**5. Material and methods**

### **5.1 Patients**

In two studies, we investigated 58 total hip arthroplasties revised for aseptic loosening or high rate of wear of the polyethylene (40 hips) and osteolysis (12 hips) in order to clarify the involvement of ROS in the process of aseptic loosening.

Between August 1999 and October 2002, periprosthetic tissues were consecutively obtained at revision of 40 primary THAs at the Department of Orthopedic Surgery, Medical University of Graz. Group I consisted of 8 men and 20 women, with mean age 66 years (range, 32–88 years) at the time of revision. The mean interval between primary THA and revision was 126 months (range, 11–320 months). In Group II, there were three men and nine women with mean age 69 years (range, 54–84 years). In this group, the mean interval between primary THA and revision was 97 months (range, 14–157 months) (p=0.405). As a control group, 16 samples of fascia lata were obtained from 16 patients during primary THA.

In a second study, periprosthetic tissues and pseudosynovial fluid were obtained at revision of 18 consecutive primary THA performed at the Department of Orthopedics and Traumatology, Medical University of Sofia. The eight men and 10 women in the series had mean age 63.2 years (range, 52 to 78 years) at the time of revision. The mean interval between primary THA and revision was 10.8 years (range, 2.1 to 22.3 years). The pseudosynovial fluid was immediately deep frozen at –80°C until analysis. The periprosthetic samples were fixed in 10% formalin until being processed. Patients with multiple revisions and infections were excluded from the studies. As a control group, 18 samples of joint fluid were obtained from 18 patients during primary TKA.
