Proximal Interphalangeal Arthrodesis of Lesser Toes Utilizing K-Wires Versus Expanding Implants: Comparative Biomechanical Cadaveric Study.

Background:: Lesser toe proximal interphalangeal (PIP) joint arthrodesis is one of the most common foot and ankle elective procedures often using K-wires for fixation. K-wire associated complications led to development of intramedullary fixation devices. We hypothesized that X Fuse (Stryker) and Smart Toe (Stryker) would provide stronger and stiffer fixation than K-wire fixation.

Methods:: 12 cadaveric second toe pairs were used. In one group, K-wires stabilized 6 PIP joints, and 6 contralateral PIP joints were fixed with X Fuse. A second group used K-wires to stabilize 6 PIP joints, and 6 contralateral PIP joints were fixed with Smart Toe. Specimens were loaded cyclically with extension bending using 2-N step increases (10 cycles per step). Load to failure and initial stiffness were assessed. Statistical analysis used paired t tests.

Results:: K-wire average failure force, 91.0 N (SD 28.3), was significantly greater than X Fuse, 63.3 N (SD 12.9) ( P < .01). K-wire average failure force, 102.3 N (SD 17.7), was also significantly greater than Smart Toe, 53.3 N (SD 18.7) ( P < .01). K-wire initial stiffness 21.3 N/mm (SD 5.7) was greater than Smart Toe 14.4 N/mm (SD 9.3) ( P = .02). K-wire failure resulted from bending of K-wire or breaching cortical bone. X Fuse typically failed by implant pullout. Smart Toe failure resulted from breaching cortical bone.

Conclusion:: K-wires may provide stiffer and stronger constructs in extension bending than the X Fuse or Smart Toe system. This cadaver study assessed stability of the fusion site at time zero after surgery.

Clinical Relevance:: Our findings provide new data supporting biomechanical stability of K-wires for lesser toe PIP arthrodesis, at least in this clinically relevant mode of cyclic loading.