Subtrochanteric femoral fractures are challenging injuries that are often associated with complications such as malrotation. Although imaging indicators such as the lesser trochanter sign are commonly used to achieve proper rotational alignment during surgery, their reliability diminishes in the presence of lesser trochanter fragments. This study investigated the relationship between lesser trochanter fragments and rotational deformities in patients treated with antegrade intramedullary nailing for subtrochanteric fractures. This multicenter retrospective analysis included 40 patients who underwent surgery for subtrochanteric fractures. Femoral anteversion was measured using preoperative and postoperative computed tomography images. Patients were divided into two groups based on the severity of rotational deformities. Predictive factors were evaluated using univariate and multivariate regression analyses. Lesser trochanter fragments were significantly associated with large rotational deformities (P < 0.001). Among patients in the large deformity group (>9°), 65.0 % had lesser trochanter fragments; however, among patients in the small deformity group (≤9°), only 10.0 % had lesser trochanter fragments. Other factors such as age, sex, operative time, and blood loss were not significantly different between the severe deformity and minor deformity groups. The presence of lesser trochanter fragments was an independent predictor of the absolute value of rotational deformity (P < 0.001) CONCLUSION: The presence of lesser trochanter fragments is a critical risk factor for postoperative rotational deformities. In such cases, visual landmarks are compromised; therefore, we recommend using objective intraoperative verification techniques rather than relying solely on the lesser trochanter shape sign to prevent malalignment.

Purpose: Fragility fractures of the pelvis (FFP) classified as Rommens-Hoffman type IVb are associated with spinopelvic dissociation and are generally considered to require surgical intervention. This study aimed to clarify the localization patterns of FFP type IVb and compare the biomechanical stability of different internal fixation techniques. Methods: In this retrospective study, morphologic mapping of sacral fracture lines was performed in 36 patients with FFP type IVb. Based on the mapping results, a finite element (FE) model of FFP type IVb was developed to evaluate the biomechanical stability of ilio-sacral screw (ISS) fixation, trans-sacral screw (TSS) fixation, spinopelvic fixation (SPF; On each side, L5 pedicle screw was connected to two iliac screws with a rod, and the bilateral constructs were linked using a cross-connector.), and bilateral triangular fixation (one TSS at S1 combined with SPF mentioned above) using finite element analysis (FEA). Results: Morphologic mapping showed that the sacrum fracture transverse line tended to pass between the S1-2 transverse lines. Although bilateral triangular fixation and SPF provided the highest stability in both U-type and H-type fractures, a TSS for U-type and two TSSs for H-type also demonstrated comparable levels of stability. ISS-based methods showed greater displacements. Conclusion: TSS-based fixation may provide stability comparable to bilateral triangular fixation and SPF in FFP type IVb, with less invasiveness when anatomy permits. Further studies are needed to optimize treatment strategies for this complex injury.