Does Transfemoral Prosthetic Socket Design and Alignment Influence Low Back Pain? A Comparison Between Ischial-Containment and Sub-Ischial Sockets

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Long-term transfemoral (i.e., above-knee) prosthesis users are at an increased risk of developing secondary musculoskeletal conditions compared to the general able-bodied population. Significant resources have been devoted to the immediate rehabilitation needs of persons undergoing lower-limb amputation, but there needs to be greater consideration for the early identification and modification of potential risk factors responsible for long- term development of secondary health conditions such as low back pain (LBP). The etiology for the development of LBP is not entirely known or understood, but in persons with unilateral amputations it is believed to relate to the asymmetries and gait deviations that are typically demonstrated and required to walk with a prosthesis. Previous studies have primarily focused on the lumbar spine and pelvis, while neglecting trunk posture and spinal segmental motions. There have been limited studies to date that have investigated or determined if transfemoral prosthesis users adopt standing and gait postures and pelvic rotation patterns that put them at increased risk of developing or worsening LBP. We propose to conduct a preliminary investigation of the trunk and pelvic positioning and motions during standing and walking to determine if long-term unilateral, transfemoral prosthesis users are at an increased risk of developing LBP due to socket design and prosthetic alignment. Therefore, the purpose of this study is to investigate and compare the effects of the standard ischial containment (IC) socket to a sub-ischial (SI) socket design on the trunk posture and pelvic motions of transfemoral prosthesis users. We propose the following specific aims for this project: • Aim 1: To measure kinematics of the pelvis and spinal segments in unilateral, transfemoral prosthesis users during gait. We will perform quantitative motion analyses on two groups of 6 research subjects with lower limb amputation using 2 different socket designs (IC and SI) walking over level ground at three self-selected walking speeds (slow, normal, fast). Data will be compared between socket type and to an able-bodied control group. Hypothesis 1a—IC socket wearers will have greater anterior pelvic tilt compared to SI socket wearers and able-bodied controls, and they will exhibit considerably greater sagittal-plane rotations of the pelvis and spinal segments during walking. Hypothesis 1b—IC socket wearers will exhibit greater lumbar erector spinae activity while walking compared to SI socket wearers and able-bodied controls. • Aim 2: To measure trunk posture and pelvic orientation in unilateral, transfemoral prosthesis users during standing. We will use a multi-segment model of the spine and pelvis of the research and control subjects to determine neutral spinal, pelvis and prosthetic alignment during standing. Hypothesis 2a—IC socket wearers will demonstrate greater trunk flexion and anterior pelvic tilt during standing compared to SI socket wearers and control subjects. Hypothesis 2b—IC socket wearers will exhibit greater erector spinae activity during standing compared to SI socket wearers and able-bodied controls. These preliminary data could be used in the future as a rationale to conduct larger, more in-depth and focused studies to investigate LBP associated with amputation and prosthesis use. Additionally, our results may suggest that conventional prosthetic socket designs should be reassessed to allow greater rotation between the pelvis and femur of the residual limb. Understanding spinal motion and compensations would improve our comprehension of the factors contributing to LBP and possibly lead to the development of new prosthetic and therapeutic interventions designed to prevent or alleviate LBP.