Biomechanical Comparison of 4 Transsacral Fixation Constructs in a Type 61C, Zone II Pelvic Fracture Model

Abstract

Objectives: OTA/AO 61C pelvic ring injuries are vertically unstable because of complete sacral fractures combined with anterior ring injury. The objective of this study was to compare the biomechanical characteristics of 4 transsacral screw constructs for posterior pelvic ring fixation, including one that uses a novel fixation method with a pair of locked washers with interdigitating cams.Methods: Type C pelvic ring disruptions were created on 16 synthetic pelvis models. Each pelvis was fixated with an S2 screw in addition to being allocated to 1 of 4 transsacral constructs through S1: (1) 8.0-mm screw, (2) 8.0-mm bolt, (3) 8.0-mm screw locked with a nut, and (4) 8.00-mm screw locked with a nut with the addition of interdigitating washers between the screw head and ilium on the near cortex, and ilium and nut on the far cortex. The anterior ring fractures were not stabilized. Each pelvis underwent 100,000 cycles at 250 N and was then loaded to failure using a unilateral stance testing model. The anterior and posterior osteotomy sites were instrumented with pairs of infrared (IR) light-emitting markers, and the relative displacement of the markers was monitored using a three-dimensional (3D) motion capture system. Displacement measurements at 25,000; 50,000; 75,000; and 100,000 cycles and failure force were recorded for each pelvis. Results:The novel washer design construct performed better than the screw construct with less posterior ring motion at 75,000 (P = 0.029) and 100,000 cycles (P = 0.029). Conclusions:The novel interdigitating washer design may be superior to using a screw construct alone to achieve rigid, locked posterior ring fixation in a synthetic pelvis model with a Type C pelvic ring disruption.

Incidence of and Risk Factors for Screw Loosening after Iliosacral Screw Fixation for Posterior Pelvic Ring Injury

“…At present, posterior pelvic ring screw-rod, iliosacral screw, minimally invasive adjustable plate, posterior tension band plating, and lumbopelvic fixations can be used to treat posterior pelvic ring injuries. 3,4 With the development of minimally invasive techniques, percutaneous iliosacral screw insertion has become the standard method for the treatment of posterior pelvic ring injuries because it is less invasive and has low infection risk and strong mechanical stability. 5 However, there are several concerns regarding the use of this method.…”

“…Surgical treatment has been shown to reduce long‐term complications such as malunion, bone nonunion, neurological dysfunction, and lower back pain. At present, posterior pelvic ring screw‐rod, iliosacral screw, minimally invasive adjustable plate, posterior tension band plating, and lumbopelvic fixations can be used to treat posterior pelvic ring injuries 3,4 …”

“…At present, posterior pelvic ring screw‐rod, iliosacral screw, minimally invasive adjustable plate, posterior tension band plating, and lumbopelvic fixations can be used to treat posterior pelvic ring injuries. 3 , 4 …”