Fractures of the pelvis constitute approximately a quarter of all fractures in small animals [1,2,3]. The majority of these cases are due to high-energy trauma, such as vehicular trauma or falling from a height [1, 3,4,5,6,7]. Fractures of the ilial body account for 18–46% of pelvic fracture cases, with the majority being long oblique fractures, and they often occur concurrently with fractures of the ischium and pubis [1, 8]. Conservative management with cage rest may be utilized for minimally displaced fractures, but can result in sub-optimal long-term function if the fracture segments are displaced [3, 4]. Surgically treated ilial fractures are generally stabilized by open reduction and lateral application of appropriately contoured plates and screws [1, 4,5,6,7,8]. Various types of plates have been employed for the stabilization of ilial fractures, including dynamic compression plates, cuttable plates, T plates, miniplates, reconstruction plates, and double plates [4, 8].
The most common complication associated with ilial fracture repair is implant failure, which occurs in up to 62% of patients. The majority of these failures are due to screw pull-out, with one of the reasons for this high incidence of screw loosening being poor bone quality in the cranial ilial wing [1, 8,9,10,11,12]. Conventional plating techniques rely on friction between the plate and bone to provide stability. The weakest point in this conventional plating system is the interface between the screw and the bone. Placing screws in poor quality bone, such as the cranial ilium, may result in an inability to generate adequate force to prevent implant and fracture motion . Furthermore, the amount of compression needed to generate friction between a standard compression plate and bone has been shown to adversely affect the periosteal blood supply, which has been linked to delayed healing, non-union, and increased susceptibility to bacterial surgical site infections after fracture repair [13, 14]. Locking implant systems have been developed to provide more stable fracture repair, especially in poorer quality bone, and to minimize the negative impact on local vascularity during fracture healing . These plating systems do not rely on plate-to-bone friction to provide stability, eliminating the need for high shear loads at the screw-to-bone interface . Less plate-to-bone contact also decreases the need for precise plate contouring and helps preserve the blood supply to the bone [13,14,15,16,17].
The String-of-Pearls™ (SOP) implant is a stainless steel locking plate made up of repeating units of spherical pearls and cylindrical rods. Each pearl is designed to engage a standard cortical bone screw in a locking fashion by the screw threads engaging a ridge within the pearl, and the plate can be contoured by twisting along its longitudinal axis and bending in multiple planes without compromising its locking ability. The ability of the SOP locking plate to utilize standard cortical bone screws allows this construct to, in general, be considerably less expensive than more traditional locking plate constructs [13, 14]. In a 2014 study of Locking Compression Plates (LCP) versus Dynamic Compression Plates (DCP) in a canine ilial fracture model, there was no demonstrable difference between the constructs’ performance in acute failure testing in vitro . In a 2015 study comparing double SOP plating versus single DCP constructs in a synthetic bone model, the double SOP constructs had significantly greater bending stiffness, bending strength, bending structural stiffness, and torsional stiffness . To the authors’ knowledge, there have been no studies reported in the literature comparing the mechanical strength of SOP plating to DCP plating in a canine ilial fracture model.
The purpose of this study was to compare the stiffness, yield load, ultimate load at failure, displacement at yield, and mode of failure in cantilever bending of SOP and DCP constructs in an acute failure ilial fracture model. The hypothesis was that the SOP plates would have superior biomechanical properties compared to the DCP constructs of comparable size.