Shoulder joint: disease – overview
Synonym(s): Scapulohumeral joint disease
Introduction
- The shoulder is an uncommon site for forelimb lameness.
- Cause: direct trauma is the most common cause. Osteochondritis dissecans may occur in immature horses.
- Signs: usually sudden onset, moderate to severe, forelimb lameness.
- Diagnosis: clinical examination and range of ancillary aids including joint anesthesia Forelimb: joint anesthesia , radiography Forelimb: radiography and scintigraphy Bone: scintigraphy .
- Treatment: depends on cause.
- Prognosis: depends on cause.
Presenting signs
- Forelimb lameness; severity depends on cause.
- Unilateral or bilateral.
- Abnormal stance.
- Pain or resentment on manipulation of shoulder joint.
- Localized swelling of overlying soft tissue structures.
- Systemic signs associated with septic arthritis.
- Some conditions may be asymptomatic, eg subchondral bone cysts and osseous cyst-like lesions.
Age predisposition
- Septic arthritis in foals <4 months old.
- Osteochondrosis may be radiographically evident from 1 year old, but may not manifest clinically until 2-5 years old; it is more prevalent in young, rapidly growing horses.
Breed/Species predisposition
- Thoroughbreds Thoroughbred and performance horses have increased risk of lameness due to trauma.
- Miniature Horses American Miniature Horse , Shetland Ponies Shetland Pony and Falabella ponies Falabella have a higher incidence of early onset osteoarthritis.
- Dysplasia is seen in Miniature Horses American Miniature Horse and Shetland Ponies Shetland Pony .
- Luxation occurs more commonly in ponies than horses.
Cost considerations
- Costs of diagnostic workup and treatments are expensive.
- Some conditions are career threatening.
Pathogenesis
Etiology
Trauma
- Most common cause of acquired shoulder conditions.
- Fractures of the humerus: deltoid tuberosity; greater/lesser tubercle Humerus: fracture .
- Fractures of the scapula (rare because of protective muscle cover): supraglenoid tubercle fractures most common type Scapula: fracture - supraglenoid tubercle .
- Luxation/subluxation of the shoulder joint can occur in any direction, proximal displacement of the humeral head usually follows because of muscle pull (lateral luxation with proximal displacement is most common) +/- fractures.
- Traumatic synovitis and capsulitis following single or repeated episodes of trauma to the shoulder joint - may progress to degenerative joint disease Musculoskeletal: osteoarthritis (joint disease) .
- Stress fractures of the humerus.
- Proximal humeral physis injuries (rare) Bone: physitis .
- Joint capsule tear.
- Biceps brachii tendonitis Humerus: bicipital bursa - disease .
- Injury to the muscles surrounding the scapulohumeral joint, or brachial plexus injury Brachial plexus: trauma can → instability of the shoulder joint because of loss of lateral and medial support.
- Suprascapular nerve injury → loss of stabilizing function of supraspinatus/infraspinatus muscles → lateral instability of scapulohumeral joint Suprascapular nerve: paralysis .
Congenital and perinatal conditions
- Dysplasia: flattening of the curvature of the glenoid cavity; a rare condition of Shetland Ponies and Miniature Horses.
Infectious
- Septic arthritis may occur secondary to trauma, joint penetration Joint: septic arthritis - adult or via hematogenous spread Joint: septic arthritis - foal .
Multifactorial
- Osteochondrosis Bone: osteochondrosis of the glenoid cavity and/or humeral head may be radiographically evident from 1 year old, but often does not manifest clinically until later.
- Osteoarthritis Musculoskeletal: osteoarthritis (joint disease) is uncommon; usually secondary to osteochondrosis, intra-articular fracture, joint capsule damage.
- Subchondral bone cysts are seen in the middle of the glenoid cavity of the scapula Bone: subchondral cysts .
- Inflammation (bursitis) of the intertubercular (bicipital) bursa Humerus: bicipital bursa - disease . Possible causes: trauma, overstretch → tear, infection from penetrating wound or hematogenous spread,Brucella abortus.
- Ossification of the biceps brachii tendon (calcifying tendonopathy) may be traumatic, degenerative or developmental Humerus: bicipital bursa - disease and physically restricts movement at the scapulohumeral joint.
Immune-mediated
- Immune-mediated polysynovitis uncommon, but may involve the elbow joint Joint: immune-mediated polysynovitis .
Miscellaneous
- Tumors are extremely rare.
- Osseous cyst-like lesions can occur in the humeral head Bone: osseous cyst-like lesions .
Predisposing factors
General- Septic conditions:
- Failure of transfer of passive immunity in the foal Foal: failure of passive transfer (IgG) , placentitis Placenta: placentitis or endometritis Uterus: endometritis - bacterial .
- Poor hygiene.
Pathophysiology
- The shoulder joint is the articulation between the humerus and the glenoid cavity of the scapula.
- The joint capsule of the shoulder joint is substantial and attaches 2 cm away from the margins of the articular surfaces.
- The joint capsule is reinforced by two elastic glenohumeral ligaments which fan out from the supraglenoid tubercle on the scapula to the humeral tuberosities on the humerus.
- The articular surface of the humeral head is approximately twice the size of the glenoid cavity.
- The joint is surrounded by the large mass of the proximal forelimb musculature.
- There is substantial flexion and extension at this joint, but limited rotation.
- The shoulder girdle, comprising muscles and ligaments, connects the shoulder joint to the trunk, neck and head.
- There is a connection between the intertubercular (bicipital) bursa and the scapulohumeral joint in some horses.
- See Joint: synovial pathobiology Joint: synovial pathobiology .
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
Other sources of information
- Dyson S J (2003) Scapulohumeral Joint. In: Diagnosis & Management of Lameness in the Horse. Eds: Ross M W & Dyson S J. Saunders, Missouri. pp 408-416.
- Stashak T S (2002) The Shoulder. In: Adams Lameness in Horses. 5th edn. Lippincott, Williams & Wilkins, Baltimore. pp 905-930.