A biomechanical comparison of shape memory compression staples and mechanical compression staples: compression or distraction?

Compression staples are a popular form of fixation for osteotomy and arthrodesis. "Mechanical compression" or "shape memory" designs are commercially available. We performed a biomechanical study comparing these designs. A load cell measured compression across a simulated fusion site. The two designs available were tested and compared. The effect of altering staple limb length was also assessed. The limbs of all mechanical compression staples diverged causing inconsistent compression and distraction. Shape memory staples all achieved consistent compression across the fusion site with significantly greater maximum force when compared to mechanical compression staples (P < 0.001). Staple limb length did not appear to alter compression force generated. Mechanical compression staples cause a distractive force, and we therefore suggest alternate forms of fixation for arthrodesis. Shape memory staples do provide compression and may be suitable for arthrodesis and osteotomy.