INFLUENCE OF THE RADIAL HEAD ON THE STABILITY AND LOADING OF THE LATITUDE TOTAL ELBOW ARTHROPLASTY

Abstract

A primary mode of failure for total elbow arthroplasty is osteolysis caused by wear debris. Loading of the polyethylene components by off-axis bearing loads is the likely cause of this debris. Load transfer at the elbow is affected by many factors, including the state of the radial head. New implant designs provide the option to use the intact, resected, or implant reconstructed radial head. However, the effect of the radial head state on stability and loading has not yet been investigated in these new implant designs.

We postulated that the presence of the native or prosthetic radial head would reduce the wear-inducing loading patterns experienced by the humeral component and improve joint stability compared to when the radial head is resected.

Seven cadaveric upper extremities, amputated at the mid humerus, were tested in a joint motion simulator equipped with an electromagnetic tracking system to quantify motion. Simulated active flexion was tested with the arm in the dependent position. Passive elbow flexion was conducted with the arm in the varus and valgus gravity-loaded orientations. After testing the intact elbow, the collateral ligaments were sectioned and a linked Latitude ulno-humeral joint replacement was performed (Tornier, Stafford, TX). The humeral component was instrumented with strain gauges for measuring varus-valgus bending and internal-external torsion. Ulno-humeral kinematics and humeral component loading were measured when the radial head was intact, resected, and following radial head arthroplasty.

An increase in varus-valgus laxity was noted following replacement of the ulno-humeral joint with the prosthesis (p< 0.05). There was no difference in joint laxity between the intact radial head, radial head excision or radial head arthroplasty (p> 0.05). Torsion moments increased, while bending loads decreased in the humeral component following radial head excision and were restored following radial head arthroplasty (p< 0.05).

No significant effect of radial head state on varus-valgus joint laxity was observed for the linked ulno-humeral prosthesis. In the absence of collateral ligaments, the observed post-operative increase in varus-valgus laxity can be attributed to the difference in laxity between the native joint and the articular components of the linked implant. Load transfer was altered by radial head excision, which may affect the magnitude of bearing wear and the incidence of aseptic loosening. Further studies are required to determine whether these changes in load transfer influence wear of the polyethylene components or implant loosening.