Metal Ion Levels in Total Hip Arthroplasty (THA) With Modular Dual Mobility Cup Compared to Conventional THA

Dislocation after total hip arthroplasty is a very serious complication not only for the patient but also for the operator, and is the second most common complication after joint dissociation. The incidence of dislocation after conventional total hip arthroplasty has been reported to be about 0.2 to 7%, and the frequency is higher in elderly patients with hip fractures and has been reported up to about 9%. In patients at high risk of dislocation, total hip arthroplasty using a dual mobility acetabular cup has the effect of reducing the risk of dislocation, and its use has been increasing in recent years. The dual mobility acetabular cup used in this study was developed in a form that can be screwed through the acetabular cup to compensate for the shortcomings of the dual mobility acetabular cup used in the past. The modular dual mobility acetabular cup, which can be fixed with screws, has a metal liner inserted therein, so there is a possibility that the concentration of metal ions in the blood may rise. Until now, studies on the concentration of metal ions in the blood after total hip arthroplasty using an modular dual mobility acetabular cup have been reported very rarely, and the results are also reported differently [4-7]. In addition, no prospective comparative study on blood metal ion concentrations after total hip arthroplasty using an modular dual mobility acetabular cup in elderly patients with femoral neck fractures has been reported. The release of metal ions due to metal corrosion or metal friction in the artificial joint is a rare phenomenon, but it can cause serious complications in the body. It has been suggested through case reports that it can cause abnormalities in the nervous system and cardiovascular system by increasing the concentration of metal ions in the body as well as bone complications such as osteolytic artificial joint relaxation pseudotumor around the artificial joint [5-7] , and a comparative analysis of the modular dual mobility acetabular cup with the conventional acetabular cup to see if there is any problem of metal ion rise in the body due to the release of metal ion concentration is a very important and meaningful study for both doctors and patients performing hip arthroplasty. In addition, it is expected that the medical and social contribution of this research will not be small, considering that the artificial prosthesis used as a material for metal-to-metal surface replacement surgery in the hip joint arthroplasty field was recalled a few years ago and caused a big wave around the world.

Matsen et al. defined significant elevation when Cobalt ≥ 1.6 mcg/L, based on previous literature that required revision for adverse local tissue reaction (ALTR). A guideline for follow-up of a metal artificial joint is attached as an appendix. Nam et al. (J Arthroplasty, 2016) reported that the frequency of patients with cobalt ion levels deviating from the normal reference values at 1 year after surgery was 4/26 (15.3%), MDM THA vs. 1/17 (5.9%) reported that it was Conventional THA. Matsen et al. did not specify the timing of the initial measurement of the ion concentration, but said that if abnormal values were observed, they were followed continuously every 6 months. Based on the previous literature that required revision for adverse local tissue reaction (ALTR), Cobalt ≥ 1.6 mcg/L was defined as significant elevation. As a result of following 100 patients, it was confirmed that the cobalt concentration was outside the normal range in 21 patients (21%), and a significant increase in the cobalt ion concentration of 1.6 mcg/L or more was reported in 9 patients (9%). And two of them had ALTR on MRI.

Metal ions can be released and the concentration of metal ions in the body can be increased in not only artificial joint replacement surgery using the assembled double movable acetabular cup but also in the solid acetabular cup. The acetabular cup and the femoral stem may be worn during joint movement due to the collision phenomenon, and if the acetabular cup screw is loosened or incorrectly inserted and corroded and worn, metal ions may be released along with the surrounding osteolysis.

The reason for performing randomization in this study is first, to ensure that the subject's characteristics do not affect the group to be assigned, so that the probability that each subject will receive surgery with which of the two substitutes is equally applied. , Second, in order to maximize the internal validity of the research results, to make the characteristics of the subjects to which the substitutes to be compared belong to be as similar as possible except for the substitutes assigned to them. Third, since statistical analysis was developed based on the theory of probability, The reason for randomizing the assignment of study subjects to the substitutions used is because it satisfies the prerequisites for applying statistical techniques to the analysis of research data.

Comparing and analyzing the difference in the concentration of metal ions in the blood through randomization is an important study that can confirm whether the difference in metal ion release can be caused by the difference in the binding mechanism between the two acetabular cups. It is an important complication after joint arthroplasty that can cause side effects and can cause harm to internal organs or revision surgery. Therefore, analyzing it is very important and meaningful research.

The purpose of this study was to compare the blood metal ion concentration in elderly patients after total hip arthroplasty using an modular dual mobility acetabular cup with the results of the conventional total hip arthroplasty patient group in a multicenter prospective study. In addition, we intend to compare clinical and radiological factors that are commonly evaluated during outpatient follow-up after surgery.