Disorders of the Equine Shoulder

Diagnostic Foundations:

Clinical Reality: Shoulder pain is a common suspicion but an uncommon origin of lameness.
Differentiation: Chronic upper limb lameness is distinguished from distal limb lameness by atrophy of proximal limb muscles (supraspinatus, infraspinatus, and cranial shoulder muscles).
Localization Tools:
- Manipulative Tests: Physical manipulation to elicit pain responses.
- Intrasynovial Anesthesia: Nerve blocks of the shoulder joint or bicipital bursa.
Imaging Modalities:
- Physiological: Scintigraphy and thermography.
- Anatomical: Radiography (caudolateral-craniomedial views) and ultrasonography.

Developmental Orthopedic Diseases (DOD):

Osteochondrosis (OC):
- General: Diagnosed primarily in weanlings and yearlings; the shoulder is considered the least forgiving site for OC.
- Subchondral Cystlike Lesions (SCLs): Develop in the glenoid of the scapula; lameness often appears only when the horse begins ridden work.
- Osteochondritis Dissecans (OCD): Usually affects the caudal humeral head; conservative treatment is often less successful than for SCLs.
Scapulohumeral Dysplasia:
- Specifics: Almost unique to miniature horse breeds.
- Pathogenesis: Size mismatch between the glenoid and humeral head leading to instability.
- Prognosis: Often advanced at diagnosis; euthanasia is frequently recommended.

Fractures of the Shoulder Region:

Scapular Fractures:
- Supraglenoid Tubercle: The most common scapular fracture (30–50% of cases).
- Treatment: Ranges from conservative stall rest for minimal displacement to surgical resection or internal fixation.
Humeral Fractures:
- Includes the humeral head, greater tubercle, and deltoid tuberosity.
- Stabilized by large shoulder muscles (supraspinatus, infraspinatus), often preventing severe displacement.
Stress Fractures:
- Patient Profile: Primarily racing Thoroughbreds.
- Behavior: Lameness is transient (resolving with rest) but recurs with exercise; requires 6–8 months of rest for recovery.

Bicipital Bursitis & Infection:

Bicipital Bursitis:
- Nature: Usually secondary to trauma, underlying bone cysts, or tendon injury.
- Clinical Signs: Shortened cranial phase of stride, decreased foot flight arc, and decreased carpal flexion.
- Treatment: Rest, NSAIDs, and intrasynovial steroids; septic cases require arthroscopic lavage and antimicrobials.
Shoulder Sepsis:
- Adults: Typically from penetrating injury.
- Foals: Often hematogenous (via blood) spread to growth plates.

Suprascapular Neuropathy (Sweeney):

Significance: The most common abnormality of the equine shoulder.
Etiology: Direct trauma to the suprascapular nerve as it courses over the cranial scapula.
Clinical Presentation:
- Profound, focal atrophy of the supraspinatus and infraspinatus muscles.
- Shoulder Instability: The joint may "pop" or subluxate sideways during weight-bearing.
Management: Rest, muscle stimulation (physiotherapy), and occasionally surgery to decompress the nerve.

Osteoarthritis (Degenerative Joint Disease):

Nature: Cartilage destruction that can be ameliorated but not cured.
Diagnosis: Identified via periarticular osteophytes on radiographs.
Management: Palliative care using analgesics and disease-modifying therapies.

Disorders of the Equine Shoulder

Diagnostic Foundations:

Clinical Reality: Shoulder pain is a common suspicion but an uncommon origin of lameness.

Differentiation: Chronic upper limb lameness is distinguished from distal limb lameness by atrophy of proximal limb muscles (supraspinatus, infraspinatus, and cranial shoulder muscles).

Localization Tools:

Manipulative Tests: Physical manipulation to elicit pain responses.

Intrasynovial Anesthesia: Nerve blocks of the shoulder joint or bicipital bursa.

Imaging Modalities:

Physiological: Scintigraphy and thermography.

Anatomical: Radiography (caudolateral-craniomedial views) and ultrasonography.

Developmental Orthopedic Diseases (DOD):

Osteochondrosis (OC):

General: Diagnosed primarily in weanlings and yearlings; the shoulder is considered the least forgiving site for OC.

Subchondral Cystlike Lesions (SCLs): Develop in the glenoid of the scapula; lameness often appears only when the horse begins ridden work.

Osteochondritis Dissecans (OCD): Usually affects the caudal humeral head; conservative treatment is often less successful than for SCLs.

Scapulohumeral Dysplasia:

Specifics: Almost unique to miniature horse breeds.

Pathogenesis: Size mismatch between the glenoid and humeral head leading to instability.

Prognosis: Often advanced at diagnosis; euthanasia is frequently recommended.

Fractures of the Shoulder Region:

Scapular Fractures:

Supraglenoid Tubercle: The most common scapular fracture (30–50% of cases).

Treatment: Ranges from conservative stall rest for minimal displacement to surgical resection or internal fixation.

Humeral Fractures:

Includes the humeral head, greater tubercle, and deltoid tuberosity.

Stabilized by large shoulder muscles (supraspinatus, infraspinatus), often preventing severe displacement.

Stress Fractures:

Patient Profile: Primarily racing Thoroughbreds.

Behavior: Lameness is transient (resolving with rest) but recurs with exercise; requires 6–8 months of rest for recovery.

Bicipital Bursitis & Infection:

Bicipital Bursitis:

Nature: Usually secondary to trauma, underlying bone cysts, or tendon injury.

Clinical Signs: Shortened cranial phase of stride, decreased foot flight arc, and decreased carpal flexion.

Treatment: Rest, NSAIDs, and intrasynovial steroids; septic cases require arthroscopic lavage and antimicrobials.

Shoulder Sepsis:

Adults: Typically from penetrating injury.

Foals: Often hematogenous (via blood) spread to growth plates.

Suprascapular Neuropathy (Sweeney):

Significance: The most common abnormality of the equine shoulder.

Etiology: Direct trauma to the suprascapular nerve as it courses over the cranial scapula.

Clinical Presentation:

Profound, focal atrophy of the supraspinatus and infraspinatus muscles.

Shoulder Instability: The joint may "pop" or subluxate sideways during weight-bearing.

Management: Rest, muscle stimulation (physiotherapy), and occasionally surgery to decompress the nerve.

Osteoarthritis (Degenerative Joint Disease):

Nature: Cartilage destruction that can be ameliorated but not cured.

Diagnosis: Identified via periarticular osteophytes on radiographs.

Management: Palliative care using analgesics and disease-modifying therapies.