NAVLE Equine Lameness and Diagnostics 4

Question 1

A 12-year-old Warmblood sport horse presents with insidious-onset bilateral forelimb lameness that is worse on hard surfaces and improves after 20 minutes of work. Flexion tests are mildly positive bilaterally. Nerve blocks are unremarkable through the pastern. Radiographs reveal bilateral palmar osteochondral fragments at the proximal interphalangeal joint. Which finding on MRI would most strongly implicate the distal interphalangeal joint collateral ligaments as the primary pain source in this presentation?

Accepted Answer

T2 hyperintensity within the collateral ligament substance with associated focal subchondral bone edema at the ligament enthesis

Answer

T2 hyperintensity within the collateral ligament substance paired with focal subchondral bone edema at the enthesis indicates active ligamentous injury with an enthesopathy response — the hallmark MRI signature of collateral ligament desmitis at the DIP joint. Joint effusion and synovial thickening are nonspecific secondary findings, cartilage thinning points to osteoarthritis rather than ligamentous origin, and increased T1 navicular signal suggests fatty change or sclerosis, not collateral ligament pathology.

Question 2

During a pre-purchase examination, a 7-year-old Quarter Horse reining prospect shows a consistent 2/5 left hindlimb lameness. Perineural anesthesia of the high plantar nerve (abaxial sesamoid level) abolishes the lameness completely. However, intra-articular anesthesia of the tarsocrural, proximal intertarsal, distal intertarsal, and tarsometatarsal joints — performed sequentially over two days — fails to improve the lameness. What is the MOST likely primary diagnosis?

Accepted Answer

Proximal suspensory desmitis of the left hindlimb

Answer

Proximal suspensory desmitis (PSD) of the hindlimb is notoriously blocked by high plantar anesthesia, which desensitizes the lateral plantar nerve branch supplying the proximal suspensory apparatus. Because PSD is a soft tissue structure — not a joint — all four tarsus joint blocks remain negative despite the lameness being in that region. This pattern (high plantar positive, all tarsus joints negative) is the classic diagnostic footprint of hindlimb PSD. Cunean tendon bursitis and central tarsal bone fracture would likely respond to tarsometatarsal or intertarsal blocks; OCD of the tarsocrural joint would be blocked by the tarsocrural anesthesia.

Question 3

A 5-year-old Thoroughbred racehorse undergoes nuclear scintigraphy for investigation of right forelimb lameness that has not localized with nerve blocks. The bone scan shows markedly increased radiopharmaceutical uptake (IRU) in the mid-diaphysis of the right third metacarpal bone on the lateral cortex. What is the most appropriate next diagnostic step to characterize this lesion before formulating a treatment plan?

Accepted Answer

CT of the right forelimb to characterize cortical integrity and quantify stress fracture propagation

Answer

Focal high IRU in the diaphyseal cortex of the third metacarpus in a racehorse is highly suspicious for a stress fracture, which carries risk of complete catastrophic fracture if the horse is exercised. CT provides detailed cross-sectional characterization of cortical integrity, fracture line orientation, and propagation depth — information critical to differentiating a stable incomplete cortical stress fracture from one approaching propagation, which directly determines surgical vs. conservative management. Repeat scintigraphy delays diagnosis without adding anatomical detail. Ultrasonography evaluates periosteal soft tissue but cannot adequately assess cortical fracture geometry. Standing MRI of the distal limb does not image the mid-diaphysis.

Question 4

A 15-year-old Hanoverian dressage horse is evaluated for progressive bilateral hindlimb weakness and hindlimb lameness. The horse exhibits a characteristic 'goose-stepping' gait, excessive hip drop bilaterally, and difficulty backing. Intra-articular analgesia of the sacroiliac joints dramatically improves the lameness score from 3/5 to 1/5. Which diagnostic imaging modality is considered gold standard for confirming sacroiliac joint pathology in the horse, and what finding would confirm active joint disease?

Accepted Answer

Transrectal ultrasonography revealing hypoechoic joint margins and loss of normal joint contour

Answer

Transrectal ultrasonography (TRUS) is considered the gold standard for imaging the sacroiliac joint in horses because it allows direct visualization of the ventral joint margin, synovium, and surrounding structures with high resolution. Findings confirming active SI joint disease include hypoechoic (thickened/inflamed) joint capsule, loss of normal smooth joint contour, and irregularity of the subchondral surfaces. Nuclear scintigraphy is useful but less specific — it reflects bone remodeling activity, not active synovitis. Standard radiography cannot adequately image the SI joint due to overlying structures. CT myelography evaluates spinal cord compression, not SI joint pathology.

Question 5

A 3-year-old Standardbred trotter presents with acute non-weight-bearing left forelimb lameness after a race. Physical examination reveals marked swelling of the fetlock, severe pain on palpation of the medial aspect of the proximal sesamoid bones, and a dropped fetlock. Radiographs confirm a comminuted biaxial proximal sesamoid bone fracture. When assessing prognosis for athletic recovery (return to racing), which specific radiographic feature carries the WORST prognostic significance?

Accepted Answer

Extension of the fracture lines into the basilar (abaxial) surface with involvement of the distal sesamoidean ligament attachment

Answer

Extension of proximal sesamoid fracture lines into the basilar surface with compromise of the distal sesamoidean ligament (DSL) attachments represents the most catastrophically poor prognostic feature. The DSLs (straight, oblique, and cruciate) are the primary stabilizers of the fetlock in weight-bearing; their avulsion renders the fetlock biomechanically unsalvageable for athletic work. This pattern, combined with biaxial comminution, essentially precludes return to racing and significantly compromises even pasture soundness. Apical fractures with a single parasagittal line, minimal displacement, and intact soft tissue structures carry a far better surgical and athletic prognosis.

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE - North American Veterinary Licensing Examination Practice Test

NAVLE Equine Lameness and Diagnostics 4