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Allograft
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Allograft

Allografting or, to give its full name, ‘fresh osteochondral allograft transplantation (OCA)’ is an operation in which a damaged or diseased area of a joint is reconstructed using a bone and cartilage transplant. The cartilage cells can survive the transplantation only if the tissue is ‘fresh’, which means it has not been exposed to radiation or prolonged freezing.

OCA was pioneered at the beginning of the 20th century, and has had a long and successful history. It is becoming increasingly popular as a treatment for large traumatic injuries, osteochondritis dissecans, and bone death (osteonecrosis) resulting from lack of blood flow to the bone supporting the joint cartilage.

The most common reasons for performing OCA are:

  • A focal cartilage lesion greater than 2 cm2
  • Re-treatment (revision or salvage) of previous cartilage surgery, such as microfracture, autologous osteochondral transfer (OAT) or autologous chondrocyte transplantation (ACI)
  • Severe (type III or IV) osteochondritis dissecans
  • Osteonecrosis (bone death)
  • Joint reconstruction after a fracture, known as post-traumatic reconstruction

The surgery itself is fairly straightforward but the patient should understand that they will receive living human tissue that has been donated. Fortunately, patients do not need to take anti-rejection drugs after surgery, as the immune response from these grafts is, in the majority of cases, mild or non-existent.

However, the tissue being donated means it is often difficult to predict availability and patients must therefore be prepared for surgery with a few days’ notice.

Intended audience

This article is intended for anyone suffering from damage to their articular cartilage and their families who would like to find out about allograft, as well as anyone interested in cartilage problems.

What is Allograft?

The scientific basis of OCA is the transplantation of fully developed, or mature hyaline (joint) cartilage containing living cartilage cells (‘chondrocytes’) that survive the transplant and support the production of the cartilage matrix indefinitely.

Theoretically, this maintains the tissue balance (‘homeostasis’) of the joint cartilage. Studies have shown chondrocytes living as long as 29 years after transplant. The graft often includes a portion of bone to help restore missing bone.

Candidates for OCA first have a careful history taken and clinical examination, and the size and type of the lesion, or defect, within the joint is documented. This involves either a photo or video taken during diagnostic arthroscopy, or an MRI (magnetic resonance imaging), along with plain X-rays. At this point, if the patient is a candidate for OCA, the size of the joint is measured. The patient is then placed on a waiting list, which can vary depending on the region or country in which the patient lives.

Donor tissue is obtained from an accredited tissue bank that specialises in the complex process of recovering and preparing fresh, living osteochondral (bone and cartilage) tissue. No tissue-type matching is performed because the allograft causes a minimal immune reaction. This is because the graft is considered to be relatively ‘immuno-privileged’. This means that cartilage is not fed by blood vessels, and the cartilage cells (‘chondrocytes’) are protected from surveillance by the immune system.

Donor–recipient matching is primarily by size to ensure the best fit of the graft. When a donor becomes available and is matched to the appropriate recipient, the patient is contacted and scheduled for surgery, ideally within 48–72 hours. The tissue is transplanted fresh (within 28 days of being taken from the donor), and is not processed like other tissue grafts. This allows the cartilage cells to survive. However, the tissue may be frozen before transplanting, as the cells within the tissue are still viable after thawing.

Surgery

The procedure takes approximately 1–3 hours and consists, essentially, of replacing the damaged surface of the joint with a carefully fitted graft from a donor joint. In summary, the surgical technique is as follows. A mini or standard ‘arthrotomy’ technique is performed and then:

  • The defect is exposed and measured, and a guide pin placed through the centre of the lesion, perpendicular (90º, or at a right angle) to the surface of the joint
  • The lesion is widened (reamed) to a modest depth to remove the diseased cartilage and a small (3–6 mm) amount of bone.
  • Depth measurements are taken from the prepared site where the transplant will be placed
  • A ‘graft plug’ is removed from the donor tissue using a special tool called a coring reamer
  • Depth measurements are marked on the plug and any excess bone removed, creating an graft matching the size and depth of the prepared site
  • The graft is washed to remove blood and debris, and the bony edges are trimmed to help insertion
  • The graft is gently inserted either with a special device or simply by moving the joint, which compresses it
  • Loose grafts are then fixed with absorbable pins or screws, if necessary.

Follow-up

Patients either go home the same day as the operation or stay in hospital for up to 3 days, depending on circumstances. Crutches are used for protected weight bearing for 4–12 weeks and physical therapy is started immediately. Patients are encouraged to complete a rehabilitation program, including range of motion and muscle exercises, which begins immediately after surgery. Follow-ups are scheduled for 4–6 weeks, 3 months, 6 months and yearly.

X-rays are taken to check graft healing. If the graft appears to be functioning and incorporating into the joint, then a progressive weight-bearing programme is started. At 4–6 months, if the individual has healed appropriately, he/she can begin more strenuous activity and return to sports or other athletic pursuits.

Most patients feel they have not completed their full recovery until up to a year after surgery. Transplant patients are followed on a routine basis every year indefinitely. This is important, as the long-term outcome of OCA procedures is not completely known.

Figures

Osteochondral allograft transplantation (OCA)

What are the advantages and disadvantages of Allograft?

What are the advantages of Allograft?

Compared to other methods of cartilage repair, OCA uniquely:

  • Allows the repair of bone defects in addition to cartilage damage;
  • Can repair almost any size defect; and
  • Restores the lesion using mature articular, or joint cartilage, rather than less durable fibrocartilage.

The outcome of this approach depends on many factors but in particular on the problem being treated, the age of the patient and the size of the lesion. Any other disease or damage in the knee, such as meniscus or ligament damage or the presence of osteoarthritis, can affect the outcome. The best outcomes are achieved with the treatment of osteochondritis dissecans.

What are the disadvantages of Allograft?

The disadvantage of OCA is that it requires allogenic tissue (i.e. from another person), which may require a significant wait for a suitable donor.

Although there is a theoretical risk of disease transmission from the donor, this has been exceedingly rare.

Frequently Asked Questions (FAQs)

What can I expect to be able to do after the procedure?

This depends on many factors but, if your knee is otherwise healthy, we would expect you to return to your previous activities. High-demand sports always carry risks, however, and there is no guarantee that you will be able to participate at the highest level.

Does rejection occur?

Immunologic rejection like that seen with organ transplants is not seen with allografts for OCA. While antibodies to the graft have been detected in about half of patients undergoing OCA, the clinical relevance is unclear.

How is the donor matched to me?

Donors for OCA are matched by size and location

How long will I have to wait for a donor?

Patients typically have to wait between 1 and 4 months for an OCA donor.

Further reading

There have been several scientific studies on the outcomes of OCA, which has been shown to have a success rate of approximately 70–90%. A study that gives a good overview of OCA is:

  • Levy YD, Gortz S, Pulido PA, McCauley JC, Bugbee WD. Do fresh osteochondral allografts successfully treat femoral condyle lesions? Clin Orthop Relat Res 2013; 471(1): 231–7.

Three studies that look at outcomes with OCA for post-traumatic reconstruction are:

  • Aubin PP, Cheah HK, Davis AM, Gross AE. Long-term followup of fresh femoral osteochondral allografts for posttraumatic knee defects. Clin Orthop Relat Res 2001; 391 Suppl): S318–27.
  • Ghazavi MT, Pritzker KP, Davis AM, Gross AE. Fresh osteochondral allografts for post-traumatic osteochondral defects of the knee. J Bone Joint Surg Br 1997; 79(6): 1008–13.
  • Gross AE, Kim W, Las Heras F, et al. Fresh osteochondral allografts for posttraumatic knee defects: long-term followup. Clin Orthop Relat Res 2008; 466(8): 1863–70.

Three studies that look at outcomes with OCA for cartilage restoration are:

  • Chu CR, Convery FR, Akeson WH, Meyers M, Amiel D. Articular cartilage transplantation. Clinical results in the knee. Clin Orthop Relat Res 1999; 360): 159–68.
  • Garrett JC. Fresh osteochondral allografts for treatment of articular defects in osteochondritis dissecans of the lateral femoral condyle in adults. Clin Orthop Relat Res 1994; 303): 33–7.
  • Gortz S, Bugbee WD. Allografts in articular cartilage repair. Instr Course Lect 2007; 56469–80.
Allografting or, to give…
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