In vitro assessment of the contact mechanics of reverse-engineered distal humeral hemiarthroplasty prostheses

• We developed distal humeral implants which replicate the native bone shape.
• We examined contact patterns before and after hemiarthroplasty with these implants.
• Cartilage contact area decreased by almost 50% following hemiarthroplasty.
• Cartilage contact locations also changed following hemiarthroplasty.

BackgroundDistal humeral hemiarthroplasty alters cartilage contact mechanics, which may predispose to osteoarthritis. Current prostheses do not replicate the native anatomy, and therefore contribute to these changes. We hypothesized that prostheses reverse-engineered from the native bone shape would provide similar contact patterns as the native articulation.MethodsReverse-engineered hemiarthroplasty prostheses were manufactured for five cadaveric elbows based on CT images of the distal humerus. Passive flexion trials with constant muscle forces were performed with the native articulation intact while bone motions were recorded using a motion tracking system. Motion trials were then repeated after the distal humerus was replaced with a corresponding reverse-engineered prosthesis. Contact areas and patterns were reconstructed using computer models created from CT scan images combined with the motion tracker data. The total contact areas, as well as the contact area within smaller sub-regions of the ulna and radius, were analyzed for changes resulting from hemiarthroplasty using repeated-measures ANOVAs.FindingsContact area at the ulna and radius decreased on average 42% (SD 19%, P = .008) and 41% (SD 42%, P = .096), respectively. Contact area decreases were not uniform throughout the different sub-regions, suggesting that contact patterns were also altered.InterpretationReverse-engineered prostheses did not reproduce the same contact pattern as the native joints, possibly because the thickness of the distal humerus cartilage layer was neglected when generating the prosthesis shapes or as a consequence of the increased stiffness of the metallic implants. Alternative design strategies and materials for hemiarthroplasty should be considered in future work.