Foot Progression Angle Modification: an Exploratory Six-week Intervention in People With Knee Osteoarthritis
Phase: NA
Conditions: Osteoarthritis, Knee
Sponsor: University of British Columbia

Official Title:  
Foot progression angle modification: an exploratory six-week intervention 
in people with knee osteoarthritis. 
 
 
NCT Number: TBD 
 
Document Date: March 24th, 2020 
 

Study Protocol 
 
Study Design 
This parallel-group randomized clinical trial will consist of a 6-week gait modification 
intervention, delivered to two groups of older adults with medial compartment knee osteoarthritis 
(OA). The first group will receive a conventional delivery of gait modification (group name: 
SMOD), whereby they will practice the gait modification with a specific target (rotate foot 15° 
inward or outward relative to baseline). The second group will self-select the amount of 
modification they perform (group name: AMAC), guided by the instruction to “change foot 
rotation as much as is comfortable”. Foot rotation (toe-in or toe-out walking) is measured during 
the stance phase of walking as the angle of the foot’s long axis (heel to toe) relative to the 
direction of walking, and termed foot progression angle (FPA). In-lab and real-world gait 
analysis will be used to examine how the modification is learned, as well as the effect of the 
modification on biomechanical and clinical outcomes relevant to knee OA. In-lab assessment 
will be performed at baseline and a 7 week follow-up, while real-world assessment will be 
performed during the intervening weeks using wearable sensor technology (a custom sensorized 
shoe design). Both within-group and between-group comparisons will be made to identify 
differences in learning, difficulty, biomechanical, and clinical outcomes. 
 
Primary Hypotheses 
H1:  Participants receiving the specific FPA target will exhibit improved learning outcomes 
(e.g. lower error in performance, higher proportion of steps with ≥7º of change from 
baseline FPA and lower variability) from week 1 to week 6, as measured during gait 
modification practice sessions, learning assessments, and during daily walking activity.  
H2:  Participants receiving the self-directed FPA modification will exhibit improved learning 
outcomes (higher proportion of steps with ≥7º of change from baseline FPA and lower 
variability) from week 1 to week 6, as measured during gait modification practice sessions, 
learning assessments, and during daily walking activity.  
H3:  We expect FPA variability will be larger in the self-directed group, but both groups will 
exhibit a similar proportion of steps with >7° of change from baseline FPA. 
Secondary Hypotheses 
H4: Those in the self-directed modification group will exhibit smaller average changes in FPA 
compared to those in the conventional gait modification group. However, those in the self-
directed modification group will report lower ratings of difficulty in performing the 
modification, compared to the specific-target gait modification group. 
H5:   Both groups will exhibit improvements in biomechanical (e.g. knee adduction moment) 
and clinical outcomes (e.g. knee pain, physical function) at follow-up, compared to 
baseline.  
H6: Biomechanical (e.g. knee adduction moment) and clinical outcome (e.g. knee pain, 
physical function) change scores from baseline to follow up will not differ between groups. 
 
Participants 
Adults with knee OA will be recruited and randomized into two treatment arms. All eligible 

participants will: 1) be 50 years of age or greater, 2) exhibit signs of tibiofemoral OA (a score of 
≥2 on the Kellgren and Lawrence (KL) grading scale [1]) predominantly in the medial 
compartment, 3) self-reported knee pain ≥ 3 / 10 on a numerical rating scale of pain (NRS; 0 = 
“no pain” and 10 = “worst pain imaginable”) during most days of the previous month, 4) are 
comfortable walking intermittently for 30 minutes, and 5) fit into the available sizes of 
sensorized shoes (sizes spanning US women’s 5 to men’s 13). 
  
Exclusion criteria include: 1) any knee surgery or intraarticular injections within the past 6 
months, 2) a history of joint replacement surgery or high tibial osteotomy, 3) current or recent 
(within 6 weeks) corticosteroid injections, 4) use of a gait aid, 5) currently on a wait list for joint 
replacement surgery or high tibial osteotomy, 6) any inflammatory arthritic condition, 7) any 
other conditions that may affect normal gait or participation in an aerobic exercise program, and 
8) cannot attend all required appointments at UBC.  Additionally, potential participants will 
undergo an initial gait screening similar to a recent study [2] (details are outlined below), with 
the goal of identifying participants who are capable of reducing their KAM magnitude when 
FPA is modified. This gait screen will examine both natural walking FPA and changes in knee 
load while walking with increased toe-in and toe-out. Those who do not elicit a reduction in 
KAM impulse ≥ 5% when FPA is changed by 10° in either direction will be excluded from the 
study as they would be considered non-responders. 
 
A total of 36 individuals will be recruited for this study, 18 in each group. Approximately 60% in 
each group will be female. The primary outcome measure of this study is the change in absolute 
FPA performance error (the difference between the performed and the targeted FPA), which is 
indicative of how ‘accurate’ the patient is when performing the modification. This outcome 
measure is only relevant to the SMOD group, who have a specific target for their modification; 
therefore, allowing an error value to be calculated. This outcome will be measured during 
immediate and delayed retention at week one compared to follow-up and will provide evidence 
of the extent to which motor learning has occurred. Previous FPA performance error during 
immediate retention testing after a six-week FPA modification resulted in a small effect (Cohens 
d = 0.35) [3]. We are also interested in exploring the clinical and biomechanical differences 
between the SMOD and AMAC gait modification groups; however, no study has previously 
compared these methods of gait modification. Therefore, we will be conservative and base our 
sample size calculation on the between-within interaction effect of a 2 x 4 (group = 2: SMOD vs 
AMAC; measure = 4: immediate and delayed retention tests at week 1 and follow up) repeated 
measures ANOVA with an effect size of f = 0.175 (f = d / 2). With power = 0.8 and alpha = 0.05, 
a total sample of 30 is required [4]. With a conservatively estimated attrition of 15%, we will 
recruit 36 participants total (18 per group). 
 
Procedures 
Recruitment and screening 
Volunteers will be recruited via print and social media, and via our database of previous 
participants who have indicated interest in participating in future studies. Interested volunteers 
will be screened via phone, email, or our lab website by the study coordinator to assess inclusion 
and exclusion criteria. Those deemed preliminarily eligible will be invited to attend a gait 
screening appointment. Eligible participants who pass the gait screen will be referred for a 
radiographic assessment of their knees to confirm the presence of structural signs of knee OA. 

Standing, semi-flexed posteroanterior radiographs of both knees will be taken. A trained assessor 
will grade all radiographs based on the KL criteria. Those passing all screening requirements will 
be invited to enroll in the study. 
 
Gait screening 
The gait screen will be performed using motion capture to measure self-selected FPA, joint 
angles, and joint moments during over-ground walking. Fifty-two retroreflective markers will be 
placed on the skin over boney landmarks and 14-high speed cameras (sample rate = 100 Hz) will 
track the positions of these markers in three dimensions. Additionally, two floor-mounted force 
platforms (sample rate = 2000 Hz) will measure ground reaction forces during walking. Natural 
walking trials across the 10m instrumented walkway will be performed first (one length equals 
one walking trial), followed by toe-in and toe-out walking. The latter will be guided verbally 
such that several walking passes are completed at a range of FPA magnitudes (small toe-in/out, 
medium toe-in/out, and large toe-in/out). The specific amount of change in FPA is not relevant, 
as long as a range of FPA magnitudes are recorded over the collected walking trials. These data 
will be used to determine whether the participant is a responder to FPA modification, and which 
direction (toe-in or toe-out) elicits the greatest response. The threshold of a 5% reduction in the 
knee adduction moment impulse (area under the knee adduction moment – time curve) with a 
10° change in FPA will be used to determine response. For recruitment purposes, those who 
respond to either toe-in or toe-out (≥5% reduction with a 10° change in FPA) will be provided 
this FPA modification. For those who elicit response to both, the modification (toe-in or toe-out) 
with the greatest reduction per 10° of change in FPA will be used in the intervention. This cutoff 
value is conservative, allowing for some regression in response while still maintaining overall 
reduced KAM impulse. A 5% threshold was chosen as the average reduction in KAM impulse 
after a 16 week toe-out modification program was 4.7% [5]. These methods of screening for 
response to FPA change and personalizing the direction of FPA change were shown to improve 
biomechanical outcomes relative to a non-personalized approach [6, 7]. 
 
Baseline and follow-up data collection 
An identical baseline and follow-up gait assessment, separated by seven weeks, will be 
conducted in the laboratory, and using both optical-motion capture and the sensorized shoe 
system. These assessments will include questionnaires, a timed stair climb, and gait analysis. 
 
A) Patient reported outcomes and physical function 
Questionnaires will be administered which will include an 11-point numerical rating scale (NRS) 
depicting average knee pain over the previous week where 0 = “no pain”, 10 = “worst pain 
imaginable”, the Knee Injury and Osteoarthritis Outcome Score (KOOS) [8], and the Pain 
Catastrophizing Scale [9]. Medical history, anthropometrics (height, body mass etc.), age, and 
symptom duration will also be recorded by the assessor. The timed stair climb (a measure of 
physical function) will be performed on a 12-stair flight. Participants will be instructed to “climb 
as quickly, but safely as possible” [10]. Two repetitions will be performed, and the fastest time 
will be used. 
 
B) Gait analysis  
A total of 52 reflective markers (45 lower limbs; 7 upper limbs) will be affixed to the skin 
bilaterally over key anatomical landmarks as is standard in our laboratory [11]. Fourteen high-

speed cameras (sample rate = 100 Hz) will track the positions of these markers and two floor-
embedded force platforms (sample rate = 2000 Hz) will measure ground reaction forces. Five 
passes along a 10m instrumented walkway will be performed barefoot and then shod. Walking 
speed at the baseline assessment will be measured using two timing gates placed at a known 
distance along the walkway. At follow-up, participants will first complete five walking passes at 
a self-selected speed and then be constrained to walk within ±5% of their baseline walking 
speed, due to the impact of walking speed on joint moments. After over-ground walking, a 5-
minute treadmill walk will be performed while wearing a pair of sensorized shoes (details 
included below). This will provide a controlled measurement of FPA from the sensorized shoe 
for comparison with FPA measured at each practice session and during daily at-home walking.  
 
A 1-minute dual-task assessment will be performed immediately after the 5-miniute treadmill 
walking trial, according to established methods [12]. Briefly, a single letter or category will be 
provided at the start of the 1-minute period. The instructions will be to continue walking 
naturally while simultaneously dictating as many words as possible (word-list generation) that 
start with the letter or belong to the category. The number of correct words dictated will be 
recorded. 
 
Stair ascent and descent will be performed while wearing the sensorized shoes. This will take 
place at a building nearby the laboratory (5-minute walk) because of the availability of 
continuous linear sets of stairs for multiple flights. This allows the use of the sensorized shoe for 
measuring FPA during stair ascent and descent. These FPA data will be compared with transfer 
test data (details included below) examined at several points throughout the intervention. These 
same shoes will be provided to the participant to measure real-world FPA during at-home and 
community walking. 
 
Sensorized shoes 
A custom inertial sensor consisting of a 3-axis accelerometer (signal range: ±4g), gyroscope 
(±500°/s), and magnetometer (±1200μT), sampling data at 100 Hz will be embedded in the sole 
of the shoe. A previously published custom sensor fusion algorithm [13], programmed into a 
microcontroller, calculates the FPA in real time and stores it on a microSD card for later 
extraction. The sensorized shoe design and algorithm has been validated during treadmill [14] 
and over-ground walking [15] with excellent validity and reliability (absolute error = 1.7º and 
intraclass correlation coefficients > 0.9).  
 
Randomization 
Once deemed eligible and baseline data collection is complete, each participant will be 
randomized to either the SMOD or AMAC group. Randomization will be performed using an a 
priori block-stratified approach based on sex and KL grade. A predetermined randomization 
matrix will be computed [16] by a team member not involved in testing or the intervention. 
Group allocations will be stored in opaque envelopes, which will be opened in a sequential 
manner after baseline testing and before the first practice session. The group allocation will be 
communicated to the study trainer via email. 
 
Gait modification intervention 
Both groups will attend six practice sessions conducted weekly, which will last approximately 1 
hour each. Walking practice will be conducted on a treadmill with a full-length mirror placed 

directly in front of the treadmill. The SMOD group will be guided to increase their FPA by 15° 
in either the toe-in or toe-out direction (determined by the gait screen). A line of tape will be 
aligned on the mirror according to the target FPA, as we have done previously [5, 17]. This 
mirror-based method of providing a target for the FPA modification was shown to be similarly 
effective when compared to feedback delivered using an expensive real-time motion capture 
system, but with significantly greater clinical feasibility. The AMAC group will be instructed to 
increase their FPA by “as much as is comfortable”. The mirror will be provided during practice 
sessions; however, no tapeline will be placed. The amount of time spent with the feedback 
(mirror) visible will be progressively reduced (faded feedback) across the six weekly practice 
sessions in order to reduce the reliance on feedback [18]. Before and immediately after the 
practice sessions, the participant will perform a warm-up and cool-down walk while wearing the 
sensorized shoes (10-minute outdoor standardized walking loop). This will provide a repeatable 
non-laboratory-based measure of FPA. Both groups will be encouraged to practice their gait 
modification at any opportunity during their daily at-home walking. Practice sessions will be led 
by a kinesiologist with experience delivering gait modification interventions. 
 
Learning will be measured during 1) practice, 2) immediate and delayed retention tests, 3) dual-
task tests, 4) transfer tests, and 5) during at-home/community walking. Each test (2-4) will last 1 
min and be collected at each practice session. For the SMOD group, the absolute performance 
error (absolute error = |performed FPA – target FPA|), FPA variability, and the proportion of 
steps with >7 of change from baseline FPA will be measured using the sensorized shoe. For the 
AMAC group, FPA variability and the proportion of steps with >7 of change from baseline FPA 
will be measured. Retention tests will occur immediately before (starting at practice session 2) 
and after practice bouts. The participant will be asked to perform their gait modification as 
accurately as possible for 1 minute. Dual-task testing will be performed identically to the 
baseline assessment described above; however, the participant will be asked to simultaneously 
perform their gait modification. Lastly, transfer testing will be performed during stair ascent and 
descent in the same manner as the baseline assessment. 
 
During each practice session, participants will be asked to rate their knee pain at the beginning, 
middle, and end of the session using an 11-point numerical rating scale (0 = “no pain” and 10 = 
“worst pain imaginable”). At the end of the sessions, they will be asked to rate the difficulty in 
achieving their FPA modification during that practice period using an 11-point numerical rating 
scale (0 = “not difficult” and 10 = “most difficult/unable to perform”). 
 
An instructional booklet will be provided which outlines details of how to care for and use the 
sensorized shoes while at home and in the community. Participants will track daily walking 
volume, walking times on each day, daily knee pain using an NRS (e.g. overall pain, pain during 
walking), non-walking exercise activities, and any adverse events related to their knees or 
walking. Additionally, an 11-point numerical rating scale will be used to report weekly 
confidence in how accurately the FPA modification was performed (0 = “no confidence at 
all/unable to perform” and 10 = “completely confident”) and difficulty in performing the 
modification (0 = “not difficulty” and 10 = “most difficult/unable to perform”). A minimum of 
10-minutes of daily walking will be requested to ensure enough data for the analysis. 
 
Data processing and analysis 

Marker-based motion capture data (as collected during the baseline and follow-up assessments) 
will be processed using commercially available software and using standard techniques our 
research group has established [5, 11, 19, 20]. Sensorized shoe data captured during the baseline 
and follow-up gait assessment, practice sessions, and at-home or community walking will be 
processed using custom MATLAB scripts. A trained research assistant, blinded to group 
allocation, will perform all data processing and analysis.   
 
 
 
 
 

References 
 
[1] Kellgren JH, Lawrence JS. Radiological assessment of osteo-arthrosis. Ann Rheum Dis. 
1957;16:494-502. 
[2] Felson DT, Parkes M, Carter S, Liu A, Callaghan MJ, Hodgson R, et al. The efficacy of a 
lateral wedge insole for painful medial knee osteoarthritis after prescreening: a randomized 
clinical trial. Arthritis Rheumatol. 2019;71:908-15. 
[3] Richards R, van der Esch M, van den Noort JC, Harlaar J. The learning process of gait 
retraining using real-time feedback in patients with medial knee osteoarthritis. Gait Posture. 
2018;62:1-6. 
[4] Faul F, Erdfelder E, Lang AG, Buchner A. G*Power 3: a flexible statistical power analysis 
program for the social, behavioral, and biomedical sciences.  Behav Res Methods. 2007/08/19 
ed2007. p. 175-91. 
[5] Hunt MA, Charlton JM, Krowchuk NM, Tse CTF, Hatfield GL. Clinical and biomechanical 
changes following a 4-month toe-out gait modification program for people with medial knee 
osteoarthritis: a randomized controlled trial. Osteoarthritis Cartilage. 2018;26:903-11. 
[6] Uhlrich SD, Kolesar JA, Silder A, Berkson MZ, Presten B, Montague-Alamin HA, et al. Six 
weeks of personalized gait retraining to offload the medial compartment of the knee reduces pain 
more than sham gait retraining. Osteoarthritis Cartilage. 2019;27:S28. 
[7] Uhlrich SD, Silder A, Beaupre GS, Shull PB, Delp SL. Subject-specific toe-in or toe-out gait 
modifications reduce the larger knee adduction moment peak more than a non-personalized 
approach. J Biomech. 2018;66:103-10. 
[8] Roos EM, Lohmander LS. The Knee injury and Osteoarthritis Outcome Score (KOOS): from 
joint injury to osteoarthritis. Health Qual Life Outcomes. 2003;1:1-8. 
[9] Sullivan MJL, Bishop SR, Pivik J. The Pain Catastrophizing Scale: Development and 
validation. Psychological Assessment. 1995;7:524-32. 
[10] Bennell K, Dobson F, Hinman R. Measures of physical performance assessments: Self-
Paced Walk Test (SPWT), Stair Climb Test (SCT), Six-Minute Walk Test (6MWT), Chair Stand 
Test (CST), Timed Up & Go (TUG), Sock Test, Lift and Carry Test (LCT), and Car Task. 
Arthritis Care Res. 2011;63 Suppl 11:S350-70. 
[11] Charlton JM, Hatfield GL, Guenette JA, Hunt MA. Ankle joint and rearfoot biomechanics 
during toe-in and toe-out walking in people with medial compartment knee osteoarthritis. 
PM&R. 2019;11:503-11. 
[12] Patel P, Lamar M, Bhatt T. Effect of type of cognitive task and walking speed on cognitive-
motor interference during dual-task walking. Neuroscience. 2014;260:140-8. 
[13] Huang Y, Jirattigalachote W, Cutkosky MR, Zhu X, Shull PB. Novel foot progression angle 

algorithm estimation via foot-worn, magneto-inertial sensing. IEEE Trans Biomed Eng. 
2016;63:2278-85. 
[14] Xia H, Xu J, Wang J, Hunt MA, Shull PB. Validation of a smart shoe for estimating foot 
progression angle during walking gait. J Biomech. 2017;61:193-8. 
[15] Charlton JM, Xia H, Shull PB, Hunt MA. Validity and reliability of a shoe-embedded 
sensor module for measuring foot progression angle during over-ground walking. J Biomech. 
2019;89:123-7. 
[16] Snow G. blockrand: Randomization for block random clinical trials. R package version 1.3. 
RStats2013. 
[17] Hunt MA, Takacs J, Hart K, Massong E, Fuchko K, Biegler J. Comparison of mirror, raw 
video, and real-time visual biofeedback for training toe-out gait in individuals with knee 
osteoarthritis. Arch Phys Med Rehabil. 2014;95:1912-7. 
[18] Winstein CJ, Schmidt RA. Reduced frequency of knowledge of results enhances motor skill 
learning. J Exp Psychol Learn. 1990;16:677-91. 
[19] Charlton JM, Krowchuk NM, Hatfield GL, Guenette JA, Hunt MA. Contralateral limb foot 
rotation during unilateral toe-in or toe-out walking in people with knee osteoarthritis. Gait 
Posture. 2018;62:132-4. 
[20] Hatfield GL, Cochrane CK, Takacs J, Krowchuk NM, Chang R, Hinman RS, et al. Knee 
and ankle biomechanics with lateral wedges with and without a custom arch support in those 
with medial knee osteoarthritis and flat feet. J Orthop Res. 2016:1597-605.