Bone vascular supply

Bone vascular supply

• Bone receives 5%–10% of the cardiac output.

• Bones with a tenuous blood supply include the scaphoid, talus, femoral head, and odontoid.

• Hypoxia, hypercapnia, and sympathectomy increase flow.

• Long bones receive blood from three sources (systems)

  • Nutrient artery system

    • Branch from systemic arteries, enter the diaphyseal cortex through the nutrient foramen, enter the medullary canal, and branch into ascending and descending arteries (Figs. 1.5 and 1.6)

    • Further branch into arterioles in the endosteal cortex, which enables blood supply to at least the inner two-thirds of the mature diaphyseal cortex via the haversian system (see Fig. 1.6)

    • BP in the nutrient artery system is high.

    • 60% of cortical bone vascularized by nutrient arteries

       

       

       

      FIG. 1.5 Intraoperative arteriogram (canine tibia) demonstrating ascending (A) and descending (D) branches of the nutrient artery. C, Cannula.

      From Brinker MR et al: Pharmacological regulation of the circulation of bone, J Bone Joint Surg Am 72:964–975, 1990.

       

       

      FIG. 1.6 Blood supply to bone.

      From Standring S et al, editors: Functional anatomy of the musculoskeletal system. In Gray’s anatomy, ed 40, London, 2008, Elsevier, Fig. 5-20.

       

  • Metaphyseal-epiphyseal system

    • Arises from the periarticular vascular plexus (e.g., geniculate arteries)

  • Periosteal system

    • Consists mostly of capillaries that supply the outer third (at most) of the mature diaphyseal cortex

    • BP in the periosteal system is low.

• Physiologic features

  • Direction of flow

    • Arterial flow in mature bone is centrifugal (inside to outside), which is the net effect of the high-pressure nutrient artery system and the low-pressure periosteal system.

    • When fracture disrupts the nutrient artery system, the periosteal system pressure predominates and blood flow is centripetal (outside to inside).

    • Flow in immature developing bone is centripetal because the highly vascularized periosteal system is the predominant component.

    • Venous flow in mature bone is

      centripetal.

    • Cortical capillaries drain to venous sinusoids, which drain to the emissary venous system.

  • Regulation of bone blood flow

    • Influenced by metabolic, humoral, and autonomic inputs

    • Arterial system: great potential for vasoconstriction (from the resting state), less potential for vasodilation

    • Vessels within bone: have several vasoactive receptors (β-adrenergic, muscarinic, thromboxane/prostaglandin)

• Bone blood flow is the major determinant of how well a fracture heals.

  • Initial response is a decrease in bone blood flow after vascular disruption at the fracture site.

  • Bone blood flow increases within hours to days (as part of the regional acceleratory phenomenon), peaks at approximately 2 weeks, and returns to normal in 3–5 months.

  • Unreamed intramedullary nails preserve endosteal blood supply.

  • Reaming devascularizes the inner 50%–80% of the cortex and delays revascularization of the endosteal blood supply.