Study design and participants
A pre-experimental study with pre-test/post-test design was conducted. Twenty-two PsA patients were recruited from the rheumatology out-patient clinics at the Université de Sherbrooke Hotel Dieu University Hospital (CHUS). Inclusion criteria were: between 20 and 70 years of age, a confirmed diagnosis of PsA by a trained rheumatologist, moderate to severe and recurrent foot pain and stable medication over three months preceding the recruitment. Patients with diabetes, neurological disease or any musculoskeletal disease that could impact the normal gait pattern, who received an intra-articular corticosteroid injection or any conservative foot treatment such as foot orthoses/footwear intervention within the past three months were excluded. The study was approved by the CIUSSS de l’Estrie-CHUS Ethics Board, and all the participants gave their informed consent prior to data collection.
Data collection procedure
Demographic and baseline characteristics were assessed on a first data collection session (T1) at Sherbrooke’s Research Center on Aging. Foot and lower limb pain, global pain, and foot function were then measured using self-reported questionnaires. Afterwards, participants were fitted with inertial measurement units (IMUs) and performed a 10 meters gait test at a self-selected speed. Participants were then examined by a podiatrist who performed foot casts and designed the CFO. At the CFO delivery visit (T2), the participants’ foot and lower limb pain, and foot function were evaluated for a second time. This second pre-intervention measurement was planned considering the T1 - T2 delay as well as the fluctuating nature of PsA patients’ pain. CFO were then dispensed and adjusted if necessary, to improve fit and comfort. The participants were then directed to wear the CFO for a 7-week period. They were provided with a diary to record daily CFO wearing time, weekly foot pain intensity and any changes in medication during the intervention period. At a final follow up visit at the end of the 7-week period (T7), foot and lower limb pain and foot function were re-assessed and the instrumented 10 meters gait test was repeated. Free walking activities (FWA) were recorded over seven consecutive days before the CFO first use, and after the seven-week intervention period using an instrumented sock (inertial sensors module positioned at the ankle and embedded in a sock) worn daily during waking hours by the participants.
Intervention
Functional foot orthoses were custom-made for each participant. The CFO were designed by the same experienced podiatrist (GBC) based on a detailed clinical and biomechanical assessment. Foot scans were obtained with the Occipital Structure Sensor 3D scanner (Occipital Inc), the patient in a prone position while the subtalar joint was held in a neutral position. The obtained scan was edited and smoothed using the MSoft software (Techmed3d Inc, Levis, QC, Canada). The prescriptions/corrections were defined by the podiatrist before manufacturing. Three-quarter length CFO were 3D printed in a rigid material (Nylon) using a MultiJet Fusion 3D printer (HP, Palo Alto, CA, USA). The thickness of the CFO ranged between 2 and 3.4 mm depending on the participants’ medial arch weight and height. Most of the orthoses included a medial arch support, a heel stabilizer and a metatarsal pad. The degrees and types of corrections added to the CFO were determined specifically for each participant based on the clinical examination and were adjusted at the CFO delivery according to each patient’s comfort and tolerance. The participants were taught to wear the CFO progressively during the first two weeks to allow for the lower limbs’ muscles and structures to adjust to the CFO, and to wear the orthoses for the next 5 weeks, 7 days a week as often as they could. To document adherence to the CFO, all the participants completed a diary to report the daily wearing time in hours. In addition, the participants were advised to wear the CFO with adapted shoes after the general characteristics (e.g. heel height, malleability of the sole etc.) of such shoes were explained.
Outcomes measures
Sociodemographic, baseline characteristics and control variables: Sex, age, body mass index, professional occupation, and previous history of foot injuries were assessed using a self-reported questionnaire. Disease duration and C-reactive protein levels (CRP) at baseline were obtained from the patients’ medical records. Foot type, foot deformities and foot pain sites were obtained from the podiatrist clinical examination records. Changes in medication that occurred during the CFO intervention period were recorded by the participant in a diary.
Foot function: Foot function was measured using the Foot function index (FFI). The FFI is a valid, reliable and responsive self-reported questionnaire widely used in studies of foot and ankle disorders previously used to evaluate CFO effects on foot function [48, 49]. The FFI is composed of 23 items divided into three subscales measuring foot pain (FFI-P), foot disability (FFI-D) and foot-related activity limitation (FFI-AL). Each item of the FFI is recorded on a 0 to 10 numeric rating scale (NRS) allowing for subscale and total scores calculation. A sub-scale score is obtained by totaling the sub-scale items’ scores and dividing the total by the sub-scale maximum possible total [48]. The total score is obtained by adding all subscales final percentages and dividing by the total number of subscales. The values reported are presented as percentages ranging between 0 and 100 %, with higher values indicating greater pain, disability, and activity limitation. The minimal clinically important difference (MCID) for the FFI total score was found to be 7 points in patients with plantar fasciitis [50].
Foot pain: The intensity of foot pain was measured using a zero-to-ten NRS considered a valid, reliable, and responsive tool for pain intensity assessment [51]. The MCID for patients with chronic pain is a 2 points change [52]. Participants were asked to circle the number between 0 and 10 that better matched their average foot pain intensity in the seven days preceding data collection. Foot pain was assessed more in detail (e.g. pain walking with foot orthoses, pain walking with shoes, pain at the end of the day etc.) with the FFI pain sub-scale. To monitor the evolution of weekly foot pain intensity during the intervention period, the patients were asked to record it at the end of each week, in a diary using 0 to 10 NRS. Foot pain and foot function were measured at three time points, at first data collection (T1), at CFO delivery (T2), and after the 7-week intervention period (T7). As there were no statistical differences in the FFI and NRS scores between T1 and T2, the average of these two time points was used as a baseline measure while the last time point (T7) represented the final measure.
CFO wearing time: CFO wearing time was assessed by asking the participants to record it in hours in a diary covering the 7-week intervention period. The CFO wearing time is reported as the average reported time per week.
Global and Lower limb pain: Global pain and pain at the knee, hip, and lower back pain, were measured at T1, T2 and T7 using the NRS (0, no pain – 10, worst imaginable pain). Similarly to foot pain and foot function, data obtained during the first two time points was used as baseline.
Gait function: Gait function was assessed using an instrumented gait analysis system. Gait spatiotemporal parameters (STPs) including cadence, gait cycle duration, gait speed, stride length, double support, swing time, foot strike angle, and stride time variability, were recorded using the Mobility Lab system (APDM Wearable Technologies) during 10 meters walk test (10MWT). Mobility Lab is a research grade system proven to accurately and reliably estimate STP [53–55]. Mobility Lab uses a set of six OPAL inertial measurement units (IMUs) and a software that allows for an automated and easy extraction of STP. All the participants performed three 10MWT trials over a 14-meters straight walkway with the Mobility lab’s IMUs fixed with elastics straps on the chest, the lower back, both wrists and feet. The 10MWT trials were performed at the participants’ comfortable speed and the average of the three trials was calculated.
Freeliving walking activities (FWA): FWA including step count, freeliving cadence, and time spent in ambulatory physical activity (APA) intensity-based categories were measured using an instrumented sock (Sensoria Inc, Redmond, WA, USA) with an embedded 9 axis IMU positioned at the ankle. The instrumented sock connects automatically, without any manipulation needed from the participants, via Bluetooth to a smartwatch (Apple Watch, series 3) where the raw inertial measures of motion (3D accelerometer) are stored and then transferred for data reduction and processing to extract walking activities specific outcomes (see Additional file for signal processing and steps identification description). Step count was assessed as the total number of steps per day. Besides, to describe the steps accumulation pattern throughout the day, the number of steps was also assessed for each of the following active events’ categories determined based on the number of consecutive steps within each category: 0 to 20 steps, 20 to 60 steps, 60 to 120 steps, 120 to 300 steps, 300 to 600 steps, and more than 600 steps. Free-living cadence included cadence averaged for total wearing time (mean cadence/day). Moreover, as cadence may vary depending on the number of consecutive steps performed, it was also assessed for each of the above active events’ categories. APA intensity-based categories were determined using cadence data and included stepping activities (0 to 59 steps/min), slow walking (60 to 79 step/min), medium walking (80 to 99 step/min), moderate intensity APA (MAPA) (100 to 119 step/min) and vigorous APA (VAPA) ( > 120 step/min), as previously defined [56, 57]. The time spent in each of the last three categories was calculated only for more than 60 steps events referred to as purposeful walking. Free-living walking activities were assessed over a 7 consecutive days period before and after the intervention during which, the participants were instructed to wear the instrumented sock during waking hours while they perform daily activities. Only valid days defined as days with at least 8 hours of recordings, and only valid participants with a minimum of one valid day were included in the analyses. Adherence to the instrumented sock use was tested by the system itself and by asking the participants to record the daily wearing time in a diary. To avoid influencing the participant’s physical activity, they were only told that the study would assess the effects of CFO on foot pain, foot function and gait STP.
Sample size and statistical analysis
Given the exploratory nature of this study, the sample size was calculated assuming a large effect size (0.8) for the pre-post differences in the FFI total score. Using a two tailed paired T-test, a significance level α of 5%, a power of 90%, and assuming a 15% dropout rate, a total sample size of 22 participants was required. The Shapiro-Wilk test was used to examine data distribution and parametric and non parametric statictical tests were used depending on data distribution. Paired t-tests (or the Wilcoxon signed-rank test) were used to assess the differences in foot pain, foot function, global and lower limb pain between baseline and T7 and Cohen’s effect size was calculated to quantify the magnitude of these differences. A one-way repeated measures ANOVA was conducted to determine whether there was a statistically significant difference in weekly recorded foot pain intensity and CFO wearing time over the 7-week intervention period. Spearman correlation coefficients were calculated to assess the relationships between the CFO wearing time, foot pain and foot function at T7. As a two-week adaptation period was required, correlation analyses were performed using the average CFO wearing time per week calculated for the last 5 weeks of the intervention period. Correlation coefficients were considered weak, moderate, and strong for values between 0.1 and 0.3, 0.3 and 0.5, and > 0.5, respectively [58]. The pre-post differences in gait function and freeliving walking activities were assessed using the Wilcoxon signed-rank test. The significance level was set at 0.05. The statistical analyses were performed using SPSS Version 26 (IBM statistics Corporation, Armonk, NY).