How Much Angular Offset is Acceptable to Achieve Minimum Contact for a Successful First Metatarsophalangeal Joint Fusion?

Abstract

First metatarsophalangeal joint (MTPJ) fusion is a surgery to treat severe joint arthritis and pain following failure of conservative treatment. A first MTPJ fusion can be performed open or via a percutaneous approach with joint fixation achieved using various techniques including dorsal plate and screw fixation. Variability in the angulation of the guide wire used for reaming during joint resurfacing and the plate angulation can compromise the amount of bony contact needed for successful fusion. The objective of the current study was to utilize a 3-dimensional computational, geometric model to quantitatively analyze the effects of guide wire placement and subsequent bone resurfacing on the achievement of bony contact criteria using 3 dorsiflexion plates in joint fixation. A superposed ideal hemisphere model of the joint interface following resurfacing of the articulating surfaces was the basis for computational analysis. A custom-written code quantified angular offset limits for selected conditions. The angular offset from the central long axis of each bone represents initial guide wire placement error, impacting subsequent fixation and union.For 60% bony contact achieved in the joint interface for 0°, 5°, and 10° dorsiflexion plates angular offset limits for both the sagittal and transverse planes were 21.6°, 20.3°, and 19.0°, respectively. These analyses provide surgical guidance by quantifying the influence of dorsiflexion plate angles for ambulation and guide wire placement on the success of a first MTPJ fusion. The computational model presented can be readily adapted for varying joint geometries and may facilitate the development of a surgical guide prototype.