Imaging

It is important to review radiographs, including anteroposterior weight bearing views, lateral non-weight bearing views, Rosenberg views (posteroanterior 45° flexion weight bearing views), and merchant views (axial views of the patellofemoral joint) ( Fig. 1 ), because the ideal candidate for MAT does not have radiographic evidence of diffuse OA. Candidates for MAT should present with radiographs showing minimal joint space narrowing, no osteophytes, and no significant bony flattening in the involved compartment. These views should be obtained with a sizing marker to determine the graft size needed for MAT. Mechanical axis views should also be reviewed to evaluate the patient’s alignment and potential need for a realignment procedure concurrently or before the transplant. An MRI should be obtained to evaluate the meniscus, specifically the amount of meniscus remaining ( Fig. 2 ). The MRI will also assess for any subchondral edema, cartilage damage, or ligamentous insufficiency, because focal chondral defects or ligamentous pathology may need to be addressed concomitantly.

Radiographical imaging needed before MAT to evaluate evidence of OA as well as for sizing of the meniscal graft. ( A ) Anteroposterior views of bilateral knees. ( B ) Non-weight bearing lateral view of operative knee with sizing marker. ( C ) Rosenberg view of bilateral knees (posteroanterior 45° flexion weight bearing view) with a sizing marker. ( D ) Merchant view of bilateral knees.

MRI of the operative knee. ( A ) Coronal view of the left knee showing medial meniscal deficiency. ( B ) Sagittal view of the left knee with evidence of medial meniscal deficiency.

Diagnostic Arthroscopy

Before MAT, the senior author (BJC) recommends the patient undergo a diagnostic arthroscopy to further evaluate and confirm the status of the meniscus ( Fig. 3 ), cartilage damage, and concomitant pathologies. The diagnostic arthroscopy helps to elucidate other possible causes of knee pain to ensure the patient is an appropriate MAT candidate. This diagnostic arthroscopy is ideally completed within 6 months of MAT in the absence of outside index information that would otherwise verify the intra-articular pathology.

Diagnostic arthroscopy revealing right knee medial meniscus deficiency.

Graft Selection and Sizing

Preoperative radiographs with sizing markers are essential for ordering a size-matched meniscal allograft. Meniscal allografts are matched to the patient’s laterality, specific compartment, and size. Size matching is important because an improperly sized meniscus can lead to increased contact pressures in unwanted areas. Sizing is as described by Pollard and colleagues, on anteroposterior films in which 2 vertical lines are drawn perpendicular to the joint line and are used to measure meniscal width. In a medial meniscus, the first line is tangential to the medial tibial metaphyseal margin and the second is through the peak of the medial tibial eminence. For a lateral meniscus, the first line is tangential to the lateral tibial margin and the second is through the peak of the lateral tibial eminence. The distance between these 2 lines is said to be the meniscal width. Of note, it is important to measure from the margin of the tibial metaphysis rather than the joint space. Meniscal length is measured on lateral radiographs in a similar manner. The first line is drawn at the anterior tibial surface above the tuberosity and the second is a parallel line tangent to the posterior margin of the tibial plateau. The medial meniscus length is 0.8 times this distance, and the lateral meniscal length is 0.7 times the distance.

In the senior author’s practice, fresh-frozen allografts are preferred. Fresh-frozen meniscal allografts are able to be stored for 5 years at −80°C in a physiologic solution with an antibiotic. Although freezing the meniscus has been shown to result in decreased cell viability, this has not been reported to have negative effects on patient outcomes or graft survivorship. Other graft options include cryopreserved and fresh grafts. Because fresh grafts do not offer the same ability to plan in advance, fresh-frozen allografts ease the burden on both the physician and patient. Meniscal allografts have shown excellent integration and repopulation with host trabeculae when a bony bed is used with minor risk of immunologic reaction.

Patient Positioning

After induction with general anesthesia, the patient is positioned supine on the operating table with the foot of the bed dropped and the hips in line with the end of the bed. The contralateral leg is positioned in a well-leg holder in flexion, abduction, and external rotation. The operative knee is positioned in a thigh holder with a tourniquet in place and allowed to hang off the end of the bed. Standard preoperative antibiotics are administered before any incisions. An examination under anesthesia is performed to assess ligamentous stability. The patient limb is then prepped and draped sterilely.

Arthroscopy

The senior author performs the same technique for both medial and lateral MATs. After creation of the anterolateral and anteromedial portals, arthroscopy is performed to evaluate once more for focal chondral defects or ligamentous insufficiency. After the evaluation of concomitant pathologies via arthroscopy, the remaining meniscus in the index compartment is debrided taking care to not violate the capsule. This should be done until there is a 1- to 2-mm peripheral rim remaining with punctate bleeding. The anterior and posterior horn remnants can serve as a footprint for allograft insertion. The residual meniscal rim is left in place to prevent radial displacement of the allograft and function as a firm bed for meniscal fixation. A limited notchplasty can be performed at this time to enhance visualization and ease of graft passage. The anterior cruciate ligament fibers at the tibial insertion should be released, as minimally as possible, to allow for visualization of the medial tibial spine.

A posteromedial or posterolateral approach is made starting one-third of the way above the level of the joint line and extending two-thirds of the way below the level of the joint line, which will later be used to pass the sutures (as described elsewhere). Next, a 3-cm transpatellar tendon incision is made, into which a 4.5-mm burr is inserted to create a provisional slot, in line with the insertion of the anterior and posterior horns. After a depth gauge is inserted into the slot to verify appropriate depth (usually 10 mm), a guide pin is placed directly underneath and seated in the posterior cortex to establish the bottom of the slot. Fluoroscopic guidance may be used to ensure proper placement of the guide pin and to not violate the posterior cortex. An 8-mm cannulated reamer is placed over the guidewire, and a box cutter osteotome is used to widen the slot to 8 mm wide and 10 mm deep. A rasp is then used to even out all the edges in the slot and to maximize congruency with the bone bridge.

Graft Preparation

The meniscal allograft is prepared on the back table during arthroscopy. The meniscal allograft is delivered by the tissue bank as a hemiplateau with attached meniscus, with all nonmensical tissue removed. The graft is debrided so only true attachment sites remain and is then prepared to dimensions appropriate for the arthroscopic tibial slot preparation ( Fig. 4 ). Of note, the bone bridge is undersized by 1 mm as a preventive measure for ease of graft passage and minimization of potential bridge fracture. As a standard, the bone bridge is cut to a width of 7 mm and a height of 10 mm. Excess bone beyond the posterior horn attachment is removed to ensure proper alignment of the bone bridge posterior wall and posterior edge of the slot. To help with graft insertion, excess bone beyond the anterior horn is preserved. The junction of the posterior horn and middle third of the meniscus are secured using a no. 0 polydioxanone with a vertical mattress traction suture ( Fig. 5 ). In the event that the anterior horn is larger, the bone bridge width on the anterior horn insertion should be appropriately increased, with the remaining bone bridge cut to 7 mm.

Medial meniscal allograft after debridement so only true attachments remain. The graft is placed into a sizer to appropriately match the size of the tibial slot prepared in the knee.

A vertical mattress traction suture is placed in the graft approximately two-thirds of the way from the posterior horn.

Graft Insertion

First, the arthroscope is placed in the corresponding compartment portal (ie, anteromedial for medial MAT), and a repair cannula is placed in the contralateral portal, aiming toward the intended position of the junction of the middle and posterior portions of the graft.

A flexible suture-passing wire is then inserted through the meniscal repair cannula, and out the posterolateral/posteromedial portal. The ends from the traction stitch of the graft are threaded through the loop of the suture passing wire, which is retrieved from the transpatellar incision. The wire and sutures are then pulled through the posterolateral/posteromedial incision, and the meniscus is carefully inserted through the anterior incision, while simultaneously pulling on the polydioxanone traction suture and applying the appropriate stress (varus for a lateral MAT and valgus stress for a medial MAT) to insert the bridge into its position ( Fig. 6 ). Proper reduction of the meniscus and visualization of the bone block in the bridge is then done arthroscopically. After a few cycles of flexion and extension to ensure appropriate graft placement relative to the condyles, a 4.75 or 5.75 mm Swivelock anchor (Arthrex, Naples, FL) is placed to fix the bone bridge ( Fig. 7 ). Eight to 10 vertical mattress sutures are then placed using an inside-out technique, taking care to not tie them until any concomitant procedures are complete ( Fig. 8 ). The anterior horn of the meniscus is repaired with an outside-in technique. After concomitant procedures are complete, the inside-out sutures are tied while the knee is in full extension.

The meniscus allograft is inserted through the anterior incision while the polydioxanone traction suture is pulled through the medial or lateral arthrotomy for medial and lateral meniscal allograft transplants, respectively.

Visualization of the appropriate placement of the 4.75 or 5.75 mm anchor to fix the meniscal allograft into the tibial bone slot.

Vertical mattress sutures are placed via an inside-out technique to secure the meniscus in place and are left untied until all concomitant procedures are completed.

Concomitant Procedures

Concomitant procedures, when indicated, can and should be performed at the time of MAT or via staged procedure. These may include high tibial or distal femoral osteotomies for varus or valgus malalignment, respectively, ligamentous procedures for ligament insufficiency or rupture, and cartilage procedures, such as microfracture, autologous chondrocyte implantation, osteochondral allograft, or osteochondral autograft, for focal chondral defects. Any chondral defects should be addressed after the MAT, because the frequent varus/valgus manipulations associated with the MAT procedure can cause improper seating of the osteochondral graft. The concomitant procedure may alter the postoperative rehabilitation protocol slightly, all of which should be discussed with the patient preoperatively.

Closure

The posterolateral/posteromedial lesions are closed in a layered fashion, and portal holes are closed with 3-0 nylon interrupted sutures. After closure, local anesthesia is injected to maximize postoperative pain relief.

Rehabilitation

The postoperative rehabilitation protocol recommended by the senior author (BJC) is as follows. The patient is made heel touch weight bearing with crutches for the first 6 weeks and can progress to full weight bearing 6 to 8 weeks postoperatively. The patient is restricted from weight bearing with flexion greater than 90° for the first 8 weeks. The brace is locked in full extension for sleeping and all activities for the first 2 weeks, after which time the brace is locked at 0° to 90° and can be removed at night. Before 6 weeks, all exercises should be done with the brace. After this timepoint, activities can be done without the brace as tolerated. The brace can be discontinued 8 weeks postoperatively. The patient should avoid any tibial rotation for 8 weeks to protect the meniscus. Range of motion should be limited to 0° to 90° when non-weight bearing for the first 2 weeks and then can progress as tolerated over weeks 2 to 8. The patient should have full range of motion by weeks 8 to 12. After 8 weeks, hamstring work, lunges, proprioception exercises, and stationary bike can begin and progress as tolerated through 20 weeks. Around 6 months, the patient is able to advance to sport-specific drills, running, and jumping after physician clearance.