Here is the design of a clinical trial:

Official Title: Efficacy of the Erector Spinae Plane (ESP) Block for Quality of Recovery in Posterior Thoraco-Lumbar Spinal Decompression Surgery: A Randomised Control Trial

Included conditions:
- Spinal Surgery

Study Armgroups:
- {'label': 'Erector Spinae Plane Block', 'type': 'ACTIVE_COMPARATOR', 'description': 'Patients will receive a ESP block with 20mls 0.25% Levobupivicaine bilaterally, pre incision plus standardised multimodal analgesia', 'interventionNames': ['Procedure: Erector Spinae Plane Block - Ultrasound guided']}
- {'label': 'Control', 'type': 'NO_INTERVENTION', 'description': 'no ESP block, standardised multimodal analgesia'}

Interventions:
- {'type': 'PROCEDURE', 'name': 'Erector Spinae Plane Block - Ultrasound guided', 'description': '20mls 0.25% Levobupivicaine ultrasound guided bilaterally', 'armGroupLabels': ['Erector Spinae Plane Block']}

Primary Outcomes:
- {'measure': 'QoR 15 score', 'description': 'a objective assessment of quality of recovery post surgery', 'timeFrame': '24 hours post operatively'}

Please estimate the sample size based on the assumption: 
Type I error = 0.05, Type II error = 0.2 (80% power), and an allowance for participant withdrawal.
Sample size and justification
        The primary outcome of this study will be the QoR-15 score at 24âh postoperatively. The established minimum clinically important difference in QoR-15 is 8.0 and the mean SD of QoR-15 scores after major spinal surgery is in the order of 14 [range of QoR score is 1â150]. Therefore, assuming type I errorâ=â0.05 and type II errorâ=â0.2 (80% power to detect this difference), then nÂ =â25 patients will be required in each group. To accommodate for participants who may withdraw from the study, we will aim to recruit nÂ =â26 patients to each study arm.