Meniscus Transplantation

Introduction

Initial treatment of most meniscus tears involves either excision or repair to prevent further propagation. The medial meniscus bears 40% of the tibiofemoral load, whereas the lateral meniscus bears 70% of the load. With a better understanding of the meniscal deficient biological environment, surgeons have transitioned in some case from removal to meniscal preservation. ^, If preservation is not possible, it is now understood that transplantation of cadaveric meniscus may lead to prevention of early osteoarthritis changes. Most meniscal transplant patients require careful selection. In general, most of these patients are relatively young (<50 years) with an intact articular surface and moderate to severe pain postmeniscectomy. If there are anatomic alignment abnormalities or more extensive cartilage wear, further concomitant procedures may be needed.

Previously it was thought that chondral defects were a contraindication for meniscal transplantation; however, further data suggest it is a not a significant risk factor for failure. Although concomitant meniscal transplant and cartilage restoration is a recent phenomenon, short-term outcomes are good. Rue et al. looked at patients who underwent combined meniscal transplantation and cartilage restoration and found that 71% were completely satisfied with their results. If careful selection is performed, combined procedures can offer excellent pain relief and improved function. ^,

Complications generally arise from a number of factors including improper preoperative assessment, poor indications, missed concomitant pathology, inadequate graft preparation, improper surgical technique, and insufficient postoperative management. All these factors will be addressed in this chapter, as well as evidence-based outcomes and preventative measures to reduce complication risk and improve results of this high-demand and complex patient population.

Preoperative Assessment and Complications

A good preoperative assessment of patients in this population is essential because they may have other factors contributing to pain or dysfunction. A variety of features must be considered when evaluating a potential candidate for meniscal allograft transplantation (MAT). ^, Obtaining a thorough history including previous injuries, comorbidities, and treatments is imperative. Furthermore, not all patients with meniscal deficiency are candidates for MAT, and a surgeon must understand appropriate indications. All previous operative notes, intraoperative photos, and imaging modalities much be reviewed in detail. Recent operative reports and arthroscopy images can be helpful to rule out diffuse arthritic changes. On examination, range of motion is usually preserved, joint effusion is present depending on recent physical activity, and occasionally palpation will reveal joint line or femoral condyle tenderness. Associated pathology, such as malalignment and ligamentous instability, should be noticed, because it would have to be addressed in a staged or concurrent fashion.

Complications can be prevented by evaluating correctable comorbidities (malalignment, ligament deficiency, uncorrected localized chondral damage in the involved compartment). Understanding general indications is essential, and these are outlined here:

1)

Patients younger than 50 years old with a chief complaint of pain limiting their desired activities
2)

Body mass index less than 35 kg/m ²and previous total meniscectomy with pain localized to the affected compartment
3)

Normal or correctable coronal and sagittal alignment
4)

Normal or correctable ligamentous stability
5)

Normal or correctable articular cartilage
6)

Willingness to comply with rehabilitation protocol

Full-thickness chondral defects have traditionally been considered a contraindication to meniscal transplantation. Several recent reports have demonstrated results of concurrent meniscal transplantation and cartilage repair that are similar to isolated meniscal transplantation. As a result, we commonly perform concurrent cartilage transplantation with MAT. Failure to recognize these comorbidities or improper indications can lead to early graft failure, lack of pain reduction, and low patient satisfaction. Finally, MAT performed as a prophylactic measure in the absence of appropriate symptoms is highly controversial and not advocated by the senior author. Following these criteria is a critical part of preventing postoperative complications, graft failure, and poor patient outcomes.

Preoperative Imaging, Sizing, and Preservation Techniques

Preoperative imaging and sizing is essential to prevent both intraoperative and postoperative complications. Routinely, we obtain weight-bearing anteroposterior (AP) and posteroanterior 45-degree flexion radiographs, nonweight-bearing 45-degree flexion lateral view, axial view of the patellofemoral joint, and a long-leg mechanical axis view to evaluate malalignment. Magnetic resonance imaging (MRI) is helpful to assess the extent of previous meniscectomy, the degree of subchondral edema in the involved compartment, and the presence of other articular comorbidities, such as ligamentous or chondral injury. Bone marrow edema underlying the cartilage defect may indicate a source of pain, and the surgeon should take this into consideration when performing MAT. Correlating this imaging with previous arthroscopic images is crucial.

Sizing the meniscal allograft is one of the most important technical aspects of a successful surgery to prevent postoperative complications. Dienst et al. published a cadaveric biomechanical study evaluating the effects of sizing meniscal allografts on contact stresses in the lateral compartment. An oversized graft led to greater contact stresses on the articular surface, whereas undersized grafts led to near-normal contact stresses but increased stresses on the allograft itself. They concluded that a size mismatch of 10% or less was needed for the allograft to function properly. Additionally, width should be considered. Huang et al. evaluated the crosssectional parameters of meniscal allografts compared with native menisci in cadaveric knees and found increased contact pressures when allografts did not match native menisci, with the greatest predictor of differences being the width of the menisci.

Currently, radiographic measurements, as described by Pollard et al., are used to appropriately size the meniscus. As a consistent relationship exists between meniscal size and bony landmarks, most tissue banks currently size the meniscus with tibial plateau width and length measurements ( Fig. 3.1 ). Sizing using MRI is reserved for cases that are not as well defined because MRI for graft size matching often underestimates meniscus length and width. We recommend using radiographs for meniscal sizing to prevent some of these potential complications.

In addition to imaging, a diagnostic arthroscopy is useful to obtain a better understanding of the pathology in the patient’s knee and aid in proper surgical planning. In all cases except when a recent (last 6 months) arthroscopy has been performed, we perform a diagnostic arthroscopy to assess the state of the femoral and tibial cartilage and confirm a majority of the meniscus is incompetent or missing.

Once sizing is complete, the appropriate preservation technique is selected based on the tissue bank. Meniscal allografts are ideally harvested within 24 hours after death and frozen. Although other graft preservation methods are used, fresh-frozen remains the most commonly used allograft preservation method. Graft shrinkage has been reported, which can alter the accuracy of meniscal sizing and compromise the outcome, so careful evaluation of your tissue bank protocols are essential because specific techniques can vary between tissue banks. Cryopreservation was found to induce significant apoptotic cell death in meniscal tissue, with a reported cell viability of only 10-40%. Furthermore, the storage of the graft itself after harvest and before transplantation must be scrutinized because a high number of freeze-thaw cycles may be detrimental to graft function. Our ideal technique is a meniscus harvest within 24 hours after death and preservation using the fresh-frozen technique because in many cases this gives the best viability and allows for proper surgical planning.

Intraoperative (Slot) Technique and Potential Complications

Numerous complications can occur during the procedure, and an in-depth understanding of surgical anatomy is necessary. In addition, the type of complication that can arise is based on specific techniques and if concomitant procedures are used.

For a MAT slot technique, surgical landmarks include the patella, patellar tendon, tibial plateau, and fibular head. During the posterolateral approach or a lateral MAT, structures most at risk during the procedure include the peroneal nerve and lateral collateral ligament. For the posteromedial approach, the saphenous nerve is most at risk. Also, needle passage during the meniscocapsular repair can injure the posterior neurovascular bundle. One more devastating complication is tibial vein or arterial perforation. This can occur with preparation of the slot, and is most likely to occur with lateral MAT given the anatomy of the arteries and vein.

The potentially worst and most preventable complications occur with preparation of the tibial slot. We initially start with slot preparation using electrocautery to center the anterior and posterior horn attachment sites with a line. This also prevents veering too close to the anterior cruciate ligament (ACL) insertion or too close to the main articulating portion of the plateau. Using this line as a guide, a 4-mm burr is used to create a superficial reference slot in the tibial plateau, making sure to follow the posterior slope of the tibia. Slot dimensions should be confirmed by placing a hooked depth gauge in the reference slot, which also measures the AP length of the tibial plateau. Using a drill guide referencing off the hooked probe, a guide pin is drilled into the proximal tibia, just distal and parallel to the reference slot. The pin is advanced to, but not through, the posterior cortex, being mindful to avoid overpenetration, which could injure the posterior neurovascular bundle. If penetration is a concern, intraoperative fluoroscopy and/or a posterior lateral or posterior medial portal may be needed to visualize the pin and protect it from further penetration if this occurs. The pin is subsequently overreamed with an 8-mm cannulated drill bit, again taking care to maintain the posterior cortex and avoid capturing the pin with the drill and advancing ahead of the working end. A box cutter is then used to create an 8-mm -wide, 10-mm -deep slot which is smoothed and refined with a rasp to ensure that the bone bridge will slide smoothly into the slot ( Fig. 3.2 ). In general, following this succinct set of steps prevents the frequent complications that can occur with tibial slot preparation.

Meniscal root anatomy is also imperative to understand, not only in the setting of an isolated MAT, but also for combination procedures. For the lateral meniscus, a bone bridge technique is used for a MAT. In contrast, the medial meniscal roots are further apart from each other; thus medial MAT can be safely performed with either a bone bridge or bone plugs.

There are other fixation techniques, and debate continues regarding the optimal procedure. Meniscal allografts can be secured by suture fixation or bony fixation ( Fig. 3.2 E–F ). Furthermore, bony fixation includes separate bone plugs on the anterior and posterior horns, or other variations such as keyhole, trough, dove-tail, and bridge-in-slot. In general, anatomic bony fixation is the gold standard for most surgeons, although several surgeons have reported excellent results with soft tissue-only MAT.

When performing a bridge-in-slot technique, bone bridge fracture is a potential complication. If this occurs, a small K-wire is used to reapproximate the bridge for insertion, or conversion to a bone plug technique is used. To prevent this from occurring, bone posterior to the posterior meniscal horn attachment is removed, but bone anterior to the anterior meniscal horn is kept intact to maintain graft integrity during graft passage.

Complications Caused by Neglecting Concomitant Procedures

As discussed earlier, a thorough preoperative evaluation of these potential patients is essential. Neglecting axial malalignment and concomitant intraarticular injuries can be detrimental to patient outcomes. Lee et al. found that axial malalignment can exert abnormal pressure on the newly placed graft, which can lead to loosening, overload, degeneration, and failure. Also, an osteotomy can independently reduce compartment loads, providing additional pain relief.

The ACL-deficient patient needing MAT may benefit from concomitant ACL reconstruction (ACLR) because long-term follow-up after this procedure is good, as opposed to outcomes in patients with untreated knees. Also, the posterior horn of the medial meniscus is an important secondary stabilizer to anterior translation and may prevent secondary stretch of the ACL-reconstructed knee. ^, These are all potential complications that can be prevented if concomitant or staged procedures, as per the surgeon’s comfort, are performed with a MAT.

Preventing Complications With Concomitant Procedures

Anterior Cruciate Ligament Reconstruction and Meniscus Allograft Transplantation

When doing a combined procedure, we use a modification of the bridge-in-slot technique using two smaller bone blocks rather than one long bridge. The technique is similar to the bone-plug technique described for medial meniscal transplantation. Usually standard femoral and tibial tunnels are drilled and prepared before meniscal allograft insertion. The use of allograft decreases associated donor-site morbidity, and tibial tunnel drilling requires special care because this tunnel often contacts the bone trough for the meniscus. Again, you can also leave the ACL drill in when making the trough to protect from “tunnel convergence.” The key is to understand the bony anatomy and start with the ACL tibial tunnel. These have good results if done properly, with Wirth et al. reporting excellent results in a series of 23 patients followed up with 14 years postprocedure ( Fig. 3.3 ).