Session VII

Bone healing

Bone Healing

Possibility 1: Primary Bone Healing:

What we Love to See. • Direct and intimate contact between fracture

fragments• ORIF with atraumatic technique

– Intact intramedullary vasculature

• New bone grows directly across the compressed bone ends

• Osteoclastic resorption followed by osteoblastic deposition

• Rigid internal fixation. No movement.

ORIF primary bone healing

2nd Possibility: Secondary Bone Healing What we usually see.

• Denotes mineralization and bony replacement of a cartilage matrix with characteristic callus formation.

• Some movement occurs at the fracture– No fixation or immobilization– Cast immobilization– External fixation– A study in the 80’s showed ORIF stronger for 4-6 weeks, then

ORIF equal to casts for 4-6 weeks, then cast fractures stronger! Casts may allow an “ideal” amount of movement for piezogenic effect on osteoblasts. But it will be secondary bone healing.

Secondary Bone Healing: The fragments move slightly generating visible bone callus.

– 1 week: resorption of necrotic bone at fracture– 10-14 days weeks: appearance of bone callus– 6-12 weeks: callus increases (if motion is moderate to

excessive) forming an exuberant callus. Creates risk of delayed union (6months+) or non-union (12months+) If motion is minimal callus gains density but not size.

– 3-6 months-bone strength increases, callus becomes more calcified and shows visible trabecular patterns.

– 6-12 months-callus remodels, reduces in size, angulation deformities may normalize.

Casts are stress sharing so secondary healing is expected.

3 months later

Secondary Bone

Callus formation expected with medullary nails.

Staging Healing Stage I: Inflammatory

• Inflammatory phase: 10%– Lasts 1-2 weeks– Increased vascularity– Hematoma is invaded by inflammatory cells

forming a meshwork• PDGF and TGF-ß -• Neutrophils, macrophages and osteoclasts

– Debridement of wound– Strength is 0/4

Callus formation with/without ORIF

Stage II: Reparative

• Duration is several months• Differentiation of pluripotential mesenchymal cells• Hematoma invaded by chrondroblasts and fibroblasts that

create a callus matrix• Formation of granulation tissue procallus. • Formation of fibrous callus. Collagen types I,II and III

– Insulin, insulin like growth factors, osteogenin and morphogenic protein

• Osteoblasts then mineralize the fibrous callus forming a hard or bony callus/woven bone.– Strength 3/4

• Weak immature bone-fracture stability indicates the end of this phase

• Delayed union and non union result from errors in this phase• Strength is 1-2/4

Bone callus just showing

4-6 weeks or more callus is more easily seen radiographically than earlier.

Stage III: Remodeling

• Months to years to complete• Replacement of immature disorganized woven

bone with mature organized lamellar bone. Increases stability. Shift to type I collagen

• Resorption of bone from convex surfaces and deposition on concave surfaces.

• Radiographically the fx is usually no longer visible.

• Strength is 4/4

Fracture Healing: Variables• Remember a transverse fx is clean and

possibly relatively atraumatic but…– May injury nutrient foramen if midshaft– Has little surface area for healing– Is mechanically very weak and unstable.

• Oblique fx may create more initial trauma but…– Nutrient artery intact?– Great surface area for healing

• Stress fx: no visible fx line. Watch for callus formation instead. May not be invisible for 10-14 days

Variables on X-ray

• Metaphyseal fractures show little callus– Impaction of fragments, interdigitation of spicules, minimum

periosteum

• Diaphyseal fx, even if fixated, show external callus– Lack of impaction, presence of gap

• Intracapsular fx show little callus because of absence of periosteum– Femoral neck intracapsular but intertrochanteric are extracapsular

• Rigidly fixated fx show less callus• Overall trauma and age

• OK, here goes a high speed review of fracture healing…

Immediate Post Op

1 day

Less than 1 week

Less than 1 week

Less than 1 week

Fuzzy more rounded fx surfaces. 1-2 weeks

3-6 weeks with stable fixation.

Some motion is occurring to produce the visible bone callous.

3-6 weeks callus is now visible.

6-10 weeks Can you explain this to your patient?

8-10 weeks

12-16 weeks Bone Callus formation is maturing

Bone Callus Formation with trabecular bridging

About 12-16 weeks post injury. The

moderate amount of callus indicates little motion has

occured. Cautious weight bearing

OK??

Delayed union at 6 months.A Non Union is determined after

about 12 months healing.

If this was your patient at 6 months what would be your assessment?