TWO CASES OF PSEUDOTUMOUR FOLLOWING METAL-ON-METAL (MOM) THA

(Introduction) Metal on Metal (MoM) THA bearing as the second generation Total Hip Arthroplasty, widely came into use in Japan since 2000s. And it was expected to be able to ensure long-term use, the range of motion in the joints after surgeries, and the resistance to the dislocation, because MoM THAhad been considered to be able to use the large diameter head for its lower wear. However, there are some reports that the metal wear debris from MoM bearing surface generates the elevated serum ion level in the blood and the incidence of pseudotumor may occur subsequent to the metal wear debris. We performed MoM THA for 291 joints in 234 patients in our hospital since May 2005. But now, we refrain to use this. In this time, we will describe two cases of pseudotumor after implantation of MoM THA. (Case1) Age 64 years, female This case showed the hip osteoarthritis on the right side, and we performed MoM THA in 2005. After that, she had slipped just prior to the three-year postoperative check-up, and started swelling up, hip joint pain, and the rise in CRP. Then, we performed to remove pesudotumor in 2008 and her CRP turned into negative. However, she was repeating hip dislocation several times and an MRI showed recur of pseudotumor. Finally, we changed her metal liner into a polyethylene liner in 2012. (Case2) Age 57 years, female This case showed the hip osteoarthritis on the bilateral side, and we performed MoM THA in 2005. We had regularly measured her serum ion levels since 2009, and her cobalt level was indicating high concentration. In addition, there was shown 46ng/ml blood concentration of cobalt in her postoperative check-up in 2013. In 2014, she came to our hospital with chief complaint of the pain in the right groin, and we confirmed pseudotumor with MRI. (Conclusion) Nowadays, there have been various reports regarding the formation of mass lesion around the joint implants with MoM bearing, and the incidence rates, the methods of the diagnosis, and the treatment policies are introduced. However, they are realistically still not standardized. For this reason, we should fully understand the properties of MoM THA to perform the surgeries. And there is a need to be performed CT scans, MRI and ultrasound examination for the patients who claim a pain or the sense of discomfort in the area after surgery.