8/13/2019 Musculoskeletal System Overview

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Musculoskeletal System Overview

Ossification is the process by which the bone matrix (collagen fibers and groundsubstance) is formed and hardening minerals (eg, calcium salts) are deposited on thecollagen fibers. The collagen fibers give tensile strength to the bone, and the calciumprovides compressional strength.

206 total bones in Human Body

Categories of Bones Long bones (eg, femur) Short bones (eg, metacarpals) Flat bones (eg, sternum) Irregular bones (eg, vertebrae)

osteoblast: bone-forming cellosteoclast: bone resorption cellosteocyte: mature bone cell

Bone Healing

Fracture healing occurs in four areas, including: Bone marrow, where endothelial cells rapidly undergo transformationand become osteoblastic bone-forming cells

Bone cortex, where new osteons are formed Periosteum, where a hard callus/bone is formed throughintramembranousossification peripheral to the fracture, andwhere a cartilage model isformed through endochondral ossification adjacent to the fracture site

External soft tissue, where a bridging callus (fibrous tissue) stabilizes the fracture

1. Hematoma and inflammation :The bodys response is similar to that aft er injuryelsewhere in the body. There is bleeding into the injured tissue and formation of afracture hematoma. The hematoma is the source of signaling molecules, such as

cytokines, transforming growth factor-beta (TGF-), and platelet-derived growthfactor (PDGF), which initiate the fracture healing processes. The fracture fragment

ends become devitalized because of the interrupted blood supply. The injured area isinvaded by macrophages (large white blood cells), which dbride the area.Inflammation, swelling, and pain are present. The inflammatory stage lasts severaldays and resolves with a decrease in pain and swelling.

2. Angiogenesis and cart i lage formation: Under the influence of signalingmolecules, cell proliferation and differentiation occur. Blood vessels and cartilageoverlie the fracture.3. Carti lage calci f ication: Chondrocytes in the cartilage callus form matrix vesicles,which regulate calcification of the cartilage.Enzymes within these matrix vesicles prepare the cartilage for calcium release anddeposit.4. Carti lage remo val: The calcified cartilage is invaded by blood vessels andbecomes resorbed by chondroblasts and osteoclasts. It is replaced by woven bonesimilar to that of the growth plate.5. Bone formation: Minerals continue to be deposited until the bone is firmly reunited.With major adult long bone fractures, ossification takes 3 to 4 months.6. Remodel ing:The final stage of fracture repair consists of remodeling the newbone into its former structural arrangement. Remodeling may take months to years,dependingon the extent of bone modification needed, the function ofthe bone, andthe functional stresses on the bone. Cancellousbone heals and remodels more rapidly than does compact cortical bone.

Types of Fracture

Greenstick fracture: an incomplete fracture in which the bone is bent. This typeoccurs most often in children.

Transverse fracture: a fracture at a right angle to the bone's axis.Oblique fracture: a fracture in which the break has a curved or sloped pattern.Comminuted fracture: a fracture in which the bone fragments into several pieces.

An impacted fracture is one whose ends are driven into each other. This iscommonly seen in arm fractures in children and is sometimes known as a bucklefracture. Other types of fracture are pathologic fracture, caused by a disease thatweakens the bones, and stress fracture, a hairline crack.

Other types of fracture are pathologic fracture, caused by a disease thatweakens the bones, and stress fracture.

Terminologiesbrace: externally applied device to support body, control movement, and prevent injurycast: rigid external immobilizing device molded to contours of body partfracture: a break in the continuity of the bonesplint: device designed specifically to support and immobilize body part in desired positiontraction: application of a pulling force to a part of the body