Do Transcortical Screws in a Locking Plate Construct Improve the Stiffness in the Fixation of Vancouver B1 Periprosthetic Femur Fractures? A Biomechanical Analysis of 2 Different Plating Constructs

Abstract

OBJECTIVES: This biomechanical study compared Vancouver B1 periprosthetic femur fractures fixed with either a locking plate and anterior allograft strut construct or an equivalent locking plate with locking attachment plates construct in paired cadaveric specimens. METHODS: After 9 pairs of cadaveric femora were implanted with a cemented primary total hip arthroplasty, an oblique osteotomy was created distal to the cement mantle. Femora underwent fixation with either: (1) a locking plate with anterior strut allograft (locking compression plating (LCP)-Allograft) or (2) a locking plate with 2 locking attachment plates (LAPs) (LCP-LAP). Construct stiffness was compared in nondestructive mechanical testing for 2 modes of compression (20 degrees abduction and 20 degrees flexion), 2 four-point bending directions (anterior-posterior and medial-lateral), and torsion. A final load to failure test evaluated the axial compression required to achieve fracture gap closure or construct yield. Fixation was compared through paired t tests (α = 0.05). RESULTS: The LCP-Allograft construct demonstrated higher stiffness values in compressive abduction (207 ± 57 vs.151 ± 40 N/mm), torsion (1666 ± 445 vs. 1125 ± 160 N mm/degree) and medial-lateral four-point bending (413 ± 135 vs. 167 ± 68 N/mm) compared with the LCP-LAP construct (P < 0.05). No differences were identified between the 2 constructs in compressive flexion, anterior-posterior bending, or the load to failure test (P > 0.05). CONCLUSION: Use of the anterior allograft strut created a stiffer construct compared with the LCP-LAP for the treatment of a Vancouver B1 periprosthetic femur fracture only in loading modes with increased medial-lateral bending. Although these static load results are indicative of the early postoperative environment, further fatigue testing is required to better understand the importance of the reduced medial-lateral stiffness over a longer period.