Answer to the “Letter to the Editor of Wu TK, et al. concerning “Osteolysis after cervical disc arthroplasty” by Joaquim AF, et al. (Eur Spine J; [2020]: doi: 10.1007/s00586-020-06578-2)”

[摘要] We agree that not all bone resorption is osteolysis. One can certainly have bone resorption without osteolysis. However, all osteolyses involve resorption of bone. We agree that remodelling requires bone resorption and that most remodelling does not result in osteolysis. However, to the best of our knowledge, early peri-CDA osteolysis cannot be distinguished on plain radiographs from simple remodelling of bone due to Wolf’s law. There are likely to be many diferent cellular and biochemical mechanisms that can result in bone resorption and even osteolysis. Infections, third body wear, activation of phagocytotic cells may occur due to numerous mechanisms but radiographically, they may have similar early features that make them indistinguishable from one another. As to the comment that, “The authors mentioned anterior bone loss following CDA in their article was mainly pertaining to bone remodelling rather than osteolysis”, we are unsure how the authors came to that conclusion. In the entire manuscript, we use the word “remodelling” once—in citing an article that was not written by us: “Chen et al. [1] evaluated 121 patients who had a 1-level Bryan CDA with a minimum 24-month follow-up. These authors categorized anterior bone loss severity as follows: grade 0—no remodelling”. We completely agree that anterior bone loss following CDA is mostly NOT due to remodelling.