Characterization of coordination patterns in lower limb amputees and healthy controls with a handless crutch

Abstract

Lower limb amputation (LLA) is an often traumatic and life altering event that can be accompanied by life-long musculoskeletal complications. This is particularly concerning when the approximately 150,000 people who undergo lower limb amputation each year in the United States are considered. From a biomechanical standpoint, unilateral or bilateral LLA impacts lower-limb architecture inducing changes to gait like slower preferred walking velocities, stance time and length asymmetries, and swing time asymmetries. Amputation also impacts trunk and pelvic range of motion. Given the upstream effects of amputation, it is not surprising that amputees experience low back pain (LBP) at higher rates than the general population. In fact, surveyed amputees report that their back pain is more bothersome than phantom limb pain and some more bothersome than residual limb pain. Interestingly amputees and those with low back pain (LBP) present with similar gait and trunk and pelvic range of motion changes. In recent years, methods that characterize relative movements or coordination patterns between spinal segments such as the trunk/torso and pelvis have proven to be more sensitive to LBP status than traditional gait and range of motion measures. These studies have found that adults with LBP, with a history of LBP, and no LBP all have distinct pelvic/trunk coordination patterns. Understanding how LLA impacts coordination patterns could lend insight into the development of LBP in both amputees and the general population. The goal of this dissertation is to begin characterizing the effects of LLA on upper-torso, torso, and pelvic coordination patterns during both running and walking. In addition, the three most ubiquitous continuous methods used for calculating coordination patterns are compared using computer generated signals. These three methods are: Continuous Relative Phase (CRP), Continuous Relative Phase using the Hilbert Transform (CRPHT) and Relative Fourier Phase analysis (RFP). This dissertation aims to provide a comprehensive comparison of these methods along with a set of best practices. The studies in this literature review reveal three overarching conclusions concerning coordination patterns in unilateral LLAs. Firstly, unilateral LLA does not impact overall patterning of pelvic/torso coordination patterns. As walking and running velocity increases pelvic/torso coordination patterns in amputees transitions from a more in-phase pattern where the pelvic and torso rotate together, to an out-of-phase pattern where there is counter rotation between segments. This is particularly apparent in lateral (frontal plane) and axial coordination patterns. These velocity dependent changes in coordination are also seen in healthy controls. However, like subjects with LBP, amputees maintain in-phase coordination patterns longer or spend a longer proportion of the gait cycle adopting in-phase coordination patterns. Secondly, in walking there were significant decreases in coordination variability. Again, echoing a pattern seen in non-amputees with LBP. Thirdly, the fourth chapter of this dissertation analyzes data on a cohort of controls walking with and without the iWalk 2.0 which was used to mimic knee disarticulation. While this is an unconventional way of analyzing the effects of LLA on gait mechanics results of this study show that it was an effective means of isolating the effects of LLA. A comparison of continuous methods used to calculate coordination patterns revealed similarities between CRP and CRPHT. While RFP consistently overestimated relative phase between computer generated signals, whether this is of concern would depend on the research question. If the research objective is to characterize changes in coordination patterns, then a 10-15º overestimation of relative phase may not be of great concern. However, if the purpose of the research is to characterize variability particularly as a proxy for stability, this overestimation could impact interpretation. Also, because RFP relies on windowing and the fundamental frequency of a signal, it is best used to analyze data where multiple cycles are collected. Overall, the work in this dissertation clarifies and provides key considerations for researchers who would like to use CRP, CRPHT, or RFP to analyze coordination between body segments. In addition, it adds to the growing body of literature characterizing coordination patterns in various populations and identifies unique changes to them that are induced by LLA.