Downloaded from http://journals.lww.com/jorthotrauma by BhDMf5ePHKbH4TTImqenVHsCMLYwnrnSi8CcQfZs/+mEJFMIjl4S+EEDGp8arb6NWHek2MvG11s= on 11/26/2018 ORIGINAL ARTICLE Biomechanical Evaluation of Osteoporotic Proximal Periprosthetic Femur Fractures With Proximal Bicortical Fixation and Allograft Struts Robert S. O’Connell, MD,* John R. Owen, MS,† Erik J. Hansen, MD,* Azhar S. Bashir, BS,‡ Jennifer S. Wayne, PhD,† Jibanananda Satpathy, MD,* and Stephen L. Kates, MD* Objectives: To evaluate the strength of proximal bicortical ﬁxation using a novel osteoporotic synthetic bone model of Vancouver B1 periprosthetic proximal periprosthetic femur fractures (PFFs) and to assess the inﬂuence of strut allograft augmentation with regard to allowing early assisted weight bearing. The secondary aim was to evaluate whether the strut position, either medial or anterior, inﬂuenced the strength of the construct. Methods: Thirty synthetic osteoporotic femurs were implanted with cemented stems. A segmental defect made distal to the stem simulated a fracture and was repaired with a stainless steel locking compression plate and 2 stainless steel proximal locking attachment plates. Specimens were then divided into 3 groups: no-strut, medial strut, and anterior strut. Cadaveric femoral struts were wired to the specimens. Cyclic axial compression simulated assisted weight bearing and was followed by loading to failure. Results: Medial struts required higher failure load than no-strut (P = 0.008) and more energy to failure than anterior (P = 0.018) or no-strut (P , 0.001). The higher load to failure, however, would not be advantageous in clinical practice because estimates for assisted weight bearing after fractures in average-weight patients are well below these failure loads. Furthermore, all specimens tolerated cycli- cal loading. All failures occurred distal to the plate originating at the last screw hole. Conclusions: Failure loads for all groups were above what would be expected for low-demand activities of assisted weight bearing. Therefore, proximal bicortical ﬁxation should allow for early, assisted weight bearing without allograft strut augmentation even with lower density bone. Key Words: proximal periprosthetic femur fracture, osteoporosis, proximal bicortical ﬁxation, locking screw, biomechanical, allograft strut (J Orthop Trauma 2018;32:508–514) INTRODUCTION As the volume of total hip arthroplasty increases, the incidence of proximal proximal periprosthetic femur fractures (PFF) also increases ranging from 0.1% to 18%. 1–3 Most PFFs occur from low-energy trauma in patients with reduced bone quality and are associated with higher mortality and ﬁnancial burden compared with primary hip replacement. 2–5 Many elderly individuals do not regain their prefracture functional status. 6,7 Treatment of periprosthetic fractures is adapted to the fracture location and pattern with the goals of bony union and early recovery of mobility. Commonly, PFFs occur around the tip of a well-ﬁxed stem, designated as Vancouver type B1 fractures. 3,5 These are technically challenging to treat, given limited proximal ﬁxation, altered surgical ﬁeld, osteoporotic bone, and patient comorbidities. Type B1 PFFs are most com- monly treated using plate stabilization with a combination of cables and allograft struts. 8 Traditional plate ﬁxation alone has been associated with high failure rates ranging between 31% and 52%, which is attributed to screw loosening or pullout from the proximal fragment. 5,9,10 Historically, plate and strut con- structs have been shown to have the highest stiffness. 11–13 Although there is no consensus on the ideal ﬁxation construct, locking plates are commonly used with or without femoral strut allografts in patients with osteoporotic bone and fracture com- minution because they have been shown to increase stability and stiffness. 14–17 However, even with stable locking plate ﬁxation, Niikura et al 16 showed that only 53% of patients recovered mobility and only 68% returned to preinjury ambulatory status. Recent advances in technology allow for locking screws with bicortical proximal ﬁxation around the stem to increase the stability of the construct potentially allowing early weight bearing. 9 Although the literature supports the use of newer proximal bicortical screw ﬁxation in PFFs, there are limited data in osteoporotic bone to evaluate its strength and if allograft struts are needed. Previous biomechanical studies evaluated the locking attachment plate (LAP; Synthes, Paoli, PA) and have shown increased stability and strength compared with traditional Accepted for publication June 8, 2018. From the *Department of Orthopaedic Surgery, VCU Health System, Richmond, VA; †Departments of Orthopaedic Surgery and Biomedical Engineering, Orthopaedic Research Laboratory, Virginia Commonwealth University, Rich- mond, VA; and ‡Virginia Commonwealth University School of Medicine, Richmond, VA. AO Trauma North America provided partial grant support. DePuy Synthes donated implants and instrumentation for this work. R. S. O’Connell, J. S. Wayne, J. Satpathy, and S. L. Kates have received grant support from AOTrauma North America for this study (Grant R16RESRCH-VCU). S. L. Kates has received grant funding/resident research support from the AO Foundation/DePuy Synthes and Arthrex. E. J. Hansen has received research support from DePuy Synthes. The remaining authors report no conﬂict of interest. Reprints: Stephen L. Kates, MD, Department of Orthopaedic Surgery, Virginia Commonwealth University, P.O. Box 980153, Richmond, VA 23298-0153 (e-mail: Stephen.kates@vcuhealth.org). Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved. DOI: 10.1097/BOT.0000000000001261 508 | www.jorthotrauma.com J Orthop Trauma  Volume 32, Number 10, October 2018 Copyright Ó 201 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited. 8