CUrlING-OUT OF THE DYNAMIC HIP SCREW RELATED TO ITS POSITION

The commonest cause of failure of fixation of extracap-sular fractures treated by a dynamic hip screw (DHS) is cutting-out of the screw from the femoral head. Incid-ences of 5.3 % (Jensen, T#{248}ndevold and Mossing 1978) and 16.8 % (Davis et al 1990) have been reported. This study aims to determine the relationship between the exact position of the screw and subsequent cutting-out. Patients and methods. The radiographs of a series of such patients were reviewed to determine the position of the screw within the femoral head immediately after opera-tion. The position in 25 patients, in whom the screw later cut out, was compared with the position in 200 cases in which there was radiographic evidence of bony union without cut-out. We defined cutting-out as projection of the screw from the femoral head by more than 1 mm. The position of the screw was determined on anteroposterior (AP) and lateral radiographs by the method shown in Figures 1 and 2, then recording the ratio of AB to AC, multiplied by 100, to give a range from 0 to 100 for each view. Results, The position of each screw within the femoral head is shown diagrammatically in Figure 3, in which a triangle represents a screw which cut out and a cross one that did not. On the AP radiograph the average position of the screw was at 45 for uneventful union and 58 for cutting