Adverse reaction to metal debris (ARMD) is an issue in metal-on-metal (MoM) total hip replacements (THR). It mainly affects large-head MoM THR, whereas 28–32 mm MoM pairings are associated with low long-term revision rates. However, the bearing surface is not necessarily the only cause of metal debris. This report documents with advanced analysis of the retrievals a particular cause of trunnionosis in late failure of a small diameter MoM THR and illustrates the importance of cleaning of the taper when seating the head in THR. A 65-year-old patient was revised due to ARMD 16 years after small diameter MoM THR. Debridement and exchange of the inlay and the head had been performed through an anterior approach. While the cup and the outer surface of the head were accessible to direct analysis by an optical coordinate measuring machine, the female taper had to be analysed indirectly by measuring an imprint. Wear from the cup and the head was within expected low ranges. The analysis of the female taper identified bone fragments, which contributed to trunnionosis. Failure due to ARMD after MoM THR is not necessarily caused by the bearing, but can be due to trunnionosis. Bone fragments within the taper contact in this case highlight the importance of meticulous cleaning of the taper before seating the head, to avoid trunnionosis.

金属碎屑（MoM）全髋关节置换术（THR）中存在对金属碎片（ARMD）的不良反应。它主要影响大头颅MoM THR，而28–32 mm MoM配对与低长期翻修率相关。但是，轴承表面不一定是金属碎屑的唯一原因。该报告对取回进行了深入分析，记录了小直径MoM THR的晚期失效中引起耳轴畸形的特殊原因，并说明了将头部固定在THR中时清洁锥度的重要性。小直径MoM THR后16年，由于ARMD对一名65岁患者进行了修订。镶嵌物和头部的清创术和交换是通过前路入路进行的。虽然可以通过光学坐标测量机直接对杯子和头部的外表面进行分析，女性锥度必须通过测量压印来间接分析。杯子和头部的磨损在预期的低范围内。对女性锥度的分析确定了骨碎片，这些骨碎片导致了耳蜗疾病。MoM THR之后由于ARMD引起的故障不一定是轴承引起的，而可能是由于耳轴后侧凸引起的。在这种情况下，锥形触点内的骨头碎片突出显示了在就座头部之前仔细清洁锥形的重要性，以免发生耳轴畸形。