Both local and systemic variables influence the rate and degree of fracture healing. When normal healing occurs, but at a slower rate than usual, it is termed delayed union. A complete cessation of the healing process, in which fibrous tissue is never replaced by bony matrix, is termed nonunion.
Systemic Factors Affecting Fracture Healing
Young patients heal rapidly and have a remarkable ability to remodel and correct angulation deformities. These abilities decrease once skeletal maturity is reached.
A substantial amount of energy is needed for fracture healing to occur. An adequate metabolic stage with sufficient carbohydrates and protein is necessary.
Diseases like osteoporosis, diabetes, and those causing an immunocompromised state will likely delay healing. Illnesses like Marfan’s syndrome and Ehlers-Danlos syndrome cause abnormal musculoskeletal healing.
Thyroid hormone, growth hormone, calcitonin, and others play significant roles in bone healing. Corticosteroids impede healing through many mechanisms.
Local Variables Affecting Fracture Healing
Type of Bone
Calcellous (spongy) bone fractures are usually more stable, involve greater surface areas, and have a better blood supply than do cortical (compact) bone fractures. Cancellous bone heals faster than cortical bone.
Degree of Trauma
The more extensive the injury to bone and surrounding soft tissue, the poorer the outcome. Mild contusions with local bone trauma will heal easily, whereas severely comminuted injuries with extensive soft tissue damage heal poorly.
Inadequate blood supply impairs healing. Especially vulnerable areas are the femoral head, talus, and scaphoid bones.
Degree of Immobilization
The fracture site must be immobilized for vascular ingrowth and bone healing to occur. Repeated disruptions of repair tissue, especially to areas with marginal blood supply or heavy soft tissue damage, will impair healing.
These fractures communicate with synovial fluid, which contains collagenases that retard bone healing. Joint movement will cause the fracture fragments to more, further impairing union. When intraarticular fractures are comminuted, the fragments tend to float apart owing to loss of soft tissue support.
Separation of Bone Ends
Normal apposition of fracture fragments is needed for union to occur. Inadequate reduction, excessive traction, or interposition of soft tissue will prevent healing.
Infections cause necrosis and edema, take energy away from the healing process, and may increase the mobility of the fracture site
Any disease process that weakens the musculoskeletal tissue, like osteoporosis or osteomalacia, may impair union.
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