title: Persons with unilateral transfemoral amputation experience larger spinal loads during level-ground walking compared to able-bodied individuals.
abstract: BACKGROUND
  Persons with lower limb amputation walk with increased and asymmetric trunk motion; a characteristic that is likely to impose distinct demands on trunk muscles to maintain equilibrium and stability of the spine. However, trunk muscle responses to such changes in net mechanical demands, and the resultant effects on spinal loads, have yet to be determined in this population.
  
  
  METHODS
  Building on a prior study, trunk and pelvic kinematics collected during level-ground walking from 40 males (20 with unilateral transfemoral amputation and 20 matched controls) were used as inputs to a kinematics-driven, nonlinear finite element model of the lower back to estimate forces in 10 global (attached to thorax) and 46 local (attached to lumbar vertebrae) trunk muscles, as well as compression, lateral, and antero-posterior shear forces at all spinal levels.
  
  
  RESULTS
  Trunk muscle force and spinal load maxima corresponded with heel strike and toe off events, and among persons with amputation, were respectively 10-40% and 17-95% larger during intact vs. prosthetic stance, as well as 6-80% and 26-60% larger during intact stance relative to controls.
  
  
  CONCLUSIONS
  During gait, larger spinal loads with transfemoral amputation appear to be the result of a complex pattern of trunk muscle recruitment, particularly involving co-activation of antagonistic muscles during intact limb stance; a period when these individuals are confident and likely to use the trunk to assist with forward progression. Given the repetitive nature of walking, repeated exposure to such elevated loading likely increases the risk for low back pain in this population.
authors.affiliation: Department of Biomedical Engineering, University of Kentucky, Lexington, KY, USA.
authors.forename: Iman
authors.initials: I
authors.lastname: Shojaei
authors.affiliation: Department of Rehabilitation, Walter Reed National Military Medical Center, Bethesda, MD 20889, USA; Center for Rehabilitation Sciences Research, Department of Physical Medicine and Rehabilitation, Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA.
authors.forename: Brad D
authors.initials: BD
authors.lastname: Hendershot
authors.affiliation: Department of Rehabilitation, Walter Reed National Military Medical Center, Bethesda, MD 20889, USA; DOD - VA Extremity Trauma and Amputation Center of Excellence, Walter Reed National Military Medical Center, Bethesda, MD 20889, USA.
authors.forename: Erik J
authors.initials: EJ
authors.lastname: Wolf
authors.affiliation: Department of Biomedical Engineering, University of Kentucky, Lexington, KY, USA. Electronic address: babak.bazrgari@uky.edu.
authors.forename: Babak
authors.initials: B
authors.lastname: Bazrgari
mesh_terms: D000328:Adult; D000671:Amputation, Surgical; D000674:Amputees; D001415:Back; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D019245:Compressive Strength; D005272:Femur Neck; D005684:Gait / Q000502:physiology*; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D010388:Pelvis; D033081:Shear Strength; D013314:Stress, Mechanical; D013909:Thorax; D060726:Torso / Q000502:physiology; D016138:Walking / Q000502:physiology*
keywords: Amputation; Gait; Low back pain; Muscle forces; Spinal loads