Reason for failed fixation with dynamic hip screws for intertrochanteric fracture: analysis based on the lever-balance-reconstruction theory / 中华创伤骨科杂志

ABSTRACT

Objective:To study the reason for failed fixation with dynamic hip screws (DHS) and the indications for DHS fixation in the treatment of intertrochanteric fracture based on the lever-balance-reconstruction theory.Methods:A retrospective analysis was performed of the data of 32 patients with intertrochanteric fracture who had been treated by DHS fixation at Department of Orthopaedic Trauma, Peking University People's Hospital from January 1999 to December 2019. There were 22 males and 10 females, aged from 34 to 91 years (average, 67.7 years). By the AO classification, 15 fractures were type 31-A1, 13 ones type 31-A2, and 4 ones type 31-A3. According to the lever-balance-reconstruction theory, after the position of postoperative fulcrum was determined depending on the relationship between fracture line and internal fixation, the medial and lateral force arms were measured after internal fixation. The 32 patients were divided into 2 groups according to the position of fulcrum after internal fixation. In group A of 13 patients, the fulcrum was located in or within the center of the medullary cavity; in group B of 19 patients, the fulcrum was located outside the center of the medullary cavity. The incidence of internal fixation failure was compared between the 2 groups.Results:Internal fixation failure occurred in 15 of the 32 patients cutting out of the head and neck screws without penetration in 2 cases, screw withdrawal in 8 cases, hip varus deformity in 10 cases, and femoral neck shortening in 15 cases. The 2 groups were comparable because there were no statistically significant differences in their preoperative general data or types of internal fixation between them except AO classification ( P>0.05). The length of medial force arm (power arm) averaged 51.12 mm (from 39.4 to 57.9 mm) and the length of lateral force arm (resistance arm) 23.37 mm (from 15.1 to 31.0 mm) in group A where 3 patients experienced internal fixation failure after operation; the length of medial force arm (power arm) averaged 63.71 mm (from 52.3 to 74.5 mm) and the length of lateral force arm (resistance arm) 9.94 mm (from 3.1 to 18.3 mm) in group B where 12 patients experienced internal fixation failure after operation. There was a significant difference between the 2 groups in internal fixation failure ( P=0.036). Conclusions:In the DHS fixation of intertrochanteric fracture, the postoperative fixation failure is associated with the fulcrum position after reconstruction. DHS is only indicated for intertrochanteric fractures whose fracture line (post-reconstruction fulcrum) is near and inside the center of the medullary cavity, but not for those whose fracture line (post-reconstruction fulcrum) is outside the medullary cavity.