Washer and Post Augmentation of 90/90 Wiring for Proximal Interphalangeal Joint Arthrodesis: A Biomechanical Study.

ABSTRACT

PURPOSE: To describe a novel construct for proximal interphalangeal (PIP) joint arthrodesis using headless cannulated screws as an intramedullary washer to augment 90/90 intraosseous wiring and compare the biomechanical properties of this construct with those of the 90/90 intraosseous wiring without headless screw augmentation. METHODS: Biomechanical evaluation of augmented 90/90 intraosseous wiring with headless cannulated screws (group 1) or 90/90 intraosseous wiring without augmentation (group 2) for PIP joint arthrodesis was performed in 3 matched-pair cadaveric specimens (12 digits per group). Each group was loaded to 10 N in the sagittal and coronal planes and the resultant stiffness from the load-displacement curve was calculated. In extension, each group then underwent load to permanent deformation and load to catastrophic failure. RESULTS: The augmented 90/90 intraosseous wiring with cannulated screws construct demonstrated significantly greater stiffness by 132%, 64%, 79%, and 75% in flexion, extension, ulnar, and radial displacement, respectively. During load to permanent deformation testing, a 42% greater force was required to create permanent deformation in group 1 compared than group 2. There was no significant difference between the 2 groups during load to catastrophic failure testing. CONCLUSIONS: Augmenting 90/90 intraosseous wiring for PIP joint arthrodesis with 2 headless cannulated screws in the sagittal plane that serve as intramedullary washers for the sagittal wire and posts for the coronal wire significantly increases stiffness in all directions as well as load to permanent deformation compared with 90/90 intraosseous wiring without cannulated screw augmentation. CLINICAL RELEVANCE Augmentation of the 90/90 intraosseous wire construct with headless cannulated screws can be considered in patients at risk for wire cutout or implant failure.