This study is exploring how a medicine called **dexamethasone** can help teenagers who have **adolescent idiopathic scoliosis (AIS)** and need a surgery called **posterior spinal fusion (PSF)**. Dexamethasone is a steroid, which is a type of medicine that can reduce swelling and pain. The study will look at how this medicine affects the **acute phase response (APR)**, which is how the body reacts to injury and starts healing.

Participants will be split into two groups. One group gets a single dose of dexamethasone during surgery, which is usual practice. The other group gets the same dose during surgery plus three more doses after surgery. The aim is to see if more doses help with less pain, less nausea, and a shorter hospital stay.

• The study will be done at Egleston Hospital during the patient's stay for surgery.
• Eligible participants are aged 10-18, undergoing PSF for AIS.
• Participants cannot be pregnant, prisoners, or have certain infections.