An Investigation of Functional Improvements in the RHEO KNEE Compared to Hydraulic Microprocessor Controlled Knees (MPKs)

Recruiting and participants:

A convenience sample of 15 transfemoral amputee users was recruited at 4 study sites. Potential subjects were identified from the customer base of study sites, local investigators evaluated , based on previous experience of interaction with and servicing of patients, if a potential participant is cognitively capable. If a potential participant fitted the inclusion and exclusion criteria the local investigator (CPO-Certified prosthetist/orthotist) contacted them via telephone. During the telephone call the investigator verified if they were interested in participating in the study. If interest was expressed and eligibility criteria was met an appointment was made for enrollment in the study. Informed consent was obtained from all participants at the beginning of the first visit, prior to clinical testing and prosthetic fitting.

Setting:

Testing was conducted in four US locations with daily mean temperature during the testing period between 79.3 to 85.3 degrees Fahrenheit, Fort Worth (Baker orthotics \& prosthetics), Jackson (Methodist Rehabilitation Center), Roanoke (Virginia Prosthetics \& orthotics) and Orlando (Ossur facility, Florida gait lab) . Participants had to visit the study location twice, for approximately 3 hours per visit. First time for the baseline measure and initial fitting and secondly after 3 weeks of accommodation on the Rheo knee XC, performing the same measures as for the baseline. No standard exists for follow up time needed for amputees to adapt to a new prosthesis however, a follow up time of at least 3 weeks is widely used and considered sufficient for functional comparison.

All users used their existing sockets throughout the testing without modifications. One group consisted of 9 previous MPK-magnetorheologic (MPK-MR), Rheo knee II and III, users and the second group of 4 previous MPK-hydraulic knee (MPK-HY), Genium, users. By maintaining alignment and foot choice in the previous Rheo knee group confounding factors could be minimized. The previous MPK-HY was provided with an alignment offset adapter and a consistent foot choice, XC Vari-Flex, at initial fitting. The load line was controlled to be equal prior and post initial fitting. During the initial fitting the MPK-HY users which were new to the XC Vari-Flex had to undergo an evaluation for the foot stiffness as defined by the manufacturer (Ossur ehf). Foot configuration had to be rated acceptable or better with all users that were provided with a XC Vari-Flex.

13 users completed a 3 week evaluation in a multi-center trial with the RHEO KNEE XC at which point they performed Borg Scale CR 10 pre, 6MWT, Borg Scale CR 10 post, L-Test, stair and bicycle evaluation and prosthesis evaluation quesionnaire mobility section) PEQ MS 12/5) on functional ability and prosthesis satisfaction in this order.

The Borg Scale CR 10 is an accepted and reliable psychophysical score which has been used to report on the perceived level of exertion in lower limb amputees. The 6MWT has shown to be a reliable measure in amputees and differentiate among functional levels with a minimum detectable change for unilateral trans-tibial and transfemoral found at 45m. The L-Test is a valid indicator for functional mobility and showed high intraclass correlation, interrater reliability, and minimal bias upon retesting with a moderate correlation to self-reports like the PEQ MS 12/522 which itself is a reliable and valid measure for lower limb amputee assessing psychometric properties.

Ambulating stairs was evaluated as a timed parameter split up in ascending and descending. An observer score/SAI for the gait quality, and a user score/self-report with a 5 point scale (Please rate your ability when using the prosthesis: unable=0, highly difficult=1, moderate difficulty=2, little difficulty=3, no problems=4) similar to the PEQ MS 12/5 scores described by Franchignoni et. al.22 was used. The Rheo Knee XC stair mode can be entered by flexing the hip of the amputated side faster and to a higher degree than in typical walking. The Rheo knee XC will then maintain a flexed position to allow the user to position the foot onto the next stair case. The Genium requires the amputee to stop in front of the stairs and initiate a fast movement into hip-hyperextension to allow the knee to maintain a flexed position. For adapting these two different techniques each user was given 30min training time with instructions to get familiar with the stairs and the operation of the knee in specific location. Equal time was given after initial fitting which was important to the previous MPK-MR knee users who have not used the stair mode before. For the bicycle evaluation the same 5 point scale for the self-report assessment was applied to report on 2 questions: Rate your ability to ride the bicycle and rate your ability to stop the bike with the prosthetic side down.