A biomechanical assessment of fixation methods for a coronoid prosthesis

Abstract

BackgroundThe coronoid process is an integral component for maintaining elbow joint stability. When fixation of a fracture is not possible, prosthetic replacement may be a feasible solution for restoring stability. The purpose of this in-vitro biomechanical study was to compare fixation methods for a coronoid implant. MethodsA coronoid prosthesis was subjected to distally-directed tip loading after implantation using four fixation methods: press-fit, anterior-to-posterior screws, posterior-to-anterior screws, and cement. Testing was performed on seven fresh-frozen ulnae in a repeated-measures model. Rounds of cyclic loading were applied at 1Hz, for 100cycles, increased in 50N increments up to a maximum of 400N. Micro-motion of the implant was quantified using an optical-tracking system. Outcome variables included total displacement, distal translation, gapping, anterior translation and axial stem rotation. FindingsCement fixation reduced implant micro-motion compared to screw fixation, while the greatest implant micro-motion was observed in press-fit fixation. Comparing screw-fixation techniques, posterior–anterior screws provided superior stability only in distal translation. The implant did not experience displacements exceeding 0.9mm with screw or cement fixation. InterpretationCement fixation provides the best initial fixation for a coronoid implant. However, the stability provided by both methods of screw fixation may be sufficient to allow osseous integration to be achieved for long-term fixation. Large displacements were observed using the press-fit fixation technique, suggesting that modifications would need to be developed and tested before this technique could be recommended for clinical application.