Effects of Malleo-Lok Stiffness on Lower Limb Mechanics
Phase: NA
Conditions: Adult ALL, Healthy
Sponsor: University of Iowa

 
 
 
 
 
 
 
 
 
 
Title: Effects of Malleo-Lok Stiffness on Lower Limb Mechanics 
NCT Number: 04806100 
Date: April 11, 2023 
 
 

Study Protocol: 
Purpose and Procedures:  
The primary goal of this line of research is to understand the effects of ankle foot orthosis (AFO) stiffness on 
gait biomechanics and overall joint level stiffness. An improved understanding of the effects of stiffness on 
joint and limb mechanics will benefit the future prescription of AFOs. 
 
The primary purpose of this research study is to determine if the stiffness of a commercially available ankle foot 
orthosis (Malleo-Lok, Bio-Mechanical Composites, Des Moines IA) impacts gait biomechanics and overall 
joint level stiffness. Previously published research suggests that AFO stiffness can affect gait biomechanics and 
patient preference. However, previous studies have focused on traditional posterior strut devices with the strut 
aligned in the frontal plane to allow sagittal plane deflection. The Malleo-Lok is a novel, low-profile carbon 
fiber device with two laterally positioned struts aligned in the sagittal plane. The proposed study will provide 
insight that can be used by certified prosthetists orthotists (CPOs), physical therapists, and physicians to select 
the device that bests meets their patients’ needs. 
 
The secondary purpose of this research study is to determine the within session repeatability of a novel 
approach for in-vivo AFO stiffness testing. AFO stiffness testing is typically performed using mechanical 
testing systems without accounting for the interaction of the individual and the device. The novel in-vivo AFO 
stiffness testing approach will be completed twice within the session to evaluate repeatability, and determine if 
the approach differentiates between NoBrace, compliant AFO, and stiff AFO conditions. Non-invasive, 
wireless, surface electromyography sensors and retroreflective markers will be placed on the participants lower 
limb to measure muscle activity and movement, respectively. Force plates embedded in the floor will be used to 
measure forces on the limb to calculate joint moments. Participants will be given visual feedback to minimize 
the effects of muscle activity on measured joint stiffness. Participants will stand and sit with their foot (side 
with the Malleo-Lok AFO) on the force plate embedded in the floor and bring their knee forward over their 
stationary foot to deflect the device while minimizing muscle activity. 
 
In this study, lower limb stiffness and gait mechanics will be evaluated in healthy, able-bodied adult participants 
across three conditions; “NoBrace” where participants are asked to walk normally with no bracing, “Stiff” 
where participants are asked to walk while wearing a Malleo-Lok with stiff struts, “Compliant” where 
participants are asked to walk while wearing a Malleo-Lok with compliant struts. Testing will occur in a 
randomized order. Questionnaires will be used to quantify participants’ pain and perceived comfort and 
smoothness during walking. A motion capture system will be used to evaluate walking biomechanics and 
overall ankle joint level stiffness, allowing for comparisons between conditions. Small reflective markers will 
be placed on the participant’s skin and lower limb forces, and body motion will be assessed using computerized 
motion capture cameras and force plates in the floor. Muscle activity data will be collected using non-invasive 
wireless surface electromyography sensors. 
 
Objectives and Specific Aims: 
Aim 1: Determine the effect of Malleo-Lok stiffness on lower limb mechanics during gait. 
Hypothesis 1.1: We hypothesize that increasing stiffness of the Malleo-Lok will result in decreased ankle range 
of motion and increased knee flexion during gait. 
Hypothesis 1.2: We hypothesize that increasing Malleo-Lok stiffness will results in an earlier, faster center of 
pressure progression 
 
Aim 2: Determine the effect of Malleo-Lok stiffness on overall joint level stiffness. 
Hypothesis 2.1: We hypothesize that measured stiffness will progressively increase between the NoBrace, 
Compliant and Stiff conditions. 
 
Aim 3. Determine the within-session reliability of a novel in-vivo weight bearing approach to evaluating AFO 

stiffness. 
Hypothesis 3.1: We expect the novel approach to demonstrate excellent within-session reliability. 
 
Background and Significance: 
A1) Ankle foot orthoses (AFOs) are medical devices often used to support the foot and ankle during daily 
activities. AFO device stiffness can influence the level of support provided and motion at the ankle. There is a 
general consensus that increasing AFO stiffness decreases overall ankle range of motion[1-3] noticeably 
reducing peak ankle dorsiflexion[1,2,4-7] and plantarflexion.[1,8] In addition to effects at the ankle, AFO 
stiffness has been found to affect the knee during gait, with increased stiffness generally resulting in increased 
knee flexion at initial contact[1] increased peak knee flexion during stance phase[1,3,8,9] and decreased peak 
knee extension.[1,4] However, previous studies have focused on traditional posterior strut devices with the strut 
aligned in the frontal plane to allow sagittal plane deflection. The effect of lower profile devices with laterally 
positioned struts are poorly understood. In this study we will determine if the Malleo-Lok, a novel carbon fiber 
brace utilizing lateral struts, produces similar effects, and determine the effect of device stiffness. 
 
A2) Although AFO stiffness is known to influence overall device function for some design approaches[1] AFO 
stiffness has only been loosely measured in the clinical setting[1,10] and is often subjectively chosen for each 
patient based on certified prosthetist orthotist (CPO) knowledge and prior experience. Multiple research teams 
have developed and tested methods to quantify AFO stiffness.[11-20] These methods are typically best suited 
for a research facility and involve a custom mechanical testing system. The testing rigs usually clamp the foot 
plate of the AFO to a rigid platform and move the proximal cuff[11-15] to quantify AFO stiffness around the 
anatomic ankle joint center[11,14,19] or the device axis of rotation.[15] Although testing devices have 
successfully estimated AFO stiffness, they generally fail to take into account the interaction between the device 
and biological limb. One device was built for use in a clinical space to test AFO stiffness while the patient is 
wearing their AFO.[16] However, the footplate is once again secured to a rigid platform, which is then rotated 
about the estimated anatomic ankle joint center to determine the overall limb stiffness while wearing the 
AFO.[16] This approach does not include the vertical load on the limb that likely influences device-limb 
interaction during gait. In this study we are testing a novel approach to measuring AFO-limb stiffness about the 
biologic ankle joint center to better represent the effects of AFOs on limb stiffness during gait. 
 
A3) AFO-limb stiffness testing will use the same motion capture system used to collect gait biomechanics. The 
ability to collect reliable gait data across sites has been previously demonstrated[21,22] and the same techniques 
will be applied to this measurement. Muscle activity will be measured using non-invasive surface 
electromyography sensors on the skin. AFO-limb stiffness will be measured twice during the testing session in 
order to determine within-session reliability of the novel AFO-limb stiffness testing procedures. 
 
Inclusion Exclusion Criteria: 
Patient Inclusion Criteria 
- Between the ages of 18 and 45 
- Healthy without current complaint of lower extremity pain, spine pain, open wounds or active infections, or 
medical or neuromusculoskeletal disorders that have limited their participation in work or exercise in the last 6 
months 
- Able to hop without pain 
- Able to perform a full squat without pain 
- Ability to speak and understand English 
 
Patient Exclusion Criteria 
- Diagnosed with a moderate or severe brain injury 
- Lower extremity injury resulting in surgery or limiting function for greater than 6 weeks 

- Injuries that would limit performance in this study 
- History of recurrent ankle sprains or chronic ankle instability 
- Diagnosed with a physical or psychological condition that would preclude functional testing (e.g. cardiac 
condition, clotting disorder, pulmonary condition) 
- Uncorrected visual or hearing impairment(s) 
- Require use of an assistive device 
- Unhealed wounds (cuts/abrasions) that would prevent AFO use 
- BMI > 35 
- Pregnancy – Per participant self-report. Due to the expected small number of pregnant individuals, and 
resulting inability to account for its effect on resulting outcomes participants will be withdrawn from the study 
 
Design and Methods: 
We anticipate the study will be completed in one visit. The approximate time to complete study activities is 3-4 
hours. Although we will attempt to collect all data in the specific order listed, the number of study activities 
completed and the specific order of completion will be dependent on participant, staff, and study equipment 
availability. 
 
Potential participants will answer pre-screening questions as listed on the Pre-Screening Checklist over the 
phone before scheduling visit one, or in person during the first visit. If they meet all inclusion and exclusion 
criteria they will be consented to participate. Following consent, subjects will be screened using the post-
screening checklist. If subjects fail to meet the inclusion or exclusion criteria, their participation will end at that 
point. 
 
We will collect anthropometric and demographic information, have participants complete questionnaires 
concerning pain and comfort and smoothness, and use a motion capture system to investigate effects of ankle 
orthosis stiffness on gait biomechanics and joint level stiffness. Study participants will undergo an evaluation of 
characteristics relevant to device design, such as anthropometrics (height, weight, etc.), ankle joint stiffness, and 
pain, among other factors. 
 
Each participant will be given time to accommodate to the brace prior to collection. Participants will then 
undergo testing in each study condition (Stiff, Compliant, NoBrace) to determine how orthosis stiffness affects 
gait biomechanics and overall joint stiffness. We will use well-established techniques to obtain a range of 
biomechanical data as individuals walk at self-selected and controlled speeds. 
 
Personal/demographic and anthropometric information will be used to fully characterize the study participants. 
Demographic factors include characteristics that are independent of the health condition but can potentially 
influence physical performance and an individual’s course of recovery. We will collect multiple variables that 
have been previously associated with outcomes, including race, ethnicity, and education to characterize the 
cohort. Anthropometric and demographic information, such as age, biological sex, height, weight, leg length, 
shoe type, shoe length and width will also be used to characterize the cohort. 
 
Patient-reported outcomes questionnaires will be used to evaluate participant pain, comfort and smoothness. 
These patient-centric assessments will provide insight that can be used to interpret other study findings. We 
have used the selected measures in the target population and expect that they will effectively capture device-
related outcomes. 
 
Comfort and smoothness will be assessed using a modified version of the Socket Comfort Score, a reliable, 
valid, and sensitive measure of device fit and comfort.[23] These measures have been shown to effectively 
capture patient perception, are responsive to simple modifications to CDO device function, and will be applied 
in a manner consistent with a prior publication by the research team.[24] Comfort scores range from 0 = most 

uncomfortable to 10 = most comfortable, and from 0 = least smooth to 10 = most smooth.[23] 
 
Pain will be assessed using a standard 11-point numerical pain rating scale, in which 0 = no pain and 10 = worst 
pain imaginable, in a manner consistent with multiple other protocols.[25,26] Using this highly reliable 
approach, participants will be asked to rate their pain at the start of each session, and report their pain with 
movement in the device (if any) during each walking condition. 
 
Ground reaction force and motion capture data will be used to evaluate the motion and loading of the lower 
limb and CDO devices as participants walk on a level walkway at self-selected speed and a controlled speed 
based on leg length.[21,27] Ground reaction force and motion capture data will be used to evaluate the motion 
and loading of the lower limb as participants walk on an over ground walkway at self-selected speed and a 
controlled speed based on leg length.[21,27] A minimum of three non-collinear reflective markers placed on the 
skin to minimize skin-bone movement will be used to determine kinematics for the segments of interest (foot, 
shank, thigh, pelvis, trunk, arms and head). A pointer wand with a rubber tip will be used to identify bony 
landmarks for segment coordinate system definition. Visual 3D software (C- Motion Inc.) will be used to 
calculate segment and joint angles and velocities. Force plates imbedded in the floor will capture ground 
reaction forces. Data from successful trials will be analyzed using Visual-3D software package (C-motion Inc., 
Germantown, MD).[21] The ability to collect reliable data across sites has been previously demonstrated.[22] 
Techniques established by Dr. Wilken will be used to assess ankle peak dorsiflexion, joint moments, and 
power.[21] The movement of the center of pressure (COP), the weighted average location of all ground reaction 
forces, has been directly related to prosthetic and orthotic device design, function, and participant 
preference.[24,28-30] The peak velocity of the COP and the time to peak will be determined as a percentage of 
stance, in a manner consistent with prior work by the research team.[24] 
 
Muscle activity will be measured using non-invasive surface electromyography sensors on the skin. A total of 8 
EMG electrodes will be placed on the participant, with 4 on each leg to measure activation of the soleus, tibialis 
anterior, and medial gastrocnemius and peroneus longus. EMG data will be collected bilaterally in the lower 
limbs and during normal walking and during in-vivo ankle stiffness testing. Participants will be given visual 
feedback to minimize the effects of muscle activity on measured joint stiffness. Participants will stand and sit 
with their foot (side with the Malleo-Lok AFO) on the force plate embedded in the floor and bring their knee 
forward over their stationary foot to deflect the device while minimizing muscle activity. 
 
Video recordings will be collected during walking trials. Recordings will include walking on the level over 
ground surface in each condition and at each walking speed. The camera will be positioned so the top of the 
field of view will be at the shoulders to minimize the likelihood of capturing the participants face, and the files 
will be stored securely as described in section X.4 and will only be available to members of the research team. 
Collection of video recordings is required during testing for quality control purposes. Video recordings will be 
removed from the video camera after being transferred to the secure network drive server and will be retained to 
facilitate future analysis consistent with "Data Storage for Future Use" section in the informed consent 
document. 
 
 

Statistical Analysis Plan: 
Analysis Methods: 
There is one independent variable (IV) in this study, stiffness of the ankle brace (compliant and stiff). All the 
primary dependent variables (e.g. ankle moments, ankle range of motion, push-off power, ankle joint stiffness) 
will be evaluated using similar statistical approaches within each group. One-way repeated measure ANOVAs 
will be used to evaluate the effect of brace stiffness. Paired t-tests with Bonferroni-Holm correction will be used 
for post-hoc comparisons. Multiple trials will be collected for each condition during in-vivo ankle-CDO 
stiffness testing. Intraclass correlation coefficients and minimal detectable changes values will be calculated for 
in-vivo ankle-CDO stiffness between the average measurement for time point 1 and time point 2. 
 
Power Analysis: 
The number of participants proposed for this study are consistent with those from prior investigations by Dr. 
Wilken related to AFO design. Thirteen participants was sufficient to detect differences associated with AFO 
stiffness in a recent study by Dr. Wilken (PMID: 25193884). A total of 20 participants were included to 
adequately evaluate reliability in Aim 3. 
 
 

Literature Cited: 
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healthy adults. Gait Posture, 2012. 35(2): p. 301-7. 
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381. 
23. Hanspal, R.S., K. Fisher, and R. Nieveen, Prosthetic socket fit comfort score. Disabil Rehabil, 2003. 25(22): 
p. 1278-80. 
24. Ikeda, A.J., J.R. Fergason, and J.M. Wilken, Effects of altering heel wedge properties on gait with the 
Intrepid Dynamic Exoskeletal Orthosis. Prosthet Orthot Int, 2018. 42(3): p. 265-274. 
25. Hjermstad, M.J., et al., Studies comparing Numerical Rating Scales, Verbal Rating Scales, and Visual 
Analogue Scales for assessment of pain intensity in adults: a systematic literature review. J Pain Symptom 
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bipedal locomotion. Gait Posture, 2005. 21(3): p. 350-62. 
28. De Asha, A.R., et al., Attenuation of centre-of-pressure trajectory fluctuations under the prosthetic foot 
when using an articulating hydraulic ankle attachment compared to fixed attachment. Clin Biomech (Bristol, 
Avon), 2013. 28(2): p. 218-24. 
29. De Asha, A.R., et al., Impact on the biomechanics of overground gait of using an 'Echelon' hydraulic ankle-
foot device in unilateral trans-tibial and trans-femoral amputees. Clin Biomech (Bristol, Avon), 2014. 29(7): p. 
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30. Klenow, T.D., J.T. Kahle, and M.J. Highsmith, The dead spot phenomenon in prosthetic gait: Quantified 
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