Disorders of the Pastern and Fetlock in Horses

Fractures of the First (P1) and Second (P2) Phalanx:

First Phalanx (P1) Fractures:
- Types: Small osteochondral "chips" (dorsal margin), sagittal (complete or incomplete), comminuted, or palmar/plantar fragments (often associated with osteochondrosis).
- Clinical Signs: Acute lameness, joint effusion, and sensitivity to firm flexion of the fetlock.
- Diagnosis: Confirmed via radiographic examination; CT imaging is essential if occult fracture lines are suspected.
- Management: Chip fractures are removed arthroscopically (excellent prognosis); sagittal fractures are repaired via internal fixation with lag screws; comminuted fractures may require cast immobilization for up to 12 weeks.
Second Phalanx (P2) Fractures:
- Etiology: Common in Quarter Horses and Warmbloods working in tight circles.
- Types: Most common are palmar/plantar eminence fractures or comminuted fractures.
- Management: Treated with internal fixation or transfixation pin casts; prognosis depends on the resulting level of comfort and the extent of osteoarthritis.

Fractures of the Proximal Sesamoid Bones:

Epidemiology: Almost exclusively an injury of racehorses.
Classification: Apical (most common, due to overextension), midbody, basilar, abaxial, axial, and comminuted.
Clinical Signs: Heat, pain, acute lameness (exacerbated by flexion), hemarthrosis, and synovial effusion.
Management & Prognosis:
- Apical: Removed arthroscopically; carries a good prognosis for return to function unless suspensory desmitis is present.
- Midbody: Typically requires lag screw fixation; fair to good prognosis.
- Basilar: Generally carries a poor prognosis if it involves most of the base or has associated articular disease.
"Breakdown": Catastrophic injury involving simultaneous fracture of both sesamoids and complete disruption of the suspensory apparatus.

Osteoarthritis of the Proximal Interphalangeal Joint (High Ringbone):

Nature: Common cause of lameness, especially in Western performance horses; affects a "low-motion" joint that is unforgiving to high loads.
Pathology: Characterized by cartilage loss and periarticular new bone formation.
Diagnosis: Subtle lameness that progresses; confirmed via diagnostic analgesia and radiographs showing bone remodeling or loss of joint space.
Treatment: Temporary relief via anti-inflammatories; permanent management often requires surgical arthrodesis (joint fusion) to restore performance.

Palmar Osteochondral Disease of the Fetlock:

Definition: Disease of the subchondral bone of the palmar/plantar metacarpal/metatarsal condyles.
Etiology: Stress remodeling response to intense activity in young racehorses.
Diagnosis: Improvement with palmar/plantar metacarpal nerve blocks; identified earliest using nuclear scintigraphy, PET, CT, or MRI rather than standard radiographs.
Management: Primarily controlled exercise.

Sesamoiditis:

Nature: Inflammation of the sesamoid bones caused by stress on the fetlock during fast exercise.
Clinical Signs: Pain, heat, and swelling on palpation; signs are similar to but less severe than fractures.
Diagnosis: Radiographic focal osteolysis and enlarged vascular channels; ultrasonography should be used to check for concurrent suspensory ligament lesions.
Management: Enforced rest and supportive anti-inflammatory care.

Chronic Proliferative Synovitis:

Definition: Enlargement of the fibrocartilaginous pad on the joint capsule attachment of the fetlock.
Etiology: Repetitive trauma from exercise; most frequent in racing Thoroughbreds.
Diagnosis: Firm swelling over the dorsoproximal fetlock; ultrasound showing a synovial pad > 4 mm thick.
Management: Surgical excision via arthroscopy.

Disorders of the Pastern and Fetlock in Horses

Fractures of the First (P1) and Second (P2) Phalanx:

First Phalanx (P1) Fractures:

Types: Small osteochondral "chips" (dorsal margin), sagittal (complete or incomplete), comminuted, or palmar/plantar fragments (often associated with osteochondrosis).

Clinical Signs: Acute lameness, joint effusion, and sensitivity to firm flexion of the fetlock.

Diagnosis: Confirmed via radiographic examination; CT imaging is essential if occult fracture lines are suspected.

Management: Chip fractures are removed arthroscopically (excellent prognosis); sagittal fractures are repaired via internal fixation with lag screws; comminuted fractures may require cast immobilization for up to 12 weeks.

Second Phalanx (P2) Fractures:

Etiology: Common in Quarter Horses and Warmbloods working in tight circles.

Types: Most common are palmar/plantar eminence fractures or comminuted fractures.

Management: Treated with internal fixation or transfixation pin casts; prognosis depends on the resulting level of comfort and the extent of osteoarthritis.

Fractures of the Proximal Sesamoid Bones:

Epidemiology: Almost exclusively an injury of racehorses.

Classification: Apical (most common, due to overextension), midbody, basilar, abaxial, axial, and comminuted.

Clinical Signs: Heat, pain, acute lameness (exacerbated by flexion), hemarthrosis, and synovial effusion.

Management & Prognosis:

Apical: Removed arthroscopically; carries a good prognosis for return to function unless suspensory desmitis is present.

Midbody: Typically requires lag screw fixation; fair to good prognosis.

Basilar: Generally carries a poor prognosis if it involves most of the base or has associated articular disease.

"Breakdown": Catastrophic injury involving simultaneous fracture of both sesamoids and complete disruption of the suspensory apparatus.

Osteoarthritis of the Proximal Interphalangeal Joint (High Ringbone):

Nature: Common cause of lameness, especially in Western performance horses; affects a "low-motion" joint that is unforgiving to high loads.

Pathology: Characterized by cartilage loss and periarticular new bone formation.

Diagnosis: Subtle lameness that progresses; confirmed via diagnostic analgesia and radiographs showing bone remodeling or loss of joint space.

Treatment: Temporary relief via anti-inflammatories; permanent management often requires surgical arthrodesis (joint fusion) to restore performance.

Palmar Osteochondral Disease of the Fetlock:

Definition: Disease of the subchondral bone of the palmar/plantar metacarpal/metatarsal condyles.

Etiology: Stress remodeling response to intense activity in young racehorses.

Diagnosis: Improvement with palmar/plantar metacarpal nerve blocks; identified earliest using nuclear scintigraphy, PET, CT, or MRI rather than standard radiographs.

Management: Primarily controlled exercise.

Sesamoiditis:

Nature: Inflammation of the sesamoid bones caused by stress on the fetlock during fast exercise.

Clinical Signs: Pain, heat, and swelling on palpation; signs are similar to but less severe than fractures.

Diagnosis: Radiographic focal osteolysis and enlarged vascular channels; ultrasonography should be used to check for concurrent suspensory ligament lesions.

Management: Enforced rest and supportive anti-inflammatory care.

Chronic Proliferative Synovitis:

Definition: Enlargement of the fibrocartilaginous pad on the joint capsule attachment of the fetlock.

Etiology: Repetitive trauma from exercise; most frequent in racing Thoroughbreds.

Diagnosis: Firm swelling over the dorsoproximal fetlock; ultrasound showing a synovial pad > 4 mm thick.

Management: Surgical excision via arthroscopy.