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An unusual shoulder injury
  1. A A Syed,
  2. P Keogh
  1. Department of Orthopaedics, Cappagh Orthopaedic Hospital, Dublin 11, Republic of Ireland
  1. Mr AA Syed, FRCS, 7 Riverwood Park, Riverwood, Castleknock, Dublin 15, Republic of Ireland

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A 23-year-old man was riding his motor bike on a wet country road. Negotiating a sharp curve the bike slipped and he landed on his outstretched left hand while the bike toppled over him, trapping the left leg underneath. On examination there was an obvious deformity of his left leg with swelling and bruising over the left shoulder along with some friction burns. Radiographs revealed a closed, displaced fracture of the tibia and fibula (figure 1). Anteroposterior, lateral and transthoracic views of the shoulder joint were read as normal in the casualty department (figure 2). A diagnosis of soft tissue injury to the shoulder was made. The patient was given a broad arm sling and was admitted for an intramedullary nailing of the tibia. On orthopaedic review in the morning the patient complained of progressive swelling and pain in his left shoulder. The limb was held close to the body with the elbow flexed. Attempts to move the shoulder generated severe pain and no active or passive external rotation was possible. The patient was taken to theatre for intramedullary nailing prior to which, under general anaesthesia, an axillary view of his left shoulder was obtained using the image intensifier (figure3).

Figure 1

Radiograph of the fractured tibia and fibula

Figure 2

Anteroposterior radiograph of the left shoulder

Figure 3

Axillary view of the shoulder under image intensifier

Questions

1
What is the diagnosis and what are the pathomechanics of the injury?
2
How would you treat the problem?

Answers

QUESTION 1

This is a posterior fracture dislocation of the anatomical head of the humerus. Electrical or neurological seizures, fall on an outstretched limb, or a blow to the anterior shoulder in trauma or sports, are events exerting large posterior forces on the shoulder joint. The continuing muscular contraction of deltoid and the subscapularis may then force the anterior portion of the humeral head onto the posterior rim of the glenoid, leading to a shearing of the anatomical head. The characteristic finding is the inability to externally rotate the shoulder. An anteroposterior and an axillary view in the scapular plane will confirm the diagnosis. On close inspection, figure 2 shows a faint fracture line across the humeral head while in figure 3 the anatomical head is separated from proximal humerus and completely displaced posterior to the glenoid.

QUESTION 2

No attempt should be made to reduce these fracture dislocations in the casualty department. Under general anaesthesia an attempt should be made to reduce the fracture manually. If unsuccessful after the first attempt, closed manipulation must be abandoned and the fracture should be exposed using an anterior deltopectoral approach. Shoulder hemi-arthroplasty has been used frequently in the past to replace the damaged head. However, it is now established that anatomical reduction of the fracture using cancellous, cannulated or Herbert screws will allow the head fragment to unite and regain its vascularity by ‘creeping substitution’ with minimal incidence of avascular necrosis.

Discussion

The majority of the daily workload in an accident and emergency department comprises musculoskeletal injuries. Rushed examination, work overload, and inadequate consideration of differential diagnosis for routine injuries have led to cases of missed diagnosis.

Posterior shoulder dislocation is a rare injury and represents 1–4% of shoulder dislocations. A fracture associated with a posterior shoulder dislocation is even more uncommon, accounting for less than 1% of all reported cases.1 Because of its rarity and deceptive clinicoradiological features, it has been called a ‘diagnostic trap’ for the unsuspecting. It is estimated that approximately 60% of posterior fracture dislocations are missed by the initial examining clinicians.2 Most of these fracture dislocations are three- or four-part, involving the surgical neck, head and the two tuberosities. Isolated fracture dislocation of the anatomical head of humerus is a rare injury, and only a few case reports are available in the literature.2-4

The vascular supply of the humeral head is mainly through the ascending branch of the anterior circumflex humeral artery, called the ‘arcuate artery’, and partly through the posterior circumflex humeral artery which enters the humeral metaphysis just below the level of the anatomic neck. Other smaller contributions arise from capsular and muscular attachments. They form a rich anastomotic network supplying the articular surface. Fractures through the anatomical neck carry the highest risk of damage to the vascular supply of the head, leading to avascular necrosis. In most cases all vessels are disrupted and soft tissue attachments torn. Avascular necrosis has been reported in 75% of patients treated with internal fixation or closed manipulation.2 To overcome this complication, which leads to bony collapse and arthritic changes in the shoulder joint, a prosthetic replacement of the fractured head has been suggested. However this seems a radical procedure, especially in young patients, as the reported functional results have been variable. Tanner and Cofield5 could not obtain more than 100° abduction in the majority of their patients, while Neer found satisfactory to excellent results in 39 of his 43 patients.6 Due to recent refinements in techniques of open reduction, encouraging results have been achieved following internal fixation of the separated head. All patients with a posterior fracture dislocation of the anatomical head treated with screw fixation have reported excellent results.2-4 However, these results could only be achieved in those patients who were promptly diagnosed and operated upon immediately.

At operation, we found complete separation of the anatomical head from its capsular attachments. This was reduced anatomically and fixed using two cancellous lag screws (figure 4A). The fracture united radiologically at 3 months and 5 months later the screws were removed (figure 4B). The head, which lost all of its blood supply, was revascularised by intra-osseous vascular growth across the fracture site extending to the articular surface, a process called ‘creeping substitution’.4 It shows no signs of avascular necrosis. On last review at 1 year since surgery the patient has made a full functional recovery and remains asymptomatic.

Figure 4

(A) Immediate post-operative film, (B) after removal of screws 8 months post-operatively

Several valuable points can help to reduce the chance of missing a posterior fracture dislocation. A thorough history and clinical examination should arouse suspicion. The majority of these injuries result from road traffic accidents involving a motorbike. Flattening of the anterior contour of the shoulder with posterior prominence, inability to rotate the shoulder externally, and prominence of coracoid process are the classic clinical features. All patients with glenohumeral trauma should have a ‘shoulder trauma series’.2 This consists of three views, anteroposterior, lateral and axillary. These radiographs are taken in reference to the plane of the scapula (30–40° anterior tilt in the coronal plane) and not the plane of the body, as the glenohumeral joint may not be adequately visualised on ordinary exposures leading to diagnostic errors. The anteroposterior view is taken at right angles to the plane of the scapula while the lateral view is taken in the plane of the scapula. Both views improve the chance of diagnosing these fracture disloca-     tions by 50%. An additional axillary view confirms the diagnosis. If doubt persists, clinical observation and comparative radiographs of the uninjured side should be used to help in the diagnosis. Computed tomography and magnetic resonance imaging are invaluable where such facilities exist.

This case is interesting since very few case reports of fracture dislocation of the anatomic head of humerus have been reported in the literature, especially with full functional recovery after open reduction and internal fixation. This result may be related to early detection and prompt intervention. It also re-emphasizes the point that these injuries can easily be missed in a busy accident and emergency department unless thorough clinical examination and proper films are obtained.

Final diagnosis

Posterior fracture dislocation of the anatomical head of humerus.

References

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