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Editor,— A 57 year old man presented with a spontaneous posterior dislocation of his right shoulder. It had happened as he reached up to open an overhead cupboard door. He had first dislocated it eight weeks before, while an inpatient receiving chemotherapy for a brain tumour.
He was accompanied by his daughter. When asked she admitted having dislocated both her shoulders in the past. From the history these seemed to be spontaneous dislocations. As there appeared to be a familial tendency she was asked about other members of the family. One of her three sisters and a niece had also suffered spontaneous dislocated shoulders. She then admitted that the patient was not her biological father: only her stepfather, but that her biological father (deceased) had a history of spontaneous shoulder dislocation. The result of this inquiry was a family tree in which three generations had suffered from spontaneous dislocations of the shoulder. There was no family history of any other joint dislocations, nor was there any history of noticeable joint laxity, or “double jointedness”. None of the family had had any surgery to prevent further recurrences.
Atraumatic dislocations of the shoulder are relatively uncommon. Rowe, in 1956, noted that atraumatic shoulder dislocations only accounted for 4% of a series of 500 dislocations.1 However, atraumatic instability of the shoulder is a well recognised phenomenon, which may be multidirectional and bilateral. Recurrent instability often results from minor trauma, such as lifting an arm, or reaching up, as described by the index case in this report.
Regarding the familial tendency seen in this case Hovelius noted that 17% of young adults (aged 23–29 years) with shoulder instability had the problem in both shoulders, and that the incidence of dislocation in other family members was 5%, compared with only 1.7% for the general population.2 Therefore, the incidence for three generations in a family with dislocating shoulders will be 0.00425% (1.7% × 5% × 5%).
Joint laxity has been suggested as a cause of familial recurrent dislocation of the shoulder.3 It is a feature of several dominantly inherited conditions, such as Ehler's-Danlos and Marfan's syndromes, and osteogenesis imperfecta. Congenital dislocations, especially of the elbow, are also a feature of Larsen's syndrome (pentasomy X). Carter and Sweetnam, who investigated the role of joint laxity in recurrent dislocations of the patella and of the shoulder, found only two families in which two family members had suffered recurrent dislocated shoulders, from their series of 40 patients with recurrent shoulder dislocations.3 In neither case did the condition extend over three generations. A three generation history of recurrent shoulder dislocation would seem to be a very rare event.