gms | German Medical Science

Objectives: As the older population in the industrial countries will grow steadily over the next few decades, osteoporosis-related pelvic fractures will increase. In the current literature, information on osteoporosis-related fractures of the posterior pelvic ring is limited. Surgical therapy involving transiliosacral screws is an important pillar of the therapy. The aim of this study was (1) to determine the bone mass distribution in the posterior pelvic ring for sacral screw corridors in a larger cohort and to (2) identify the optimal areas for screw placement within the sacral bone by visualizing the bone mass as a thermal map of bone density to allow a better understanding of surgical possibilities and screw positioning.

Methods: The datasets consisted of 324 CT raw datasets. Mean age of the study population was 60.4 ± 17.6 years (17 to 93 years). There were 33%vfemale and 67% male patients. The screw trajectories running through the S1 corridor were defined by placing points manually at the surface of the calculated template of the pelvis. For the S2 screw channel a constant corridor was defined in the same way, see Figure 1 and 2. In addition, mean bone density of L5 was determined and two groups were formed based on mean bone density of =/< 100 HU (n = 52) and mean bone density of >100 HU (n = 272). Two graphs and a thermal map were created to show the mean bone density of the entire screw corridor of S1 and S2 in relation to pelvic width, divided into groups 1 and 2, see Figures 1 and 2.

Results and conclusion: The bone density of the S1 corridor, vertebral body and alae were significantly higher than of the S2 corridor (p < 0.001).

The gender distribution showed a significantly larger relative proportion of women in group 2 compared to the total study population (p = 0.03) and a higher average in age (group 1 = 57 ±17.3y; group 2 = 75 ± 9y; p < 0.001). The mean bone density of L5 was 179.1 ± 60 HU for group 1 and 76 ± 22 HU for group 2 (p < 0.001). In all measurements of the bone density the vertebral bodies of S1, S2, the alae and the entire screw corridor group 2 showed significantly lower values than group 1 (p < 0.001), for an overview see Table 1 and Figures 1 and 2.

The usability of a thermal map of the pelvis depicting the bone mass distribution can be of great value to estimate the probability of implant stability and to give guidance especially in patients with a reduced bone quality. The overall bone mass distribution in the S2 corridor was significantly lower than in S1.

The the bone mass distribution of the posterior pelvic ring correlates strongly with the bone mass of the vertebral body of L5 and that the typical fracture patterns occurring in osteoporosis-related fractures can be explained by this 3D model.

The exact bone mass distribution of the vertebral body of S1 showed a denser region in the posterior and upper part, which contradicts the clinical practice of higher stability in the anterior third.