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VOLUME 5, ISSUE 2 

 2022 

 

RESEARCH ARTICLE 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, 

Issue 2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

https://online-publication.com/wp/
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https://doi.org/10.33137/cpoj.v5i2.38802


 

1 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

 

 

RESEARCH ARTICLE 

 

A NOVEL QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 

Li W1, Baddour N1, Lemaire E.D 2,3* 
 
1 Department of Mechanical Engineering, University of Ottawa, Ottawa, Canada. 
2 Department of Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Canada. 
3 Centre for Rehabilitation Research and Development, Ottawa Hospital Research Institute, Ottawa, Canada. 

  
 

 

 

 

  

 

 

 

 

 

 

 

 
 

 

 

 

INTRODUCTION   

An ankle foot orthosis (AFO) improves mobility by 

diminishing foot drop during swing phase and providing gait 

control during stance.1 A recent advancement in AFO 

design used a posterior strut to store and return energy 

during movement. An appropriate posterior strut can be 

selected to accommodate the user’s need for AFO stiffness  

 

 

 

 

 

based on their weight and activity level.2,3 However, further 

functional improvements could be achieved if the person 

could have different AFO stiffness depending on their 

chosen activity. For example, less stiffness for driving a car, 

medium stiffness for walking, high stiffness for high-active 

movements (running, downhill walking etc.). 

The Intrepid Dynamic Exoskeletal Orthosis (IDEO) is an 

energy storing device that supports and protects users 

following lower extremity limb salvage procedures.4 This 

AFO was crafted with three carbon fiber components: 

ground reaction cuff for circumferential support providing 

 
OPEN  ACCESS 

ABSTRACT 

BACKGROUND: A posterior dynamic element ankle-foot orthosis (PDEAFO) uses a stiff carbon fibre 

strut to store and release energy during various mobility tasks, with the strut securely attached to the 

foot and shank-cuff sections. A design that allows the user to swap struts for specific activities could 

improve mobility by varying PDEAFO stiffness, but current approaches where bolts securely connect 

the strut to the orthosis make quick strut swapping time-consuming and impractical.  

OBJECTIVES: Design a novel quick release AFO (QRAFO) that can enable daily living strut-swapping 

and thereby enable better ankle biomechanics for the person’s chosen activity. 

METHODOLOGY: The novel QRAFO enables device stiffness changes through a quick release 

mechanism that includes a quick-release key, weight-bearing pin, receptacle anchor, and immobi-

lization pin. A prototype was modelled and simulated with SolidWorks. Mechanical tests were performed 

with an Instron 4482 machine to evaluate quick release mechanism strength with running and 20° slope 

downhill walking loads. Quick release efficiency was then evaluated via two quick release functional 

tests, with four participants wearing a 3D printed QRAFO. 

FINDINGS: Simulated stress on the weight bearing pin, anchor, and surrounding carbon fibre structure 

under running and downhill walking loads did not exceed the yielding stress. Mechanical tests verified 

the simulation results. Four participants successfully swapped the strut within 25.01 ± 3.66 seconds, 

outperforming the 60.48 ± 10.88 seconds result for the hand-tightened bolted strut. A learning 

evaluation with one participant showed that, after approximately 30 swapping iterations, swap time was 

consistently below 10 seconds. 

CONCLUSION: The quick release mechanism accommodated running and slope walking loads, and 

allowed easy and fast strut removal and attachment, greatly reducing strut swap time compared to 

screw-anchor connections. Overall, the novel quick release AFO improved strut-swapping time without 

sacrificing device strength, thereby enabling people to use the most appropriate AFO stiffness for their 

current activity and hence improve mobility and quality of life. 

ARTICLE INFO 

Received: June 15, 2022 

Accepted: December 4, 2022     

Published: December 18, 2022 

CITATION 

Li W, Baddour N, Lemaire E.D. A 

novel quick release mechanism for 

ankle foot orthosis struts. Canadian 

Prosthetics & Orthotics Journal. 

2022; Volume 5, Issue 2, No.3. 

https://doi.org/10.33137/cpoj.v5i2.3

8802 

KEYWORDS 

Ankle Foot Orthosis, Dynamic Gait 

Rehabilitation, Multi-Stiffness Ankle 

Foot Orthosis, Quick Release, 

Orthosis. 

 

* CORRESPONDING AUTHOR: 

Edward D. Lemaire, PhD 
Centre for Rehabilitation Research and Development, Ottawa Hospital 
Research Institute, Ottawa, Canada. 

Email: elemaire@ohri.ca 

ORCID ID: https://orcid.org/0000-0003-4693-2623 

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

Volume 5, Issue 2, Article No.3. 2022 

 

 

https://doi.org/10.33137/cpoj.v5i2.38802
https://doi.org/10.33137/cpoj.v5i2.38802
https://doi.org/10.33137/cpoj.v5i2.38802
mailto:elemaire@ohri.ca
https://orcid.org/0000-0003-4693-2623
https://jps.library.utoronto.ca/index.php/cpoj/index


 

2 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 
Li et al., 2022 

off-loading to alleviate ankle pain, posterior strut that 

deforms for energy storage and return, and footplate. The 

IDEO modular design allows strut changes as motion ability 

changes and can be easier to don and doff.4,5 The Posterior 

Dynamic Element AFO (PDEAFO), developed by Fabtech 

Systems (Everett, WA, USA), is a commercial AFO 

fabricated entirely from carbon fiber. Similar to IDEO, the 

PDE AFO consists of a stiff strut that stores energy during 

weight loading and stance, and returns the energy during 

late stance. The strut attaches to the AFO shank and sole 

through bolts, secured with Locktite. An anchor system is 

integrated by laminating a pre-threaded metal plate within 

the carbon fibre matrix, thereby facilitating strut adjustment 

while customizing. The strut stiffness and dimensions can 

be selected to match the user’s activity level.  

A modularized posterior strut AFO design provides possib-

ilities for strut swapping, thereby swapping AFO stiffness. 

However, bolt connections between the strut and AFO 

prevent effective strut changing during the day (i.e., requires 

tools, more time, etc.). A quick release connection between 

the strut and AFO could be an alternative that enables fast 

strut-swapping to change stiffness for different activities. 

The purpose of this research was to develop a novel quick 

release AFO (QRAFO) that provides safe and secure 

energy storage and return, but also allows the QRAFO user 

to swap struts within 30 seconds, to provide appropriate 

stiffness for their current activity. Upon successful 

simulation, mechanical, and functional tests, the QRAFO 

could be used in daily living to enhance mobility and thereby 

improve quality of life.  

Quick release mechanism design 

The new quick release mechanism6 (Figure 1) consists of 

five components: quick release key, weight bearing pin, 

receptacle, anchor, and immobilization pin. The quick 

release key is affixed on the strut and the anchor is affixed 

on the receptacle. A panel between the anchor and quick 

release key fits the gap between the strut and orthosis when 

installing thinner struts. The anchor is moulded into the 

AFO. Pushing and twisting the quick release key allows the 

user to pull the strut out of the anchor. A titanium alloy 

weight bearing pin (Ti-pin) bore most of user’s weight during 

movement. To prevent strut rotation along the weight 

bearing pin, an immobilization pin (IM pin) was included 

between the quick release key and weight bearing pin.  

The weight bearing pin was designed to bear all transverse 

forces on the quick release mechanism (QRM) during 

movement. Titanium alloy Ti-6Al-4V was selected due to its 

high yield and ultimate strength. To construct a lightweight 

device, aluminium 6061 was selected for the anchor. Quick 

release key and receptacle were also made of aluminium 

6061 due to its light weight and appropriate strength. The 

total QRM weight was 30 g. 

 

 

Figure 1: Quick release AFO with quick release mechanism 

 

METHODOLOGY 

Three analyses were performed to assess QRAFO strength 

and functionality. FEA simulation was performed on the 

QRM, including yielding analysis and safety factor analysis 

under walking load (fatigue load), running load (intense 

load), and downhill walking load (bending load). Mechanical 

testing was performed on the QRM to analyse the stress-

displacement curve and material deformation. QRM 

functional testing compared QRM strut swap efficiency to 

the PDEAFO screw-anchor mechanism. 

Strength analysis 

Finite Element Analysis 

A QRAFO for daily use must not fail during occasional 

intense activities and long periods of walking. SolidWorks 

2019 (Dassault Systèmes, Vélizy-Villacoublay, France) was 

used to perform finite elements analysis (FEA) to simulate 

the load exerted on the quick release mechanism under 

three scenarios: level walking, running, and downhill 

walking (Figure 2). The designed device capacity was based 

on a 120 kg user. 

    

Shank 

Sole 

Strut 

Anchor 

IM pin 

Receptacle 

Ti-pin 

Panel 

Quick-release 
key 

https://doi.org/10.33137/cpoj.v5i2.38802


 

3 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 
Li et al., 2022 

 

 

Figure 2: Load and fixture conditions on meshed QRM with two 

loading types: shearing caused by either walking or running (Left); 

bending caused by landing on uneven ground, representing 

downhill walking load (Right). 

Only shear loads were considered for daily walking and 

running loads, while bending was included in downhill 

walking. The 95th percentile Canadian male weighs 113.5 

kg.7 Considering that users may carry personal belongings, 

a QRAFO should withstand daily use by a 1200 N person. 

Peak ground reaction forces for testing were bodyweight for 

walking,8 3 times bodyweight for running,9 and 1.2 times 

bodyweight for downhill walking.8 Considering the AFO cuff 

off-weighting function (i.e., supporting body weight for some 

AFO applications), the vertical force applied on the QRM 

was 80% of the peak ground reaction forces.10 The QRM 

was modelled with virtual jigs (strut to apply load, fixed quick 

release male components, and shell to fix quick release 

female components, Figure 2). Shearing and bending loads 

were applied to the top of the strut (250 mm long). The shell 

was globally fixed. 

Since AFO devices are suggested to last three years11 with 

10,000 walking steps per day as a common goal for 

adults,12 the QRM should last 107 regular walking cycles. 

Mechanical Tests 

Mechanical tests were performed with running and downhill 

walking loads using an electromechanical testing machine 

(4482, InstronR, Norwood, MA) with a 10 kN static load cell 

(10 N resolution, ISO-376, InstonR, Norwood, MA). 2880 N 

maximum force was applied at a constant speed of 1 

mm/min for the running load and 1080 N maximum vertical 

force at the same speed for a 20-degree downhill walking 

load. A special triangular fixture with a surface angle of 20 

degrees was machined to apply a moment to the quick 

release mechanism (Figure 3). The load cell initial position 

was manually set to approximately one millimetre from the 

iron shell. A smartphone was fixed on a tripod to video 

record the trials. When the force sensed by the load cell 

reached the maximum load or the displacement reached   

10 mm, the load cell terminated action and returned to the 

origin position. Ten trials were collected and analysed for 

each test. 

The Instron machine recorded data at 10 Hz. After testing, 

the force-displacement relation was explored by analysing 

the slope of the curve. Quick release component 

dimensions were measured by a caliper (Accusize Industrial 

Tools, AB11-1106) before and after testing to determine if 

surface damage occurred between the Ti-pin and aluminum 

anchor. 

 

Figure 3: Anchor fixed to vertical loading strut (i.e., represents 

shank connection) (A); quick release key and weight bearing pin 

fixed to clamp (i.e., represents foot-ankle unit connection) (B); 

Testing setup for running load (C); downhill walking load with 

angled loading plate (D). 

Functional Analysis 

Two AFOs were 3D printed for the functional analysis. The 

two AFOs had identical components but different 

connection mechanisms: one with the quick release 

mechanism and another with a PDEAFO screw-anchor 

mechanism. While screws are typically secured using 

D C 

A B 

Loading  

plate 

Loading  

plate 

https://doi.org/10.33137/cpoj.v5i2.38802


 

4 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 
Li et al., 2022 

Locktite to ensure that the strut does not loosen, the screws 

were hand tightened for this test to enable comparison. 

Four able bodied participants were recruited (3 males, 1 

female). Ethical approval was received from the University 

of Ottawa Research Ethics Board (File number H-10-19-

4767). All participants provided informed consent. 

While sitting on a chair, participants donned the AFO with 

quick release mechanism. After self-finding a comfortable 

position, the participant removed the strut, waited 2 to 4 

seconds, and then reattached the strut. This swap trial was 

performed 10 times. Then, the participant donned the AFO 

with the screw anchor mechanism and repeated the swap 

trial 10 times. All swap trials were recorded with a GoPro 

camera (San Mateo, California, USA) affixed on a tripod. All 

participants were asked to adjust their posture and position 

to provide a clear side view to the camera. 

To investigate the learning process for strut swapping, one 

participant performed the strut swap trial 50 times for each 

device. The time to complete each strut removal and each 

strut attaching were extracted from the digital video using 

MATLAB R2019b (MathWorks, Natick, Massachusetts, 

USA). Strut removal started when the hand touched any 

strut component and ended when all strut components were 

not contacting the AFO. Strut removal with the screw-

anchor connection started when the screwdriver touched 

any strut component and ended when all strut components 

were not contacting the AFO. Strut attaching with the QRM 

started when any strut component touched the AFO and 

ended when hand not contacting the AFO. Strut attaching 

with the screw-anchor connection started when any strut 

component touched the AFO and ended when the 

screwdriver was not touching any strut components. 

RESULTS 

FEA simulation 

The Modified Goodman equation was used to calculate the 

safety factor of fatigue given by: 

𝜎𝑎
𝑆𝑒
+
𝜎𝑚
𝑆𝑢𝑡

=
1

𝑛
 (1) 

where 𝜎𝑎 is the amplitude component of stress, 𝜎𝑚 is the 

midrange stress component, Se is the fatigue strength, and 

Sut is the ultimate strength and n is the safety factor. The 

fatigue strength of aluminium is 117 MPa and grade 5 

titanium is 280 MPa.10 Figure 4 shows the stress 

distributions over QRM components with the three loads. 

 

By assuming the amplitude and midrange stress are equal 

(i.e., half the maximum stress) the safety factor to fatigue 

under walking load was 5.09 for the weight bearing pin and 

1.37 for the anchor. Compared with the Ti-pin (880 MPa) 

and anchor (270 MPa) yielding strengths, yielding safety 

factors were 5.5 for the Ti-pin and 1.07 for the anchor with 

running load. Downhill walking load produced more stress 

on the components, with yielding safety factors of 1.17 for 

Ti-pin and 1.02 for anchor. The bending force also 

generated a pulling force on the quick release key and 

receptacle, with safety factors of 10.38 for the quick release 

key and 6.14 for the receptacle. 

 

(a) (e) 

(b)  (f) 

(c) (g) 

(d) (h) 
 

Figure 4: Simulation results for QRM components: stress 

distributions of weight bearing pin with (a) walking load; (b) running 

load; (c) downhill walking; (d) stress distribution of quick release 

key with downhill walking load; (e) stress distributions of anchor 

with walking load; (f) running load; (g) downhill walking; and (h) 

stress distribution of receptacle with downhill walking load. 

 

https://doi.org/10.33137/cpoj.v5i2.38802


 

5 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 
Li et al., 2022 

Mechanical testing results 

From the mechanical tests, force-displacement analysis 

indicated no yielding with running and downhill walking 

loads, demonstrated by the curve increasing monotonically 

(Figure 5). The QRM materials were in their elastic region 

when the maximum loads were applied. 

 

 

  

 

 

Figure 5: Force-displacement curves from running load test (Top) 

and downhill walking load test (Bottom). 

 

Pearson correlation coefficients between force-displace-

ment curves were larger than 0.99. Therefore, both running 

and downhill walking load tests were repeatable. 

Table 1 shows the mean and standard deviation of the 

measured dimensions before and after testing. The mean 

Ti-pin diameter (6.29 mm), Ti-pin length (21.10 mm), and 

anchor hole diameter (6.38 mm) were within 0.02 mm of 

their original dimensions. Standard deviations were smaller 

than 0.02 mm, so measurements along one surface were 

consistent. Therefore, surfaces were not damaged due to 

running and downhill walking loads. 

 

Table 1: Means and standard deviations (mm) of the original Ti-pin 

diameter, length, and anchor hole diameter dimensions. 

Dimensions are before testing, after running load, and after 

downhill walking load tests. 

 
Before 
Testing 

Running 
Load 

Downhill 
Load 

Ti-pin diameter (mm) 
6.29 

(0.01) 
6.29 

(0.02) 
6.28 

(0.01) 

Ti-pin length (mm) 
21.10 
(0.01) 

21.11 
(0.01) 

21.09 
(0.01) 

Anchor hole diameter (mm) 
6.37 

(0.01) 
6.38 

(0.01) 
6.38 

(0.01) 

 

Quick release efficiency test 

The average swap time across the four participants with 

QRM was 25.01 ± 3.66 seconds. All participants swapped 

the strut within 30 seconds, on average (Figure 6). The best 

swap time was 13.83 ± 3.08 seconds and the worst swap 

time was 53.82 ± 18.90 seconds, among all participants. As 

a comparison, the average screw anchor mechanism swap 

time was 60.48 ± 10.88 seconds, 142% longer than QRM 

swap time. The best swap time was 38.71 ± 3.43 seconds, 

180% longer than swap with QRM and the worst swap time 

was 98.23 ± 22.19 seconds, 83% longer than swapping with 

QRM. All participants failed to swap screw anchor 

mechanism struts within 30 seconds (Figure 6). 

 

Figure 6: Range and mean of total swap time for QRM and screw 

anchor connection. 

Strut swap learning 

For the participant who completed the 50 trial test, the 

average swap time with the QRM was 13.85 ± 6.52 seconds 

F
o
rc

e
 m

e
a
s
u
re

d
 f
ro

m
 l
o
a
d
 c

e
ll 

(N
) 

Mean 

Standard Deviation 

Mean 

Standard Deviation 

Displacement after touching point (mm) 

Displacement after touching point (mm) 

F
o
rc

e
 m

e
a
s
u
re

d
 f
ro

m
 l
o
a
d
 c

e
ll 

(N
) 

Range and mean of total swap time of QRM 

 

Range and mean of total swap time of screw anchor mechanism 

Participants 

Participants 

T
o
ta

l 
S

w
a
p
 T

im
e
 (

s
) 

T
o
ta

l 
S

w
a
p
 T

im
e
 (

s
) 

 

 
Maximum swap time 

Average swap time 

Minimum swap time 

Maximum swap time 

Average swap time 

Minimum swap time 

 
30 second  

criterion 

 

  30 second  

criterion 

https://doi.org/10.33137/cpoj.v5i2.38802


 

6 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 
Li et al., 2022 

and with the screw-anchor was 58.41 ± 11.16 seconds. As 

the participant learned how to best swap the strut, swap 

time improved from a maximum of 35.95 seconds to 6.81 

seconds. Figure 7 shows the learning effect since strut 

swapping time decreased over the first 30 trials. The first 

ten strut swaps averaged 23.97 seconds and the last ten 

swaps averaged 8.92 seconds. Standard deviation also 

improved, with a standard deviation of the first ten trials of 

5.22 seconds and the last ten trials of 1.43 seconds. 

 

Figure 7: Time to swap strut with QRM and screw-anchor 

mechanism; including, strut removal time, strut attaching time, and 

total strut swap time. 

Less time was needed to remove the strut than attach the 

strut. The average time to remove the strut, over the first ten 

trials, was 4.27 ± 0.68 seconds and over the last ten trials 

was 2.68 ± 0.82 seconds (37.2% decrease). QRM swapping 

time was much less than the 30-second design criteria. 

In comparison, the screw-anchor mechanism averaged 

58.41 ± 11.16 seconds to swap. A milder learning effect was 

seen on screw anchor mechanism swapping (Figure 7). The 

average time to swap the strut for the first ten trials was 

73.39 ± 7.98 seconds, including a mean attaching time of 

50.37 ± 4.71 seconds and a mean removing time of 23.01 ± 

6.23 seconds. The average time to swap the strut for the 

last ten trials was 47.85 seconds, with a mean attaching 

time of 33.07 seconds and a mean removing time of 14.78 

seconds. The time decrease in total swap time between the 

first ten trials and last ten trials was 34.8%, including a 

34.3% decrease in attaching and 35.8% decrease in 

removing. Standard deviations were also larger than the 

QRM results. The standard deviation of the first ten trials 

was 7.98 seconds, and the last ten trials was 3.74 seconds. 

More time was required to swap struts when using an AFO 

with the screw-anchor mechanism, and the 30-second 

swapping criterion was not achieved. 

DISCUSSION 

A new quick release mechanism was successfully designed 

and prototyped to enable a person using a posterior-strut 

style AFO to quickly swap the strut, enabling different strut 

stiffnesses that would better relate to the person’s chosen 

activity. Swap time was below the 30 second target, and 

with practice can be consistently below 10 seconds. Since 

the QRM strut can be swapped without tools, this 

mechanism has a greater potential to be used in daily living 

than approaches requiring screw drivers or other tools. 

Mechanical testing revealed that the QRM could bear 

running and downhill walking loads for a 120 kg person with 

no failure from material or connections. Force-displacement 

curve analysis revealed that QRM materials remained in 

their elastic region under the maximum target loads. The ten 

trials showed high repeatability, indicating that the 

connection was not failing (slipping, dislocating, etc.) under 

running and downhill walking loads. Titanium did not harm 

the aluminum anchor’s surface, inferred from low dimension 

variation between trials.  

All QRM component safety factors under walking loading, 

running load, and downhill walking load were greater than 

one. The lowest safety factor was for walking on a 20-

degree descending hill; however, the mechanical test force-

displacement results gave confidence in the design since no 

plastic deformation occurred under maximum running or 

downhill walking loads. As well, the Ti-pin did not damage 

the aluminum anchor surface under large loads since the 

weight bearing pin and anchor dimensions did not change 

after each test. Pearson correlation coefficients between 

trials were close to 1, reflecting high similarity between trials 

from the same test. While the evidence proved that the 

QRM can withstand a range of daily activity loads, safety 

factors close to the yielding margin for highly active users 

such as athletes would require further testing to verify the 

QRAFO loading parameters under higher loading 

conditions.  

QRM functional tests revealed that participants can quickly 

swap struts while sitting. The time was substantially lower 

than the screw-anchor mechanism swap time. During 

testing, participants spent more time at the beginning and 

tended to swap faster after they became accustomed to the 

swap method and posture. After learning, a user can swap 

struts in under 10 seconds and with less variability, which 

outperformed our design criteria. The actual swap time 

could be much less than we observed in experiments since 

AFO users would have many more swap instances over the 

years of AFO use. 

Time to swap strut with QRM 

 

Time to swap strut with screw anchor mechanism 

Trial 

Trial 

T
im

e
 (

s
) 

T
im

e
 (

s
) 

Remove the strut 

Attach the strut 

Total swap time 

 

Remove the strut 

Attach the strut 

Total swap time 

https://doi.org/10.33137/cpoj.v5i2.38802


 

7 

Li W, Baddour N, Lemaire E.D. A novel quick release mechanism for ankle foot orthosis struts. Canadian Prosthetics & Orthotics Journal. 2022; Volume 5, Issue 
2, No.3. https://doi.org/10.33137/cpoj.v5i2.38802 

CANADIAN PROSTHETICS & ORTHOTICS JOURNAL 

ISSN: 2561-987X QUICK RELEASE MECHANISM FOR ANKLE FOOT ORTHOSIS STRUTS 
Li et al., 2022 

Various limitations should be considered for this study. 

Under extreme cold weather, the high thermal conductivity 

of aluminum alloy can result in the metal components being 

cold to the touch when swapping struts. Due to the high 

tolerance of the Ti-pin and anchor, if small particles such as 

sand stay inside the anchor more push and pull force could 

be required while swapping struts and may damage the 

anchor hole inner surface with prolonged wear. This issue 

can also occur for muddy roads since mud could stay in the 

anchor hole, thereby leading to difficulty while swapping 

struts. These conditions could be mitigated with a proper 

device cleaning regiment. Though functional tests 

successfully verified QRM function on a 3D printed AFO, 

QRM performance with a complete carbon fibre posterior 

strut AFO was not evaluated. Further testing with a larger 

sample size is required to confirm QRM performance in 

daily living environments. 

CONCLUSION 

In this research, the quick release strut swapping system of 

a novel QRAFO was designed and evaluated. The quick-

release mechanism allows individuals with dorsiflexor/ 

plantarflexor weakness to tune their AFO to their daily 

activities, such as driving, walking, downhill walking, and 

running. This design was low profile allowing the orthosis to 

fit beneath regular clothing. The weight added to the strut is 

minimal, which motivates users to carry extra struts with 

different stiffness levels for use during the day, or have 

various stiffness struts in their car, sport bag, or at work. 

Simulation and mechanical tests demonstrated that the 

components should withstand running and downhill walking 

loads. Functional testing showed that people could swap 

struts quickly, thereby encouraging use in daily living. 

Future research should evaluate QRAFO use with current 

posterior strut AFO users. 

ACKNOWLEDGEMENTS 

This project was funded by Natural Sciences and Engineering 

Research Council of Canada (NSERC). The QRAFO was 

developed in consultation with the staff of the Ottawa Hospital 

Rehabilitation Centre, with special acknowledgement to Patrick 

Lebel and Paul Nichols. 

DECLARATION OF CONFLICTING INTERESTS 

The authors report no conflicts of interest to disclose. 

AUTHORS CONTRIBUTION 

Wentao Li: Conceptualization, design, methodology, analysis, 

investigation, writing original draft, data interpretation, ethic 

certification application. 

Natalie Baddour: Conceptualization, supervision, methodology, 

reviewing/revising manuscript, final manuscript approval. 

Edward D. Lemaire: Conceptualization, supervision, 

methodology, reviewing/revising manuscript, final manuscript 

approval. 

SOURCES OF SUPPORT 

This project was funded by Natural Sciences and Engineering 

Research Council of Canada (NSERC). 

ETHICAL APPROVAL 

The study was approved by the University of Ottawa Research 

Ethics Board, University of Ottawa, Canada. Signed informed 

consent was obtained from each participant before commencing. 

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