Lumbar loads and trunk kinematics in people with a transtibial amputation during sit-to-stand.

People with a transtibial amputation have numerous secondary health conditions, including an increased prevalence of low back pain. This increased prevalence may be partially explained by altered low back biomechanics during movement. The purpose of this study was to compare trunk kinematics and L4-L5 lumbar loads in people with and without a transtibial amputation during sit-to-stand. Motion capture, ground reaction force and electromyographic data were collected from eight people with a unilateral transtibial amputation and eight people without an amputation during five self-paced sit-to-stand motions. A musculoskeletal model of the torso, lumbar spine, pelvis, lower limbs, and 294 muscles was used in a static optimization framework to quantify L4-L5 loads, low back muscle forces, and trunk kinematics. Participants with an amputation had greater peak and average L4-L5 loading in compression compared to control participants, with peak loading occurring shortly after liftoff from the chair. At the instant of peak loading, participants with an amputation had significantly greater segmental trunk lateral bending and trunk-pelvis axial rotation toward the intact side, and significantly greater segmental trunk axial rotation toward the prosthetic side compared to control participants. Participants with an amputation also had greater peak frontal plane and transverse plane segmental trunk angular velocity. The postural differences observed in people with a transtibial amputation were consistent with their ground reaction force asymmetry. The cumulative effects of the altered movement strategy used by people with an amputation may result in an increased risk for low back pain development over time.