NAVLE Equine Lameness and Diagnostics 6

Question 1

A 12-year-old Warmblood sport horse presents with subtle, intermittent right forelimb lameness that worsens on soft footing and improves on firm ground. Flexion tests are negative. Diagnostic analgesia of the distal limb fails to improve the lameness. MRI reveals focal cartilage erosion on the palmar aspect of the lateral trochlear ridge of the distal radius. Which condition does this BEST describe?

Accepted Answer

Palmar osteochondral disease (POD) of the radiocarpal joint

Answer

Palmar osteochondral disease (POD), also called 'sport horse carpus,' involves cartilage erosion and subchondral bone pathology on the palmar aspects of the radiocarpal and intercarpal joints. It is characteristically worse on soft footing because greater fetlock extension loads the palmar carpal structures. Distal limb analgesia does not block this region, explaining the negative response. MRI is often required for definitive diagnosis as radiographs may be unremarkable early in the disease.

Question 2

A 7-year-old Thoroughbred racehorse undergoes nuclear scintigraphy after a 4-week history of right hindlimb lameness. The scan shows intense increased radiopharmaceutical uptake (IRU) at the right tuber sacrale. Standing rectal palpation reveals mild asymmetry. Radiographs are normal. Which diagnosis BEST explains these findings, and what is the primary mechanism of injury?

Accepted Answer

Sacroiliac joint desmopathy secondary to repetitive torsional loading during racing

Answer

Sacroiliac joint desmopathy is the most common cause of intense IRU at the tuber sacrale in racehorses with hindlimb lameness and pelvic asymmetry. The SI joint undergoes repetitive torsional and shear forces during gallop and tight turns, causing ligamentous strain and enthesopathy without early radiographic changes. Scintigraphy is the most sensitive early modality. Stress fractures of the ilial wing would show IRU at a different site, and septic arthritis would typically present with systemic signs.

Question 3

During a pre-purchase examination, a 5-year-old Dutch Warmblood mare shows a 2/5 lameness on the lunge that is eliminated by an abaxial sesamoid nerve block but NOT by a palmar digital nerve block. High-field MRI of the pastern and foot is normal. Which structure, when anesthetized by the abaxial block but not the palmar digital block, MOST likely harbors the pathology?

Accepted Answer

The collateral ligaments of the proximal interphalangeal (PIP) joint

Answer

The palmar digital nerve block desensitizes the caudal third of the foot including the navicular region, the DIP joint, and solar corium. The abaxial sesamoid block additionally desensitizes the PIP joint, fetlock, and proximal pastern structures. When the abaxial block is positive but the palmar digital block is negative, the pathology must lie in the region uniquely anesthetized by the more proximal block — most commonly the collateral ligaments or the PIP joint itself. MRI being normal of the distal foot further narrows the source to the pastern/PIP region.

Question 4

A 9-year-old Quarter Horse barrel racing horse presents with bilateral hindlimb lameness worse on the right. Intra-articular analgesia of both distal tarsal joints resolves the lameness 70%. Radiographs show periarticular osteophytes at the centrodistal and tarsometatarsal joints bilaterally but no joint space narrowing. What is the MOST appropriate next step in management, and why?

Accepted Answer

Computed tomography-guided chemical arthrodesis with sodium monoiodoacetate to accelerate fusion of the affected joints

Answer

CT-guided chemical arthrodesis using sodium monoiodoacetate (or alcohol) is an advanced technique used to accelerate the natural fusion of the distal tarsal joints (centrodistal and tarsometatarsal), which are the joints involved in bone spavin. These joints have minimal range of motion and are better pain-free when fused. When conservative corticosteroid management is insufficient or short-lived, and radiographic changes confirm bone spavin, chemical arthrodesis provides a definitive solution. Repeated methylprednisolone is not appropriate as a long-term sole strategy and may accelerate cartilage degradation. Cunean tenectomy is an older, rarely indicated procedure.

Question 5

An 11-year-old Andalusian dressage horse presents with progressive bilateral forelimb 'pottery' gait, stumbling, and a short, stabbing stance phase. Nerve blocks are unhelpful. Radiographs show extensive remodeling and irregular sclerosis of both proximal sesamoid bones with fragmentation at the base. Which long-term structural consequence makes the prognosis for return to full work GUARDED to POOR?

Accepted Answer

Progressive failure of the suspensory apparatus with risk of catastrophic fetlock breakdown due to compromised sesamoid bone structural integrity

Answer

Chronic sesamoiditis with fragmentation and sclerosis represents advanced degenerative disease of the proximal sesamoid bones, which are critical structural components of the suspensory apparatus. The sesamoid bones serve as the fulcrum for the suspensory ligament and distal sesamoidean ligaments; structural failure predisposes to catastrophic breakdown — fetlock 'drop,' complete support limb failure, or fracture under athletic loading. This is distinct from navicular disease or DDFT pathology, which are secondary events. The bilateral involvement and advanced bony changes make return to high-level sport inadvisable.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Equine Lameness and Diagnostics 6