Reconstructive surgery

13.6 Reconstructive surgery

13.6.1 Plastic surgery

The many different biomaterials used in plastic surgery include collagen, silicone (polydimethylsiloxane), Teflon , polyethylene, Dacron and polyglocolic acid. Polysiloxanes are widely used in reconstructive plastic surgery because of their lack of any tissue reactivity, mechanical properties and structure. Polysiloxane may

be either heat vulcanized or vulcanized at room temperature for more delicate structures and is ideal for soft tissue replacement where repeated flexure occurs. In applications where strength is also required, steel wire reinforcement is necessary. The material is used not only for implants but also for explants where it is moulded to fit a specific shape, coloured to give a skin match and fixed with tissue adhesive. Common examples are ear prosthesis or facial reconstruction after loss due to injury or cancer surgery. Silicone

Figure 13.7 Shoulder joint prosthesis (courtesy P. Marquis, mammary implants are now widely used for cosmetic

Dental School, Birmingham) .

Biomaterials 401

Patella bearing

Femoral

surface

bearing surface

Femoral guide surface

FGS Tibial

guide surface

TGS Mobile bearing

Smooth metal tibial plate

(a)

(b)

Figure 13.8 A total knee replacement joint (a) schematic diagram (after Walker and Sathasiwan, 1999 and (b) photograph of a stainless steel prosthesis (courtesy R. Grimer, Royal Orthopaedic Hospital, Birmingham) .

reasons or after mastectomy for breast cancer. These Often the effective prostheses can improve the confi- have an outer shell with the appropriate shape and

dence and well-being of the patient beyond the imme- resilience covering an inner volume of silicone gel.

diate functional repair. The jaw, and jaw bone area, can In these reconstructions Dacron may be used as a

utilize many of the metal implants already discussed. lining for the ear and as a backing in a breast implant

Commercially pure titanium in perforated sheet form to provide a better fastening of the implant to the

has been used because of its biocompatibility and ease surrounding tissue.

of manipulation and fixing.

Polymers, particularly silicones and polyurethanes,

may be used to replace flexible tissues of the nose, Disease or injury to the oral and facial area may be

13.6.2 Maxillofacial surgery

cheek and ear regions of the face. Polysiloxanes have repaired by implants from a range of biomaterials.

been used for onlays in the area of the molar bone in

402 Modern Physical Metallurgy and Materials Engineering the lateral side of the mandible or over the forehead to

to give valve recipients anticoagulant drugs. Nowa- smooth it. Reinforced with stainless steel wires they

days, advanced valves are made with Co–Cr or tita- can also replace the mandible. A porous composite

nium bodies with metal or graphite discs, or occluders, of polytetrafluoroethylene (PTFE) strengthened with

coated with pyrolytic carbon. These coatings are made carbon fibres may be used to replace damaged bone

by heating a hydrocarbon, such as methane, to about structures. Both PTFE and carbon are biocompatible

C depositing the carbon vapour on the graphite and fibrous tissue growth into the pores ensures bond-

surface to a thickness of about 1 mm. Small amounts ing of the artificial and natural bone. Composites of

of silane mixed with the CH 4 adds Si to the deposit, hydroxyapatite in a polyethylene matrix HAPEX have

increasing its strength. Pyrolytic carbon is strong and been used for patients who had either fractured the

wear resistant but, more importantly, resists the forma- orbital floor supporting the eye or had lost an eye. A

tion of blood clots on its surface. The discs are attached great advantage of such material implants is that they

by a coated Ti metal arm to a fabric ring made of poly- can be shaped during the operation and inserted on

mer (PTFE) which is sewn to the tissue of the heart the base of the eye socket and bonded firmly to the

valve opening. Dacron cloth has also been used and supporting bone.

encourages tissue growth with better anchorage and thromboembolic resistance.

The prosthesis has moving parts and thus catas- HAPEX

13.6.3 Ear implants

trophic failure by fracture is a finite possibility. As an has been also used successfully for other clin-

alternative, the construction of artificial valves from ical replacements, mainly middle-ear implants. These

biological tissue has been developed. Collageneous transmit sound from the outer to inner ear where the

vibrations are translated into electrical signals to be tissue from the heart wall of cows and heart valves processed by the brain. Middle-ear malfunction can

from pigs have been used to make these ‘bioprosthetic’ lead to deafness (conduction deafness) which may

valves. These valves are naturally biocompatible with

be cured by implant surgery. Otosclerosis (middle-ear deafness) may result from fibrosis of the middle ear caused by repeated infections or from an hereditary disease. A stapedectomy removes a small amount of bone and immobilized tissue and replaces it with bio- material. The implant has a hydroxyapatite head on a HAPEX shaft which can be trimmed and shaped in the operating theatre using an ordinary scalpel to fit the individual patient.