Introduction

• Cause: fast work with abrupt stops and turns, eg polo, Western performance horses or stock work.
• Signs: acute, moderate - severe lameness Musculoskeletal: gait evaluation; pain on manipulation Musculoskeletal: manipulative tests; pastern swelling, chronic lameness due to degenerative joint disease Musculoskeletal: osteoarthritis (joint disease).
• Diagnosis: clinical signs, radiography of pastern Forelimb: radiography Hindlimb: radiography, CT Computed tomography if comminuted fractures are being repaired, intra-articular anesthesia (forelimb Forelimb: joint anesthesia or hindlimb Hindlimb: joint anesthesia) in osteochondral chip fractures.
• Treatment: conservative - cast Musculoskeletal: external fixation - casts as a low cost salvage procedure. Removal of osteochondral fragments via arthroscopy Fetlock: arthroscopy. Internal fixation Bone: internal fixation - screws or PIP arthrodesis PIP joint: arthrodesis.
• Prognosis: good for osteochondral chips; guarded for other fracture.
  Repair of comminuted fractures is challenging and comes with a poor-guarded prognosis for future performance.

Pathogenesis

Etiology

• Polo games.
• Western performance classes.
• Stock work.
• Free paddock exercise.

Predisposing factors

Specific

• Abrupt stops, with/without abrupt turns increases bending and torsional forces within the lower limb. Often performed by western performance horses and polo ponies which have the highest incidence of these fractures.
• Hindlimb fractures are up to three times more common than forelimb.

Pathophysiology

• Proximal interphalangeal joint (pastern) is high load, low motion joint.
• Distal articulation with distal phalanx and navicular bone (coffin joint) is high motion joint.
• Hyperextension of the proximal interphalangeal joint → insertions of the superficial digital flexor tendon, superficial distal sesamoidean ligament, and palmar and plantar ligaments of the pastern joint → tensile forces on palmar and plantar eminences → eminence fractures - vary in ize from small chips to those large enough for internal fixation.
• In addition, sudden pastern extension, eg sliding stops → distal displacement of the proximal phalanx → axial compression focused on the palmar or plantar aspect of the eminences → shear forces contribute to fracture. Eminence fractures are almost exclusively seen in the hindlimb:
  • Uni-axial fractures → no compromise of proximal interphalangeal joint stability.
  • Bi-axial fractures or complete avulsion of fibrous tissue attachments leads to instability and subluxation or luxation of proximal interphalangeal joint PIP joint: luxation. Fracture extends from near the junction of the middle and palmar/plantar thirds of the articular surface to the distal aspect of the palmar/plantar eminences, extending in the frontal plane across the bone. Attempts by the horse to weight bear on the injured limb may cause significant injury to the digital sheath and DDFT.
• Axial compression, bending and torsion forces at the same time, eg hoof fixed relative to digit → comminuted fracture. Use of shoes with caulks or rims may increase the risk of these injuries. These are the most common configuration of fracture in the middle phalanx (38 of 47 in one survey). Comminution is more common in the forelimb.
• Hyperextension of the proximal interphalangeal joint → partial avulsion with fibrous tissue attachments → osteochondral chip fractures. These are uncommon. Besides Quarterhorses Quarterhorse also noted in Thoroughbred Thoroughbred racehorses. Can be incidental and careful consideration of significance is required.

Timecourse

• Usually acute presentation.

Diagnosis

Treatment

Outcomes