The first metatarsal bone is the medialmost and shortest of the five metatarsal bones in the human foot, characterized by its robust, prismoid-shaped shaft that articulates proximally with the medial cuneiform bone and distally with the proximal phalanx of the hallux (great toe).[1] It features a broad base with a medial tuberosity for muscle attachments, a sturdy shaft, and a head with two plantar grooved facets that accommodate the sesamoid bones within the flexor hallucis brevis tendon.[2] This bone is uniquely thickened and strengthened compared to the other metatarsals, enabling it to bear 30-50% of the body's weight during gait and propulsion phases.[1]Structurally, the first metatarsal contributes to the proximal half of the metatarsophalangeal joint and the tarsometatarsal (TMT) joint, which is part of the Lisfranc joint complex, providing stability to the midfoot.[1] Its base articulates exclusively with the medial cuneiform, unlike the more lateral metatarsals that may connect to multiple tarsal bones, and it forms a lateral intermetatarsal joint with the second metatarsal.[3] The bone's dorsal convexity and overall thickness support its role in force absorption and transmission, while its mobility allows adaptation to uneven surfaces during walking.[3]Functionally, the first metatarsal is integral to the medial longitudinal arch of the foot, aiding in weight distribution, balance, and efficient locomotion by serving as a key insertion point for muscles such as the tibialis anterior and peroneus longus.[1] It facilitates push-off during the terminal stance phase of gait and helps maintain foot alignment under load, with the underlying sesamoids enhancing ground contact and reducing friction on the flexor hallucis longus tendon.[2] Clinically, its prominence and load-bearing nature make it susceptible to conditions like hallux valgus and stress fractures, underscoring its biomechanical importance in lower limb function.[1]
Anatomy
Location and orientation
The first metatarsal bone is the medialmost of the five metatarsal bones in the human foot, forming the medial border of the forefoot and extending proximally from the first tarsometatarsal joint to the first metatarsophalangeal joint distally.[4] It articulates proximally with the medial cuneiform bone and distally with the proximal phalanx of the hallux, positioning it as a key weight-bearing structure in the medial column of the foot.[5] Laterally, it lies adjacent to the second metatarsal bone, contributing to the transverse arch of the forefoot.[2]This bone is notably shorter and thicker than the other metatarsals, providing enhanced stability and load distribution for the hallux during gait and propulsion.[4] Its shaft exhibits a characteristic curvature, with dorsal convexity and plantar concavity, which aligns with the overall arched configuration of the foot to facilitate efficient force transmission.[5] In normal alignment, the first metatarsal demonstrates a slight medial deviation relative to the second metatarsal, typically measuring about 7-8 degrees, ensuring balanced medial forefoot positioning without pathological varus or valgus shifts.[6]These positional relations and orientations underscore the first metatarsal's role in maintaining forefoot stability, with its medial adjacency to the first cuneiform reinforcing the longitudinal arch and preventing excessive medial column collapse under load.[3]
Bony structure
The first metatarsal bone is the shortest and stoutest among the five metatarsal bones, with an average length of approximately 67-70 mm in adults.[7] It features a robust shaft that is triangular in cross-section proximally and more prismatic distally.[5] Like other long bones, it is composed of compact cortical bone forming the external layer and cancellous bone internally, enclosing a medullary cavity that extends through the shaft.[1]The distal head is rounded and broader than in the lateral metatarsals, presenting a pulley-like shape with two grooved facets on the plantar surface to accommodate the sesamoid bones.[5] The proximal base is wedge-shaped to enhance stability and bears a large, kidney-shaped articular surface.[5]Anatomical variations include an occasional accessory facet on the lateral aspect of the base, allowing articulation with the second metatarsal in about 25% of individuals.[8] Accessory ossicles near the first metatarsal occur occasionally, with reported prevalence up to 13% in anatomical dissections.[9]
Surfaces and features
The dorsal surface of the first metatarsal bone is smooth and convex along its shaft and head, providing a gliding surface for overlying extensor tendons. This convexity increases distally toward the head, contributing to the bone's overall prismoid shape.[2][10]The plantar surface is slightly concave along the shaft, accommodating plantar soft tissues. At the base, a prominent tubercle is present on the lateral aspect for the insertion of the peroneus longus tendon. Distally, the head features two condyles separated by a shallow groove for flexor tendons, with the medial condyle's groove being larger than the lateral; these include grooves for the flexor hallucis brevis and articulate with the sesamoid bones, while a crista ridge extends plantarly from the anterior cartilage margin.[11][10]The medial surface is rounded and largely featureless along the shaft, serving primarily as an attachment site for the medial collateral ligament. A tuberosity is located at the base for additional structural support.[2][3]The lateral surface is relatively flat proximally at the base, occasionally presenting a small oval facet for articulation with the second metatarsal. A roughened area along the shaft provides attachment for the intermetatarsal ligament.[11][2]The distal head is quadrilateral and robust, larger than those of the lateral metatarsals, with two sesamoid facets on the plantar aspect separated by an intersesamoidal ridge. These facets are grooved to facilitate sesamoid gliding and enhance biomechanical stability during weight-bearing.[12][2]
Articulations
The base of the first metatarsal bone articulates proximally with the distal surface of the medial cuneiform bone, forming the medial tarsometatarsal joint as part of the Lisfranc joint complex. This is a planesynovial joint characterized by gliding motions that allow limited mobility, including approximately 5-10 degrees of dorsiflexion and plantarflexion to facilitate foot adaptation to uneven terrain.[1][13][14]Distally, the head of the first metatarsal articulates with the base of the proximal phalanx of the hallux, constituting the first metatarsophalangeal joint. This condyloid synovial joint supports biaxial movements, permitting dorsiflexion and plantarflexion ranging from 70-90 degrees of dorsiflexion to 35-50 degrees of plantarflexion, along with abduction and adduction of 10-20 degrees.[13][15][16]On the plantar aspect of the head, two constant sesamoid bones are embedded within the tendons of the flexor hallucis brevis muscle and articulate with the corresponding medial and lateral plantar facets of the metatarsal head, separated by an intersesamoidal ridge. These sesamoids enhance leverage and distribute forces across the joint.[4][1]The articulations are enclosed by fibrous joint capsules lined with synovial membranes that secrete lubricating fluid. Stability is provided by reinforcements from collateral ligaments medially and laterally, as well as the plantar plate inferiorly, forming a robust capsuloligamentous complex.[13][17]
Muscle and ligament attachments
Muscular attachments
The first metatarsal bone provides attachment sites for both extrinsic and intrinsic muscles of the foot, with specific roughened areas on its base, shaft, and head facilitating secure anchorage for origins and insertions. These attachments are crucial for the muscle-tendon units that influence toe movement and foot arch stability.On the dorsal surface, the first dorsal interosseous muscle originates from the lateral surface of the shaft and medial surface of the second metatarsal shaft, enabling abduction of the second toe relative to the axis of the second metatarsal.[18]Plantar attachments include the flexor hallucis brevis tendon, which passes over the two sesamoid bones on the plantar aspect of the first metatarsal head; the muscle itself originates from the plantar surfaces of the cuboid and lateral cuneiform bones. The tendon inserts on the medial and lateral sides of the base of the proximal phalanx of the hallux.[19][20]At the base, extrinsic muscles insert to influence overall foot positioning: the tibialis anterior tendon inserts on the medial surface of the base, supporting inversion and arch maintenance, while the peroneus longus (fibularis longus) inserts on the lateral tubercle and plantar surface of the base, aiding eversion and transverse arch support. These sites feature tuberosities and roughened ridges for tendon grip. Minor slips from the dorsal interossei may occasionally attach to the shaft, enhancing intermetatarsal stability.[1][21]
Ligamentous attachments
The first metatarsal bone articulates proximally with the medial cuneiform via the tarsometatarsal joint, reinforced by dorsal and plantar tarsometatarsal ligaments. The dorsal tarsometatarsal ligament forms a broad, thin band connecting the dorsal surface of the medial cuneiform to the base of the first metatarsal, contributing to the stability of the Lisfranc joint complex. On the plantar aspect, the plantar tarsometatarsal ligament consists of short, strong fibrous slips from the inferior surface of the medial cuneiform to the plantar base of the first metatarsal, limiting excessive eversion and supporting the medial longitudinal arch of the foot.[1][22]Laterally, the base of the first metatarsal connects to the second metatarsal through intermetatarsal ligaments, including oblique and transverse bands that span the adjacent bases. These ligaments, along with the deep transverse metatarsal ligament, prevent splaying of the metatarsal heads during weight-bearing and maintain forefoot integrity.[1][23]Distally, at the metatarsophalangeal joint, the head of the first metatarsal receives attachments from the medial and lateral collateral ligaments, which originate from the medial and lateral aspects of the metatarsal head and insert onto the base of the proximal phalanx of the hallux. These ligaments provide crucial varus-valgus stability to the joint. The plantar plate, a thick fibrocartilaginous structure, attaches proximally to the transverse groove on the plantar surface of the first metatarsal head and extends distally to blend with the proximal phalangeal base and joint capsule, enhancing plantar stability and resisting hyperextension.[24]The first metatarsal also benefits from indirect ligamentous support via the Lisfranc ligament complex, which includes the interosseous ligament between the medial cuneiform and the base of the second metatarsal, as well as associated dorsal and plantar components. This complex stabilizes the second metatarsal base, thereby anchoring the first ray and preventing medial displacement during propulsion.[25][1]
Development and blood supply
Ossification process
The first metatarsal bone originates from a cartilaginous model formed by mesenchymal condensation within the lower limb bud during early embryonic development, around the sixth to seventh week of gestation. This precursor undergoes endochondral ossification, where a perichondral bone collar initially forms around the diaphysis through intramembranous ossification, followed by vascular invasion and endochondral replacement of cartilage by bonetissue.[26][1]The primary ossification center emerges in the midshaft (diaphysis) of the first metatarsal between the 8th and 10th weeks of fetal life. This center expands longitudinally and radially, gradually replacing the cartilaginous diaphysis with trabecular bone while preserving epiphyseal cartilage plates at the proximal and distal ends. By birth, the primary center is well-established and visible on radiographs, providing structural support as the bone elongates postnatally.[27][28][29]Secondary ossification occurs at the proximal base, where the epiphyseal center appears around the third year of age, distinguishing the first metatarsal from the other metatarsals, which develop their secondary centers distally at the head. This basal epiphysis contributes to the bone's proximal articulation and growth, with fusion to the diaphysis typically completing between 17 and 20 years of age, marking skeletal maturity. Unlike the distal end, the head of the first metatarsal does not routinely form a separate secondary center, though multipartite ossification variants may occasionally involve the head region.[30][31][32]
Vascular supply
The arterial supply to the first metatarsal bone is primarily derived from the dorsalis pedis artery, which continues as the first dorsal metatarsal artery at the level of the tarsometatarsal joint, providing branches to the base and proximal shaft.[33] The distal shaft and head receive additional perfusion from the first plantar metatarsal artery, a branch of the deep plantar arch formed by the lateral plantar artery, as well as contributions from the medial plantar artery.[34] These dorsal and plantar sources establish a dual vascular network that ensures comprehensive nourishment across the bone's length.A key component of the intraosseous circulation is the nutrient artery, which typically arises from the first dorsal metatarsal artery and enters the medullary cavity via a foramen located on the lateral cortex of the shaft, usually at the junction of the middle and distal thirds or within the distal third, approximately 22-23 mm proximal to the metatarsal head.[35] This artery supplies the endosteal surface and marrow cavity, supporting internal bone metabolism and growth. In some cases, the nutrient artery may originate from the first plantar metatarsal artery or deep plantar branches, reflecting anatomical variations observed in up to 40% of specimens.[36]Venous drainage parallels the arterial pathways, with venae comitantes accompanying the dorsal and plantar metatarsal arteries to converge into the dorsal and plantar venous arches of the foot.[37] These arches facilitate return flow toward the greater and lesser saphenous veins, maintaining efficient deoxygenated blood clearance from the first metatarsal region.The vascular architecture features a rich anastomotic network, particularly around the tarsometatarsal and metatarsophalangeal joints, where branches from the first dorsal metatarsal, first plantar metatarsal, and medial plantar arteries interconnect to form periarticular plexuses that enhance collateral circulation.[38] This interconnected system, including dorsal-to-plantar communications via perforating branches, provides redundancy in blood flow and is essential for the bone's vitality during development, such as supporting ossification centers.[39]
Function and biomechanics
Role in weight-bearing
The first metatarsal serves as the primary weight-bearing bone in the medial forefoot, transmitting approximately 40% of body weight during static stance phase.[40][41] This substantial load distribution underscores its role in supporting the body's mass while maintaining foot stability, with the bone's robust structure enabling efficient force transfer from the medial cuneiform through the Lisfranc joint complex.[40]Structural adaptations of the first metatarsal, including its thick and broad base, facilitate optimal load handling and contribute to the stability of the transverse arch via articulations at the Lisfranc joint.[42] The sesamoid bones embedded in the tendons of the flexor hallucis brevis at the metatarsal head further enhance this function by distributing plantar pressures across the first ray and preventing excessive dorsiflexion at the metatarsophalangeal joint.[43] These mechanisms collectively reduce localized stress concentrations, promoting even pressure dissipation during weight-bearing activities.[43]Biomechanically, the first metatarsal endures primarily axial compressive forces, reaching up to 1.9 times body weight at the head during normal gait, with peak loads escalating to 2-3 times body weight in dynamic scenarios such as running.[44][45] Its rounded head and medial contour provide resistance to shear forces, ensuring alignment and minimizing lateral deviation under load.[45] Through these interactions, the bone integrates with the overall foot architecture to sustain both static posture and preparatory phases of locomotion.[46]
Contribution to gait and propulsion
During the gait cycle, the first metatarsophalangeal (MTP) joint of the first metatarsal bone undergoes slight dorsiflexion at heel strike to facilitate initial ground contact and accommodate the foot's transition into stance phase.[47] As the body advances over the foot during mid-stance, coordinated muscle action maintains stability, with the extensor hallucis longus helping to stabilize the first metatarsal head and keep the distal pad of the great toe in contact with the ground.[48] Toward the end of stance, the joint progresses to greater dorsiflexion before engaging the windlass mechanism at toe-off, where dorsiflexion of the hallux winds the plantar fascia around the head of the first metatarsal, effectively plantarflexing the metatarsal relative to the proximal phalanx and elevating the medial longitudinal arch to create a rigid lever arm.[49]In propulsion, the head of the first metatarsal serves as a primary fulcrum for forward thrust generation during toe-off, with the flexor hallucis longus muscle and associated sesamoids playing a key role in applying force across the joint to produce efficient push-off.[50] The flexor hallucis longus excursion averages approximately 6.6 mm during the stance phase.[51] This mechanism transforms the flexible foot into a stable platform, optimizing energy transfer for locomotion.The kinematic range of the first MTP joint allows for a total motion of 60-70 degrees during the transition from swing to stance, encompassing both plantarflexion and dorsiflexion excursions that are essential for smooth weight transfer and preventing gait inefficiencies.[47] This range supports the joint's overall function in dynamic foot mechanics, where precise coordination between the first metatarsal and surrounding structures ensures effective propulsion without excessive stress.[1]
Clinical significance
Fractures and injuries
Fractures of the first metatarsal bone are relatively uncommon compared to those of the central metatarsals, accounting for approximately 4-5% of metatarsal fractures (which represent about 35% of all foot fractures), with a notably higher incidence among athletes due to repetitive loading activities.[52][53][54] Stress fractures, often occurring at the shaft, are particularly prevalent in runners and other endurance athletes from repetitive impact and overload, while traumatic fractures at the base may result from avulsion due to tension from the Lisfranc ligament complex during hyperdorsiflexion or twisting injuries.[52][55] Mechanisms typically involve direct trauma, such as stubbing the toe or crush injuries from heavy objects, or indirect forces like axial loading in falls; these injuries disrupt the bone's critical role in weight distribution, potentially leading to complications if healing is impaired by vascular supply limitations in the diaphysis.[52][55]Classification of first metatarsal fractures distinguishes between displaced and non-displaced types, with displacement defined as greater than 2-3 mm or angulation exceeding 10 degrees, which influences management decisions.[52][55] In pediatric cases, epiphyseal injuries are categorized using the Salter-Harris system, where types I and II involve extra-articular extensions that risk growth disturbances, while types III and IV affect the joint and physis, increasing the potential for angular deformities.[55] Stress fractures are graded by severity, from low-risk (periosteal reaction) to high-risk (cortical disruption), based on imaging findings like MRI or bone scans, guiding conservative versus operative approaches.[53]Initial treatment emphasizes restoring alignment and promoting union, with non-displaced fractures managed conservatively through immobilization in a cast or walking boot for 4-6 weeks, accompanied by non-weight-bearing or partial weight-bearing as tolerated to allow bone remodeling.[52][55] Displaced fractures, intra-articular involvement, or those with instability—such as base avulsions exceeding 2 mm displacement—require surgical intervention via open reduction and internal fixation (ORIF) using screws, plates, or K-wires to maintain length and prevent transfer of load to adjacent metatarsals.[52][56] Early diagnosis via radiographs or advanced imaging is crucial to avoid nonunion, especially in athletes where return to activity protocols include gradual loading after radiographic confirmation of healing.[55]
Deformities and associated conditions
Hallux valgus, commonly known as a bunion, is a prevalent forefoot deformity characterized by lateral deviation of the great toe at the first metatarsophalangeal joint, accompanied by medial prominence of the first metatarsal head.[57] This condition affects approximately 23% of adults aged 18 to 65 years and is strongly associated with ill-fitting footwear that compresses the forefoot, as well as genetic factors.[58] A family history of the deformity is reported in up to 83% of cases, underscoring its hereditary component.[59]Hallux rigidus represents another significant pathology involving the first metatarsal, defined as degenerative arthritis of the first metatarsophalangeal joint that progressively limits dorsiflexion and leads to joint stiffness and pain.[60] It typically arises from repetitive microtrauma or overload on the joint, with a prevalence of about 2.5% in individuals over 50 years, increasing with age.[61]Genetic predisposition may contribute, particularly in those with inherent cartilage vulnerabilities.[62]Metatarsalgia, or pain at the metatarsal heads, can occur due to a shortened first metatarsal, often termed Morton's toe variant, where the second metatarsal is relatively longer, shifting excessive weight-bearing load laterally.[63] This congenital or acquired shortening affects 20-25% of the population and predisposes individuals to overload-related discomfort under the second metatarsal head.[64]Untreated deformities of the first metatarsal, such as hallux valgus and hallux rigidus, elevate the risk of secondary osteoarthritis in the first metatarsophalangeal joint, with genetic factors implicated in up to 40% of predisposed cases across these conditions.[65] Early intervention is crucial to mitigate progression to advanced joint degeneration.[66]
Surgical interventions
Surgical interventions for the first metatarsal bone are indicated for displaced fractures, unstable deformities such as hallux valgus or hallux rigidus, and joint instability requiring fusion, aiming to restore alignment, function, and weight-bearing capacity.[67][68]For fractures, particularly those at the base or head with displacement or lack of intermetatarsal ligament support, operative treatment involves open or percutaneous reduction and internal fixation to maintain length and prevent transfer metatarsalgia.[67] Common techniques include percutaneous pinning in antegrade or retrograde fashion for minimally displaced fractures, lag screws for diaphyseal injuries, and mini-fragment plates for length-unstable or comminuted patterns at the base.[67][69][70]In cases of hallux valgus deformity, the Chevron osteotomy corrects mild to moderate intermetatarsal angles by excising a medial wedge from the distal first metatarsal, typically achieving 10-15 degrees of realignment at the metatarsophalangealjoint.[68] This procedure, often combined with lateral soft tissue release, is widely adopted for its stability and minimal invasiveness in symptomatic patients.[71] For hallux rigidus with degenerative changes, Keller arthroplasty involves excision of the base of the proximal phalanx to relieve pain and improve motion, particularly in adults with associated valgus deformity.[72] Modified versions, such as the oblique Keller with capsular interposition, preserve some joint function while addressing rigidity.[73]Tarsometatarsal joint arthrodesis, or modified Lapidus procedure, addresses instability or severe deformities by fusing the first metatarsal base to the medial cuneiform, using screws or plates for fixation and achieving union rates of 90-95%.[74][75] This fusion stabilizes the medial column and corrects alignment in cases not amenable to osteotomy alone.[76]Postoperative management typically includes non-weight-bearing or protected weight-bearing restrictions for 6-8 weeks to promote healing, with radiographic monitoring for union.[77] Complications such as non-union occur in approximately 5% of cases, often managed with revision fixation or bone grafting.[78]