The primary aim of this study is to examine if Periacetabular Osteotomy (PAO) followed by 4 months of usual care followed by 8 months of progressive resistance training (PRT) is superior to 12 months of a PRT intervention in patients with hip dysplasia eligible for PAO in terms of self-reported pain on the HAGOS questionnaire. Secondary aims are to investigate changes in patient-reported symptoms, physical function in daily living, physical function in sport and recreation, hip and/or groin-related quality of life, generic health status, functional performance, muscle strength, physical activity and adverse events between PAO followed by usual care+PRT compared to PRT only. We hypothesise that in patients with hip dysplasia, PAO followed by usual care+PRT, results in significantly less pain at 12 months follow-up, compared to PRT only.

Group 1 (PAO+usual+PRT):

PAO will be performed as the trans-sartorial approach or the anterior pelvic approach. Patients commence post-operative rehabilitation as usual and follow the rehabilitation program guided by a physiotherapist specialized in hip problems until 4 months after the operation. 4 months postoperative the patients complete usual care and continue with the same PRT intervention program as the PRT group, with 4 months of supervised sessions (see description below).

Group 2 (PRT):

The PRT group receives 4 months of supervised PRT 2 times per week. A physiotherapist or students will supervise all training sessions the first 4 weeks. The following 4 weeks, 6 out of 8 training sessions are supervised and from week 9-16, half of the training sessions (8 out of 16) are supervised. After these 4 months (16 weeks), patients receive a free membership to a fitness center near their home address and are encouraged to train on their own 2 times per week until 12 months follow-up with one supervised session per month. The PRT program involves 10-min of warm up followed by 50-min of bilateral resistance exercises including sets of loaded squats, hip extension, hip flexion, and hip abduction. The absolute training load will be individually adjusted on a set-by-set basis, using the plus two principle (if the patient is able to perform two or more repetitions than required, the load is increased). Hip related pain levels up to 5 on the VAS is considered acceptable during exercise.

The study is a multicentre randomised controlled and assessor blinded trial. Primary endpoint will be 12 months after initiation of surgical/non-surgical treatment. Secondary endpoints will be measured at 4 months after the start of the treatment (surgical/non-surgical). In addition, 5-year and 10-year follow-up with questionnaires is planned.

Inclusion Criteria:

1. Patients aged 18-45 years and diagnosed with hip dysplasia referred from primary care to the Department of Orthopaedic Surgery at one of the two participating hospitals.
2. Considered eligible for PAO by a surgeon.
3. Radiographic verified hip dysplasia (CE-angle <25 degrees and AI-angle >10 degrees) and clinical symptoms.
4. Range of motion: internal rotation >15 degrees, external rotation >15 degrees, hip flexion >110 degrees.
5. Able to commute to training sessions.

Exclusion Criteria:

1. OA degree ≥1 on classification of Tönnis'.
2. CE-angle <10 degrees.
3. Previous pelvic surgery for hip dysplasia (affected side).
4. Calvé Legg Perthes or epifysiolysis.
5. Simultaneous bilateral PAO.
6. Previous surgery for herniated disc, spondylodesis, arthroplasty of hip, knee or ankle.
7. Previous surgery of the hip (tenotomy of iliopsoas tendon, z-plastic of the iliotibial tract or hip arthroscopy) in index leg.
8. Neurological or rheumatoid diseases that affect the hip function.
9. Inadequacy in written and spoken Danish or Norwegian.
10. Body Mass Index (BMI) >25 in Aarhus and BMI >30 in Oslo and Odense

Aarhus University Hospital is responsible for handling all personal data provided by both sites in accordance to the Clinical Trial Agreement and the EU General Data Protection Regulation (GDPR).

End of study and 5 years ahead

Oslo University Hospital agree that information directly related to the protocol and trial, including data, material, Intellectual Property and results generated from the trial shall be the property of Aarhus University Hospital, and shall be treated in strict confidence, and shall not be disclosed to any third party, or use for its benefit or the benefit of any third party, without the prior written consent of Aarhus University Hospital, except for data that is (i) publicly known or available from other sources who are not under a confidentially obligation to the other party; (li) has been made available by the other party without confidentiality obligation; or (iii) is independently developed or otherwise already known by or available to the other party without a confidentiality obligation; or (iv) is already required disclosed by law.

Blinding