A network of trans-cortical capillaries as mainstay for blood circulation in long bones

Abstract

Closed circulatory systems (CCS) underlie the function of vertebrate organs, but in long bones their structure is unclear, although they constitute the exit route for bone marrow (BM) leukocytes. To understand neutrophil emigration from BM, we studied the vascular system of murine long bones. Here we show that hundreds of capillaries originate in BM, cross murine cortical bone perpendicularly along the shaft and connect to the periosteal circulation. Structures similar to these trans-cortical-vessels (TCVs) also exist in human limb bones. TCVs express arterial or venous markers and transport neutrophils. Furthermore, over 80% arterial and 59% venous blood passes through TCVs. Genetic and drug-mediated modulation of osteoclast count and activity leads to substantial changes in TCV numbers. In a murine model of chronic arthritic bone inflammation, new TCVs develop within weeks. Our data indicate that TCVs are a central component of the CCS in long bones and may represent an important route for immune cell export from the BM.

Chronic anterior tibial stress fractures in athletes: No crack but intense remodeling

“…The hypoxic conditions in the anterior tibial cortex might lead to disturbances in the equilibrium between resorption and bone formation with an overweight of resorption. A recently detected specific type of trans‐cortical vessel might be responsible for these specific circulatory conditions and the sensitivity to mechanical overload in the anterior tibial cortex . These trans‐cortical vessels appear to contribute extensively to the total blood flow of long bones and connect endosteal vessels with the periosteal blood circulation.…”

“…These vessels appear to interact with canaliculi of intra‐osseous osteocytes and thereby might have a direct influence on bone remodeling. A decreased number of these vessels might play an important, yet unexplored role in the pathogenesis of stress fractures …”

Engineering tissue‐specific blood vessels

“…H vessels have high oxygen content and L vessels have low oxygen content . A recent study has identified a previously unknown type of blood vessel that are seen in bones called trans‐cortical vessels . They cross through the bone and connect in the periosteum.…”

“…They cross through the bone and connect in the periosteum. The exact functions are unknown but some proposed functions are immune cell transport, nutrient transport for osteocytes within bones, hematopoiesis, and connecting osteocytes and osteoclasts …”

“…11 A recent study has identified a previously unknown type of blood vessel that are seen in bones called trans-cortical vessels. 28 They cross through the bone and connect in the periosteum. The exact functions are unknown but some proposed functions are immune cell transport, nutrient transport for osteocytes within bones, hematopoiesis, and connecting osteocytes and osteoclasts.…”