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.

Assessment of Workspace Attributes Under Simulated Index Finger Proximal Interphalangeal Arthrodesis

This article presented an assessment of quantitative measures of workspace (WS) attributes under simulated proximal interphalangeal (PIP) joint arthrodesis of the index finger. Seven healthy subjects were tested with the PIP joint unconstrained (UC) and constrained to selected angles using a motion analysis system. A model of the constrained finger was developed in order to address the impact of the inclusion of prescribed joint arthrodesis angles on WS attributes. Model parameters were obtained from system identification experiments involving flexion–extension (FE) movements of the UC and constrained finger. The data of experimental FE movements of the constrained finger were used to generate the two-dimensional (2D) WS boundaries and to validate the model. A weighted criterion was formulated to define an optimal constraint angle among several system parameters. Results indicated that a PIP joint immobilization angle of 40–50 deg of flexion maximized the 2D WS. The analysis of the aspect ratio of the 2D WS indicated that the WS was more evenly distributed as the imposed PIP joint constraint angle increased. With the imposed PIP joint constraint angles of 30 deg, 40 deg, 50 deg, and 60 deg of flexion, the normalized maximum distance of fingertip reach was reduced by approximately 3%, 4%, 7%, and 9%, respectively.