Three-dimensional computed tomography-based differentiation of engaged versus displaced intertrochanteric fractures using the anterior fracture line: a cross-sectional study from Korea

Background: With the advent of an aging society, osteoporotic fractures—particularly hip fractures—are increasing, with a 1-year mortality rate of 17%. Achieving stable fixation that enables early ambulation is essential but remains challenging because complex intertrochanteric (IT) fracture patterns are often underestimated on plain radiographs. Using three-dimensional computed tomography (3D-CT), this study analyzed whether the anterior fracture line lies medial or lateral to the IT line and examined its relationship with displacement or distal medullary canal engagement, highlighting the potential influence of the joint capsule and capsular ligaments on fracture morphology and fixation stability.Methods: A retrospective review was conducted on 96 osteoporotic IT fractures in patients aged ≥60 years treated between April 2013 and December 2022 at National Police Hospital and Asan Medical Center, Seoul, Korea. Fractures were classified as engaged, completely displaced, and partially displaced based on 3D-CT findings. The anterior fracture-line position (medial or lateral to the IT line) and the status of the lesser trochanter (LT) were evaluated. The chi-square or Fisher exact test was used for statistical comparisons.Results: In total, 96 patients were analyzed. Of these, 49 cases (51.0%) were classified as engaged type, 27 cases (28.1%) as completely displaced type, and 20 cases (20.8%) as partially displaced type. When comparing fracture pattern with anterior fracture-line position, the completely displaced type showed a significantly higher proportion of lateral anterior fracture lines than the other two types (P<0.001). However, no significant association was identified between fracture pattern and LT displacement. When the anterior fracture-line position and LT displacement were evaluated together, only the engaged type demonstrated a possible association between a lateral anterior fracture line and LT displacement, though the statistical significance was weak (P=0.047).Conclusions: Fracture lines lateral to the IT line were strongly associated with displacement in IT fractures; however, their relationship with LT involvement, reflecting iliopsoas tendon traction, was not clearly demonstrated. Although the factors contributing to the engaged-type fracture remain uncertain, the statistical association between fracture pattern and anterior fracture-line position suggests that capsular structures may play a stabilizing role in select fracture configurations. Further studies are needed to clarify these anatomical interactions.Level of evidence: