Failure rates of Asian-type anatomic medullary locking stemmed metal-on-metal total hip replacement: A cause for adverse tissue reactions to metal debris (ARMD).

BACKGROUND: Adverse tissue reaction to metal debris (ARMD) as a secondary complication of Metal-on-metal total hip replacement (MoM THR) has been of concern. We have been performing cementless MoM THR using an Asian-type anatomic medullary locking (AML) stem. The purpose of this study is to examine the incident rate of ARMD, and the implant survival rate.

METHODS: The study included 187 patients (211 hip joints) who underwent MoM THR between February 2007 and November 2009 at our hospital and who were followed up for a minimum of 6 years. The cases included 174 female joints and 37 male joints. The average age at the time of surgery was 68.4 years. The average postoperative follow-up period was 87.5 months.

RESULTS: ARMD was observed in 23 joints postoperatively, and the incidence rate was 10.9%. Most of the instances occurred within the first 30 months postoperatively. Revision surgery was performed for 14 joints after conservative treatment failed, and we changed the bearing surface. During the intraoperative observation, black-colored deposition of metal debris on the head-neck junction was observed in 13 cases. Kaplan-Meier analysis using the replacement surgery as the end point showed that this implant has a survival rate of 93.8% 7 years after the primary surgery.

CONCLUSIONS: We conclude that the major cause of failure of Asian-type AML stemmed MoM THR is likely the breakage of the fixation between the taper neck and metal head at the head-neck junction.