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VOLUME 8, ISSUE 1 

 2025 
 

RESEARCH ARTICLE 

 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian 

Prosthetics & Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

 

  

 

https://jps.library.utoronto.ca/index.php/cpoj/index
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https://pmc.ncbi.nlm.nih.gov/journals/?term=%22Canadian+Prosthetics+%26+Orthotics+Journal%22
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https://doi.org/10.33137/cpoj.v8i1.45286
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1 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

 

 

RESEARCH ARTICLE 

 

SOUTH AFRICAN USERS’ FUNCTION AND EXPERIENCE WITH A MAGNETORHEOLOGICAL 

MICROPROCESSOR KNEE: A MIXED METHODS STUDY 

Visagie S1*, Theron B2  

1. University of Stellenbosch, Division of Disability and Rehabilitation Studies, Faculty of Medicine and Health Sciences, South Africa. 
2. Össur South Africa, Cape Town, South Africa. 
 
  
 

 

 

 

  

 

 

 

 

 

 

 

 

 

 

 

 

INTRODUCTION   

Persons with amputations expressed the notion that 

prostheses “normalize” their functionality and physical 

appearance.1,2 Over the years, prosthetic development has 

aimed to enhance this sense of “normalization” and 

minimize functional loss, benefiting from advanced 

materials  and  the integration of software technologies. An   

 

 

 

 

example is the use of sensors and microprocessor-

controlled software in prosthetic knee and ankle 

components.3  

Microprocessor knees (MPKs) provide high levels of safety, 

consistency, and confidence during walking.3 One of the 

most widely recognized benefits of MPKs is their ability to 

reduce stumbles and falls.4 Research has also shown 

improved physiological functions such as a decrease in 

oxygen cost when walking with MPKs compared to non-

microprocessor knees (NMPKs).5 MPKs enhance walking 

speed, stair climbing, hill descent, walking on uneven 

terrain, and the ability to multitask while walking.5 However, 

MPKs are expensive, with prices starting at over R600,000 

(US$32,000) and reaching up to R1 million (US$55,000). 

 
OPEN  ACCESS 

ABSTRACT 

BACKGROUND: Microprocessor knees (MPKs) support safe and confident prosthetic walking. Their cost often 

prohibits prescription in low-and middle- income settings like South Africa. Funding of high-end prosthetic products 

in South Africa is dependent on justifications that explain why the component is prescribed, and how it can improve 

the user`s function. There is little local evidence to support these justifications.  

OBJECTIVE: To explore and describe South African users’ function and experience with the Rheo XC 

microprocessor knee (MPK). 

METHODOLOGY: An explanatory sequential mixed methods design was used. A pre-test, post-test study was 

followed by a descriptive qualitative study to explore and explain the observed outcomes. In the pre-test phase, 

baseline data were collected while participants used their regular non-microprocessor knees (e.g., mechanical or 

hydraulic joints). Post-test data were collected after a two-week trial with the Rheo XC knee joint. Data were 

collected from 16 consecutively sampled participants, using a self-developed functional level scale and the L-Test. 

Nine (56.3%) participants had a transfemoral amputation, six (37.5%) had a knee disarticulation and one (6.3%) 

had bilateral amputations (transtibial and transfemoral). Baseline and follow-up data were paired for each 

participant and analyzed with the Wilcoxon Signed-Rank test. The descriptive qualitative study explored six 

purposively sampled participants’ experiences of the trial knee through semi-structured interviews. Inductive 

thematic analysis was done. 

FINDINGS: The time to complete the L-Test decreased on average 7.5 s between baseline (35.4 s) and post-test 

(27.9 s) data. L-Test Wilcoxon Singed-rank findings showed a significant increase in walking speed (p < 0.001). 

Mean functional level scores increased by an average of 12.7 points (p < 0.001) with improvements observed 

across all activities except running, for which scores remained unchanged. Two themes emerged from the 

qualitative data. Theme 1: Acceptance of the MPK showed enthusiasm for the MPK. However, Theme 2: Real-

world limitations of the MPK cautioned that the MPK is not suitable for everybody. 

CONCLUSION: This study provides context specific scientific evidence that may support funding decisions for 

MPKs in South Africa. However, it is not suitable for everyone, and a trial period to assess appropriateness is 

advised before prescription. The test period in this study was short, and further research over longer durations is 

recommended. 

 

 

ARTICLE INFO 

Received: April 29, 2025 

Accepted: June 6, 2025 

Published: June 12, 2025 
 

CITATION 

Visagie S, Theron B. 

South African users’ 

function and experience 

with a magnetorheological 

microprocessor knee: A 

mixed methods study. 

Canadian Prosthetics & 

Orthotics Journal. 2025; 

Volume 8, Issue 1, No. 5. 

Https://doi.org/10.33137/c

poj.v8i1.45286 

KEYWORDS 

Amputation; South Africa; 

Lower Middle-Income 

Countries; Prosthetic 

Prescription; Rheo XC; 

Transfemoral; Transtibial; 

Rehabilitation; L-Test; 

Microprocessor Knee; 

Knee Disarticulation; 

MPKs.  

* CORRESPONDING AUTHOR: 
Surona Visagie, PhD  

Affiliation: University of Stellenbosch, Division of Disability and 
Rehabilitation Studies, Faculty of Medicine and Health Sciences, South 
Africa. 

E-Mail: suronav@sun.ac.za  

ORCID ID: https://orcid.org/0000-0003-4575-479X  

 

Journal Homepage: https://jps.library.utoronto.ca/index.php/cpoj/index 

Volume 8, Issue 1, Article No. 5. 2025 

 

 

https://doi.org/10.33137/cpoj.v8i1.45286
https://doi.org/10.33137/cpoj.v8i1.45286
https://doi.org/10.33137/cpoj.v8i1.45286
mailto:suronav@sun.ac.za
https://orcid.org/0000-0003-4575-479X
https://jps.library.utoronto.ca/index.php/cpoj/index


 

2 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

Even though research shows that future savings and 

financial benefits might offset the initial high cost of the 

MPK6,7 the expense remains a barrier to prescription.  

Provision of prosthetic components—whether costly or 

not—is hampered by a shortage of financial resources, poor 

social security systems, and little health insurance in low-

and middle- income countries (LMICs).8,9 Service-related 

factors such as limited access to equipment and materials, 

limited numbers of adequately trained prosthetists, 

clustering of prosthetic services in metropoles and 

bureaucratic red tape further obstructs prosthetic 

services.8-13 There is also limited awareness of services, 

service pathways, and device options among users.8,9,14 

Geographical challenges, large rural areas, inadequate 

transport systems, and poor infrastructure further decrease 

access to prosthetic devices.8,10,14-16 Finally, prosthetic 

components dependent on computer software such as 

MPKs are sometimes considered too fragile for the harsh 

environments and employment requirements in LMICs.10 

Therefore, context specific research is required to ensure 

that products which has shown superior function in Global 

North settings are appropriate for use in the LMICs.10,14  

The only statistics currently available on the need for 

prosthetics in South Africa comes from the 2022 national 

census which states that there are around 430,000 upper 

and lower limb prosthetic users in the country.17 Waiting 

periods9,15,16,18 and waitlists for prostheses19 are long. In 

addition, while a prosthesis is often promised at the time of 

amputation20 receiving one is not a given.21,22 For those who 

do receive a prosthesis, functional ability is often not 

optimally supported by the componentry provided in both 

the private9 and public sectors.15  

In the South African private sector, the funding of high-end 

prosthetic products, including MPKs, is dependent on 

special justifications explaining the functional benefits of the 

more expensive component, and lengthy waiting periods 

before authorization for the components are received.9 

MPKs are seldom covered by medical insurance, but are 

provided through the Road Accident Fund.9 In the public 

sector, which provides the bulk of prosthetic services in the 

country and will play an even larger role after the 

implementation of the National Health Insurance Act, high-

end products are not currently funded.15 Prosthetic 

component selection is based on empirical knowledge and 

financial considerations rather than evidence-based 

guidelines in both the government and private sectors. 

Inconsistencies, over, and under prescription, which are at 

least in part due to insufficient local evidence, are real 

concerns.9   

Therefore, the aim of the study was to explore and describe 

users’ function and experience with an MPK, the Rheo XC, 

which generates knee joint resistance through a 

magnetorheological clutch mechanism23 in comparison to 

the NMPKs participants normally use in South Africa. It is 

hoped that the results will contribute to the evidence base 

for prosthetic practice in South Africa. The study focused on 

a specific microprocessor knee (MPK) because, although 

MPKs are similar in type, they differ in the specific functional 

features they provide.24  

METHODOLOGY 

To ensure robustness and rigor, an explanatory sequential 

mixed methods design was employed. Changes in user 

function were determined using a quantitative pre-test, post-

test design. Functional changes were contextualized and 

further explored with a qualitative descriptive study. The 

results were analyzed separately and triangulated in the 

discussion.25 

Pre-test, post-test 

Sixteen consecutively sampled prosthetic users were 

included in the pre-test, post-test study. They had to: 

• Be older than 18 (age of majority in South Africa) 

• Have a transfemoral amputation or knee disarticulation 

• Have an amputee activity level of K2-K4 on the 

AMPPRO.26 

• Use a prosthesis for more than four months to ensure 

sufficient adaptation to the prosthesis.27  

Users who did not complete the two-week trial period or who 

experienced a health crisis such as a stroke that might 

influence their functioning, during the two weeks, would 

have been excluded. However, these situations did not 

occur. Four users who started the trial did not complete the 

study (one had a faulty MPK and the other three did not 

complete the post-test). Baseline and follow up data on 

functioning and walking speed with the participant`s 

conventional knee and the Rheo XC were collected 

between 01 March 2023 to 31 January 2025. The pre-test 

was completed before the Rheo XC was fitted, and post-test 

data were collected two weeks after fitting the device.  

History, maturation, cognitive learning, interrater reliability, 

statistical regression, and sensitization all pose threats to 

the internal and external validity of the pre-test, post-test 

design.28 These challenges of one group designs are 

acknowledged. However, in this study, with its short time 

frame and contained independent variable (i.e. a different 

knee component), many of these concerns were mitigated. 

External changes should not influence the function with the 

knee because the physical environment in which the user 

operated remained the same. To prevent maturation 

effects, users had to have been walking with a prosthesis 

for four months or more at the time of the pre-test. Function 

is physical in nature; thus, cognitive learning was not a 

concern. Spontaneous remission does not pose a risk to 

validity as an amputation is a permanent impairment. 

Factors such as interest level, and general fatigue could not 

be controlled and might have influenced scores. Clinical 

https://doi.org/10.33137/cpoj.v8i1.45286


 

3 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

evaluation commonly involves pre-test, post-test 

assessments.29 Thus, this design was deemed suitable for 

the current study with its focus on clinical application. In 

addition, results were verified through triangulation with 

qualitative descriptive findings.  

The supplier of the Rheo XC, Össur, offers trial periods with 

the knee to users in South Africa (this service has been 

offered for years; it was not started with the current study in 

mind). The current study utilized data collected during this 

trial period. Prosthetists request trial units for users based 

on the user’s function and physical ability. During the study 

period, the prosthetist was informed about the research only 

after a trial request for the MPK knee being studied was 

received. They were asked to provide users with the 

information leaflet and informed consent form, and to obtain 

written consent from those willing to participate in the study. 

Participation was voluntary, and the informed consent form 

emphasized that the decision to participate was entirely up 

to the user. The decision did not affect access to a trial MPK, 

or any other service provided to them by the company or 

prosthetist. All users who trialed the MPK during the study 

period were approached consecutively to participate in the 

study. Twenty agreed to participate, of whom 16 completed 

the study. The number of users who requested a trial period 

and who were approached to participate is unfortunately not 

known. This omission and the small sample size reduced 

internal validity and generalizability of the findings. 

Data were collected using a functional level scale and the 

L-Test of Functional Mobility (L-Test). The functional level 

scale was developed though combining The Trinity 

Amputation and Prosthesis Experience Scales – Revised 

(TAPES-R),30 the Locomotor Capabilities Index-5 (LMCI-

5)31 and the Prosthetic Limb Users Survey of Mobility 

(PLUS-M).32 These scales assess slightly different 

functional aspects and through combining them a 

comprehensive picture of changes in functional ability could 

be obtained. All three of these scales are valid and 

reliable.30-32 However, the combination used in this study 

was not tested for reliability and validity. This is a limitation 

that can negatively affect the study’s reliability and external 

validity. Questions focused on indoor and outdoor mobility, 

as well as participation in community, sport, and work 

activities. Scoring was based on a five-point Likert scale, 

with total scores ranging from 20 to 80. Higher scores 

indicated better function.  

The L-Test is a simple and quick mobility test. It measures 

the time to get up from a chair (seat height 46 cm), walk 3 

meters, turn 90o, walk 7 meters, turn 180o, and walk back to 

the chair in seconds.33 The L-Test has shown high levels of 

inter- and intra-rater reliability (0.97 and 0.97 respectively) 

as well as concurrent validity.33 It also has a low ceiling 

effect in higher functioning prostheses users.33 Prosthetists 

measured the L-Test times with a smart phone stopwatch. 

In addition, data on demographic variables, amputation 

details, and the prosthetic components habitually used were 

collected and coded. Items that were scored as “not 

applicable” were removed from the pre- and post-test 

scores for that specific participant. Descriptive analysis was 

done after which the Wilcoxon Signed-Rank test was used 

to evaluate for significant differences in function and L-Test 

scores between matched pairs. 

Qualitative descriptive study  

During an iterative process, six prosthetic users who had 

completed the trial period were purposively sampled using 

a maximum variation strategy.34 Variables used to ensure 

maximum variation included gender, age, level of 

amputation, K-Level, differences in L-Test and functional 

level scores. Data were collected with a 30-minute audio 

recorded, telephonic, semi-structured interview. Interviews 

were guided by an interview schedule developed by the 

authors. Questions focused on the participants’ opinion of 

the Rheo XC and their thoughts on why their function and 

L-test scores were different or similar in the pre- and post-

test. Inductive thematic analysis was done.35  

The first author identified codes (meaningful parts, ideas, 

and key concepts in the data), through line-by-line coding, 

and provisional themes manually, as interviews were 

completed. Provisional themes and questions raised by the 

analysis informed further sampling, data collection and 

analysis. Data saturation was reached after the 6th 

interview. Codes and themes were finalized and verified by 

the second author. Trustworthiness is supported by 

purposive sampling, using an interview schedule, data 

saturation, a second person verifying themes and 

describing participants’ demographic details. An additional 

limitation of the study is the absence of independent coding 

and consensus-building between the two authors, which 

would have enhanced trustworthiness. 

Publication ethics 

The study was approved by Stellenbosch University’s 

Health Research Ethics Committee (N22/08/097). The risk 

for physical harm during the test period was very low since 

the participants had been walking with the prosthesis for at 

least four months and had a minimum ability to walk in the 

community on level surfaces as per inclusion criteria. 

RESULTS 

Quantitative  

Of the 20 participants who agreed to take part, 16 

completed the study, of whom 13 (81.25%) were men. Nine 

(56.25%) had transfemoral amputations and functioned at a 

K3 level (Table 1). For four participants with knee 

disarticulation, a low-profile foot was required to 

accommodate the length of the Rheo XC knee. The reasons 

for the foot changes in the other two cases were unclear. 

These changes negatively affect the internal validity of the 

study. 

https://doi.org/10.33137/cpoj.v8i1.45286


 

4 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

Table 1: Demographic and amputation related information of 

participants (n=16). 

 

  No. (%)  

Gender 
Men 13 (81.3)  

Women 3 (18.8) 
 

Cause of 
Amputation 

Vascular 3 (18.8) 

Trauma 11 (68.8) 

Cancer 1 (6.3) 

Congenital 1 (6.3) 
 

Level of 
Amputation 

Transfemoral 9 (56.3) 

Knee Disarticulation 6 (37.5) 

Bilateral (TF & TT) 1 (6.3) 
 

K-Level 

K2 2 (12.5) 

K3 9 (56.3) 

K4 5 (31.3) 
 Pre-Test No. (%) Post-Test 

Prosthetic 
Knees  

Paso Knee (Ossur) 4 (25.0) 

Rheo XC 

3R31 (Otto Bock) 1 (6.3) 

3R106 (Otto Bock) 2 (12.5) 

3R80 (Otto Bock) 3 (18.8) 

3R95 (Otto Bock) 1 (6.3) 

3R78 (Otto Bock) 1 (6.3) 

OHP5 (Ossur) 1 (6.3) 

Aspire H1 (Ossur) 1 (6.3) 

Balance Knee (Ossur) 1 (6.3) 

Total 2100 (Ossur) 1 (6.3) 
  

Prosthetic 
Feet  

Vari-Flex (Ossur) 5 (31.3) Unchanged 

Triton (Otto Bock) 1 (6.3) 
Changed to 
Pro-Flex LP 

Balance J (Ossur) 1 (6.3) 
Changed to 

Breeze 
(Steeper) 

Trias (Otto Bock) 2 (12.5) 
Changed to 
Pro-Flex LP 

Taleo (Otto Bock) 1 (6.3) Unchanged 

1D10 (Otto Bock) 1 (6.3) Unchanged 

SACH (Otto Bock) 1 (6.3) 
Changed to 
Pro-Flex ST 

DP Flexion (Ossur) 1 (6.3) 
Changed to 
Pro-Flex ST 

Pro-Flex ST (Ossur) 1 (6.3) Unchanged 

Triton Sideflex (Otto Bock) 1 (6.3) Unchanged 

Breeze (College Park) 1 (6.3) Unchanged 

 

 

Table 2: Descriptive summary of age, pre-test, post-test, L-Test 

and function scores. 

 Low High 
Mean 
(SD) 

Cohen’s 
d 

Z- 
value 

P-
value 

Age 26 74 
51.9 

(14.9) 
 

Pre-Test  
L-Test (s) 

17.5 71.0 
35.4 

(16.4) 
0.52 -3.52 0.00 

Post-Test 
L-Test (s) 

14.0 62.2 
27.9 

(12.3) 

Pre-Test 
Function* 

31 76 
52.7 

(12.2) 
1.22 -3.41 0.00 

Post-Test 
Function* 

49 78 
65.4 
(8.3) 

 

*Higher scores indicate better function. 

Their average age was 51.9 (SD = 14.9) ranging from 26 to 

74 (Table 2). Participants completed the L-Test on average 

7.5 s faster in the post-test than in the pre-test. The mean 

function score was 12.7 higher in the post-test than the pre-

test (Table 2). 

L-Test scores were consistently lower in the post-test 

indicating faster walking and turning speeds with the Rheo 

XC (Figure 1). This difference varied from 0.3 s to 20.9 s. 

The Wilcoxon signed-rank test of matched L-Test data 

showed a Z-value of -3.52 and p < 0.001. 

 

Figure 1: L-Test times before and after the intervention. 

 

Figure 2: Functional scores before and after the intervention.  

Figure 2 shows improved function with the Rheo XC. The 

Wilcoxon-Signed- Rank Test found a z value of -3.41 with  

p < 0.001. 

Higher scores indicate better function. All but one activity 

(running, which remained the same) scored higher in the 

post-test than the pre-test (Figure 3). The variables of work 

(18 points), walk 100 m (15 points), carry shopping, walking 

hills, walking in mud /dust (14 points), hiking, and walking 

on uneven outdoor surfaces (13 points) showed the biggest 

positive change. All participants indicated that it would be 

easy to charge the battery. 

Qualitative 

Among the six participants one was a woman, and one had 

an amputation due to vascular reasons. Their age ranged 

between 26 and 74. L-Test speed differences ranged from 

0.2 s to 19.3 s. The differences in functional scores ranged 

between 2 and 16 (Table 3). 

0

10

20

30

40

50

60

70

80

T
im

e
 I
n
 S

e
c
o
n
d
s

Participants

Pre test Post test

0

10

20

30

40

50

60

70

80

S
c
o
re

s

Pre test Post test

Participants 

https://doi.org/10.33137/cpoj.v8i1.45286


 

5 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

Participants were enthusiastic about the Rheo XC, as 

illustrated by Theme 1: Acceptance of the MPK. However, 

concerns were raised as well, indicating that MPK is not 

suitable for everybody, as explained in Theme 2: Real-world 

limitations of the MPK. 

Theme 1: Acceptance of the MPK 

Participants found the Rheo XC safe, easy to walk with, and 

responsive to their mobility needs. “It was immediately 

comfortable. I felt safe. The knee became my own, in other 

words, like my living knee. That was what it felt like. The 

quick responses…I liked it. It is an absolute pleasure to put 

it on. The control of the knee gives you many options. You 

can walk faster with confidence. The knee gives that to you, 

the confidence….I did not want to give it back!” P6  

Participant 1 felt that the Rheo XC joint allowed a more 

natural walking pattern which he thought led to an increase 

in walking speed. “It mimics natural walking…It is definitely 

a more natural walking pattern, which result in me being 

able to walk faster. Even turning on my left leg [prosthetic 

side] was very natural.” P1 

The quick response of the joint to changes in walking speed 

and/or direction aided a normal walking pattern. “I can move 

faster. I can turn easier. It is easier to pick up stuff, 

especially large items. On uneven ground, much safer, 

sturdy. You are so confident. You can walk like you want to. 

You do not have to worry about stepping on a pebble, or a 

clump of grass. You walk; this is just fantastic.” P4 

Even though Participant 2’s L-Test results showed only a 

0.2 second difference (between pre- and post-test data), he 

was more satisfied with the new joint due to its agility, lower 

energy consumption, and better support of the residual limb. 

“After walking on the microprocessor knee for two weeks it 

was difficult to go back to the hydraulic knee. I will not call it 

a shock, but I quickly realized how much I used the functions 

of the microprocessor knee. My brain adapted quickly to 

 

Figure 3: Comparison of individual functional scores. 

Activities with no applicable scores included run (1), hobbies (1), walk in bad weather (2), sport (2), work (2), and walk in mud/sand (3). 

Numbers in parentheses indicate the number of participants who marked the activity as “not applicable.” 

0

10

20

30

40

50

60

70

80

Pre test Post test

Table 3: Demographic and prosthetic characteristics of participants in the qualitative phase. 

Subject Gender 
Cause of 

Amputation 
Age 

K 
level 

Amputation 
Level 

Foot (Pre-
test & Post-

test) 
Pre-test knee 

L-Test speed 
difference (m/s) 

Function 
difference 

P1 Male Trauma 35 K3 KD 
Triton & Pro-

Flex LP 
3R31 

(Otto Bock) 
6.4 7 

P2 Male Congenital 31 K3 KD 
Triton 

Sideflex  
3R80  

(Otto Bock) 
0.2 2 

P3 Male Trauma 26 K4 Bilateral Vari-Flex  
Paso knee 

(Ossur) 
10.5 10 

P4 Male Trauma 65 K4 KD 
Trias & Pro-

Flex LP 
3R80  

(Otto Bock) 
3.4 16 

P5 Female Trauma 74 K4 KD 
Balance J & 

Breeze)  
3R106  

(Otto Bock) 
15.7 11 

P6 Male Vascular 
68 

 
K2 TF Pro-Flex ST  

Aspire H1 
(Ossur) 

19.3 6 

 

S
c
o
re

s
 

https://doi.org/10.33137/cpoj.v8i1.45286


 

6 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

everything the microprocessor offered me in comparison 

with my other knee…The swing through of the knee was just 

easier. Overall, I required less energy to walk with the knee. 

The knee helped a lot to decrease the effect and strain on 

my stump. I felt less tired at the end of the day.” P2 

Participants extolled how safe they felt using the Rheo XC 

joint. “It is very safe. You feel safe on it. It will not give way 

under you. You have confidence. You do not have to be 

careful to prevent a fall. That [the guardedness against 

falling] is gone. It gives you confidence to walk and you can 

walk faster. It is the best leg I ever had… You have more 

control, balance and confidence. For sure. When you stand 

you stand solidly.” P4 

These advantages translated into improved functionality. “I 

like fishing, I am next to the water, big clumps of grass, 

uneven ground. I do not want to place the other knees in a 

bad light, but if you put your weight wrongly on the foot it 

gives in. Not this one. If there is weight on it, it is solid. That 

is a huge benefit.” P4 

Participant 6 felt a waterproof knee will enhance his 

functionally further. “I would have liked it to be waterproof. 

And that I can walk in the sand, in the swimming pool. In the 

sea… with my grandchildren in the shallow water.” P6 

Theme 2: Real-world limitations of the MPK 

The weight of the Rheo XC in relation to user strength must 

be considered during prescription. “The weight, it was 

extremely heavy. After the first 2 days I thought my left hip 

was dislocated.” P5 

“Obviously, the weight of the knee one can feel it 

immediately. Even though there is less strain on your 

[remaining] knee you can tell you are walking with a 

prosthesis or a knee that is much heavier.” P2 

The size of the Rheo XC adds to the overall length of the 

prosthesis, which can be problematic for shorter people or 

those with long residual limbs. “I am short, so the knee with 

its fixed length and the foot that was at its lowest was still 

longer than my real right leg.” P5 

Participants felt the battery life was short. “I walked through 

the shops through the day then it starts peeping at me. I 

cannot understand why it is peeping. Then I see the battery 

is going flat.” P4 

Another challenge that was raised was that the knee can 

hamper driving a vehicle as it might interfere with the 

pedals. “You struggle in a car because it just wants to go 

forward. Then it is in the way of the pedal, the 

accelerator…you just lift your foot slightly and ‘zoep’ [local 

slang for something happening without warning] it wants to 

straighten.” P4 

Thus, for a successful prescription, knee characteristics 

must match user abilities. To ensure challenges are 

identified and the MPK is prescribed appropriately, a trial 

period is recommended. “The fact that there is a trial period 

is very good. Walk with the knee. See what it does for you. 

Is it sufficient for your needs? And if you feel it works for 

you, you have compared it with other knees and feel it ticks 

more boxes for you in your daily activities I will recommend 

it rather than a hydraulic or polycentric knee.” P2 

DISCUSSION 

This mixed methods study explored and described South 

African users’ function and experience with the Rheo XC 

knee. Both user function and L-Test scores showed 

improvement from pre-test to post-test. The positive impact 

of the knee joint was further supported by qualitative data.  

L-Test scores exceeded both the normative values and the 

minimum detectable change (MDC95), which is the smallest 

improvement needed to be 95% confident that the change 

is clinically meaningful. The L-Test norm is 41.7 s ± 16.8.33 

The pre-test score was 6.3 s below this norm and the post-

test score was 13.8 s below the norm. This might be due to 

the normative data being from 2005. The advancement of 

prosthetic components over the last 20 years should impact 

walking speed positively. The L-Test MDC95 for persons 

with transfemoral amputations are 2.9 s.36 Current data 

showed that 11 (68.75%) participants’ scores decreased 

with more than 2.9 s, with an average decrease of 7.51s 

across the group. From this it can be concluded that the 

change in scores is clinically meaningful and infers a 

change in ability rather than measurement error.37  

The reduction in L-Test time in the current study was similar 

to what was documented in previous similar studies. Davie-

Smith and Carse (2021)38 found that L-Test scores 

decreased on average with 5.15 s after 6 months. 

Participants in the study by Davie-Smith and Carse (38) 

used a variety of MPKs, with the most common being the 

Kenevo and various versions of the C-Leg. Howard et al 

(2018)29 found a mean decrease of 7.4 s among three 

participants after switching from a NMPK to the Rheo Knee 

3. They indicated that the L-Test score for the other four 

participants was inconclusive without providing a mean for 

L-Test score change across the group.  

Functional level scores also improved significantly. 

Previous research on the Ottobock C-Leg® and the 3E80, 

which features a microprocessor-controlled stance-swing 

phase switch, has similarly shown improvements in 

functional performance39 and walking speeds.40  

The clinical value of the magnetorheological MPK was 

further supported by qualitative data, with participants 

reporting a positive experience using the device. In their 

opinion decreased energy use, a more fluid walking pattern, 

https://doi.org/10.33137/cpoj.v8i1.45286


 

7 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

as well as improved agility, and safety translated to higher 

walking speeds. Decreased energy consumption,5 

increased agility5 and safety3,4,41 has been identified as 

advantages of MPKs in previous research. For some 

participants, the Rheo XC came close to replicating the 

function of their natural knee—an outcome that previous 

studies have shown users desire from their prostheses.1,2 

The results showed that participants experienced important 

clinical benefits compared to their non-MPK knee. 

Higher-level functions such as working, walking 100 meters, 

carrying shopping, and walking on uneven surfaces and 

hills showed the greatest improvement. This might be due 

to the safety features of the Rheo XC, which allows 

movement, weight shift, turning, and change of direction 

without fear of falling as described by participants during the 

interview and shown in previous studies.4,7 At the same time 

activities requiring speed and high levels of agility such as 

running and participating in sport remained a challenge for 

many.  

Although concerns have been raised that African conditions 

might be too harsh for an MPK, the current short-term 

findings did not support this. However, longer-term studies 

are needed to confirm its durability and performance. Most 

participants indicated the ability to function on uneven 

surfaces and in mud and dust. Qualitative findings provide 

examples of walking effectively in pastoral areas and 

pursuing outdoor activities. All participants had access to 

electricity to charge the battery. Although a longer battery 

life would be beneficial.  

With these functional gains and previous research showing 

the long-term economic benefits of MPKs,6,7 it is important 

that the South African government and other funders of 

prosthetic components in South Africa consider MPKs 

alongside other prosthetic knees. The initial monetary 

outlay might be compensated for by savings in the long run 

and better user function. Savings occur because MPKs 

have a longer life cycle than mechanical knees as reported 

by Kuhlman et al,7  come with a warrantee (two years in the 

case of the Rheo XC knee), of which the cost is included in 

the initial price of the MPK,7 that guarantee free of charge 

maintenance, and reduces falls and thus costs incurred 

because on injury.6,7 The economic benefits of better 

function and a wider range employment options have not 

been researched.  

While quantitative findings indicate that Rheo XC knee joint 

improved function for all the participants, qualitative data 

showed that it was not the most optimal solution for all. The 

size of the joint makes it unsuitable for a shorter person with 

a through knee amputation or with a long transfemoral 

residuum. The weight was also concerning to some as also 

shown previously.38 Lighter MPKs or NMPKs might be more 

suitable for frail users or users with weak residual leg 

muscles. These findings support the notion that prosthetic 

knee prescription should be based on user characteristics 

and functional needs. Ideally users should be offered trial 

periods with different components before a knee is 

prescribed.  

The study results must be interpreted against the limitations 

discussed in the methods section and summarized here. 

The pre-test, post-test design suffers from a lack of a control 

group. The reasons for choosing this design, along with 

potential challenges, are outlined in the Methods 

section.28,29 These challenges were further mitigated by 

triangulating the pre- and post-test results with qualitative 

findings.25 The small number of participants, lack of 

information on users whose trial requests were rejected, 

and the need to change the foot in some instances to a low 

profile foot reduce the generalizability and internal validity of 

the results. The combined data collection tools were not 

tested for reliability and validity. Additionally, interrater bias 

may have occurred during the L-Test, as different 

prosthetists timed different users. While the second author 

verified the codes and themes, independent coding and 

consensus-building were not conducted during the 

qualitative data analysis.    

CONCLUSION 

This study provides context specific evidence that may 

support funding of the magnetorheological MPK in South 

Africa. However, it is not suitable for everyone, and a trial 

period to assess appropriateness is advised before 

prescription. This evidence may benefit South African 

users, providers, and funders by assisting in the selection 

and prescription of appropriate knee components. 

Research is recommended to determine whether the 

improved functioning supported by MPKs translates into 

enhanced employment opportunities and income 

generation. 

ACKNOWLEDGEMENTS 

Thank you to the participating prosthetists and users without whom 

this study would not have been possible.   

DECLARATION OF CONFLICTING INTERESTS 

The study was funded by the Ossur company. The primary author 

is not employed by the company, but she was re-imbursed for her 

work on this study. The second author is employed by the company. 

This conflict of interest might have an influence on the interpretation 

of findings. The data are available upon request for independent 

analysis.  
 

AUTHORS CONTRIBUTION 

• Surona Visagie: Assisted with study conceptualization and 

qualitative data collection, analyzed both qualitative and 

quantitative data, and drafted and finalized the article.  
 

• Benje Theron: Assisted with study conceptualization, 

managed quantitative data collection, contributed to qualitative 

https://doi.org/10.33137/cpoj.v8i1.45286


 

8 

Visagie S, Theron B. South African users’ function and experience with a magnetorheological microprocessor knee: A mixed methods study. Canadian Prosthetics 
& Orthotics Journal. 2025; Volume 8, Issue 1, No. 5. Https://doi.org/10.33137/cpoj.v8i1.45286  

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X MAGNETORHEOLOGICAL KNEE USE IN SOUTH AFRICA: FUNCTION AND EXPERIENCE 

Visagie S and Theron B, 2025 

data collection, verified themes, and provided input on the 

article. 

 

SOURCES OF SUPPORT 

The study was funded by the Ossur company.  

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