The primary aim of this study is to determine the efficacy of hip arthroscopic surgery compared to a sham surgery (diagnostic arthroscopy only) for patients with symptomatic and radiological findings related to impingement (FAI) and/or labral tears using a randomized controlled design (HIPARTI Study: Primary aim and the main paper: primary end point: iHOT 1 year follow-up)).

Our main hypothesis is that surgical procedures of the hip will demonstrate greater efficacy than sham surgery (diagnostic hip arthroscopy only) for hip related quality of life (iHOT-33) after 1 year and at further (HIPARTI Study).

The secondary aim of this study is to establish modifiable risk factors associated with pain, function, work participation and quality of life over 1 year in people aged 18-50 years with hip impingement and/or labral tears diagnosed at hip arthroscopy. (HARP Study: A separate paper will be published with this main aim for the HARP Study) Long-term follow-ups for HIPARTI Study as well as HARP Study will be performed at 2, 5 and 10 years (secondary aims and separate papers).

This is a multicenter, international, assessor and patient blinded clinical RCT with two groups (primary aim). the HIPARTI Study with The design of this trial conforms to the SPIRIT guidelines.

All patients with hip pain eligible for hip arthroscopy in our routine care pathways will be identified in our outpatient clinics. Consultant orthopedic surgeons will determine a patient's eligibility for the study (based on inclusion and exclusion criteria for the study) and members of their team introduce the study to the patients and refer them to the research coordinators for further information. Patients will be provided with oral and written information about the study and be introduced to our consent form. If interest continues the patient will be provided with further information and arrangements will be made for a baseline appointment for assessment and consenting.

The baseline assessment appointments will occur within one month of the initial approach. At the baseline appointment patients will meet with the research coordinator and the independent research assistant/tester (physical therapist) who will be the blinded tester. Patients will return their signed informed consent form and baseline questions completed. Those who are not willing to participate in the RCT (HIPARTI Study), will be asked if interested in being included in a prospective longitudinal cohort study including similar baseline and follow-up tests as those in the RCT (this will be the HARP Study with separate papers published). All patients in the HARP Study will undergo hip arthroscopy surgery. The Australian site will include most of their patients in the HARP Study, since the majority of orthopedic surgeons working privately will not participate in the HIPARTI Study. Data collection will be performed electronically for both the HIPARTI and the HARP Studies entering all data in the approved Checkware system (www.checkware.no).

Each collaborating center will apply to the ethical committee and the Data Inspectorate in each country/institution. Approval was confirmed for Oslo University Hospital (HIPARTI) and Australia (HARP Study) in January 2016.

Randomization (HIPARTI) will occur prior to surgery, after final eligibility is confirmed. Randomizations will be performed centrally using an automated computer generated system. Block randomization and stratification for each center will be performed.

All patients will undergo imaging (which may include CT scan or at least 1.5 Tesla magnetic resonance imaging MRI) prior to the surgical assessment as part of routine care. All patients will also undergo standardized radiographs of the hips and pelvis also as part of routine care. Plain radiographs will be examined for evidence of osteoarthritis as joint space narrowing, osteophytes, cysts and subchondral hypertrophy. Several radiographic measurements will be performed among them: the alpha angle and lateral center-edge angle will be determined for the presence of FAI. Radiographs will also be part of follow-ups.

Participating orthopedic surgeons will be asked to coordinate their waiting lists to ensure the hip arthroscopy patients are called for surgery in accordance with the study protocol. Ideally, patients will complete their baseline assessment as close to the randomized treatment as possible (within 1 months). In the event that surgery cannot be performed within 1 month after baseline assessment, the same questions and assessments completed at baseline will be completed again. The standard followed-ups at the 6 months and 1 year include primary and secondary outcomes. One year is the primary end point where randomization code will be broken according to a predefined published statistical protocol (HIPARTI).

At all follow-ups the research coordinator/independent tester will attend. At the 6 month follow-up an independent orthopedic surgeon will attend regularly and take care of patients who are not satisfied. The aim is to use the following criteria as subjective complaint: equal or worse than 10 points for the IHOT-33 score compared to baseline. All patients can withdraw without giving a reason at any time (stated in the consent form that all patients need to sign). An unblinded orthopedic surgeon will of course be able to have access to the medical record regarding performed procedures at any time if need for the health of the patient.

All patients (in both groups in the RCT (HIPARTI) as well as in the HARP study) will undergo a postoperative rehabilitation program based on the best available evidence. Each patient will be treated by physical therapists who will be trained and proficient in post-hip arthroscopy rehabilitation. Rehabilitation will be delivered a minimum of 8 sessions over 3-months and then once a month for the following three months. Details of rehabilitation are outlined in Appendix Rehabilitation. This contains a treatment algorithm to guide clinical reasoning and progression of treatment (manual therapy, exercises and education) through weeks 1-12.

Long term follow-ups will be performed at 2, 5 and 10 years Due to lack of studies published within this field: clinical relevant differences as well as changes within groups and SD are difficult to estimate. Our sample size calculations are based on primary outcome iHOT 33 at 1 year: estimated effect-size to 0.6 and a power of 90, will give 60 in each group, and with expected 15% dropout will give 138 patients in total. Electronic randomization lists will be generated, and estimations of inclusion rates per site are included. Statistical analysis procedures will be published and analysis performed prior to opening the group allocation when all patients are included and followed through to the 1 year follow-up (main outcome).

Inclusion Criteria:

• hip pain during daily and/or spor t ing activities;
• intra-articular hip pain with radiological signs of FAI and/or labral tears eligible for hip arthroscopy (to be determined in a pragmatic fashion by the surgeon based on clinical examination and imaging
• the patient is able to give written informed consent and to participate fully in the interventions and follow-up procedures

Exclusion Criteria:

• pain that is not confirmed by physical examination of the hip
• evidence of preexisting osteoarthritis, defined as Tonnis grade >1, or less than 3mm superior joint space width on AP pelvic radiograph
• center edge angle on radiograph <25°; (v) previous known hip pathology such as Perthes' disease, slipped upper femoral epiphysis or avascular necrosis
• previous hip injury such as acetabular fracture, hip dislocation or femoral neck fracture
• previous hip surgery
• medical conditions complicating surgery (ASA 3); (ix) inflammatory joint disease (RA, Bechterew etc)
• physical inability to undertake testing procedures
• expected lack of compliance such as cognitive impairment, drug abuse or similar;
• inability to understand the written and spoken language of the treatment centre;
• contra-indications to placebo surgery, which will include large loose body, chondral flap >1cm2 detached at 3 sides, complete labral radial flap tear and labral bucket-handle tear with complete avulsion >1.5cm long

Data will be shared across the sites participating in the HIPARTI and the HARP Study, according to the protocol and the decisions made by the Advisory Committee

This is only for the RCT Study - the double-blinded study. The HARP study consists of only a prospective longitudinal study With same outcome measure and follow-ups; hence, given 3 arms. The below "Allocation" and "Number of Subjects" is ONLY for the RCT part of the study