Evaluation of Uncemented Echo Bi-Metric Full Proximal Profile THA Stem Versus Uncemented Bi-Metric Porous Primary THA Stem in a Randomized Controlled Trial Using RSA and DXA

Material and Methods Hypothesis The uncemented Echo® Bi-Metric® Full proximal Profile THA stem shows less migration and less bone loss of the periprosthetic bone compared to the uncemented Bi-Metric® Porous Primary THA stem.

Operation All operations will be performed by 4 experienced hip surgeons from the Hip unit at the Department of Orthopedic Surgery, Gentofte Hospital, Gentofte, Denmark. Each of the surgeons performs approximately 120 THA-operations a year.

Surgery is performed according to a standard procedure with a postero-lateral approach and following the manufacturers' recommendations. During surgery a minimum of 4 Tantalum markers (0.8mm) are inserted in the bone of the proximal femur for defining the bone segment in the RSA analysis. All patients receive the same uncemented hemispheric acetabular cup (Exceed) with a highly cross-linked polyethylene liner. No local analgesic is injected. Physiotherapy begins on the day of surgery and the patients will be mobilized with full weight-bearing using crutches. All patients will get oral anticoagulants according to praxis of the department (Xarelto until discharge), and prophylactic antibiotics (Dicloxacillin, 2 g preoperatively and 1g x 2 postoperatively) during the first 24 hours.

Research plan

1. Clinical examination performed preoperatively and with follow-up after 1 and 2 years with evaluation of the hip function using the Harris Hip Score (HHS); HHS is a questionnaire in which the patients reveal their level of pain, function, mobility and range of motion.
2. Conventional X-rays: To evaluate possible aseptic loosening, all patients will have a standardized full pelvic antero-posterior X-ray and a lateral X-ray with fixed magnification both preoperatively, postoperatively, at the 2 years follow-up visit and at the 5 years follow-up visit. Radiolucent lines at the bone-implant interface and evidence of osteolysis will be measured on both recordings. The standard Gruen zones will be used to record radiolucency surrounding the femoral component and the acetabular zones described by DeLee and Charnley will be used to record radiolucency surrounding the acetabular component. The apparent thickness of the radiolucency within these zones will be recorded. Evidence of osteolysis (radiolucency >2mm thickness) in the periprosthetic tissue of the acetabular or femoral component will be considered a failure.
3. DXA analysis of the changes in BMD of the periprosthetic Gruen zones will be used to evaluate the adaptive bone remodeling after the implantation of the two different stems. DXA analysis will be performed preoperatively of the hip and proximal tibia as baseline, then again within the first postoperative week and subsequently at 3 months, 6 months, 1 year, 2 years and 5 years. The precision of the BMD measurements of the proximal femur will be estimated from double measurements of patients (n=12) included in the study.
4. MB-RSA measurements of migration of the femoral component. A MB-RSA system will be used; a technique in which the position of the prosthesis is assessed by matching a virtual projection of a 3D-model of the prosthesis to the actual radiographic projection. It does not require former times' special implants with attached markers. The patients will be x-rayed within the first postoperative week and subsequently at 3 months, 6 months, 1 year, 2 years and 5 years using 2 fixed X-ray tubes with the patient in supine position and a uniplanar calibration cage will be used. The precision of the measurements of migration will be estimated from sets of double X-rays of patients (n=12) included in the study.
5. Patient reported outcome measurements. It is planned also to ask the patients preoperatively and after 6, 12 and 24 months to do a patient-reported outcome measurement using the Oxford Hip Score (OHS).
6. Long term follow-up. 5-year follow-up including all above mentioned parameters will be performed.