A meniscus transplant or meniscal transplant is a transplant of the meniscus of the knee, which separates the thigh bone (femur) from the lower leg bone (tibia). The worn or damaged meniscus is removed and is replaced with a new one from a donor. The meniscus to be transplanted is taken from a cadaver, and, as such, is known as an allograft. Meniscal transplantation is technically difficult, as it must be sized accurately for each person, positioned properly and secured to the tibial plateau. Its success also depends on donor compatibility, stability of the transplant, and long-term health of the underlying articular cartilage.
Background Each knee has an inside (medial) and an outside (lateral) meniscus. The menisci play several key roles that are vital in maintaining the health of the knee. Specifically, they act as shock absorbers and load sharers, increase the stability of the knee, and provide lubrication and nutrition to the bearing surface (articular cartilage) of the knee. They were once thought of as vestigial structures that served no real purpose. If injured and problematic, they were routinely excised through a procedure called meniscectomy. It is now known that a knee joint without healthy menisci is at significantly increased risk of developing wear and tear arthritis (post-traumatic or osteoarthritis). The arthritis is a result of the increased contact forces and shear that results from loss of shock absorption and stability after meniscectomy. For this reason, current surgical strategies are focused on preserving as much of the meniscus as possible or replacing it if necessary. Certain meniscal tears are repairable with sutures, predominantly those that are freshly torn and involve healthy tissue. The closer the tear is to the peripheral blood supply the higher the likelihood of successful repair. Patients with unrepairable meniscal injuries usually have symptoms of pain, catching, swelling or locking in the knee. The surgeon may perform a partial or complete meniscectomy to alleviate the symptoms in the short-term. The more meniscal tissue removed, the higher the likelihood of subsequently developing arthritis. Recognizing the biomechanical importance of the menisci, surgeons in the late 1980s proposed meniscus transplantation and meniscus reconstruction as two new surgical options for the patient with a meniscus deficient knee. Recognizing from experiments performed by R.J. Webber, PhD that meniscus cells have the ability to grow in tissue culture, K.R. Stone, M.D. developed the first meniscus reconstruction device called a collagen regeneration template in 1986. The template or scaffold was composed of glycosaminoglycan (sugar/proteins that make up cartilage tissue) and was designed to have pores into which cells could grow. Its cross-linking preserved the scaffold in the knee joint long enough for new meniscus tissue to grow into it. (Patents 5,158,574, 5,116,374, 5,007,934) This scaffold was tested in animals and subsequently in people and was found to successfully replace lost segments of meniscus tissue (Fig 1). It became widely available in Europe and temporarily in the US in 2009. However, in cases where large areas of meniscus are missing, full intact meniscus transplantation has been suggested.
Indications for meniscus transplantation Most people who are meniscus deficient already have some arthritic changes in their knee. Early reports of meniscus transplantation done in arthritic knees suggested a higher incidence of transplantation failure if the irregular cartilage surfaces were not simultaneously addressed with cartilage grafting techniques. Therefore, the standard orthopaedic literature recommended that meniscus transplantation be performed in meniscus deficient patients only if they are young and free from arthritis of the knee. The most recently published indications for meniscal transplantation include:
Prior meniscectomy Age ≤ 50 years Pain in the meniscectomized tibiofemoral compartment No radiographic evidence of advanced joint deterioration ≥ 2mm of tibiofemoral joint space on 45 degrees weight-bearing posteroanterior radiographs No or only minimal bone exposed on tibiofemoral surfaces Normal axial alignment In the same textbook, contraindications are listed as:
Advanced knee joint arthrosis (flattening of the femoral condyle, concavity of the tibial plateau, osteophytes that prevent anatomic seating of the meniscus transplant) Uncorrected varus or valgus axial malalignment Uncorrected knee joint instability Anterior cruciate ligament deficiency Knee arthrofibrosis Significant muscular atrophy Prior joint infection with subsequent arthrosis Symptomatic noteworthy patellofemoral articular cartilage deterioration Obesity (body mass index > 30) Prophylactic procedure (asymptomatic patient with no articular cartilage damage)
Debate of indications Many orthopaedists have challenged these contraindications and have advocated meniscal transplantation, in conjunction with cartilage repair, ACL reconstruction or osteotomy in patients with evidence of arthritic deterioration, instability or malalignment. One paper demonstrated that results of meniscus transplantation in patients with arthritic changes were similar to that of previous reports of meniscus transplantation in patients without arthritic changes, so long as articular cartilage defects were addressed at the time of surgery. In the same paper, the success of meniscus transplantation was not affected by mal-alignment.
Meniscus transplant preparations
Meniscus tissue processing Meniscal allograft processing, sterilization and storage procedures vary from center to center. Some surgeons, particularly in Europe, prefer to harvest the meniscal graft themselves in a sterile fashion and use them when they are fresh, usually within two weeks of procurement. On the other hand, some American centers harvest the graft outside of a sterile operating room environment and then perform a sterilization wash. These grafts are then packaged and frozen at -80 °C, until they are to be transplanted. To decrease the risk of disease transmission, irradiating the graft has been used in the past to enhance sterilization. However, it has been shown to degrade most collagen-based tissues and the meniscus is particularly susceptible. Tissue preservation techniques such as cryo-preservation and freeze-drying have shown little benefit and have generally been abandoned except by a few tissue banks.
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