CHAPTER 11 • BONE INJURY AND FRACTURE HEALING 63PHYSIOLOGY OF BONE REPAIR
AND INCORPORATION
- Several physiologic properties of bone grafts directly
affect the success or failure of graft incorporation.
OSTEOGENESIS(BRIGHTON, 1984; MUSCHLER,
LANE, ANDDAW S O N, 1990)
- The ability of the graft to produce new bone. This
process is dependent on the presence of live bone cells
in a graft material. - Contain viable cells with the ability to form bone
(osteoprogenitor cells) or the potential to differentiate
into bone forming cells. - Osteogenesis is a property found only in fresh auto-
genous bone and in bone marrow cells.
OSTEOCONDUCTION(HOLLINGER ET AL, 1996;
GAZDAG ET AL, 1995)
- The physical property of the graft to serve as a scaf-
fold for viable bone healing. - Allows for the ingrowth of neovasculature and the
infiltration of osteogenic precursor cells into a graft
site. - Osteoconductive properties are found in cancellous
autografts and allografts, demineralized bone matrix,
hydroxyapatite, collagen, and calcium phosphate.
OSTEOINDUCTION(CONNOLLY, 1998; MOHAN
ANDBAYLINK, 1991)
- The ability of graft material to induce stem cells to
differentiate into mature bone cells
•Typically associated with the presence of bone growth
factors within the graft material
a. BMPs and demineralized bone matrix are the prin-
cipal osteoinductive materials.
b. Autograft and allograft bone also have some osteoin-
ductive properties (Muschler, Lane, and Dawson,
1990).
CREEPINGSUBSTITUTION(PROLO, 1990; STEINBERG
ET AL, 1989)
- An integrated process in which old necrotic bone is
slowly reabsorbed and simultaneously replaced with
new viable bone, thus incorporating bone grafts
a. Permanent mesenchymal cells differentiate into
osteoblasts and deposit osteoid around cores of the
necrotic bone.
b. Eventually results in the replacement of necrotic
bone within the graft.
BONE HEALING PROCESS- Fracture healing restores the tissue to its original
physical and mechanical properties and is influenced
by a variety of systemic and local factors (Kalfas,
2001; Perlman and Thordarson, 1999).- The most critical period of bone healing is the first
1–2 weeks. During this period, inflammation and
vascularization occur. - Systemic factors can inhibit bone healing includ-
ing the following:
a. Cigarette smoking (Glassman, 1998)
b.Malnutrition (Mankin, 1990)
c. Diabetes (Macey et al, 1995)
d. Rheumatoid arthritis
e. Osteoporosis (Kelsey and Hoffman, 1987)
f. Steroid medications: First week has most
impact (Jones, 1994)
g. Cytotoxic agents
h.Nonsteroidal anti-inflammatory medications
(Glassman et al, 2000)
- The most critical period of bone healing is the first
- Healing occurs in three distinct but overlapping stages
(McKibbin, 1978; Perren, 1979).
INFLAMMATORYSTAG E- A hematoma develops within the fracture site during
the first few hours and days. Inflammatory cells and
fibroblasts infiltrate the bone under prostaglandin
mediation. This results in the formation of granulation
tissue, ingrowth of vascular tissue, and migration of
mesenchymal cells. - Exposed skin cells, bone, and muscle provide the pri-
mary nutrients of this early process. - Anti-inflammatory or cytotoxic medications during
this first week are particularly detrimental (Kalfas,
2001).
REPAIRSTAG E- Fibroblasts begin to lay down a stroma that helps sup-
port vascular ingrowth. - At this stage nicotine can inhibit capillary ingrowth
(Daftari et al, 1994; Riebel et al, 1995).
•As vascular ingrowth progresses, a collagen matrix is
laid down while osteoid is secreted and subsequently
mineralized. This leads to the formation of a soft
callus around the repair site.- Callus is very weak in the first 4–6 weeks and
requires adequate protection (Kenwright and
Gardner, 1998). - Eventually, ossified callus forms a bridge of woven
bone between the fracture fragments. If proper
immobilization is not employed, failure of ossifi-
cation results in a fibrous union (Burchardt and
Enneking, 1978).
- Callus is very weak in the first 4–6 weeks and