Protocol for a randomised, assessor-blinded, parallel group feasibility trial of flat flexible school shoes for adolescents with patellofemoral pain

Experimental/trial design

This study is an assessor blind, randomised, feasibility trial, with two parallel groups of adolescents with PFP. The research proposal has been developed in consultation with the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2013 statement [35] and the Consolidated Standard of Reporting Trials (CONSORT) 2010 guidelines for randomised pilot and feasibility trials [36].

Ethical approval was granted through the Deakin University Human Research Ethics Committee (2021–135). The trial was prospectively registered on the Australian and New Zealand Clinical Trials Registry (ACTRN12621001525875, Date registered: 9th November 2021). Written informed consent will be obtained from all participants and their parents/guardians prior to participation within the study.

Participants

Male and female adolescents will be eligible for inclusion if they meet the following criteria: (i) aged between 12–18 years, (ii) have PFP from a non-traumatic onset of at least six weeks duration, (iii) have pain ≥ 30/100 mm (mm) on a visual analogue scale (VAS), and (iv) have knee pain which is aggravated by activities that load the patellofemoral joint (e.g., squatting, stair ascent or descent, running).

Adolescents will be excluded if they (i) have pain at sites other than the anterior knee (e.g., other knee structures, hip, pelvis, lumbar spine), (ii) have a history of hip, knee or spine surgery, or other suspected knee joint pathology (e.g., Sinding Larsen Syndrome, Osgood Schlatter’s Disease), (iii) have planned lower limb surgery, (iv) have a neurological condition or systemic arthritis, (v) are currently wearing flat flexible footwear for school and/or (vi) have any condition which prevents them from wearing flat flexible footwear (e.g., calcaneal apophysitis).

Adolescent volunteers will be recruited from the community using a targeted comprehensive recruitment strategy with proven efficacy in previous studies of PFP [28, 37, 38]. Recruitment strategies will include paid social media advertising, dissemination through social media networks and flyers displayed at local sports medicine and allied healthcare clinics, footwear stores and sporting clubs/recreational facilities where PFP is likely to be prevalent. Eligibility criteria are based on previous high quality RCTs for PFP [13, 37].

To observe feasibility outcome of adherence, we plan to recruit 24 participants with PFP. A minimum of 23 participants are required to observe the feasibility outcome of adherence ≥ 75% allocated shoe wear indicating progression to a full trial is feasible. If adherence to allocated shoe wear is ≤ 50% (i.e., two school days per week, excluding a sporting day) progression to a main trial is not feasible (alpha < 0.05, β 0.2) [37, 39, 40].

Study procedures

Following contact with the research team, potential participants will be telephone screened for inclusion and exclusion criteria. Participants will then undergo a physical assessment at Deakin University to confirm diagnosis of PFP and the exclusion of other diagnoses of knee pain (e.g., Osgood Schlatter’s disease). All screening procedures will be performed by a registered podiatrist (NM) with more than nine years of clinical practice experience who has undergone additional training in PFP diagnosis by an experienced physiotherapist (JB).

Eligible participants will provide written consent to participate along with their parent or guardian for those under 18 years of age. Following baseline data collection eligible participants will be randomised to receive either (i) a flat, flexible school shoe, or (ii) a traditional school shoe to be worn throughout the 12-week study period. Randomisation procedures will be performed by a researcher external to this project.

As the outcomes within this study are patient reported, this study is considered assessor-blinded which is consistent with other RCTs utilising footwear interventions [39]. The research team processing the participant-reported data will be blinded to group allocation. Due to the inability to blind participants to the shoe they are wearing, participants will not be informed of the hypotheses of the study, nor of the differences between the shoes [39]. They will simply be recommended to wear the shoe at all times they would usually wear their school shoe. Participants will be able to keep their allocated shoe at the cessation of the trial. Participant flow through the study is outlined in Fig. 1.

Fig. 1figure 1

Participant flow through the study

Randomisation

Randomisation procedures will be performed via fixed concealed allocation. The randomisation sequence will be computer generated with permuted blocks of four or six participants. All assessors responsible for measuring and analysing key outcomes will be blinded to participant allocation.

Interventions

Participants will be fitted into both types of footwear at baseline by a podiatrist (NM) with nine years of clinical and footwear fitting experience to ensure they are comfortable and correctly fitted [41]. At this time, participants will be issued with an information sheet (see Additional file 1) outlining important information about their shoes, the study, and the requirements of participation within the study. Participants will be advised to wear their allocated shoe for the duration of time per week they would normally wear their school footwear.

Flat, flexible school shoe

Participants randomised to flat, flexible school shoes will receive the Vivobarefoot Primus Lite and/or the Vivobarefoot RA II (Fig. 2), which are both commercially available flat, flexible black lace up shoes (Vivobarefoot, Freiburg, Germany). The Primus Lite and the RA II are lightweight, have a 3 mm outsole, zero heel-toe offset, a mass of 180 g, and no stability or motion control features. The Primus Lite and the RA II score 25/25 on the minimalist shoe index [42]. Participants will receive either the RA II or the Primus Lite dependant on shoe size and stock availability. Participants will wear this shoe as per school requirements throughout the 12-week intervention period.

Fig. 2figure 2

Flat, flexible footwear to be used within study, Vivobarefoot Primus Lite (left) & Vivobarefoot RA II (right) (Vivobarefoot, Freiburg, Germany)

Traditional school shoe

Participants randomised to the traditional school shoe will receive a pair of Clarks Daytona (Fig. 3) (Clarks, Street, England). The Clarks Daytona has a stiff midsole and heel counter, a 12 mm heel-toe offset, and mass of 350 g. The Clarks Daytona scores 2/25 on the minimalist shoe index indicating a low degree of minimalism and flexibility [42].

Fig. 3figure 3

Traditional school shoe to be used within study, Clarks Daytona (Clarks, Street, England)

Concomitant care

If participants are taking medication for their knee pain, they will be permitted to continue this throughout the study duration. This is consistent with other studies performed in adolescents with PFP [13, 37]. At the time of entry within the study, participants will be asked to refrain from commencing new treatments for their knee pain for the duration of the study and to avoid using other assistive devices such as braces or orthotics for the study duration. Participants will be asked to report any use of co-interventions in the weekly log sheet (see Additional file 2).

Outcome assessment

Once consent is provided, baseline testing will follow at the Deakin University 3D Gait Laboratory. The duration of testing will be approximately 1.5 h. Baseline information will be obtained from participants including demographic data, body mass and height, sex, affected knee/s, duration of symptoms, previous treatments, and aggravating activities [43]. To assess the stage of adolescence, participants will complete the modified Pubertal Maturational Observational Scale at baseline [44]. This scale has been used in other studies involving adolescents and can be used to reliably classify adolescent developmental stages [45,46,47].

Participants will complete self-reported outcome measures at baseline, six weeks, and 12 weeks. Data collection will be performed through self-reported questionnaires performed via Qualtrics™ (Qualtrics, Provo, United States of America). Throughout the duration of the study participants will be asked to keep a weekly log (see Additional file 2) of the type of shoe worn that day; hours spent wearing that shoe; any adverse events associated with the allocated school shoe; use of co-interventions (e.g., pain medication, other footwear, taping); and any other comments. Participants will complete this in an online format distributed to them weekly via Qualtrics™. If participants do not have the equipment required to access the online format, a hard copy will be provided.

Outcomes measuresPrimary outcome measures

The primary outcome from this study is to determine the feasibility of conducting a full-scale RCT in adolescents with PFP. Feasibility will be assessed by the following outcome parameters; (i) adherence to allocated shoe wear of ≥ 75% of their total weekly school shoe wear time, (ii) a recruitment rate of one participant per fortnight, and (iii) a dropout rate of ≤ 20%. Success of blinding and participants’ expectations of treatment will be evaluated using the Credibility and Expectancy Questionnaire [48]. This will be completed at the end of the baseline assessment immediately after participants have been fitted into their shoes and then at the end of week one [37].

Secondary outcome measures

Secondary outcome measures will include the following patient reported outcomes taken at baseline, six weeks, and 12 weeks.

Knee Pain Severity will be assessed using a 100 mm VAS, with 0 mm indicating no pain and 100 mm indicating the worst pain imaginable. Participants will be asked to report their worst pain and usual pain in the past week. The VAS for usual or worst pain has been shown to be reliable and valid in assessing treatment outcomes in PFP [49].

Knee Injury and Osteoarthritis Outcome Score- Child Version (KOOS-Child)—The KOOS-Child is a patient reported outcome measure assessing (i) pain; (ii) symptoms; (iii) difficulty during daily activity; (iv) function in sports and play; and (v) knee-related quality of life [50]. Participants respond to each item using a 5-point Likert scale from 0 (no problem) to 4 (extreme problems). The scores are combined and displayed on a 0–100 scale with 0 indicating no problem and 100 indicating extreme knee problems. The KOOS-Child is recommended to evaluate knee function in adolescents and young people with a broad range of knee pain [51].

Knee Injury and Osteoarthritis Outcome Score- Patellofemoral Pain (KOOS-PF)—The KOOS-PF is a patient reported subscale of the KOOS for use in patients with PFP and patellofemoral osteoarthritis. This subscale of the KOOS is designed to be used in conjunction with the KOOS and/or KOOS-Child and has 11 items with the same response scales. The KOOS-PF has been shown to be valid and reliable when tested in adults but has yet to be assessed in adolescents and young people [52]. The KOOS-PF has been used by other RCTs conducted on adolescents, therefore it has been selected to ensure consistency of outcome measure assessments [37].

Anterior Knee Pain Scale (AKPS)—The AKPS is a patient reported assessment of 13 items related to symptoms and functional limitations. The AKPS is scored from 0 to 100 with lower scores indicating greater pain and functional limitations. The AKPS has been shown to be reliable and valid in assessing treatment outcomes in PFP [49].

Youth Quality of Life Short Form (YQOL-SF)—The YQOL-SF is a reliable tool used to assess the generic quality of life in adolescents aged 11–18 years with and without chronic conditions or disability [53]. The short form, derived from the Youth Quality of Life- Research, measures four domains including sense of self, social relationships, environment, and general quality of life. Participants respond to several statements on a scale from 0 (not at all) to 10 (completely). The total participant score is then transformed with a higher score indicating a better self-reported quality of life.

Global Rating of Change (GROC)—A 7-point Likert scale will be used to evaluate GROC at six weeks and 12 weeks [54]. Participants will be asked how their knee pain has changed since the start of the trial using the following responses: ‘completely recovered’, ‘strongly recovered’, ‘slightly recovered’, ‘same’, ‘slightly worse’, ‘much worse’, and ‘worse than ever’. The GROC has been used as an outcome measure in previous RCTs of adolescents with PFP [13, 37].

Biomechanical analysis—Lower limb kinematics and kinetics will be measured while walking and running on an instrumented treadmill (Bertec, Ohio, United States of America) at baseline and 12 weeks. Participants walking and running biomechanics will be assessed while wearing the traditional school shoe; flat, flexible school shoe; and a standard athletic shoe (Asics Gel Cumulus 16 [Asics, Kobe, Japan]) at baseline and their allocated school shoe and the standard athletic shoe at 12 weeks. Outcome measures will include: (i) hip, knee and ankle joint angles and torques in the sagittal, frontal, and transverse planes and (ii) patellofemoral joint forces. Biomechanical analysis will be used to understand the immediate (within session) and short-term (12 weeks) effects of flat, flexible school footwear on lower limb kinematics and kinetics and patellofemoral joint loads.

Adverse events

For the study duration participants will be advised to report information on adverse events and/or use of concomitant care within their weekly log sheet. Participants will be encouraged to report any discomfort they experience to the research team. If required, participants will attend an additional appointment with the research team to discuss any discomfort they may be experiencing. In this instance, standard clinical practice principles will be applied. The researcher may recommend strategies to improve the adaptation (e.g. a return to their regular footwear until pain settles). These events will be recorded as adverse events and if the discomfort cannot be reduced or tolerated, the participant will be encouraged to return to using their normal footwear and the individual’s participation with the intervention will be ceased.

Use of co-interventions

Participants will be asked to report any use of co-interventions within their logbook (e.g., pain medication, taping). This will be recorded in their logbooks over the three-month period. The reporting of co-interventions is common in other trials of adolescent PFP [37].

Planned statistical analysis

Data processing, data entry and data analysis will be performed by an assessor who is blinded to group allocation. All statistical analysis will be performed using SPSS version 27.0 or later (SPSS, Chicago, USA). Descriptive statistics will be used for the primary outcomes of feasibility and reported in relation to the pre-specified feasibility criteria. Patient reported outcome measures will be described with means and standard deviations for continuous data and counts and percentage for categorical data.

Data management

Data gathered throughout the study will be coded in a re-identifiable format and stored on a separate database to group identifier to maintain blinding of the primary investigator. All electronic data will be stored on a shared drive of password protected computers.

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