Prevalence of dysmorphic sacral features in the general population

Background Posterior pelvic ring injuries, including sacral fractures and sacroiliac (SI) joint disruption, can have potentially serious sequelae and are becoming increasingly common. Management, especially in the setting of instability, consists of internal fixation to decrease the risk of complications. Placement of SI screws requires a thorough knowledge of normal pelvic anatomy and the available osseous fixation pathways. The aim of this study was to define the prevalence of individual features of sacral dysmorphism in the general population. Methods We conducted a retrospective review of standard and 3D-reconstructed computed tomography (CT) images of the pelvis to record the presence or absence of each dysmorphic feature. All adult trauma patients who presented within a 5-year period at a single, academic, Level I trauma center were eligible for inclusion. Patients <18 years of age, without advanced pelvic imaging, or who presented with any current or prior pelvic ring injury, tumor, or instrumentation were excluded. The prevalence of each dysmorphic feature was calculated and associations between dysmorphism and demographic factors were investigated. Results A total of 2667 patients were eligible for inclusion and the first 1000 were selected for review. Six subjects were excluded during review of CT images. One or more dysmorphic feature was seen in 96.8% of subjects. Each subject displayed an average of 2.7 abnormal features. Residual S1 discs were the most prevalent feature (72.2%). While tongue-in-groove (TIG) sacroiliac (SI) joints were the rarest (7.7% prevalence), they were associated with a significantly higher average number of concurrent dysmorphic features (3.29, P < .0001). Demographic subgroup analysis demonstrated a significantly higher prevalence of S1 discs ( P = .0007), TIG SI joints ( P < .0001), and colinear upper sacra ( P < .0001) in women. Residual S1 discs were also significantly more common in White patients ( P < .0001). Conclusions Sacral anatomy exists on a spectrum from normal to dysmorphic. This study demonstrates that completely “normal” sacral morphology is seen in <4% of patients. TIG sacroiliac joints may serve as a quick indicator for a higher degree of dysmorphism which may complicate or preclude transiliac-transsacral screw placement.