Humerus
The humerus is the bone of the upper arm. It articulates proximally with the scapula to form the shoulder joint and distally with the radius and ulna to form the elbow. Compared with the lower limb bones it is relatively short. Important landmarks include the deltoid tuberosity and the musculospiral (spiral) groove where the radial nerve wraps around the bone. The bone provides leverage for the large muscles of the shoulder and arm and forms the proximal joints of the forelimb. Because the humerus is covered by thick muscle, fractures are hard to image with plain radiographs and difficult to stabilize. Humeral fractures are most common in foals and in racehorses. Radial-nerve damage is a frequent complication because the nerve lies in the spiral groove; paralysis produces a dropped elbow and inability to extend the limb.
Adult humeral fractures carry a poor prognosis. Foals have a better chance of successful repair. Radial-nerve paralysis can accompany the fracture or occur independently from trauma or prolonged lateral recumbency under anesthesia. Diagnosis requires careful radiographic technique or advanced imaging.
## Overview Osteochondrosis of the shoulder is a developmental lesion, most often of the humeral head or glenoid cavity. It is less common than hock or stifle OCD but causes more significant lameness
## Overview Deltoid bursitis is inflammation of the bursa associated with the deltoid muscle in the shoulder region. True bursitis in this location is uncommon in horses. When present, it produces lo
## Overview Humeral fracture is a break of the upper arm bone. In adult horses it usually results from trauma or a stress fracture propagating to completion (especially in racehorses). Signs are acut
## Overview Radial nerve paralysis results from damage to the nerve that innervates the extensors of the elbow, carpus, and digit. Common causes are prolonged lateral recumbency during anesthesia or
Sudden non-weight-bearing forelimb lameness after a fall, kick, or racing accident should be treated as a potential fracture. Keep the horse quiet and call the veterinarian immediately. Do not force the horse to walk on a suspected fracture.
## Overview Osteochondrosis of the shoulder is a developmental lesion, most often of the humeral head or glenoid cavity. It is less common than hock or stifle OCD but causes more significant lameness. Young horses show forelimb lameness and sometimes shoulder-muscle atrophy. Arthroscopic treatment is possible but technically demanding, and the prognosis is more guarded than for other joints. ## Causes Failure of normal cartilage ossification. ## Diagnosis Radiographs of the shoulder, sometimes with contrast or advanced imaging. ## Treatment Arthroscopic debridement when feasible. Conservative management for some lesions. Athletic prognosis is guarded. ## Recovery and Prognosis Guarded compared with hock or stifle OCD. ## Prevention Growth and nutrition management. Signs include: forelimb lameness in a young horse; shoulder muscle atrophy in chronic cases; radiographic osteochondrosis of the humeral head or glenoid
## Overview Deltoid bursitis is inflammation of the bursa associated with the deltoid muscle in the shoulder region. True bursitis in this location is uncommon in horses. When present, it produces localized swelling, heat, and pain, and may contribute to shoulder lameness. ## Causes Direct trauma or repetitive strain. Septic bursitis can follow penetrating injury. ## Diagnosis Palpation of swelling and pain in the shoulder region, ultrasound, and response to diagnostic analgesia. Other causes of shoulder lameness are excluded. ## Treatment Rest, anti-inflammatories, and, if septic, drainage and antibiotics. Removal of ongoing trauma is important. ## Recovery and Prognosis Good for non-septic cases with rest. Septic bursitis requires more aggressive treatment. ## Prevention Avoidance of shoulder trauma. Signs include: localized swelling and heat over the shoulder; pain on palpation; shoulder-region lameness
## Overview Humeral fracture is a break of the upper arm bone. In adult horses it usually results from trauma or a stress fracture propagating to completion (especially in racehorses). Signs are acute non-weight-bearing lameness, marked upper-arm swelling, and often a dropped elbow if the radial nerve is affected. Prognosis in adults is poor. ## Causes Trauma or fatigue fracture. ## Diagnosis Clinical signs and radiographs. The limb may appear shortened. Crepitus is often present. ## Treatment Internal fixation is rarely successful in adults because of bone size and opposite-limb complications. Most adult horses are euthanized. Foals have a better chance with surgery in selected cases. ## Recovery and Prognosis Poor in adults. Guarded in foals. ## Prevention Training management to reduce stress-fracture risk in racehorses. Signs include: acute severe forelimb lameness; marked swelling of the upper arm; non-weight-bearing; possible dropped elbow from radial nerve damage
## Overview Radial nerve paralysis results from damage to the nerve that innervates the extensors of the elbow, carpus, and digit. Common causes are prolonged lateral recumbency during anesthesia or humeral fracture. The horse has a dropped elbow, cannot extend the limb, knuckles at the fetlock, and drags the toe. ## Causes Compression during anesthesia or trauma (including humeral fracture). ## Diagnosis Characteristic posture and gait. The limb can bear weight if the elbow and carpus are splinted in pure nerve paralysis. ## Treatment Supportive care, splinting, anti-inflammatories, and time for compressive injuries. Humeral fracture cases have a poor outlook. ## Recovery and Prognosis Good for many post-anesthetic compressive injuries if the limb is protected. Poor if associated with fracture. ## Prevention Proper padding and positioning during anesthesia. Signs include: dropped elbow; inability to extend the elbow and carpus; knuckling at the fetlock; dragging the toe
Adult humeral fractures carry a poor prognosis. Foals have a better chance of successful repair. Radial-nerve paralysis can accompany the fracture or occur independently from trauma or prolonged lateral recumbency under anesthesia. Diagnosis requires careful radiographic technique or advanced imaging.
Sudden non-weight-bearing forelimb lameness after a fall, kick, or racing accident should be treated as a potential fracture. Keep the horse quiet and call the veterinarian immediately. Do not force the horse to walk on a suspected fracture.
See the Humerus (Right) on our interactive 3D horse model. Open 3D Model