The primary hypothesis that orthopaedic surgery induces a neuroinflammatory response within 48 hours after elective hip or knee surgery and that there is an association between exaggerated CNS inflammatory response or impaired inflammatory resolution and postoperative cognitive dysfunction within one week and at three months postoperatively.

Patients at 50-85 years of age undergoing orthopedic surgery will be investigated in the perioperative period to detect signs of neuroinflammation using serial CSF and blood sampling for 48 hours in combination with cognitive testing preoperatively, at 3-7 days and after 3 months.

Inclusion Criteria:

• ASA Physical Health Class 1-4
• Age 50-85 years
• Fluent in Swedish language
• Scheduled for primary hip replacement surgery due to arthrosis
• MMSE (minimental state test score >= 25.

Exclusion Criteria:

• Patient refusal to participate in the trial
• Current autoimmune disease, including arthritis
• Ongoing smoking, snuff or other nicotine compound treatment
• Significant neurologic or psychiatric disorder (such as Alzheimer's disease, Parkinson's disease, Multiple sclerosis, schizophrenia, depression, diagnosis of dementia or cognitive impairment as defined by a preoperative MMSE score ≤ 24
• History of stroke with neurological sequelae.
• Current severe cardiac (NYHA>IV) or renal (plasma creatinine> 0.250 mmol/l) Coagulopathy making spinal anesthesia and intrathecal catheter placement impossible
• Terminal phase of a chronic disease.
• Patient on chronic steroidal therapy
• Poorly controlled diabetes mellitus.
• Presumed uncooperativeness or legal incapacity.

34 elective orthopedic patients undergoing hip or knee arthroplasty