Evaluation of Transfemoral Amputees When Transitioning From a Mechanical to a Microprocessor Prosthetic Knee

Research Hypothesis The central hypothesis of this proposal is that real-life benefits of microprocessor knees (MPK) are largely underappreciated because of the lack of sensitive and ecologically valid methods for evaluating motor performance. This makes it difficult to justify MPKs for many amputees who could benefit from it. The investigators' recent research on the stride length-cadence relationship and dual-task gait analysis offers a new direction to overcome some of these limitations.

Why stride length-cadence relationship for MPKs? Because stride length and cadence form a strong linear relationship over a range of gait velocities, examining the strength of their association offers a unique way to characterize natural gait. The investigators found that the stride length-cadence relationship is disrupted in prosthesis users. Also, the step length-cadence relationship is disrupted bilaterally, indicating altered neurocontrol of gait. Unlike a mechanical knee, MPKs adjust properties to accommodate changes in velocity, resembling more natural gait pattern. Thus, the stride length-cadence relationship is expected to be tighter for MPKs than a mechanical knee.

Why dual-task gait for MPKs? Dual-task gait is the act of walking while performing an additional task (talking, texting, etc.). The additional load imposed on the nervous system alters gait. Thus, "walking while talking" better reflects real-life gait than standard gait analysis. Dual-task gait studies in prosthetic users are rare. The classic outcome measure in dual-task studies is a standard deviation divided by the mean for each gait parameter separately, which ignores their dependence on changes in speed. The investigators recently developed a new method for analyzing dual-task gait based on the linear relationship that stride length and cadence have with velocity. The standard deviations of the difference between the actual data point for stride length or cadence from the point predicted by the line that represents the best fit with velocity are compared between the free walking and dual-task walking. This calculation of variability in stride length or cadence accounts for their trial-to-trial changes with the velocity that can influence results. Previous studies indicate that MPKs require less additional thought during gait. If indeed the case, the users should be able to shift motor and cognitive resources from gait to other activities and, at the same time, have less variable gait under dual-task condition. Since decreased gait variability has been related to better neurocontrol of gait and lesser risk for falls, the proposed proof-of-principle study will be the first step toward providing critical missing evidence for justifying the use of MPKs in a broader population of amputees, particularly in K2 users or persons with cognitive impairments as a result of vascular disease or diabetes.

Objective: Evaluate differences in gait and function between an MPK (RheoKnee®, Ossur) and a mechanical knee in K2 and K3 prosthesis users in an A-B-A and B-A-B single-subject design.

Specific Aim 1: Assess the stride length-cadence relationship during gait with the MPK compared to the mechanical knee.

Hypothesis 1.1: The stride length-cadence linear relationship will significantly improve after wearing the MPK. Hypothesis 1.2: The linearity of the stride length-cadence relationship will be significantly higher for the MPK than the mechanical knee.

Specific Aim 2: Determine the changes in dual-task cost while walking with the MPK compared to the mechanical knee.

Hypothesis 2.1: Under the dual-task condition, the variability in stride length and cadence will be significantly smaller while wearing the MPK than the mechanical knee.

Specific Aim 3: Compare the performance between the MPK and the mechanical knee on clinical measures of mobility, balance, and user preference.

Hypothesis 3.1: Measures of functional mobility will improve more while wearing the MPK than the mechanical knee Hypothesis 3.2: Balance measures will improve more while wearing the MPK more than the mechanical knee.

Hypothesis 3.3: Joint range of motion and ground reaction force symmetry will improve while wearing the MPK.

Study Design:

The study will use an A-B-A and B-A-B single-subject design (A- the subject's current mechanical knee; B- MPK: RheoKnee®). The purpose of B-A-B design is to control for a learning effect due to multiple repetitions of cognitive tasks during dual-task gait, which may contribute to hypothesized improvements in phase B of the A-B-A design. Each phase will last 4 weeks.

Protocol:

Eligible subjects who signed the consent form will be randomly allocated to the A-B-A or B-A-B group. The proper fit/alignment of the current mechanical knee will be verified, and, if fine, the 3D gait analysis and functional assessment (Full Evaluation) will be performed at baseline. Walking at up to 5 self-selected speeds (very slow to very fast) and dual-task gait (Gait Evaluation) will also be evaluated at baseline and then on a weekly basis throughout each phase. At the end of each phase, Gait Evaluation and Full Evaluation are repeated. The end of each current phase and the beginning of a new phase are separated by a transition period. The transition period starts with the alignment of a new device followed by 2 weeks of accommodation during which up to 6 gait training sessions are provided by a physical therapist (PT) and the alignment is checked. All efforts will be made to maintain the subject's current socket style and suspension system. The B-A-B design is identical to the A-B-A design except for an additional transition period at the very beginning since the naive subjects are fit for the first time with the MPK.

Methods:

Users of a mechanical prosthetic knee will be recruited from the population served by Methodist Rehabilitation Center if they meet the enrollment criteria. After signing the consent form, the subjects will be allocated to the A-B-A or B-A-B group using a random number sequence.

Gait Evaluation:

Self-Selected Speeds:

Temporal and spatial footfall data will be collected by an electronic walkway (20 ft) as the subject walks at five self-selected speeds (very slow, slow, normal, fast, very fast). An area at each end of the walkway will allow for acceleration and deceleration so that only steady-state gait is recorded. Subjects will complete a minimum of 4 passes at each speed, which they will freely select to achieve the most natural walking pattern. The normal gait speed will always be collected first. The order of slower/faster speed categories will be randomized with the very slow/fast speed collected last in each category. Subjects will be instructed to modulate the speed within safety limits and encouraged to complete all speeds, to the extent possible.

Dual-Task Gait:

Four cognitive tasks will be used for dual-task gait; backward spelling, serial subtraction, digit span, and category listing. Three tasks will be used at each assessment point to curb the effect of learning. Tasks will be selected at random so that each is given an equal number of times in each phase. All four tasks will be used at baseline. Different prompts will be given to ensure no task is presented the same way twice.

Before each assessment, the subject will practice the selected tasks while seated to familiarize with the protocol. For the dual-task gait, the subject will be instructed to walk at a comfortable pace and simultaneously perform cognitive tasks without specific instructions on prioritization. The cognitive tasks will be block randomized with each block containing 4 walking trials. At the end, the subject will be asked to rate the task difficulty on a 7-point Likert scale.

Full Evaluation:

• Functional prosthetic assessment (Amputee Mobility Predictor, L-test, 6-minute Walk Test, Berg Balance Scale, Physiological Cost Index,Temporal/Spatial Gait Assessment)
• User evaluation of the prosthesis (Prosthesis Evaluation Questionnaire, study specific knee preference evaluations)
• Computerized 3D gait assessment (3D gait kinematics and kinetics)
• Cognition/mood (Modified Mini-Mental State Exam, Trails A \& B, Patient Health Questionnaire)

Outcome Measures:

Specific Aim 1: Stride-length cadence relationship

• Main outcome: coefficient of determination (R2) of the linear regression line
• Secondary outcomes: peak velocity \& range of velocities

Specific Aim 2: Cost of dual-task gait

• Main outcome: variability (standard deviation) of stride length and cadence under unconstrained and dual-task conditions
• Secondary outcomes: peek/range of velocities under the two conditions; the rating of difficulty

Specific Aim 3: Comparison of change between K2 and K3 users

• Main outcomes: scores from the Berg Balance Scale, Prosthesis Evaluation Questionnaire, Amputee Mobility Predictor, L-test, 6-minute Walk Test, Physiological Cost Index
• Secondary outcomes: Temporal/Spatial Gait Assessment, 3D joint range of motion, joint angles at critical instants, the ground reaction force

Analysis:

Due to the nature of the single-subject design, the data will be evaluated both qualitatively and with small-n design statistical methods.