Bone grafts

BONE GRAFTS

BONE STRUCTURE Bone is not a uniformly solid material,

but rather has some spaces between its hard elements.

CORTICAL /COMPACT BONE - The hard outer layer of bones is composed of compact bone tissue, so-called due to its minimal gaps and spaces. Its porosity is 5–30%.

- 80% of total bone mass of a skeleton - consists of haversian canal and osteons

CANCELLOUS/SPONGY/TRABECULAR BONE

- Filling the interior of the bone is the trabecular bone tissue - composed of a network of rod- and plate-like elements that allow room for blood vessels and marrow. - accounts for the remaining 20% of total bone mass. - Its porosity is 30–90%

BONE GRAFTING Bone grafting is a surgical procedure

that places new bone or a replacement material into spaces between or around broken bone (fractures)

or in holes in bone (defects) to aid in healing.

USES Used to repair bone fractures that are

extremely complex, pose a significant risk to the patient or fail to heal properly.

Used to help fusion b/w vertebrae, correct deformities or provide structural support for fractures of the spine.

To repair defects in bone caused by congenital disorders, traumatic injury, or surgery for bone cancer.

Also used for facial or cranial reconstruction

MAJOR FUNCTIONS OF GRAFT MATERIAL OSTEOGENESIS

OSTEOINDUCTION

OSTEOCONDUCTION

Hemorrhage Inflammatory response

OSTEOGENESIS - formation of new bone by the cells contained within the graft.

OSTEOINDUCTION involves the stimulation of osteoprogenitor cells to diffr. into osteoblasts that begin new bone formation. Most widely studied type of osteoinductive cell mediators in grafts are bone morphogenetic proteins (BMPs).

OSTEOCONDUCTION bone graft material serves as a scaffold

for new bone. Osteoblasts from the margin of the

defect utilize the bone graft material as a framework upon which cells spread and generate new bone

INDICATIONS To promote union as in - Fresh fractures - Delayed union - Malunion - Osteotomies

To bridge joints and thereby provide arthrodesis.

To bridge major defects or establish the continuity of a long bone.

To fill cavities/defects secondary to - Trauma - Tumor - Infections and other conditions

CLASSIFICATION1)based on the donor origin - autograft - allograft - xenograft2)based on composition -cortical -cancellous -osteochondral

3) Blood supply: Non-vascularised Vascularised

4) Preservation

- fresh - frozen - freeze dried - demineralized

5) based on anatomical features - epiphyseal -metaphyseal -diaphyseal

AUTOGRAFT Bone harvested from the patient’s own

body. Gold standard - sufficient bone of the

sort required is available & at the recipient site, there is a clean vascular bed.

Iliac crest – commonest site.

SOURCES1) Cortical bone graft – for filling bone gaps Tibia mainly, iliac crest & fibula also.

2) Cancellous bone graft – for osteogenic purpose (eg: non-union). Thicker portions of the ilium, greater

trochanter, proximal metaphysis of the tibia, lower radius, olecranon or from an excised femoral head.

3) Whole bone graft – fibula.

Cancellous grafts become incorporated more quickly & more completely than cortical grafts

The graft stimulates an inflammatory response with the formation of a fibrovascular stroma; through this, blood vessels & osteoprogenitor cells can pass from the recipient bone into the graft.

Disadvantages donor site morbidity Ambulation is delayed until the defect is

partially healed pain and infection at the site from which

the graft is taken Vascularized grafts - sophisticated

microsurgical techniques are necessary & in major sites of loading , osseous hypertrophy may occur

VASCULARISED GRAFTS Muscle-pedicle bone grafting bone graft is taken along with pedicle of muscle (with intact blood supply which will supply blood to graft). - eg: non-union fracture neck of femur.

Free vascularised grafting – bone (fibula) is taken along with the vessels supplying it.

- eg:- the iliac crest (complete with one of the circumflex arteries), the fibula (with the peroneal artery).

- Middle 1/3rd of fibula– used as a vascularised free autograft based on the peroneal artery and vein pedicle using microvascular technique - for treatment of large defects in cong pseudarthrosis of tibia.

ALLOGRAFT Graft obtained from a person other than

the patient (live or dead). Indicated in 1) small children, where the usual donor

sites don’t provide cortical grafts large enough to fill a large cavity and when there is possibility of physeal injury.

2) aged persons 3) patients with poor operative risks Usually taken from cadavers; it is

typically sourced from a bone bank.

There are three types of bone allograft available:

1. Fresh or fresh-frozen bone2. Freeze-dried bone allograft (FDBA)3. Demineralized freeze-dried bone allograft (DFDBA)

Advantages Using allograft tissue from another

person eliminates the need for a second operation to remove autograft bone or tendon.

It also reduces the risk of infection, and safeguards against temporary pain and loss of function at or near the secondary site.

Disadvantages Bone variability because it is harvested

from a variety of donors. Longer time to incorporate with the

host bone and may be less effective than an autograft.

Possibility of transferring diseases to the patient(viral transmissions).

Potential immune response complications.

XENOGRAFT (HETEROGENOUS GRAFTS) Graft obtained from another species. Xenograft bone substitute has its origin

from a species other than human, such as bovine.

Xenografts are usually only distributed as a calcified matrix.

S/E- foreign body reaction.

SYNTHETIC VARIANTS (BONE SUBSTITUTES) Material derived from corals Artificial bone can be created

from ceramic such as calcium phosphates – porous str. (e.g.hydroxyapatite and tricalcium phosphate), Bioglass and calcium sulphate; all of which are biologically active to different degrees depending on solubility in the physiological environment.

Hydroxyapatite is crystalline calcium phosphate. Slow resorption

ALLOPLASTIC GRAFTS made from hydroxylapatite, a naturally

occurring mineral that is also the main mineral component of bone. They may be made from bioactive glass.

calcium carbonate - unpopular ;completely resorbable in short time which make the bone easy to break again

These materials can be doped with growth factors, ions such as strontium or mixed with bone marrow aspirate to increase biological activity.

The presence of elements such as strontium can result in higher bone mineral density and enhanced osteoblast proliferation in vivo.

DIAGNOSIS/PREPARATION The surgeon does a clinical examination,

and conducts tests to determine the necessity of a bone graft,to determine the precise location of damage,exact amount of damage.

These tests include x-rays, MRI, CT scan

Arrange for blood in case a transfusion is needed

Proper nutrition to achieve good nutritional status before and after surgery.

VARIOUS TECHNIQUES Single onlay cortical graft: was mainly used

for ununited diaphyseal fractures , used for a limited group of fresh, malunited and ununited fractures.

- bridging joints to produce arthrodesis, for both fixation and osteogenesis.

Dual onlay grafts: used in treating difficult and unusual nonunions or for bridging of massive defects.

- eg: for nonunion near a joint - not as strong as metallic fixatives - not very osteogenic

Inlay Grafts: - A slot or rectangular defect is created in the cortex of the host bone. - occasionally used in arthrodesis particularly at ankle. - complex and less efficient

Peg Grafts- for fixation alone - weaker - use limited to non-union of medial malleolus and small bones of hand ,wrist or foot. Medullary Graft - poor healing,

interferes with endosteal circulation; rarely used except in metatarsals, metacarpals and distal radius.

Osteoperiosteal Grafts- less osteogenic than multiple cancellous grafts ,and are rarely used.

Multiple cancellous chip grafts -widely used, best osteogenic material. -useful for filling cavities & cysts ,for establishing bone blocks, and for wedging in osteotomies. -Soft and friable.

Hemicylindrical grafts- for obliterating large defects in tibia and femur.

- massive hemicylindrical cortical graft from affected bone is placed across the defect and is supplemented by cancellous bone.

TIBIAL GRAFT HARVESTING Tourniquet to be applied. Make a slightly curved longitudinal

incision over AM aspect of tibia Incise and reflect the periosteum Drill a hole at each corner of the

anticipated area. Remove the graft by cutting through the

cortex at an oblique angle. Remove cancellous bone from the

proximal end of tibia with a curet.

Disadvantages - normal limb is jeopardised - Convalescence is prolonged - Tibia more prone for fractures for 6-12 months.

FIBULAR GRAFT HARVESTING3 points to be considered:--peroneal nerve must not be damaged.-distal 1/4th of the bone must be left to maintain a stable ankle.-do not cut peroneal muscles. Resect the middle 1/3rdDissect along the anterior surface of septum b/w peroneus longus and soleus.

Reflect peroneal muscles anteriorly. Start stripping till fibula exposed. Drill holes through fibula at the

anticipated area of graft. Graft harvested

RISKS OF ILEAL GRAFT HARVESTING acquired bowel herniation (this becomes

a risk for larger donor sites (>4 cm)). meralgia paresthetica (injury to the

lateral femoral cutaneous nerve also called Bernhardt-Roth's syndrome)

pelvic instability fracture (extremely rare and usually

with other factors)

injury to the ilioinguinal nerve infection minor hematoma (a common

occurrence) deep hematoma requiring surgical

intervention seroma ureteral injury pseudoaneurysm of iliac artery (rare)

BONE BANKING To efficiently provide safe and useful

allograft material. Uses thorough donor screening,rapid

procurement, and safe sterile processing.

Donor screening for bacterial,viral and fungal infection.

C/I- malignancy( except BCC), collagen vascular diseases,metabolic bone dissease and presence of toxins.

Bone can be harvested in a clean nonsterile environment, sterilised by irradiation,strong acid or ethylene oxide , and then freeze dried for storage.

Bone under sterile conditions , can be deep frozen (70-80 deg) for storage.

Fresh frozen bone is stronger than freeze-dried bone.

Cancellous bone can be obtained in a demineralised form.

RECENT ADVANCES New BMP products are expected to be

strong inducers of bone growth (osteoinductive).

These new products will be relatively expensive, but will grow bone better than the patient's own bone, eliminating the need for bone graft harvesting.

The INFUSE Bone Graft (rhBMP-2, BMP 7) has received approval.

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