What are the Menisci?

The menisci are important shock absorbers in the knee.  There are two menisci in the knee – one located on the medial side and the other on the lateral side.  Together, each meniscus helps with knee stability and the preservation of joint health.

The medial meniscus, on the inside of the knee, absorbs about 50% of impact to the knee joint – thus, it helps to prevent osteoarthritis, especially in somebody who is bowlegged (varus alignment). The role of the medial meniscus is also important in patients who are missing an anterior cruciate ligament (ACL) or who have previously received an ACL reconstruction.  The posterior horn of the medial meniscus serves as a backup to anterior sliding of the knee, which can cause an ACL reconstruction to fail if the meniscus is not present to act as a bumper.

The lateral meniscus absorbs more shock than the medial meniscus.  The lateral meniscus has been noted to absorb about 70% of the impact on the lateral compartment in the knee.  This is why young, active patients can develop arthritis within a few months after having a partial lateral meniscectomy.  In addition to shock absorption, the lateral meniscus also plays a key role in the protection of an ACL reconstruction and provides stability in the presence of a torn ACL.  In the absence of an ACL and lateral meniscus – there is a significant amount of rotatory instability – this instability can be exemplified by the pivot-shift test.

Meniscus Transplant Patient Evaluation

A proper medical examination is essential for evaluating a meniscus transplant.  One must make sure that the knee is stable, has normal alignment, and has normal cartilage surfaces on both sides of the joint.  If any of these are lacking, they should be corrected either before, or during the surgical procedure.  The amount of surface area the cartilage protects is also important to assess.  We prefer to use high field MRI scans to look at the amount of cartilage remaining to determine if there are any bare areas of cartilage with bone exposed.  If only one side of the joint has exposed bone surfaces, then it is an option to resurface this area with a microfracture or a cartilage replacement surgery, such as a fresh osteoarticular allograft.  When both sides of the joint have bare bone, it is usually difficult to transplant a meniscus and at that point it is felt that the joint is “too far gone” to be a candidate for a meniscus transplant.  Thus, it is very important to follow patients who have had their meniscus taken out to make sure that they do not develop severe osteoarthritis.

The evaluation for a meniscus transplant includes x-rays with sizing markers.  One must have a meniscus sized to their knee to make sure it is not too big or too small.  Proper sizing for a meniscus transplant is very important to make sure that the patient has it fit in the right spot such that it can preserve joint health.  In addition, one should obtain long-leg x-rays to make sure that the alignment is neutral or through the opposite compartment or correctible to a normal alignment.

There are some instances where a meniscus cannot be saved and repaired.  In these circumstances, we recommend that patients be closely followed to ensure that osteoarthritis is not developed.  Osteoarthritis can develop quickly and one should be aware of the symptoms of osteoarthritis, which include pain or swelling with activities.  In young patients, we recommend that they follow-up with x-rays on a regular basis to look for bone spurs (osteophytes) and any potential joint space narrowing, especially on standing AP or Rosenberg views of the knee.  In those circumstances, one may need a meniscus transplant in the knee to preserve joint health.

Description of Meniscus Transplant Surgery

A meniscus transplant is potentially the most technically involved surgery in sports medicine.  It is well recognized that there is a long learning curve and one needs to have a very adept surgical team to be able to perform this procedure.  Both medial and lateral transplants involve making an incision next to the patellar tendon to be able to make an incision into the joint to be able to slide the meniscus into place.  In addition, we strongly recommend the use of bone plugs or a bone trough for meniscus transplants due to the multiple studies, which have demonstrated this to be important in preserving meniscal function.  For the medial meniscus, a bone plug is placed both at the front and back of the meniscus and a tunnel is reamed to be able to place it into its normal anatomic attachment site.  The rest of the meniscus is then sewn into place both at the back, front and sides of the meniscus to make sure that it is held into correct position.  Our European colleagues have performed second look arthroscopies on meniscus transplants, and have noted that the healing process takes 6 weeks postoperatively.  Thus, we keep our patients nonweightbearing for the first 6 weeks to maximize healing.

The technique of a lateral meniscus transplant involves making a bony trough and sliding the trough with the meniscal attachments into place in the joint.  The trough is necessary instead of 2 bone plugs because the attachment sites of the lateral meniscus are between 12 to 14-mm apart.  Thus, it is very difficult to be able to correctly prepare bone tunnels separately for the anterior and posterior attachments of the lateral meniscus.  The rest of the technique involving sewing the meniscus into place is very similar to the medial meniscus.

Are you a candidate for a meniscal transplant?

There are two ways to initiate a consultation with Dr. LaPrade:

You can provide current X-rays and/or MRIs for a clinical case review with Dr. LaPrade.

You can schedule an office consultation with Dr. LaPrade.

(Please keep reading below for more information on this treatment.)

Post-Operative Protocol for a Meniscal Transplant

Our center has performed over 300 meniscal transplantations.  Our published outcomes are very similar to others in the literature both in North America and Europe.  In general, about 80% of patients note good or excellent results for resolution of pain and swelling with activities.  In addition, when performed with a revision ACL reconstruction, the majority of knees have a restoration of normal stability and a return to improved function.

Returning to impact activities after meniscus transplant is still controversial.  In general, we believe that if one has some chondromalacia, which in effect is early arthritis, of the affected compartment, that one should be careful about returning back to impact activities after a meniscus transplant.  This is because we believe that one would normally not return back to impact activities if they had their own meniscus, and relying on a cadaver meniscus to function at a high level to prevent too much joint overload of the affected compartment is probably asking too much of that meniscal graft.  Thus, we recommend that patients return back to walking, swimming, cycling and the use of an elliptical machine as their main forms of cross training and activities after a meniscus transplant.

Related Studies

Meniscal Transplant FAQ

1. What is a meniscus transplant?

A meniscus transplant is indicated when one has had their own meniscus taken out and they have pain, swelling, or instability after this.  A donor meniscus transplant from a person that has died, called a cadaver graft, has to be matched to the same size knee and side of the knee and can be put back into the knee to try to address the deficiency that one has from having a meniscus excised. This is a meniscus transplant.

2. How is a meniscal transplant done?

A meniscus transplant is performed arthroscopically. First, the surgeon will remove any remaining meniscus back to about a 1 to 2 mm rim of tissue. This is where there is a good blood supply still present. In general, removing the whole meniscus back to the joint lining may not be indicated because it can result in the meniscus squirting out of the joint, which we call extrusion. After the meniscus remnant has been removed, then one can prepare to insert the meniscus in the joint. In general, the medial meniscus is placed with some bone plugs, whereas the lateral meniscus is placed with a trough of bone. Preparing the tunnels to place the bone plugs in at the normal attachment site of the meniscus is essential, and placing the trough for a lateral meniscus transplant as far towards the middle of the knee as possible is also important. Once these areas for the meniscus attachments have been prepared, an incision can then be made and the meniscus can be slid into the joint. The meniscus can then be sewn to the joint lining either with an inside-out suture technique or an all-inside technique. We recommend the inside-out technique because the all-inside technique makes bigger holes in the transplant graft and these can serve as locations where the meniscus transplant could tear in the future.

3. Can a meniscus transplant be performed for osteoarthritis?

In general, if one has a lot of osteoarthritis, a meniscus transplant would be ineffective.  Mild amounts of arthritis, which we would call grades 1 to 2 chondromalacia, usually are mild enough areas of arthritis that a meniscus transplant can be effective. However, more advanced amounts of arthritis with grade 3 or 4 chondromalacia, would usually mean that one is not indicated for a transplant graft unless it was totally located on the femur and the tibia cartilage was still fairly intact. In that circumstance, replacing both the femur cartilage and the meniscus at the same time could be indicated.

4. When is a meniscus transplant performed with an ACL reconstruction?

There are 2 main times that one can have a meniscus transplant with an ACL reconstruction. First, for the medial meniscus, it is usually indicated in a revision case. The posterior horn of the medial meniscus is an essential secondary restraint to preventing one’s knee from slipping forward. If one does not have their posterior horn of the meniscus because it needed to be taken out, or was taken out previously, an ACL reconstruction graft is at a much higher risk of stretching out and potentially failing.  If one has had the meniscus taken out previously and the knee is really unstable or if one has had a failed ACL reconstruction graft because there was a lack of medial meniscus, a concurrent medial meniscus transplant and ACL reconstruction may be indicated. The other indication may be when one does not have a lateral meniscus present. While the lateral meniscus is super essential for preventing arthritis of the outside of the knee, it is also important to prevent one from having increased twisting and turning when one has an ACL-deficient knee. Therefore, if one has a very large amount of motion on their pivot shift test, or notes significant problems with twisting, turning, and pivoting, they may be indicated to have a lateral meniscus transplant if they are lateral meniscus deficient along with an ACL reconstruction or revision ACL reconstruction.

5. What is the relationship between a meniscus transplant and an osteotomy?

Meniscus transplants have been found to fail much more commonly when one has a malaligned knee. Therefore, if one is bow-legged (in varus) and has a medial meniscus transplant, there is a high risk that it will fail unless a proximal tibial osteotomy is performed first to unload the compartment. Similarly, if one has a lateral meniscus deficiency and is knock-kneed, which we call valgus alignment, they are also at a high risk of having a lateral meniscus transplant fail if a distal femoral osteotomy is not performed to unload their lateral compartment.

6. What are the indications for a meniscus transplant?

In addition to having a meniscus taken out previously, the indications are that one should have neutral or correctable alignment, should have a stable or correctable knee ligament status, they should have no more than grade 1 to 2 chondromalacia of the affected compartment, and they should have symptoms from having no meniscus, which usually will include pain and swelling with activities. While studies are being performed to determine if meniscal transplants should be performed preemptively to prevent arthritis, we don’t have sufficient data right now that would indicate that a patient should go directly to having a meniscus transplant when their cartilage is intact. This is because meniscus transplants are some of the most complex surgeries that we perform in sports medicine and are usually only performed at select centers. Until we prove that meniscus transplants slow down the progression of arthritis, especially younger patients, we want to follow the patients closely and determine if they do have symptoms from having their meniscus taken out.

7. What is the recovery time for a meniscus transplant?

The true recovery time for a meniscus transplant has not been well established to date. This may be because there are limited centers who treat them and there are varying rehabilitation protocols between the centers.  In our hands, we keep patients who have a meniscus transplant nonweightbearing for 6 weeks to give the best chance for the transplant to heal around the edges of the joint lining where it was sewn too. We then have the patients avoid any significant impact activities until a minimum of 9 months when they have sufficient return of strength and when they don’t have pain or swelling because their thigh muscles are still weak. It is important to recognize that because most patients who do have a meniscus transplant do have some underlying arthritis, returning back to significant impact activities after a meniscus transplant is generally not indicated.

8. What is the surgical time for a meniscus transplant?

The surgical time for a meniscus transplant can depend upon many factors. First, there is a long learning curve for a meniscal transplant surgery.  Second, having a well prepared surgical team to assist one with a meniscus transplant can help decrease the operative time. Third, if the surgery is only a meniscus transplant versus a concurrent revision ACL reconstruction or osteotomy, the operative time can be quite extended. In general, in our hands, a meniscus transplant takes approximately 1 hour when it is performed by itself.

9. What are the long-term results of meniscus transplants?

The long-term results of meniscus transplants are best evaluated from our European colleagues who are able to follow patients in socialized medicine systems for longer periods of time. It appears that most meniscus transplants would last 12 to 15 years and some may last longer. Therefore, the current belief is that the transplants will slow down the progression of arthritis for a decade or more, but patients may need a second meniscus transplant if the transplant were to wear out a tear and their cartilage is still in fairly good condition.

10. What are the failure rates for meniscus transplants?

In general, about 20% to 25% of meniscus transplants will have a tear of the transplant tissue in the first 5 years.  This incidence will increase over time with most patients getting 12 to 15 years of good function after a meniscus transplant. After this, there is a higher rate of re-tear and wearing out of the transplant tissue and this is something that we are just beginning to recognize as our colleagues and friends in Europe follow their patients over the long term.

11. What are the rejection chances with a meniscus transplant?

It is generally believed that a chance of rejection, whereby the meniscus may be absorbed or may decrease in size, is about 2% to 5%.  Currently, we don’t have any means to check with blood tests or other studies to determine who may be at an increased risk of having a transplant graft be rejected, but the likelihood is still quite low for this happening.

12. What are some of the side effects of meniscus transplants?

Around the time of surgery, patients can expect to have a moderate amount of knee pain after a meniscus transplant. This is because this is one of the more complex surgeries that we do and inserting the meniscus and sewing it in place will cause knee pain.  In addition, because of the extensive nature of the surgery, there is an increased risk of blood clots with a meniscus transplant, so one should be on blood thinners for the first weeks after a transplant to minimize this risk. Also, because one does have surgical incisions with a meniscus transplant, one can expect numbness around the surgical incision as a routine part of the surgery. Longer term, underlying arthritis can, and usually will, progress depending upon one’s activity levels. In addition, the meniscus transplant does have a higher risk of tearing compared to one’s normal meniscus.  Processing companies for the meniscus transplants and surgeons do not obtain MRIs or have the ability to look in the main substance of the meniscus. They rely mainly on the surface changes of the meniscus and the age of the patient to determine which grafts are ideal, so underlying defects in the meniscus are unknown.

13. What are the contraindications to a meniscus transplant?

The contraindications to a meniscus transplant are in patients who have too much arthritis or in those who have significant instability in their knee and do not wish to have ligament reconstruction, or where malalignment and too much bow-leggedness or knock-kneed alignment and do not wish to have an osteotomy. In particular, having grade 3 to 4 chondromalacia or Kellgren-Lawrence changes of 3 to 4 usually are contraindications to having any success with a meniscus transplant.

14. What are the results of meniscus transplants in athletes?

There are very few meniscus transplants that have been performed in athletes. This is often because the transplant graft is at a higher risk of tearing with return to sporting activities, as well as the fact that the downtime for a meniscus transplant can be up to a year for recovery. However, meniscus transplants have been noted to restore and prolong the careers of Olympic athletes and some professional athletes. These athletes are usually counselled that returning to high-level activities puts them at a higher risk of having their grafts fail and they are willing to take that risk in these circumstances.

15. What are the clinical outcomes for a meniscus transplant?

In general, the clinical outcomes for a meniscus transplant are that they are very effective in restoring function and decreasing pain and swelling in 80% to 85% of patients.  It is not a perfect surgery to relieve pain in all patients, so ensuring that one follows the steps for their workup to determine if they are the best candidate would increase one’s chance of having a good postoperative restoration of function.

16. What does a meniscus transplant look like on MRI?

The appearance of meniscal transplants on MRI can be very complicated. This is because there can be small pieces of metal from the preparation of the tunnels and meniscus rim that can cause artifact and interfere with the MRI appearance. In addition, the multiple sutures that are placed for a meniscus transplant  also cause some artifact. Therefore, working with a radiologist who has seen meniscus transplants and understands the procedure is important to obtain a correct interpretation of the MRI appearance. In addition, most sports medicine surgeons who perform meniscus transplants should also view the MRI scan and correlate it with their own experience to help interpret the MRI appearance of a meniscus transplant graft. In my hands, I have often seen MRI readings that are incorrect because of artifact from metal or sutures, when in fact a meniscus transplant graft may be healing well and a patient’s pain may be coming from other sources.

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