The aim of this study is to investigate the effect of a single preoperative high-dose steroid injection on complications in the immediate postoperative phase after periacetabular osteotomy. Primary outcome is the proportion of patients who have moderate to severe postoperative pain in the post anaesthesia care unit. Secondary outcomes are organspecific complications in the post anaesthesia phase, pain and nausea the first 5 days, wound infection and readmissions the first 30 days after surgery.

The investigators hypothesize that the frequency of moderate to severe pain and organspecific complications in the post anaesthesia care unit will be lower among patients receiving high dose dexamethasone. The investigators hypothesize, that there will be no difference in wound infections or readmissions.

Post-surgery, patients are traditionally observed and treated in post-anesthesia care units (PACU) until they are discharged to the ward (or directly home) assessed by standardized international discharge criteria.

The research project "Why in PACU?" (Rigshospitalet, Denmark), has since the beginning of 2016 systematically collected and analyzed procedure-related complications in the recovery phase. The complications include pain, nausea/vomiting, circulatory and respiratory problems, orthostatic intolerance and cognitive disorders. Common to all the above-mentioned post-operative problems are the possible links to the inflammatory response caused by the surgical trauma.

Glucocorticoids can in this context be central for the reduction of acute postoperative organ dysfunctions, caused by the anti-inflammatory effect. In a number of different surgical procedures, single dose, pre-operative glucocorticoids have been shown to reduce post-operative nausea and vomiting (PONV), acute pain and need of opioids as well as accelerate the convalescence.

Meta-analyses also showed that single-dose administration of glucocorticoids (methylprednisolone and dexamethasone) for surgical patients is safe as opposed to long-term treatment.

The "Why in PACU?" database shows that 70 % of patients experience moderate to severe pain in the immediate postoperative phase. This is despite a multimodal analgesic regime with preoperative analgesics and local analgesic catheter in the surgical site.

Opioids are frequently administered to relieve pain, resulting in sedation, risk of hypoxia and delaying mobilization.

Patients having Ganz osteotomy are primarily young women with hipdysplasia, that are otherwise healthy. Lenght of stay is typically 5 days, due to pain and lack of mobilisation.

In this study patients are randomized to either high dose (48 mg) or standard/low dose (8 mg) dexamethasone, administered preoperatively. The hypothese is that patients receiving high dose dexamethasone will experience less pain in the immediate postoperative course and receive less opioids.

The study is not placebo-controlled since the positive effects of dexamethasone 8 mg on PONV have been shown in numerous trials, and is already being administered to all patients at the clinic. It would therefore not be ethically correct to withdraw from this practise.

Inclusion Criteria:

• planned unilateral periacetabular osteotomy
• informed signed consent

Exclusion Criteria:

• Chronic/ongoing (<30 days) use of glucocorticoids (except inhalation therapy)
• ongoing (<30 days) use of immunosuppressive therapy
• insulin dependent diabetes
• pregnancy/breastfeeding
• allergies toward study medication, or medication in the standard treatment
• surgery cannot be performed

60 hours after administration of trial drug(collection of possible adverse drug reactions), for readmissions and woundinfections: 30 days.