Historically, the role of normal meniscal cartilage was greatly under appreciated, and up until some 30 years ago, torn and damaged menisci were routinely excised. However, it is now known that the menisci are an integral structural component of the human knee, functioning to absorb shocks, provide joint stability, congruity, and nutrition. In addition, total and partial meniscectomy are associated with altered load bearing across the joint, frequently resulting in degenerative osteoarthritis. The integrity of the menisci are particularly important in knees in which the anterior cruciate ligament (ACL) has been damaged; in these situations, the menisci act as secondary stabilizers of anteroposterior and varus-valgus translation. With this greater understanding, the surgical principles of treating torn or damaged menisci evolved to their repair and preservation whenever possible. Moreover, meniscal allograft transplantation has been investigated in patients with a previous meniscectomy or for those requiring total or near total meniscectomy for irreparable tears.
Meniscal allograft transplantation is intended to restore knee function among patients with injured menisci from arthritis or trauma. The meniscus is a “c” shaped piece of cartilage in the knee. There are two in each knee; one on the inner and one on the outer side of the joint. Their purpose is to reduce the amount of friction between the thigh bone (femur) and the shin bone (tibia) and to also help with weight distribution within the knee joint. Meniscal allograft transplantation is a procedure that attempts to re-establish the function of an absent or badly deteriorating meniscus by transplanting a meniscus cartilage from a donor. The allograft is transplanted by arthroscopic insertion or via open techniques using an arthrotomy approach.
Meniscal allograft transplantation has been investigated in patients with a previous meniscectomy or who are requiring total or near total meniscectomy for irreparable tears. There are three general groups of patients who have been treated with meniscal allograft transplantation:
- young patients with a history of meniscectomy who have symptoms of pain and discomfort associated with early osteoarthrosis that is localized to the meniscus-deficient compartment;
- those who are undergoing ACL reconstruction in whom a concomitant meniscal transplant is intended to provide increased stability; OR
- young athletes with few symptoms in whom the allograft transplantation is intended to deter the development of osteoarthritis; due to the risks associated with this surgical procedure, prophylactic treatment is not frequently recommended.
The following different types of allografts have been investigated:
- Fresh - Fresh implants, harvested under sterile conditions, typically are not a practical option. The grafts must be used within a couple of days to maintain viability.
- Fresh Frozen - After sterile harvest, the meniscus can be frozen for storage until thawed for use. The freezing process may destroy donor cells and decrease the size of the graft.
- Freeze Dried (Lyophilized) - In addition to freezing, the tissue may be dehydrated, permitting storage at room temperature. Before transplantation, the graft is thawed and rehydrated. Lyophilized grafts have been shown to be prone to reduced tensile strength, graft shrinkage, poor rehydration, post-transplantation joint effusion, and synovitis, and are no longer used in the clinical setting.
- Cryopreserved - Cryopreservation freezes the graft in glycerol, preserving the cell membrane integrity and donor fibrochondrocyte viability. Cryolife (Marietta, Ga.) is a commercial supplier of such grafts.
In addition, several secondary sterilization techniques have been used, with gamma irradiation being the most common.
Meniscal allograft transplantation has moved into mainstream orthopedics. With proper patient selection, recognition and treatment of co-morbid conditions, meniscal allograft transplantation offers a solution that can at least temporarily decrease pain and increase function.