Blood Supply of Long Bone - Anatomy Short Note

Overview

Sources of Blood Supply

1. Nutrient Artery System (Diaphyseal/Medullary System)

• Pressure: High-pressure system
• Supplies: Inner two-thirds of the diaphyseal (cortical) compact bone
• Origin: Branch from a systemic/regional artery (e.g., the humeral nutrient artery arises from the brachial artery; the tibial nutrient artery from the posterior tibial artery)
• Entry: Enters via the nutrient foramen (an oblique canal in the diaphysis), directed away from the growing end in most bones
• Course: Enters the medullary cavity, divides into ascending and descending medullary arteries, which branch into arterioles supplying the endosteal cortex and inner 2/3 of compact bone via the Haversian system
• Significance: Accounts for ~60% of cortical bone vascularization

Fig: Arterial supply regions of a long bone - Histology: A Text and Atlas (Wheater)

2. Metaphyseal-Epiphyseal System

• Origin: Arises from the periarticular vascular plexus (e.g., geniculate arteries around the knee; circumflex arteries at the shoulder/hip)
• Epiphyseal arteries enter through nutrient foramina at the epiphysis and supply the trabecular (spongy) bone of the epiphysis
• Metaphyseal arteries arise from periosteal vessels incorporated into the metaphysis during bone growth (widening). They supplement diaphyseal supply and are especially important in the growing bone
• In the growing skeleton, the physis (growth plate) acts as a barrier - epiphyseal and metaphyseal circulations are largely separate, making the metaphysis vulnerable to hematogenous infection (osteomyelitis)

3. Periosteal System

• Pressure: Low-pressure system
• Supplies: Outer one-third of the diaphyseal compact bone
• Consists mostly of capillaries that penetrate the outer cortex via Volkmann canals
• These vessels communicate with Haversian canals to form an anastomotic network
• Also drains lymphatic vessels (the periosteum is the only part of bone with lymphatics - bone tissue itself lacks lymphatics)

FIG 1.5 Blood supply to bone (from Gray's Anatomy, as cited in Miller's Review of Orthopaedics 9th Ed.)

Direction of Blood Flow

• In the mature bone, arterial flow is centrifugal - driven by the net effect of the high-pressure nutrient artery overcoming the low-pressure periosteal system
• When a fracture disrupts the nutrient artery or in immature/growing bone, the periosteal system pressure predominates and flow reverses to centripetal

Venous and Lymphatic Drainage

• Veins exit via the nutrient foramina and through bone tissue of the shaft, continuing out through the periosteum - venous flow is centripetal
• Lymphatic vessels are present only in the periosteum - the bone tissue itself has no lymphatics

Intracortical Vascular Architecture

• Within compact bone, blood moves through Haversian canals (run parallel to the long axis) - each contains a single arteriole + venule or capillary
• Volkmann canals run perpendicular to Haversian canals and provide the major entry route for vessels into compact bone from the periosteum
• These two canal systems form an interconnected network throughout the cortex

Regulation of Bone Blood Flow

• Influenced by metabolic, humoral, and autonomic inputs
• Hypoxia, hypercapnia, and sympathectomy increase blood flow
• Vessels have vasoactive receptors: β-adrenergic, muscarinic, thromboxane/prostaglandin
• Bone blood flow is the primary determinant of fracture healing:
  • Initially decreases after fracture
  • Increases within hours-to-days (regional acceleratory phenomenon)
  • Peaks at ~2 weeks
  • Returns to normal by 3-5 months

Bones with Tenuous Blood Supply (Clinically Important)

• Scaphoid (proximal pole supplied retrogradely)
• Talus (body supplied retrogradely)
• Femoral head (retinacular vessels; disrupted in intracapsular neck fractures)
• Odontoid process (C2 dens)
• Lunate (Kienböck disease)

Summary Table

Blood Supply of Long Bone

Introduction

1. Nutrient Artery System

• The principal source of blood supply to the diaphysis
• Arises from a regional systemic artery and enters the bone obliquely through the nutrient foramen, directed away from the growing end
• Passes through the nutrient canal into the medullary cavity, where it divides into ascending and descending branches
• These branch into arterioles that supply the inner two-thirds of the cortex via Haversian canals
• Supplies ~60% of cortical bone

2. Metaphyseal-Epiphyseal System

• Arises from the periarticular vascular plexus surrounding each joint
• Epiphyseal arteries enter through small foramina at the bone ends and supply the epiphyseal trabecular bone
• Metaphyseal arteries supplement supply at the flared ends of the diaphysis
• In growing bone, the growth plate (physis) separates these two circulations - making the metaphysis vulnerable to hematogenous osteomyelitis due to sluggish sinusoidal blood flow

3. Periosteal System

• Low-pressure system supplying the outer one-third of the cortex
• Small periosteal capillaries enter compact bone via Volkmann canals (perpendicular) and communicate with Haversian canals (longitudinal)

Direction of Flow

• Normal mature bone: Arterial flow is centrifugal (medulla → cortex → periosteum), driven by the high-pressure nutrient artery overcoming the low-pressure periosteal system
• After fracture / immature bone: Nutrient artery is disrupted; periosteal system predominates → flow becomes centripetal
• Venous drainage is always centripetal (outside → inside), exiting via nutrient foramina

Clinical Significance

• Bones with retrograde or tenuous supply (femoral head, scaphoid, talus, odontoid) are prone to avascular necrosis (AVN) after fracture
• Unreamed intramedullary nails preserve endosteal blood supply better than reamed nails
• Bone blood flow peaks at ~2 weeks post-fracture and is the major determinant of fracture healing