Case report of the double-headed extensor hallucis longus.

BACKGROUND: We present a case report of double-headed extensor hallucis longus (EHL) with potential clinical significance. MATERIALS AND METHODS: Cadaveric dissection of the right lower limb of a 70-year- -old at death female was performed for research and teaching purposes at the Department of Anatomical Dissection and Donation, Medical University of Lodz. The limb was dissected using standard techniques according to a strictly specified protocol. Each head and tendon of the muscle was photographed and subjected to further measurements. RESULTS: During dissection, an unusual type of EHL muscle was observed. It consisted of two muscle bellies, a main tendon and an accessory tendon. Both muscle bellies were located on anterior surface of the fibula and the interosseous membrane. The main tendon insertion was located on the dorsal aspect of the base of the distal phalanx of the big toe, while the accessory tendon insertion was located medially. CONCLUSIONS: The EHL muscle is highly morphologically variable at both the point of origin and the insertion. Knowledge of its variations is connected to several pathologies such as foot drop, tendonitis, tendon rupture, and anterior compartment syndrome.

Coexistence of accessory band with the second type of extensor hallucis longus.

The main muscles responsible for extension of the toes are the extensor digitorum longus and extensor hallucis longus. Morphological variants of both of these muscles are mostly related to the numbers of tendons and their unusual points of insertion. The case presented shows an accessory band deriving from the extensor digitorum longus and fusing with the extensor hallucis longus, a concomitant additional tendon of the latter inserting to the proximal phalanx of the hallux. Knowledge of these anatomical patterns is important not only from the anatomical but also the clinical point of view and can be useful in lower limb surgery.

The hallucal interphalangeal ossicle: anatomy and basis for ultrasound-guided surgical shaving.

Painful lesions on the plantar aspect of the first interphalangeal joint (IPJ) of the hallux can be attributed to structures called ossicles, nodules, or sesamoids. The aims of the present study were first to verify that ultrasonography (US) is a high-sensitivity tool for diagnosing an interphalangeal ossicle (IO), and second to prove that US-guided-shaving surgery ("milling") is a safe and feasible technique for remodeling the IO. The study is divided into three parts. In the first part, the prevalence of IOs was estimated in 12 cadaver feet using US, anatomical dissection, and fluoroscopy. In the second, a detailed US and morphological description of the IO was obtained. In the third, six cadaver feet were subjected to surgical milling. IO prevalence was 41.6% in gross anatomy, 41.6% in US examination and just 16.6% in fluoroscopy. The ossicles had a mean length of 4 mm (± 2 mm) and a width of 7 mm (± 2 mm). The ossicles could be completely shaved in all specimens without injuring important anatomical structures. Our results indicate that US is a more precise tool for diagnosing an IO than X-ray. Moreover, our US-guided mini-invasive surgical technique appears feasible and safe.

Anatomical Study of the Accessory Tendon of the Extensor Hallucis Longus Muscle and Its Clinical Application.

BACKGROUD: The accessory tendon of the extensor hallucis longus (ATEHL) muscle is a common abnormal structure, and its clinical significance remains debatable. In this study, we provide the incidence of the ATEHL and characterize its morphological types in Asian cadavers and investigate its clinical applications. METHODS: The tendons from 50 adult cadaveric feet, fixed in 10% formalin, were analyzed. We measured the length and width of both the ATEHL and the extensor hallucis brevis (EHB). RESULTS: All dissected specimens had an ATEHL. The first metatarsophalangeal joint was surrounded by an accessory tendon that inserted onto the joint capsule and the dorsal base of the proximal phalanx. We classified the ATEHL into 3 types based on their directions. Differences in ATEHL type based on sex were not statistically significant. CONCLUSIONS: We found an ATEHL in all cadaveric specimens in this study. We surmise that the ATEHL acts as an antagonist with the EHB when the toe is extending, which might help prevent the occurrence of hallux valgus deformity.

Comparison of the insertion patterns of the extensor hallucis longus muscle in Korean focusing on the regional difference.

PURPOSE: From the evolutionary myology, the additional tendon of the extensor hallucis longus (EHL) muscle represents the sample of a new acquisition. We aimed to determine whether the insertion pattern of the EHL muscle differs in Koreans according to demographic populations, especially between Jeju islanders and the Korean Peninsula inhabitants. METHODS: We used 69 Korean cadavers and classified the tendinous insertion of the EHL muscle as Pattern I, Pattern II, and Pattern III. The ratio of each Pattern in adult cadaveric samples was compared between demographic populations. RESULTS: The proportion of Pattern I, Pattern II, and Pattern III of the EHL muscle was 30.43, 63.77, and 5.80%, respectively, further divided into 18.00 vs. 36.04%, 72.00 vs. 60.47%, 10.00 vs. 3.49% in Jeju islanders vs. peninsular Koreans. There was a considerable difference in the insertion patterns of the EHL muscle in each regional group (p = 0.032), but not in each gender, age, and body sides of lower limbs. CONCLUSION: The findings of this study indicate that there was a higher incidence of the accessory tendon(s) of the EHL muscle in Koreans and the distributed insertion patterns of the EHL muscle was significantly different between Jeju islanders and peninsular Koreans.

Posterior Ankle Impingement and Flexor Hallucis Longus Pathology.

Posterior ankle pain is a common complaint, and the potential causative pathologic processes are diverse. The constellation of these numerous etiologies has been collectively referred to as posterior ankle impingement syndrome. The pain associated with posterior ankle impingement is caused by bony or soft tissue impingement of the posterior ankle while in terminal plantar flexion. This condition is most frequently encountered in athletes who participate in sports that involve forceful, or repetitive, ankle plantar flexion. This article discusses the associated pathology, diagnosis, conservative treatment, and surgical techniques associated with flexor hallucis longus and posterior ankle impingement syndrome.

Biometría de los músculos extensor corto de los dedos y extensor corto del hallux en individuos brasileños: análisis anatómico para su uso como colgajo muscular en cirugías reconstructivas / Biometry of the extensor digitorum brevis and extensor hallucis brevis muscles in Brazilian individuals: anatomical analysis for use as a muscle flap in reconstructive surgeries

RESUMEN: El músculo extensor corto de los dedos (ECD) se sitúa junto con el músculo extensor corto del hallux (ECH) en la región dorsal del pie y están encargados de colaborar con la acción agonista de los músculos extensor largo de los dedos (ELD) y extensor largo del hallux (ELH), en la extensión de los cuatro dedos mediales en las articulaciones metatarsofalángicas. Esta condición complementaria permite su transferencia quirúrgica hacia otras regiones receptoras sin afectar la funcionalidad extensora de los dedos del pie motivo por el cual durante las últimas décadas se ha convertido en un tejido importante para la reconstrucción de lesiones tisulares, sin embargo, son escasos los estudios biométricos que lo describan en detalle. El objetivo de esta investigación fue establecer la longitud, ancho y área de extensión de estos músculos acompañada de la determinación de las distancias de éstos respecto a la cuña medial y la base del quinto metatarsiano para su uso quirúrgico. Sumado a lo anterior y posterior a la descripción de las variantes musculares encontradas se determinó los puntos motores de inervación de estos dos músculos. Para ello se estudiaron 36 miembros inferiores formolizados de individuos adultos brasileños pertenecientes a la Universidad Federal de Alagoas (UFAL), Maceió, Brasil. Las mediciones se realizaron con un cáliper marca Mitutoyo de 0,01 mm de precisión obteniendo una longitud, ancho y área de 6,89 ± 1,64 cm, 3,81 ± 0,42 cm y 31,98 ± 7,60 cm2 en el lado derecho de 6,91 ± 1,64 cm, 3,68 ± 0,46 cm y 30,75 ± 7,61 cm2 en el izquierdo respectivamente. En el 17 % de los casos hay presencia de tendones accesorios para el músculo ECD. La distancia desde el margen medial del músculo ECH respecto a la cuña medial y del margen lateral del músculo ECD a la base del quinto metatarsiano fue de 1,97 ± 0,43 y 1,72 ± 0,41 al lado derecho y de 2,01 ± 0,62 y 1,87 ± 0,36 al lado izquierdo respectivamente. Los puntos motores (Pm) predominaron en un 64 % en el tercio medio del músculo ECH y en un 64 % en el tercio proximal del músculo ECD. Estos resultados son un aporte significativo, tanto para quienes realizan cirugía ortopédica como para el conocimiento detallado de la anatomía dorsal del pie.

SUMMARY: The extensor digitorum brevis muscle (EDB) is located along with the extensor hallucis brevis (EHD) in the dorsal region of the foot and are responsible for collaborating with the agonist action of the extensor digitorum longus muscles (EDL) and extensor hallucis longus (EHL) in the extension of the four medial fingers in the metatarsophalangeal joints. This complementary condition allows its surgical transfer to other receptor regions without affecting the extensor functionality of the toes, which is why during the last decades it has become an important tissue for the reconstruction of tissue injuries, however, there are few studies biometrics that describe it in detail. The objective of this investigation was to establish the length, width and area of extension of these muscles accompanied by the determination of their distances from the medial wedge and the base of the fifth metatarsal for surgical use. In addition to the above and after the description of the muscle variants found, the innervation motor points of these two muscles were determined. To do this, 36 formalized lower limbs of Brazilian adult individuals belonging to the Federal University of Alagoas (UFAL), Maceió, Brazil, were studied. Measurements were made with a 0.01 mm precision Mitutoyo caliper obtaining a length, width and area of 6.89 ± 1.64 cm, 3.81 ± 0.42 cm and 31.98 ± 7.60 cm2 on the right side of 6.91 ± 1.64 cm, 3.68 ± 0.46 cm and 30.75 ± 7.61 cm2 on the left, respectively. In 17 % of cases there is presence of accessory tendons for the EDB muscle. The distance from the medial margin of the EHB muscle with respect to the medial wedge and the lateral margin of the EDB muscle to the base of the fifth metatarsal was 1.97 ± 0.43 and 1.72 ± 0.41 on the right side and 2,01 ± 0.62 and 1.87 ± 0.36 on the left side respectively. Motor points (Pm) predominated in 64 % in the middle third of the EHB muscle and in 64 % in the proximal third of the EDB muscle. These results are a significant contribution both for those who perform orthopedic surgery and for detailed knowledge of the dorsal foot anatomy.

The morphological affinity of the Early Pleistocene footprints from Happisburgh, England, with other footprints of Pliocene, Pleistocene, and Holocene age.

Fossil hominin footprints provide a direct source of evidence of locomotor behavior and allow inference of other biological data such as anthropometrics. Many recent comparative analyses of hominin footprints have used 3D analytical methods to assess their morphological affinities, comparing tracks from different locations and/or time periods. However, environmental conditions can sometimes preclude 3D digital capture, as was the case at Happisburgh (England) in 2013. Consequently, we use here a 2D geometric morphometric approach to investigate the evolutionary context of the Happisburgh tracks. The comparative sample of hominin tracks comes from eight localities that span a broad temporal range from the Pliocene to Late Holocene. The results show disparity in the shapes of tracks ascribed to hominins from the Pliocene (presumably Australopithecus afarensis), Pleistocene (presumably Homo erectus and Homo antecessor), and Holocene (Homo sapiens). Three distinct morphological differences are apparent between time samples: changes in adduction of the hallux, changes in the shape and position of the medial longitudinal arch impression, and apparent changes in foot proportions. Linear dimensions classified the potential H. antecessor tracks from Happisburgh as being most similar to the presumed H. erectus prints from Ileret. We demonstrate using 2D geometric morphometric methods and linear dimensions that the Happisburgh tracks are morphologically similar to other presumed Homo tracks and differ from the Laetoli footprints. The probable functional implications of these results fit well with previous comparative analyses of hominin tracks at other sites.

Properties and Function of the Flexor Hallucis Capsularis Interphalangeus Tendon.

INTRODUCTION: The fibrocartilagenous plantar plates of the forefoot are biomechanically important, forming the primary distal attachment for the plantar aponeurosis. They are integral to the function of the windlass mechanism in supporting the arches of the foot in gait. Dissection of the cadaveric hallux revealed an organised sagittal thickening of the dorsal side of the flexor hallucis longus (FHL) sheath, which attached the interphalangeal plantar plate to the metatarsophalangeal (MTP) plantar plate. A description of a similar structure was made in 1984 when it was termed the flexor hallucis capsularis interphalangeus (FHCI) - however, it has not been researched since, and we aim to study it further and identify its characteristics. METHOD: Eight specimens were dissected from four cadavers. Two were stained and examined under magnification in both polarized and non polarized light. The remaining 6 were subjected to micrometer testing of their tensile properties. RESULTS: Both the histological features and mechanical properties were consistent with tendon; with cross sectional area, ultimate tensile strength and stiffness varying between specimens. CONCLUSIONS: Based on its location and properties, the FHCI tendon may be involved in limiting dorsiflexion of the first MTP joint and could have clinical relevance in pathological processes around both the first and second MTP joints. Clin. Anat., 33:689-695, 2020. © 2019 Wiley Periodicals, Inc.

MR imaging-anatomical correlation of the metatarsophalangeal joint of the hallux: Ligaments, tendons, and muscles.

OBJECTIVE: To perform an MR imaging-anatomical correlation to elucidate the anatomy of muscles, tendons, and ligaments about the hallux as seen on MR imaging. MATERIALS AND METHODS: Four fresh and 4 embalmed cadaver specimens were used for this study. The embalmed specimens and one fresh specimen were dissected by three investigators. The fresh specimens were preserved deep frozen. They were thawed and imaged with a 3 T MR system. Proton density weighted images were obtained. The specimens were refrozen and sectioned with a band saw into 3 mm thick slices. RESULTS: Musculotendinous structures were equally well seen in the fresh and embalmed specimens. The capsular ligaments could best be studied in the fresh specimens. Proximal to the sesamoids the following muscle and tendon anatomy was delineated: the abductor hallucis tendon inserted on the medial sesamoid bone together with the medial belly of the flexor digitorum brevis; the adductor hallucis (transverse and oblique heads) inserted on the lateral sesamoid together with the lateral head of the flexor hallucis brevis. At the level of the sesamoid bones and distally, the ligaments making up the plantar plate were delineated, including the presesamoid band, the flexor hallucis longus pulley, the sesamometatarsal ligaments, the sesamophalangeal ligaments, and the capsular ligaments. CONCLUSION: MRI allows for accurate assessment of the complex anatomy of the hallux. At the level proximal to the sesamoids the muscle and tendon insertions are well demonstrated. At the level of the sesamoids and distally, the ligaments making up 'the plantar plate' are well demonstrated.

Measuring Visualized Joint Surface in Hallux Metatarsophalangeal Arthroscopy.

BACKGROUND: Arthroscopy has been increasingly used to evaluate small joints in the foot and ankle. In the hallux metatarsophalangeal (MTP) joint, little data exist evaluating the efficacy of arthroscopy to visualize the articular surface. The goal of this cadaveric study was to determine how much articular surface of the MTP joint could be visualized during joint arthroscopy. METHODS: Ten fresh cadaveric foot specimens were evaluated using standard arthroscopy techniques. The edges of the visualized joint surface were marked with curettes and Kirschner wires; the joints were then surgically exposed and imaged. The visualized surface area was measured using ImageJ® software. RESULTS: On the distal 2-dimensional projection of the joint surface, an average 57.5% (range, 49.6%-65.3%) of the metatarsal head and 100% (range, 100%-100%) of the proximal phalanx base were visualized. From a lateral view of the metatarsal head, an average 72 degrees (range, 65-80 degrees) was visualized out of an average total articular arc of 199 degrees (range, 192-206 degrees), for an average 36.5% (range, 32.2%-40.8%) of the articular arc. CONCLUSION: Complete visualization of the proximal phalanx base was obtained. Incomplete metatarsal head visualization was obtained, but this is limited by technique limitations that may not reflect clinical practice. CLINICAL RELEVANCE: This information helps to validate the utility of arthrosocpy at the hallux metatarsophalangeal joint.

Increasing the safety of minimally invasive hallux surgery-An anatomical study introducing the clock method.

BACKGROUND: The purpose of this study is to describe a simple and reproducible method to localize the neurological structures at risk and to describe a safe zone for hallux minimally invasive surgery (MIS) procedures. METHODS: Ten fresh-frozen cadaveric feet were dissected to identify the dorsomedial digital nerve (DMDN) and the dorsolateral digital nerve (DLDN) of the first toe. Axial sections were performed at the sites of metatarsal osteotomies. We documented the position of the nerves with respect to the extensor hallucis longus (EHL) tendon using a clock method superimposed on the axial section RESULTS: The DMDN was found at an average of 26.2° medial to the medial border of the EHL tendon. (SD 11.26, range 14.5-45.5), whereas the average distance of the DLDN was 32.3° lateral to the medial border of the EHL tendon. (SD 6.29, range 13.5-40). CONCLUSIONS: Using the clock method the DMDN and DLDN were found consistently between 10 o'clock and 2 o'clock in either right and left feet. The clock method may facilitate avoiding the area where these nerves are located serving as a valuable tool in minimally invasive foot surgery.

Estudo anatômico das variações da inserção do músculo abdutor longo do polegar / Anatomical study of variations of the long abductor thumb muscle insertion

Este é um estudo da variação anatômica da inserção do tendão do músculo abdutor longo do polegar.O objetivo deste estudo foi realizar uma descrição das variações antômicas do tendão do músculo Abdutor Longo do Polegar (ALP), por meio de uma dissecção anatômica de 20 cadáveres, todos afrodescendentes, no laboratório de anatomia humana da faculdade de medicina de Santos UNIMES.

Radiographic Measurements of the Affected and Unaffected Feet in Patients with Unilateral Hallux Limitus A Case-Control Pilot Study.

BACKGROUND: Controversy exists regarding the structural and functional causes of hallux limitus, including metatarsus primus elevatus, a long first metatarsal, first-ray hypermobility, the shape of the first metatarsal head, and the presence of hallux interphalangeus. Some articles have reported on the radiographic evaluation of these measurements in feet affected by hallux limitus, but no study has directly compared the affected and unaffected feet in patients with unilateral hallux limitus. This case-control pilot study aimed to establish whether any such differences exist. METHODS: Dorsoplantar and lateral weightbearing radiographs of both feet in 30 patients with unilateral hallux limitus were assessed for grade of disease, lateral intermetatarsal angle, metatarsal protrusion distance, plantar gapping at the first metatarsocuneiform joint, metatarsal head shape, and hallux abductus interphalangeus angle. Data analysis was performed using a statistical software program. RESULTS: Mean radiographic measurements for affected and unaffected feet demonstrated that metatarsus primus elevatus, a short first metatarsal, first-ray hypermobility, a flat metatarsal head shape, and hallux interphalangeus were prevalent in both feet. There was no statistically significant difference between feet for any of the radiographic parameters measured (Mann-Whitney U tests, independent-samples t tests, and Pearson χ(2) tests: P > .05). CONCLUSIONS: No significant differences exist in the presence of the structural risk factors examined between affected and unaffected feet in patients with unilateral hallux limitus. The influence of other intrinsic factors, including footedness and family history, should be investigated further.

The Hallucal-Sesamoid Complex: Normal Anatomy, Imaging, and Pathology.

The first metatarsophalangeal joint and hallucal-sesamoid complex are critical structures in weightbearing and susceptible to several pathologies including turf toe, sesamoiditis, degenerative or inflammatory arthritides, infection, and avascular necrosis. This review article summarizes the complex anatomy of the region, covers common pathologies while clarifying terms such as turf toe and sesamoiditis, reviews imaging techniques, and discusses management.

Minimally invasive Akin osteotomy and lateral release: Anatomical structures at risk-A cadaveric study.

BACKGROUND: Among the many surgical techniques used for hallux valgus correction, different osteotomies may be performed in the proximal phalanx as well as lateral release as associated procedures. The aim of this study is to analyze the anatomical relationships and the risks for the soft tissue lessions when performing the dorsomedial minimally invasive surgery (MIS) portal for the Akin osteotomy, and the MIS dorsolateral portal for lateral release, in order to define a safety zone when conducting the procedure in order to avoid complications. MATERIALS AND METHODS: The procedures were carried out on 16 fresh-frozen cadaveric feet. A MIS dorsomedial and dorsolateral portals were performed. The anatomical dissection of the cadaveric pieces was carried out and the different anatomic and surgical relationships were analyzed and measured. RESULTS: No nerve injury was found. Injury of the extensor hallucis longus (EHL) paratendon were seen in 9 cases (56%). There was no injury of the flexor hallucis longus (FHL) tendon and or collateral plantar nerves. A partial injury of the FHL sheath was observed in 44% of the samples. CONCLUSIONS: Although percutaneous Akin osteotomy is clinically effective, the possibility of injury of anatomic structures is high (9-55%), however injuries upon vascular or nerve structures were not seen.

Normative data for the American Orthopedic Foot and Ankle Society ankle-hindfoot, midfoot, hallux and lesser toes clinical rating system.

PURPOSE: Despite some theoretical reservations, the AOFAS clinical rating system with its scales for ankle-hindfoot, midfoot, hallux and lesser toes is one of the most widely used assessment tools in foot and ankle surgery. This study was designed to generate age- and gender-related norm values for all four subscales. METHODS: Despite not being used in a self-administered manner, the AOFAS score underwent cross cultural adaptation to guarantee unrestricted comparability of data. A data pool was generated using the results of personal interviews and clinical examination of 625 individuals, including staff and visitors to our hospital, and excluding people scheduled for foot surgery or in after-treatment. These data served as a basis to calculate all four parts of the AOFAS clinical rating system. RESULTS: Mean value for the ankle-hindfoot scale was calculated as 91.6 points (±0.9 confidence interval), and 89.3 points for the midfoot scale (±1.0 CI), 88.3 for the hallux metatarsophalangeal-interphalangeal scale (± 0.9 CI) and 91.0 for the lesser metatarsophalangeal-interphalangeal scale (± 0.8 CI). Results showed a decrease with age in all four scales. Males showed better results than females. Individuals with previous surgery showed lower results in the respective score. CONCLUSIONS: While lowered scoring results prior to surgery reflect the degree of restrictions due to pain, function and alignment problems, post-operative increases in clinical scoring should indicate return to age-related norm values. Our data calculated these norm values for the first time for all four AOFAS scales, giving a basis for better interpretation of published results in foot and ankle surgery. Our data showed and quantified the decrease of norm values with age, especially for hallux and lesser toes scores, as well as lower norm values for females and for individuals that had had surgery of the foot. LEVEL OF EVIDENCE: Level I, diagnostic study.

Skeletal development of hallucal tarsometatarsal joint curvature and angulation in extant apes and modern humans.

The medial cuneiform, namely the curvature and angulation of its distal facet with metatarsal 1, is crucial as a stabilizer in bipedal locomotion and an axis upon which the great toe medially deviates during arboreal locomotion in extant apes. Previous work has shown that facet curvature and angulation in adult dry-bone specimens can distinguish African apes from Homo, and can even distinguish among species of Gorilla. This study provides the first ontogenetic assessment of medial cuneiform curvature and angulation in juvenile (n = 68) and adult specimens (n = 102) using computed tomography in humans and extant ape specimens, including Pongo. Our data find that modern human juveniles initially have a convex and slightly medially oriented osseous surface of the developing medial cuneiform distal facet that flattens and becomes more distally oriented with age. The same pattern (though of a different magnitude) occurs developmentally in the chimpanzee medial cuneiform, but not in Gorilla or Pongo, whose medial cuneiform facet angulation remains unchanged ontogenetically. These data suggest that the medial cuneiform ossifies in a distinguishable pattern between Pongo, Gorilla, Pan, and Homo, which may in part be due to subtle differences in the loading environment at the hallucal tarsometatarsal joint-a finding that has important implications for interpreting fossil medial cuneiforms.

Hallux metatarsophalangeal arthroscopy: indications and techniques.

With mounting attention focused on decreasing postsurgical pain and dysfunction, emphasis has been placed on approaching disorders using minimally invasive techniques. Surgical procedures of the hallux, such as hallux valgus correction, have earned the reputation for high postsurgical pain and prolonged recovery. Arthroscopic hallux procedures have the advantages of minimizing pain, swelling, and disability. Certain conditions, such as synovitis, loose bodies, and early-grade hallux rigidus, are better addressed arthroscopically. With the correct indications, hallux metatarsophalangeal arthroscopy can be a valuable tool for the foot and ankle surgeon.

Mouse hallucal metatarsal cross-sectional geometry in a simulated fine branch niche.

Mice raised in experimental habitats containing an artificial network of narrow "arboreal" supports frequently use hallucal grasps during locomotion. Therefore, mice in these experiments can be used to model a rudimentary form of arboreal locomotion in an animal without other morphological specializations for using a fine branch niche. This model would prove useful to better understand the origins of arboreal behaviors in mammals like primates. In this study, we examined if locomotion on these substrates influences the mid-diaphyseal cross-sectional geometry of mouse metatarsals. Thirty CD-1/ICR mice were raised in either arboreal (composed of elevated narrow branches of varying orientation) or terrestrial (flat ramps and walkways that are stratified) habitats from weaning (21 days) to adulthood (≥4 months). After experiments, the hallucal metatarsal (Mt1) and third metatarsal (Mt3) for each individual were isolated and micro-computed tomography (micro-CT) scans were obtained to calculate mid-shaft cross-sectional area and polar section modulus. Arboreal mice had Mt1s that were significantly more robust. Mt3 cross sections were not significantly different between groups. The arboreal group also exhibited a significantly greater Mt1/Mt3 ratio for both robusticity measures. We conclude that the hallucal metatarsal exhibits significant phenotypic plasticity in response to arboreal treatment due to habitual locomotion that uses a rudimentary hallucal grasp. Our results support the hypothesis that early adaptive stages of fine branch arboreality should be accompanied by a slightly more robust hallux associated with the biomechanical demands of this niche.