Bone Remodeling - Basic Science

Introduction

Wolff's Law
- bone remodels in response to mechanical stress
Piezoelectic charges
- bone remodels is response to electric charges
- compression side is electronegative and stimulates osteoblast formation
- tension side is electropostive and stimulates osteoclasts
Hueter-Volkmann Law
- theory that bone remodels in small packets of cells known as Basic Multicellular Units (BMUs)
- theory suggest that mechanical forces influence longitudinal growth
- compressive forces inhibit growth
- may play role in scoliosis

Remodeling Mechanism

Cortical bone
- remodels by osteoclastic tunneling (cutting cone)
  - osteoclastic resorption > layering of osteoblasts > layering of lamellae > cement line laid down
  - osteoclast make up head of cutting cone, followed by capillaries and then osteoblasts which lay down the osteoid to fill the cutting cone
  - sclerostin inhibits osteoblastogenenesis to decrease bone formation
- cortical bone continues to change over time
  - cortical area decreases as age increases
    - linked to increase fracture risk
  - medullary canal volume increases as age increases
Cancellous bone remodels by
- osteoclastic resorption
- osteoblastic deposition of layers of lamellae