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Fractures of the scapula occur infrequently, with a fracture of the acromion being an even rarer entity. Acromial fractures constitute 9% of fractures of the scapula, which amounts to 3–5% of shoulder girdle injuries.1 Fractures of the acromion are generally secondary to trauma, with only a few cases of stress fracture having been reported.2–5
Reports published in English have described stress fractures of the acromion at the base of the acromion extending to the spine of the scapula,2 neck of the acromion,3 medial aspect of the acromion,4 and the base of the acromion only.5 These cases occurred in young to middle aged patients and were associated with a single violent muscle contraction or repetitive subcritical load to the shoulder. We present a case of an atraumatic osteoporotic stress fracture at the base of the acromion associated with chronic rotator cuff tear arthropathy.
The patient, an 82 year old woman, was admitted to the medical ward with heart failure and varicose ulcers. She was referred to the orthopaedic department because of a three day history of left shoulder pain without trauma. She was mostly wheelchair bound but did walk indoors with a Zimmer frame.
Examination showed mild tenderness and crepitus at the base of the acromion where a fracture gap could be palpated. Active shoulder movements were restricted to 90° of both flexion and abduction. She also had a senile osteoporotic kyphosis of her thoracic spine. Anteroposterior and axillary radiographs of the shoulder showed a displaced fracture of the base of the acromion with superior subluxation of the head of the humerus, suggesting chronic rotator cuff tear arthropathy (figs 1 and 2). A radiograph of her spine confirmed the osteoporotic kyphosis of the thoracic vertebrae. Blood tests including full blood count, erythrocyte sedimentation rate (ESR), bone biochemistry, and myeloma screen were normal. She was treated conservatively in a broad arm sling with gradual mobilisation as her pain subsided. She recovered nearly full movements of her shoulder in four weeks. A follow up x ray examination at six months showed a non-union of the fracture, which was not painful.
Osteoporotic fractures without a history of trauma usually occur in the legs, pelvis or spine and rarely in the arms. Repetitive subcritical trauma or single violent muscular pulls have occasionally been associated with fractures of the acromion.1–5 Of the previous four cases of a similar type of injury reported, two were professional sports players,5 one was a car mechanic who felt a sudden crack in his shoulder while applying torque with a screwdriver,3 and the fourth was a woman playing golf, who suddenly felt acute pain in her shoulder as she hit the ball.2 It was not possible to correlate our patient's injury with any trauma, indeed she recalled waking up in the morning with sudden pain, which gradually got worse. Dennis et al reported three cases of stress fracture of the anterior impingement zone of the acromion.6 All three patients had severe rotator cuff arthropathy and two had steroid dependent rheumatoid arthritis.6 Surgical excision of the fragments was carried out in all three of his patients when conservative treatment had failed, with one patient eventually requiring shoulder replacement. Pain improved in the other two patients, but there was no improvement in the range of motion. All the fractures reported united after conservative treatment except in the series reported by Dennis et al.6
It is sometimes difficult to visualise this fracture without adequate penetration of radiographs in the appropriate plane. These fractures are best visualised in the axillary view in our opinion (fig 2). All previous cases have been either linear undisplaced fractures or diagnosed by an isotope bone scan. One case did show sclerosis at the base of the acromial arch on x ray examination, which on subsequent bone scan was confirmed to be a fracture.5 We believe that abnormal pressure from the humeral head on the acromion, due to the rotator cuff arthropathy, leads to excessive movement at the fracture site causing a non-union of the fractured acromion.
Shoulder pain is a common complaint in elderly people. A stress fracture of the acromion should be considered in patients with chronic rotator cuff tear arthropathy who have osteoporosis and whose shoulder pain increases spontaneously. Routine use of good quality axillary radiographs in such patients should lead to a higher rate of diagnosis of such injuries.
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