Morphologic analysis of the medullary canal in rheumatoid elbows.

Total elbow arthroplasty is a standard approach for patients with arthritic elbows. To design appropriate stems for elbow prostheses, it is important to understand the shape of the medullary canals. The purpose of this study was to evaluate the shape and size of the medullary canals from normal cadavers and rheumatoid arthritis patients. These canals were measured based on geometric constructions of the 3-dimensional bone models generated from computed tomography images. The cross-sectional area of the medullary canals in rheumatoid arthritis patients decreased near the elbow joint as a result of morphologic changes after a long-standing inflammatory reaction. When designing the press-fit component of the humerus, an increase in the width of the transverse diameter of the intramedullary stem could increase stability in the canal. In contrast, for the ulnar component, such morphologic changes would impose difficulty in placing the press-fit model despite an anatomically designed stem. Therefore, a cement technique would be required for improved stabilization of the ulnar component.