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Constrained arthroplasty: its use and misuse.

Constrained arthroplasty is occasionally needed to salvage a destroyed glenohumeral joint when the rotator cuff is nonfunctioning and when an unconstrained prosthesis will not suffice. There is a high failure rate because of the severe forces between such a device and the contiguous bone. Accordingly, it is essential to know the limitations of constrained arthroplasty and when it should be avoided. For example, when the bone of the glenoid vault is highly demineralized or deficient or if there is a history of seizure disorder or alcoholism, use of such a device is contraindicated. Postoperatively, excessive force and extremes of motion should also be avoided during the rehabilitation program to avoid bone fracture or dislocation of the prosthesis. Various complications have been observed with constrained arthroplasty, including dislocation, bone fracture, pullout of the glenoid, infection, radial nerve injury after extrusion of bone cement through the humeral cortex when the cement has been pressurized, and screw breakage in a relative small number of cases after metal fatigue and loosening of the glenoid component. When the glenoid component has pulled away from the glenoid vault, it may be necessary to remove this component; the humeral head may be fitted with a bipolar 40- to 44-mm acetabular component, thereby allowing at least preservation, if not the active function of the shoulder contour.