Medial Meniscal Allograft Transplantation: The Bone Plug Technique

Abstract

Background:

The medial and lateral menisci act as shock absorbers for the knee joint by converting and redistributing axial load into circumferential hoop stresses. Disruptions of these hoop stresses occur in the setting of meniscal deficiency and lead to long-term degenerative changes. Therefore, maintaining the distinctive composition and organization of the menisci is essential. In selective cases of meniscal deficiency, meniscus allograft transplantation can be a valuable treatment option.

Indications:

Meniscus transplantation should be considered in patients with symptomatic meniscal deficiency, without the presence of advanced degenerative pathologies, who have failed all conservative treatments.

Technique description:

We can divide the surgery into 4 steps: (1) graft preparation, (2) arthroscopic joint preparation, (3) allograft attachment preparation, and (4) graft fixation.

Results:

Meniscus allograft transplantation yields good to excellent results in up to 85% of cases. Improvement of pain and knee function occurs in approximately 70% of the patients at 10 years. The associated complications are mainly joint stiffness, early osteoarthritis, and incomplete healing accompanied by graft failure. Graft failure is the most feared complication, yet shows good results over the midterm.

Conclusion:

The bone plug technique we have shown here is a hybrid approach combining soft tissue and bone fixation techniques. It provides synergistic advantages with good osseous integration and is minimally invasive through arthroscopy without true arthrotomy. In our experience, this approach elegantly eases the complexity of this demanding surgery while yielding excellent results for patients.

Patient Consent Disclosure Statement:

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

In the following video, we will present our surgical technique for medial meniscal allograft transplantation using bone plugs. The procedure is being performed by lead surgeon, Dr Seth Lawrence Sherman and his team at Stanford University.

Before starting the practical demonstration, we will provide some general background information regarding meniscus transplantation. Starting at about minute 5:00, we are going to demonstrate the individual steps of the procedure, and we will conclude with some pearls and pitfalls.

The medial and lateral meniscus absorb shock by converting and redistributing axial load into circumferential hoop stresses. Disruptions of these hoop stresses occur in the setting of meniscal deficiency and lead to long-term degenerative changes. Partial and especially total meniscectomy result in poor tibiofemoral biomechanics, higher peak cartilage stresses, and early osteoarthritis. Therefore, maintaining the distinctive composition and organization of the menisci is essential. In selective cases of meniscal deficiency, meniscus allograft transplantation can be a valuable treatment option.

Two main techniques for fixation of meniscal allografts have been described: soft tissue–only fixation and bony fixation. Both have been successful at increasing contact area and redistributing hoop stresses. Bony fixation can be achieved through 2 distinct methods: the bone plug and bone bridge or slot technique. However, due to the more widely spaced roots of the medial meniscus, the use of the slot technique should be carefully considered when working in the medial compartment. The bone-plug technique has demonstrated improved tibiofemoral contact pressure compared with soft tissue fixation. ¹ We, therefore, prefer it as a viable option to restore biomechanics.

Meniscus transplantation should be considered in patients with symptomatic meniscal deficiency without the presence of advanced degenerative pathologies, who have failed all conservative treatments. Comorbidities such as instability, malalignment, or localized osteochondral defects should be addressed. The presence of advanced degenerative pathologies as well as a wide spread of concomitant pathologies stressing the medial compartment are contraindications. In these patients, complication rates are high. ¹⁰

Meniscus allograft transplantation yields good to excellent results in up to 85% of cases.^3,9 Complications are mainly joint stiffness, early osteoarthritis, and incomplete healing accompanied by graft failure. Joint stiffness is the main reason for the high reoperation rate of up to 30% for medial meniscal transplantation; nonetheless, as meniscus transplantation is a salvage procedure, it is highly successful at extending time to arthroplasty. The burden of osteoarthritis may be dependent on timing as earlier meniscus transplantation has been shown to lead to lower rates of degenerative cartilage changes. ⁴ Graft failure is the most feared complication, yet meniscus transplantation shows good results over the midterm. ⁷ Other risks such as bleeding, infection, or damage to posterior cruciate ligament (PCL) or nearby associated neurovascular structures are low.

Prior to surgery, the standard medical history, clinical examination, and radiograph images should be obtained. To fully detect concomitant pathologies, we generally obtain a standard weightbearing knee radiograph in 3 planes, a 3-joint standing radiograph to evaluate coronal alignment, a magnetic resonance imaging study of the knee, and often we will perform a staging arthroscopy to fully document the extent of the meniscal deficiency and health of the cartilage in all 3 compartments.

These images are then also used for sizing the graft, which must be matched to within 10% of the native meniscus. ² The graft measurement can be done with radiographs, magnetic resonance imaging, or computed tomography scans. Obtaining the correct graft size is critical: Oversizing the graft results in inadequate transmission of the compressive loads with greater forces across the articular cartilage and meniscus extrusion. Undersizing the graft results in poor joint congruity and increases the shear forces on the graft itself. Different measurement methods have been described, including the Pollard and Yoon method using plain radiographs or the anthropometric method published by Van Thiel, besides the volumetric measurements of 3-dimensional reconstructions of axial slices. ⁵ In cases of total meniscectomy, it is important to point out that there is a high variability between contralateral knees and the opposite knee should not be used as a reference.

The patient we are presenting is a 45-year-old healthy, active male cyclist. He has a complex history, including a previous anterior cruciate ligament (ACL) reconstruction and partial medial meniscectomy that unfortunately had to be revised years later with further meniscectomy. He presents with postmeniscectomy syndrome with right-sided one-finger pain directly over his medial joint line and persistent effusions that are refractory to all conservative treatments. He has full range of motion equal to the other knee, a stable ligamentous examination, and satisfactory alignment.

We can divide the surgery into 4 steps: (1) graft preparation, (2) arthroscopic joint preparation, (3) allograft attachment preparation, and (4) graft fixation.

Our setup for the procedure includes a standard arthroscopy set and the following disposables as implants.

The patient is positioned supine on the operating table with a lateral post and adjustable foot rest with the knee flexed to 90°.

We are now showing you the first step of the graft preparation. This can be started prior to the incision and performed simultaneously to the arthroscopy. The graft usually comes with a large bone block on the tibial plateau. We are just incorporating the anterior and posterior roots, so are separating the bone block using 2 cuts and removing the middle portion. Out of these, we are making 2 bone plugs measuring 9 mm in diameter and 2 to 3 mm deep. You can see here the different morphology of the anterior and posterior horns of the meniscus. Identification of proper orientation is important at all times. After rough downsizing of the bone block, the plugs will be fashioned to their final size. Using the 9 mm graft sizer as a size template can be helpful, but it can also be done with a ruler. This is done for both roots. Plug size is important as a too thin plug can crack, and if the plug is too thick it can be difficult to place and incorporate. Throughout the process, it is important to keep the graft from drying out. We also soak the graft in vancomycin to reduce the risk of infection. A suspensory button fixation system is then attached on the anterior plug and a nonabsorbable #2 suture on the posterior plug. We prefer to start the suture from the superior aspect of the graft and to start the suspensory button fixation system from its inferior side to minimize friction on the femoral condyle. The last stitch exists inferiorly. Two meniscotibial soft tissue fixations are placed as horizontal mattress at the junction of the mid meniscus; for this, we use two 1.3-mm flat-braided nonabsorbable sutures. Prior to graft implantation, we mark the orientation of the graft: we imprint it with A and P for anterior and posterior. This is what the final graft looks like.

Next, or simultaneous to graft preparation, is the diagnostic arthroscopy. For this, establish standard arthroscopy portals, allow for good visualization, and resect as much of the fatpad as needed. We prefer to perform a reverse notchplasty to ease access to the posterior root. If needed, trephinate the deep medial collateral ligament for better access. Perform diagnostic arthroscopy. In our case, the patient had a deficient medial meniscus, intact cartilage, and an intact ACL graft.

Next, attention was turned to the preparation of the allograft root attachment sites. Debridement of the remnant of the medial meniscus was completed to expose the vascular edge, leaving approximately 2 mm of the outer rim. We start here with preparing the posterior root. Localize the correct location of the native posterior root, which inserts on the downslope of the posterior intercondylar fossa, between the articular margin of the posteromedial tibial plateau and the tibial insertion of the PCL, but be aware of the proximity to the anterolateral bundle of the PCL to not injure it during tunnel drilling. Alternatively, the root can be placed approximately 1 cm posteriorly and slightly lateral to the apex of the medial tibial eminence. After reliable identification of the correct location for the root, we use a guide pin and a reamer from a point medial to the tibial tubercle to create a 9 × 3 mm posterior socket. A shuttle suture is passed and it is brought out of the anterolateral portal and snapped. Then, the anterior root footprint is prepared. Locate the anterior root insertion. The anterior meniscus root attachment lies anterior to the apex of the medial tibial eminence and between the articular margin, the anteromedial tibial plateau, and anterior border of the ACL. Another arthroscopic landmark can be the medial tibial eminence. Locate its apex and go approximately 27 mm anterior to it. ⁶

After identifying our landmarks, we place a K-wire in deep knee flexion and then follow with a low-profile cannulated 9 mm reamer through an additionally placed high anteromedial portal to drill a socket for the bone graft of 9 mm diameter and 10 mm depth. This extra depth can be important later to compensate for graft mismatch by sinking the anterior aspect of the graft deeper into the tibia. Afterward, we create a guide pin tunnel from medial to the prior drilled bone tunnel using the ACL drill guide and pass another shuttle suture, which is then brought out through the anteromedial portal. Be aware of your posterior bone tunnel to not accidentally cross it. Now both bony fixations are prepared. An inside-out meniscal repair system is used for the soft tissue fixation sites at the junctions of the middle meniscus with the anterior and posterior horn to pass 2 shuttle sutures, which we will use later for the meniscus fixation. A cannula is then placed in the medial portal and the shuttle sutures are brought out through it to avoid soft tissue bridges. The cannula is then removed to allow easy graft passage.

The meniscal allograft is then inserted and fixated: Start with the posterior shuttle suture, and then shuttle both anterior and posterior soft tissue fixations. Be careful to shuttle these to the correct anteroposterior location. Pen markings on the sutures can help with differentiating the locations. Afterward, the allograft is inserted into the joint with the help of a grasper to avoid tearing out the sutures. During this, look at your allograft markings to confirm proper graft orientation. After the allograft is roughly inserted, shuttle the anterior suspensory button. Finetune the meniscus allograft position by pulling carefully on the anterior and posterior meniscus fixation sutures, to insert the bone plugs into their intended sockets. The posterior bone block is inserted fully into its bone tunnel first, and rigidly fixated with a 4.75 mm fully threaded knotless anchor on the anterior tibia. Then, the anterior bone block is inserted into its bone tunnel and provisionally fixated with the button of the suspensory fixation system. Only provisional fixation is achieved, so we have the possibility to later sink the bone plug further into the deeper bone tunnel to compensate for size mismatch. Next, fixate the body of the meniscus allograft using a standard inside-out technique. Then, we fixate the meniscotibial sutures with two 2.4-mm knotless suture anchors. Additional all-inside and outside-in meniscus sutures can be placed from posterior to anterior if necessary. After the soft tissue fixation, probe your meniscus transplant for stability and adjust tension if necessary with tightening on the suspensory fixation system to its final fixation tension. Finally, irrigate the joint, suction any loose debris, and drain excess fluid. Close your portal sites and incision and apply sterile dressing, ace wrap, and a hinged brace.

For postoperative treatment, the patient is allowed to flat foot weight bear at a maximum of 10% body weight with crutches. At 6 weeks, the patient can begin weightbearing as tolerated. A hinged knee brace is worn for 6 weeks and is initially locked in full extension for 2 weeks.

Passive range of motion begins at 2 weeks and active range of motion at 4 weeks postoperatively. The patients all begin physiotherapy at 2 weeks. The goal is for most patients to regain activities of daily life with low-impact activities. But in active individuals, we allow return to sport at 12 months postoperatively after a gradual progression through a functionally based return to sport protocol. Stone and colleagues ⁸ showed that 73.5% of meniscus-transplanted patients were able to participate in sporting activities postoperatively, supporting that this is also a valuable procedure for active individuals.

Some final comments are as follows: Correctly indicating patients and meniscus size estimation is the first critical step in meniscus transplantation. Before surgery, ensure that alignment, stability, and other comorbidities have been assessed and addressed to optimize the environment of the compartment and unload your graft as much as possible. A major pitfall during surgery is malorientation of the graft. To avoid this, mark the graft and maintain good visualization. In addition, a mis-sized graft can be catastrophic. We drill extra depth into our anterior socket and use a tightrope to allow for selective tensioning on the anterior limb to compensate for possible graft size mismatch.

In summary, the bone plug technique demonstrated here is a hybrid approach combining soft tissue and bone fixation techniques. It provides synergistic advantages with good osseous integration and is minimally invasive through arthroscopy without arthrotomy. In our experience, this approach elegantly eases the complexity of this demanding surgery while yielding excellent results for patients.