Foot-ankle complex injury risk curves using calcaneus bone mineral density data.

OBJECTIVE Biomechanical data from post mortem human subject (PMHS) experiments are used to derive human injury probability curves and develop injury criteria. This process has been used in previous and current automotive crashworthiness studies, Federal safety standards, and dummy design and development. Human bone strength decreases as the individuals reach their elderly age. Injury risk curves using the primary predictor variable (e.g., force) should therefore account for such strength reduction when the test data are collected from PMHS specimens of different ages (age at the time of death). This demographic variable is meant to be a surrogate for fracture, often representing bone strength as other parameters have not been routinely gathered in previous experiments. However, bone mineral densities (BMD) can be gathered from tested specimens (presented in this manuscript). The objective of this study is to investigate different approaches of accounting for BMD in the development of human injury risk curves. METHODS Using simulated underbody blast (UBB) loading experiments conducted with the PMHS lower leg-foot-ankle complexes, a comparison is made between the two methods: treating BMD as a covariate and pre-scaling test data based on BMD. Twelve PMHS lower leg-foot-ankle specimens were subjected to UBB loads. Calcaneus BMD was obtained from quantitative computed tomography (QCT) images. Fracture forces were recorded using a load cell. They were treated as uncensored data in the survival analysis model which used the Weibull distribution in both methods. The width of the normalized confidence interval (NCIS) was obtained using the mean and ± 95% confidence limit curves. PRINCIPAL RESULTS The mean peak forces of 3.9kN and 8.6kN were associated with the 5% and 50% probability of injury for the covariate method of deriving the risk curve for the reference age of 45 years. The mean forces of 5.4 kN and 9.2kN were associated with the 5% and 50% probability of injury for the pre-scaled method. The NCIS magnitudes were greater in the covariate-based risk curves (0.52-1.00) than in the risk curves based on the pre-scaled method (0.24-0.66). The pre-scaling method resulted in a generally greater injury force and a tighter injury risk curve confidence interval. Although not directly applicable to the foot-ankle fractures, when compared with the use of spine BMD from QCT scans to pre-scale the force, the calcaneus BMD scaled data produced greater force at the same risk level in general. CONCLUSIONS Pre-scaling the force data using BMD is an alternate, and likely a more accurate, method instead of using covariate to account for the age-related bone strength change in deriving risk curves from biomechanical experiments using PMHS. Because of the proximity of the calcaneus bone to the impacting load, it is suggested to use and determine the BMD of the foot-ankle bone in future UBB and other loading conditions to derive human injury probability curves for the foot-ankle complex.

[1]  Glenn R. Paskoff,et al.  Trabecular bone density of male human cervical and lumbar vertebrae. , 2006, Bone.

[2]  Narayan Yoganandan,et al.  Bone Mineral Density of Human Female Cervical and Lumbar Spines From Quantitative Computed Tomography , 2006, Spine.

[3]  Albert I. King,et al.  Dynamic human ankle response to inversion and eversion , 1993 .

[4]  Harold J. Mertz,et al.  Hybrid III: The First Human-Like Crash Test Dummy , 1994 .

[5]  J. Melvin,et al.  Accidental Injury: Biomechanics and Prevention , 1993 .

[6]  Luis Martínez,et al.  Development of injury risk functions for use with the THORAX Demonstrator; an updated THOR , 2014 .

[7]  Jeff R Crandall,et al.  Survival Model for Foot and Leg High Rate Axial Impact Injury Data , 2015, Traffic injury prevention.

[8]  Jeffrey Richard Crandall,et al.  Leg, Foot, and Ankle Injury Biomechanics , 2015 .

[9]  Narayan Yoganandan,et al.  Hybrid III Lower Leg Injury Assessment Reference Curves Under Axial Impacts Using Matched-Pair Tests. , 2015, Biomedical sciences instrumentation.

[10]  N Yoganandan,et al.  Effect of Age and Loading Rate on Human Cervical Spine Injury Threshold , 1998, Spine.

[11]  Xavier Trosseille,et al.  Injury risk curves for the WorldSID 50th male dummy. , 2009, Stapp car crash journal.

[12]  C. Bir,et al.  Lower extremity injury criteria for evaluating military vehicle occupant injury in underbelly blast events. , 2009, Stapp car crash journal.

[13]  Narayan Yoganandan,et al.  Normalization and Scaling for Human Response Corridors and Development of Injury Risk Curves , 2015 .

[14]  Steven Millington,et al.  Injury tolerance and response of the ankle joint in dynamic dorsiflexion. , 2004, Stapp car crash journal.

[15]  W. C. Hayes,et al.  Ultrasound and densitometry of the calcaneus correlate with the failure loads of cadaveric femurs , 1995, Calcified Tissue International.

[16]  Rolf H Eppinger,et al.  Development of Side Impact Thoracic Injury Criteria and Their Application to the Modified ES-2 Dummy with Rib Extensions (ES-2re). , 2003, Stapp car crash journal.

[17]  Narayan Yoganandan,et al.  Lower Leg Injury Reference Values and Risk Curves from Survival Analysis for Male and Female Dummies: Meta-analysis of Postmortem Human Subject Tests , 2015, Traffic injury prevention.

[18]  Rolf H. Eppinger,et al.  DYNAMIC AXIAL TOLERANCE OF THE HUMAN FOOT-ANKLE COMPLEX , 1996 .

[19]  Narayan Yoganandan,et al.  Optimized Lower Leg Injury Probability Curves From Postmortem Human Subject Tests Under Axial Impacts , 2014, Traffic injury prevention.

[20]  N Yoganandan,et al.  Axial impact biomechanics of the human foot-ankle complex. , 1997, Journal of biomechanical engineering.

[21]  N Yoganandan,et al.  Experimental production of extra- and intra-articular fractures of the os calcis. , 2000, Journal of biomechanics.

[22]  T Hansson,et al.  The Relation Between Bone Mineral Content, Experimental Compression Fractures, and Disc Degeneration in Lumbar Vertebrae , 1981, Spine.

[23]  Jeffrey Richard Crandall,et al.  MECHANISMS OF INJURY AND INJURY CRITERIA FOR THE HUMAN FOOT AND ANKLE IN DYNAMIC AXIAL IMPACTS TO THE FOOT , 1997 .

[24]  Rolf H Eppinger,et al.  The axial injury tolerance of the human foot/ankle complex and the effect of Achilles tension. , 2002, Journal of biomechanical engineering.

[25]  Yuichi Kitagawa,et al.  A Severe Ankle and Foot Injury in Frontal Crashes and Its Mechanism , 1998 .

[26]  Erik G. Takhounts,et al.  DEVELOPMENT OF IMPROVED INJURY CRITERIA FOR THE ASSESSMENT OF ADVANCED AUTOMOTIVE RESTRAINT SYSTEMS - II , 1999 .

[27]  T Hansson,et al.  The Influence of Age, Height, and Weight on the Bone Mineral Content of Lumbar Vertebrae , 1980, Spine.

[28]  Michael Kleinberger,et al.  Vertical accelerator device to apply loads simulating blast environments in the military to human surrogates. , 2015, Journal of biomechanics.