The classification of sacral foramina in a South African sample using cadaveric and osteological remains

Sacroiliac (SI) joint fixation is a technique used for SI joint fractures, SI joint dislocations and sacral fractures. Sacral screws can be placed either into the S1 or the S2 vertebrae if S1 is insufficient. Malpositioning of the screws is a common surgical complication as sacral variations exists amongst populations. Complications associated with the misposition of screws can lead to injury of the sacral venous plexus, iliac vessels, or sacral nerve roots. Therefore, this study aimed to evaluate sacral variations in a South African sample by determining distances between the first and second sacral foramina and classifying the common types of sacra found.

A quantitative cross-sectional comparative study was conducted. One hundred and twenty (n = 120) dry human sacra and 11 formalin-fixed cadavers were measured to determine the linear distances between the first two anterior and posterior sacral foramina. Additionally, the dry human sacra were classified according to Mahato's classification system. A cadaver SI joint fixation simulation was performed by an orthopaedic surgeon.

The mean sacral promontory height was found to be 31.81 mm and 37.52 mm in osteological and cadaver specimens, respectively. The mean anterior pedicle height was significantly different for the left (18.81 mm) and right (21.67 mm) side measurements. A statistically significant difference was found between cadavers and osteological samples for all measurements taken. In the osteological sample, ancestry and age mostly influenced the variations noted.

Using Mahato's classification system, sacra with five sacral segments, auricular surfaces extending from the superior part of S1 to the middle of S3 and no accessory L5/S1 articulations had the highest prevalence of 59.17 %.

The South African sample exhibited similarities but did not fully compare to other populations. The results in this study should be considered as a reference for surgeries involving the SI joint and sacral foramina. However, where possible, the exact anatomy with possible variations of the patient should be evaluated preoperatively using X-rays and angiograms.