Which AO/OTA 31-A2 pertrochanteric fractures can be treated with a dynamic hip screw without developing a lateral wall fracture? A CT-based study

Purpose To determine whether radiographic measurements derived from standard computed tomography (CT) evaluation can be used to predict likelihood of a peri-operative lateral femoral wall fracture in AO/OTA 31-A2 pertrochanteric fractures treated with a dynamic hip screw (DHS). Methods Fifty-one patients with AO/OTA 31-A2 classified pertrochanteric fractures were evaluated using a pre-operative CT scan of the pelvis with both hips. Dimensions of the lateral wall were calculated for each patient using four parameters: (1) height of the lateral wall above the vastus ridge; (2) circumference of the lateral wall 2 cm below the vastus ridge at an angle of 135 degrees; this circumference was further divided into an anterior, lateral and posterior component; (3) cortical thickness at the centre of the lateral component of the lateral wall; and (4) cortical index. All patients were treated with a 135 degrees DHS. Postoperative radiographs were assessed for lateral femoral wall fracture. Results Patients with a lateral wall fracture (17/51) had a smaller circumference (4.47 cm vs 5.44 cm p value<0.001) as well as a lower height of the lateral femoral wall (1.37 cm vs 2.21 p value<0.001). Analysis of the three components of the circumference revealed a significant difference for the anterior component only and not for the lateral and posterior components. There was no statistical difference in the cortical thickness or cortical index in the two groups. The cutoff values for height of the lateral wall and anterior component were calculated using ROC curves and found to be 1.68 cm (AUC 0.918) and 2.10 cm (AUC 0.851) respectively. Conclusion AO/OTA 31-A2 pertrochanteric fractures with a lateral wall height of >1.68 cm and an anterior component of >2.10 cm in circumference are not likely to sustain a lateral wall fracture when treated with a DHS.