Rockwood Adults CH34

1080

SECTION TWO • Upper Extremity

C

D

Figure 34-23.  ( Continued ) C: CT with 3D reconstruction shows the Hills–Sachs lesions ( stars ). D: CT with 3D reconstruction shows the anterior bone Bankart lesions ( arrow ) and glenoid bone loss.

to the contralateral normal side to calculate for the amount of glenoid bone loss based on the assumption that there are no side-to-side differences. 189,210 Most of these techniques use the ratio of the width of the missing bone anteriorly to the antero- posterior diameter of the uninjured glenoid or the diameter of the best fit circle on the affected glenoid. 168,226 The “cir- cle method” is the most widely used method for estimating glenoid bone loss and provides useful presurgical planning information. This utilizes surface area measurements that can be performed accurately on the sagittal view of a 2D or 3D volume-rendered CT reformat or 2D sagittal MR image of the glenoid fossa (Fig. 34-24A). En face, the normal inferior gle-

noid contour can be approximated to a true fit circle. Thus, the size of a Bankart lesion or glenoid bone loss can be calcu- lated by comparing the surface area of the bone defect with the expected normal surface area of the glenoid fossa as measured by the best fit circle (Fig. 34-24B). Sugaya 226 proposed an en face 3D CT view of the glenoid and quantifying the amount of glenoid bone loss as a percentage defect of the glenoid based on a ratio of the missing anterior glenoid width against the diameter of the assumed inferior circle of the entire glenoid (Fig. 34-24C). This method has been shown to be both very reproducible and accurate in calculating the amount of gle- noid bone loss.

A, B

C

Figure 34-24.  A: CT image with 3D reconstruction of the glenoid and en face view of the glenoid fossa. A large bony Bankart lesion is seen anteriorly with critical bone loss. B: Perfect circle is drawn to match the inferior 2/3 of the glenoid. Using the surface area method, the size of the glenoid defect is calculated by dividing the surface area of the bone defect ( red ) with the normal surface area of the entire glenoid fossa ( circle ). C: Another method of measuring glenoid bone loss is calculating the percentage defect of the gle- noid based on a ratio of the missing anterior glenoid width ( A ) against the diameter of the assumed inferior circle of the entire glenoid ( B ). The percentage bone loss is A / B × 100 = % bone loss.