Meniscal allograft transplantation: a second look

Issue: August 2003

This is the second interview in Orthopedics Today on the subject of meniscal allograft transplantation (MAT). This procedure is done by a relatively limited number of orthopedists and not considered by many. Because we are starting to have intermediate-term results presented and reported, I felt that I and our readers would benefit from concise clinical questions related to the experience of two respected physicians working in this area.

As medical editor, I selected to interview Dr. Marlowe Goble and Dr. Frank Noyes because they have had an ongoing interest and experience with MATs. I have been impressed with their patient evaluation and follow-up. Dr. Goble’s interview, “Meniscal allograft transplantation: when and how to proceed,” appeared in the July issue. My interview with Dr. Noyes is printed below.

— Douglas W. Jackson, MD
Chief Medical Editor

Douglas W. Jackson, MD: What special arthroscopic and surgical principles and techniques are required for successful meniscus transplantation?

Frank Noyes, MD [photo]
Frank Noyes, MD
Professor, Department of Orthopaedic Surgery, University of Cincinnati
Professor, Noyes Tissue Engineering and Biomechanics Laboratory, Department of Biomedical Engineering, University of Cincinnati
Chairman and Medical Director, Cincinnati Sportsmedicine and Orthopaedic Center

Frank Noyes, MD: The lateral meniscus, with the anterior and posterior horns attached to a central bone slot, provides the most ideal transplant. The normal physiological hoop stress is maintained because the attachment sites and circumference tension relations are not disturbed. Careful sizing at surgery is necessary to locate the central bone slot in the host in the correct coronal distance (lateral to medial) so that the meniscus body is adjacent to the peripheral edge of the tibial plateau and does not overhang at the tibial margin. The common mistake is not to adequately place the anterior horn attachment far enough medially to establish the correct weight-bearing position of the anterior horn.

The medial meniscus transplant has separate anterior and posterior bone attachments that must be securely placed at anatomic attachment sites to maintain the desired position in the knee joint and provide circumferential tension in the transplant.

The technique for implantation is much more difficult than the lateral meniscus. The bone plugs are carefully fashioned to be 8 mm in diameter and 12 mm to 14 mm in length, with two #2 nonabsorbable sutures placed through the center of the bone plug, then through the meniscus and passed again retrograde through the bone plug. Two additional sutures are placed into the meniscus adjacent to the bone attachment providing a total of four sutures to maintain the bone plug within the desired tibial tunnel. It is technically difficult to pass the posterior bone plug and a limited medial femoral notchplasty is necessary.

Jackson: Dr. Goble suggested an osteotomy of the proximal insertion of the MCL in real tight and/or knees that are difficult. What is your preference in tight knees?

Noyes: In very tight knees with limited tibiofemoral separation, a partial detachment of the MCL distally at the tibia will allow a few extra millimeters of joint opening. The MCL distal tibial attachment is fixated with bone anchor sutures and quick healing is expected. Due to the difficulties of the posterior bone plug passage, modifications of either using a smaller diameter bone plug or not using a bone attachment are not recommended as they risk inadequate restoration of the posterior meniscus attachment.

Jackson: Dr. Noyes, for those starting or considering doing these procedures, what do you suggest?

Noyes: Special attention should be paid to sizing and fitting the transplant into place. This requires meticulous suturing routines at the time of an arthroscopic-assisted meniscus transplant to seat and fixate the transplant in the most ideal position to allow for maximal transmission of weight-bearing forces. We consider cadaver practice mandatory before actual patient surgical cases.

Jackson: What special sizing routines do you employ at the time of meniscus transplantation?

Noyes: For both medial and lateral transplants, the sizing by radiographic techniques is only approximate, and the positioning of the implant on the respective tibial surface in the coronal and sagittal planes is critical for proper meniscus function. A paper cut-out and paper ruler can be fit into the knee joint to make appropriate marks based on the size of the meniscus transplant and respective tibial surface. After the initial seating of the transplant, knee flexion and extension, and internal and external tibial rotation with observation of the transplant position confirms placement. Careful placement of multiple vertical divergent sutures (2-0 Ethibond) at the outer one-third, avoiding the relatively avascular central portion, is performed with sutures placed to tension the transplant, taking out any redundancy, tying each suture sequentially to observe the position of the transplant in the joint. Meniscus fixators are not used and should be avoided.

One problem of concern is the anatomic variation that is possible in meniscus transplants. The medial meniscus may have a deficient and very narrow anterior horn region contraindicating its implantation. The lateral meniscus may have a narrow (less than 10 mm) anterior and middle body width, contraindicating its implantation in patients who are not small in stature. The transplant should be viewed and prepared just prior to the surgical procedure to make sure that the transplant is ideal. Unfortunately, tissues banks do not take pictures of the meniscus for exact viewing and measurements, and thus the surgeon may not know the individual characteristics of the meniscus that is supplied.

Jackson: What are the time considerations for a meniscus transplantation after prior meniscectomy in a young patient?

Noyes: After total meniscectomy, there may occur progressive loss of the joint space with arthroscopic evidence of early joint deterioration and fragmentation of the articular cartilage without major joint symptoms of pain or swelling. In this situation, particularly in young active patients, it is justified to proceed with early meniscus transplantation and not to wait for advanced symptoms.

In patients who are many years post-meniscectomy, the arthrosis frequently has progressed to the point where a meniscus transplant would not relieve symptoms and in fact would be displaced outside the tibiofemoral compartment due to abnormal femoral flattening and tibial concavity. In our first prospective study on meniscus transplants, we included younger patients with advanced joint arthrosis hoping to avoid knee replacements. We rated patients into mild, moderate and advanced arthrosis based on radiographic and MRI appearance of the joint. The advanced arthrosis group still had areas of articular cartilage remaining, with no more that 15 mm of bone exposed on the tibial and femoral surfaces. However, there was increased joint concavity and peripheral spurring. The failure rate in the three groups was mild arthrosis, 28%; moderate arthrosis, 57%; and advanced arthrosis, 80%. We therefore limit our candidates to those patients who have only mild or moderate joint arthrosis.

drawing
Final fixation of the anterior and posterior bone attachments of a medial meniscus allograft.

COURTESY OF CRYOLIFE

drawing
Lateral meniscus allograft sutured and in anatomically correct position.

Jackson: What type of transplant processing do you use for your MATs?

Noyes: In our initial prospective study of 96 meniscus transplants implanted from 1988 to 1992 and followed for a mean of 30 months (range, 22 to 58 months), graft processing involved low-dose irradiation for purposes of bacterial sterilization. At present, we use both Cryolife and fresh-frozen transplants due to the limited availability of suitable transplants and lack of scientific information that would support one type of processing over another type. This is an important area for future research. All transplants are from AATB-certified and FDA-inspected tissue banks.

Jackson: Dr. Noyes, you recently presented at the 2003 AOSSM Specialty Day Meeting the findings of your prospective clinical study on 40 consecutive meniscus allografts in 38 patients followed an average of 3.3 years postoperatively. How are all of the data from your study put together to provide the big picture for our readers?

Noyes: We developed a classification system to describe meniscal allograft characteristics based on MRI, arthroscopic, clinical, and subjective findings. The overall classification of the 40 meniscus allografts revealed 16 (40%) with normal characteristics, 14 (35%) with altered characteristics, and 10 (25%) failed. Of the 14 allografts with altered characteristics, seven had minor displacement noted on MRI, four had a return of mild tibiofemoral compartment pain, two had both displacement and pain, and one had partial (less than one-third) allograft removal.

In the current study, 26 allografts studied with MRI showed a loss of the normal low signal intensity and appearance of increased signal intensity within the meniscus, indicative of a remodeling process. A more ideal appearance of the meniscus would be to have less signal intensity changes, indicative of retention of the native transplanted collagen and matrix structure.

We recognize that the long-term function of meniscal transplants is still unknown. Meniscal allografts that heal early and function postoperatively may degenerate or tear many months later due to incomplete remodeling and an altered collagen and matrix structure. We hypothesize that all meniscus allografts will undergo a deleterious remodeling process at different time periods post-implantation, resulting in altered mechanical properties and potential for tearing, fragmentation, and degeneration under joint loading conditions. We have concerns regarding the long-term survival rates of meniscus transplants, believing future replacement or other procedures will be required. The transplant undergoes limited remodeling which results in alterations in meniscus collagen fiber micro-architecture, matrix, and cellular function required for load-sharing and long-term survival. Patients indicated for this procedure are those in whom there are few other options for treatment after meniscectomy, and they should be advised that the procedure is not curative in the long term and additional surgery may be required.

Jackson: What are the important research areas to improve meniscal transplantation success?

Noyes: These include issues related to transplant remodeling; collagen fiber restoration of micro-architecture to resist tensile, compressive and shear forces; implant collagen matrix changes with altered material and structural properties; cellular repopulation and function in maintaining implant homeostasis; role of fresh transplants with viable cells; and role of meniscus scaffolds and tissue engineering.