Total shoulder replacement by magnetic arthroplasty.

Permanent magnets offer a novel solution to the problem of shoulder implant instability when the rotator cuff has been destroyed. We report a case of their use in a 66-year-old patient with a large proximal humerol breast cancer metastasis. Humerol resection was below the deltoid insertion. The polyacetal device had samarium-cobalt magnets in the humeral head. The glenoid component (the keeper in the magnetic circuit) was made of titanium nitride-coated F17 stainless steel. The system's breakaway force was ca. 40 N. At 24 months the shoulder was free of pain and stable, with an active range of movement of 30 degrees flexion, 45 degrees external rotation, and internal rotation to T8. The patient could perform household tasks and drive an automatic car. Radiography showed no implant loosening or upward humeral head dislocation. Subsequently, the patient's condition deteriorated; at 33 months she was bedridden, and radiography showed dislocation of the humeral component.