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Method and Instrumented Fixture for Femoral Fracture Testing in a Sideways Fall-on-the-Hip Position
Published on: August 17, 2017
Hip position may be associated with susceptibility to Rommens type IIIa fragility fractures of the pelvis during
Kunihiko Arakawa1, Takashi Suzuki2,3, Yoshinobu Watanabe2
1Department of Orthopaedic Surgery, Teikyo University School of Medicine, 2-11-1, Kaga, Itabashi, Tokyo, 173-8605, Japan. k.arakawa.0405@gmail.com.
Background:
The incidence of fragility fractures of the pelvis (FFP) has increased, significantly impacting healthcare systems. While the Rommens classification comprehensively categorizes FFP, the injury mechanism-particularly in type IIIa FFP, which involves an externally rotated iliac wing fracture and a pubic rami fracture-remains unclear. This study investigated the injury mechanism of type IIIa FFP using a quantitative computed tomography-based finite element analysis (QCT/FEA).
Methods:
A patient-specific QCT/FEA model of the hemi-pelvis and femur on the healthy side was developed using CT data from a patient with type IIIa FFP. The sacrum was fully constrained, whereas the pubic symphysis and the femur were partially constrained. Direct loading conditions were applied from the iliac wing, the greater trochanter, and the ischial tuberosity. Indirect loading conditions were applied from the greater trochanter under various hip positions (0º to 90º flexion at 15º intervals). Compressive and tensile failure clusters were evaluated under nonlinear analyses. Loading was increased in 40 N increments up to 2000 N. Additionally, force-displacement curves and external constraint forces were measured in models with 3-mm forced displacement.
Results:
Direct horizontal loading from the iliac wing produced clusters of tensile failure elements in the posterior ilium. In contrast, indirect loading transmitted through the hip joint along the axis of the femoral neck predominantly produced clusters of compressive failure elements in the posterior ilium, particularly in the 30º-60º flexion models. The lowest peak load in the force-displacement curve was observed in the 60º flexion with internal rotation model. These findings suggest that different load transmission pathways produce distinct failure distributions during lateral compression loading.
Conclusion:
The injury mechanism of Rommens type IIIa FFP may involve both direct lateral impact to the ilium and indirect load transmission through the hip joint. In addition, hip position may influence load transmission through the hip joint during lateral falls.
