Bone & Cartilage

At a glance

Mature bone shows cortical (compact) and trabecular (cancellous) patterns; osteocytes reside in lacunae connected by canaliculi.
Osteoblasts line active bone surfaces; osteoclasts sit in Howship lacunae; marrow space varies with age.
Cartilage is avascular, chondrocytes in lacunae, matrix basophilic (hyaline) or eosinophilic (fibrocartilage), elastic fibers in elastic cartilage.
Growth plates (pediatric) show ordered zones: reserve → proliferation → hypertrophy → calcification → ossification.

Cortical: osteons with central Haversian canal, concentric lamellae; Volkmann canals connect.
Trabecular: delicate lamellae with lining osteoblasts; intertrabecular marrow hematopoietic or fatty depending on site/age.
Lining cells: flat inactive osteoblasts; osteoclasts multinucleated, TRAP+.

Hyaline: glassy matrix, type II collagen; examples include articular surfaces, costal cartilage, respiratory cartilages.
Elastic: elastic fibers in matrix (special stains), found in ear, epiglottis.
Fibrocartilage: thick type I collagen bundles, rows of chondrocytes; intervertebral discs, menisci.

Periosteum has outer fibrous and inner cambium layer with osteoprogenitors; essential for appositional growth and repair.
Endosteum lines inner surfaces and trabeculae; contains osteoblasts and progenitors.

Bone matrix: osteoid highlights on trichrome; osteocalcin/osteonectin for active bone.
Osteoclasts: TRAP+, CD68+; multinucleated.
Cartilage: S100+, SOX9+, type II collagen in hyaline/elastic cartilage; type I collagen in fibrocartilage.