Assessment of Hip Fracture Risk in Astronauts Exposed to Long-Term Weightlessness

Background: A human exploration mission to Mars could take place within 10 years. During the 6 to 12 month journey astronauts would likely lose bone mineral density (BMD) at a mean rate of 1-2 percent per month in weight-bearing areas, approximately 10 times the rate associated with normal ageing. There exists an important need to quantify the fracture risk associated with this loss. .

Methods: Using computational modeling, the factor of risk for hip fracture (applied load divided by failure load) was assessed following 0, 6, and 12 months of weightlessness for: 1) the mid-stance phase of gait, and 2) a fall to the side impacting the greater trochanter. Peak applied loading was calculated for Earth and Mars gravity levels using the equations of motion for three-segment models representing locomotion and falls. Mars simulations included extravehicular activity (EVA, with spacesuit) and intravehicular activity (IVA). The structural properties of the femur were analyzed using a three-dimensional finite element model derived from quantitative computed tomography scans of a representative cadaveric femur. Space flight associated changes in density, geometry, and muscle strength were incorporated.

Results: Peak applied joint contact force ranges for mid-stance were: 1.2- 2.5 kN (Earth), 0.9-1.8 kN (Mars IVA), and 1.5-2.4 kN (Mars EVA). Peak applied joint contact forces for fall impact were: 4.2-8.0 kN (Earth), 2.7-5.1 kN (Mars IVA), and 3.1-5.0 kN (Mars EVA). Femoral strength in mid-stance decreased from 5.9-6.1 kN (0 months) to 5.1- 5.4 kN (12 months), while femoral strength in fall impact decreased from 4.2-4.4 kN (0 months) to 3.8-4.0 kN (12 months). Typically, the factor of risk for hip fracture was highest for falls in Earth gravity following 12 months of weightlessness (1.12-2.08), and lowest for IVA locomotion in Mars gravity (0.26-0.49). All fall conditions yielded a high likelihood of fracture. Astronauts are advised to take precautions against falling following long duration space flight and could benefit from the temporary use of hip pads.

Year	Entry
1993	Lauritzen JB, Petersen MM, Lund B. Effect of external hip protectors on hip fractures. Lancet. January 2, 1993;341(8836):11-13.
1991	Lotz JC, Cheal EJ, Hayes WC. Fracture prediction for the proximal femur using finite element models, I: linear analysis. J Biomech Eng. 1991;113(4):353-360.
1987	McMahon TA, Valiant G, Frederick EC. Groucho running. J Appl Physiol. June 1987;62(6):2326-2337.
1988	Ashman RB, Rho JY. Elastic modulus of trabecular bone material. J Biomech. 1988;21(3):177-181.
1989	Ashman RB, Rho JY, Turner CH. Anatomical variation of orthotropic elastic moduli of the proximal human tibia. J Biomech. 1989;22(8-9):895-900.
1990	McMahon TA, Cheng GC. The mechanics of running: how does stiffness couple with speed? J Biomech. 1990;23(suppl 1):65-78.
1989	Eriksson SAV, Isberg BO, Lindgren JU. Prediction of vertebral strength by dual photon absorptiometry and quantitative computed tomography. Calcif Tiss Int. April 1989;44(4):243-250.
1991	Snyder SM, Schneider E. Estimation of mechanical properties of cortical bone by computed tomography. J Orthop Res. May 1991;9(3):422-431.
1978	Crowninshield RD, Johnston RC, Andrews JG, Brand RA. A biomechanical investigation of the human hip. J Biomech. 1978;11(1-2):75-85.
1985	Cezayirlioglu H, Bahniuk E, Davy DT, Heiple KG. Anisotropic yield behavior of bone under combined axial force and torque. J Biomech. 1985;18(1):61-69.
1985	Gibson LJ. The mechanical behaviour of cancellous bone. J Biomech. 1985;18(5):317-328.
1990	Keyak JH, Meagher JM, Skinner HB, Mote CD Jr. Automated three-dimensional finite element modelling of bone: a new method. J Biomed Eng. 1990;12(5):389-397.
1993	Keyak JH, Fourkas MG, Meagher JM, Skinner HB. Validation of an automated method of three-dimensional finite element modelling of bone. J Biomed Eng. November 1993;15(6):505-509.
1992	Keyak JH, Skinner HB. Three-dimensional finite element modelling of bone: effects of element size. J Biomed Eng. 1992;14(6):483-489.
1996	van den Kroonenberg AJ, Hayes WC, McMahon TA. Hip impact velocities and body configurations for voluntary falls from standing height. J Biomech. June 1996;29(6):807-811.
1987	Hedlund R, Lindgren U. Trauma type, age, and gender as determinants of hip fracture. J Orthop Res. 1987;5(2):242-246.
1998	Keyak JH, Rossi SA, Jones KA, Skinner HB. Prediction of femoral fracture load using automated finite element modeling. J Biomech. February 1998;31(2):125-133.
1980	Mochon S, McMahon TA. Ballistic walking. J Biomech. 1980;13(1):49-57.
1987	Goldstein SA. The mechanical properties of trabecular bone: dependence on anatomic location and function. J Biomech. 1987;20(11-12):1055-1061.
1998	Morey-Holton ER, Globus RK. Hindlimb unloading of growing rats: a model for predicting skeletal changes during space flight. Bone. May 1998;22(5)(suppl):83S-88S.
1982	Leichter I, Margulies JY, Weinreb A, Mizrahi J, Robin GC, Conforty B, Makin M, Bloch B. The relationship between bone density, mineral content, and mechanical strength in the femoral neck. Clin Orthop Relat Res. March 1982;163:272-281.
1998	Kopperdahl DL, Keaveny TM. Yield strain behavior of trabecular bone. J Biomech. July 1998;31(7):601-608.
1992	Cooper C, Atkinson EJ, O'Fallon WM, Melton JL III. Incidence of clinically diagnosed vertebral fractures: a population‐based study in Rochester, Minnesota, 1985‐1989. J Bone Miner Res. February 1992;7(2):221-227.
1976	Carter DR, Hayes WC. Bone compressive strength: the influence of density and strain rate. Science. September 10, 1976;194(4270):1174-1176.
1977	Carter DR, Hayes WC. The compressive behavior of bone as a two-phase porous structure. J Bone Joint Surg. 1977;59A(7):954-962.
1998	Zannoni C, Mantovani R, Viceconti M. Material properties assignment to finite element models of bone structures: a new method. Med Eng Phys. December 1998;20(10):735-740.
1972	Burstein AH, Currey JD, Frankel VH, Reilly DT. The ultimate properties of bone tissue: the effects of yielding. J Biomech. January 1972;5(1):35-44.
1990	Cummings SR, Black DM, Nevitt MC, Browner WS, Cauley JA, Genant HK, Mascioli SR, Scott JC, Seeley DG, Steiger P, Vogt TM; The Study of Osteoporotic Fractures Research Group. Appendicular bone density and age predict hip fracture in women. JAMA. February 2, 1990;263(5):665-668.
1994	Oden ZM. Computational Prediction of Functional Adaptation in Canine Radii [PhD thesis]. Tulane University; 1994.
1976	Dalén N, Hellström L-G, Jacobson B. Bone mineral content and mechanical strength of the femoral neck. Acta Orthop Scand. 1976;47(5):503-508.
1995	Ensrud KE, Palermo L, Black DM, Cauley J, Jergas M, Orwoll ES, Nevitt MC, Fox KM, Cummings SR. Hip and calcaneal bone loss increase with advancing age: longitudinal results from the study of osteoporotic fractures. J Bone Miner Res. November 1995;10(11):1778-1787.
1999	Oden ZM, Selvitelli DM, Bouxsein ML. Effect of local density changes on the failure load of the proximal femur. J Orthop Res. September 1999;17(5):661-667.
1990	Beck TJ, Ruff CB, Warden KE, Scott wW Jr, Rao GU. Predicting femoral neck strength from bone mineral data: a structural approach. Invest Radiol. January 1990;25(1):6-18.
1995	Courtney AC, Wachtel EF, Myers ER, Hayes WC. Age-related reductions in the strength of the femur tested in a fall-loading configuration. J Bone Joint Surg. March 1995;77A(3):387-395.
1992	Cheal EJ, Spector M, Hayes WC. Role of loads and prosthesis material properties on the mechanics of the proximal femur after total hip arthroplasty. J Orthop Res. May 1992;10(3):405-422.
1988	Rice JC, Cowin SC, Bowman JA. On the dependence of the elasticity and strength of cancellous bone on apparent density. J Biomech. 1988;21(2):155-168.
1974	Reilly DT, Burstein AH, Frankel VH. The elastic modulus for bone. J Biomech. May 1974;7(3):271-275.
1975	Reilly DT, Burstein AH. The elastic and ultimate properties of compact bone tissue. J Biomech. 1975;8(6):393-405.
1988	Alho A, Husby R, Høiseth A. Bone mineral content and mechanical strength: an ex vivo study on human femora at autopsy. Clin Orthop Relat Res. February 1988;227:292-297.
1984	Lanyon LE, Rubin CT. Static vs dynamic loads as an influence on bone remodelling. J Biomech. 1984;17(12):897-905.
1998	Lengsfeld M, Schmitt J, Alter P, Kaminsky J, Leppek R. Comparison of geometry-based and CT voxel-based finite element modelling and experimental validation. Med Eng Phys. October 1998;20(7):515-522.
1980	Hansson T, Roos B, Nachemson A. The bone mineral content and ultimate compressive strength of lumbar vertebrae. Spine. January–February 1980;5(1):46-55.
1995	Looker AC, Johnston CC Jr, Wahner HW, Dunn WL, Calvo MS, Harris TB, Heyse SP, Lindsay RL. Prevalence of low femoral bone density in older U.S. women from NHANES III. J Bone Miner Res. May 1995;10(5):796-802.
1998	Schwartz AV, Kelsey JL, Sidney S, Grisso JA. Characteristics of falls and risk of hip fracture in elderly men. Osteoporos Int. May 1998;8(3):240-246.
1995	Lotz JC, Cheal EJ, Hayes WC. Stress distributions within the proximal femur during gait and falls: implications for osteoporotic fracture. Osteoporos Int. July 1995;5(3):252-261.
1988	Harrigan TP, Jasty M, Mann RW, Harris WH. Limitations of the continuum assumption in cancellous bone. J Biomech. 1988;21(4):269-275.
1997	Robinovitch SN, Hayes WC, McMahon TA. Distribution of contact force during impact to the hip. Ann Biomed Eng. May 1997;25(3):499-508.
1989	Nordin M, Frankel VH, eds. Basic Biomechanics of the Musculoskeletal System. 2nd ed. Philadelphia, PA: Lea & Febiger; 1989.
1988	Ruff CB, Hayes WC. Sex differences in age‐related remodeling of the femur and tibia. J Orthop Res. November 1988;6(6):886-896.
1996	Ford CM, Keaveny TM, Hayes WC. The effect of impact direction on the structural capacity of the proximal femur during falls. J Bone Miner Res. March 1996;11(3):377-383.
1995	Robinovitch SN, McMahon TA, Hayes WC. Force attenuation in trochanteric soft tissues during impact from a fall. J Orthop Res. November 1995;13(6):956-962.
1984	Carter DR. Mechanical loading histories and cortical bone remodeling. Calcif Tiss Int. March 1984;36(suppl 1):S19-S24.
1991	Hayes WC, Piazza SJ, Zysset PK. Biomechanics of fracture risk prediction of the hip and spine by quantitative computed tomography. Radiol Clin North Am. 1991;29(1):1-18.
1996	Pinilla TP, Boardman KC, Bouxsein ML, Myers ER, Hayes WC. Impact direction from a fall influences the failure load of the proximal femur as much as age-related bone loss. Calcif Tiss Int. April 1996;58(4):231-235.
1990	Lotz JC, Gerhart TN, Hayes WC. Mechanical properties of trabecular bone from the proximal femur: a quantitative CT study. J Comput Assist Tomogr. January–February 1990;14(1):107-114.
1996	Merz B, Niederer P, Müller R, Rüegsegger P. Automated finite element analysis of excised human femora based on precision-QCT. J Biomech Eng. August 1996;118(3):387-390.
1998	Duda GN, Heller M, Albinger J, Schulz O, Schneider E, Claes L. Influence of muscle forces on femoral strain distribution. J Biomech. September 1998;31(9):841-846.
1991	Lotz JC, Cheal EJ, Hayes WC. Fracture prediction for the proximal femur using finite element models, II: nonlinear analysis. J Biomech Eng. 1991;113(4):361-364.
1998	Qin Y, Rubin CT, McLeod KJ. Nonlinear dependence of loading intensity and cycle number in the maintenance of bone mass and morphology. J Orthop Res. July 1998;16(4):482-489.
1995	Robinovitch SN, Hayes WC, McMahon TA. Energy-shunting hip padding system attenuates femoral impact force in a simulated fall. J Biomech Eng. November 1995;117(4):409-413.
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.
1990	Leblanc AD, Schneider VS, Evans HJ, Engelbretson DA, Krebs JM. Bone mineral loss and recovery after 17 weeks of bed rest. J Bone Miner Res. August 1990;5(8):843-850.
1992	Beck TJ, Ruff CB, Scott WW Jr, Plato CC, Tobin JD, Quan CA. Sex differences in geometry of the femoral neck with aging: a structural analysis of bone mineral data. Calcif Tiss Int. January 1992;51(1):24-29.
1983	Huiskes R, Chao EYS. A survey of finite element analysis in orthopedic biomechanics: the first decade. J Biomech. 1983;16(6):385-409.
1998	Mosley JR, Lanyon LE. Strain rate as a controlling influence on adaptive modeling in response to dynamic loading of the ulna in growing male rats. Bone. October 1998;23(4):313-318.
1993	Bergmann G, Graichen F, Rohlmann A. Hip joint loading during walking and running, measured in two patients. J Biomech. August 1993;26(8):969-990.
1993	Beck TJ, Ruff CB, Bissessur K. Age-related changes in female femoral neck geometry: implications for bone strength. Calcif Tiss Int. 1993;53(suppl 1):S41-S46.
1998	Viceconti M, Bellingeri L, Cristofolini L, Toni A. A comparative study on different methods of automatic mesh generation of human femurs. Med Eng Phys. January 1998;20(1):1-10.
1998	Greenspan SL, Myers ER, Kiel DP, Parker RA, Hayes WC, Resnick NM. Fall direction, bone mineral density, and function: risk factors for hip fracture in frail nursing home elderly. Am J Med. June 1998;104(6):539-545.
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.

Year

Entry

1993

Lauritzen JB, Petersen MM, Lund B. Effect of external hip protectors on hip fractures. Lancet. January 2, 1993;341(8836):11-13.

1991

Lotz JC, Cheal EJ, Hayes WC. Fracture prediction for the proximal femur using finite element models, I: linear analysis. J Biomech Eng. 1991;113(4):353-360.

1987

McMahon TA, Valiant G, Frederick EC. Groucho running. J Appl Physiol. June 1987;62(6):2326-2337.

1988

Ashman RB, Rho JY. Elastic modulus of trabecular bone material. J Biomech. 1988;21(3):177-181.

1989

Ashman RB, Rho JY, Turner CH. Anatomical variation of orthotropic elastic moduli of the proximal human tibia. J Biomech. 1989;22(8-9):895-900.

1990

McMahon TA, Cheng GC. The mechanics of running: how does stiffness couple with speed? J Biomech. 1990;23(suppl 1):65-78.

1989

Eriksson SAV, Isberg BO, Lindgren JU. Prediction of vertebral strength by dual photon absorptiometry and quantitative computed tomography. Calcif Tiss Int. April 1989;44(4):243-250.

1991

Snyder SM, Schneider E. Estimation of mechanical properties of cortical bone by computed tomography. J Orthop Res. May 1991;9(3):422-431.

1978

Crowninshield RD, Johnston RC, Andrews JG, Brand RA. A biomechanical investigation of the human hip. J Biomech. 1978;11(1-2):75-85.

1985

Cezayirlioglu H, Bahniuk E, Davy DT, Heiple KG. Anisotropic yield behavior of bone under combined axial force and torque. J Biomech. 1985;18(1):61-69.

1985

Gibson LJ. The mechanical behaviour of cancellous bone. J Biomech. 1985;18(5):317-328.

1990

Keyak JH, Meagher JM, Skinner HB, Mote CD Jr. Automated three-dimensional finite element modelling of bone: a new method. J Biomed Eng. 1990;12(5):389-397.

1993

Keyak JH, Fourkas MG, Meagher JM, Skinner HB. Validation of an automated method of three-dimensional finite element modelling of bone. J Biomed Eng. November 1993;15(6):505-509.

1992

Keyak JH, Skinner HB. Three-dimensional finite element modelling of bone: effects of element size. J Biomed Eng. 1992;14(6):483-489.

1996

van den Kroonenberg AJ, Hayes WC, McMahon TA. Hip impact velocities and body configurations for voluntary falls from standing height. J Biomech. June 1996;29(6):807-811.

1987

Hedlund R, Lindgren U. Trauma type, age, and gender as determinants of hip fracture. J Orthop Res. 1987;5(2):242-246.

1998

Keyak JH, Rossi SA, Jones KA, Skinner HB. Prediction of femoral fracture load using automated finite element modeling. J Biomech. February 1998;31(2):125-133.

1980

Mochon S, McMahon TA. Ballistic walking. J Biomech. 1980;13(1):49-57.

1987

Goldstein SA. The mechanical properties of trabecular bone: dependence on anatomic location and function. J Biomech. 1987;20(11-12):1055-1061.

1998

Morey-Holton ER, Globus RK. Hindlimb unloading of growing rats: a model for predicting skeletal changes during space flight. Bone. May 1998;22(5)(suppl):83S-88S.

1982

Leichter I, Margulies JY, Weinreb A, Mizrahi J, Robin GC, Conforty B, Makin M, Bloch B. The relationship between bone density, mineral content, and mechanical strength in the femoral neck. Clin Orthop Relat Res. March 1982;163:272-281.

1998

Kopperdahl DL, Keaveny TM. Yield strain behavior of trabecular bone. J Biomech. July 1998;31(7):601-608.

1992

Cooper C, Atkinson EJ, O'Fallon WM, Melton JL III. Incidence of clinically diagnosed vertebral fractures: a population‐based study in Rochester, Minnesota, 1985‐1989. J Bone Miner Res. February 1992;7(2):221-227.

1976

Carter DR, Hayes WC. Bone compressive strength: the influence of density and strain rate. Science. September 10, 1976;194(4270):1174-1176.

1977

Carter DR, Hayes WC. The compressive behavior of bone as a two-phase porous structure. J Bone Joint Surg. 1977;59A(7):954-962.

1998

Zannoni C, Mantovani R, Viceconti M. Material properties assignment to finite element models of bone structures: a new method. Med Eng Phys. December 1998;20(10):735-740.

1972

Burstein AH, Currey JD, Frankel VH, Reilly DT. The ultimate properties of bone tissue: the effects of yielding. J Biomech. January 1972;5(1):35-44.

1990

Cummings SR, Black DM, Nevitt MC, Browner WS, Cauley JA, Genant HK, Mascioli SR, Scott JC, Seeley DG, Steiger P, Vogt TM; The Study of Osteoporotic Fractures Research Group. Appendicular bone density and age predict hip fracture in women. JAMA. February 2, 1990;263(5):665-668.

1994

Oden ZM. Computational Prediction of Functional Adaptation in Canine Radii [PhD thesis]. Tulane University; 1994.

1976

Dalén N, Hellström L-G, Jacobson B. Bone mineral content and mechanical strength of the femoral neck. Acta Orthop Scand. 1976;47(5):503-508.

1995

Ensrud KE, Palermo L, Black DM, Cauley J, Jergas M, Orwoll ES, Nevitt MC, Fox KM, Cummings SR. Hip and calcaneal bone loss increase with advancing age: longitudinal results from the study of osteoporotic fractures. J Bone Miner Res. November 1995;10(11):1778-1787.

1999

Oden ZM, Selvitelli DM, Bouxsein ML. Effect of local density changes on the failure load of the proximal femur. J Orthop Res. September 1999;17(5):661-667.

1990

Beck TJ, Ruff CB, Warden KE, Scott wW Jr, Rao GU. Predicting femoral neck strength from bone mineral data: a structural approach. Invest Radiol. January 1990;25(1):6-18.

1995

Courtney AC, Wachtel EF, Myers ER, Hayes WC. Age-related reductions in the strength of the femur tested in a fall-loading configuration. J Bone Joint Surg. March 1995;77A(3):387-395.

1992

Cheal EJ, Spector M, Hayes WC. Role of loads and prosthesis material properties on the mechanics of the proximal femur after total hip arthroplasty. J Orthop Res. May 1992;10(3):405-422.

1988

Rice JC, Cowin SC, Bowman JA. On the dependence of the elasticity and strength of cancellous bone on apparent density. J Biomech. 1988;21(2):155-168.

1974

Reilly DT, Burstein AH, Frankel VH. The elastic modulus for bone. J Biomech. May 1974;7(3):271-275.

1975

Reilly DT, Burstein AH. The elastic and ultimate properties of compact bone tissue. J Biomech. 1975;8(6):393-405.

1988

Alho A, Husby R, Høiseth A. Bone mineral content and mechanical strength: an ex vivo study on human femora at autopsy. Clin Orthop Relat Res. February 1988;227:292-297.

1984

Lanyon LE, Rubin CT. Static vs dynamic loads as an influence on bone remodelling. J Biomech. 1984;17(12):897-905.

1998

Lengsfeld M, Schmitt J, Alter P, Kaminsky J, Leppek R. Comparison of geometry-based and CT voxel-based finite element modelling and experimental validation. Med Eng Phys. October 1998;20(7):515-522.

1980

Hansson T, Roos B, Nachemson A. The bone mineral content and ultimate compressive strength of lumbar vertebrae. Spine. January–February 1980;5(1):46-55.

1995

Looker AC, Johnston CC Jr, Wahner HW, Dunn WL, Calvo MS, Harris TB, Heyse SP, Lindsay RL. Prevalence of low femoral bone density in older U.S. women from NHANES III. J Bone Miner Res. May 1995;10(5):796-802.

1998

Schwartz AV, Kelsey JL, Sidney S, Grisso JA. Characteristics of falls and risk of hip fracture in elderly men. Osteoporos Int. May 1998;8(3):240-246.

1995

Lotz JC, Cheal EJ, Hayes WC. Stress distributions within the proximal femur during gait and falls: implications for osteoporotic fracture. Osteoporos Int. July 1995;5(3):252-261.

1988

Harrigan TP, Jasty M, Mann RW, Harris WH. Limitations of the continuum assumption in cancellous bone. J Biomech. 1988;21(4):269-275.

1997

Robinovitch SN, Hayes WC, McMahon TA. Distribution of contact force during impact to the hip. Ann Biomed Eng. May 1997;25(3):499-508.

1989

Nordin M, Frankel VH, eds. Basic Biomechanics of the Musculoskeletal System. 2nd ed. Philadelphia, PA: Lea & Febiger; 1989.

1988

Ruff CB, Hayes WC. Sex differences in age‐related remodeling of the femur and tibia. J Orthop Res. November 1988;6(6):886-896.

1996

Ford CM, Keaveny TM, Hayes WC. The effect of impact direction on the structural capacity of the proximal femur during falls. J Bone Miner Res. March 1996;11(3):377-383.

1995

Robinovitch SN, McMahon TA, Hayes WC. Force attenuation in trochanteric soft tissues during impact from a fall. J Orthop Res. November 1995;13(6):956-962.

1984

Carter DR. Mechanical loading histories and cortical bone remodeling. Calcif Tiss Int. March 1984;36(suppl 1):S19-S24.

1991

Hayes WC, Piazza SJ, Zysset PK. Biomechanics of fracture risk prediction of the hip and spine by quantitative computed tomography. Radiol Clin North Am. 1991;29(1):1-18.

1996

Pinilla TP, Boardman KC, Bouxsein ML, Myers ER, Hayes WC. Impact direction from a fall influences the failure load of the proximal femur as much as age-related bone loss. Calcif Tiss Int. April 1996;58(4):231-235.

1990

Lotz JC, Gerhart TN, Hayes WC. Mechanical properties of trabecular bone from the proximal femur: a quantitative CT study. J Comput Assist Tomogr. January–February 1990;14(1):107-114.

1996

Merz B, Niederer P, Müller R, Rüegsegger P. Automated finite element analysis of excised human femora based on precision-QCT. J Biomech Eng. August 1996;118(3):387-390.

1998

Duda GN, Heller M, Albinger J, Schulz O, Schneider E, Claes L. Influence of muscle forces on femoral strain distribution. J Biomech. September 1998;31(9):841-846.

1991

Lotz JC, Cheal EJ, Hayes WC. Fracture prediction for the proximal femur using finite element models, II: nonlinear analysis. J Biomech Eng. 1991;113(4):361-364.

1998

Qin Y, Rubin CT, McLeod KJ. Nonlinear dependence of loading intensity and cycle number in the maintenance of bone mass and morphology. J Orthop Res. July 1998;16(4):482-489.

1995

Robinovitch SN, Hayes WC, McMahon TA. Energy-shunting hip padding system attenuates femoral impact force in a simulated fall. J Biomech Eng. November 1995;117(4):409-413.

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.

1990

Leblanc AD, Schneider VS, Evans HJ, Engelbretson DA, Krebs JM. Bone mineral loss and recovery after 17 weeks of bed rest. J Bone Miner Res. August 1990;5(8):843-850.

1992

Beck TJ, Ruff CB, Scott WW Jr, Plato CC, Tobin JD, Quan CA. Sex differences in geometry of the femoral neck with aging: a structural analysis of bone mineral data. Calcif Tiss Int. January 1992;51(1):24-29.

1983

Huiskes R, Chao EYS. A survey of finite element analysis in orthopedic biomechanics: the first decade. J Biomech. 1983;16(6):385-409.

1998

Mosley JR, Lanyon LE. Strain rate as a controlling influence on adaptive modeling in response to dynamic loading of the ulna in growing male rats. Bone. October 1998;23(4):313-318.

1993

Bergmann G, Graichen F, Rohlmann A. Hip joint loading during walking and running, measured in two patients. J Biomech. August 1993;26(8):969-990.

1993

Beck TJ, Ruff CB, Bissessur K. Age-related changes in female femoral neck geometry: implications for bone strength. Calcif Tiss Int. 1993;53(suppl 1):S41-S46.

1998

Viceconti M, Bellingeri L, Cristofolini L, Toni A. A comparative study on different methods of automatic mesh generation of human femurs. Med Eng Phys. January 1998;20(1):1-10.

1998

Greenspan SL, Myers ER, Kiel DP, Parker RA, Hayes WC, Resnick NM. Fall direction, bone mineral density, and function: risk factors for hip fracture in frail nursing home elderly. Am J Med. June 1998;104(6):539-545.

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.

Year	Entry
2006	Ferguson PA. Quantifying and Modelling Adaptive Astronaut Movement: Motion Strategies for Long-Duration Spaceflight Missions [PhD thesis]. Cambridge, MA: Massachusetts Institute of Technology; May 2006.
2007	Wagner EB. Musculoskeletal Adaptation to Partial Weight Suspension: Studies of Lunar and Mars Loading [PhD thesis]. Cambridge, MA: Massachusetts Institute of Technology; September 2007.

Year

Entry

2006

Ferguson PA. Quantifying and Modelling Adaptive Astronaut Movement: Motion Strategies for Long-Duration Spaceflight Missions [PhD thesis]. Cambridge, MA: Massachusetts Institute of Technology; May 2006.

2007

Wagner EB. Musculoskeletal Adaptation to Partial Weight Suspension: Studies of Lunar and Mars Loading [PhD thesis]. Cambridge, MA: Massachusetts Institute of Technology; September 2007.