Study Design. This was a prospective comparative observational study of children with JIA and age-matched healthy controls. All study procedures followed the requirements for the protection and treatment of human subjects as outlined in the Declaration of Helsinki. This study and all of its procedures were approved by the University of Florida Institutional Review Board (UFIRB) under the study number 201903394. All participants read and signed a UFIRB-approved informed consent document and children provided assent.
Participants. Enrolled participants had to meet the following inclusion/ exclusion criteria: aged 7-21 years; free of pediatric diseases such as reactive arthritis or pigmented villonodular synovitis; no history of surgical instrumentation to joints under study (such as arthroscopy, synovectomy) or joint fusions and free of obesity (body mass index>95th percentile). Children with JIA were under the care of a board-certified pediatric rheumatologist. The diagnosis of JIA was made by International League of Associations for Rheumatology (ILAR) criteria with current or previous sacroiliac joint or lower extremity joint involvement.(17)
Clinical Exam. Each patient underwent a physical exam which included assessment of each joint for swelling, range of motion and pain on range. Physician global assessment of disease activity (MD global) were also recoded. Laboratory studies that are part of standard care for JIA including antinuclear antibody (ANA) status, rheumatoid factor (RF), anti-citrullinated protein (anti-CCP) antibody, and HLA-B27 were recorded from the electronic medical record. The Childhood Health Assessment Questionnaire (CHAQ), is a widely-used, reliable and valid tool for the general physical functional assessment of children with JIA.(18) The CHAQ is comprised of eight domains (dressing, rising, eating, walking, hygiene, reach, grip, and activities), each containing different items that are scored from 0 to 3 points by level of difficulty (where 0 = “able to do with no difficulty” and 3 = “unable to do”). Global pain scores over the last seven days were obtained using an 11-point numerical pain rating scale (NRS; 0-10 points) to estimate current pain burden.
Experimental Procedures. All participants completed a single testing session in the University of Florida Human Dynamics Laboratory in the Orthopedics and Sports Medicine Institute. Several self-reported and performance-based measures were obtained during this visit, including walking gait speed, functional tasks, patient-reported outcomes and kinesiophobia. Before testing height and weight were measured using a medical grade scale, and body mass index was calculated (BMI = body weight(kg)/height(m2)).
Functional Task Performance and Functional Pain Severity. Gait speed was captured on an instrumented treadmill (AMTI; Watertown MA) at self-selected and fastest tolerable speeds. Standardized instructions were provided to each participant for each test from written scripts. After acclimation for three minutes on the treadmill, the participant was asked to: 1) self-select a speed at which they felt represented a typical comfortable speed while taking a walk on the street, followed by 2) selection of the fastest comfortable speed they could achieve similar to ‘what they would use trying to speed up to catch a bus’, or ‘move in the hallway to avoid being late for a class.’
Two measures of leg power that were recommended for use by the OARSI initiative among people with arthritis were administered here: the 30-second chair rise test (repetitions in 30-seconds) and stair ascent-descent (time to completion).(19) First, each child was instructed to rise from a chair (seat height 45 cm) with armrests and sit back down as many times as possible in 30 seconds. If the child’s feet were not able to touch the floor, a footstool was positioned under the foot so that in sitting position the knee was flexed at 90°. Children performed the tests with arms crossed in front of the body. The number of repetitions was recorded as the score. Second, the times to complete a climb up a standard flight of 12 stairs (each stair riser was 17.5 cm high) and to complete the descent back down were individually recorded by stopwatch. Children were instructed to climb stairs without the handrail. Slow times to complete the chair rise and stair climb and descent would be interpreted as impeded functional performance compared to faster times.
Pain elicited during the four functional task tests was described as functional pain.(20) Functional pain severity was obtained from each participant using the Wong-Baker FACES™ Pain Rating Scale, which is a visual pain scale ranging from 0-10 points. This scale was created for children to help facilitate communication and improve pain assessment.(21)
Patient Reported Survey Outcomes. All participants completed paper-based surveys including Patient Reported Outcome Measurement Information System (PROMIS®; Pain Interference, Physical Function Mobility and Global Health instruments) and the Hospital for Special Surgery Pediatric Functional Activity Brief Scale (Pedi-FABS).(22) PROMIS instruments assess physical, mental and social wellbeing in children and young adults across a variety of diseases.(23) We administered the pediatric short form versions for Pain Interference (Form 8a, v 2.0), Global Health (form 7, v 1.0), Physical Function and Mobility (Form 8a, v 2.0), and Upper Extremity (Form 8a v 2.0). The Pedi-FABS was administered to the participants and families to determine the child’s current participation over the past month in sports and physical therapy, sedentary behavior, frequency of performing different actions (e.g., running, cutting, endurance, jumping) and how different sports impact joint pain and swelling.(22) The Pedi-FABS is moderately related to PROMIS Physical Function and Mobility scores, and has excellent test-retest reliability (ICC= 0.91) and internal consistency (Cronbach’s alpha = 0.914).(22, 24) PROMIS pain interference and Mobility scores are strongly related to CHAQ pain scores.(25, 26)
The Tampa Scale of Kinesiophobia (TSK-11) is a brief, reliable, two-factor instrument comprised of 11 items that are scored on a 4-point Likert scale (ranging from 1=’strongly disagree’ to 4=’strongly agree).(27, 28) Items are designed to assess fear of movement/ re-injury due to pain. Two factors, Somatic Focus (TSK11-SF) and Activity Avoidance (TSK-11 AA) were calculated from the sum of the scores from items in each factor (see Figure 1 for description).(10) Across a range of adult pain populations, the internal consistency of the two factors ranges from 0.64-0.80.(10)
Statistics. Statistical analyses were conducted using SPSS version 26.0 (Chicago, IL; USA). For this relatively small sample, normality of data was visually inspected through distribution plots of each variable to ensure there were no obvious outliers. Descriptive statistics (means and standard deviations for continuous variables, frequencies and percentages for categorical variables) were calculated on all demographics, including race, sex, ethnicity, medication number and clinical characteristics for JIA. To determine whether group differences in patient reported measures, Welch’s t-tests were performed assuming unequal variance. To determine whether kinesiophobia predicted functional performance and physical activity, stepwise regression analyses were performed. Dependent variables were scores for 30-second chair rise, stair climb and descent, gait speed and Pedi-FABS. For each model sex and NRS Global pain level were entered into the models as covariates, and TSK-11 scores were entered last. The a level was set at .05 to establish statistical significance for all tests. Pearson correlations were performed between TSK-11 scores, performance-based test scores and Pedi-FABS scores; a Bonferroni correction was therefore applied for multiple comparisons for these four correlations with TSK scores; the a level was set as 0.012.