IMPLANTS IN ORTHOPAEDICS

PRESENTOR-DR MOHAMMED NAYEEMUDDIN

MODERATOR-DR SACHIN SHAH

OVERVIEW OF THE TOPICS COVERED METALS AND IMPLANTS IN ORTHOPAEDICS---HISTORY---IMPLANTS OF FRACTURE FIXATION :EVOLUTION---PHYSICAL PROPERTIES---TESTING OF IMPLANTS---METALLIC IMPLANTS---NON METALLIC IMPLANTS---BIOMATERIALS USED IN ORTHOPAEDICS---CARBON COMPOUNDS AND POLYMERS BIOABSORABLE IMPLANTS IN ORTHOPAEDICS---ADVANTAGES---DISADVANTAGES ---FUTURE.

BASIC TERMS.  Implants are devices or tissues that are

placed inside or on the surface of the body. Many implants are prosthetics, intended to

replace missing body parts. STIFFNESS – it is the resistance of a

structure to deformation. RIGIDITY – it is used in context of fracture

fixation describes an implant or of a bone-implant construct physical property of resisting deformation under load.

ELASTICITY- it is the ability of a material to recover its original shape after deformation.

BASIC TERMS PLASTICITY – the ability of a material

to be formed to a new shape without fracture and retain that shape after load removal.

DUCTILITY – the ability of solid material is to be deformed under tensile stress and to be stretched into a wire without fracture. It also bestows capacity to be shaped eg. Construction of bone plates.

METALS AND IMPLANTS IN ORTHOPAEDICS

HISTORY- With the advent of antiseptic surgery

b/w 1860s and 1870s by LORD JOSEPH LISTER and anaesthesia by MORTON (ETHER) and SIMPSON (CHLOROFORM),the surgery developed rapidly.

When the development of technology in metallurgy and plastic took place – IMPLANT SURGERY simultaneously developed rapidly.

A further impetus to internal fixation was given by discovery of X –RAYS BY ROENTGEN in 1896.

LORD LISTER

Wilhelm Conrad Röntgen

IMPLANTS FOR FRACTURE FIXATION : EVOLUTION In the pre listerian days , many surgeons

were using hooks , pins and wires made of various metals – gold ,silver ,platinum or iron to manipulate and hold fracture fragment in position.

Bell in 1804 used silver coated steel pins and noted corrosion in them.

It was noted even at that time two different metals produced electrolytic corrosion.

LAVERT in animal experiment found platinum was the most inert metal but platinum, gold and silver were found to be too soft for clinical use.

EVOLUTION : CONTD The real development of implant surgery for

fracture fixation started advent of aseptic surgery.

LISTER himself was one of the first to successfully wire a fractured patella using a silver wire.

HANSMANN(1866) was one of the early person to fix a fracture with PLATE AND SCREW.

--his implants were made of nickel plated sheet steel, since corrosion and breakup of implants was well known then , he used plates which were bent at right angles and use to protrude out of wound and likewise screw heads were outside the skin,

--the whole implant was removed by 6-8wks ,when the fracture fragment was expected to be GUMMY.

EVOLUTION CONTD SIR WILLIAM ARBUTHNOT LANE

(BRITISH SURGEON & PHYSICIAN ) He was the early pioneer, who placed plate

and screw fixation on sound footing. He devised his form of plates. It was made of “STOUT STEEL” a high

carbon steel of fairly high percentage of carbon.

He devised “NO TOUCH” technique , to prevent wound infections and his own results bear testimony of his great skills.

However he and many other surgeons fail to distinguish b/w real wound infection vs infection caused by corrosion of metals.

His implants became brittle in nature and used to break at the junction of central bar and the 1st hole.

Sir William Arbuthnot Lane

EVOLUTION CONTD At the time that LANE was popularizing his

ideas in UK , the LAMBOTTE BROTHERS , ELIE and especially ALDIN were working in belgium on the fixation on fractures

They used other metals like aluminium, silver ,brass , magnesium and copper plates as well as steel coated with gold and silver.

Their plates were curved to fit the curvature of the bone.

The total disintegration of the magnesium plates used with steel screws underlined the effects of electrical corrosion when two separate metals were used.

EVOLUTION CONTD SHERMAN(1912). He improved the design of LANE’S plate

to make it stronger. His implants were made of “VANADIUM

STEEL”, an alloy containing much less carbon and 0.1-0.15% of vanadium along with small amounts of chromium and molybdenum.

In spite of this, staining of tissue was found by iron indicating presence of corrosion products.

EVOLUTION CONTD VON BAYER in 1908 introduced pins for

fixation of “small fragments” at the intra articular level.

EARNEST HEY GROVES in 1893 stressed the value of rigid fixation and showed that movement at the fracture site encouraged corrosion and break up of the fixation device.

He was the 1st to try fixing fractures of the femoral neck by round pins introduced through the trochanter , as well as the use of round intramedullary rods for the fractures of the shaft of long bones.

This idea was forgotten till revived by KUNTSHER in 1940.

Ernest William Hey Groves

EVOLUTION CONTD The story of stainless steel, it is said ,

started in SIBERIA with discovery of a new mineral “CHROMITE” way back in 1776.

The metal chromium extracted from chromite , a decade later, was found to posses an unusual property, AN EXTREMELY GOOD RESISTANCE TO CORROSION.

Then onwards chromium plating of metallic surface became popular.

EVOLUTION CONTD The discovery of chromium prompted

scientists in Europe and America to alloy with IRON.

The idea was to produce a good engineering material at a reasonable cost.

It was L GULLIET of France who was the 1st to make alloy systems close to what we call stainless steel.

P MONNARTZ of Germany after a research of 3 years 1st noticed that its rustlessness comes with making alloy when the concentration of CHROMIUM is atleast 13%.

EVOLUTION CONTD The 18-8 SMo was the 1st stainless

steel to give satisfactorily as an SURGICAL IMPLANT.

Its corrosion resistance is high and it is one of the best form of steel available.

But In 1959 ,BECHTOL,FERGUSSON AND LAING published their authoriatative work , ” Metals and Engineering in Bone and Joint Surgery ” , which described the superior property of type 316 stainless steel, after further work 316L STAINLESS STEEL is used coz of low carbide content.

EVOLUTION CONTD In last 30 years another metal which came

into use is TITANIUM because of its total inertness(chemically inactive) in the body.

Titanium has found more favours with neuro surgeons for covering the skull defects .

TITANIUM,VITALLIUM have the fabrication(invention)versatility and strength of stainless steel and excellent compatibilty in the body.

This metal was primarily used for aerospace application and is just starting to be used in the fabrication of surgical implants.

EVOLUTION CONTD A brief review of the various advances in

the design of implants for fracture fixation other than plates and screws is interesting

For fractures of femoral neck , SMITH-PETERSON in 1937 introduced the solid triflanged nail.

JOHNSON modified it into cannulated nail. TOURNTON AND MCLAUGHLIN separately

introduced the extra plate attachment to improve the fixation of the distal fragment.

Numerous other models including the JEWETT ONE PIECE FIXATION device has been introduced since then.

EVOLUTION CONTD For the fracture of shaft of long bones

especially femur , tibia and humerus , kuntscher revived the idea of intra medullary fixation but improved on hey groves original idea of round rods by using clover leaf or V-shaped nails.

Use of compression to bring about early fracture healing has found increasing favours.

DANIS of BELGIUM was the 1st to write about the biomechanics of fracture healing produced by a compression plate and screws.

He was the 1st to describe “PRIMARY HEALING ” of fracture.

EVOLUTION CONTD Sir JOHN CHARNLEY introduced and

popularised the compression method of arthodesis of joints especially the knee.

The AO GROUP (ARBEITGEMEINTSCHAFTS FUR OSTEOSYNTHESEFRAGEN) was formed in BIEL , switzerland by 13 surgeons on NOVEMBER 6th 1958.

A combination of high powered technology, metallurgical excellence and a high level of technical skill in optimum operating conditions has allowed a total change in the concept of many fractures by combining the principles of rigid fixation ,compression and early mobility.

Sir John Charnley(1911-1982)

AO CENTRE AT DAVOS,SWITZERLAND

PHYSICAL PROPERTIES When formulating a standard specification for

instrument and an implant , the following requirements are given due to consideration.

• Material sharpness of cutting instruments, freedom from surface defects

• Corrosion resistance • Fatigue resistance • Shape and dimensional compatibility • Tensile, torsional and bending properties • Interchangeability • Performance and ease of operation • Sterilization • Freedom from toxic effects • Marking and packaging.

TESTING OF IMPLANTS

Implants can be tested under following categories:

1) • Physical2) • Chemical3) • Structural4) • Biological.

TESTING OF IMPLANTS(CONTD) I.Physical Tests Following points are considered under this

category:a)• Appearance: Indian Standards Institute

[(ISI), the former name of the Bureau of Indian Standards (BIS)]

Specification directs that the implants should be free from cracks, draw marks, pits, burrs and surface contamination.

They should be polished bright .b).Weight: Screws of identical diameter,

geometry and length should weigh same, provided they are of the same alloy.

PHYSICAL TESTS (CONTD)

c)• Magnetism: The austenitic(primary phase) stainless

steel (ISI 316) is nonmagnetic. A magnet is applied to the implant

and tested for its magnetism. A small implant can be lifted up by

the magnet , A large implant when suspended will

be found to zoom(move) with the magnet.

PHYSICAL TESTS (CONTD)d)• Hardness: It is the ability to resist plastic

deformation under identical load. Rockwell superficial hardness

testing to scale 30T is used to comply with nondestructive testing and to check even the small components as well.

• This test involves a load of 30 kg and an indentor of 1/16 inch diameter ball. Two readings are taken and the mean is calculated.

PHYSICAL TESTS (CONTD) • Other methods. “IMPACT TEST” -- with an elevated

standard pendulum, the implant is struck and the energy absorbed in the fracture is measured.

•” Spark test”: Molybdenum has a characteristic

spark profile. • The implant is abraded on a standard

grinding wheel, and spark trajectories are noted for the characteristics.

II. CHEMICAL TESTS

These are studied under the following heads:

A. • Molybdenum detection testB. • Molybdenum percentage estimationC. • Corrosion test.

ISI 316 steel should contain molybdenum between 2.0% and 3.5%.

CHEMICAL TESTS(CONTD)A. Molybdenum Detection Test “Mini-Moly Detector” kit (produced by Met

Associates, Navsari, Gujarat State) is available in the market. It consists of an especially developed electrolyte solution and electrodes with a portable dry cell power source. The test procedure is as follows.

A drop of the electrolyte is placed on the stainless steel under test, and the electrodes are placed against the electrolyte solution. to turn pink or rosy red. If molybdenum is present, the drop will retain its hue and if not, the hue will fade rapidly.

CHEMICAL TESTS(CONTD)B. Molybdenum Percentage

Estimation This can be carried out by various metal

testing laboratories in all major cities.C. Corrosion Test (Aqua Regia) It contains hydrochloric acid and nitric

acid in the proportion of 3:1, and it is a strong solvent.

If the implants are of identical alloys, they should dissolve identically. The percentage loss is estimated and compared with the standard one.

III. STRUCTURAL CHARACTERISTICS These are considered under the following two heads: 1. Design specification 2. Mechanical stability.

1.Design Specification. ISI has laid down specifications for each implant. For example, bone screw can be checked against the following points: • Angle and diameter of the head • Slots • Thread diameter • Core diameter • Edge width • Angle of the thread and pitch • Angle of the tip and flutes. 2. Mechanical Stability. Geometry of the bone plates with regard to the location of screw

holes, thickness and acute bends are studied and compared with the ISI specifications.

IV. BIOLOGICAL COMPATIBILITY ISI has specified methods for testing biological

compatibility of metals for surgical implants.

Magnetic implants are liable to corrode by galvanic reaction in the body and hence should be rejected.

There has been argument that during manufacturing process, cutting tools would impart certain magnetism to implants. This argument is not tenable since in the process of buffing and subsequent cleaning, the magnetic particles would be wiped away and the implant should become nonmagnetic.

Every surgeon should test all his implants before purchase by various methods mentioned before.

Regarding mechanical stability, certain biomechanical principles need to be strictly adhered to,

They are:1. • Holes in the plates are potential sites

of weakness2. • Thicker the plate, more rigid it is3. • Acute angles and sharp bends in the

implants should be avoided, and4. • One piece implant is better

mechanically than joined implant.

METALLIC IMPLANTS STAINLESS STEEL 316L

(Fe+Cr+Ni+Mo+C+Mn+Si) There are at least 50 alloys and grades of alloys identified as

commercial stainless steel. Only a few are useful as implant biomaterial in fracture surgery.

Stainless steel designated as ASTM(American Society for Testing and Materials) F-55, -56 (grades 316 and 316L) is used extensively for fracture fixation implants.

Type 316L stainless steel is an iron-based alloy. Alloying with chromium generates a protective, self-

regenerating chromium oxide layer which provides a major protection against corrosion.

The addition of molybdenum decreases the rate of slow, passive dissolution of the chromium oxide layer by up to 1,000 times. Molybdenum further protects against pitting corrosion. Nickel imparts further corrosion resistance and facilitates the production process, while limited quantities of manganese and silicon are added to control some manufacturing problems.

STAINLESS STEEL 316L (FE+CR+NI+MO+C+MN+SI) The carbon component increases the

strength but in the alloy is undesirable. Type 316L stainless steel has a very low

permissible level of carbon to minimize this problem.

Though it is a strong, stiff and biocompatible material, 316L stainless steel has a slow but finite corrosion rate.

Concerns about the long-term effects of nickel ions, however, prevail. Stainless steel is best suited for short-term implantation in the body as in fracture fixation

STAINLESS STEEL 316L (FE+CR+NI+MO+C+MN+SI) Stainless steel is frequently used because the base materials are cheap, the alloy can be formed using common

techniques, and its mechanical properties can be controlled over a wide range for strength and ductility(is when a solid material stretches under tensile stress)

The elastic modulus(absolute value) of stainless steel is approximately 12 times higher than the elastic modulus of cortical bone.

COBALT-CHROMIUM ALLOYS

The cobalt-chromium-tungsten-nickel alloy (ASTM F-90) is used for manufacture of fracture fixation implants.

In clinical practice it is used to make wire and internal fixation devices including plates, intramedullary rods, and screws.

TITANIUM ALLOYS Titanium is the ninth most abundant element

in the earth’s crust. The pure element is very reactive; it is the only

element that burns in nitrogen. However, the metal rapidly becomes coated

with an oxide layer, making it physiologically inert and resistant to most chemicals.

Titanium is used for making orthopedic implants in two forms:

1. commercially pure 2. variety of alloys. Titanium-aluminum-vanadium alloy (ASTM F-

136) is commonly referred to as Ti6AI4V. This alloy is widely used to manufacture implants.

TITANIUM ALLOYS(CONTD). Commercially, pure titanium is not a single

chemical element, but is alloyed by a level of oxygen dissolved into the metal. It also has traces of iron, nitrogen, carbon and hydrogen.

Titanium has an elastic modulus approximately half that of the stainless steel and cobalt-chromium alloys.

The corrosion resistance of pure titanium is outstanding because a very dense and stable layer of titanium oxide (Ti02) is formed. This protective oxide layer may be destroyed mechanically during implantation by instruments such as bending pliers.

TITANIUM ALLOYS(CONTD). The passive layer is restored

spontaneously, rapidly and effectively (repassivation).

In the presence of unstable fixation, the titanium components of an internal fixation system are subjected to fretting conditions and produce metal debris.

Such debris causes gray or black coloration of the surrounding tissues.

This discoloration, which is not a result of corrosion, is “harmless”.

STAINLESS STEEL VS TITANIUM ALLOY

FACTORS STAINLESS STEEL

TITANIUM ALLOY

1. ELASTICITY AND DUCTILITY

LESS MORE

2.ENDURANCE LIMITS(STRESS LIMITS)

SAME SAME

3.COST CHEAP COSTLY

4.CORROSION RESISTANCE & TOXIC IONS

+VE COZ OF CHROMIUM N NICKEL

-VE

5.ALLERGIC REACTION. +VE -VE6.SECOND OPERATION MAY REQUIRE HIGH COST IS OFTEN

COMPENSATED COZ IMPLANT CAN BE LEFT INSITU & 2ND SURGERY IS OFTEN UNNECESSARY.

NICKEL-TITANIUM ALLOY / NITINOL

It is a Shape Memory Alloy (SMA) was discovered in 1965.

Nitinol is an acronym for nickel titanium naval ordnance laboratory, where the alloy’s remarkable properties were discovered.

The alloy contains nearly equal numbers of nickel and titanium atoms, leading to its common compositional representation as NiTi.

Shape Memory Alloy can be “trained” to take on a predetermined shape in response to a stimulus such as a change in temperature.

NICKEL-TITANIUM ALLOY / NITINOL Implant made from SMA has the ability to

return to its original shape after the environment temperature rises to a certain level (e.g. 37 deg C). Its shape can be changed easily at low temperature (e.g. O-5 deg C).

SMA can be bent, compressed, or deformed in many other ways, but can then be made to recover its original shape by heating.

USES/CLINICAL APPLICATIONS:a. Compressive staples for fibula and scaphoid, b. Clamp-on bone plates, c. long bone fixator and patella fixator

NONMETALLIC IMPLANTS

Biomaterials now have a large subsection of nonmetallic implants which find use in miscellaneous other indications.

Biomaterials can be defined as being “natural or synthetic substances, capable of being tolerated permanently or temporarily by the human body.’

Biocompatibility of these biomaterials could be graded as inert (ceramics), interactive (tantalum), viable (biodegradable polymers), replant (cultured native tissue).

BIOMATERIALS USED IN ORTHOPEDICS

• Metal and metal alloys: As discussed earlier in this chapter

• Ceramics and ceramo-metallic materials

• Carbon materials and composites, polymers.

Ceramics and Ceramometallic Materials

CERAMICS AND CERAMO-METALLIC MATERIALS

Ceramic is a synthesized, inorganic, solid, crystalline material excluding metals.

They can be classified into: 1.Bioinert Ceramics 2. Bioactive ceramics

3.Bioresorable ceramics 1. BIOINERT CERAMICS They are incorporated in the bone in accordance

with pattern of contact osteogenesis. There two types , alumina ceramics (A1203) and

zirconia ceramics (Zr02). Alumina is chemically more stable than PSZ in vivo, While PSZ is mechanically stronger than alumina

and both of them exhibit much better wear resistant characteristics compared to stainless steel .

Used in making ceramic hip prostheses

CERAMICS AND CERAMO - METALLIC MATERIALS 2. Bioactive Ceramics These have a characteristic of osteoconduction and

the capability of chemical bonding with living bone tissue in accordance with the pattern of “bonding osteogenesis’

These include glasses, glass ceramics and ceramics that elicit a specific biological response at the interface between the material and the bone tissue which results in the formation of a bond between them.

Bioglass , apatitewollastonite containing glass ceramics (AW-GC) and synthetic hydroxyapatite (HA) are representative materials currently used for clinical applications.

Using AW-GC various bone prostheses like vertebral prosthesis, iliac crest prostheses, intervertebral spacers, laminoplasty spacers were fabricated.

CERAMICS AND CERAMO - METALLIC MATERIALS

3.Bioresorbable Ceramics These are gradually absorbed in vivo

and replaced by bone in the bone tissue. The pattern of their incorporation in the

bone tissue is considered similar to contact osteogenesis, although the interface between bioresorbable ceramics and bone is not stable as that observed with bioinert ceramics.

 

CARBON COMPOUNDS AND POLYMERS

Carbon Compounds In spite of unrivalled endurance to fatigue,

biomedical carbon is not gaining popularity.

Due to less structural flexibility, less bending resistance, intolerance to lengthening it is not gaining popularity.

Particles found in the spleen means that we should be careful in using these components.

Polymers Silicones These are chemically inert, have good biotolerance, and high

hydrophobic capacity. They are used in plastic surgery or in orthopedics in the form

of elastomer, rubbers for joint prostheses of fingers. Polyacrylics Polymethyl methacrylate (PMMA) is used as the

polymer of choice in securing implant to bone since its introduction in 1970s by Sir John Charnley.

It is provided in two parts, liquid monomer which helps methacrylate powder to polymerize. Radiopaque barium sulfate or zirconia helps its visualization on radiographs.

The reaction is exothermic. Clinical studies show that thermal necrosis caused

by the heat does not affect overall performance. Antibiotics added can aid in prophylaxis or treatment of infection.

BIOMATERIALS PRODUCED BY HUMAN CELLULAR AND TISSUE ENGINEERING

Tissue engineering is a multidisciplinary field that enlists the knowledge and experience of scientists involved in materials science, biomedical engineering, cell and molecular biology, and clinical medicine to produce of biomaterials that can replace ill functioning or missing tissues or organs.

Tissue engineered biomaterials are clearly an important development.

We can imagine being able to reach into the freezer, take out a cell culture, treat it with growth factors on a scaffold matrix, and produce almost any tissue in the human body. This may be a common clinical practice in future.

BIOABSORBABLE IMPLANTS IN ORTHOPAEDICS

BIOABSORBABLE IMPLANTS IN ORTHOPAEDICS

Introduction The principal focus in modern implant development is

on developing devices that are stronger, durable and more acceptable to the body.

Biodegradable implants have allowed a paradigm shift away from bionic (mechanical replacement) engineering toward true biologic solutions in orthopaedics reconstruction.

There are inherent problems with the use of these metallic devices like stress shielding phenomenon( reduction in bone density (osteopenia) as a result of removal of typical stress from the bone by an implant ), pain, local irritation.

Retained metallic implants carry risk of infection. Metal ion release implants are recorded, though long-term effects of these are not yet known.

BIOABSORBABLE IMPLANTS IN ORTHOPAEDICS History Low molecular weight polyglycolic acid (PGA)

was synthesized by Bischoff and Walden in 1893. ‘the first synthetic absorbable suture was developed from PGA by American Cyanamid Co. in 1962.

‘Vicryl’ has been successfully used since 1975; similar materials have shown no carcinogenic, teratogenic, toxic, or allergic side effects; mild nonspecific inflammation may be encountered sometimes.

Use of PGA as reinforcing pins, screws, and plates for bone surgery was first suggested by Schmitt and Polistina.

POLYGLYCOLIC ACID(PGA) It is a hard, tough, crystalline polymer with an

average molecular weight of 20,000-145,000 and melting point of 224-230°C.

In orthopedic implants poly-L-lactic acid (PLLA) has been used more extensively because it retains its initial strength longer than poly-D-lactic acid (PDLA).

PGA belongs to the category of fast degrading polymers, and intraosseously implanted PGA screws have been shown to completely disappear within 6 months.

PLLA, on the other hand, has a very long degradation time and has been shown to persist in tissues for as long as 5 years post- implantation.

BIOABSORBABLE IMPLANTS Advantages The biggest advantage is that since these

implants have the potential for being completely absorbed, the need for a second operation for removal is overcome

Long-term interference with tendons, nerves and the growing skeleton is avoided.

Additionally, the risk of implant-association stress shielding and infections is reduced.

An important aspect is that these implants do not interfere with clinical imaging, allowing MRIs at any stage after surgical implantation.

CURRENT USES1. Biodegradable implants are available for stabilization

of fractures, osteotomies, bone grafts and fusions particularly in cancellous bones, as well as for reattachment of ligaments, tendons, meniscal tears and other soft tissue structures.

2. Arthroscopic surgery is the most recent orthopedic discipline to embrace biodegradable implant technology. It is used extensively for anterior cruciate ligament (ACL) reconstruction in the form of interference screws and transfixion screws. In the shoulder rotator cuff tears, shoulder instability, and biceps lesions that require labrum repair or biceps tendon tenodesis can be managed with these implants.

3. Bioresorbable material use in pediatric situations was perhaps the earliest recorded use in orthopedic literature. These have been used as self-reinforced absorbable rods for fixation of physeal fractures, in paediatric olecranon and elbow #s.

CURRENT USES4.Ankle fracture fixation is another area where self-

reinforced absorbable rods have been successfully employed. Bioabsorbable implants offer specific advantages in the foot where removal of the hardware is mandatory in some fixations like syndesmotic disruptions and Lisfranc’s dislocations.

5.There are bioabsorbable implants now available for use in humeral condyle, distal radius and ulna, radial head and other metaphyseal areas. Bioabsorbable meshes are available for acetabular reconstructions.

6. Bioabsorbable implants are also variously used in cranio-maxillofacial surgery and dental surgery.

DISADVANTAGES. There are quite a few problems that need to be addressed with the

use of these devices. Primarily, the inadequate stiffness of the device and weakness

compared to metal implant can pose implantation difficulties like screw breakage during insertion and also make early mobilization precarious.

The other potential disadvantages are an inflammatory response described with bioabsorbable implants, rapid loss of initial implant strength and higher re-fracture rates.

Bostman et al. reported an 11% incidence of foreign body reaction to PGA screws in malleolar fracture. However, the fracture fixation did not suffer in any case.

Problem areas of concern regarding faster resorbed implants are due to the fact that the body mechanisms are not able to clear away the products of degradation, when they are produced at faster rate. This leads to a foreign body reaction, which however, has only been recorded in the clinical situation. No experimental study has been able to document this, nor have the exact mechanisms and causes identified.

Many manufacturers are introducing colored implants, but the literature records significantly higher rates of inflammatory reaction with the use of colored implants.

FUTURE Bioabsorbable implant research is an evolving science.

Resorbable plates can be covalently BMP-2 and represents a novel protein delivery technique. BMP-2 covalently linked to resorbable plates has been used to facilitate bone healing. Covalent linking of compounds to plates represents a novel method for delivering concentrated levels of growth factors to a specific site and potentially extending their half-life.

An area for future development would have to focus on developing implants that degrade at the “medium term’ Since the screw that persists in its track for 5 years or more does not offer the advantage of bioresorbability, newer molecules may have to be studied.

In vitro studies have shown promising results of antibiotic elution from bioabsorbable microspheres and beads.

Animal in vivo tests have shown that antibiotic impregnated polymers can successfully treat induced osteomyelitis in rabbits and dogs.

All in one, this is a concept that has perhaps come to stay. What the future holds in this sphere, is something we will have to wait and see.