Biomechanical Comparisons of Trochanteric Hip Fracture Fixation Using Short-, Mid-, and Long-Length Proximal Femoral Nails

Abstract

Introduction For trochanteric hip fractures, proximal femoral nails (PFNs) have been frequently used for surgical treatment. No study has clarified whether length of the nail affected the wiper motion; the repetitive motion of the distal nail inside canal after surgery. Methods Thirty synthetic femora were used to biomechanically evaluate construct lateral angular movement of 3 different lengths of PFN [TFN-ADVANCED Proximal Femoral Nailing System (TFNA) 170 (short-length), 235 (mid-length), and 300 (long-length) mm] constructs for the fixation of stable pertrochanteric fractures. Cyclic testing and radiological evaluation were performed to investigate the loosening patterns in 3 different fixation constructs. Migration along the mechanical axis during the cyclic testing from 1-100th, 100-500th, 500-1000th, 1000-1500th, and 1500-2000th cycles was compared between TFNA lengths. Also, before and after cycling changes in tip to apex distance, angulation of fracture line, and lateral angular movement of the distal stem inside the canal were compared between TFNA lengths. Results Migration along the mechanical axis during cyclic loading, plus changes after cycling in tip to apex distance, and fracture line angulation did not differ between TFNA lengths for the fixation of stable intertrochanteric fracture model using synthetic femora. Conversely, one-way analysis of variance revealed a significant difference in lateral angular movement of the distal stem inside the canal after cyclic testing between groups (1.4 ± 1.6°, .21 ± .35°, and .26 ± .57° in 170-mm short nail, 235-mm middle nail, and 300-mm long nail, respectively; P = .026), and post-hoc analysis also revealed that middle nail yielded significantly less lateral angular movement compared with short nail ( P = .047) but did not significantly differ from the long nail. Conclusions Mid-length TFNA for the fixation of stable trochanteric hip fracture model using synthetic femora resulted in significantly smaller lateral angular movement of the distal stem after cyclic loading.