title: Age-related changes in dynamic compressive properties of trochanteric soft tissues over the hip.
abstract: Hip fracture risk increases dramatically with age, and 90% of fractures are due to falls. During a fall on the hip, the soft tissues overlying the hip region (skin, fat, and muscle) act as shock absorbers to absorb energy and reduce the peak force applied to the underlying bone. We conducted dynamic indentation experiments with young women (aged 19-30; n=17) and older women (aged 65-81; n=17) to test the hypothesis that changes occur with age in the stiffness and damping properties of these tissues. Tissue stiffness and damping were derived from experiments where subjects lay sideways on a bed with the greater trochanter contacting a 3.8cm diameter indenter, which applied sinusoidal compression between 5 to 30Hz with a peak-to-peak amplitude of 1mm. Soft tissue thickness was measured using ultrasound. On average, stiffness was 2.9-fold smaller in older than young women (5.7 versus 16.8kN/m, p=0.0005) and damping was 3.5-fold smaller in older than young women (81 versus 282Ns/m, p=0.001). Neither parameter associated with soft tissue thickness. Our results indicate substantial age-related reductions in the stiffness and damping of soft tissues over the hip region, which likely reduce their capacity to absorb and dissipate energy (before "bottoming out") during a fall. Strategies such as wearable hip protectors or compliant flooringmay compensate for age-related reductions in the shock-absorbing properties of soft tissues and decrease the injury potential of falls.
authors.affiliation: Department of Physical Therapy, Chapman University, Irvine, CA, USA. Electronic address: wchoi@chapman.edu.
authors.forename: W J
authors.initials: WJ
authors.lastname: Choi
authors.affiliation: Deptarment of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada.
authors.forename: C M
authors.initials: CM
authors.lastname: Russell
authors.affiliation: Deptarment of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada.
authors.forename: C M
authors.initials: CM
authors.lastname: Tsai
authors.affiliation: Mechatronic Systems Engineering, Simon Fraser University, Burnaby, BC, Canada.
authors.forename: S
authors.initials: S
authors.lastname: Arzanpour
authors.affiliation: Deptarment of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, BC, Canada; School of Engineering Science, Simon Fraser University, Burnaby, BC, Canada.
authors.forename: S N
authors.initials: SN
authors.lastname: Robinovitch
mesh_terms: D000058:Accidental Falls; D000273:Adipose Tissue / Q000000981:diagnostic imaging / Q000502:physiology*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001696:Biomechanical Phenomena / Q000502:physiology; D019245:Compressive Strength / Q000502:physiology*; D004548:Elasticity / Q000502:physiology; D005260:Female; D005269:Femur / Q000502:physiology*; D006620:Hip Fractures / Q000453:epidemiology; D006801:Humans; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000502:physiology*; D012307:Risk Factors; D012867:Skin / Q000000981:diagnostic imaging; D012879:Skin Physiological Phenomena; D014463:Ultrasonography
keywords: Aging; Damping; Falls; Hip fracture; Injury prevention; Mechanical properties; Soft tissue; Stiffness; Ultrasound; Vibration analysis