Individuals with a lower-limb amputation have an increased prevalence of chronic low back pain (LBP), relative to the general adult population. Altered, dynamic whole-body biomechanics resulting from limb loss are thought to be a primary cause of the increased susceptibility. However, biomechanical LBP development is a multi-factorial problem, and a definitive cause has yet to be ascertained using only traditional, laboratory methods.

Thus, the purpose of this work was to compare dynamic, in vivo low back biomechanics between individuals with and without unilateral, transtibial amputation during walking, estimated using patient-specific computational modeling and simulation. A generic, muscle-actuated whole-body model with additional detail in the L1-L5 lumbar was adjusted to represent each individual. Experimentally-measured motion capture, ground reaction force, and surface electromyography for each individual were used to simulate a gait cycle to estimate concurrent internal low back biomechanics.

Results showed several group differences in computed low back metrics during particular phases of the gait cycle. Most significant in individuals with an amputation was greater lateral trunk motion towards the residual side during residual single limb stance, concurrently with greater intact-side trunk muscle forces and a greater L4L5 lumbar joint contact force. A greater range of axial trunk rotation near toe off of the residual limb was also found concurrently with greater force in residual-side erector spinae and psoas. The repetition of such abnormal biomechanics over time has potential to cause deficiencies in muscular endurance, strength asymmetries, inhibited proprioception, and myofascial pain, each associated with increased susceptibility to chronic, biomechanical LBP and other secondary musculoskeletal disorders. This work contributes to a broader goal of developing computational modeling and simulation into a supplementary clinical tool to aid in diagnosis and treatment of biomechanical disorders.