Reproducing Valgus Angle in Uncemented Humeral Hemiarthroplasty.

PURPOSE: Hemiarthroplasty may be considered for treatment of elbow arthritis with successful implantation requiring reproduction of native anatomy. This study identifies whether an uncemented hemiarthroplasty implant that achieves fixation with intramedullary (IM) screws can restore the valgus alignment of the distal humerus flexion-extension axis of rotation when assessed through radiographic parameters.

METHODS: We stripped six cadaveric specimens of soft tissues and obtained orthogonal radiographs to characterize native distal humerus anatomy. We implanted hemiarthroplasty components using IM screw fixation and obtained postimplantation radiographs. We compared the coronal plane angle between the IM canal and the flexion-extension axis of the native humerus with the angle between the IM canal and the implant's centerline of rotation. We identified the respective angulation between the IM canal of the humerus and the IM screw and body component.

RESULTS: Six cadavers (five men and one woman) underwent implantation. The average age of the cadavers was 62.7 years (range, 53-74). The mean difference in articular spool valgus was 3.64° (1.86-5.84). The angulation between the IM canal of the humerus and the IM screw was between 1° and 2.3°and angulation between the IM canal of the humerus and the body component was <3.5°.

CONCLUSIONS: This study identified radiographic recreation of distal humerus valgus angulation within 4°with an uncemented hemiarthroplasty implant. Angulation that occurs between the humeral body and the IM screw as well as different screw lengths and thread diameters likely contribute to the implant's ability to accommodate for different anatomic features.

CLINICAL RELEVANCE: These results suggest that uncemented hemiarthroplasty can reproduce valgus angulation of the centerline of rotation based on radiographic parameters.