Meniscal Transplantation

Total and Segmental Meniscal Allograft Transplants:

Anatomy:

The ends of the thigh (femur) and shin (tibia/fibula) bones are covered with articular cartilage which assuages with providing a smooth surface which allows the respective bones to glide over one another with minimal friction¹.

The menisci are two crescent-shaped pieces of fibrocartilage between the thigh (femur) and shin (tibia/fibula) bones in between the articular cartilage. Each knee is composed of two menisci, one on each side of the knee joint which aid with stabilizing the patellar cavity, bearing weight and absorbing shock to decrease the amount of strain that is delivered to the lower part of the leg².

Meniscal Damage and Tears:

There are multiple mechanisms in which the menisci can become damaged. For example, sudden twisting or bending of the knee can lead to a traumatic meniscal tear which is a common sports-related injury³. However, tears can also develop spontaneously and gradually in older patients since the cartilage within the joints begins to wear down with decades of use; this is referred to as a degenerative meniscal tear⁴.

Regardless of the mechanism of injury to the meniscus, a torn or damaged meniscus can cause the femur and tibia to scrape against each other without an adequate layer of protection which was previously provided by the meniscus. This can lead to a range of symptoms such as knee pain, stiffness, swelling and eventually persistent wearing down of the cartilage can lead to the development of osteoarthritis⁵.

Treatment Options for Damaged or Torn Meniscus:

Occasionally, a minimally torn meniscus can be healed on its own without any intervention, however oftentimes surgery is needed. A torn meniscus can frequently be successfully treated when a surgeon trims out only the damaged parts of the affected meniscus which is a procedure referred to as an arthroscopic partial meniscectomy. Unfortunately, in cases where the meniscus is more severely damaged or torn, the surgeon must remove the entire meniscus which is called a total meniscectomy. However, complete removal of the menisci causes the articular cartilage, that once allowed the femur and tibia to glide smoothly across one another, becomes worn down. This increases the likelihood of the patient developing osteoarthritis later in their life⁶.

Total vs Segmental Meniscal Allograft Transplant Surgery:

If the meniscus has been severely damaged or completely removed, a surgical procedure called a total meniscal transplant surgery is an option for patients in order to preserve knee function, provide significant pain relief and reduce the likelihood of these patients developing osteoarthritis. The main long-term goal of total meniscal allograft transplantation is to delay the degeneration of articular cartilage⁷. A total meniscal transplant surgery involves replacing an entire damaged meniscus with a cadaver meniscus, this procedure is also referred to as an total meniscus allograft transplantation. Since this tissue is transplanted from a nonliving human cadaver, the recipient patient’s immune system is not able to reject the transplanted tissue. Therefore, patients undergoing meniscal allograft transplantation do not take anti-rejection medications after their surgical procedure⁸.

For patients that suffer from focal meniscal damage (either due to a prior partial meniscectomy or meniscal tear) and want to preserve meniscus function, a segmental meniscal transplant is indicated. This procedure is similar to a total meniscal allograft transplantation, however instead only the deficient meniscal areas are removed and replaced with a cadaver meniscus of a similar size9. It is important to note that segmental meniscal transplants are only indicated for focal damage; if there is evidence of meniscal deficiency that extends beyond the body of the meniscus then a total meniscal transplantation may be indicated⁹.

Indications:

Total meniscal allograft transplants are indicated for patients missing an entire or significant portion of a meniscus whereas segmental meniscal transplants are indicated for patients with focal meniscal injuries. Further indications for transplant procedures include patients with normal alignment of the knee joint with stable ligaments, younger than 50 years of age, body mass index (BMI) under 30, persistent knee pain moderate enough to limit physical activity, loss of articular cartilage in the affected knee joint or localized osteochondral damage¹⁰.

Contraindications:

Contraindications for both total and segmental meniscal allograft transplant procedures include patients who are asymptomatic, active bacterial or viral infection, uncorrectable misalignment/instability of the knee or ligaments, above 50 years of age, obesity, inflammatory arthritis, septic arthritis, severe chondral damage and synovial disease¹⁰.

Sizing the Graft:

Once a patient is confirmed to be an adequate candidate for either type of meniscal transplant, a series of imaging of the affected knee will be performed to determine the size of the patient’s meniscus in order to match to an appropriately sized cadaver meniscus. The size of cadaver graft must be within 10% of the size of the patient’s affected meniscus. An oversized graft can result in an increased load force applied on the joint whereas an undersized graft can potentially lead to tears in the cadaver graft. The most common method for determining meniscus size is through the Pollard Method which obtains lateral and anterior-posterior (AP) x-ray views of the knee in order to determine the size of the affected meniscus, however magnetic resonance imaging (MRI) can be utilized as well¹⁰.

Processing the Graft:

There are currently two methods to process the cadaver graft, these methods are cryopreservation or utilization of fresh frozen allografts. Fresh frozen allografts have been shown to show some structural modification to the collagen network of the allograft, whereas cryopreservation does not alter the mechanical structure of the allograft. However, cryopreservation induces a significant cellular death, via apoptosis, in meniscal tissue. There is no established superiority of one method versus the other, however a survey found that 68% of surgeons prefer the use of a fresh frozen allograft for a meniscal allograft transplantation¹⁰.

Surgical Technique:

Before a segmental meniscal allograft transplantation can be performed, the surgeon must perform a diagnostic arthroscopy to ensure that there isn’t meniscal loss or damage. Once inside of the knee joint, the areas of meniscal defect are identified via utilization of two spinal needles to estimate anterior and posterior borders of the defect. The knee joint capsule is then opened to further reveal the meniscal defect which is then surgical excised carefully. Next, the rims of the deficient meniscus are measured and the allograft is cut to appropriate size for the transplantation. The segmental allograft is then excised from the donor and fixed with sutures into the patient’s meniscus remnant. After the graft has been fixed into the meniscal remnant, a high-strength suture is used to fix the graft anteriorly. In order to secure the meniscal graft anteriorly onto the patient's tibial plateau, a knotless anchor is placed. Finally, arthroscopy is utilized to evaluate the final positioning and stability of the allograft⁹.

A total meniscal allograft transplant is performed via knee arthroscopy in which the surgeon makes two to three small surgical incisions on the knee and then inserts a miniature camera called an arthroscope to obtain visualization of the knee cavity. Once the surgeon is able to visualize the field, they will initially clean the affected area by removing any debris in addition to removing any remaining meniscal tissue. The cadaver meniscus is then stitched into place on the shinbone (tibia) when a suture-only fixation technique is used. There are two other methods to fixate the meniscal allograft; double plug fixation, and the keyhole technique. The double plug technique involves attaching a 7mm bone plug to each root of the meniscal graft which will allow easy alignment onto the tibia. After doing so, the rest of the meniscal graft is fixed into place via sutures. With the keyhole technique, the anterior and posterior root of the meniscus is utilized to prepare a 10 mm bone bridge¹⁰.

Surgical Outcomes:

Although these are complex surgical procedures with various techniques, meta-analysis demonstrated that 89.2% of lateral meniscal allograft transplants and 85.8% of medial meniscus allograft transplants survive 5-10 after surgery¹¹. Additionally, a significant number of patients that undergo total meniscal transplants report improvement in outcomes and 90% of patients agree that they would be willing to undergo the procedure again¹².

Risks:

For both total and segmental meniscal allograft transplants, there are various risks such as; persistent swelling and stiffness of the affected knee joint after surgery, tear of the meniscal allograft requiring subsequent surgery (there is a 32% reoperation rate for total meniscal transplants), tear of the cadaver meniscus, bacterial or viral infection, damage to surrounding nerves, anesthesia complications or excessive bleeding¹².

Post-operative Care:

4-6 weeks post-op:

Patients are required to wear a postoperative knee brace on the affected knee and use crutches to aid with ambulation. In doing so, this allows the transplanted tissue adequate time to firmly attach to the recipient patient’s bone¹⁰.

7-12 weeks post-op:

Patients are able to wean off crutches and postoperative knee brace. They are also encouraged to perform mild strength-training exercises that aim to rebuild the range of motion, strength and flexibility of the knee and hip¹⁰.

12-24 weeks post-op:

Patients are allowed to perform more difficult/intense strength-training exercises¹⁰.

24-28 weeks post-op:

Patients will gradually continue to perform more intense strength-training exercises that strengthen the knee. These exercises may include jogging, running or jumping¹⁰.

References:

1. Kopf, S., Sava, M. P., Stärke, C., & Becker, R. (2020). The menisci and articular cartilage: a life-long fascination. EFORT open reviews, 5(10), 652–662. https://doi.org/10.1302/2058-5241.5.200016
2. Raj MA, Bubnis MA. Knee Meniscal Tears. [Updated 2022 Jul 18]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK431067/
3. Luvsannyam, E., Jain, M. S., Leitao, A. R., Maikawa, N., & Leitao, A. E. (2022). Meniscus Tear: Pathology, Incidence, and Management. Cureus, 14(5), e25121. https://doi.org/10.7759/cureus.25121
4. Özdemir, M., & Kavak, R. (2019). Meniscal Lesions in Geriatric Population: Prevalence and Association with Knee Osteoarthritis. Current aging science, 12(1), 67–73. https://doi.org/10.2174/1874609812666190628112103
5. Frank, R. M., & Cole, B. J. (2015). Meniscus transplantation. Current reviews in musculoskeletal medicine, 8(4), 443–450. https://doi.org/10.1007/s12178-015-9309-4
6. Bhan K. (2020). Meniscal Tears: Current Understanding, Diagnosis, and Management. Cureus, 12(6), e8590. https://doi.org/10.7759/cureus.8590 Lee, B. S., Kim, J. M., Sohn, D. W., & Bin, S. I. (2013). Review of Meniscal Allograft Transplantation Focusing on Long-term Results and Evaluation Methods. Knee surgery & related research, 25(1), 1–6. https://doi.org/10.5792/ksrr.2013.25.1.1
7. Figueroa, F., Figueroa, D., Calvo, R., Vaisman, A., & Espregueira-Mendes, J. (2019). Meniscus allograft transplantation: indications, techniques and outcomes. EFORT open reviews, 4(4), 115–120. https://doi.org/10.1302/2058-5241.4.180052
8. Jang, S. H., Kim, J. G., Ha, J. G., & Shim, J. C. (2011). Reducing the size of the meniscal allograft decreases the percentage of extrusion after meniscal allograft transplantation. Arthroscopy: The Journal of Arthroscopic & Related Surgery, 27(7), 914-922.
9. Bin, S. I., Nha, K. W., Cheong, J. Y., & Shin, Y. S. (2018). Midterm and Long-term Results of Medial Versus Lateral Meniscal Allograft Transplantation: A Meta-analysis. The American journal of sports medicine, 46(5), 1243–1250. https://doi.org/10.1177/0363546517709777
10. Gilat, R., & Cole, B. J. (2020). Meniscal Allograft Transplantation: Indications, Techniques, Outcomes. Arthroscopy : the journal of arthroscopic & related surgery : official publication of the Arthroscopy Association of North America and the International Arthroscopy Association, 36(4), 938–939. https://doi.org/10.1016/j.arthro.2020.01.025