A two-arm, double-blind randomized controlled clinical trial will be conducted. 140 patients will be recruited in two study centres and will undergo a clinical assessment to assess potential eligibility for the study. Potentially eligible patients who consent to participate will undergo arthroscopy and those with arthroscopic evidence of capsulolabral damage will be randomly allocated during the procedure into one of two groups: a stabilization surgery group and a control group. The primary outcome (pain and functional impairment) and secondary outcomes (participant-reported improvement and number of shoulder dislocations sustained) will be evaluated at baseline and 6, 12 and 24 months after randomization. Additional secondary outcomes of shoulder rotation range of motion and strength will be evaluated at 6 months after randomization. Ethics approval to conduct this study has been granted by the NRES Committee London-Stanmore and NRES Committee Wrightington, Wigan and Leigh.
Patients over 18 years of age of all activity levels will be eligible to participate if they report insecurity (apprehension) at the shoulder joint, have physical signs of shoulder instability (provocation of apprehension with drawer and apprehension tests), and have evidence of capsulolabral damage in the shoulder joint on arthroscopic examination. Damage to the capsulolabral complex includes any splits, fraying or detachment of any region of the glenoid labrum including the superior labrum. Patients will be excluded if they have a history of a high collision shoulder injury precipitating their apprehension symptoms, evidence of bony injury around the glenoid rim and/or humeral head or rotator cuff tear on arthroscopic examination, neural damage affecting the upper limb, or previous shoulder surgery. Prior physiotherapy treatment will not exclude eligible patients from participating in this clinical trial.
Potential participants will be identified from patients attending clinics conducted at the participating hospitals. Experienced clinicians in these clinics will inform potential participants of the clinical trial and provide them with information regarding the trial in the form of a written information sheet. With the patient’s permission this clinician will forward contact information to the research team. An experienced research assistant, who will be a registered health professional, will contact the potential participant to discuss the purpose of the study and to answer any questions this patient may have regarding the study. The research assistant will them seek written consent from those who volunteer to participate.
140 participants will be recruited and randomly allocated to either a:
stabilization surgery group (70 participants). Participants in this group will receive an arthroscopic investigation of the shoulder joint followed by arthroscopic stabilization surgery and postoperative physiotherapy rehabilitation.
control group (70 participants). Participants in this group will receive an arthroscopic investigation of the shoulder joint followed by postoperative physiotherapy rehabilitation.
All potentially eligible patients will undergo arthroscopic examination of the shoulder under general anaesthetic. Arthroscopy is the gold standard for diagnosing subtle capsulolabral lesions at the shoulder [21, 22]. The patient will be prepped and draped on the operating table in the beach chair position. A 1 cm incision will be made over the back of the shoulder joint and a metal trochar used to penetrate the joint capsule. An arthroscope will be introduced into the joint. Another 1 cm incision will be made over the anterior aspect of the joint and a metal probe introduced into the joint to palpate and move intra-articular structures in order to fully assess the joint. The arthroscope will then be replaced through the front of the joint in order to visualize the posterior joint structures.
Following confirmation that the patient is eligible to participate in the trial surgery theatre staff will open a pre-prepared sealed envelope identifying group allocation for each participant and inform the surgeon if stabilization is to proceed. To ensure blinding of the participants, physiotherapy staff associated with post-operative care and research assistants, the surgeon and theatre staff will be asked not to reveal group allocation (i.e., whether stabilization surgery was performed) to anyone associated with the study.
Participants allocated to the stabilization surgery group will undergo capsular plication and labrum repair surgery as appropriate. Capsular plication surgery will involve the placement of suture anchors into the bony glenoid with sutures passed through the shoulder joint capsule to secure the redundant capsule to the glenoid fossa, effectively ‘tightening’ the joint. Labrum repair will be performed using standard suture anchors incorporating the plication where appropriate. All participants will receive the same post-operative clinical care from the surgical team to monitor progress and deal with any complications that may arise. Standard care includes review at 1, 3 and 6 months post surgical examination/intervention.
All participants will receive the same post-operative physiotherapy protocol aimed at improving shoulder muscle function based on a pre-prepared treatment algorithm. All participants will be immobilized in a sling for four weeks following the surgical procedure but will be allowed to perform controlled scapular and glenohumeral joint movements within ranges which would not compromise a capsulolabral repair. Thus restrictions on post-operative treatment to protect the surgical procedure will apply to all participants. Thereafter, the aim of physiotherapy treatment will be to improve the function of the rotator cuff muscles by an active home-based exercise program. The treatment algorithm allows the physiotherapist to choose specific exercises directed to the rotator cuff or to improve their function by incorporating exercises which involve the entire kinetic chain. To ensure accurate exercise performance multimodal feedback (visual, biofeedback, taping) can be utilized. The type, load and frequency of exercises will be individually tailored to the needs of each participant by the physiotherapist who will monitor and upgrade the exercises as rotator cuff muscle function improves. A maximum of 12 treatment sessions with the physiotherapist over a maximum period of six months after surgery will be conducted.
Primary outcome measure
Pain and functional impairment, measured using the Western Ontario Shoulder Instability Index (WOSI), will be the primary outcome. The WOSI is a disease specific, self-administered questionnaire consisting of 21 items assessing the physical symptoms associated with shoulder instability (10 items) as well as the impact of shoulder instability on sport/recreation/work (4 items), lifestyle (4 items) and emotional state (3 items). It was rigorously developed using patient input, demonstrates good construct validity and excellent reliability and is responsive to change .
Secondary outcome measures
Data on four secondary outcomes will be collected:
global perceived effect assessing participant-reported improvement measured on an 11 point scale from −5 (“vastly worse”) to +5 (“completely recovered”) .
active external and internal shoulder rotation range of motion measured using digital photography [24–26] This method was chosen over goniometry as it is less likely to exacerbate shoulder symptoms due to the shorter time required to complete measurements.
isometric external and internal shoulder rotation strength measured using a hand-held dynamometer which has been shown to exhibit acceptable reliability when tested on patients with strength deficits 
number of episodes of post-operative shoulder dislocation. An episode of shoulder dislocation will be defined as separation of the articular surfaces of the shoulder joint which require assistance to be relocated.
All outcome measurements will be re-assessed 6 months after randomization by a research assistant who will be blind to treatment group allocation. At 12 and 24 months after randomization pain and functional impairment, participant-reported improvement and number of shoulder dislocations sustained will again be re-assessed by a blinded assessor.
The sample size was calculated assuming a 10.4% change on the WOSI given a standard deviation of 18% change, a significance level of 5% and assuming a 10% (worst-case) loss to follow-up. A 10.4% change in total WOSI score represents the minimally important change required to represent a clinically significant improvement . This is a conservative sample size estimate as it ignores the additional power conferred by the longitudinal analysis that is to be used in this study.
An allocation assignment schedule will be prepared prior to commencement of the clinical trial using random numbers generated with the ralloc command in the Stata statistical package . The random allocation schedule will be prepared by a member of the research team not associated with identification of potential participants or any aspects of recruitment, treatment or assessment of participants, and will remain concealed until the analysis is complete. Allocation will be in randomly permuted blocks.
Participants in this clinical trial will be subjected to the risks associated with orthopaedic surgery under general anaesthesia. However, participation in this clinical trial will not entail additional risks beyond those associated with standard care options for atraumatic shoulder instability at the clinical sites involved in the study. Information regarding adverse events will be monitored throughout this clinical trial and reported on a regular basis to the Trial Management Group and Steering Committee associated with the Stanmore Clinical Research Centre. Both closed and open questioning will be utilized to seek information from participants and physiotherapy staff involved in post-operative treatment, all of whom will be unaware of whether stabilization surgery was performed.
One interim analysis of efficacy will be conducted when 50% of the estimated sample has completed one year follow-up assessment. The decision to continue the trial or stop the trial early will be made by the Trial Management Group and Steering Group, informed by an analysis of the Haybittle-Peto boundary . The p-value threshold for this interim analysis will be set at 0.001. The final analysis will be evaluated at the significance level specified in the sample size calculation i.e. p < 0.05.
The primary analyses will be conducted on an intention-to-treat basis. The focus will be on estimation of the effect  at 2 years, but hypothesis tests will also be conducted. Between-group comparisons will be conducted using a linear model in which the outcome is a linear function of a dummy-coded variable representing group membership (stabilization surgery or control group) and baseline score . For the outcomes of pain and functional impairment, participant-reported improvement and incidence of shoulder dislocations, all of which are measured at baseline and 6, 12 and 24 months, mixed models will be used. The mixed models will incorporate a random intercept for subject. A negative binomial model will be used to analyze data on the incidence of dislocations. A sensitivity analysis will be conducted in which multiple imputation is used to account for missing data [33, 34].