Scaphoid Excision with Four-Corner Fusion: A Biomechanical Study

Abstract

Partial wrist arthrodesis is a commonly performed procedure for the treatment of posttraumatic wrist arthritis because of its ability to provide pain relief without sacrificing complete wrist motion. The purpose of this study was to evaluate the redistribution of force after four-corner fusion and scaphoid excision, and to correlate the findings with the reported clinical outcomes. Fifteen cadaveric wrists were used to study the biomechanics of the four-corner fusion. Pressure-sensitive film (super-low-pressure-indicating film-Pressurex, Sensor Products Inc, Madison, NJ) was inserted into the radiocarpal joint. Using the MTS 858 Mini Bionix (MTS System, Eden Prairie, MN), 50-kg loads (220 N) were applied to the wrists before and after simulated four-corner fusion and scaphoid excision. Statistically, we compared the pressure in the normal (intact) wrists versus four-corner fusion and scaphoid excision. The pressure measurements across the scaphoid fossa, lunate fossa, and triangular fibrocartilage complex (TFCC) were compared. There is a statistical significant difference between scaphoid, lunate, and TFCC mean total force when pre and post-fusion were compared (p = 0.0001). Our study revealed a statistical significant decrease in the mean scaphoid total force after scaphoid excision and four-corner fusion (p = 0.0001). We also found a subsequent increase in mean total force after scaphoid excision and four-corner fusion for the lunate fossa that did not reach statistical significance (p = 0.08), and no difference in load across the TFCC area (p = 0.995). Our findings suggest that load is preferentially transferred to the radiolunate joint after scaphoid excision with four-corner fusion.