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Navicular bone
Navicular bone
Navicular bone
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Navicular bone
Bones of the human foot, with navicularis labeled at upper left in image.
Details
Identifiers
Latinos naviculare
TA98A02.5.12.001
TA21484
FMA24499
Anatomical terms of bone

The navicular bone /nəˈvɪkjʊlər/ is a small bone found in the feet of most mammals.

Human anatomy

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The navicular bone in humans is one of the tarsal bones, found in the foot. Its name derives from the human bone's resemblance to a small boat, caused by the strongly concave proximal articular surface. The term navicular bone or hand navicular bone was formerly used for the scaphoid bone,[1] one of the carpal bones of the wrist.

The navicular bone in humans is located on the medial side of the foot, and articulates proximally with the talus, distally with the three cuneiform bones, and laterally with the cuboid.

It is the last of the foot bones to start ossification and does not tend to do so until the end of the third year in girls and the beginning of the fourth year in boys, although a large range of variation has been reported.[2]

Navicular bone. Superior view.
Navicular bone. Inferior view.
Fracture of the navicular bone

The tibialis posterior is the only muscle that attaches to the navicular bone. The main portion of the muscle inserts into the tuberosity of the navicular bone.[3] An accessory navicular bone may be present in 2–14% of the general population.[4][5][6]

Clinical significance

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The human navicular is not a commonly broken bone but it breaks due to two reasons. The first mechanism is a stress fracture which happens commonly in athletes,[7] and the other mechanism is a high energy trauma.

The navicular bone is a keystone of the foot: it is part of the coxa pedis and articulates with the talus, first, second and third cuneiform, cuboid and calcaneus. It plays an important role in the biomechanics of the foot, helping in inversion, eversion, and motion; it is a structural link between midfoot and forefoot and it is part of the longitudinal and transverse arch of the foot.

Horse anatomy

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Main article: Navicular syndrome

The horse has a sesamoid bone called the navicular bone, located within the hoof, that lies on the palmar aspect of the coffin joint between the second phalanx and third phalanx (coffin bone). The navicular bone in the horse is supported by the distal sesamoidean impar ligament and two collateral sesamoidean ligaments. The navicular bursa is located between the flexor surface of the navicular bone and the deep digital flexor tendon, which runs between the bursa and the distal phalanx.[8] The central tarsal bone in the hock of the horse is homologous and analogous to the navicular bone of the human foot, and thus the navicular bone in the horse is a different structure from the eponymously labeled bone in humans.[9]

The navicular region is an important structure in relation to lameness, particularly in the front feet, and is involved with a significant disease process called navicular disease or navicular syndrome. Recently much of the original literature concerning navicular disease has been called into question, particularly the significance of radiographic changes as a sole diagnostic criterion.[10] Navicular syndrome may be responsible for as much as 1/3 of all cases of lameness in horses, but radiographic changes in the navicular bone do not always provide a definitive diagnosis. Newer imaging techniques have shown that damage to the soft tissues in the region may be significant contributors to lameness and that multiple causes may result in visible lameness.[8]

See also

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Notes

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Navicular bone

View on Grokipedia
from Grokipedia
The navicular bone, also known as the distal , is an important tarsal found in the feet of humans and many animals, including horses. In humans, it is a wedge-shaped situated in the midfoot, serving as a key component in the transverse arch and medial longitudinal arch. It articulates proximally with the head of the talus via a concave surface that contributes to the acetabulum pedis of the , and distally with the three anteriorly and the laterally, forming syndesmotic joints that enhance foot stability. The bone's medial surface features a prominent tuberosity for the insertion of the tibialis posterior , which is essential for foot inversion and arch support. In horses, the navicular bone is a small, boat-shaped bone located within the capsule, behind the , acting as a fulcrum for the deep digital flexor to guide its insertion and reduce friction during locomotion. Structurally, the navicular bone possesses four sides—anterior (articular for cuneiforms), posterior (non-articular), dorsal (convex), and plantar (with a groove for the of flexor hallucis longus)—along with distinct medial and lateral ends. Its blood supply primarily arises from branches of the dorsally and the medial plantar artery plantarly, though the central third of the bone receives limited vascularization, rendering it susceptible to ischemic conditions such as osteonecrosis. Innervation is mediated by the ventrally and the deep peroneal nerve dorsally, supporting sensory and proprioceptive functions in the midfoot. Functionally, the human navicular bone transmits weight from the talus to the forefoot during , absorbs shock, and maintains the foot's arched architecture critical for bipedal locomotion and efficient propulsion. The tibialis posterior tendon's attachment to its tuberosity reinforces the medial arch, preventing excessive pronation. Clinically, the navicular is prone to stress fractures, which account for approximately one-third of all tarsal stress injuries and carry a high risk of due to poor vascularity; these often occur in athletes or from repetitive impact. Accessory navicular bones, present in 4% to 21% of the population, represent a congenital variant that may lead to pain or flatfoot if symptomatic. Other notable pathologies include (avascular in children) and Müller-Weiss syndrome (spontaneous osteonecrosis in adults), both highlighting the bone's vulnerability to vascular compromise.

Structure

In humans

The navicular bone is a boat-shaped tarsal bone located on the medial side of the midfoot, between the talus proximally and the cuneiform bones distally. It has four surfaces: the anterior surface is convex and kidney-shaped, subdivided into three facets by dorsoplantar crests that articulate with the medial, intermediate, and lateral cuneiform bones; the posterior surface is concave and covered in cartilage, articulating with the head of the talus to form part of the acetabulum pedis in the talocalcaneonavicular joint; the dorsal surface is convex and provides attachments for capsular and ligamentous structures; and the plantar surface is irregular, featuring a medial tuberosity (navicular tuberosity) for the insertion of the tibialis posterior tendon and other plantar ligaments. The medial end includes the prominent tuberosity and may present an accessory navicular ossicle as a congenital variant, while the lateral end has a superior segment for the medial calcaneonavicular ligament and an inferior segment that connects ligamentously to the cuboid bone. The bone's blood supply is derived mainly from 3-5 dorsal branches of the supplying the dorsum and an anastomotic network from the medial plantar artery on the plantar aspect, with the central third receiving limited vascularization via nutrient arteries entering the medial and lateral aspects. Innervation is provided by the deep peroneal nerve dorsally and the plantarly. The navicular is the last tarsal bone to ossify, typically between ages 3-5 years.

In horses

The navicular bone in horses, also called the distal sesamoid bone, is a small, flat, boat-shaped structure embedded within the hoof capsule on the palmar (forelimb) or plantar (hindlimb) aspect of the distal interphalangeal (coffin) joint. It features two main surfaces: the flexor surface, which faces the deep digital flexor tendon (DDFT) and is covered in fibrocartilage with a central eminence or ridge that guides the tendon; and the articular surface, comprising hyaline cartilage-covered facets—a larger proximal facet conforming to the condyles of the middle phalanx and a smaller distal facet articulating with the distal phalanx, often parallel but sometimes convergent. The bone has two borders: the proximal border, which is smoothly marginated and attaches to the paired suspensory ligaments of the navicular bone originating from the proximal phalanx; and the distal border, which includes variable cone-shaped synovial invaginations (fossae) and a central projection connecting to the distal sesamoidean impar ligament that extends to the distal phalanx deep to the DDFT. The medial and lateral extremities are bluntly pointed and symmetric, serving as attachments for the suspensory ligaments and containing nutrient foramina. The navicular bone ossifies from a single center and is stabilized by the collateral sesamoidean ligaments and the navicular bursa, which lies between the flexor surface and the DDFT. Its blood supply enters primarily through the proximal and distal borders via vessels traversing the attached ligaments, ramifying into the and synovial structures.

Function

In humans

The navicular bone plays a crucial role in the of the foot by forming a key part of the medial longitudinal and transverse arches, which provide shock absorption and distribute weight during . It articulates proximally with the talus head in the , forming the pedis, and distally with the three via syndesmotic joints that enhance midfoot stability. The prominent medial tuberosity serves as the primary insertion site for the tibialis posterior tendon, which inverts the foot and supports the medial arch to prevent excessive pronation. During locomotion, the navicular transmits forces from the hindfoot to the forefoot, facilitates smooth articulation, and contributes to efficiency in bipedal movement.

In horses

In horses, the navicular bone functions as a within the navicular apparatus, primarily acting as a fulcrum for the deep digital flexor (DDFT) to maintain a constant angle of insertion onto the distal phalanx (), thereby optimizing force transmission during weight-bearing and flexion of the digit. Its fibrocartilage-covered flexor surface provides a low-friction gliding interface for the DDFT, reducing wear and minimizing energy expenditure in the tendon's action. The bone, along with its suspensory and impar ligaments, helps dissipate compressive and shear forces in the , supporting the stay apparatus for efficient locomotion and stability on varied terrain. This organ adaptation at the bone- interface is essential for the horse's ability to stand and move with minimal fatigue.

Clinical significance

In humans

Stress fractures of the navicular bone are a common overuse injury in athletes, particularly runners and dancers, resulting from repetitive hyperextension and plantarflexion forces that lead to avulsion and partial sagittal-plane fractures. These injuries often present with insidious midfoot pain that worsens with activity, and due to the bone's role in supporting the medial longitudinal arch, overload during high-impact sports increases susceptibility. Diagnosis is frequently delayed because initial radiographs may appear normal, but advanced imaging confirms the fracture line. Nonoperative management includes immobilization and non-weight-bearing for 6-8 weeks, though surgical screw fixation is recommended for complete or displaced fractures to promote union and allow return to sport within 4-6 months. Accessory navicular syndrome arises from a symptomatic accessory ossicle, known as os tibiale externum, which is a congenital variant present in 10-14% of the and causes medial foot due to inflammation at the posterior tibial insertion. The condition typically manifests in or early adulthood with swelling, tenderness along the medial arch, and exacerbated by activities. While many cases remain , symptomatic ones disrupt function and may contribute to flatfoot if untreated. Kohler's disease, a form of , primarily affects children aged 4-6 years, leading to ischemia of the navicular bone that causes flattening, sclerosis, and fragmentation on , often resulting in a and midfoot . It is more common in boys and typically involves the dorsal-central portion of the bone due to its late . The condition is self-limiting, with most cases resolving within 2-3 years through conservative measures such as casting or to relieve pressure and promote , avoiding long-term sequelae like persistent flattening. Mueller-Weiss syndrome, also called spontaneous osteonecrosis of the navicular, occurs in adults over 40, often bilaterally, and features subchondral collapse and fragmentation that produce severe midfoot pain and hindfoot deformity. Predominantly affecting women, it presents with progressive swelling and instability, mimicking other midfoot pathologies. The comma-shaped navicular on radiographs indicates advanced disease, and while the remains idiopathic, vascular compromise is implicated. Diagnosis of navicular bone disorders relies on clinical history and imaging, with MRI preferred for detecting inflammation, bone marrow , and early stress changes, while CT excels in delineating bony details like extent or fragmentation. Treatments vary by but generally start conservatively with , immobilization, and activity modification; refractory cases, such as symptomatic accessory navicular or nonunion stress fractures, may require surgical excision or fusion to alleviate pain and restore function. Rarely, the navicular bone can be involved in tumors like , a benign causing nocturnal relieved by NSAIDs, or infections such as , which presents with insidious swelling and may require for confirmation. These conditions are uncommon in the foot but can mimic other disorders, necessitating histopathological evaluation for targeted therapy like for or antitubercular drugs for infection.

In horses

Navicular , also known as palmar foot or podotrochlosis, is a chronic, progressive condition causing lameness in , primarily affecting the navicular bone, its , the deep digital flexor tendon (DDFT), and supporting ligaments within the . It accounts for approximately 20-35% of chronic forelimb lameness cases in aged 4-15 years, with higher incidence in among Quarter Horses and Thoroughbreds. Risk factors include conformational issues such as long toes with low heels, upright pasterns, or small hooves relative to body size, which increase biomechanical stress on the navicular apparatus; additionally, geldings are overrepresented, and heavy workloads in performance disciplines exacerbate susceptibility. The pathophysiology centers on vascular compromise and chronic mechanical overload at the navicular bone-tendon interface, conceptualized as an organ designed to dissipate compressive and shear forces through transitions between the DDFT and bone. This leads to medullary sclerosis, with formation on the flexor surface, , and DDFT desmitis, often resembling with subchondral bone changes and synovial proliferation. Proposed etiologies include ischemia from vascular , repetitive trauma causing flexor pressure, and degenerative , resulting in progressive heel pain and altered to offload the caudal foot. Diagnosis relies on clinical history of bilateral forelimb lameness worsened by exercise on hard surfaces, confirmed by a positive distal limb flexion test that accentuates heel pain upon release, and palmar digital nerve blocks that abolish lameness, localizing pain to the navicular region. Radiographic findings typically show enlarged or irregular synovial fossae (vascular channels), cortical lucencies or irregularities on the flexor surface, and proximal border syndrome with enthesophytes, though these are not pathognomonic and may appear in asymptomatic horses. Advanced imaging via MRI reveals soft tissue involvement, such as DDFT tears or desmitis and ligamentous damage, providing definitive evidence in ambiguous cases. Differential diagnoses include deep digital flexor tendonitis, which may mimic navicular pain but shows primary tendon lesions on ultrasound; heel abscesses or bruises causing acute rather than chronic lameness; and distal interphalangeal joint (coffin joint) pathology, differentiated by intra-articular blocks. Management focuses on to alleviate pain and address underlying , starting with corrective farriery such as rolled toes, wedge pads, or egg-bar shoes to improve hoof balance and reduce strain, often combined with rest and non-steroidal anti-inflammatory drugs (NSAIDs) like for inflammation control. Bisphosphonates, such as clodronate or tiludronate, inhibit and are effective for cases with active remodeling, providing relief for 6-12 months in many . As a last resort for refractory cases, palmar digital severs sensory nerves to the , yielding short-term improvement in up to 80% of , though complications like nerve regrowth and return of lameness occur within 1-2 years. Prognosis is guarded to fair, with approximately 50-60% of horses showing clinical improvement through and medical management, allowing return to light work, though progression to severe degeneration limits athletic careers in 30-40% of cases. Prevention emphasizes regular hoof trimming for balance, gradual conditioning to avoid overload, and early screening in at-risk breeds. Historically, navicular syndrome has been recognized since the , initially described in as bone changes linked to lameness, evolving in the to include soft tissue roles; modern understanding, informed by MRI since the , highlights the organ model at the bone-tendon interface as key to its degenerative process.

References

  1. https://www.ncbi.nlm.nih.gov/books/NBK547675/
  2. https://extension.usu.edu/equine/research/equine-navicular-syndrome
  3. https://veteriankey.com/the-equine-navicular-bone/
  4. https://open.lib.umn.edu/largeanimalsurgery/chapter/navicular-syndrome/
  5. https://pmc.ncbi.nlm.nih.gov/articles/PMC8251969/
  6. https://www.aafp.org/pubs/afp/issues/2003/0101/p85.html
  7. https://pubmed.ncbi.nlm.nih.gov/8153501/
  8. https://www.foothealthfacts.org/article/athletes-listen-to-your-body
  9. https://pubmed.ncbi.nlm.nih.gov/17144953/
  10. https://www.hss.edu/health-library/conditions-and-treatments/list/accessory-navicular
  11. https://posna.org/physician-education/study-guide/accessory-navicular
  12. https://pmc.ncbi.nlm.nih.gov/articles/PMC6604528/
  13. https://www.ncbi.nlm.nih.gov/books/NBK507831/
  14. https://rarediseases.org/rare-diseases/kohler-disease/
  15. https://www.stlouischildrens.org/conditions-treatments/kohler-disease
  16. https://rarediseases.org/rare-diseases/mueller-weisse-disease/
  17. https://radiopaedia.org/articles/muller-weiss-syndrome
  18. https://ajronline.org/doi/10.2214/AJR.15.15843
  19. https://ajronline.org/doi/10.2214/ajr.160.1.8416606
  20. https://pmc.ncbi.nlm.nih.gov/articles/PMC9213275/
  21. https://pmc.ncbi.nlm.nih.gov/articles/PMC4712193/
  22. https://www.vetmed.auburn.edu/wp-content/uploads/2015/01/PV1110_waguespack_Surgical-1.pdf
  23. https://vet.purdue.edu/esmc/documents/EHU_Winter_2019.pdf
  24. https://pubmed.ncbi.nlm.nih.gov/833042/
  25. https://ker.com/equinews/navicular-syndrome-horses/
  26. https://www.merckvetmanual.com/musculoskeletal-system/disorders-of-the-foot-in-horses/navicular-syndrome-in-horses
  27. https://www.vetmed.msstate.edu/sites/www.vetmed.msstate.edu/files/presentations/10.20.17%2520Equine%2520Navicular%2520Syndrome%2520%2528Hannah%2520Plaugher%2529.pdf
  28. https://pubmed.ncbi.nlm.nih.gov/10779069/
  29. https://pubmed.ncbi.nlm.nih.gov/21882161/
  30. https://www.lsuagcenter.com/articles/page1744919611234
  31. https://nebraskaequine.com/storage/app/media/OsPhos-Tildren_October_2015.pdf
  32. https://www.vetfolio.com/learn/article/surgical-views-treating-navicular-syndrome-in-equine-patients
  33. https://madbarn.com/navicular-syndrome-in-horses/
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