Wednesday, March 25, 2009

De Mayo Universal Distractor™

De Mayo Universal Distractor™

A solution that works better for doctors
and patients

The ingenious, new De Mayo Universal Distractor™ gives you a clear, unobstructed view of the surgical field, while delivering precise, finite joint distraction. The patentpending technology employs an external positioner that works without tying up a pair of hands or relying on lamina spreaders. You get finite distraction and reduced procedure time for Unicompartmental and TKA surgeries.

De Mayo Universal Distractor

De Mayo Universal Distractor

Sunday, March 8, 2009

Types of Bone Fractures

Fractures can occur when too much pressure is applied to a bone. Learn about the different types of bone fractures.
video

Trauma and orthopaedic surgery

Trauma and orthopaedic surgery

MRCS candidates should:

  • Have a knowledge of the surgical conditions listed below
  • Know the principles of investigations used by the speciality
  • Know the principles of the main surgical procedures used

Skeletal fractures

Soft tissue injuries and disorders

Common disorders of the extremities

Degenerative and rheumatoid arthritis

Infections of bones and joints

Locomotor pain

Bone tumours and amputations

General

  • Imaging techniques
  • Neurophysiological investigations

Trauma and orthopaedic surgery

MRCS candidates should:

  • Have a knowledge of the surgical conditions listed below
  • Know the principles of investigations used by the speciality
  • Know the principles of the main surgical procedures used

Skeletal fractures

Soft tissue injuries and disorders

Common disorders of the extremities

Degenerative and rheumatoid arthritis

Infections of bones and joints

Locomotor pain

Bone tumours and amputations

General

  • Imaging techniques
  • Neurophysiological investigations

Wednesday, March 4, 2009

Floating Elbow: Multimedia

Multimedia

Grade IIIA open ulna fracture in a motorcyclist w... Media file 1: Grade IIIA open ulna fracture in a motorcyclist with associated radial head humeral injuries.
Grade IIIA open ulna fracture in a motorcyclist w...

Grade IIIA open ulna fracture in a motorcyclist with associated radial head humeral injuries.

Close-up of radial head dislocation with evidence... Media file 2: Close-up of radial head dislocation with evidence of air in soft tissues.
Close-up of radial head dislocation with evidence...

Close-up of radial head dislocation with evidence of air in soft tissues.

Ipsilateral segmental humeral fracture. Media file 3: Ipsilateral segmental humeral fracture.
Ipsilateral segmental humeral fracture.

Ipsilateral segmental humeral fracture.

Initial management of the Monteggia injury consis... Media file 4: Initial management of the Monteggia injury consisted of debridement and irrigation of the extensively contaminated ulna fracture and application of an external fixator for stability and reduction of the radial head dislocation. The humeral fracture was splinted.
Initial management of the Monteggia injury consis...

Initial management of the Monteggia injury consisted of debridement and irrigation of the extensively contaminated ulna fracture and application of an external fixator for stability and reduction of the radial head dislocation. The humeral fracture was splinted.

Definitive management of the fractures was perfor... Media file 5: Definitive management

Metallic Alloys

Introduction

Metal has been used extensively in the manufacturing of orthopedic implants in a multitude of different forms. Multiple different materials throughout history have been tested as replacements for bone. Materials as diverse as ivory, wood, rubber, acrylic, and Bakelite have been used in the manufacture of prosthetic implants.

The extensive use in modern times of metallic alloys is related to the availability and success at the beginning of the 20th century of several different alloys made of the noble metals. Implants made from iron, cobalt, chromium, titanium, and tantalum are commonly used. Clinical studies have demonstrated that alloys made from these metals can be used safely and effectively in the manufacturing of orthopedic implants that are left in vivo for extended periods. The mechanical, biologic, and physical properties of these materials play significant roles in the longevity of these implants.

Implants are made in 3 basic ways:

  • Implants can be machine milled or drilled into a desired shape.
  • Implants can be cast, which means that the implant is formed from molten metal that is poured into a mold.
  • Implants can be forged, which means that the implant is shaped into its final form with the use of forces such as bending or hammering.

Alloys that provide for a long-term stable implant need to have a high level of corrosion resistance as well as certain mechanical properties (see Immune Response to Implants).

Metals

An element is considered metallic if a positive charge is demonstrated on an electrolysis test.1 This test consists of dissolving the element in acid and running a current through the solution. When such elements are fully reduced, their metallic nature is recognized and they and their alloys are called metals; when oxidized, they can serve as ceramic materials.

Metals have several properties that are specific to them, including malleability, which allows the shaping of metal into implants, and ductility, which refers to the ability to draw out metal in the shape of wire and is an important property in allowing the manufacture of intramedullary rods, screws, and long stems. By combining several metallic elements together in alloys, improved properties can be achieved beyond those of a single element. The alloys used in orthopedic surgery need to have certain specific properties. Because the alloy of the implant is bathed in body fluid, a low rate of corrosion and relative inertness are imperative in the material.

All metallic alloys have a modulus of elasticity significantly higher than that of bone. This mechanical incompatibility causes implants to be structurally stiffer than bones. Alloys with elastic moduli closer to bone may cause less stress shielding.

Different metals can form a battery effect when in solution in the body. The galvanic series provides electrochemical comparisons that allow for predictions of corrosion between 2 different metals when they are in physical contact in saline solution.2 Galvanic corrosion occurs if stainless steel surgical wire is wrapped over a cobalt- or titanium-based alloy femoral component or if a cobalt-chromium femoral head is placed on a titanium alloy femoral stem, so this metal mismatch is not recommended. Cobalt- and titanium-based alloy components may be used in contact with each other, and stainless steel components, such as sutures, may be used with either if actual physical contact is avoided.

Surgical Stainless Steel

The introduction of steel plates for fracture treatment is credited to Sherman.3 Surgical stainless steel alloys (316L) made with varying amounts of iron, chromium, and nickel are presently used in the manufacture of prostheses. The low carbon (L) in surgical stainless steel diminishes corrosion and decreases adverse tissue responses and metal allergies. While many implants are still manufactured from this excellent material, its use is relegated mainly to plates, screws, and intramedullary devices that are not meant to be weight bearing for an extended period. Fatigue failure and relatively high corrosion rates make it a poor candidate for the manufacture of modern joint replacement implants.

Chromium-containing iron (and cobalt base) alloys have a chromium oxide–based surface that is a result of passivation or oxidation of the surface. The chromium oxide forms a very thin invisible shield that provides resistance to biodegradation. Because this oxide layer slowly dissolves in vivo, these alloys have a relatively high rate of corrosion. This is evident as a propensity toward both fretting and crevice corrosion, which limits the possibility for biologic fixation or for the manufacture of modular implants.

Cobalt-Based Alloys

Venable and Stuck discovered the battery effects of metals in the body through their testing of the electrolytic effects of various metals on surrounding tissue and bone.1 These tests demonstrated the low level of corrosion of the cobalt-based alloy vitallium. Alloys made of cobalt, chromium, and molybdenum can be used in various different porous forms to allow for biologic fixation by ingrowth. These alloys are among the least ductile when compared to either iron- or titanium-based alloys, making manufacture of these intramedullary rods and spinal instrumentation more difficult. These alloys have some of the highest moduli of elasticity observed in orthopedic implants, and as a result, this was a factor in the stress shielding and thigh pain observed in the first generation of biologically fixed femoral hip implants made with cobalt alloys.4

These alloys are well suited for the production of implants that are designed to replace bone and to be load bearing for an extended period, if not permanently.

The Austin Moore prosthesis and the Thompson prosthesis were manufactured from the cobalt-based alloys. The first-generation biologically fixed implants (ie, porous-coated anatomic [PCA] and anatomic medullary locking [AML] implants) were manufactured of this material. Numerous modern prostheses are still manufactured from this excellent alloy and are used in both cemented and porous forms for hip and knee replacement.

Titanium-Based Alloys

In 1951, Levanthal introduced titanium as a metal for surgery.5 Titanium-based alloys have excellent properties for use in porous forms for biologic fixation of prostheses. The most common is Ti-6 aluminum Ti-4 vanadium (Ti6Al4V), but other more modern alloys are coming into use. Because of the lower moduli of elasticity than cobalt-based alloys or surgical stainless steel, titanium-based alloys have not been found to be as reliable a material when used as a cemented hip replacement. Moreover, its use in total knee replacements has been limited to the nonarticulating parts of the tibial component because of significant wear observed in femoral heads.

Titanium's high level of biocompatibility, low level of corrosion, and modulus of elasticity closer to that of bone allow for its use in numerous porous implants that have yielded excellent long-term results. The low level of corrosion allows for the construction of modular implants that saves in inventory and allows for more precise implant fit.

Current use in various forms is in the production of fracture plates and intramedullary rods and in the production of both femoral and acetabular implants designed for bone ingrowth. Fracture fixation components fabricated from titanium-based alloys are also used preferentially when the implant site is known to be infected or when postoperative shadow-free imaging is desired.

Tantalum and Composites

Tantalum

Tantalum is also remarkably resistant to corrosion and has been used as an ingredient in super alloys, principally in aircraft engines and spacecraft, although 50% of current use is in the form of powder metal for the manufacture of transistors and capacitors. Tantalum can be fabricated in a highly porous form, which has a modulus of elasticity closer to that of bone than stainless steel or the cobalt-based alloys. Tantalum balls have been used in studies that have required bone markers; however, it has not been used in the manufacture of implants until recently. Because of its remarkable resistance to corrosion, tantalum is well suited to a biologic ingrowth setting.

Recent use of tantalum has been in the form of a honeycombed structure that is extremely porous and conducive to bone ingrowth. It is currently available in several forms for bridging bone defects, but its use in the manufacture of femoral stems has yet to occur. Tantalum appears to be a promising metal for use in acetabular reconstruction, but long-term studies need to be conducted.6, 7

Composites

The combination of metallic alloys with other biomaterials can result in implants with improved mechanical and physical properties. Current attempts in designing composite implants have not yielded highly successful results; however, the future possibilities for improvement are promising.

Wear

Different alloys demonstrate different rates of wear. The hardness of an alloy and the smoothness of the bearing surfaces determine its relative rate of wear. Cobalt-chromium-molybdenum alloys and alloys made of stainless steel are more wear resistant than titanium or titanium-based alloys. When breakdown with titanium-based alloys occurs, it is often observed as black areas within the tissues.

Metallic ion release occurs in vivo, and numerous studies demonstrate soluble and precipitated corrosion products, as well as metallic wear debris, in the liver, spleen, lungs, and even remote bone marrow of the iliac crest. The constant motion of the metal-on-metal prosthesis causes a wearing away of the passivated surface and an increase in metallic ion release. The recent interest in metal-on-metal prostheses raises questions of biocompatibility and possible carcinogenic effects that these metallic ions can cause.8, 9, 10

Future Developments

Hopefully, further developments in metallurgy will allow for the development of new alloys that, when compared to current alloys, will have better mechanical and physical properties yielding better long-term results with implants.

The concurrent developments in other biomaterials, such as ceramics, and newer modified polyethylenes, such as cross-linked polyethylene, hopefully will result in improvements in longevity of total joint replacements either with the success of alternative bearing surfaces or with the use of composite materials. The total joint replacement that will last the life of the patient may be a reality one day.11, 12

Multimedia

Metallic alloys. Tantalum (left) and titanium (ri... Media file 1: Metallic alloys. Tantalum (left) and titanium (right) fiber mesh acetabular cups.
Metallic alloys. Tantalum (left) and titanium (ri...

Metallic alloys. Tantalum (left) and titanium (right) fiber mesh acetabular cups.

Metallic alloys. Stainless steel Charnley stem (l... Media file 2: Metallic alloys. Stainless steel Charnley stem (left) and a cobalt-chromium Mueller (right).
Metallic alloys. Stainless steel Charnley stem (l...

Metallic alloys. Stainless steel Charnley stem (left) and a cobalt-chromium Mueller (right).

Metallic alloys. Composite stems combine the phys... Media file 3: Metallic alloys. Composite stems combine the physical properties of alloys with those of other biomaterials. Note, ceramic or metal femoral heads are used on composite hip stems because composites have relatively poor wear properties.

Immune Response to Implants

Introduction

Immune response to implants is commonly reported in the literature and can include hypersensitivity related to pacemakers, dental implants, and orthopedic hardware.1 Furthermore, up to 13% of people are sensitive to nickel, cobalt, or chromium.1, 2, 3, 4, 5, 6, 7, 8, 9 The development of metal sensitivity after implantation of orthopedic hardware is common.1, 10, 11, 12

Osteolysis around a total knee implant.

Osteolysis around a total knee implant.

Osteolysis around a total knee implant.

Osteolysis around a total knee implant.


Metal sensitivity is also correlated with osteolysis and aseptic loosening of implanted metal hardware.5, 10, 12, 13, 14, 15, 16, 17, 18 However, statistical reviews of cases involving adverse reactions after implantation of metal hardware demonstrate that metal sensitivity can be proven causative in less than 0.1% of cases in which sensitivity reactions exist.1, 19, 20, 21, 22 Therefore, the clinical significance of metal sensitization remains a question. Nonetheless, the orthopedic surgeon must be aware of the potential problem, and when other more common causes of implant failure have been excluded, the possibility of allergic reaction to the metal must be considered, evaluated, and treated.

According to Huber et al, the presence of corrosion products and a hypersensitivity reaction in patients suggests that there is a relationship between corrosion and implant-related hypersensitivity. In 11 cases in which periprosthetic tissue contained corrosive elements (solid chromium orthophosphate corrosion products) after aseptic loosening of articular implants, immune-response tissue reactions were identified in all 11 cases.23

For excellent patient education resources, visit eMedicine's Foot, Ankle, Knee, and Hip Center. Also, see eMedicine's patient education articles Total Hip Replacement and Knee Joint Replacement.

Related eMedicine topics:

Implantable Cardioverter-Defibrillators

Total Knee Arthroplasty

Arthroplasty Component Failure

Arthroplasty-Associated Infections

Immunosuppression

Literature Review

This issue of the clinical significance of sensitization to implanted metals has long been a matter of debate in the literature. While some studies have shown that sensitization to metal implants is prevalent,1, 10, 11, 12 others refute these data and have concluded that not only does hypersensitivity fail to develop24; but patients with metal hypersensitivity prior to implantation actually become desensitized and anergic after implantation.25 Some authors have further suggested that metal hypersensitivity may be associated with bone loss and aseptic loosening of implanted devices,5, 11, 14 while other authors have concluded that even if a metal allergy exists, no adverse effects occur.13, 24, 26, 27

These contradicting studies make it difficult for the orthopedic surgeon to make the diagnosis of symptomatic metal allergy with confidence. The confusion could be the result of the presence of different metals in the implants, different manufacturing methods, small numbers of patients in the studies, and difficulty in achieving adequate diagnosis. More research is clearly needed. In the meantime, the diagnosis must be made with caution. Infection, nonunion, aseptic loosening, other inflammatory conditions, mechanical failure of the implant, and malalignment issues must be excluded first before assuming the problem is an allergic reaction.

Workup And Diagnosis

Clinical presentation

The presenting signs and symptoms of a nickel hypersensitivity to an implanted orthopedic device are variable but usually consist of the expected complaints of a patient with hardware failure. Patients with joint replacements have symptoms of loosening, including pain and instability. (For example, with a total hip replacement, the patient often has groin pain radiating to the medial thigh.) Patients with hardware for fractures have symptoms of nonunion, including pain and motion at the fracture site. Local inflammatory symptoms similar to the symptoms of infection are also possible, including warmth, erythema, and swelling over the implant, although systemic complaints such as fever are unlikely. A skin rash may develop over the metal device but is not always present.28, 29, 30

Osteolysis due to implant loosening is always in the differential diagnosis. The mechanism of osteolysis is primarily a local reaction to particulate debris,31 which leads to a cascade of cellular reactions (including activation of monocytes/macrophages, phagocytosis, release of cytokines) that eventually lead to increased osteoclastic activity around the prosthesis. Osteolysis is a reaction to local irritation, not an immune hypersensitivity response.32

Workup

Blood tests

Currently, blood tests are rarely performed in the workup of immune responses to implants. Generally, white blood cell counts and other inflammatory mediators (such as platelet counts, C-reactive protein levels, and sedimentation rates) are not elevated, or are only minimally elevated, and they are not specific or reliable enough to help in the diagnosis.

Radiologic studies

Careful radiographic assessment of the implant is required. Radiolucencies around the hardware, screw migration, and change in position of the implant imply loosening that could be due to hypersensitivity to the metal. Cystic changes, as seen in osteolysis, may be seen (see Image below and Image 1 in Multimedia). CT scans and MRIs are not especially helpful. A bone scan may be positive, but the findings are nonspecific.



Osteolysis around a total knee implant.

Osteolysis around a total knee implant.

Osteolysis around a total knee implant.

Osteolysis around a total knee implant.


Skin patch testing

Traditionally, skin patch testing has been the standard screening test for metal hypersensitivity. This method is limited by the fact that a positive result is not indicative of a true hypersensitivity but must be considered in the context of a patient's medical history and physical findings.33, 34 A routine skin test reveals a prevalence of metal sensitivity of 0.2% for chromium, 1.3% for nickel, and 1.8% for cobalt. After placement of metal implants, sensitization (change from negative to positive) occurs in 2.7% for chromium, 3.8% for nickel, and 3.8% for cobalt. Desensitization (change from positive to negative) occurs in 0% for chromium, 2.1% for nickel, and 3.8% for cobalt.35

Many patients with implanted metal hardware have positive skin test results for those metals but are completely asymptomatic.13, 24 If the skin patch test finding is positive, the patient can be designated allergic. However, the clinical significance of the allergy is controversial. Most allergy skin patch tests that show skin reactivity have no clinical implications.

The causes of these skin immunologic reactions are unclear.1, 34 It is thought that antigen-presenting cells that are localized to the skin (dendrite cells) may handle antigens differently than the antigen-presenting cells that are systemic (macrophages and monocytes). Therefore, many people who have skin reactivity to metals may never develop any reactivity at the site of prosthesis composed of that metal. Skin test results may not return to normal after metal removal.16 Conclusions based on skin patch testing should therefore be made with caution and only assumed valid if the whole clinical picture supports the finding of symptoms related to metal allergy. Preoperative skin patch testing is not typically recommended unless there is a strong suggestion of established sensitivity by history, because of a slight chance of sensitization and the high cost/low yield results expected.

Lymphocyte transformation test

Tests that may be more specific include the lymphocyte transformation test (LTT) and the lymphokine migration inhibition factor (MIF) test, which have been used to help diagnose metal hypersensitivity.

In vitro LTT proliferation testing is perhaps the most prevalent method after patch testing for assessing hypersensitivities. It involves measuring the proliferative response of lymphocytes following activation. A radioactive marker is added to lymphocytes along with the desired challenge agent. The incorporation of radioactive H3 -thymidine marker into cellular DNA on division facilitates the quantification of a proliferation response through the measurement of amassed radioactivity after a time period of 3-6 days. At day 6, H3 -thymidine uptake is measured by using liquid scintillation. The proliferation factor or stimulation index is calculated by using measured radiation counts per minute (cpm), as follows:

Proliferation factor = (mean cpm with treatment)/(mean cpm without treatment).

The use of proliferation testing in the assessment of metal sensitivity has been well established as a method for testing metal sensitivity in a variety of clinical settings.36, 37, 38, 39, 40, 41 The technical sophistication and high expense of LTT testing for implant-related metal sensitivity has limited its use; therefore, few conclusions can be drawn.42, 43, 44 These few investigations using LTT testing report that increased rates of metal sensitivity can be detected above that determined by dermal patch testing.42, 44, 45 Such reports seem to indicate LTT testing may be equally or better suited for the testing of implant-related sensitivity than dermal patch testing.37, 38, 39, 40, 41, 42, 43, 44

Lymphokine migration inhibition factor test

Another in vitro test that has shown promise in diagnosing metal hypersensitivity involved the use of MIF. MIF acts to prevent lymphocytes from leaving a site where foreign antigens are present. This test selectively detects lymphokine MIF, which, when present, does indicate an active immune response and metal sensitivity.26

The test is performed by obtaining a blood sample and isolating the lymphocytes. The lymphocytes are then mixed with solutions of specific metal ions, such as nickel, chromium, cobalt, or titanium. The test result is considered positive if the lymphocytes stay in the metal ion solution, indicating a cellular reaction to the metal dissolved in that solution. (In a positive result, no migration occurs.) The test result is considered negative if the lymphocytes migrate away from the particular metal ion solution, indicating that they are not reacting to the dissolved metal.1

Studies reveal that positive MIF test results to metals implanted in an orthopedic patient are well correlated with pain, swelling, and dermatological reactions over that area. Furthermore, after the implanted materials are removed, these signs and symptoms improve and the MIF test result returns to normal.16 The lymphokine MIF is the most useful clinical test for diagnosis of hypersensitivity reaction to orthopedic implants (see Image below and Image 2 in Multimedia).46 Cement wear particles are immunologically inert and have specifically been found not to cause a lymphocyte response in vitro,47 so the lymphokine MIF result should be negative in osteolysis.

(Click Image to enlarge.) Lymphokine migration te...

(Click Image to enlarge.) Lymphokine migration test.

(Click Image to enlarge.) Lymphokine migration te...

(Click Image to enlarge.) Lymphokine migration test.

Case Example

A 71-year-old woman had a right intertrochanteric hip fracture and underwent open reduction and internal fixation (ORIF) by using a standard stainless steel hip fracture implant (Synthes DHS; Paoli, PA). Postoperatively, the patient did well, with evidence of fracture healing, full weight bearing, and full range of motion by 3 months after surgery.

Approximately 6 months later, the patient began to complain of right hip pain laterally over the area of the implanted hardware. The fracture was radiologically healed, but, because of the patient's unbearable pain, a technetium bone scan and tomogram of the area were obtained. The results demonstrated increased uptake and lucency around the lag screw, indicative of hardware loosening.

The patient underwent debridement, hardware exchange, and an iliac crest bone graft. Intraoperative cultures were obtained that all proved negative for an infectious cause. Again, 4 months postoperatively, the patient began to complain of similar right hip pain, although images showed good bone graft incorporation and fracture healing (see Image below and Image 4 in Multimedia).

Case example. Second stainless steel implant in t...

Biomechanics

Bone Graft Substitute Materials

Introduction

In 1998, slightly more than 300,000 bone graft procedures were performed in the United States. Currently, this figure exceeds 500,000 in the US and approximately 2.2 million worldwide (Giannoudis et al, 2005). The estimated cost of these procedures approaches $2.5 billion per year.
Of the 300,000 procedures performed in 1998, 9 of 10 involved the use of either autograft or allograft tissue. The current standard is for autograft tissue bone grafts, in which tissue is harvested from the patient, usually from the iliac crest, but possibly from the distal femur or the proximal tibia. The graft is then placed at the injury site. This tissue is ideal as a bone graft because it possesses all of the characteristics necessary for new bone growth—namely, osteoconductivity, osteogenicity, and osteoinductivity.
Osteoconductivity refers to the situation in which the graft supports the attachment of new osteoblasts and osteoprogenitor cells, providing an interconnected structure through which new cells can migrate and new vessels can form. Osteogenicity refers to the situation when the osteoblasts that are at the site of new bone formation are able to produce minerals to calcify the collagen matrix that forms the substrate for new bone. Osteoinductivity refers to the ability of a graft to induce nondifferentiated stem cells or osteoprogenitor cells to differentiate into osteoblasts.
Harvesting the autograft requires an additional surgery at the donor site that can result in its own complications, such as inflammation, infection, and chronic pain that occasionally outlasts the pain of the original surgical procedure. Quantities of bone tissue that can be harvested are also limited, thus creating a supply problem.
Allografts are alternatives to autografts and taken from donors or cadavers, circumventing some of the shortcomings of autografts by eliminating donor-site morbidity and issues of limited supply. However, allografts present risks as well; although allograft tissue is treated by tissue freezing, freeze-drying, gamma irradiation, electron beam radiation, ethylene oxide, etc, the risk of disease transmission from donor to recipient is not completely removed. Some (Boyce et al, 1999) have estimated that the risk of human immunodeficiency virus (HIV) transmission alone with allograft bone is 1 case in 1.6 million population. A case of hepatitis B transmission (Tomford, 1995) and 3 cases of hepatitis C transmission (Conrad et al, 1995) have been reported with allograft tissue. More recently, cases of disease transmission have been reported (Centers for Disease Control and Prevention [CDC], 2001, 2002).
Although rigorous donor screenings and tissue treatments have greatly reduced the incidence of HIV and hepatitis transmission, other diseases have been passed on as recently as 2000 and 2001. In April 2000, 2 different patients received bone-tendon-bone allografts for anterior cruciate ligament reconstruction from a common donor. Each patient developed septic arthritis from the donor tissue (CDC, 2001). In November 2001, a patient underwent reconstructive knee surgery, and within 4 days of the surgery, the patient died of infection caused by Clostridium sordellii (CDC, 2002). After these and similar cases were reported, the CDC (2002) began an investigation that revealed 25 other cases of allograft-related infection or illness. Although many methods can reduce the risk of disease transmission, the treatments used to sterilize the tissue remove proteins and factors, reducing or eliminating the osteoinductivity of the tissue.
Despite the benefits of autografts and allografts, the limitations of each have necessitated the pursuit of alternatives. Using the 2 basic criteria of a successful graft, osteoconduction and osteoinduction, investigators have developed several alternatives, some of which are available for clinical use and others of which are still in the developmental stage. Many of these alternatives use a variety of materials, including natural and synthetic polymers, ceramics, and composites, whereas others have incorporated factor- and cell-based strategies that are used either alone or in combination with other materials. This article reviews what is currently available and what is on the horizon.

Bone Graft Classification System

Several categories of bone graft substitutes exist (see the Table below) and encompass a variety of materials, material sources, and origins (natural vs synthetic). Many are formed from composites of 1 or more types of material; however, the composite is usually built on a base material.

Laurencin et al (2006) have suggested a classification scheme of material-based groups:

  • Allograft-based bone graft substitutes involve allograft bone, used alone or in combination with other materials (eg, Allogro [AlloSource, Centennial, Colo], Opteform [Exactech, Inc, Gainesville, Fla], Grafton [BioHorizons, Birmingham, Ala], OrthoBlast [IsoTis OrthoBiologics, Irvine, Calif]).
  • Factor-based bone graft substitutes are natural and recombinant growth factors, used alone or in combination with other materials such as transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and bone morphogenetic protein (BMP).
  • Cell-based bone graft substitutes use cells to generate new tissue alone or are seeded onto a support matrix (eg, mesenchymal stem cells).
  • Ceramic-based bone graft substitutes include calcium phosphate, calcium sulfate, and bioglass used alone or in combination (eg, OsteoGraf [DENTSPLY Friadent CeraMed, Lakewood, Colo], Norian SRS [Synthes, Inc, West Chester, Pa], ProOsteon [Interpore Cross International, Irvine, Calif], Osteoset [Wright Medical Technology, Inc, Arlington, Tenn]).
  • Polymer-based bone graft substitutes, degradable and nondegradable polymers, are used alone or in combination with other materials (eg, Cortoss [Orthovita, Inc, Malvern, Pa], open porosity polylactic acid polymer [OPLA], Immix [Osteobiologics, Inc, San Antonio, Tex]).

ClassDescriptionExamples
Allograft basedAllograft bone, used alone or in combination with other materialsAllogro, OrthoBlast, Opteform, Grafton
Factor basedNatural and recombinant growth factors, used alone or in combination with other materialsTGF-beta, PDGF, FGF, BMP
Cell basedCells used to generate new tissue alone or seeded onto a support matrixMesenchymal stem cells
Ceramic basedIncludes calcium phosphate, calcium sulfate, and bioglass, used alone or in combinationOsteograf, Norian SRS, ProOsteon, Osteoset
Polymer basedBoth degradable and nondegradable polymers, used alone or in combination with other materialsCortoss, OPLA, Immix