The goal of this randomized controled trial is to compare if using of ancillary screws yields equal results as no use of ancillary screws in the ACE acetabulum cup of a total hip arthroplasty. Further, the migration of the Avanteon stem over time will be assessed. Patients included are patients with hip osteoarthritis from 65-80 years old. The purpose of this study is to compare implant migration and early fixation of a hybrid hip replacement combining the uncemented ACE acetabular component and the cemented Avanteon femoral stem, by using CT based Radiostereometric Analysis, a new innovative method for evaluating implant migration. Our study may predict the long term survival of the implants used.

Participants will go through total hip arthroplasty, and be followed by CT-RSA, plain x-rays and patients reported outcome measures.

Hip and knee osteoarthritis OA is one of the leading causes of disability worldwide. The lifetime risk of developing hip OA is estimated to be 25%, in people who reach the age of 85. Total hip replacement THR is considered to be a safe and reliable surgical treatment for end stage hip OA and was described as "Surgery of the century". One of the challenges in hip replacement surgery is to ensure the longevity and durability of the implants used. New implants are designed to improve the primary stability and long-term survival of the implant. Early failure of implants and the need for revision surgery, is a major concern. Revision hip replacement surgery is a surgical procedure with high rates of postoperative complications and overall re-revision rate of 15,8% within 1 year. In the Norwegian arthroplasty register 10 year failure rate of hip revision prostheses is 26%. Thus, the longevity and durability of implants is a continuous challenge in which the ultimate goal is to develop well-functioning implants which will last a lifetime.

The purpose of this study is to compare implant migration and early fixation of a hybrid hip replacement combining the uncemented ACE acetabular component and the cemented Avanteon femoral stem, by using CT based Radiostereometric Analysis, a new innovative method for evaluating implant migration. Our study may predict the long term survival of the implants used. This will be the first ever CT-RSA study in Norway and one of the first world-wide, evaluating hip implants.

Radiostereometric analysis RSA is a method used to measure implant migration and micromotion after joint replacement surgery, with high precision and accuracy. It is considered the gold standard for to assess migration in orthopedic implants. Early implant migration predicts later loosening, and failure of the implant. Subsidence of the femoral stem of more than 1.2 mm at 24m months is predictive of revision. Proximal migration of the acetabular component of up to 0.2mm is considered acceptable, 0.2-1mm is considered at risk, and above 1mm is unacceptable. RSA is thereby used as an early measure of longevity and durability of new implants. However, RSA is an expensive and time consuming procedure. It requires special equipment such as RSA cages, software, and special x-ray setup. It also requires specially trained personnel to do the examination. Loss of data due to occlusion of tantalum beads from metallic implants, is unavoidable in RSA. Over the last years CT-RSA has evolved to overcome some of the challenges of RSA. CT-RSA has been validated to have similar or even higher precision and accuracy than RSA in both hip and knee implant analysis.By using CT-RSA we can evaluate implant migration without the need for implant or bone markers, by using bone surface anatomy. One of the authors (FDØ) has recently shown that a vast decrease of effective radiation doses of CT-RSA in total knee arthroplasty yields equal precision in a cadaver study (publication in press). We assume this applies to CT-RSA of the hip as well. We therefore would like to perform a study on ultra low dose CT-RSA of hip implants, to evaluate the precision. This could have a major impact for future CT-RSA studies of the hip, since we potentially could reduce the effective radiation dose.

Previous cadaveric studies have shown that screw fixation increases initial stability of acetabular components. In long term, press-fit screwless fixation achieve sufficient stability.The use of augmented screw fixation may increase the risk of particle debris and osteolysis around the acetabular component. The use of ancillary screw fixation may thereby increase the risk of loosening, and need for major revision surgery. There is also a risk for iatrogenic damage to nearby vessels and pelvic organs, due to screw misplacement.

The Avanteon JRI is a highly polished double tapered femoral stem, designed by force-closed principles. The stem is intended to subside gradually in the cement mantle over time. Highly polished femoral stems have shown excellent results, and lower revision rates compared to shape-closed design stems. New implants are developed to increase early fixation and long term survival, to avoid the need for revision surgery.

In the field of orthopedic surgery, our study may predict the long term survival of the implants used, and thereby contributing to the goal of life-long lasting implants. This will also contribute to lower the need for revision surgery, avoiding the risk of major complications for our patients. The economic impact off revision surgery is of great concern for both the patient and the society, and avoiding the need for revision arthroplasty is of economic importance.

Research questions and goals In our study we will evaluate the migration of the Avanteon femoral stem using CT-RSA, to predict long-term survival. We will also evaluate the role of ancillary screw fixation of the new ACE acetabular component by using CT-RSA, to see if ancillary screw fixation increases stability of the implant. By using a patient attached accelerometer-based activity monitor ActivePAL, we can measure patient activity to see if the screw fixation has any effect on activity levels.

Hypotheses; Article 1

• H0-hypothesis; subsidence of the Avanteon femoral stem is less than 1.2mm at 24 months
• H1-hypothesis; subsidence of the Avanteon femoral stem is more than 1.2mm at 24 months

Article 2

• H0-hypothesis; ancillary screw fixation of the ACE acetabular component does not increase stability of the implant
• H1-hypothesis; ancillary screw fixation of the ACE acetabular component increases stability of the implant

Article 3

• H0-hypothesis; ancillary screw fixation of the ACE acetabular component does not increase patient activity
• H1-hypothesis; ancillary screw fixation of the ACE acetabular component increases patient activity

Article 4

• H0-hypothesis; reducing the effective radiation dose does not reduce the precision of CT-RSA of hip implants
• H1-hypothesis; reducing the effective radiation dose reduce the precision of CT-RSA of hip implants

Short term goals;

• Demonstrating the stability and migration of the Avanteon femoral stem
• Evaluate the stability and migration of the ACE acetabular component with and without ancillary screw fixation
• Demonstrate the clinical efficacy and safety of the ACE acetabular component and Avanteon femoral stem
• Demonstrate the effect of acetabular screw fixation on patient activity levels in the postoperative period Demonstrate the precision of ultra low dose CT-RSA Long term goals;
• Contributing to the development of longer lasting hip replacement implants
• Evaluate the increase in activity levels after hip replacement surgery

Results expected to be achieved during the project period;

• Establishing the new innovative CT-RSA as a method for hip implant migration analysis in Norway
• Develop recommendation for the routine use of ancillary screw fixation of acetabular components

This is a single blinded randomized controlled trial. Eligible patients referred will be evaluated for inclusion consecutively from the outpatient clinic of the research department at Kristiansund hospital.

Inclusion Criteria:

• • Patients with primary hip osteoarthritis between the age of 65 and 80 years at time of surgery

  • Patients requiring primary total hip replacement
  • Patients who understand the conditions of the study, are willing to, and able to comply with the postoperative scheduled clinical and radiographic evaluations

Exclusion Criteria:

• • Patients who are unable to provide informed consent

  • Patients who require revision hip arthroplasty
  • Patients who have had a previous osteotomy or osteosynthesis of the femur or acetabulum
  • Patients with metabolic bone disease, other than osteoporosis
  • Patients with inflammatory arthritis
  • Obese patients where obesity is severe enough to affect the patient's ability to perform activities of daily living (BMI > 40)
  • Patients with active or suspected infection
  • Patients with malignancy
  • Patients unable to cooperate caused by language or psychosocial conditions

Upon request with proper reasons, we will share data with other researchers including CT-RSA data and PROMs. This will of course be performed within the laws of Norway and totally anonymized.

From 3 years from now and as long as the data is stored.

Proper request to the corresponding author.