Blood Supply of Long Bone

·     Blood supply of long bone accounts for 5 to 10 % of the cardiac output.

·     Long bone receives blood supply from various sources-

1.   Nutrient arteries

2.   Epiphy­seal arteries

3.   Metaphyseal arteries

4.   Periosteal arteries.

Arterial Supply

1. Nutrient artery  

·     One or two diaphyseal nutrient arteries enter the shaft through nutrient foramina.

·     In the medullary cavity, the nutrient arteries divide into ascending and descending branches.

·     Each branch divides into number of small parallel channels, after reaching the epiphysis they divide repeatedly into small rami which pursue spiral courses.

·     Near the epiphysis, they are joined by metaphyseal and epiphyseal arteries.

ð   Primary direc­tion of the blood flow is centrifugal.

ð   The nutrient artery supplies the bone marrow and inner two-third of the compact bone of diaphysis.

ü The artery enters the compact bone through haversian canal.

ü The osteocytes in the lamellae of haversian system receive nutrition by diffusion through the anastomosing canaliculi.

ü These terminate into arteriole which has endothe­lium with basement membrane and a smooth muscle layer.

ü This further continues into sinusoids which do not have basement membrane.

2. Epiphyseal arteries  

·     When articular cartilage and epi­physeal cartilage are continuous, the epiphyseal arteries pierce the epiphyseal cartilage and supply the epiphysis.

•      If these arteries are damaged in epi­physeal separation, avascular necrosis of epiphysis may occur, e.g. head of the femur.

·     In others, where the articular cartilage is not continuous with epi­physeal cartilage, the epiphyseal arteries enter the epiphysis without piercing it.

o In these cases, epi­phy­­seal separation will not cause avascular necrosis.

·     Epiphyseal arteries are derived from the peri­arti­­cular vascular arcades.

·     Out of many vascular foramina near epiphysis, very few admit arteries and rest are venous exits.

·     Epiphyseal arteries anasto­mose with metaphyseal and nutrient arteries after fusion of diaphysis and epiphysis.

3. Metaphyseal arteries

·     Numerous small blood ves­sels arising from the anastomosis around the joint pierce the metaphysis along the attachment of the joint capsule.

·     Metaphyseal arteries freely anas­to­­mose with spiral branches of nutrient arteries, so metaphysis is the most vascular area of the long bone.

4. Periosteal arteries

·     Many blood vessels anasto­mose beneath the periosteum and enter the Volkmann’s canal and supply the outer third of the compact bone.

·     Periosteal arteries penetrate bone at these sites where fascial sheath or aponeurosis gain attachment to the shaft.

·     Function of these arteries is controversial.

Blood Supply of Other Bones

¤ Short bones are supplied by numerous periosteal vessels.

¤ In vertebra

è the body is supplied by anterior and posterior vessels and

è vertebral arches by large vessels, entering the base of the transverse pro­cesses.

¤ A rib is supplied by nutrient artery, which enter just beyond the tubercle and by periosteal arteries.

Venous Drainage

·     Valveless nutrient veins accompany the arteries.

·     In medullary cavity, a central venous sinus is present which is served by radial collecting sinuses.

·     The general layout is fan-shaped with cortical sinusoids radiating outwards towards periosteal surface.

·     Each haversian canal is supplied by a solitary sinusoid.

Hemodynamic Regulation of Bone Blood Flow

·     The assessment of hemodynamic regulation of blood flow requires sophisticated techniques.

·     The various regulating mechanisms are as follows.

1.  Neural control

ü Increase in blood flow after sympathectomy is demonstrated in animals.

2.  Hormonal control

ü Osseous circulation contains alpha-1 adrenoceptors, muscarinic receptors and prostaglandin receptors.

ü Circulating adrenaline may open arteriovenous shunts between nutrient arteries and sinusoids draining into cent­ral venous sinus which would provide a mecha­nism for increased transosseous venous return during exercise.

3.  Metabolic control  

ü Following period of ische­mia restoration leads to 2-3 fold increase in blood flow which is probably by metabolic control.