Bone Healing

BONE HEALING

Requires immobilization (fixation) and compression (optimal is 12 to 18 lb per in²)

Bone can regenerate back to 100% of its strength following a fracture.

The body has a difficult time healing bone ends that are greater than 1 cm apart or fractures where the gap is greater than the radius of the bone at that level.

Osteoblasts deposit bone, and osteoclasts resorb bone.

Four Overlapping Stages of Bone Healing

Inflammation

Peaks at 48 hours and subsides at about a week

Inflammation, in addition to its normal role, also acts as an immobilizer by causing:

Pain—patient protects the area

Edema—acts as a hydrostatic splint

Soft Callus

Begins several days after injury and persists for about 1 to 2 months

Fibrous and cartilaginous tissue develops at each end of the fracture

If the soft callus fails to unite the two sides of the fracture (as with an amputation), it will cease to grow and be resorbed.

Hard Callus

If a soft callus is successful in connecting the fracture, it begins to ossify.

Occurs at around 3 to 4 months

Remodeling

Lasts for several years

Excess callus is resorbed.

Final bone morphology is determined by Wolff’s law. Wolff’s law: bone will adapt to the loads under which it is placed.

Two Types of Bone Healing

Bones heal by either primary (intramembranous) or secondary (endochondral) ossification. Fracture stability dictates which type of healing will occur. Bone healing may occur as a combination of both processes.

Primary (Intramembranous)	Secondary (Endochondral)
Bone heals by haversian remodeling (simultaneous remodeling and direct formation of new bone)	Involves the formation of cartilaginous and fibrous tissue intermediates that are later replaced by bone
Little to no callus formation	Callus formation (irritation callus)
Requires good bone opposition and no motion at the fracture or osteotomy site	Occurs when there is motion at the fracture or osteotomy site
Preferred method of bone healing	Less desirable method of bone healing

Bone Healing Complications

Type	Definition	Treatment
Delayed union	Healing has not advanced at the average rate for the location and type of fracture/osteotomy. Time frame cannot be arbitrarily set, but most doctors consider a delayed union at around 4 to 6 months.	Delayed unions can often be healed by strict immobilization alone.
Nonunion	A fracture or osteotomy that is a minimum of 9 months old and has not shown radiographic progress for 3 months.	Generally, intervention including a bone stimulator or operative means are required to heal a nonunion. Atrophic nonunions often require a bone graft.
Pseudoarthrosis	End stage of a nonunion. A fibrocartilaginous surface develops at the bone fracture site, and a joint space develops that may contain synovial fluid.	Operative intervention is the only reliable method of forming a union involving a pseudoarthrosis.
NOTE: A malunion is a fracture that heals in an anatomically incorrect position.