Biomechanical analysis of a novel femoral neck locking plate for treatment of vertical shear Pauwel’s type C femoral neck fractures Peter J. Nowotarski a , Bain Ervin a, *, Brian Weatherby b,c , Jonathan Pettit d , Ron Goulet e , Brent Norris f a University of Tennessee, College of Medicine Chattanooga, Department of Orthopaedics, 975 East Third Street, Hospital Box 287, Chattanooga, TN 37403, USA b Orthopaedic Surgery, Surgery of the Foot and Ankle Steadman-Hawkins Clinic of the Carolinas, 200 Patewood Drive, Suite C100, Greenville, SC 29615, USA c University of Texas Health Science Center, College of Medicine Houston, Department of Orthopaedics, 6410 Fanin St Ste 1535, Houston, TX 77025, USA d Middle Tennessee Bone & Joint, 1050 N James Campbell Blvd, Suite 20, Columbia, TN 38401, USA e University of Tennessee Chattanooga, College of Engineering and Computer Science, EMCS, Dept 2452, 615 McCallie Avenue, Chattanooga, TN 37403, USA f Orthopaedic Trauma Services of Oklahoma, 2424 E. 21st Street, Suite 320, Tulsa, OK 74114, USA Femoral neck fractures in young patients (<50 years) are usually the result of high-energy trauma. Excellent results have been reported for emergent open reduction and internal fixation (ORIF) of femoral neck fractures in young patients with high union rates (83–100%) and low incidence of avascular necrosis. 1–3 Anatomic reduction and stable internal fixation are essential for a good outcome. Increasing fracture angle (verticality) in Pauwels type C or III femoral neck fractures has been implicated in causing higher rates of fixation failure and nonunion as a result of the higher shear forces and varus instability that are generated. 4–7 Many internal fixation constructs have been used with varying clinical and biomechanical results in multiple studies. A recent retrospective clinical study confirmed better union rates for vertical femoral neck fractures treated with fixed angle devices compared with cannulated screws alone. 8 Earlier biomechanical studies demonstrated both the compression hip screw with derotation screw and multiple ‘cross’ screws (transverse calcar lag screw) to be superior to parallel cannulated screws. 9–12 Locking plate technology, which allows multiple points of fixed angle fixation into short epiphyseal segments, has recently been investigated for fixation of vertical femoral neck fractures. The Synthes proximal femoral locking plate (Synthes, Paoli, PA, USA) provided the strongest fixation of fresh-frozen cadaveric vertical femoral neck fractures when compared with multiple parallel cannulated screws and conventional fixed-angle implants. 13 Because of the authors’ less than ideal clinical experience with the existing implants for vertical femoral neck fracture fixation in young patients, we (PJN and BLN), along with the support of biomechanical engineers at Smith & Nephew, Inc. (Memphis, TN, USA) sought out to design a femoral neck locking plate (FNLP) that combines the desirable features of a transverse calcar lag screw for compression with multiple fixed angle locking screws. The purpose Injury, Int. J. Care Injured 43 (2012) 802–806 A R T I C L E I N F O Article history: Accepted 12 September 2011 Keywords: Hip Plate Biomechanical Locking Cyclic A B S T R A C T Background: The purpose of this study is to determine the biomechanical stability of a novel prototype femoral neck locking plate (FNLP) for treatment of Pauwels type C femoral neck fractures compared with other current fixation methods. Methods: Forty femur sawbones were divided into groups and a vertical femoral neck fracture was made. Each group was repaired with one of the following: (CS) three parallel cancellous screws; (XCS) two cancellous lag screws into the head and one transverse lag screw into the calcar; and (FNLP) a novel FNLP with two 5.7 mm locking, one lag screw into the calcar and two screws into the shaft; and (AMBI) a two- hole, 1358 AMBI plate with a derotation screw. All groups were tested for change in axial stiffness over 20 000 cycles, and rotational stiffness was measured before and after cyclic testing. A maximum load to failure test was also conducted. Results were compared with one-way analysis of variance (ANOVA) and Fisher protected least significant difference (PLSD). Results: Results for axial stiffness show that AMBI, CS, XCS and FNLP are 2779.0, 2207.2, 3029.9 and 3210.7 N-m mm À1 , respectively. Rotational rigidity results are 4.5, 4.1, 17.1 and 18.7 N-m mm À1 . The average cyclic displacements were 0.75, 0.88, 0.80 and 0.65 mm, respectively. Destructive failure loads for AMBI, CS, XCS and FNLP were 2.3, 1.7, 1.6 and 1.9 kN, respectively. Conclusions: The results of this experiment show statistically significant increases in axial stiffness for the FNLP compared with three traditional fixation methods. The FNLP demonstrates increased mechanical stiffness and combines the desirable features of current fixation methods. ß 2011 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +1 423 778 5596; fax: +1 423 778 7370. E-mail address: timothy.ervin@erlanger.org (B. Ervin). Contents lists available at SciVerse ScienceDirect Injury jo ur n al ho m epag e: ww w.els evier .c om /lo cat e/inju r y 0020–1383/$ – see front matter ß 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.injury.2011.09.012