There is a greater risk of hip fracture if an individual falls, does not recover, and impacts on the hip. Despite this, until recently, there have been few studies on motion in the lateral-medial plane, on the biomechanics of large postural disturbances, and on the descent or impact phases of falls.
We hypothesized that there exists a disturbance threshold (the magnitude of a disturbance that is just sufficient to prevent recovery) that depends on lower extremity strength, reaction time and recovery capabilities. We also hypothesized that certain disturbances are more likely to result in an impact on the hip and that fast walking speed is protective against impacting on the hip.
Using both experiments and computer simulations, we determined the disturbance threshold of a trip as a function of strength, reaction time and recovery capabilities, by increasing the magnitude of a trip, or trip hold duration, until recovery was no longer possible. We also assessed the effect of disturbance type and gait speed on fall direction, impact location and impact velocity by studying four disturbances (faint, slip, step, trip) and three gait speeds (fast, normal, slow) without recovery.
For the trip, there exists a disturbance threshold that depends on lower extremity strength, reaction time and recovery capabilities. Compared to other disturbances and gait speeds, slipping or fainting while walking slowly was more likely to result in an impact on the hip, suggesting a greater risk for hip fracture. Finally, fall and fall-arresting attempt simulations using the ATB model provide an excellent alternative research tool to experiments with volunteers.
High-risk fallers are individuals with slow reaction times, small recovery capabilities and weak strengths since they are less capable of recovering. Highrisk fall situations are disturbance magnitudes that are greater than an individual’s disturbance threshold since he is, in general, unable to recover. Moreover, individuals with reduced gait speed and who are unable to make any fall-arresting attempts are also high-risk fallers since they are more likely to impact the hip. Slips and faints are also high-risk fall situations since they are more likely to result in an impact on the hip.
|1997||Ray NF, Chan JK, Thamer M, Melton LJ III. Medical expenditures for the treatment of osteoporotic fractures in the United States in 1995: report from the National Osteoporosis Foundation. J Bone Miner Res. January 1997;12(1):24-35.|
|1994||Cheng H, Obergefell L, Rizer A. Generator of Body (GEBOD) Manual. Wright-Patterson AFB OH; March 1994. Armstrong Laboratory Report AL/CF-TR-1994-0051.|
|1995||Ma D, Obergefell LA, Rizer AL. Development of human articulating joint model parameters for crash dynamics simulations. In: Proceedings of the 39th Stapp Car Crash Conference. November 8-10, 1995; San Diego, CA. Warrendale, PA: Society of Automotive Engineers:239-250. SAE 952726.|
|1994||Greenspan SL, Myers ER, Maitland LA, Resnick NM, Hayes WC. Fall severity and bone mineral density as risk factors for hip fracture in ambulatory elderly. JAMA. January 12, 1994;271(2):128-133.|
|1994||Courtney AC, Wachtel EF, Myers ER, Hayes WC. Effects of loading rate on strength of the proximal femur. Calcif Tiss Int. 1994;55(1):53-58.|
|1993||Hayes WC, Myers ER, Morris JN, Gerhart TN, Yett HS, Lipsitz LA. Impact near the hip dominates fracture risk in elderly nursing home residents who fall. Calcif Tiss Int. March 1993;52(3):192-198.|
|1991||Grisso JA, Kelsey JL, Strom BL, Chiu GY, Maislin G, O'Brien LA, Hoffman S, Kaplan F; Northeast Hip Fracture Study Group. Risk factors for falls as a cause of hip fracture in women. NEJM. May 9, 1991;324(19):1326-1331.|
|1987||Hedlund R, Lindgren U. Trauma type, age, and gender as determinants of hip fracture. J Orthop Res. 1987;5(2):242-246.|
|1991||Robinovitch SN, Hayes WC, McMahon TA. Prediction of femoral impact forces in falls on the hip. J Biomech Eng. November 1991;113(4):366-374.|