Here is the design of a clinical trial:

Official Title: A Modified Placement of Two Additional Pedicle Screws at the Fracture Level for the Treatment of Thoracolumbar Burst Fractures--a Study Protocol of a Randomised Controlled Trial

Included conditions:
- Posterior Short-segment Pedicle Instrumentation

Study Armgroups:
- {'label': 'Screw-Distraction (SD) group', 'type': 'PLACEBO_COMPARATOR', 'description': 'six pedicle screws were implanted firstly, then distraction was achieved.', 'interventionNames': ['Device: fractured level screws-distraction']}
- {'label': 'Distraction-Screw (DS) group', 'type': 'EXPERIMENTAL', 'description': 'four pedicle screws were implanted firstly, then distraction was achieved, two additional screws were introduced at the fracture level at last.', 'interventionNames': ['Device: fractured level screws-distraction']}

Interventions:
- {'type': 'DEVICE', 'name': 'fractured level screws-distraction', 'description': 'four pedicle screws were implanted into the upper vertebra and the lower vertebral body of the fractured vertebra. Then, immediate reduction and decompression were achieved by applying distraction of rod. Finally, two additional screws were introduced at fracture level', 'armGroupLabels': ['Distraction-Screw (DS) group', 'Screw-Distraction (SD) group']}

Primary Outcomes:
- {'measure': 'compression ratio change of anterior border of vertebral body height', 'description': 'using X-ray fluorescence', 'timeFrame': 'preoperatively, intraoperatively, on day 3 postoperatively and then at 1, 3, 6, 12 and 24 months postoperatively'}
- {'measure': 'Depth of nail into injured vertebrae', 'description': 'using X-ray fluorescence', 'timeFrame': 'at postoperation immediately'}
- {'measure': 'Kyphosis (Cobb) angle change', 'description': 'using X-ray fluorescence', 'timeFrame': 'preoperatively, intraoperatively, on day 3 postoperatively and then at 1, 3, 6, 12 and 24 months postoperatively'}

Please estimate the sample size based on the assumption: 
Type I error probability of 5%, 80% power, and a 20% dropout rate.
Sample size calculation
        As no previous similar trial has been conducted using our RCT design, we performed a power analysis to determine the sample size required to show safety with a type I error probability of 5% and an 80% probability of avoiding a type II error. In related studies,18 19 the mean of the control group was 0.891 and the mean of the intervention group was 0.914 (Ï=3 was adopted). We carried out two independentÂ samples t-tests using the Power Analysis and Sample Size software and obtained a result of 28. We propose to enrol 56 participants (28 randomised to each arm) and suggest recruitment of an effective sample size of at least 70 participants to allow for a 20% drop-out rate.