Long bone landmarks & organization

Diaphysis: shaft of the bone

• Contains central medullary cavity containing yellow bone marrow (adipose deposits and storage)
• Has outer compact bone and internal spongy/trabecular bone
  • Compact bone is covered exteriorly by the periosteum, and interiorly by the endosteum (separating compact from spongy)
• Innervated by the nutrient foramen (where nutrient artery/vein run through)

Epiphysis: expanded ends of the bone

• Also has outer compact bone and internal spongy/trabecular bone
• Has articular cartilage at joint ends
• Epiphyseal line: remnant of epiphyseal/growth plate (disk of hyaline cartilage from bone growth phase during childhood)
• Innervated by the epiphyseal artery/vein

Metaphysis: flared portion where diaphysis and epiphysis meet

Periosteum: covers entire bone surface except at joint surfaces (which are covered by cartilage)

• Is richly innervated (periosteal artery/vein) and secured to underlying bone via perforating fibers (collagen fiber bundles)
• Two layers:
  • Outer fibrous layer: dense CT
  • Inner osteogenic layer: contains osteoprogenitors of osteoblasts and osteoclasts

Endosteum: covers spongy trabeculae and compact bone canals

Bone structural classification

Long bones (Figure 1): long, cylindric shaft (diaphysis) with 2 distinct ends (epiphysis)

• Locations: arms, forearms, thigh, leg, palms, soles, digits

Short bones: cuboidal, boxlike

• Locations: wrist carpal bones, ankle tarsal bones

Sesamoid bones: special type of short bone within tendons to minimize friction

• Locations: knee (patella), hands, feet

Flat bones: thin, curved; provides extensive surface area for the attachment of skeletal muscles

• Locations: skull roof, sternum, ribs scapulae, cranial bones

Irregular bones: short, flat, notched/ridged (unusual shapes that don’t fall within other categories)

• Locations: vertebra, pelvic bones

Sutural/Wormian bones: small, irregular shaped bones

• Locations: cranial sutures between skull flat bones