Cortisol is a hormone that increases after trauma or surgery and has circadian rhythm. It has a form that is increased in the morning and decreased in the evening. The investigators expected to be influenced by circadian rhythm according to the time of operation, and compared morning and afternoon surgery.

44 patients to undergo hip hemiarthroplasty or total hip replacement were divided to morning surgery group(Group A) and afternoon surgery group(Group P). All surgery was done by the same orthopedic surgeon. Anesthesia of Group A was started at 8 a.m. and Group P was at 12~2 p.m. Blood sampling was performed at 7:30 a.m., after induction of anesthesia, 6, 12, 24 and 48 hours after surgery in all patients of both groups. Cortisol, IL-6, and IL-8 was measured immediately after blood sampling. Visual analogue scale(VAS) was used to assess the degree of pain at before start of anesthesia, 6, 12, 24 and 48 hours after surgery. The postoperative hospital stay was calculated. Postoperative management was done by the same management team. Surgical wounds were treated at the same 24 hour intervals.

A sample size was calculated to differentiate between groups. Because difference of cortisol according to groups in ANOVA based on pilot study, the sample size was 20 patients per group. (Effect size f(v)= 0.5297047, α=0.05, 1-β=0.90) The investigators recruited total 44 patients to cover dropout 10%.

Inclusion Criteria:

• Patients scheduled for hip hemiarthroplasty
• Patients scheduled for total hip replacement

Exclusion Criteria:

• Sleep disorder
• Mental disorder
• Psychiatric medication