An Adams' Arch -based anatomical classification system guiding internal fixation strategies for non-displaced femoral neck fractures in elderly patients: a finite element analysis.

BACKGROUND: Femoral neck fractures constitute the predominant type of hip fracture in the elderly population and pose significant therapeutic challenges. Although internal fixation remains the standard treatment for non-displaced fractures, existing classification systems, such as the traditional anatomical categories (subcapital, transcervical, and basicervical), lack precise anatomical definitions needed to guide instrumentation therapy. Therefore, this study aims to develop a novel classification system based on the Adams' Arch to enhance fixation strategy selection.

METHODS: Forty-two fracture line models were created based on quantified relationships between fracture orientation, the proximity to Adams' Arch, and neck axis alignment. Each model underwent evaluation under two fixation protocols: (1) conventional triple cannulated screw fixation and (2) hybrid fixation combining cannulated screw with medial buttress plating, resulting in 84 computational models. Physiological loading conditions simulating upright human posture were applied with validated boundary constraints.

RESULTS: First, regardless of whether the support was positive or negative, smaller angles between the fracture line and the cannulated screws were associated with increased femoral stress, with higher stress observed under positive buttress conditions. Second, as the length of Adams' Arch increased, the stress on cannulated screw 3 in both fixation groups initially rose and then declined.Notably, the cannulated screw group classified as 6-5 failed to converge. Third, increasing Adams' Arch length decreased relative displacement along the X-axis at the fracture site, corresponding with an increased angle between the fracture line and cannulated screw. Moreover, increased femoral neck distance reduced relative displacements along the X- and Y-axes as the fracture line extended further from the femoral neck.

CONCLUSION: This finite element analysis identifies four critical insights: 1. The Adams' Arch-based classification provides effective biomechanical guidance for surgical management of femoral neck fractures (The classification of Subcapital, Transcervical and Basicervical was enhanced). 2.The stress on the cannulated screw peaks at intermediate lengths of the Adams' Arch.with an initial increase followed by a decline. 3. Femoral stress was higher under positive buttress support than under negative buttress conditions. 4. In elderly patients with 6-5 fracture line classification, cannulated screws alone provide insufficient fixation strength; alternative strategies such as medial plate augmentation should be considered.