The effect of distal humeral hemiarthroplasty on articular contact of the elbow.

BACKGROUND

Hemiarthroplasty is a treatment option for selected distal humerus fractures. The purpose of this study was to determine the effect of distal humeral hemiarthroplasty and implant size on elbow articular contact. We hypothesized that implants of varying sizes produce different contact patterns compared with the native elbow.

METHODS

Eight cadaveric arms were tested in an elbow simulator and the kinematics recorded. Three-dimensional reconstructions of bones and cartilage were generated from computed-tomography images to determine contact patterns. The native articulation was compared to optimal, oversized, and undersized implants (Latitude Anatomic Hemiarthroplasty). Changes in contact patterns relative to the native articulation were measured using total contact area and contact patch agreement scores, defined as the sum of distance between contact patches×area, indicating how well contact patches agree with the native contact pattern.

FINDINGS

The native articulation had significantly lower ulnohumeral contact patch agreement scores compared to all tested implants (P<0.05). Mean ulnohumeral and radiocapitellar contact area decreased an average 44% (P=0.03) and 4% (P=0.07) following placement of an optimally sized implant. There was no effect of implant size on contact area or contact patch agreement score (P>0.05).

INTERPRETATION

Shape differences of elbow implants relative to the native joint may be responsible for altered contact patterns and could be improved with design modifications. These changes may predispose the elbow to arthritis. The lack of influence of implant size suggests that implant shape and materials may be more important than implant sizing during surgery.