Figure 1.
Cortical Thickness Colour Mapping using ordinary clinical CT data.
Femora and pelvis from an 84-year-old osteoporotic female who sustained a fracture without falling. She felt her right hip break as she placed her right foot on a low step. Femoral neck BMD was 0.46 g/cm2, T score −3.3. From the Arthritis Research UK FEMCO study (07/H0305/61).
Figure 2.
1. Measurements are performed at every vertex in an approximate segmentation of the hip. 2. At each vertex, the CT data is sampled on a line passing through the cortex. 3. A model-based fit is used to estimate the cortical thickness, allowing for image blur. 4. The thickness is mapped back to the surface (here blue is thick, pink is thin). 5. An average femur (red) is deformed to match the current femur (green). 6. Thickness estimates are then transferred to the average femoral surface and smoothed. 7. This process is repeated for all subjects, producing subject-specific thickness estimates all mapped to the same, average surface. 8. The data is analysed using statistical parametric mapping, to obtain mean thickness differences between groups and also the significance of these differences.
Figure 3.
Results for femoral neck fracture (left) and trochanteric fracture (right).
Upper colour maps show the average percentage difference in cortical thickness for each fracture type versus control (displayed on an average right femur model). The lower colour maps are the significance of the differences adjusted for age, height and weight, either point by point (vertex) or as a whole patch (blue clusters). Note that all the blue clusters extend uninterrupted beneath their respective orange/yellow vertices. Table 1 gives adjusted thickness values and significance of the clusters a–e.
Table 1.
Details of thinner patches of femoral cortex in hip fracture.
Figure 4.
Anatomical context of focal thinning in women with femoral neck fracture.
The left pane is a right proximal femur model seen from the front. The thin patch of cortex (fig 3c) in femoral neck fracture patients occurs on the domed ridge called the femoral neck eminence [25]. The right pane is a high resolution CT image through the femoral head of a 90 year old female (aBMD total hip T-score −1.9) which suggests that the patch is osteoporotic with microarchitectural thinning (white arrow). Femur courtesy of the Melbourne Femur Collection, Chairman Professor John Clement (Melbourne Dental School).
Figure 5.
Approximate orientation of the focally thin (red) zone during the different phases of gait.
Right femur (a) toe-off, (b) single leg stance and (c) heel strike. A slightly modified stance position (b) conferred the greatest risk of spontaneous femoral neck fracture in the laboratory simulations of Cristofolini et al [3]. The focally thin patch we identified coincides with a region of high tensile stress during simulations of spontaneous fracture.