Overview

The metaphysis is the zone of active bone formation in a growing bone: on its epiphyseal side, osteoblasts lay bone onto calcified cartilage spicules produced by the epiphyseal plate, creating primary spongiosa that is then remodelled and funnelled (narrowed) by osteoclasts to the width of the shaft. Its cortex is thin and its interior trabecular.

The metaphysis has a rich but sluggish blood supply: terminal branches of the nutrient and metaphyseal arteries form hairpin loops draining into large sinusoids just below the growth plate. Slow flow and fenestrated vessels make the metaphysis the classic site for haematogenous osteomyelitis in children and for many primary bone tumours (osteosarcoma, osteochondroma, giant-cell tumour extends to the epiphysis after fusion).

Location: Between diaphysis and epiphysis at each end of a long bone.

Anatomy

Arterial supply: Metaphyseal arteries from periarticular anastomoses plus terminal nutrient artery branches.

Function

Site of new bone formation during longitudinal growth
Transitions from the wide epiphysis to the narrow shaft
Transfers load from spongy to compact bone

Clinical significance

Osteomyelitis and tumours

Acute haematogenous osteomyelitis in children localises to the metaphysis; osteosarcoma most often arises in the metaphyses around the knee (distal femur, proximal tibia) and proximal humerus.

Rickets

Defective mineralisation of the zone of provisional calcification causes metaphyseal widening, cupping and fraying on X-ray.

Test yourself

In a child, haematogenous osteomyelitis of a long bone usually begins in which region?

Epiphysis
Articular cartilage
Mid-diaphysis
Metaphysis

Answer: Metaphysis

The metaphysis has looping capillaries draining into large sinusoids with sluggish flow beneath the growth plate, which favours bacterial seeding (most commonly Staphylococcus aureus).