Arthritis Care & Research Vol. 66, No. 11, November 2014, pp 1680 –1687 DOI 10.1002/acr.22350 © 2014, American College of Rheumatology

ORIGINAL ARTICLE

Effects of Two Physiotherapy Booster Sessions on Outcomes With Home Exercise in People With Knee Osteoarthritis: A Randomized Controlled Trial KIM L. BENNELL,1 MARY KYRIAKIDES,1 PAUL W. HODGES,2

AND

RANA S. HINMAN1

Objective. Enhancing exercise adherence over the longer term is an important goal in self-management of knee osteoarthritis (OA). Following an initial period of more intensive exercise supervision, this study investigated whether 2 additional physiotherapy visits improved outcomes with continued home exercise over a subsequent 24-week period. Methods. A total of 78 people with medial knee OA (mean ⴞ SD age 62.1 ⴞ 6.9 years, mean ⴞ SD body mass index 29.4 ⴞ 4.0 kg/m2, and radiographic disease severity 19% mild, 49% moderate, and 32% severe) who completed a 12-week physiotherapist-supervised exercise trial were randomly allocated to 2 30-minute physiotherapy booster sessions (delivered by 8 physiotherapists in private clinics) or no booster sessions for the subsequent 24 weeks. All participants were asked to continue home exercises 4 times weekly. Primary outcomes were change in pain, using a 100-mm visual analog scale, and self-reported physical function, measured using the Western Ontario McMaster Universities Osteoarthritis Index. Participants and physiotherapists were unblinded to group allocation, although participants were blinded to the study hypothesis. Results. A total of 74 participants (95%) completed the trial. There was no significant difference between groups for change in pain (mean difference [95% confidence interval (95% CI)] 0.7 mm [ⴚ9.4, 8.0]; P ⴝ 0.88) or physical function (ⴚ0.3 units [95% CI ⴚ4.0, 3.5]; P ⴝ 0.88). The mean ⴞ SD percentage of home exercise sessions completed was 56% ⴞ 34% in the booster group and 51% ⴞ 37% in the control group (P > 0.05). Conclusion. Two booster sessions with a physiotherapist did not influence pain or physical function outcomes, or measures of home exercise adherence. These findings suggest other more effective strategies are needed to maximize longer-term adherence with the aim to achieve greater improvements in clinical outcomes from exercise in this patient population.

INTRODUCTION Knee osteoarthritis (OA), predominantly involving the medial compartment, is a common chronic joint disease resulting in pain, physical dysfunction, and impaired quality of life (1). As there is currently no cure for OA and given the chronicity of the condition, effective treatANZCTR: 12612000595819. Supported by the National Health and Medical Research Council (631717). Dr. Bennell’s work was supported by an Australian Research Council Future Fellowship. Dr. Hodges’s work was supported by a National Health and Medical Research Council Senior Principal Research Fellowship (APP-1002190). 1 Kim L. Bennell, BAppSc(Physio), PhD, Mary Kyriakides, BAppSc, Rana S. Hinman, BPhysio, PhD: University of Melbourne, Centre for Health, Exercise and Sports Medicine, Melbourne, Victoria, Australia; 2Paul W. Hodges, BPhty (Hons), PhDMedDr, DSc, FACP: University of Queensland, Centre of Clinical Research Excellence in Spinal Pain,

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ments that reduce symptoms and encourage patient selfmanagement are needed. Exercise is recommended by all clinical guidelines for the management of knee OA (2–5). There is strong evidence of short-term beneficial effects of exercise on pain and function for knee OA (6), with effect sizes similar in magnitude to those observed with analgesics and nonsteroidal antiinflammatory drugs (7). Better adherence to prescribed home exercises improves the longer-term effectiveness of exercise in people with knee OA (8 –10). Pa-

Injury and Health, School of Health and Rehabilitation Sciences, Brisbane, Queensland, Australia. Address correspondence to Kim L. Bennell, BAppSc (Physio), PhD, Centre for Health, Exercise and Sports Medicine, Department of Physiotherapy, University of Melbourne, 3010, Victoria, Australia. E-mail: [email protected]. Submitted for publication December 8, 2013; accepted in revised form April 15, 2014.

Significance & Innovations ●

The results suggest that alternate strategies are needed to maximize adherence to home exercise in this patient group.

SUBJECTS AND METHODS Trial design. The study design was a parallel 2-group RCT (Figure 1). The institutional human ethics committee approved the study. All participants provided written informed consent. Participants were blinded to the study hypothesis.

Did not meet study adherence criteria of ≥10 physiotherapy visits (n=14)

Randomized (n=78)

Allocation: Physiotherapists Treatment phase Week 24 Assessment: Patients

tient adherence is often good during the first few months of commencing an exercise program, particularly while under therapist supervision, but typically reduces over time with a consequent decline in clinical benefits (11). Enhancing longer-term exercise adherence is therefore an important aim in the self-management of knee OA. Numerous strategies have been proposed to assist with patient adherence (9) and there is some suggestion that the addition of “booster” sessions with a therapist after an initial period of exercise treatment can improve longerterm clinical outcomes (12). However, a recent Cochrane Review investigating a range of interventions to improve adherence to exercise in patients with chronic musculoskeletal pain concluded that further high quality clinical trials are needed (13). A recent randomized controlled trial (RCT) by our group compared the effects of 2 different physiotherapistsupervised exercise programs (quadriceps strengthening and neuromuscular exercise) (14). Both exercise programs resulted in significant clinically relevant reductions in pain and physical dysfunction after 12 weeks with no difference in effect between programs. The primary aim of the present study was to evaluate whether 2 physiotherapy booster sessions could improve pain and function outcomes from continued home exercise over a subsequent 24-week period. As there was no evidence to guide selection of the number and time interval of booster sessions, we took a pragmatic approach and tested a protocol that would be practical, feasible, and inexpensive to implement within a clinical setting. We hypothesized that participants performing home exercises and randomized to receive booster sessions would maintain or show less decline in pain and self-reported physical function, as well as report greater adherence to home exercise than those performing home exercises without booster sessions.

Completing participants from the original RCT screened (n=92)

Baseline assessment (n=78)

Allocation: Patients

●

This study provides the first randomized controlled trial evidence to specifically investigate whether additional face-to-face booster sessions with a physiotherapist post– exercise treatment improves subsequent adherence to home exercise and clinical outcomes in people with knee osteoarthritis.

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Enrollment: Patients

Influence of Exercise Booster Sessions on Knee OA Outcomes

Allocated to Booster group (n=40)

Allocated to Control group (n=38)

Physiotherapists and centres (n=9), performing the intervention. Number of patients treated by each physiotherapist (median=5 [IQR=4, min=1, max=10])

2 x individual treatment sessions and home exercises

24-week assessment (n=38) (had knee replacement n=1, could not contact n=1)

Home exercises only

24-week assessment (n=36) (had knee replacement n=1, death in family n=1)

Figure 1. Flow diagram of study protocol. RCT ⫽ randomized controlled trial; IQR ⫽ interquartile range.

Participants. Participants were recruited from the cohort that had completed our original RCT comparing 2 exercise interventions (14). Eligibility criteria for participants in the original RCT recruited from the community in metropolitan Melbourne, Australia, included average knee pain over the past week ⱖ25 on a 100-mm visual analog scale (VAS), pain/tenderness predominantly over the medial knee region, and radiographic medial tibiofemoral joint OA. Major exclusion criteria included knee surgery or intraarticular corticosteroid injection within 6 months, systemic arthritic conditions, prior hip or knee joint replacement or tibial osteotomy surgery, and body mass index (BMI) ⬎36 kg/m2. People were eligible to be included in the present study if they had 1) attended at least 10 of the 14 physiotherapy sessions for the original RCT so as to include those who were initially adherent in the short term, and 2) completed posttreatment measurements for the original RCT (14). Nine physiotherapists in private practices, all of whom took part in the original RCT, delivered the booster sessions. They had an average of 12 (range 2–30) years of clinical musculoskeletal experience. Three (30%) had postgraduate, master’s degree–level qualifications.

1682 Procedure. Participants were consecutively randomized to receive either booster physiotherapy sessions or no booster sessions (control group). All participants performed home exercises, and those in the booster group visited their original RCT physiotherapist twice over the 24-week trial. Outcome measures were collected at baseline (conclusion of the original RCT and designated as week 0) at the Department of Physiotherapy, University of Melbourne, and at 24 weeks via mail. There was no outcome assessor as measures were self-report questionnaires. Randomization, allocation concealment, and blinding. Group allocation was randomized within random permuted blocks of 6 or 8 generated a priori, using a computergenerated random number table and stratified according to the type of exercise (neuromuscular or strengthening) performed by the participant in the original RCT. Consecutively numbered, sealed opaque envelopes containing group allocation were prepared by a different researcher with no other involvement in the study and kept in a locked central location. Another researcher not involved in recruitment opened the next sequential envelope and informed the participant of their group allocation once they had completed the original RCT. By necessity, neither the participants nor the physiotherapists were blinded to group allocation. Home exercise program. All participants were instructed to continue with their physiotherapist-prescribed home exercise program from the original RCT (14,15). In the original RCT, all participants attended a physiotherapist appointment 10 –14 times over 12 weeks for exercise prescription, monitoring, and progression. Each supervised exercise session lasted 30 – 40 minutes. Participants were asked to perform prescribed exercises at home 4 times per week. In the original RCT, 2 types of exercise programs were prescribed according to random allocation: 1) weight-bearing neuromuscular exercises focused on quality and control of movement (6 exercises, including knee bending ⫻ 2, wall squats, step-ups (all 3 sets of 10 repetitions), hip muscle strengthening (2 sets of 5 repetitions), and balance (2 minutes), or 2) non–weight-bearing quadriceps strengthening exercises (3 sets of 10 repetitions for 5 exercises, including inner range knee extension, sitting knee extension, isometric knee extension holds, straight leg raise, and outer range knee extension). Resistance was provided through ankle weights or elastic bands. For the current RCT, all participants were asked to continue their home exercise program 4 times per week for 24 weeks. An optional exercise log book to record exercise sessions was provided to participants to assist with motivation. Physiotherapy booster sessions. Participants in the booster group only received 2 30-minute individual physiotherapy booster sessions at weeks 8 and 16 (from the end of the original RCT). At these visits, the physiotherapist reviewed the home exercise program content and dose, increased the dose, observed the patient performing the home exercises and corrected form if necessary, and discussed progress and adherence with the participant. Dis-

Bennell et al cussion particularly focused on barriers to home exercise performance and strategies to overcome these barriers. Physiotherapists received brief training in the conduct of booster sessions by the investigators as part of their training for the original trial. We checked physiotherapy treatment notes to document therapist adherence to the protocol. Outcome measures. Primary outcomes: self-reported pain and physical function. Overall average knee pain during the past week was assessed using a 0 –100-mm VAS with terminal descriptors of “no pain” and “worst pain possible” (16). Physical function was assessed using the disease-specific Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), Likert format (17). The physical function subscale comprises 17 questions with scores ranging from 0 – 68, with higher scores indicating worse function. Given that the purpose of enhancing exercise adherence is to improve patient-relevant outcomes, we chose pain and function as the primary measures. Secondary outcome: adherence. The number of booster sessions attended was recorded by the physiotherapist. Adherence to home exercise was assessed via 2 methods. First, participants completed a questionnaire at weeks 8 and 16 that asked how many times they had completed the home exercises (6 neuromuscular exercises or 5 quadriceps strengthening exercises) in the previous week (out of the required number of 4). The number of reported sessions from these 2 time points was summed (maximum total of 8) and converted into a percentage adherence for each participant. Second, participants self-rated their overall average adherence to the home exercise program during the preceding 8 weeks at 3 time points (week 8, 16, and 24) using an 11-point numeric rating scale, with terminal descriptors of 0 ⫽ not at all to 10 ⫽ completely as instructed. The average of these 3 ratings was taken to indicate self-rated adherence throughout the trial. For both methods, questionnaires were mailed to participants and returned via the mail. Other measures. Descriptive information included disease severity from knee radiographs, classified using the Kellgren/Lawrence grading system (18), and demographic factors, including age, BMI, sex, medication use, and comorbidities. Cointerventions and adverse effects during the study were determined by questionnaire at week 24. Statistical analysis and sample size. Main comparative analyses between groups were performed using an intent to treat approach with P values of less than 0.05 considered significant. To account for missing data, the last value carried forward approach was used. For the 2 primary outcome measures of pain and physical function, differences in mean change (followup minus baseline) were compared between groups using analysis of covariance adjusted for baseline values of the outcome of interest. Results are presented as estimated differences with 95% confidence intervals. Within-group changes over time were evaluated using paired t-tests. Differences in adherence between groups were assessed using Mann-Whitney U tests. Correlations between measures of adherence and

Influence of Exercise Booster Sessions on Knee OA Outcomes

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Table 1. Demographic and clinical characteristics of participants in the present trial, together with the original trial cohort*

Characteristic Age, years Symptom duration, median (IQR) months Height, cm Body mass, kg Body mass index, kg/m2 Male Affected knee, right:left ratio Unilateral symptoms Radiographic disease severity† Grade 2 Grade 3 Grade 4 Current drug use‡ Analgesia (paracetamol combinations) Nonsteroidal antiinflammatories COX-2 inhibitors Opioids Topical antiinflammatories Glucosamine/chondroitin products Topical liniment rubs Fish oil Home exercise sessions completed during original RCT, mean ⫾ SD %§ Self-reported adherence to home exercises during original RCT (0–10)# Number of physiotherapy sessions (10–14) attended during original RCT, median (IQR)

Booster group (n ⴝ 40)

Control group (n ⴝ 38)

Original RCT cohort (n ⴝ 100)

60.5 ⫾ 6.6 66.0 (36–120) 166.4 ⫾ 10.9 81.6 ⫾ 15.1 29.4 ⫾ 3.8 16 (40) 24:16 12 (30)

63.7 ⫾ 7.0 84.0 (27–120) 166.6 ⫾ 9.0 82.2 ⫾ 13.8 29.6 ⫾ 4.3 20 (53) 20:18 11 (29)

62.4 ⫾ 7.3 60.0 (24–120) 166.8 ⫾ 97.2 82.7 ⫾ 14.3 29.6 ⫾ 4.1 48 (48) 53:47 33 (33)

8 (20) 18 (45) 14 (35)

7 (18) 20 (53) 11 (29)

22 (22) 43 (43) 35 (35)

8 (20) 5 (13) 1 (3) 0 (0) 2 (5) 25 (63) 4 (10) 1 (3) 88 ⫾ 17

9 (24) 7 (18) 2 (5) 1 (3) 3 (8) 18 (47) 5 (13) 4 (11) 78 ⫾ 20¶

37 (37) 21 (21) 7 (7) 2 (2) 8 (8) 47 (47) 19 (19) 11 (11) 76 ⫾ 27

9.1 ⫾ 1.5

8.8 ⫾ 1.5

8.3 ⫾ 2.5

13 (12–14)

13 (12–14)

12 (10–14)

* Values are the mean ⫾ SD or number (percentage) unless indicated otherwise. RCT ⫽ randomized controlled trial; IQR ⫽ interquartile range; COX-2 ⫽ cyclooxygenase 2. † Using the Kellgren/Lawrence grading system. ‡ Defined as at least once per week. § Assessed from a daily log book. ¶ P ⫽ 0.01 comparing booster and control groups. # Scored on a numeric rating scale, where 0 ⫽ not at all to 10 ⫽ completely as instructed.

changes in pain and physical function were performed using Pearson’s r correlation coefficients. Cointervention use between groups was compared using chi-square tests. Given that the sample size was constrained by the number completing the original RCT, a formal a priori sample size calculation was not performed. However, we planned to conduct a post hoc calculation of the power of the study to detect minimal clinically important differences between groups of 18 mm (of 100 mm) in pain on a VAS (19) and 6 units (of 68 units) on the WOMAC physical function measure (20), given the sample size.

RESULTS Participants were recruited from November 2010 to September 2012, with followup completed April 2013. The flow of participants through the trial is shown in Figure 1. Of the 92 participants who completed the original RCT, 78 (85%) met eligibility criteria for the current RCT and were randomized into the booster or control group. The sample (n ⫽ 78) and original study cohort (n ⫽ 100) were comparable for descriptive characteristics (Table 1). Four partic-

ipants (5%), 2 in each group, withdrew from the study; therefore 74 participants (95%) completed the trial. The groups were comparable on baseline characteristics, except that the booster group had significantly higher levels of adherence to home exercise during the original RCT (88%) compared with the control group (78%) (Table 1). Of the participants in the booster group, 25 of 40 (63%) attended both physiotherapy sessions, 10 of 40 (25%) attended 1 physiotherapy session, and 5 of 40 (12%) didn’t attend any sessions. There was no difference in baseline participant characteristics comparing these 3 subgroups. There was no significant difference between the booster and control groups for the change in overall average pain and change in WOMAC physical function (Table 2). These results were similar when analyses were performed controlling for the difference between groups in home exercise adherence during the original trial, as well as when excluding the participants who did not attend any booster session and including only those who attended both booster sessions. Furthermore, neither group showed significant change in pain or function over the 24 weeks. Booster physiotherapy sessions did not influence exer-

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Bennell et al

Table 2. Mean ⴞ SD of groups, mean ⴞ SD change within groups, and mean (95% CI) difference in change between groups, adjusted for baseline scores* Outcome Overall VAS pain (0–100 mm)

WOMAC function (0–68)

Groups, week 0† Booster (n ⫽ 40) 33.0 ⫾ 21.1 18.5 ⫾ 9.0 Control (n ⫽ 38) 27.7 ⫾ 19.5 18.5 ⫾ 9.8 Groups, week 24 Booster (n ⫽ 38) 37.1 ⫾ 20.5 20.2 ⫾ 12.4 Control (n ⫽ 36) 35.5 ⫾ 20.2 21.0 ⫾ 12.3 Change within groups‡ Week 24 ⫺ week 0 Booster 4.3 ⫾ 23.4 2.1 ⫾ 9.1 Control 7.1 ⫾ 23.4 2.3 ⫾ 7.3 Difference in change between groups§ Week 0 ⫺ week 24 Booster ⫺ control¶ ⫺0.7 (⫺9.4, 8.0) ⫺0.3 (⫺4.0, 3.5) * 95% CI ⫽ 95% confidence interval; VAS ⫽ visual analog scale; WOMAC ⫽ Western Ontario McMaster Universities Osteoarthritis Index. † Week 0 refers to immediately post–12-week supervised exercise program (conclusion of original trial). ‡ Missing values replaced by last observation carried forward. Positive change means worsening. § Missing values replaced by last observation carried forward. Adjusted for week 0 values. ¶ Negative difference in change favors control group.

DISCUSSION Our results showed that 2 booster sessions at 2 and 4 months after completion of a physiotherapist-supervised home-based exercise program did not alter either pain or physical function outcomes, or reduce declines in home exercise adherence in people with knee OA. These findings suggest that other, more effective strategies are needed to maximize adherence and improve longer-term clinical outcomes from exercise in this patient population. This is important as, compared with more closely supervised programs, home programs are more convenient for patients, feasible in community settings, and cost effective. Each of these elements increases their suitability as a public health approach (21). The original RCT showed that the exercise interventions resulted in significant clinically relevant reductions in pain and physical dysfunction after 12 weeks. The current study found that continued home exercise was sufficient to maintain these initial improvements over 24 weeks, irrespective of the inclusion of 2 booster sessions (Figure 2). During the original RCT, participants in the booster and control groups completed 88% and 78% of the required 100 80

VAS pain (mm) 60

10-14 x PT visits & Home exercises 4 x weekly

Home exercises 4 x weekly

Booster Control

40 20

cise adherence levels. The mean ⫾ SD percentage of reported home exercise sessions completed was 56% ⫾ 34% in the booster group and 51% ⫾ 37% in the control group (P ⬎ 0.05), with a range in both groups of 0 –100%. Mean ⫾ SD self-reported adherence to home exercise over the 24 weeks was 6.1 ⫾ 3.2 of 10 for the booster group and 5.5 ⫾ 3.5 for the control group (P ⬎ 0.05), with a range in both groups of 0 –10. In both groups combined, there were no significant relationships between the number of exercise sessions or self-rated adherence with change in overall pain (r ⫽ ⫺0.11, P ⫽ 0.34 and r ⫽ ⫺0.21, P ⫽ 0.07, respectively) and change in WOMAC physical function (r ⫽ 0.08, P ⫽ 0.48 and r ⫽ 0.10, P ⫽ 0.38, respectively). There were few reported adverse events. These included 6 participants who reported increased knee pain (n ⫽ 4 for booster group, n ⫽ 2 for control group) and 1 control group participant who reported increased hip pain. Cointerventions included other physiotherapy (n ⫽ 3 for booster group), other forms of exercise (n ⫽ 3 for booster group, n ⫽ 3 for control group), knee injection (n ⫽ 1 for control group), knee surgery (n ⫽ 2 for control group), and acupuncture (n ⫽ 1 booster group). Medication use included paracetamol (n ⫽ 10 for booster group, n ⫽ 16 for control group), nonsteroidal antiinflammatory drugs (n ⫽ 15 for booster group, n ⫽ 15 for control group), glucosamine/ chondroitin (n ⫽ 24 for booster group, n ⫽ 14 for control group), and fish oil (n ⫽ 4 for booster group, n ⫽ 4 for control group). These did not differ between groups.

0 -12

0

24

Weeks

A 60

WOMAC Physical Function

Booster Control

45

30

15

0 -12

0

24

Weeks

B Figure 2. Group means over time for pain (A) and physical function (B) in the booster and control groups, combining data from the original trial (14) and the current trial. The shaded region represents the original trial, where participants undertook a 12week program of physiotherapist-supervised exercise sessions and home exercises (week ⫺12 refers to the start of the 12-week exercise program in the original trial and week 0 is at the conclusion of the original trial). As evident, improvements in pain and physical function were maintained over the subsequent 24-week period in both groups with no difference between groups. PT ⫽ physiotherapist; VAS ⫽ visual analog scale; WOMAC ⫽ Western Ontario and McMaster Universities Osteoarthritis Index.

Influence of Exercise Booster Sessions on Knee OA Outcomes

Figure 3. Home exercise adherence in both groups defined as the percentage of required home exercise sessions completed in the original trial (14) and in the current trial. RCT ⫽ randomized controlled trial.

home exercise sessions, respectively. This relatively high initial adherence was likely due to the novelty of the exercise program and the fact that participants attended 10 –14 physiotherapy sessions, where therapists monitored adherence, discussed any issues, and checked participants’ exercise log books. In the current RCT, home exercise adherence declined in both groups to approximately 50% of the required sessions (Figure 3). Therefore, maintenance of clinical benefits occurred despite reduced exercise adherence. Although not measured, it is possible that a concomitant increase in general physical activity levels, as a result of improved pain and function, may have contributed to maintenance of improvements. The small number of booster sessions may have been insufficient to influence outcomes. We chose 2 sessions over 24 weeks as a realistic achievable number from the perspectives of health policy, funding, and patient burden. Despite the small number of sessions and inclusion of an initially adherent group (from the original RCT), only 63% of participants attended both sessions and 12% did not attend either session. However, there was no significant relationship between the number of booster sessions attended and either measure of home exercise adherence (data not reported). The optimal number and timing of booster sessions is unknown and a greater number may achieve better outcomes. There is some indirect support for this. A long-term study showed that a 12-week behavioral graded activity program followed by 5–7 booster sessions over the subsequent 9 months resulted in better adherence and a more physically active lifestyle at 60 months than usual exercise therapy (22). In another study, an individualized physical activity maintenance plan was more effective when coupled with tapered telephone reinforcement than without, with a dose-response relationship between the number of telephone calls and outcomes (23). However, given that a proportion of our participants were disinclined to attend even 2 sessions, this has practical implications for a more intensive booster regimen. The content of the booster sessions may have played a role. Physiotherapists were advised to check exercise performance and dose and to discuss adherence. However, they were not specifically instructed or trained in behavior change techniques. Increasing evidence shows that the nature of the therapeutic relationship between the physio-

1685 therapist and the patient influences treatment adherence and clinical outcomes (24). Adherence is greater when practitioners are perceived as supportive rather than paternalistic (25). A recent meta-analysis (26) showed that effective communication and support from practitioners is vital to promote patients’ self-belief with regard to exercise and long-term motivation. These are important factors related to patient adherence (27–29). Research has indicated that when interacting with patients with knee OA, practitioners often adopt a controlling rather than supportive approach and consider adherence to be the patient’s responsibility (30). As we did not evaluate the communication style adopted by the physiotherapists in our study, it is not possible to know whether this was suboptimal and as such attenuated or counteracted any potential benefits of the booster sessions. A complex array of factors can influence adherence to exercise programs in individuals with OA. Studies have identified both internal and external facilitators and barriers to exercise (28,29,31). Internal factors include individual attributes such as motivation, personality, self-image, exercise attitude, exercise history, and disease knowledge, as well as personal experience. External factors include the social environment, such as family and practitioner support and encouragement, and socioeconomic status, as well as the physical environment such as weather and accessibility of facilities and transportation. As such, it is likely that a multifaceted and individualized approach would be more effective. Another explanation for the lack of effect of booster sessions might relate to the sample characteristics. Given that we only included participants who had reached a threshold level of adherence during the original trial, it is possible that we had a more motivated group of individuals. This motivated group might have been better able to perform exercises at home by themselves. Therefore, 2 additional booster sessions may not have been necessary to influence adherence levels. This however, might be different in clinical practice. With any nonsignificant finding, the possibility of a lack of statistical power must be considered. We utilized a sample of convenience, by recruiting eligible participants from those completing another exercise RCT. As such, our sample size was constrained by that of the original RCT (total sample of 100 participants recruited), and in particular to those who completed the followup assessment for the original RCT and had attended a minimum number of physiotherapy sessions. By utilizing this sample, we were able to conduct the current RCT at considerably reduced expense (as all patients had already been prescribed their home exercise programs and had been screened for eligibility). Using the between-participant SDs from our data, our sample size of 78 participants gave us more than 80% power to detect minimum clinically important differences in pain (19) and physical function (20). Furthermore, no clear trends were seen in the data to suggest that our nonsignificant findings represent a Type II error. To our knowledge, our RCT is the first to specifically evaluate the isolated effects of booster sessions in people with knee OA by comparison of groups undertaking exercise with and without the addition of booster sessions. As

1686 such, no direct comparisons with other studies can be made. A 2007 systematic review found 11 RCTs comparing an exercise group to a no exercise control group with ⱖ6-months postexercise treatment followup (12). Of these, 3 RCTs (1 of high methodology quality and 2 of low quality) included additional booster sessions for the exercise group during the followup phase. The authors suggested that booster sessions had a positive influence on the maintenance of posttreatment exercise effects on pain and function in the longer term, because effects declined in the other studies where no booster sessions were included (12). However, unlike the present study, the RCTs included in the systematic review all utilized nonexercising control groups rather than exercising groups with no booster sessions, thereby precluding a specific analysis of the effects of booster sessions to be evaluated (separate to home exercise). While numerous strategies are suggested to help improve adherence to exercise interventions in people with OA (9,13,28), there are few RCTs in this area. A 2010 Cochrane Review of adherence strategies in chronic musculoskeletal pain, including OA, stated that the most promising strategies are those that include supervised exercise, individualized exercise, booster sessions, provision of supplementary materials such as exercise audiotapes/ videotapes, and that incorporate graded activity, selfmanagement programs, and cognitive behavioral principles (13). However, the authors of the review also concluded that firm conclusions could not be drawn given limited and inconsistent effects across studies and variations in implemented strategies. Although the results of the current study add to the body of knowledge in this area, further research is urgently needed. There is no “gold standard” method to assess exercise adherence. Various methods have been described in the literature, including diaries, recall questionnaires, and activity monitors (13). These all have limitations, including the fact that recording exercise adherence may actually influence the behavior of interest. Variable exercise adherence rates reported in the literature may reflect the use of different measurement methods. We questioned participants about the number of home exercise sessions performed in the previous week (to minimize recall bias) on 2 occasions to provide a snapshot of exercise behavior. However, it is possible that these 2 time points were not necessarily representative of adherence to exercise across the entire 24 weeks. We considered asking participants to maintain a diary of all exercise sessions completed during the study, but our previous experience with this method has found that this is burdensome on participants and results in substantial missing data. We also asked participants to self-rate their overall exercise adherence using an 11-point numeric rating scale. This was highly correlated with the self-reported number of exercise sessions performed (r ⫽ 0.88, P ⫽ 0.000) and similarly showed no difference between booster and control groups, providing some concurrent validity to these different adherence measures. Strengths of this study include its RCT design and low dropout rates. A limitation is that half the participants performed an exercise program of quadriceps strengthen-

Bennell et al ing while the other half performed neuromuscular exercise. However, we stratified randomization to ensure similar proportions of each type of exercise in the booster and control groups. Furthermore, a Cochrane Review found no evidence to show that the type of exercise influences adherence levels (13). Neither participants nor the treating physiotherapists were blinded. Nevertheless, any bias introduced by lack of blinding would be in the direction of an increased effect in the booster group, which was not evident. It may have been that our followup duration of 24 weeks was too short to demonstrate effects. We did not include all participants from the original trial. While this can potentially introduce bias, the 2 samples were comparable on participant characteristics. Finally, our adherence measure of number of weekly exercise sessions only covered 16 weeks and as such may not necessarily reflect adherence across the entire 24-week trial. In summary, 2 booster sessions with a physiotherapist over 24 weeks were insufficient to improve clinical outcomes and home exercise adherence in people with knee OA. It is not known whether outcomes would have been enhanced by a greater number of booster sessions, by additional training of therapists in behaviorial change strategies (e.g., communication style), or by a different adherence strategy. It is also possible that strategies need to be individualized and multifaceted given the complex interaction of factors that influence exercise adherence in this patient population.

ACKNOWLEDGMENTS The authors wish to acknowledge members of the research team from the original neuromuscular exercise (NEXA) trial: Ewa Roos, Michael Hunt, Eva Ageberg, and Tim Wrigley, as well as Ben Metcalf who assisted with data compilation. The study physiotherapists who provided the physiotherapy treatments were Katherine Edmonds, Frances Gray, Jonathan Harris, Susan Hong Labberton, Arthur Lee, Tim McCoy, Jack Mest, Gabrielle Molan, Michael Ranger, and Tim Simpson. AUTHOR CONTRIBUTIONS All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Bennell had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design. Bennell, Hodges, Hinman. Acquisition of data. Kyriakides. Analysis and interpretation of data. Bennell, Hodges, Hinman.

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