Here is the design of a clinical trial:

Official Title: Efficacy of Tofacitinib in Reduction of Inflammation Detected on MRI in Patients With Psoriatic ArthritiS PresenTing With Axial InvOlvement - a Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial

Included conditions:
- Psoriatic Arthritis
- Spondylitis
- Sacroilitis

Study Armgroups:
- {'label': 'Tofacitinib', 'type': 'ACTIVE_COMPARATOR', 'description': '5 mg oral BID', 'interventionNames': ['Drug: Tofacitinib 5 MG Oral Tablet [Xeljanz]']}
- {'label': 'Placebo', 'type': 'PLACEBO_COMPARATOR', 'description': 'matching Placebo BID', 'interventionNames': ['Drug: Placebo oral tablet']}

Interventions:
- {'type': 'DRUG', 'name': 'Tofacitinib 5 MG Oral Tablet [Xeljanz]', 'description': 'verum tablets', 'armGroupLabels': ['Tofacitinib'], 'otherNames': ['Xeljanz']}
- {'type': 'DRUG', 'name': 'Placebo oral tablet', 'description': 'tablets containing placebo', 'armGroupLabels': ['Placebo']}

Primary Outcomes:
- {'measure': 'MRI Berlin Score', 'description': 'Improvement of the Berlin MRI score for sacroiliac joints and spine. Scoring includes spinal inflammation (Lucas C et al, J Rheumatol 2007): 23 vertebral units with semiquantitative range of inflammation between 0 to 3 (min. score = 0, max. score = 69, the higher the worse). Additionally, inflammation of the sacroiliac joints is scored (Hermann KG, Rheumatologe 2004; scoring each quadrant between 0 and 4, max. score 16, the higher, the worse).', 'timeFrame': 'Week 12 vs Baseline'}

Please estimate the sample size based on the assumption: 
Power of 80%, significance level (alpha) of 0.05, and an anticipated standard deviation (SD) of 3.0. Consideration of dropout and protocol violations.
Sample size calculation
        The sample size is calculated based on results from phase II study with tofacitinib in patients with radiographic axial SpA.27 Treatment with tofacitinib 5âmg two times per day was associated with a mean (SD) absolute reduction of the Berlin MRI osteitis score for the spine (range 0â69) of 2.2 (0.4) points as compared with a reduction of 0.4 in the placebo group after 12 weeks. We assume that in patients axial PsA who treated with tofacitinib, a mean reduction of at least 2.5 points of the total MRI osteitis score including spine and SIJs (range 0â93) at week 12 as compared with baseline will be achieved, while a mean 0.5 points reduction is anticipated in placebo-treated patients. In order to demonstrate a significant difference between tofacitinib and placebo groups using the two-sample t test for the mean difference with the power of 80% and alpha=0.05 (anticipated SD=3.0), at least 74 patients (37 per arm) should be included in the analysis set. Considering some uncertainty in the effect estimation in the given patient population, and some expected dropout and protocol violations, we planned to include a total of 80 patients (n=40 per group) to demonstrate the expected treatment effect.