Equis ISSN 2398-2977

Shoulder joint: disease - overview

Synonym(s): Scapulohumeral joint disease

Contributor(s): Stephen Adams, Graham Munroe

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.

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

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

Miscellaneous

Predisposing factors

General

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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Outcomes

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Further Reading

Publications

Refereed papers

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.


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