The ideal patient for a meniscal allograft transplantation is one who presents with pain in a meniscus-deficient compartment, is not significantly overweight, has normal alignment, is ligamentously stable, has normal cartilage, and is relatively young but skeletally mature. Although there is no upper chronologic age limit, patients who have a meniscus-deficient knee and are over the age of 50 often have significant arthritis. Skeletal maturity is necessary to avoid causing asymmetric physeal arrest and progressive angular deformity with the use of current meniscal allograft techniques.

Contraindications include inflammatory arthritis, synovial disease, a history of knee infections, immunodeficiency, obesity, and skeletal immaturity. The most common contraindications include advanced arthritis (outerbridge grade III or IV) on the tibia, flattening of the femoral condyle, or marked osteophyte formation (11,12). As they are considered relative contraindications, comorbidities such as ligamentous instability, malalignment, and focal chondral defects must be addressed at the time of or prior to meniscus transplantation.

The surgeon must identify the specific motivation for a patient seeking transplantation and adjust expectations for partial, short-term pain relief. Meniscal allograft transplantation may potentially delay osteoarthritis, but it is primarily a pain relieving operation. The patient should seek treatment for pain in the meniscal deficient compartment and understand that at best, meniscal transplantation does not prevent the need for total knee arthroplasty.

Postmeniscectomy patients usually present with subtle joint line pain, swelling with activity, and knee pain induced by changes in the ambient barometric pressure. At times, they also present with occasional painful giving way and crepitus. After taking a detailed history, the physical exam should assess the status of ligament stability, alignment, and the articular cartilage. It is also of the utmost importance to request and review previous operative pictures and video if available. Evaluation of the location and reason for previous incisions is also critical as many of these patients have undergone prior surgical procedures including ligament reconstructions and attempted meniscal repair. Patients generally will have tenderness in the involved joint line, full range of motion, and potentially a slight effusion.

Routine radiographs include weight-bearing anteroposterior (AP) views of both knees in full extension, a non-weight-bearing 45-degree flexion lateral view, and a merchant view of the patellofemoral joint. A 45-degree flexion weight-bearing posteroanterior (PA) view should also be taken to identify joint space narrowing not appreciated on the full extension views (13). Furthermore, long leg alignment films must be taken if there is any suspicion of malalignment. Articular cartilage may be assessed by MRI. MRI, in conjunction with intraoperative pictures, is useful in determining how much meniscus remains (Fig. 25.1A and B). A three-phase bone scan is rarely indicated. If the status of the cartilage and the amount of meniscus that was previously resected are unclear, it is strongly encouraged to perform a diagnostic arthroscopy in order to evaluate the knee for a meniscal allograft. This is especially true if the patient has not had any surgical intervention for over a year as it is not uncommon for articular cartilage degeneration to occur over this time-frame. This is particularly true on the lateral side where once articular cartilage begins to breakdown, it can be quite a rapid progression.

The appropriate size of an absent meniscus cannot be determined by measuring the meniscus in the opposite knee as meniscal allografts are side and compartment specific. While newer information is emerging in support of MRI, MRI and CT scans are not recommended as they have been shown in previous studies to misjudge the size of the allograft (14). The best method for estimating the appropriate size of an absent meniscus is with plain radiographs (14,15). The technique described by Pollard is commonly used. Preoperatively, measurements are made on AP and lateral radiographs, with magnification markers placed on the skin at the level of the proximal tibia. The meniscal width is calculated based on the width of the compartment as seen on AP radiographs after correction for magnification. The meniscal length is based on the lateral radiograph using the sagittal length of the tibial plateau (Fig. 25.2A and B). Following correction for magnification, the length is multiplied by 0.8 for the medial meniscus and by 0.7 for the lateral meniscus. This technique has been shown to lead to a size match in at least 95% of cases, which is crucial to optimizing graft survival and protection of the articular surfaces (15). This is especially true when using a bone bridge technique as the distance between the anterior and posterior horns of the lateral meniscus is a fixed distance and attached to the bone bloc. Underestimating the size of the graft will lead to meniscal tears once activities are resumed.

Because of inherent difficulties in harvesting and distributing fresh donor allografts to a size-matched recipient within a few days of harvest, fresh menisci suitable for allograft implantation have been replaced by tissue bank preserved meniscal allografts. Therefore, the first, and most critical, step in graft procurement is stringent donor screening and selection. The American Association of Tissue Banks has defined a stringent protocol to increase the likelihood of obtaining disease-free grafts (16). Serologic screening is performed for HIV p24 antigen, HIV-1/HIV-2 antibody, human T-lymphocyte virus 1 and human T-lymphocyte virus 2, hepatitis B core antibody, antibodies to hepatitis C virus, and syphilis. Most banks also perform polymerase chain reaction testing, which can detect one HIV-infected cell in over 1 million cells. The current window of time for development of detectable antibodies to HIV is approximately 20 to 25 days. Blood cultures for aerobic and anaerobic bacteria are conducted as well and lymph node sampling may be performed.

Graft processing including debridement, ultrasonic/pulsatile washing, and use of ethanol to denature proteins, further lowers disease transmission risk. Freezing also lowers the risk, but HIV can survive these graft processing measures (17). Safety clearly relies heavily on adequate screening and not necessarily graft processing. Nevertheless, the current risk for HIV transmission from frozen connective-tissue allografts is estimated to be 1 in 8 million (18).

The tissue is procured within 12 hours after death or within 24 hours after death if the body has been stored at 4°C. Currently, tissue may be harvested with the use of sterile surgical technique or it may be procured in a clean, nonsterile environment and secondarily sterilized. Harvested tissue may be preserved in one of the four ways: cryopreservation, fresh-frozen, fresh, or freeze dried (lyophilization). Fresh and cyropreserved allografts contain viable cells, whereas fresh-frozen and lyophilized tissues are acellular at the time of implantation. Fresh tissue is harvested under sterile conditions within 12 hours after death. The tissue is stored in a culture medium at 4°C or 39°F to maintain cell viability. These grafts must be transplanted within several days after being harvested and are therefore logistically difficult to work with (19). Cryopreservation includes the use of a cryoprotectant, dimethylsulfoxide. Fresh-frozen grafts are rapidly frozen to −80°C, killing cells but maintaining material properties. Lyophilization is uncommonly used as it is implicated in graft shrinkage, decreased cell viability, and diminished biomechanical properties (20). Unlike fresh osteochondral grafts, the morphologic and biochemical characteristics of meniscal allografts do not depend heavily on cell viability. Therefore, the most commonly implanted grafts are either fresh-frozen or cyropreserved (21). Animal studies have not shown any significant differences between these two preservation methods.

Animal studies have not demonstrated a predictable humeral or cellular-based immunologic rejection response from bone allografts in rabbits or implanted meniscal allografts in goats or mice (22,23

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