Relationship between anterior fracture line location and rotational instability during inserting lag screw of cephalomedullary nail in intertrochanteric femoral fracture

Abstract

Background: Rotational instability of the proximal fragment in intertrochanteric femoral fractures increases the risk of fixation failure. However, most prior research has focused on the analysis of bony structures. To confirm the characteristics of rotational instability in intertrochanteric femoral fractures, this study evaluated the fracture morphology and soft tissue attachment relationship at the fracture site using computed tomography. Methods: The anteroposterior fracture line of the proximal fragment and the attachment of capsular ligaments were compared between patients with confirmed rotational instability during cephalomedullary nailing for 372 intertrochanteric fractures and 1 to 1 matching controls. Rotational instability was defined based on whether the proximal fragment rotation occurred during lag screw insertion. The anterior fracture line was classified as medial, lateral, or crossing, according to its positional relationship with the femoral intertrochanteric line. Concerning the posterior fracture line of the proximal fragment, the study evaluated whether the posterior fracture line was located at the medial base of the intertrochanteric crest. In addition, separation of the greater and lesser trochanters was evaluated. Results: Rotational instability was confirmed in 40 patients (10.8 %). The patients included 4 men and 36 women with a mean age of 84.7 years (range: 63–97 years). In the group with rotational instability, the anterior fracture line was more commonly located medial or lateral to the femoral intertrochanteric line in 11 and 13 cases, respectively, whereas the group without rotational instability showed a fracture line crossing the femoral intertrochanteric line in 35 cases (P < 0.001). No significant differences were observed in the posterior fracture characteristics between the two groups. Conclusions: In intertrochanteric femoral fractures, if the location of the anterior fracture line deviates from the femoral intertrochanteric line, there is a possibility of rotational instability, which seems to be related to the attachment of the anterior capsular ligament around the fracture. In these fractures, attention must be paid to the rotation of the proximal fragment during the insertion of a lag screw or blade during osteosynthesis. © 2025 The Japanese Orthopaedic Association