Navicular Disease: Modern Understanding
Navicular disease is now understood as a broader syndrome of palmar foot pain, with many contributing factors beyond just the navicular bone.
Diagnostic Approach for Palmar Foot Pain
Diagnostic Imaging Options
| Diagnostic Tool | What It Shows | When Used |
|---|---|---|
| Hoof testers | Pain response in frog/heel | Initial exam |
| Nerve blocks | Localizes pain to palmar foot | Diagnostic phase |
| Radiographs | Navicular bone changes, DJD | Standard imaging |
| MRI | Soft tissue, DDFT lesions | Advanced cases |
| CT | 3D bone detail, cysts | Pre-surgical |
Navicular Disease Management
| Use corrective shoeing — egg bar or rolled toe shoes | |
| Provide deep, forgiving footing in turnout areas | |
| Provide moderate, controlled exercise | |
| Consider NSAIDs for acute flare-ups (under vet guidance) | |
| Investigate with MRI if standard diagnostics are inconclusive | |
| Assume navicular disease is a death sentence — many horses return to work | |
| Skip MRI if initial imaging is negative — soft tissue lesions are common | |
| Work on hard ground during acute episodes | |
| Rely solely on stall rest — controlled movement aids healing |
The term 'navicular disease' is being replaced by 'palmar foot pain syndrome' because it more accurately describes the multifactorial nature of the condition.
MRI has revolutionized diagnosis of palmar foot pain — deep digital flexor tendon (DDFT) injuries and collateral ligament desmitis are now identified where they were previously missed.
"Navicular disease" is a term that has largely been replaced in equine medicine by the broader concept of palmar foot pain syndrome (PFPS) or caudal heel pain -- a recognition that the original diagnosis oversimplified a complex of conditions affecting multiple structures in the back third of the horse's foot. The navicular bone is one possible site of pathology, but the navicular bursa, deep digital flexor tendon, impar ligament, and collateral sesamoidean ligaments are all involved to varying degrees in horses with caudal foot pain. Modern imaging -- MRI in particular -- has transformed diagnosis and treatment planning.
| Structure Affected | Diagnostic Tool | Primary Treatment |
|---|---|---|
| Navicular bone | MRI (standing low-field) or radiograph | Bisphosphonates + remedial farriery |
| Deep digital flexor tendon | MRI — radiographs miss DDFT lesions | Bursal injection; guarded prognosis |
| Navicular bursa | MRI + intrathecal nerve block | Intrathecal corticosteroid injection |
What Was Wrong With "Navicular Disease"
For most of the 20th century, navicular disease was diagnosed based on radiographic changes to the navicular bone (caudal cortical lysis, "lollipop" lesions, synovial invaginations) combined with clinical signs of heel pain. The problem: many horses with radiographic navicular changes showed no lameness, while many lame horses with positive palmar nerve blocks had normal navicular radiographs. The diagnosis was imprecise.
High-field MRI studies of horses with caudal heel pain (Dyson et al., Animal Health Trust) demonstrated that the primary pathology varied widely: some horses had primarily navicular bone changes; others had deep digital flexor tendon lesions at the navicular level; others had primarily bursal or ligament pathology. Lumping all of these under one name led to poorly targeted treatments and variable outcomes.
Clinical Signs
Horses with palmar foot pain show a characteristic bilateral forelimb lameness -- short, choppy stride, worse on circles, on hard surfaces, and when the toe is elevated (positive hoof testers across the heel). Toe-first landing (avoiding heel impact) is a behavioral indicator. The condition is almost exclusively forelimb; hindlimb navicular pathology occurs but is uncommon.
Lameness is often mild to moderate -- Grade 2--3 on the AAEP 5-point scale. It may be noticed after work, improve with warm-up (classic "warming out" pattern), and worsen with strenuous work or hard surfaces.
Diagnosis
Nerve blocks confirm the location of pain (palmar digital nerve blocks eliminate pain from the caudal heel region). Radiographs identify bony changes but have limited sensitivity for soft tissue pathology. MRI is the gold standard: it identifies the specific structures involved, guiding targeted treatment. Standing low-field MRI units at many referral facilities allow assessment of the foot without general anesthesia.
Treatment
Treatment is tailored to the pathology identified. Remedial farriery is the cornerstone for all palmar foot pain cases: egg-bar shoes, heart-bar shoes, or wide-web shoes with appropriate breakover modification reduce the load on the navicular apparatus. Oral phenylbutazone or flunixin meglumine manages pain during treatment. Intrathecal corticosteroid injection (into the navicular bursa) reduces inflammation. Bisphosphonates (tiludronate, clodronate) reduce bone resorption and are used in horses with primary navicular bone pathology. Extracorporeal shock wave therapy has evidence for soft tissue lesions. Neurectomy (palmar digital neurectomy) is a salvage procedure when conservative management fails -- it eliminates pain but carries risks of deep digital flexor tendon rupture and requires careful management of the now-desensitized foot.
Prognosis
Prognosis depends on the specific pathology. Horses with isolated navicular bone changes and appropriate foot care have a reasonable prognosis for continued work. Those with deep digital flexor tendon lesions at the navicular level have a more guarded prognosis, particularly for high-performance work. Early diagnosis and appropriate management significantly improve outcomes.
Sources: Dyson SJ (2011), "The palmar foot, the navicular and related structures," in "Diagnosis and Management of Lameness in the Horse"; Dyson S et al. (2012) MRI findings in horses with palmar foot pain, Equine Veterinary Journal; AAEP lameness scale; Merck Veterinary Manual equine navicular syndrome.