Biomechanical Analysis of Micromotion of Proximal Interphalangeal Joint Arthrodeses During Activities of Daily Life In Vitro

Background/Objectives: Proximal interphalangeal joint (PIJ) arthrodesis is a common surgical intervention for patients with PIJ osteoarthritis or trauma-related joint destruction. The objective of this study was to evaluate the biomechanical stability of various arthrodesis techniques under forces comparable to activities of daily living (ADL) to assess their suitability for early active movement protocols. Methods: In this in vitro study, composite cylinders simulating PIJ arthrodesis were subjected to standardized fusion angles of 40 degrees using different fixation techniques, including crossed K-wires, compression screws, cerclage wires, tension band wiring, anatomical fixation plates, and locking grid plates. Forces representing ADLs such as typing, holding a pencil, carrying weight, and opening a jar were applied using a universal testing machine in a four-point bending setup. Micromotion and gap clearance were calculated and analyzed. Results: Techniques involving compression, such as compression screws, tension bands, and cerclage wires, exhibited lower micromotion and gap clearance under forces up to 17 N, suggesting potential suitability for early active movement protocols. In contrast, fixation plates demonstrated structural failure or excessive clearance during early active motion ADLs. K-wires showed intermediate results with moderate gap clearance and micromotion. Conclusions: Compression-based fixation techniques for PIJ arthrodesis may permit early active movement without external stabilization, while fixation plates are prone to failure under ADL forces. Further dynamic biomechanical testing and clinical studies are recommended to confirm these findings.