Here is the design of a clinical trial:

Official Title: Prospective Evaluation of Non-Surgical and Arthroscopic Treatment for Hip Microinstability

Included conditions:
- Musculoskeletal Abnormalities
- Hip Injuries

Study Armgroups:
- {'label': 'non-surgical treatment', 'type': 'OTHER', 'description': 'All participants will undergo 6 months of non-surgical treatment.', 'interventionNames': ['Procedure: physiotherapy']}
- {'label': 'arthroscopic treatment', 'type': 'OTHER', 'description': 'Those participants with failed non-surgical treatment at 6 months will undergo arthroscopic treatment.', 'interventionNames': ['Procedure: physiotherapy', 'Procedure: arthroscopy']}

Interventions:
- {'type': 'PROCEDURE', 'name': 'physiotherapy', 'description': 'Six months physiotherapy aimed at hip stability.', 'armGroupLabels': ['arthroscopic treatment', 'non-surgical treatment']}
- {'type': 'PROCEDURE', 'name': 'arthroscopy', 'description': 'Arthroscopic plication of hip joint capsule.', 'armGroupLabels': ['arthroscopic treatment']}

Primary Outcomes:
- {'measure': 'Mean Change from Baseline in Hip Function on the International Hip Outcome Tool (iHOT-12) at 24 Months', 'description': 'Participant-reported hip function. Minimum score 0, maximum score 100 (higher score mean a better outcome).', 'timeFrame': '24 Months'}
- {'measure': 'Mean Change from Baseline in Hip Function on the Copenhagen Hip and Groin Outcome Score (HAGOS) at 24 Months', 'description': 'Participant-reported hip function. Minimum score 0, maximum score 100 (higher score mean a better outcome).', 'timeFrame': '24 Months'}
- {'measure': 'Mean Change from Baseline in Maximal Isometric Hip Muscle Force in Newton at 24 Months', 'description': 'Maximal hip isometric muscle force will be assessed using a dynamometer (Hoggan MicroFET2, Hoggan, Scientific L.L.C., Salt Lake City, USA) for hip flexion, adduction, abduction, and extension. The maximal developed force in Newton will be recorded. Higher Newton value means a better outcome.', 'timeFrame': '24 Months'}
- {'measure': 'Mean Change from Baseline in Hop Performance at 24 Months', 'description': 'Hop performance will be measured with 3 single-leg hops: vertical hop (Muscle lab, Ergotest Technology, Oslo, Norway), hop for distance and a 30-second side-hop test. Each hop test is performed with the patients holding their hands behind their back. For the vertical hop, the time from take-off to landing is converted into hop height in centimeters. In the hop for distance test, the distance between top of the toes at take-off to heel at landing is measured in centimeters. For the 30 second side hop test, one trial per leg is allowed, where the patient is instructed to hop as many times as possible over 2 lines 40 centimeters apart. The number of hops is recorded. Higher height, longer distance and higher number of hops means a better outcome.', 'timeFrame': '24 Months'}

Please estimate the sample size based on the assumption: 
power 80%, significance level (alpha) 0.05, standard deviation (sigma) 25.5
Sample size calculation
        Based on previous results of arthroscopic hip preservation surgery, for the comparison of pre- and post-treatment hip function, a minimum sample size of 26 patients for each treatment group is needed to reach a power of 80% with the iHOT-12 (sigma 25.5, alpha 0.05, effect size 20) [30].