Os sesamoideum distale (os naviculare)
The navicular bone (distal sesamoid) is a small, boat-shaped bone at the palmar aspect of the coffin joint. It acts as a fulcrum for the deep digital flexor tendon. Navicular disease/syndrome is one of the most common causes of chronic forelimb lameness.
Proximal sesamoid bones serve as fulcrums for the suspensory apparatus. Biaxial fractures are catastrophic, usually fatal injuries.
[Navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb) fractures are distinct from the chronic degenerative podotrochlear syndrome, although they can occur in horses with pre-existin
Navicular bursitis refers to inflammation of the navicular bursa, the small synovial structure that lies between the [DDFT](/anatomy/deep-digital-flexor) and the fibrocartilage-covered flexor surface
Erosion of the flexor surface
Navicular syndrome is a complex, progressive condition affecting the podotrochlear apparatus in the heel of the horse's foot and is one of the most common causes of chronic forelimb lameness. It invol
[Navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb) fractures are distinct from the chronic degenerative podotrochlear syndrome, although they can occur in horses with pre-existing navicular degeneration (pathological fracture through weakened bone) or lead to secondary degenerative changes. The [navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb) is small and subjected to significant forces; fractures disrupt its structural integrity and pulley function for the [DDFT](/anatomy/deep-digital-flexor). Common types include parasagittal fractures (vertical splits through the body of the bone, which may or may not involve the articular surface of the coffin joint), transverse fractures, comminuted fractures, and avulsion fractures (where the impar or collateral ligaments pull off a fragment). Fractures may be complete or incomplete, displaced or nondisplaced, and can result from acute trauma (kick, fall, awkward landing) or repetitive stress in athletes. ## Causes & Risk Factors Acute trauma or repetitive high-impact loading (jumping, racing, or sudden stops/turns). Pre-existing navicular degeneration or bone weakening increases susceptibility to pathological fracture. Poor hoof conformation or inadequate farriery may contribute indirectly by altering load distribution. Congenital bipartite or tripartite navicular bones (failure of fusion) can be mistaken for fractures on radiographs. ## Diagnosis Clinical exam and history of trauma or acute lameness change. Radiographs are primary; the 55-65 degree dorsoproximal-palmarodistal oblique view usually demonstrates the fracture line. Frog sulci must be packed with modeling compound to eliminate gas artifacts that can mimic fractures. Multiple views or repeat radiographs after several days may be needed for nondisplaced fractures. CT or MRI provides superior detail for surgical planning, assessment of displacement, articular involvement, and concurrent soft-tissue or ligament damage. ## Treatment Conservative management includes stall rest, supportive shoeing (bar shoe with heel elevation to unload the [navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb) and reduce [DDFT](/anatomy/deep-digital-flexor) tension), and bandaging for swelling. Many fractures heal with fibrous union, but residual lameness or secondary DDFT damage can occur. Surgical repair using lag screw compression is possible for suitable parasagittal fractures, ideally planned with CT guidance for precise screw placement. In chronic or complicated cases, palmar digital neurectomy may be considered after confirming limited additional apparatus damage. ## Prognosis Guarded to poor for return to full athletic function. Many horses achieve pasture soundness or limited riding comfort with conservative care. Complications include nonunion or fibrous union with ongoing pain, implant failure, secondary [coffin bone](/anatomy/coffin-bone-distal-phalanx-p3) joint osteoarthritis, [DDFT](/anatomy/deep-digital-flexor) injury during convalescence, and progression of any pre-existing degenerative changes. ## Prevention Careful workload management, especially in horses with known navicular degeneration or conformational risk factors. Use of protective boots in high-risk disciplines, good footing, and prompt veterinary attention to any foot trauma or sudden lameness change. Routine farriery to maintain balance reduces abnormal stresses. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: - Acute onset of moderate to severe lameness - Localized swelling, heat, or digital pulse elevation in the affected foot - Marked heel or frog sensitivity on hoof testers - Usually improves substantially with palmar digital nerve block - In horses with pre-existing navicular issues, may present as acute worsening of chronic low-grade lameness - Some nondisplaced or stress fractures cause more subtle, intermittent signs initially - Related conditions: [Navicular fractures](/conditions/navicular-fractures), [Navicular syndrome (podotrochlosis)](/conditions/navicular-syndrome-podotrochlosis)
Navicular bursitis refers to inflammation of the navicular bursa, the small synovial structure that lies between the [DDFT](/anatomy/deep-digital-flexor) and the fibrocartilage-covered flexor surface of the [navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb), providing lubrication and shock absorption. While bursal inflammation or effusion frequently occurs as part of the broader podotrochlear syndrome ([Navicular syndrome (podotrochlosis)](/conditions/navicular-syndrome-podotrochlosis)), primary or isolated navicular bursitis is less common. Aseptic bursitis arises from repetitive friction, strain, or biomechanical overload within the apparatus. Septic (infectious) bursitis is a distinct and serious entity, usually resulting from penetrating solar injury (nail, sharp object, or deep wound) that introduces bacteria directly into the bursa; it can rapidly progress to osteomyelitis of the [navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb) or involve adjacent structures such as the [DDFT](/anatomy/deep-digital-flexor) sheath or [coffin bone](/anatomy/coffin-bone-distal-phalanx-p3) joint. ## Causes & Risk Factors Aseptic: Repetitive stress or part of degenerative apparatus disease. Septic: Penetrating wounds to the frog or sole, especially in horses worked on uneven or debris-laden surfaces, or those with thin soles or poor hoof quality. Delayed wound care or inadequate tetanus prophylaxis increases risk. ## Diagnosis Clinical exam, history, and imaging. Ultrasound or MRI can demonstrate bursal distension, synovial thickening, or debris. For suspected septic cases, bursal fluid analysis (cytology, culture, protein) via ultrasound-guided aspiration is critical. Radiographs assess concurrent bone involvement or foreign material. Bursoscopy provides both diagnostic confirmation and therapeutic access. ## Treatment Aseptic bursitis is managed as part of the podotrochlear syndrome: corrective farriery, rest, NSAIDs, and targeted bursal or DIP joint injections. Septic bursitis demands aggressive intervention: broad-spectrum systemic antibiotics, local antimicrobial delivery (intravenous regional limb perfusion), and surgical lavage/debridement via navicular bursoscopy or bursotomy to remove infected tissue, fibrin, and debris. Drains or repeat lavages may be required. Supportive shoeing and prolonged rest follow. ## Prognosis Aseptic cases carry a similar guarded-to-fair outlook to the syndrome and often respond well to multimodal management. Septic navicular bursitis has a more guarded prognosis for athletic return, though survival and pasture soundness are achievable with prompt, aggressive treatment. Complications include chronic adhesions, navicular osteomyelitis or sequestration, spread of infection, and progressive degenerative changes. ## Prevention For aseptic: Same principles as navicular syndrome prevention. For septic: Diligent hoof care and prompt, thorough treatment of any solar penetrating wounds, including professional debridement, antibiotics when indicated, and tetanus protection. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: - Aseptic cases present similarly to navicular syndrome: heel pain, shortened stride, pointing, and positive response to blocks - Bursal effusion detectable on ultrasound or MRI - Septic cases show more acute, severe lameness, heat, swelling, and systemic signs (fever, lethargy) if infection spreads - Marked sensitivity over the frog or heel - Sometimes visible or draining tracts from a penetrating wound - Horses with septic bursitis often have a history of recent solar trauma - Related conditions: [Navicular syndrome (podotrochlosis)](/conditions/navicular-syndrome-podotrochlosis), [Cyst-like lesions of the navicular bone](/conditions/cyst-like-lesions-of-the-navicular-bone)
Erosion of the flexor surface Signs include: Consult veterinarian for specific symptoms.
Navicular syndrome is a complex, progressive condition affecting the podotrochlear apparatus in the heel of the horse's foot and is one of the most common causes of chronic forelimb lameness. It involves degeneration or injury to any combination of the [navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb), navicular bursa, [deep digital flexor tendon](/anatomy/deep-digital-flexor), and supporting ligaments rather than being a single disease of the navicular bone alone. Modern imaging has shown that soft tissue lesions often play a larger role than previously recognized. ## What it is The podotrochlear apparatus functions as an integrated unit in which the [navicular bone](/anatomy/navicular-bone-distal-sesamoid-right-forelimb) acts as a pulley for the [deep digital flexor tendon](/anatomy/deep-digital-flexor). The navicular bursa provides lubrication and cushioning between the tendon and bone, while the collateral sesamoidean ligaments and distal sesamoidean impar ligament stabilize the navicular bone. Repetitive stress from performance work, conformational factors, or poor hoof balance can lead to microdamage, inflammation, altered bone remodeling, and soft tissue degeneration within this apparatus. Current understanding recognizes that many cases involve primary lesions in the deep digital flexor tendon or bursa even when radiographs of the navicular bone appear relatively normal. The condition is almost always bilateral, though one foot is often more painful than the other. It is seen most frequently in Quarter Horses, warmbloods, and Thoroughbreds between approximately 7 and 15 years of age. ## Signs and symptoms - Bilateral forelimb lameness that is often asymmetric - Shortened stride with toe-first landing - Pointing one or both front feet forward at rest - Worsening lameness on hard ground or when circling - Positive response to palmar digital nerve blocks - Heel or frog sensitivity on hoof testers - Stiff or shuffling gait that owners sometimes mistake for shoulder lameness - Performance decline or intermittent stiffness in early stages - Contracted heels in long-standing cases ## Causes and risk factors Navicular syndrome develops from repetitive biomechanical stress on the podotrochlear apparatus. Contributing factors include poor hoof conformation (long toes, underrun heels, upright feet), inconsistent or improper farriery, high-impact disciplines, and genetic predisposition in certain breeds. The condition is multifactorial; no single cause has been identified. Horses with small feet relative to body size or those worked intensely on hard surfaces appear to be at increased risk. ## How it is diagnosed Diagnosis begins with a thorough lameness examination and diagnostic analgesia, particularly palmar digital nerve blocks. Radiographs can reveal changes in the navicular bone such as enlarged vascular channels, sclerosis, or cyst-like lesions, but many horses with significant lameness have minimal radiographic abnormalities. MRI is currently the most valuable imaging modality because it can identify soft tissue lesions in the [deep digital flexor tendon](/anatomy/deep-digital-flexor), bursa, and ligaments that are not visible on radiographs. Ultrasound and CT are used in selected cases. ## Treatment and management Treatment is multimodal and aimed at reducing pain and slowing progression rather than providing a cure. Core components include corrective farriery to improve breakover and support the heels, controlled exercise programs, and anti-inflammatory medication. Many horses benefit from targeted injections into the navicular bursa or [coffin joint](/anatomy/coffin-bone-distal-phalanx-p3) and systemic bisphosphonates to modulate bone remodeling. In refractory cases, navicular bursoscopy or palmar digital neurectomy may be considered after advanced imaging. Prognosis varies widely depending on the structures involved and how early treatment begins. Many horses can remain comfortable and functional for years with good management, though high-level athletic careers are often limited. ## When to call the vet Contact your veterinarian if your horse shows persistent forelimb stiffness, shortened stride, or pointing at rest, especially if the lameness worsens on hard surfaces or circles. Early evaluation allows for better diagnostic imaging and more effective long-term management. Do not assume the issue is simply "stiffness" or shoulder pain. ## Prevention Prevention centers on maintaining excellent hoof balance through regular professional farriery, avoiding sudden increases in workload on hard surfaces, and addressing conformational issues when possible. Early intervention at the first sign of heel-region discomfort offers the best chance of slowing disease progression. Horses with known risk factors benefit from proactive monitoring and conditioning programs. ## Frequently asked questions **Is navicular syndrome curable?** No. It is a chronic, progressive condition. Many horses can be managed successfully for years, but ongoing care is usually required. **Does my horse need an MRI for diagnosis?** Radiographs are a good starting point, but MRI provides the most complete picture of soft tissue involvement and helps guide specific treatment decisions. **Can a horse with navicular syndrome still be ridden?** Many horses return to light to moderate work with proper management. The level of return depends on the severity of lesions and response to treatment. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Bilateral forelimb lameness that is often asymmetric; shortened stride with toe-first landing; pointing one or both front feet forward at rest; worsening lameness on hard ground or when circling; positive response to palmar digital nerve blocks; heel or frog sensitivity on hoof testers; stiff or shuffling gait that owners sometimes mistake for shoulder lameness; performance decline or intermittent stiffness in early stages; contracted heels in long-standing cases
Proximal sesamoid bones serve as fulcrums for the suspensory apparatus. Biaxial fractures are catastrophic, usually fatal injuries.
See the Navicular Bone / Distal Sesamoid (Left Forelimb) on our interactive 3D horse model. Open 3D Model