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 humeral breast cancer metastasis. Humeral 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 systemʹs 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° flexion, 45° 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 patientʹs condition deteriorated; at 33 months she was bedridden, and radiography showed dislocation of the humeral component. (J Shoulder Elbow Surg 1998;7:13-8.)