This is the first feasibility trial of a group-based theoretically informed complex self-management intervention for both OA and chronic LBP that has evaluated its acceptability alongside testing the proposed trial procedures from the perspectives of both healthcare providers and patients. Preliminary effects of the intervention were also explored, as was the proposed process model of behaviour change.
Feasibility: Acceptability, demand and necessary adaptations of the SOLAS intervention
The findings of the qualitative interviews and self-report measures demonstrated that the SOLAS intervention content, support materials, and group-based mode of delivery were acceptable and appropriate to participants with OA and CLBP and physiotherapists alike. These findings are reinforced by our previous report of high fidelity to these elements of the intervention . Feasible adaptations for a future definitive trial include simplifying the education content of the first session to increase its acceptability and fidelity and ensuring the materials are suitable for participants with low health literacy.
Fifty seven percent of participants attended five out of six SOLAS classes. This is a higher attendance rate than other RCTs of 6-week group interventions for CLBP delivered in the Irish health service [32-33], and comparable to the ESCAPE-knee pain intervention in the UK health service . However, the small class sizes with an average of four participants rather than our target of six and inconsistent participant attendance placed demands on the practicality of PTs delivery of the intervention with high fidelity , and thus challenge the viability of a future definitive trial of this intervention and its future implementation within the health system, as discussed below.
Feasibility: Trial recruitment, retention and follow-up procedures
The trial was successful in recruiting 14 clusters demonstrating the strong partnership between the research team and PCCC areas established during the development phase . Nonetheless, four clusters withdrew consent after randomisation and treatment allocation for reasons unforeseen at the outset of the trial (i.e. proximity to other clusters and non-availability of suitable participants), and which are partly due to the time lag of at least 9 months between randomisation and commencement of the trial in some of these sites. Overall, 21% of potential participants sent invitation letters were recruited, which is within the range of other trials of group-based programmes for these populations [15, 32-35]. Furthermore, the recruitment protocol successfully enrolled participants with OA of the hip, knee, lumbar spine and CLBP, with the latter being the most prevalent in line with population data. In contrast to the FASA intervention, which restricted recruitment to individuals with OA aged at least 50 years , our findings have demonstrated the feasibility of enrolling and retaining younger participants with CLBP to a group-based programme alongside older people with OA. Nonetheless, the average cluster size of five participants in both arms, the average class size of four participants and the overall recruitment rate were below the target of 144 required to demonstrate feasibility, but enough for a sample size calculation for a definitive trial as discussed below.
Despite the recruitment protocol being embedded within the health system and developed in partnership with PTs , several challenges beyond our control impacted upon its success. First, the research ethics committee requirement that potentially suitable participants contact study staff resulted in a 66% response to the invitation letter. Second, the need for individual participant consent for data collection prior to enrolment rather than employing a more pragmatic service-based quality improvement protocol that would have automatically enrolled all patients at the cluster level negatively impacted on our ability to reach our target population. Third, participant recruitment was outside routine PT practice and was conducted by non-clinical research PTs thus potentially increasing the complexity for patients in accessing physiotherapy.
Despite increases in the recruitment rate, cluster size and response to invitation letters across waves as study procedures were improved, further protocol changes would be required to ensure recruitment targets and the optimal class size of six are achievable in any future definitive trial. For example, the time-consuming paper-based exclusion of most referrals for physiotherapy due to diagnosis and age is not an effective use of trial resources or feasible for a definitive trial. Recruitment efficiency would be increased if computer-generated identification codes were available in Ireland’s health service as in other jurisdictions. Furthermore, despite high levels of reported participant satisfaction and acceptability of the SOLAS intervention, some of the main reasons for excluding participants at the phone screen stage were their preference for individual PT, their inability to commit to the 6-week class and their poor English fluency, which challenge the feasibility of a future definitive trial within Ireland’s public health system. The high percentage of potentially suitable participants expressing a preference for individual treatment is an accurate reflection of the real world setting in which SOLAS would be offered to interested patients in future clinical practice and illustrates that a definitive trial based on individual patient randomisation would not have a higher likelihood of successful recruitment than the cluster design utilised in this feasibility trial. Further pragmatic obstacles to individual participant randomisation in a definitive trial are the inconsistency in the availability of sufficient physiotherapists within these relatively small PCCC clinics (1-3 musculoskeletal PTs per clinic) who could provide both treatment arms independently, and the need to train 2 PTs per site in the SOLAS arm to mitigate against frequent maternity, parental, sick and study leave who are not replaced if staff are absent.
Since the completion of this trial, the importance of patient and public involvement (PPI) in research has become increasingly recognised in Ireland [36-37]. Therefore, the development of a revised recruitment pathway for a definitive trial would warrant further PPI engagement to address barriers and optimise enablers to participation in the group-based class arm in particular [38-40].
The response rate at 2 months was acceptable but the 6-month response rate at 72% was below the assumed loss to follow-up rate of 25%. It is likely that despite the support of our researcher and the preference of the majority of respondents for telephone follow-up, the average 41 minutes to complete it at 2-months and the addition of the CSRI at 6 months were off putting to some non-respondents. Therefore, the number of follow-up points and multiple outcome measures that accounted for each joint condition and the complex behaviour change process would need to be reduced to maximise response rates and optimise follow-up procedures for a future definitive trial as discussed below. Furthermore, an additional strategy to protect against loss to follow-up would be to offer a telephone interview to collect data points required for analysis of the primary outcome only, in the case of participant non-response.
Feasibility: design of a definitive trial
The above findings inform the most efficient and effective study design for any future definitive trial. Some expert trialists have raised problems with the cluster trial design due to compromised concealment of allocation and improper randomisation (i.e. clusters are recruited and randomised and then participants are enrolled as occurred in this feasibility trial causing differential recruitment and imbalance between groups) , arguing in favour of individual participant randomisation . There is no evidence that the SOLAS feasibility trial displayed selection bias as the recruitment rate and cluster size were comparable between arms across the three study waves, the two arms were balanced at baseline for all sociodemographic variables for both participants and physiotherapists and there was minimal crossover from the Intervention to the Control arms during the treatment phase (i.e. n=1 participant), indicating minimal contamination. Nonetheless, the authors have considered the feasibility of incorporating recommendations to cluster trial recruitment processes to minimise these challenges in the design of a future definitive trial . These include the screening and enrolment of all participants prior to cluster randomisation or (if this is not possible) the randomisation of clusters after the enrolment of the first participant. While ideal these solutions would be challenging in Ireland’s health system due to the nature of the SOLAS intervention (i.e. the impossibility of blinding PTs and the 2 month lead in time for PT training that would cause lengthy waiting times for participants after cluster randomisation), and the complexity of the multi-stakeholder recruitment process described previously. A further recommendation to use blinded independent recruiters who are separate from the allocation process  could be used in a definitive trial with greater resources than our feasibility trial where staff involved in the central recruitment processes were blinded to the cluster allocation of individual participants and followed the same protocol regardless of cluster allocation.
In determining the proposed sample size for a definitive trial based on our secondary outcome results, the authors selected the SF12-PCS as the primary outcome with a primary endpoint of 6 months based on other RCTs of self-management for chronic musculoskeletal pain and other chronic conditions [43-44]. The minimal clinical important change for the SF12-PCS is reported as 3.2 , giving an estimated sample size for a definitive trial using a cluster design with a cluster size of six, using the observed cluster ICC (conservatively, 0.01) and estimated standard deviation for baseline-adjusted 6-month SF12-PCS (8.49), a definitive trial would require 117 participants per arm to achieve 80% power at a type I error rate of 0.05. A further increase of at least 25% of this sample size target would be required for retention at 6 months as discussed above resulting in a recruitment target of 156 participants per arm. Based on the previously discussed challenges to the recruitment, retention and follow-up of participants in this feasibility trial at both the cluster and total sample size levels, the likelihood of reaching this recruitment target in a definitive trial in Ireland’s health system is low.
Changes in secondary outcomes
The finding of comparable small effects for both SOLAS and individual PT for the majority of secondary outcomes is consistent with our rapid review  and other systematic reviews of education and exercise SM programmes for OA  and LBP . The larger improvements in pain intensity in the UP group at 2 months and in LBP-related functional disability at 6 months could be associated with the multi-modal treatments utilised targeting analgesia, including clinical guideline endorsed manual therapy . A recent trial of SDT-driven individual physiotherapy for LBP found limited effects for pain, function or quality of life compared to usual PT, with similar group differences to the current study . The minimal change in the WOMAC-physical function subscale for OA hip or knee participants may reflect its poor responsiveness compared to other measures or physical performance tests and warrants omission in any future definitive trial , with the use of only the SF-12 for all diagnostic subgroups to further reduce respondent burden.
The SOLAS intervention maximal dose of nine hours over 6 weeks, which was agreed with PTs during the development phase and found to be acceptable in this feasibility trial, is relatively low compared to other group-based interventions (including FASA) that have shown larger between and within group effects on pain, function and quality of life outcomes for OA knee [15, 47-48]. Conversely, clinical LBP guidelines recommend group-based exercise programmes that promote self-management but were unable to recommend the intensity of the programme .
SOLAS process model of behaviour change
The effect of the intervention on LBP-related determinants was minimal, with weak effects in the full sample for pain catastrophizing and no effect on fear at completion of the 6-week programme [5, 49]. The measurement of fear avoidance may have been underestimated due to the use of the 6-item activity avoidance subscale of the TSK 11  to reduce respondent burden. Nonetheless, it is proposed that these variables should be removed from the process map of behaviour change given their tentative evidence, its complexity and the multi-joint focus of the intervention.
In line with the assumptions of SDT, there were small changes in participants’ perceived competence and motivation for both PA and self-management that favoured SOLAS at week six, but these changes alone were not enough to promote long term increases in participant behaviour. These findings are consistent with previous literature and suggest sustained increases in autonomous motivation may be required for behaviour change [51-52]. Although PTs underwent training and were deemed competent to deliver SOLAS within the feasibility trial, they struggled to effectively utilise specific strategies related to goal setting [25-26]. This is noteworthy as a collaborative goal-setting process between a health care professional and patient is likely to be important in increasing and sustaining a patient’s autonomous motivation and competence for the particular behaviour [53-55]. Additionally, some PTs in the qualitative interviews felt they needed further training to augment their use of autonomy supportive language (i.e., flexible and suggestive rather than pressurising language) when delivering SOLAS, an important communication technique for promoting autonomous motivation . This requirement was reinforced by independent observers who rated PTs' average use of autonomy supportive language as moderate (4.2 on a 7-point Likert scale) .
The small increases found in subjectively measured PA and in the SM behaviours related to PA within SOLAS up to 2 months provide preliminary evidence of its effect on these behaviours. PTs overall moderate fidelity to the intervention BCTs and their inability to deliver all 26 BCTs targeting PA within the trial may have contributed to these small effects . If a definitive trial is to take place, first, the core intervention BCTs must be identified and second, training enhancements are required to target PTs’ use of particular BCTs.
The limitation of self-report measures of PA is well recognised in the literature, due to recall bias, social desirability bias and poor correlation with objective measures . There is currently no evidence that an increase in self-reported PA is associated with improvements in pain and disability outcomes for OA  and LBP , but the quality of current research is low, the majority of current interventions lack a strong theoretical basis and have failed to evaluate treatment fidelity and the findings of the current study shed some light on these elements for future interventions targeting PA.
The higher use of mental relaxation techniques in the SOLAS group at 2 and 6 months may reflect the greater focus on the uptake of these skills within the Intervention, and may be associated with the consistent small reductions in HADS subscale scores in favour of SOLAS, suggesting the relatively short time focusing on this SM skill could be increased given the moderate levels of anxiety and depression of the sample at baseline. Conversely, the marginally lower use of pain relief techniques in the UP group at 2 and 6 months could be related to the greater reduction in pain intensity at 2 months in this group.
The major strengths of this feasibility trial relate to the use of a comprehensive range of quantitative and qualitative methods and the inclusion of a high number of clusters across a range of sites and geographical areas to address clearly defined feasibility objectives and a priori criteria for moving to a definitive trial from both participant and PT perspectives. The design of the feasibility trial was guided by the MRC framework, underpinned by behaviour change theory and extensive stakeholder engagement, and its reporting conforms to CONSORT guidelines for feasibility  and cluster trials  (see Additional file 13). There were also some limitations that should be acknowledged including the unforeseen withdrawal of consent of four clusters after treatment allocation, below target recruitment rate and the high number of secondary outcomes that probably contributed to the below expected response rate at 6 months. While adherence to the intervention SM skills (apart from specific exercise) were measured by an unvalidated researcher-designed questionnaire, consistent with many similar studies , the qualitative participant interviews of participants enactment of SM skills supported these findings and could contribute to its future validation. A self-report measure was used to assess participant PA, the inclusion of a user-friendly low-cost objective measure of PA in any future definitive trial is warranted. It was not possible to blind participants or PTs due to the nature of the study and we did not interview participants who did not complete the 6-month follow-up or those with low attendance rates.