||BIOMECHANICAL COMPARISON OF THREE FIXATION TECHNIQUES OF FOUR CORNER ARTHRODESIS: K-WIRES VERSUS CIRCULAR PLATE (SPIDER PLATE) AND LOCKED CIRCULAR PLATE (XPODE PLATE).
Shin A.Y., Kraisarin J., Berglund L. J., An K. N., Dennison D. G. (Rochester MN USA)
Four-corner arthrodesis is a common technique for salvage of degenerative wrist problems. Advocates of plate fixation state rigid fixation allows early motion, which improves outcome, however,no biomechanical studies have evaluated these plates. The purpose of this study is to compare biomechanical profile of Kwires versus locked and unlocked dorsal circular plate in four-corner arthrodesis in physiologic condition mimicking early active range of motion.
Materials and Methods:
6 paired(12wrists) of fresh frozen cadaveric wrists underwent scaphoidectomy and four corner arthrodesis using K-wires (0.045” x 4) , unlocked stainless steel dorsal circular plates(Spider plate, Kinetikos Medical Inc.) or locked polyethlyethlyketone circular plate (Xpode, Trimed Inc.) An electromagnetic motion sensor was placed in the capitate and lunate. The specimens were placed in a cyclical flexion-extension wrist joint simulator(Figure 1). Repetitive cyclic wrist flexion and extension was applied using both displacement and force control. Hardware failure or motion > 2 mm was considered a failure of fixation.
The biomechanical profiles for 5000 cycles and the initial 100 cycles are shown below(Figure 2). 67% in the K wire group catastrophically failed, and 67% of the Spider plate group failed. There were no failures of the Xpode plate fixation group. Mode of failure in K-wire group were including pin breakage, bending, and loosening. For the spider group failure mechanism involved loosening screws.
This study determined the immediate stability of each fixation technique for cyclical loading mimicking early motion. Spider plate provide more rigid fixation in flexion and abruptly increase motion when more than 35 degree wrist extension occur. Xpode plate provided more stability in extension and was able to withstand cyclical loading in this experiment, and could tolerate simulated early range of motion without failure.
Comparison of displacement