There were 7 males and 2 females with a median age of 23 years old (range, 15-40 years). The duration of cicatricial contracture was 4-23 years (mean, 9 years). In addition, 3 cases had combined stiffness of finger joints, 2 cases of tendon exposure, and 2 cases with exposed tendon and nerve. The range of flap was 4.5 cm×4.0 cm to 8.0 cm×6.0 cm. The vessel pedicle of the flap was 7-8 cm in length, with an average length of 7.5 cm. Grafting and repairing were performed with full-thickness skin graft from the ilioinguinal region in the donor site., Results: All flaps and skin grafts survived after operation, and all wounds healed at first intention. All 9 patients were followed up 5-22 months (mean, 10 months). The flap exhibited smooth appearance and soft texture, which was similar to that of the normal skin around. The recovery time of dermal sensation was 5-12 months (mean, 9 months). At last follow-up, the flap recovered to level S 4 in 5 cases, level S 3 in 3 cases, and level S 3 in 2 cases. The two-point discrimination was 6.0-10.0 mm (mean, 8.5 mm). According to the assessment of the upper limb function issued by the Hand Surgery Society of Chinese Medical Association, the hand function was excellent in 5 cases, good in 2 cases, and fair in 2 cases. Additionally, the abduction and flexion activities of the great toe of the donor foot were not affected, and the skin grafting area was slightly colored., Conclusion: The modified free medial plantar flap for repairing cicatricial contracture deformity of palm has such advantages as no impact on abductor hallucis, small damage of the donor area, improved survival rate of skin grafting, and the unaffected function of the donor foot.

Background: Strengthening the intrinsic foot muscles is a poorly understood and largely overlooked area. In this study, we explore the feasibility of strengthening m . abductor hallucis (AH) with a specific paradigm of neuromuscular electrical stimulation; one which is low-intensity in nature and designed to interleave physiologically-relevant low frequency stimulation with high-frequencies to enhance effective current delivery to spinal motoneurones, and enable a proportion of force produced by the target muscle to be generated from a central origin. We use standard neurophysiological measurements to evaluate the acute (~ 30 min) peripheral and central adaptations in healthy individuals., Methods: The AH in the dominant foot of nine healthy participants was stimulated with 24 × 15 s trains of square wave (1 ms), constant current (150% of motor threshold), alternating (20 Hz-100 Hz) neuromuscular electrical stimulation interspersed with 45 s rest. Prior to the intervention, peripheral variables were evoked from the AH compound muscle action potential (M wave ) and corresponding twitch force in response to supramaximal (130%) medial plantar nerve stimulation. Central variables were evoked from the motor evoked potential (MEP) in response to suprathreshold (150%) transcranial magnetic stimulation of the motor cortex corresponding to the AH pathway. Follow-up testing occurred immediately, and 30 min after the intervention. In addition, the force-time-integrals (FTI) from the 1st and 24th WPHF trains were analysed as an index of muscle fatigue. All variables except FTI (T-test) were entered for statistical analysis using a single factor repeated measures ANOVA with alpha set at 0.05., Results: FTI was significantly lower at the end of the electrical intervention compared to that evoked by the first train ( p  < 0.01). Only significant peripheral nervous system adaptations were observed, consistent with the onset of low-frequency fatigue in the muscle. In most of these variables, the effects persisted for 30 min after the intervention., Conclusions: An acute session of wide-pulse, high-frequency, low-intensity electrical stimulation delivered directly to abductor hallucis in healthy feet induces muscle fatigue via adaptations at the peripheral level of the neuromuscular system. Our findings would appear to represent the first step in muscle adaptation to training; therefore, there is potential for using WPHF for intrinsic foot muscle strengthening., Competing Interests: This study received prior approval from the local University Research Ethics Committee (UREC 1350) and all participants gave written informed consent to participate in the study, in accordance with the Declaration of Helsinki.The research consent form required participants to accept prior knowledge of how the study findings would be disseminated.The authors declare that they have no competing interests.Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Maintaining standing balance involves multisensory processing and integration to produce dynamic motor responses. Electrical vestibular stimulation (EVS) delivered over the mastoid processes can be used to explore the vestibular control of balance. The purpose of this study was to determine whether intrinsic foot muscles exhibit vestibular-evoked balance responses and to characterize the traits associated with these responses. Electromyography (EMG) of the abductor hallucis (AH), abductor digiti minimi (ADM) and medial gastrocnemius (MG) and anterior-posterior (AP) forces were sampled while quietly standing participants were subjected to a random continuous EVS signal (peak-to-peak amplitude = ±3 mA). The relationship between EVS input and motor output was characterized in both the frequency (coherence) and time (cumulant density) domains. When head orientation was rotated in yaw from left to right, the biphasic cumulant density function was inverted for all muscle (EVS-EMG) and whole-body (EVS-AP forces) balance responses. When vision was occluded, the EVS-EMG and EVS-AP forces coherence function amplitude increased at low frequencies (<2 Hz) and was accompanied by a heightened medium-latency peak amplitude for all muscles as well as the whole-body balance response (AP forces) compared to when static visual cues were present. The enhanced coherence amplitudes at lower frequencies may highlight a mechanism for the increase in postural sway from vision to occluded vision. The current findings indicate that the vestibular control of standing balance can be represented by the intrinsic foot muscles and implicate a postural role for these muscles in modulating quiet standing., (Copyright © 2018 IBRO. Published by Elsevier Ltd. All rights reserved.)

Maintaining balance is vitally important in everyday life. Investigating the effects of individual foot muscle morphology on balance may provide insights into neuromuscular balance control mechanisms. This study aimed to examine the correlation between the morphology of foot muscles and balance performance during single-leg standing. Twenty-eight recreational runners were recruited in this study. An ultrasound device was used to measure the thickness and cross-sectional area of three intrinsic foot muscles (abductor hallucis, flexor digitorum brevis and quadratus plantae) and peroneus muscles. Participants were required to perform 30s of single-leg standing for three trials on a force plate, which was used to record the center of pressure (COP). The standard deviation of the amplitude and ellipse area of the COP were calculated. In addition, stabilogram diffusion analysis (SDA) was performed on COP data. Pearson correlation coefficients were computed to examine the correlation between foot muscle morphology and traditional COP parameters as well as with SDA parameters. Our results showed that larger abductor hallucis correlated to smaller COP sway, while larger peroneus muscles correlated to larger COP sway during single-leg standing. Larger abductor hallucis also benefited open-loop dynamic stability, as well as supported a more efficient transfer from open-loop to closed loop control mechanisms. These results suggest that the morphology of foot muscles plays an important role in balance performance, and that strengthening the intrinsic foot muscles may be an effective way to improve balance., (Copyright © 2017. Published by Elsevier B.V.)

Objective: To identify the anatomical motor points of the abductor hallucis muscle in cadavers., Methods: Motor nerve branches to the abductor hallucis muscles were examined in eight Korean cadaver feet. The motor point was defined as the site where the intramuscular nerve penetrates the muscle belly. The reference line connects the metatarsal base of the hallux (H) to the medial tubercle of the calcaneus (C). The x coordinate was the horizontal distance from the motor point to the point where the perpendicular line from the navicular tuberosity crossed the reference line. The y coordinate was the perpendicular distance from the motor point to the navicular tuberosity., Results: Most of the medial plantar nerves to the abductor hallucis muscles divide into multiple branches before entering the muscles. One, two, and three motor branches were observed in 37.5%, 37.5%, and 25% of the feet, respectively. The ratios of the main motor point from the H with respect to the H-C line were: main motor point, 68.79%±5.69%; second motor point, 73.45%±3.25%. The mean x coordinate value from the main motor point was 0.65±0.49 cm. The mean value of the y coordinate was 1.43±0.35 cm. All of the motor points of the abductor hallucis were consistently found inferior and posterior to the navicular tuberosity., Conclusion: This study identified accurate locations of anatomical motor points of the abductor hallucis muscle by means of cadaveric dissection, which can be helpful for electrophysiological studies in order to correctly diagnose the various neuropathies associated with tibial nerve components., Competing Interests: CONFLICT OF INTEREST: No potential conflict of interest relevant to this article was reported.

Over-pronated feet are common in adults and are associated with lower limb injuries. Studying the foot muscle morphology and foot kinematic patterns is important for understanding the mechanism of over-pronation related injuries. The aim of this study is to compare the foot muscle morphology and foot inter-segmental kinematics between recreational runners with normal feet and those with asymptomatic over-pronated feet. A total of 26 recreational runners (17 had normal feet and 9 had over-pronated feet) participated in this study and their foot type was assessed using the 6-item Foot Posture Index. Selected foot muscles were scanned using an ultrasound device and the scanned images were processed to measure the thickness and cross-sectional area of the muscles. Muscles of interest include abductor hallucis, abductor digiti minimi, flexor digitorum brevis and longus, tibialis anterior and peroneus muscles. Foot kinematic data during walking was collected using a 3D motion capture system incorporating the Oxford Foot Model. The results show that individuals with over-pronated feet have larger size of abductor hallucis, flexor digitorum brevis and longus and smaller abductor digiti minimi than controls. Higher rearfoot peak eversion and forefoot peak supination during walking were observed in individuals with over-pronated feet. However, during gait the forefoot peak abduction was comparable. These findings indicate that in active asymptomatic individuals with over-pronated feet, the foot muscle morphology is adapted to increase control of the foot motion. The morphological characteristics of the foot muscles in asymptomatic individuals with over-pronated feet may affect their foot kinematics and benefit prevention from injuries., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Background and Objectives: Excessive activity of the tibialis anterior muscle may be a causal mechanism in overuse injuries such as stress fracture in pes planus patients. However, information about this relationship is limited. In this study, we compared the angle of the medial longitudinal arch, the activities of the abductor hallucis and tibialis anterior muscles, and the activity ratio of tibialis anterior/abductor hallucis in individuals with pes planus and those with a neutral foot position during short-foot exercises conducted while sitting., Methods: Differences between the groups were analyzed using an independent t-test. In all, 28 university students participated in this study (14 subjects in each group)., Results: The activity of the abductor hallucis muscle was significantly lower (p < 0.001), and the activity ratio of tibialis anterior/abductor hallucis was significantly greater (p = 0.012) in the pes planus group than in the neutral foot group during the exercise., Conclusions: Clinicians should recognize that pes planus patients may compensate for reduced activation of the abductor hallucis to maintain the angle of the medial longitudinal arch during the sitting short-foot exercise.

[Purpose] The purpose of the present study was to examine the effects of toe-spread (TS) exercises and hip external rotator strengthening exercises for pronated feet on lower extremity muscle activities during stair-walking. [Subjects and Methods] The participants were 20 healthy adults with no present or previous pain, no past history of surgery on the foot or the ankle, and no foot deformities. Ten subjects performed hip external rotator strengthening exercises and TS exercises and the remaining ten subjects performed only TS exercises five times per week for four weeks. [Results] Less change in navicular drop height occurred in the group that performed hip external rotator exercises than in the group that performed only TS exercises. The group that performed only TS exercises showed increased abductor hallucis muscle activity during both stair-climbing and -descending, and the group that performed hip external rotator exercises showed increased muscle activities of the vastus medialis and abductor hallucis during stair-climbing and increased muscle activity of only the abductor hallucis during stair-descending after exercise. [Conclusion] Stair-walking can be more effectively performed if the hip external rotator muscle is strengthened when TS exercises are performed for the pronated foot.

Introduction: Abductor hallucies tenotomy sometimes necessary in treatment of clubfoot., Material and Methods: Thirty children (45 feet) of one day old up to six months presented with idiopathic clubfoot. Patients were treated using the technique of Ponseti combined by abductor hallucies tenotomy after serial casting., Results: At a mean follow up period of 16.7 months, 43/45 feet were good (95%), 2/45 feet were bad (5%). The mean Pirani score at the final follow up was 1.05., Conclusion: Abductor hallucies tenotomy shortens the duration of casts, decrease the cost and risk of leg atrophy.

[Purpose] The purpose of this study was to identify the effects of an inclined ankle on the activation of the abductor hallucis muscle during short foot exercises. [Subjects] We recruited 14 healthy volunteers who were free of pain, and did not suffer from arthritis or osteomuscular problems related to the foot or ankle. [Methods] The subjects performed short foot exercises and short inclined foot exercises with 30° passive ankle dorsiflexion. [Results] The exercise with an inclined foot showed a significantly larger activation of the abductor hallucis than that shown during the neutral short foot exercises. [Conclusion] These results suggest that passive ankle dorsiflexion during short foot exercise for strengthening the abductor hallucis is a more effective clinical treatment exercise.

Abductor hallucis is the largest muscle in the arch of the human foot and comprises few motor units relative to its physiological cross-sectional area. It has been described as a postural muscle, aiding in the stabilization of the longitudinal arch during stance and gait. The purpose of this study was to describe the discharge properties of abductor hallucis motor units during ramp and hold isometric contractions, as well as its discharge characteristics during fatigue. Intramuscular electromyographic recordings from abductor hallucis were made in 5 subjects; from those recordings, 42 single motor units were decomposed. Data were recorded during isometric ramp contractions at 60% maximum voluntary contraction (MVC), performed before and after a submaximal isometric contraction to failure (mean force 41.3 ± 15.3% MVC, mean duration 233 ± 116 s). Motor unit recruitment thresholds ranged from 10.3 to 54.2% MVC. No significant difference was observed between recruitment and derecruitment thresholds or their respective discharge rates for both the initial and postfatigue ramp contractions (all P > 0.25). Recruitment threshold was positively correlated with recruitment discharge rate (r = 0.47, P < 0.03). All motor units attained similar peak discharge rates (14.0 ± 0.25 pulses/s) and were not correlated with recruitment threshold. Thirteen motor units could be followed during the isometric fatigue task, with a decline in discharge rate and increase in discharge rate variability occurring in the final 25% of the task (both P < 0.05). We have shown that abductor hallucis motor units discharge relatively slowly and are considerably resistant to fatigue. These characteristics may be effective for generating and sustaining the substantial level of force that is required to stabilize the longitudinal arch during weight bearing.