Osteoclasts, the multinucleated cells responsible for bone resorption, have an enormous destructive power which demands to be kept under tight control. Accordingly, the identification of molecular signals directing osteoclastogenesis and switching on their resorptive activity have received much attention. Mandatory factors were identified, but a very essential aspect of the control mechanism of osteoclastic resorption, i.e. its spatial control, remains poorly understood. Under physiological conditions, multinucleated osteoclasts are only detected on the bone surface, while their mono-nucleated precursors are only in the bone marrow. How are pre-osteoclasts targeted to the bone surface? How is their progressive differentiation coordinated with their approach to the bone surface sites to be resorbed, which is where they finally fuse? Here we review the information on the bone marrow distribution of differentiating pre-osteoclasts relative to the position of the mandatory factors for their differentiation as well as relative to physical entities that may affect their access to the remodelling sites. This info allows recognizing an “osteoclastogenesis route” through the bone marrow and leading to the coincident fusion/resorption site – but also points to what still remains to be clarified regarding this route and regarding the restriction of fusion at the resorption site. Finally, we discuss the mechanism responsible for the start of resorption and its spatial extension. This review underscores that fully understanding the control of bone resorption requires to consider it in both space and time - which demands taking into account the context of bone tissue.

破骨细胞是负责骨吸收的多核细胞，具有巨大的破坏力，需要严格控制。因此，鉴定指导破骨细胞生成和开启其吸收活性的分子信号受到了广泛关注。确定了强制性因素，但破骨细胞吸收控制机制的一个非常重要的方面，即其空间控制，仍然知之甚少。在生理条件下，多核破骨细胞仅在骨表面检测到，而其单核前体仅在骨髓中存在。前破骨细胞如何靶向骨表面？它们的渐进分化如何与它们接近要再吸收的骨表面部位的方法相协调，他们最终融合在哪里？在这里，我们回顾了有关分化前破骨细胞的骨髓分布的信息，这些信息相对于它们分化的强制性因素的位置以及可能影响它们进入重塑部位的物理实体。该信息允许识别通过骨髓并导致重合融合/再吸收位点的“破骨细胞生成途径”——但也指出了关于该途径和在再吸收位点融合的限制仍有待澄清的内容。最后，我们讨论了吸收开始及其空间扩展的机制。