Overview of Osteochondral Allograft
Injuries to the tissue deep in the joint, known as subchondral bone, and to the soft, slippery cartilage at the end of the bone, can be found in nearly two-thirds of all joint surgeries. These types of injuries can be hard to treat and frequently become worse, often leading to a joint disease called osteoarthritis.
There are a number of treatments for these kinds of injuries. These include reshaping the bone (osteotomy), making tiny holes in the bone to help new tissue grow (microfracture), grinding down the bone (abrasion arthroplasty), transplanting cartilage cells (autologous chondrocyte transplantation), inserting small cartilage plugs into knee joint (mosaicplasty), transplanting sections of bone and cartilage from the patient (autologous osteochondral graft), and replacing the injured joint or part of it (arthroplasty). However, these methods have drawbacks and are not optimal for larger, deep cartilage damages.
Since 1908, when Eric Lexner first used it, techniques using transplants of cartilage and bone from another person (osteochondral allografts) have improved. These transplants are generally used for larger defects (bigger than three cm) in active, young people who would benefit from preserving their own cartilage instead of getting an artificial joint. These osteochondral allografts offer active cartilage and bone cells that can renew the joint surface with promising results according to medical research.
The use of these types of grafts has become more common in the thigh bone, shin bone, kneecap, and ankle. Recently, they have also been used in other joints like the elbow and shoulder.
Why do People Need Osteochondral Allograft
Osteochondral transplantation is a medical procedure done to improve the function of a joint, relieve discomfort, and delay the need for joint replacement surgery. This is achieved by restoring the surface of the joint with an implant that encourages natural biological healing. This procedure is particularly useful for younger, active individuals and for conditions like osteonecrosis (where bone tissue dies due to lack of blood supply), injuries to the surface of joints due to trauma, improperly healed fractures, and osteochondritis dissecans (a joint condition where a small section of bone begins to separate from its surrounding region due to a lack of blood).
The main reasons for carrying out an osteochondral allograft transplantation procedure include:
* The presence of painful full-thickness injuries to the surface of joints that are larger than 3 cm
* Injuries to the surface of joints that are coupled with diseases affecting the layer of bone just beneath it, like in the case of avascular necrosis
* As a revision treatment in patients who did not see improvement after previous procedures aimed at repairing cartilage damage
When a Person Should Avoid Osteochondral Allograft
Under certain conditions, a patient may not be suitable for a bone and cartilage transplant (osteochondral allograft). Here are some reasons why:
* Advanced joint disease affecting multiple sections of the joint
* Two opposing parts of the joint surfaces having defects down to the bone
* Conditions that cause joint inflammation
* If the patient has other health issues that involve long-term use of steroids
* Misuse of smoking and alcohol
There are also certain circumstances that ideally don’t happen, but if they do, wouldn’t completely stop a bone and cartilage transplant:
* Conditions such as unstable ligaments, missing knee cushion (meniscus), misaligned bones, and being overweight.
It’s also important to note that:
If the patient is missing more than half of the meniscus (knee cushion on the inside of the knee) in the same compartment, it may be beneficial to have a meniscal transplant at the same time.
If your joint is misaligned, it must first be corrected with bone cuts or rearrangements (osteotomies) to reduce the pressure on the damaged compartments. This will help to increase the survival of the transplanted graft (the new bone and cartilage).
Equipment used for Osteochondral Allograft
Advancements and consistent methods in how we store things have made it possible to keep chondrocytes, or cartilage cells, alive for extended periods. However, how long these cells can survive depends on the exact method used. Allografts, which are tissue transplants from one person to another, are stored in low temperatures and checked for infectious diseases over a two-week period.
Fresh grafts are collected within one day of the donor’s passing and stored at a cool 4°C (39.2°F). The health of these cells begins to drop off between day 14 to 21, so it’s best to use them within 15 to 28 days of collection. This way, up to 70% of the cells are still viable, or healthy and functioning. However, it’s also important to use them as soon as they’re cleared from disease testing. At most, they should be used within 28 days of collection.
In general, fresh allografts are preferred because they have been shown to keep more healthy chondrocytes, have firmer cartilage, have more cells, and have more matrix content compared to frozen and cryopreserved, or extremely cold-stored, osteochondral allografts. These benefits are seen even six months after being transplanted.
Allografts that are frozen or cryopreserved are stored at much lower temperatures (-80 degrees C and -70 degrees C, respectively) and can be stored longer. However, they have noticeably fewer viable chondrocytes after being implanted, which limits their usefulness.
Preparing for Osteochondral Allograft
Before undergoing surgery, doctors must thoroughly take into account a patient’s clinical history, including any past injuries, pain, swelling, or previous procedures they might have had. They will also perform a thorough physical examination to check for possible issues like limited range of motion, signs of unstable ligaments or a meniscus tear, and any misalignment in the limbs.
Doctors will also carry out a complete assessment using X-rays, taken from various angles while the patient is standing and bearing weight. The aim of this assessment is to observe the alignment of the patient’s leg.
A Magnetic Resonance Imaging (MRI) scan is usually done as part of the pre-surgery planning. This scan helps the doctors estimate the size and location of the cartilage defect, if there is any swelling in the bone underneath the cartilage, tears in the ligaments, and meniscus tears. It’s worth noting that in up to 60% of cases, MRI scans may underestimate the extent of cartilage damage.
When the patient is set for surgery, they will be under general anesthesia, meaning they will be completely asleep and won’t feel a thing. In preparation for the surgery, the following steps will be followed:
* An antibiotic will be administered through a vein to prevent infection.
* The patient will be positioned lying flat on the operating table.
* A device called a tourniquet is placed on the thigh, which is used to control blood flow during surgery.
* Usually, the surgical procedure will be assisted by a technique called arthroscopy, which uses a small camera to look inside the knee.
* To ensure the best outcomes, patients receiving allografts (transplants of cells, tissues, or organs sourced from another person) and the donors will be matched beforehand based on the size derived from radiographs (a type of X-ray), with an acceptable matching size being within 2mm above or below.
How is Osteochondral Allograft performed
Let’s talk about a procedure known as Knee Osteochondral Allograft Transplantation. There are two main techniques used for this procedure: the Dowel Technique and the Shell Technique. These are strategies to replace a section of damaged knee joint cartilage (the knee ‘lesion’) with healthy cartilage from a donor (the ‘allograft’).
The Dowel Technique involves the surgeon creating a circular ‘socket’ in your knee lesion and transplanting a similarly shaped piece of cartilage. The procedure starts with the surgeon measuring your knee lesion and choosing appropriately sized instruments. The surgeon ensures the lesion is thoroughly covered. Then, a guide tool is used to select a specific area in the center of the lesion, from which a circular piece of bone and cartilage will be removed. This rhole is usually about 7 to 8 mm deep (but not more than 10 mm deep) to fit the new cartilage appropriately.
The surgeon also carefully prepares the replacement cartilage. This cartilage is also shaped into a round ‘plug’ fitting the hole’s dimensions. It is important to clean this plug properly with saline solution to remove any remaining elements that could cause an immune reaction. Once the plug is inserted into the created hole, the surgeon ensures that it is at the same level as the surrounding cartilage. This is to ensure smoothness and seamless function of the knee.
In some instances, your knee lesion might be too big for just one plug. In such a case, the surgeon might have to use multiple plugs. But it’s crucial to keep some space between each plug so that they fit securely and don’t move against each other.
On the other hand, the Shell Technique is particularly useful for larger and irregularly shaped lesions. This process involves manually shaping the graft so that it comfortably fits the size and shape of the ‘recipient site’ or the lesion being treated. Like with the Dowel Technique, the surgeon also makes sure that the new graft is precisely and securely fitted into the treated area. Again, absorbable pins or screws might be used to keep it in place.
Each technique has its strengths, and the one used will depend on the specific needs of your knee. Rest assured that your surgeon will use the method best suited to your situation to aid your recovery.
Possible Complications of Osteochondral Allograft
After allograft surgery, in which a bone or cartilage is transplanted from a donor to a patient, around 25% of patients experience what’s known as graft collapse and fragmentation. This is a situation in which the transplanted tissue fails to hold up or breaks down. This has been reported happening after 12 years of graft surgery.
Some signs that the allograft might be failing are persistent pain, joint tenderness, or fluid buildup known as effusion. Early warning signs can also be seen in X-rays which may reveal hardening of the bone (sclerosis), extra bone growth (osteophytes), small fluid-filled sacs (subchondral cysts), and loss of space in the joint.
Between 12 to 18% of patients end up needing to go back for more surgery which could be a revision procedure to correct or adjust the previous transplantation, or a joint replacement surgery. Worse survival rates have been observed in revision cases, in situations where the joint forms bone spurs (osteoarthritis), in grafts larger than 10mm, and when both sides of a joint need an allograft (bipolar allografts).
Thankfully, the immune system rejecting the graft (immunological reactions) rarely happens. This is because the thick protective covering of the graft can block it from body fluids that could cause an immune response. Also, the matching of the graft is based on blood type, which makes it even more unlikely for rejection to happen and doesn’t require additional immune suppressant drugs.
Disease transmission from the donor to the patient is another unlikely complication. Since 1998, testings have been put in place to screen donors for infectious diseases, making this risk quite small.
However, an infection in the surgical site is a serious complication and happens in about 1.8% of patients. If a patient experiences persistent pain, swelling, and fluid buildup, doctors will rule out an infection. If it is an infection, further surgery may be needed to clean the area (debridement), wash it out with fluid (irrigation), and maybe remove the graft.
What Else Should I Know About Osteochondral Allograft?
In recent times, there have been more and more studies being published about the long-term results of treating cartilage defects in the knee area.
These scientific studies have shown that the treatment of cartilage damage is quite successful. After ten years, the treated cartilage was still healthy in about 72 to 85% of the cases in the femoral condyles (part of the thigh bone that forms the knee), in 68 to 88% in the tibial plateau (top part of the shin bone), and in 71 to 78% of patella-femoral grafts (surgical graft involving knee cap and thigh bone).
There’s a treatment type called bipolar allograft transplantation, used for treating bipolar defects (defects that affect both sides of a joint). In these cases, the successful “survival” rate was lower at 39% after ten years and these patients were more likely to require additional surgery than patients who received unipolar transplantation (treatment of one side of a joint).
Most patients report feeling better after their surgery: 88% of patients report improved knee health and function, and 74 to 85% of folks noticed significant reduction in their knee pain.
Research studies have discovered that most patients can return to their sports activities after treatment – with about 79% of people being able to go back to the same level as before their injury, and almost 88% returning to sports activities at any level about 9 to 10 months after their treatment. But it’s important to note that more high-quality studies are needed on these outcomes.
Certain factors like your body weight, your age at the time of the surgery, and the number of previous surgeries aimed at preserving cartilage can affect how successful the treatment is. For example, if you’re over 30 years old when having surgery, your risk of the treatment failing increases by 3.5 times, and if you have had previous surgeries, the risk increases by 2.5 times. For athletes, age and duration of symptoms before treatment matter, too. Athletes who are over 25 years old or who received cartilage grafting after 12 months or more since their symptoms started are less likely to return to their sports activities at the same level as before the injury.