The incidence of and factors affecting iliosacral screw loosening in pelvic ring injury

Introduction: Iliosacral screw fixation has been commonly used for stabilization of the posterior ring in unstable pelvic fractures. However, loosening of the screw may develop with or without redisplacement of the fracture. This study was undertaken to evaluate the incidence of iliosacral screw loosening and to identify its predictive factors. Materials and methods: In total, 110 patients whose posterior pelvic ring was stabilized with iliosacral screws were enrolled. These included 9 cases of anteroposterior compression, 64 cases of lateral compression, and 37 cases of vertical shear (VS) injuries. Among those with posterior pelvic ring injuries, 95 had sacral fractures (zone I: 52, zone II: 43) and 15 had sacroiliac joint dislocations. The screws were fixed to the anterior one-third region of the first sacral (S1) body in 46 cases, and to the middle one-third region in the remaining 64 cases. If loosening of the iliosacral screw influenced the pelvic ring stability, it was considered a failure. The relationship between iliosacral screw loosening and the possible influencing factors were analyzed. Results: Nineteen patients (17.3 %) were found to have loosening of the iliosacral screw at a mean 25.3 days postoperatively. Of these, 13 patients (11.8 %) had failure of the screws. The incidence of iliosacral screw loosening was significantly higher in those with VS injury (29.7 %, p = 0.014), in those with screw fixed to the middle one-third region of the S1 body (23.4 %, p = 0.044), and in those with VS injury combined with zone II sacral fracture (43.5 %, p = 0.019). With respect to failure of the iliosacral screw, patients with VS injury also had a higher incidence of failure (21.6 %, p = 0.036). Conclusions: Our findings demonstrate that cases with VS injuries are prone to screw loosening, especially when combined with zone II sacral fracture. Accordingly, alternative fixation methods should be considered in such cases.