AJVR, Vol 70, No. 1, January 2009 23 C omplex, nonreconstructable fractures of the femur are one of the most commonly encountered and challenging types of fractures in dogs. 1 Currently, biological bridging osteosynthesis is the treatment of choice for many comminuted nonreconstructable fractures. 2 Bridge plating preserves biological potential for healing while creating an internal splint and stable fixation. Spatial alignment of the bone is restored without precise anatomic reconstruction of bone fragments, thereby preserving blood supply from soft tissue attachments. 2–6 Newer techniques of Comparison of the mechanical behaviors of semicontoured, locking plate–rod fixation and anatomically contoured, conventional plate–rod fixation applied to experimentally induced gap fractures in canine femora Clara S. S. Goh, BVSc; Brandon G. Santoni, PhD; Christian M. Puttlitz, PhD; Ross H. Palmer, DVM, MS Objective—To compare the mechanical behaviors of a semicontoured, locking compres- sion plate–rod (LCP-rod) construct and an anatomically contoured, limited-contact dynamic compression plate–rod (LC–DCP-rod) construct applied to experimentally induced gap frac- tures in canine femora. Sample Population—16 femora from 8 cadaveric dogs. Procedures—8 limbs from 8 dogs were assigned to the LCP-rod construct group or the LC–DCP-rod construct group. In each femur, a 39-mm mid-diaphyseal ostectomy was per- formed at the same plate location and the assigned construct was applied. Construct stiff- ness and ostectomy gap subsidence were determined before and after cyclic axial loading (6,000 cycles at 20%, 40%, and 60% of live body weight [total, 18,000 cycles]). Three constructs from each group further underwent 45,000 cycles at 60% of body weight (total, 63,000 cycles). Following cyclic loading, mode of failure during loading to failure at 5 mm/ min was recorded for all constructs. Results—After 18,000 or 63,000 cycles, construct stiffness did not differ significantly between construct groups. No implant failure occurred in any construct that underwent 63,000 cycles. In both construct groups, ostectomy gap subsidence similarly increased as axial load increased but did not change after 18,000 cycles. Mean ± SEM loads at failure in the LCP-rod (1,493.83 ± 200.12 N) and LC–DCP-rod (1,276.05 ± 156.11 N) construct groups were not significantly different. The primary failure event in all constructs occurred at the screw hole immediately distal to the ostectomy. Conclusions and Clinical Relevance—Biomechanically, the semicontoured LCP-rod construct is similar to the anatomically contoured LC–DCP-rod system. (Am J Vet Res 2009;70:23–29) percutaneous plate application (termed MIPO) may further hasten bone healing as a result of improved periosteal perfusion. 7,8 From a mechanical perspective, bridge plating demands maximal performance from the bridging implants, which may be subject to plastic deformation or breakage early in the postoperative period or fatigue failure over time, depending on the healing potential of the patient. Addition of an IMR to the construct reduces stress applied to the plate; as much as a 10-fold extension of the fatigue life of the bone plate can be achieved. 9 The IMR can also assist in reestablishment of the spatial alignment of the limb and main fracture segments. 10 Requirements of the IMR and screws for available bone stock often dictate the Received January 23, 2008. Accepted April 8, 2008. From the Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences (Goh, Palmer), and Department of Mechanical Engineering, School of Biomedical Engineering (San- toni, Puttlitz, Palmer), Colorado State University, Fort Collins, CO 80523. Supported by the Colorado State University College of Veterinary Medicine and Biomedical Sciences Research Council (grant No. 1-68611), Synthes Veterinary Incorporated (plate and screw im- plants), and IMEX Veterinary Incorporated (Steinmann pins). Address correspondence to Dr. Palmer. ABBREVIATIONS BMD Bone mineral density IMR Intramedullary rod LC–DCP Limited-contact dynamic compression plate LCP Locking compression plate MIPO Minimally invasive plate osteosynthesis Unauthenticated | Downloaded 08/20/22 07:53 AM UTC