Introduction

• Uncommon - 15% of non-traumatic elbow lameness.
• Cause: congenital developmental abnormality.
• 2 types:
  • Severe disability: about 90° of outward rotation of proximal ulna; trochlear notch and anconeal process disarticulated from humerus; displacement of triceps tendon (divided radiographically into types II and III).
  • Disability not as severe proximal radius displaced caudally and laterally; normal relationship between humerus and ulna; proximal radial epiphysis may be deformed. Radiographic changes defined as type I.
• Signs: lameness.
• Diagnosis: radiography.
• Treatment: closed reduction if possible, surgical if not.
• Prognosis: worse when surgery required or in neglected cases.

Pathogenesis

Etiology

• Congenital developmental anomaly.

Pathophysiology

• Unknown - ?failure of development of medial collateral and annular ligaments and hypertrophy of lateral collateral ligament allowing outward rotation of ulna to occur.
• Changes seen may be secondary: a) Severe disability: 90° outward rotation of proximal ulna; removing trochlear notch and anconeal process from effective articulation with humerus; displacement of triceps tendon. b) Less severe disability: normal relationship between humerus and ulna; proximal radius displaced laterally and caudally.
• Long-standing cases - articular surface of proximal radius deformed due to lack of contact with humerus.

Timecourse

• Weeks to months.

Diagnosis

Treatment

Outcomes