"Floating-socket" total shoulder replacement: anatomical, biomechanical, and surgical rationale.

A prosthesis based on a new concept of gleno-humeral motion has been developed and clinically tested for the past 2 years. The "floating-socket" total shoulder replacement contains a nondislocatable, dual spherical bearing system consisting of a small sphere within a larger sphere with their centers offset to provide the physiologic "floating fulcrum" for mechanically advantageous motion. This geometric configuration allows a prosthetic range of motion in excess of anatomical limits to allow soft tissue structures to limit motion rather than mechanical impingement. The device is constructed from Co--Cr--Mo alloy and RCH-1000 polyethylene such that no metal--metal contact can occur. Experimental results in a 112-lb adult male chimpanzee and six clinical cases have revealed superior fixation strength of both glenoid and humeral components, as well as functional adaptation of the prosthesis without fracture of fixturing bone or prosthetic dislocation.

Cylindrical total ankle joint replacement: surgical and biomechanical rationale.

Incongruent designs of total ankle arthroplasty are all unsatisfactory owing to inherently poor wear, deformation resistance, and poor stability. Several congruent designs are capable of providing good function. It is concluded that a cylindrical surface with a horizontal axis located at the center of curvature of the lateral border of the talar dome seems most desirable where adequate subtalar motion is present and a spherical type seems most desirable where such motion is not present. The "New Jersey" cylindrical total ankle arthroplasty using a cylindrical surface uses an ultrahigh molecular weight polyethylene talar component and a mortised cobalt-chromium alloy tibial component both stabilized with methylmethacrylate bone cement and dual fixation fins.

Pyarthrosis of the manubriosternal joint.

This is a case report of primary osteomyelitis of the sternum, the only case of pyarthrosis of the manubriosternal joint the authors are able to find in the American literature. The diagnosis was established by tomogram and open biopsy. The treatment was thorough and specific antibiotic coverage.