Indications

Success of MAT hinges on proper patient selection. Prior total or subtotal meniscectomy and pain with activity localized to the meniscectomized compartment are the most common indications. Ideally patients should be younger than 50 years, have minimal Outerbridge changes to their articular cartilage (grade I or II), and possess an optimal mechanical environment from a stability and alignment perspective. Patients who do not fit all these criteria at the time of clinical presentation should not be precluded from undergoing MAT. Instead, a detailed single or staged surgical plan should be formulated to make sure that all knee abnormalities are addressed and that native knee anatomy, stability, and kinematics are restored, thereby giving the meniscal allograft the best chance of incorporation at the time of implantation.

Though beyond the scope of this chapter, concomitant procedures performed with MAT include anterior cruciate ligament (ACL) reconstruction, revision ACL reconstruction, posterolateral corner (PLC) reconstruction, osteotomies of the distal femur and proximal tibia to correct for coronal plane malalignment, and any number of procedures to address focal, cartilaginous defects (e.g., autologous chondrocyte implantation [ACI], osteochondral autograft transplantation surgery [OATS]). Patients need to be willing to comply with postoperative rehabilitation protocols and should be thoroughly counseled that the intent of the MAT is to restore knee function and decrease pain, not return patients to their peak, preinjury level of activity, especially high-performance athletes.

Contraindications

Patients should not undergo MAT if they are asymptomatic; possess overt signs of joint degeneration on plain radiographs (joint space narrowing, osteophytes, subchondral cysts, sclerosis); demonstrate diffuse, high-grade cartilage changes (Outerbridge grade III or IV) on magnetic resonance imaging (MRI); or have fixed sagittal or coronal plain deformities. In addition, muscular atrophy, history of knee sepsis, history of inflammatory arthritis, and conditions such as immune disorders, diabetes mellitus, gout, and marked obesity are relative contraindications. Last, but important, patients who are not willing to comply with the postoperative rehabilitation or who seek unrealistic outcomes are not ideal candidates for MAT.

Graft Sizing

Meniscal allografts must be appropriately sized to prevent overstuffing of the joint leading to stiffness, or conversely to prevent undersizing, which leads to poor joint surface coverage and increased forces across the graft. The senior author has consistently used one tissue bank over the course of his career and receives a size-matched meniscal allograft based on the preoperative MRI scan supplied to the tissue bank. Other surgeons use measurements made from radiographs to arrive at the appropriate graft size, but this has not been the experience of the senior author.

Imaging

A standard set of weight-bearing plain radiographs should be obtained for all patients being evaluated for MAT and should include the following views: 45-degree posteroanterior (PA), anteroposterior (AP) in full extension, 45-degree lateral, Merchant views of the patella, and full-length mechanical axis films of the lower extremity. Magnification markers placed on the skin are important for sizing of the meniscal allograft before surgery. CT scan has a limited role in preparing for MAT surgery except when a revision ACL procedure needs to be performed and there is concern for lysis around the bone tunnels. MRI is useful to assess the extent of meniscal damage and the integrity of the articular cartilage, and to identify ligamentous damage and the presence of any subchondral edema. Bone scans have been described in the literature for differentiation of compartment stress overload from overt arthritis, but they are rarely ordered in the clinical setting of patients being evaluated for MAT.

Overview

Many techniques for MAT have been described in the literature. The technique the senior author has used for the past 15 years uses bone plugs to secure either the medial or the lateral meniscal allograft or both to the anatomic insertion sites of both meniscal horns. The graft is placed arthroscopically via the ipsilateral anterior portal and secured to the capsule with permanent inside-out sutures. The bone plugs roughly measure 9 mm in diameter and 7 mm in height; they are placed into 10-mm bone sockets. This particular configuration makes bone plugs a viable option for medial as well as lateral MAT despite the closer proximity of the lateral menisci’s horn insertion sites. This technique has relatively low morbidity in the hands of the senior author, enabling it to be performed in the outpatient setting.

Anesthesia and Positioning

The patient is placed supine on the surgical bed with a thigh tourniquet applied, though rarely inflated. A lateral post allows for application of a valgus force to open the medial compartment. The foot of the bed is flexed maximally with enough room behind the passively flexed knee to allow a fist to be placed. Two rolled sheets placed under the pad of the bed prevent hyperextension at the hip. The contralateral lower extremity is safely cradled in a well leg holder with the hip and knee slightly flexed in an abducted position (Fig. 58-1). The graft is checked by the surgeon at least 1 day before the scheduled surgery to verify it is for the correct limb and for the correct compartment. While the patient is being brought into the room and positioned for surgery, the graft is thawed and prepared for transplantation on the back table. The graft is usually ready for implantation as the leg is being prepared and draped. Anesthesia routinely includes a regional block performed in the preoperative area once the patient’s site is signed by the surgeon. A general anesthetic is used as well to help expedite the surgery.

Specific Steps

Box 58-1 outlines the specific steps of this procedure.

Box 58-1   Surgical Steps

Graft Preparation

• Anchoring and vertical sutures

• Guide markings

Knee Preparation

• Removal of meniscal remnant

• Arthroscopic portals and incisions

• Posterior bone plug socket

Graft Placement

• Passage of sutures

• Reduction of graft into knee joint

• Securing of posterior third of graft

• Preparation of anterior horn socket

• Securing of anterior bone plug

• Inside-out sutures through remaining meniscal body

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