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Shoulder joint: disease – overview

ISSN 2398-2977

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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

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

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

Presenting problems

  • Forelimb lameness.

Client history

  • Acute lameness in traumatic condition, eg fractures and luxations, and sepsis. 
  • Lower grade lameness in osteoarthritis and tenosynovitis. 
  • Abnormal stance.

Clinical signs

  • Unilateral or bilateral forelimb lameness   Musculoskeletal: gait evaluation  :
    • Shortened cranial phase to stride.
    • Reduced height foot flight arc.
    • Marked head lift.
    • Resents turning on affected limb may pivot.
    • Lameness worse when affected limb on outside of the circle.
  • Abnormal stance: 
    • Weight inclined towards contralateral limb.
    • Not fully weight-bearing.
    • Deviation of distal limb.
  • Abnormal hoof wear, eg small foot with high heel and excessive toe wear in osteochondrosis   Foot / shoe: examination  .
  • Localized swelling and/or pain on palpation of overlying soft tissues   Musculoskeletal: physical examination - adult  .

Localized palpation of the brachiocephalicus muscles often illicits a painful response in the normal horse.

  • Joint effusion is almost always impossible to palpate because of the overlying musculature, except in wasting conditions or immature animals.
  • Pain or resentment on manipulation   Musculoskeletal: manipulative tests  often unrewarding.
  • Joint instability on manipulation and palpation.
  • Abnormal position of palpable landmarks, ie the cranial and caudal eminences of the greater tubercle of the humerus (fractures), the scapula spine (luxation)   Musculoskeletal: physical examination - adult  .
  • Crepitus.

Diagnostic investigation

Radiography  Forelimb: radiography 

  • Useful for assessment of fractures, luxations, bone cysts, osteoarthritis, and OCD lesions   Shoulder: OCD 01 - LM radiograph      Shoulder: OCD 02 - LM radiograph  .
  • Contrast radiography may aid evaluation of osteochondritis dissecans lesions.
  • High exposures are required, using rare earth screens, fast-speeds +/- a grid.
  • Mediolateral and craniomedial-caudolateral oblique (CrMCdLO) views should be taken   Shoulder: radiology    Shoulder: normal - LM oblique radiograph  .
  • Cranioproximal-craniodistal oblique (CrPCrDO) views of the humeral tubercles may be useful in some cases.
  • Evaluation of the scapula is not easy because of superimposition over the thoracic vertebrae and opposite limb.

A small, circular area of radiolucency in the subchondral bone in the centre of the glenoid cavity is sometimes seen and is a normal finding.

Superimposition of the lateral rim of the glenoid cavity may result in a lucent band crossing the humeral head.

Other

Intrasynovial analgesia   Forelimb: joint anesthesia 

  • Intrasynovial analgesia of the shoulder joint.
  • There is a connection between the intertubercular (bicipital) bursa and the scapulohumeral joint in some horses which can confuse the result of intrasynovial analgesia of either structure   Anesthesia: intra-articular  .

In some horses intrasynovial analgesia results in leakage into the musculature surrounding the joint and joint instability (shoulder slip) for up to 2 h, which will confuse the result of the block.

  • Subchondral bone pain is not always blocked out by intrasynovial analgesia.

Scintigraphy    Bone: scintigraphy 

  • Useful if no localizing signs, if other findings equivocal, or if intrasynovial analgesia and perineural anesthesia are inconclusive or cannot be undertaken safely.
  • Particularly useful in diagnosing early stress-related subchondral bone injury and stress fractures.

Arthrocentesis and synovial fluid analysis 

2-D Ultrasonography  Ultrasonography: bone / joints    Ultrasonography: overview 

  • Useful for examination of the shoulder joint musculature: hyperechoic regions may indicate: muscle necrosis, fibrosis or mineralization.

Musculature should be under tension to avoid artefacts - ensure that the animal is fully weight-bearing on the limb.

  • The intertubercular bursa, biceps brachii tendon, muscle insertions, humeral tubercles and the infraspinatus bursa can be assessed.

Arthroscopy    Shoulder: arthroscopy 

  • One of the more difficult joints on which to perform arthroscopy because of the surrounding musculature and strong, tight joint capsule.
  • Useful for diagnosis and treatment of osteochondrosis and bone cysts.

Other imaging

Thermography  Thermography 

  • May be useful for detecting superficial inflammation or determining whether soft tissue pain on palpation is associated with inflammation.

Confirmation of diagnosis

Discriminatory diagnostic features

  • History. 
  • Clinical signs. 
  • Manipulative tests. 
  • Thermography.

Definitive diagnostic features

  • Radiography. 
  • Scintigraphy. 
  • Intrasynovial analgesia. 
  • Ultrasonography. 
  • Synovial fluid analysis.

Treatment

Standard treatment

  • See individual conditions.

Prevention

Outcomes

Prognosis

  • See individual conditions.

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.