Navicular syndrome (also termed navicular disease, podotrochlear syndrome, or palmar foot pain) represents a chronic, progressive degenerative condition affecting the podotrochlear apparatus of the equine foot.
Overview and Clinical Importance
Navicular syndrome (also termed navicular disease, podotrochlear syndrome, or palmar foot pain) represents a chronic, progressive degenerative condition affecting the podotrochlear apparatus of the equine foot. This syndrome accounts for approximately one-third of all chronic forelimb lameness cases in horses and is one of the most commonly tested equine lameness topics on the NAVLE examination.
The condition primarily affects the forelimbs and is almost always bilateral, though one limb is typically more severely affected. Understanding the anatomy, pathophysiology, diagnosis, and treatment of navicular syndrome is essential for NAVLE success.
| Structure |
Description and Clinical Significance |
| Navicular Bone |
Also called distal sesamoid bone. Boat-shaped bone located palmar to the DIP joint between P2 and P3. Acts as a fulcrum for the DDFT. |
| Deep Digital Flexor Tendon (DDFT) |
Runs down palmar aspect of limb, wraps around navicular bone, inserts on solar surface of P3. DDFT lesions are common and significantly affect prognosis. |
| Navicular Bursa |
Synovial structure between flexor surface of navicular bone and DDFT. Reduces friction during movement. Commonly injected for diagnosis/treatment. |
| Collateral Sesamoidean Ligaments (CSL) |
Paired ligaments attaching proximal border of navicular bone to P1. Suspensory ligaments of navicular bone. Injury seen in 25% of horses with foot pain. |
| Distal Sesamoidean Impar Ligament (DSIL) |
Single unpaired ligament attaching distal border of navicular bone to P3. One of the most commonly injured structures (25% of cases). |
| Distal Interphalangeal Joint (DIP) |
Coffin joint. Navicular bone forms part of this joint. DIP injection may partially desensitize navicular structures. |
Anatomy of the Podotrochlear Apparatus
The podotrochlear apparatus (navicular apparatus) is a complex of structures located in the palmar aspect of the equine foot. Understanding this anatomy is critical for interpreting diagnostic findings and planning treatment.
Key Structures
High-YieldMRI studies show only 8.8% of horses with foot pain have primary navicular bone injuries. More commonly affected: DSIL/CSL (25.6%), DDFT (9.8%), or combined pathology (13.1%). This explains why "navicular disease" has evolved to "navicular syndrome."
| Higher Risk Breeds |
Lower Risk Breeds |
| Quarter Horses, Thoroughbreds, Warmbloods, Standardbreds, Paint Horses, Appaloosas |
Arabians, Friesians, Ponies (rarely affected) |
Etiology and Risk Factors
Proposed Pathophysiological Theories
Biomechanical Theory (Most Supported): Repetitive mechanical stress causes cumulative damage to navicular bone and supporting structures. Compression from DDFT and concussive forces lead to cartilage degeneration, bone remodeling, and soft tissue injury.
Vascular Theory: Proposed thrombosis or arteriosclerosis of navicular arteries causing ischemic necrosis. Less supported by current evidence.
Breed Predispositions
Risk Factors and Conformational Predispositions
- Age: Most commonly diagnosed 7-14 years; peak incidence at 9 years
- Conformation: Small feet relative to body size, upright pasterns, long toe/low heel, broken-back hoof-pastern axis
- Work type: High-concussion activities (jumping, cutting, reining, roping), hard surfaces
- Hoof care: Irregular farrier care, hoof imbalance, underrun heels, contracted heels
NAVLE TipNAVLE commonly tests breed predisposition. Remember: Quarter Horses and Thoroughbreds = HIGH risk; Arabians = LOW risk. Mnemonic: "QT horses get Navicular" (Quarter horses, Thoroughbreds).
| Clinical Finding |
Description |
| Lameness Pattern |
Bilateral forelimb lameness (usually asymmetric); insidious onset; progressive; intermittent early, persistent later |
| Gait Abnormalities |
Short, choppy stride; shuffling gait; stumbling; toe-first landing (heel avoidance); difficulty turning sharply |
| Pointing |
Affected limb held forward at rest to reduce heel pressure |
| Worsening Factors |
Hard surfaces, downhill work, tight circles, lunging |
| Hoof Tester Response |
Pain over central sulcus of frog, heel region; not always present |
| Flexion Tests |
Positive to distal limb flexion; exacerbated by toe wedge test |
Clinical Signs and Presentation
Classic Presentation
High-YieldOwners often mistakenly think lameness originates from the shoulder due to shortened stride. When bilateral navicular is present, blocking one foot often reveals lameness in the contralateral limb.
| Block |
Interpretation |
| Palmar Digital Block |
90% or greater improvement in lameness = pain localized to palmar foot. Not specific for navicular bone alone. |
| DIP Joint Block |
May partially desensitize navicular structures. Improvement suggests DIP joint involvement or shared innervation. |
| Navicular Bursa Injection |
More specific for navicular apparatus. Improvement indicates bursal or DDFT/navicular bone involvement. |
Diagnostic Approach
Diagnostic Analgesia (Nerve Blocks)
The palmar digital nerve block (PD block) is the cornerstone of navicular syndrome diagnosis. This block desensitizes the entire palmar third of the foot including the navicular bone, navicular bursa, heels, bars, sole, and DDFT within the hoof capsule.
NAVLE TipFor NAVLE, remember that positive PD block = heel pain, NOT specifically navicular bone disease. MRI is required to determine exactly which structure is affected.
Diagnostic Imaging
Radiography
Standard radiographic views for navicular evaluation include: Lateromedial (LM), Dorsoproximal-palmarodistal oblique (upright navicular), and Palmaroproximal-palmarodistal oblique (skyline navicular).
High-YieldCRITICAL for NAVLE: Radiographic changes do NOT always correlate with clinical signs. Horses can have significant changes without lameness, and horses with severe pain may have normal radiographs. MRI provides superior soft tissue evaluation.
MRI (Gold Standard)
MRI is the gold standard for navicular syndrome diagnosis because it visualizes both bone and soft tissue structures. Studies show 86% of horses with normal radiographs have MRI-detectable abnormalities.
MRI Findings in Horses with Recent-Onset Navicular Syndrome (Normal Radiographs):
- Navicular bone signal abnormality: 33% (most severe finding)
- DDFT pathology: 18%
- Collateral sesamoidean ligament: 15%
- Distal sesamoidean impar ligament: 10%
- Multiple abnormalities: 18%
- No abnormalities detected: 5%
| Radiographic Finding |
Clinical Significance |
| Enlarged Synovial Invaginations |
Distal border radiolucencies (lollipops). May be normal variant but increased number/size associated with disease. |
| Medullary Sclerosis |
Increased medullary opacity with loss of corticomedullary distinction. Indicates chronic bone remodeling. |
| Flexor Cortex Erosions |
Lucencies in palmar cortex. Significant finding indicating DDFT-bone interface damage. |
| Enthesiophytes |
New bone at proximal border (CSL insertion). Indicates chronic ligament stress. |
| Distal Border Fragments |
May be developmental or degenerative. Clinical significance depends on associated soft tissue changes. |
Treatment and Management
Key principle: Treatment is palliative, not curative. Goals are pain relief, slowing disease progression, and maintaining function. Treatment must be individualized based on specific structures affected.
Corrective Shoeing (First-Line Treatment)
Proper farriery is the cornerstone of navicular syndrome management and accounts for the majority of improvement seen with treatment. Goals include reducing breakover, supporting the heel, and restoring proper hoof-pastern axis.
Medical Management
High-YieldBisphosphonates (Tildren, Osphos) are FDA-approved ONLY for horses 4 years or older. Contraindications: renal disease, concurrent NSAID use (avoid NSAIDs from 48 hours before to 24 hours after).
Surgical Treatment
Palmar Digital Neurectomy (PDN)
Neurectomy is a salvage procedure reserved for horses that fail medical management. It involves surgical transection and removal of a segment of the palmar digital nerves.
NAVLE TipCRITICAL NAVLE POINT: Neurectomy is CONTRAINDICATED in horses with DDFT core or linear lesions (high risk of tendon rupture). MRI evaluation before neurectomy is essential. Median sound period is 20 months post-surgery.
| Shoeing Modification |
Mechanism and Application |
| Rolled/Rockered Toe |
Eases breakover, reduces DDFT tension and compressive force on navicular bone |
| Egg Bar Shoes |
Provides caudal heel support, distributes load, reduces force on navicular bone. More effective than natural balance shoes. |
| Wedge Pads (2-4 degrees) |
Raises heel, reduces DDFT tension. NOTE: 1 degree decrease in palmar angle = 4-fold increase in navicular bone force. |
| Set Shoe Back |
Positioning shoe palmarly decreases breakover distance |
Prognosis
Exam Focus: Overall prognosis is GUARDED TO FAIR. Navicular syndrome is progressive and typically requires lifelong management. Horses with DDFT lesions have significantly shorter lameness resolution after any treatment.
| Treatment |
Dosing |
Notes |
| NSAIDs |
Phenylbutazone 2.2-4.4 mg/kg PO q12-24h; Firocoxib 0.1 mg/kg PO q24h |
Symptomatic relief. Avoid with bisphosphonates. |
| Tiludronate (Tildren) |
1 mg/kg IV slow infusion over 90 minutes |
FDA-approved for navicular. Peak effect 6-8 weeks. |
| Clodronate (Osphos) |
1.8 mg/kg IM divided into 3 sites |
FDA-approved for navicular. May cause injection site soreness. |
| DIP Joint Injection |
Triamcinolone 6-12mg or Betamethasone with/without HA |
May diffuse to navicular region. |
| Navicular Bursa Injection |
Corticosteroid plus hyaluronic acid |
Requires imaging guidance. |
Memory Aids for NAVLE
"NAVICULAR" Mnemonic for Clinical Signs:
N = Negative to frog pressure (variable)
A = Asymmetric bilateral forelimb lameness
V = Variable intensity (intermittent early)
I = Improvement with PD nerve block
C = Circles and hard surfaces worsen
U = Upright pasterns predispose
L = Landing toe-first (heel avoidance)
A = Appears as shoulder lameness to owner
R = Radiographs may be normal despite pain
"PALMAR" Mnemonic for Treatment:
P = Proper shoeing (first-line)
A = Anti-inflammatories (NSAIDs)
L = Limited activity/rest
M = Medication (bisphosphonates, joint injections)
A = Assess with MRI before surgery
R = Resect nerves as last resort (neurectomy)
| Prerequisites |
Complications |
| Complete lameness resolution with PD block
Failed medical management
MRI evaluation (NO significant DDFT damage)
Client understands risks |
Painful neuroma formation (36%)
Nerve regrowth (1-2 years)
DDFT rupture (if pre-existing damage)
DIP joint luxation
Undetected hoof infections |
| Treatment |
Expected Outcome |
| Conservative Management |
Approximately 50% of horses remain useably sound for 1 year regardless of treatment. Disease is progressive. |
| Corrective Shoeing |
30% improvement in lameness with proper trimming/shoeing |
| Bisphosphonates |
70-80% improved at 56 days (best in recently diagnosed cases). Effect lasts up to 6 months. |
| Neurectomy |
88-92% sound at 1 year. Median 20 months lameness-free. 36% develop complications. |