Thursday, November 25, 2010

Allografts and the risks of infection and disease transmission

Here is some valuable information on the risks associated with implantation of allografts [i.e. cadaver grafts in nose surgery]

 AAOS 2004: All About Allografts -- Select Highlights of the 71st Annual Meeting of the American Academy of Orthopaedic Surgeons

 Controlling Infection is Crucial

In limiting infection during allograft procedures, it is important to determine whether the tissue bank that you or your hospital is using is a member of the American Association of Tissue Banks (AATB). This organization requires that its members perform full screening that meets US Food and Drug Administration requirements; however, secondary sterilization of the grafts is still optional. Not all tissue banks are members of AATB, and not all tissue banks are inspected. The review by Vangsness and colleagues[2] describes the process of procurement, processing, and storage, and should be required reading for anyone who is using allograft tissue. Be sure that you know your tissue bank and its procedures.
Infection of tissue can be controlled by screening the tissue donor and through secondary sterilization of the tissue. At this time, we can screen for both hepatitis B and C, which should prevent infection by these entities. There have only been 2 cases of HIV infection through allograft tissue, and both of these incidents occurred in the 1980s. These reported infections occurred with frozen bone as the vector, but none of the freeze dried grafts from the same donor transmitted the disease. The AATB has formulated guidelines for their members; these guidelines recommend donor screening.

There are a number of methods and federal guidelines for storing tissue after procurement. The methods of storing the tissue are: fresh frozen, deep frozen, freeze dried, demineralized, and proprietary treatments, such as CryoLife (CryoLife Inc., Kennesaw, Georgia

Factoring Relative Risk
The risk of hepatitis B after blood transfusion is 1/63,000. The risk of hepatitis C is 1/100,000, and the risk of HIV is 1/1,000,000. The risk of HIV after bone transplantation is 1/1,500,000. The risk of HIV after soft tissue transplantation is 1/1,600,000 with secondary sterilization.
To put this in the proper perspective, one should remember that the risk of death due to pregnancy is 1/10,000, the risk of death from administration of penicillin is 1/30,000, and the risk of death with oral contraceptives is 1/50,000. In fact, it may be more dangerous driving to the hospital than receiving a bone graft at the hospital.
In summary, allografts are a valuable treatment option for today's orthopaedic practice. The academy believes allografts to be safe if used within the guidelines, when they are supplied by an accredited tissue bank, and if the appropriate surgical techniques are employed.

How safe are soft-tissue allografts?

By C. Thomas Vangsness Jr., MD

 Although several cases of viral infection—specifically human immunodeficiency virus (HIV), viral hepatitis, and human T-lymphotropic virus (HTLV)—have been reported, these transmissions occurred before the guidelines for donor screening for viruses and bacteria were implemented and before the availability of currently validated serologic tests.

Sterility is expressed as a mathematic probability of relative risk. According to the FDA, a sterility assurance level (SAL) of 10-3 means there is a 1 in 1,000 chance that a nonviral viable microbe exists in or on the implanted material. The Association for the Advancement of Medical Instrumentation (AAMI) states that an SAL of 10-6 (one in a million chance) in organisms is more desirable. The American Association of Tissue Banks (AATB) requires an SAL of 10-6 for tissue bank allografts.

Contamination of the graft can also occur during the final handling and packaging of tissue. Gamma irradiation is commonly used to terminally sterilize allograft tissue with lower doses of radiation.

Freeze drying (lyophilization) is a preservation process that allows tissues to be stored at room temperature. Lyophilization freezes the tissue and reduces the water content to less than 6 percent of initial weight through a primary drying process (sublimation) and a secondary drying process (desorption). Although freeze-dried allografts (lyophilized grafts) are not commonly used for sports medicine applications in the United States, this process is commonly used with soft-tissue patches.

With improved donor screening techniques, such as nucleic acid testing (NAT), the current risk of transplanting tissue from an HIV-infected donor is reported to be between 1 in 1 million and 4 in 1 million.

According to a recent AATB survey covering data from 2003 to 2004, the current risk of an allograft infection to the average patient appears to be much less than the risk of infections surrounding the surgery itself. According to the report, there were 192 reports of suspected allograft-related infections in 2003-2004; 42 percent involved soft-tissue grafts and 37 percent involved bone grafts, with an overall incidence of 0.014 percent. Currently, better reporting of infections is actively under investigation to improve the accuracy of these numbers.

Do not do routine culturing of allograft tissue in the operating room immediately prior to implantation. These cultures are documented to be inaccurate and may reflect the native airborne or backtable contamination.

Musculoskeletal tissue regeneration: biological materials and methods  By William S. Pietrzak, Charles A. Vacanti

Although the risk is low, bacteria, hepatitis, HIV, and syphilis can be transmitted from donor to recipient. There is also the theoretical possibility of transmitting slow viruses (prions) with allograft use.
Irradiation of the soft tissue allografts with high dose (>3Mrad) radiation can sterilize allograft tissue, destroying bacteria and viruses including HIV and hepatitis. Bone plug allografts may still be capable of transmitting hepatitis despite treatment with 3 Mrad irradiation. Although, allograft irradiation will reduce the risk of disease transmission, it does so at the expense of diminishing the biomechanical properties of the tissue. Newer screening tests such as polymerase chain reaction (PCR) and nucleic acid testing (NAT) improve the detection of viral and bacterial DNA and RNA, and many increase the accuracy of identifying infected donor tissue and minimizing false-negatives. By improving the sensitivity and specificity of infected donor  tissue identification, the risk of bacterial and viral disease transmission should be less, thereby increasing the safety of allograft use. These newer techniques could potentially decrease the need for graft irradiation and other sterilization techniques that many affect allograft properties.

Surgeons can minimize complications associated with infected allograft tissue by only using tissue processed from a tissue bank accredited by the American Association of Tissue Banks (AATB). It is imperative that surgeons know the source of their allograft tissue, particularly if they rely on the hospital or a surgery center to obtain the allograft tissue for their patients.

Wednesday, November 24, 2010

Using freeze dried bone grafts for Nasal Dorsal Augmentation

Recently in a PRSjournal a study was conducted and reported by Dr.Richard Clark called Nasal Dorsal Augmentation with Freeze dried allograft bone. Non irradiated freeze dried bone typically comes from tibia and femur shafts (more specifically cortical shafts).

Here's some general background information on bone grafts.

Type of Grafts:

Per definition there are four types of grafts, i.e. autografts, allografts, alloplasts and xenografts:

Autografts refers to tissue transplanted from one site to another
within the same individual.
Allografts are obtained from cadavers or living individuals from the same species. In human medicine they can be obtained from tissue banks (KÜBLER 1997).
Alloplasts are synthetic materials consisting of biological inert substances.
Xenografts are composed of tissue taken from another species (i.e. from an animal source, usually bovine). In case the organic material is removed from xenogenic bone, it may be considered as an alloplast (GARG 1999).
The term 'composite grafts' refers to grafts that are composed of materials from different origins, usually autogenous bone mixed with other materials (HABAL1991).

Depending on where the bone graft is needed, a different doctor may be requested to do the surgery. Doctors that do bone graft procedures are commonly orthopedic surgeons, otolaryngology head and neck surgeons, neurosurgeons, craniofacial surgeons, oral and maxillofacial surgeons, and periodontists.[9]
There are three types of bone allograft available:
  1. Fresh or fresh-frozen bone
  2. Freeze-dried bone allograft (FDBA)
  3. Demineralized freeze-dried bone allograft (DFDBA)
Freeze dried bone describes the method used to process the bone, not the source, and there is freeze dried bone available that comes from cadavers.

The most commonly used allograft is demineralized and freeze-dried bone.
The latter is used for minimising the antigenicity (BLOCK and POSER 1995), resulting in a demineralized bone matrix (DFDBA).

Freeze-drying and gamma irradiation are the techniques widely use in tissue banking for preservation and sterilization of tissue grafts respectively.
Frozen allografts are stored at temperatures below −60°C,
which decreases enzyme degradation and host immune response.
Freeze-drying involves removal of water from the tissue
with subsequent vacuum packing and storage at room temperature.

Some medical terminology:
➤Osteoinduction is a process that supports the mitogenesis of undifferentiated mesenchymal cells, leading to the formation of osteoprogenitor cells that form new bone.
➤ The human skeleton has the ability to regenerate itself as part of the repair process.
➤ Recombinant bone morphogenetic protein has osteoinductive properties, the effectiveness of which is supported by Level-I evidence from current literature sources.
➤ Osteoconduction is a property of a matrix that supports the attachment of bone-forming cells for subsequent bone formation.
➤ Osteogenic property is a relatively new term that can be defined as the generation of bone from boneforming cells.

For more info on bone grafts:

Related articles: 
Does Type of Bone Graft Used in Spinal Fusion Increase Risk of Infection? 

Effect of freeze-drying and gamma irradiation on the mechanical properties of human cancellous bone 

Bone graft substitutes

According to Dr.Clarks site; 

Dr. Clark has currently published pilot study using freeze dried and frozen bone to augment and straighten the nasal dorsum (bridge). Dr. Clark uses American Bone Bank approved treated bone which has an excellent history of use in orthopedic surgery for over 10 years without transmission of any disease or rejection of implants. (For details of the extensive evaluation of bone donors and cleansing of the bone, please contact Dr. Clark.) The first patient receiving a dorsal implant with a frozen bone was in June, 2004. That patient's bone graft remains in perfect position and has maintained it's size and remains thus far to be a success. This bone graft has revascularized and become live healthy bone. We are following over 10 patients with excellent results, and time will tell as to whether this will be an answer to the quandary of dorsal augmentation, and we remain very hopeful.
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Sunday, November 7, 2010

Techniques used to lessen the degree of rib (costal) graft warping in nose surgery

Rib carving is a tedious procedure, says Dr. Paul Nassif in this video. He soaks the rib graft in normal saline solution to soften it up and gives you the curve of where the cartilage is going to go.  The inner cortex of rib has less chance of warping, so its left intact. For rim grafts you need to carve the cartilage which is very delicate process, since you have to make sure the graft doesn't end up splintering.

Symmetric carving of the costal cartilage graft will minimize the chance of the graft warping over time.

Here's an interesting study on comparison of  warping after using different techniques of carving.  Concentric grafts warped less than Eccentric grafts.

David W. Kim, MD; Anil R. Shah, MD; Dean M. Toriumi, MD

Dr.Jack Gunter, has devised a technique in which the larger grafts, the dorsal onlay graft and the columellar strut, are reinforced with a centrally placed Kirschner (K)- wire to decrease warping and provide a more stable and predictable result.
"Graft warping can occur in autogenous rib cartilage and lead to long-term postoperative distortions of nasal shape. The use of stabilizing K-wires placed through the center of these grafts has been a successful technique to counterbalance the tendency of the grafts to warp. To avoid warping of smaller grafts, we follow the principle of carving balanced cross-sections originally described by Gibson and later substantiated by Kim et al"

Control of grafted rib cartilage warping using K wire by Dr. A. Nakamura

More info regarding techniques to avoid warping of costal grafts:

Controversies in Otolaryngology: By Myles L Pensak

Revision Rhinoplasty: By Daniel G. Becker, Stephen S. Park