Musculus flexor digitorum profundus
The deep digital flexor (DDF) has three heads in the forelimb: humeral (from the medial epicondyle of the humerus), ulnar (from the olecranon), and radial (from the caudal radius). These unite into a single tendon that runs down the back of the limb, receives the accessory (inferior check) ligament from the carpus, passes through the sleeve formed by the superficial digital flexor, and inserts on the flexor surface of the coffin bone (distal phalanx, P3). Innervation is via the median and ulnar nerves. In the foot the tendon passes over the navicular bone (which acts as a pulley) and is separated from it by the navicular bursa. Its dorsal surface in this region is fibrocartilaginous to resist compression. The muscle/tendon unit flexes the coffin joint and digit and provides critical passive support during stance via the check ligament and the stay apparatus. Lesions of the DDFT (deep digital flexor tendon) within the digital flexor tendon sheath or navicular bursa are among the most common soft-tissue causes of foot lameness.
Origin: Medial epicondyle of humerus, olecranon, and caudal radius (three heads)
Insertion: Palmar surface of the distal phalanx (coffin bone, P3)
Action: Flexes the coffin joint and digit; supports the limb during stance
Innervation: Median and ulnar nerves (C8-T2)
DDFT tendinopathy is highly significant, especially in the podotrochlear region. Core lesions, sagittal splits, and dorsal abrasions are common MRI findings. Navicular bursitis frequently accompanies DDFT lesions. Ultrasound (including transcuneal) and MRI are the primary imaging modalities. Treatment ranges from rest and regenerative therapies to navicular bursoscopy.
## Overview Lesions of the deep digital flexor tendon (DDFT) within the hoof capsule are a common cause of chronic foot lameness. These include core lesions, dorsal border tears, and insertional inju
## Overview Tendinitis of the deep digital flexor tendon (DDFT) in the metacarpal (cannon) region is less common than superficial digital flexor tendon injury but still clinically important. Swelling
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
Persistent heel pain, a shortened stride, or lameness that improves with rest but returns with work often involves the DDFT or related structures. Have a veterinarian localize the pain rather than assuming it is “just navicular.” Sudden severe lameness after a misstep can indicate a tear.
## Overview Lesions of the deep digital flexor tendon (DDFT) within the hoof capsule are a common cause of chronic foot lameness. These include core lesions, dorsal border tears, and insertional injuries, most often identified by magnetic resonance imaging (MRI) because they lie beyond the reach of ultrasound. ## Causes Repetitive loading as the tendon passes over the navicular bone, combined with degenerative change or acute overload. Concurrent navicular bone or ligament pathology is frequent. ## Diagnosis Lameness that improves with palmar digital nerve block but may not fully block to the coffin joint. MRI gives the most complete characterization of lesion type, size, and associated structures; CT can also identify some DDFT lesions. ## Treatment Rest, corrective shoeing, anti-inflammatories, and intralesional or navicular bursa therapies. Selected cases undergo bursoscopy or other surgical debridement. Rehabilitation is prolonged. ## Recovery and Prognosis Guarded to fair. Many horses return to a lower level of work; extensive or multifocal lesions carry a poorer outlook. ## Prevention Early management of foot balance and workload in at-risk performance horses. Signs include: chronic low-grade forelimb lameness; positive palmar digital nerve block; worse on soft footing; intermittent or waxing and waning lameness
## Overview Tendinitis of the deep digital flexor tendon (DDFT) in the metacarpal (cannon) region is less common than superficial digital flexor tendon injury but still clinically important. Swelling is often less obvious because the tendon lies deep to other structures. Ultrasound is required for diagnosis. ## Causes Overload, often in performance horses. May occur with or without concurrent superficial digital flexor tendon injury. ## Diagnosis Lameness, pain on deep palpation, and ultrasound demonstration of fiber disruption or core lesions within the DDFT. ## Treatment Rest and controlled, ultrasound-guided rehabilitation similar to other flexor tendon injuries. Adjunctive therapies are sometimes used. ## Recovery and Prognosis Fair to guarded, depending on lesion size. Re-injury risk exists. ## Prevention Gradual conditioning and monitoring for early heat or sensitivity. Signs include: swelling deep in the palmar metacarpal region; pain on deep palpation; lameness; ultrasound evidence of tendon damage
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
DDFT tendinopathy is highly significant, especially in the podotrochlear region. Core lesions, sagittal splits, and dorsal abrasions are common MRI findings. Navicular bursitis frequently accompanies DDFT lesions. Ultrasound (including transcuneal) and MRI are the primary imaging modalities. Treatment ranges from rest and regenerative therapies to navicular bursoscopy.
Persistent heel pain, a shortened stride, or lameness that improves with rest but returns with work often involves the DDFT or related structures. Have a veterinarian localize the pain rather than assuming it is “just navicular.” Sudden severe lameness after a misstep can indicate a tear.
See the Deep Digital Flexor on our interactive 3D horse model. Open 3D Model