PA 15-6-2811 Anatomical and biomechanical considerations for shunting-type hip protector function

Abstract

Hip fracture remains a major cause of death and disability among older persons. Anatomical and biomechanical design considerations for shunting-type hip-protectors were investigated to address low user compliance among older-persons.Aims were to assess the hip muscle morphology as a load-attenuating medium during shunting: determine the material properties of skeletal muscle; and assess shunting-type hip-protector function in lateral falls.Low and high hip fracture risk groups were identified based on BMI. A three dimensional map was developed to measure muscle thickness at 15 points and volume (of gluteal and quadriceps) using CT. A new method was developed to measure material properties of skeletal muscle under fall conditions by impacting muscles in the in-situ state, substituting ovine for human specimens. Biomechanical kinematic data, the effect of specimen size and impact velocity were also analysed. Finite element simulations were then conducted to evaluate hip-protector function.Significant differences in muscle thickness were revealed between hip fracture risk groups. The strong relationship of muscle thickness to subjects’ body mass allowed development of mathematical models that estimate the maximum muscle thickness and muscle thickness based on location, both from subject mass. An average 17% increase in muscle volume was quantified for an equivalent 10 kg increase in subject mass. Males exhibited 3%–23% increased volume over females depending on the muscle. Material properties of skeletal muscle revealed an average Young’s Modulus of 0.06 MPa. Fall simulations quantified peak loads shunted to the iliac bone, greater trochanter and femoral shaft.FindingsSuggest reducing protector size for greater wearer acceptance may cause injury elsewhere, especially for lean individuals at high fracture risk. Rather, hip-protector design should be based more on individual body constitution to increase effectiveness and comfort, and therefore user compliance. Muscle size should be maintained to allow effective use of preventive strategies within normal anatomical limits.