The Journal of Bone and Joint Surgery

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Commentary & Perspective

Commentary & Perspective on
"Meniscal Transplantation in Symptomatic Patients Less Than Fifty Years Old"
by Frank R. Noyes, MD, et al.

Commentary & Perspective by
Scott A. Rodeo, MD*,
Sports Medicine and Shoulder Service, The Hospital for Special Surgery, New York, NY

Meniscal transplantation is currently being performed in some patients who have undergone total meniscectomy and who have symptoms in the involved compartment of the knee. The primary goal of this procedure is to relieve symptoms (typically, pain and swelling). A secondary goal is to prevent or forestall progressive degenerative changes that occur following meniscectomy. Noyes et al. have carefully evaluated forty meniscal allograft transplants in thirty-eight such patients and have reported significant improvements in knee symptoms (p < 0.0001), findings that support the efficacy of this procedure in relieving compartment pain in meniscus-deficient knees. This has been my experience with this procedure as well. Noyes et al. make the important point that the results of meniscal transplantation are directly related to the degree of associated arthrosis of the knee.

It has become clear from this and other studies that meniscal transplantation should not be performed in knees with advanced degenerative changes. Specifically, the presence of large areas of exposed subchondral bone and flattening of the femoral condyle are associated with high failure rates with meniscal transplantation. Despite the exclusion of patients with advanced degenerative changes, Noyes et al. still reported a 28% failure rate, indicating that this procedure, although beneficial, is not a panacea. Patients should be informed of these substantial failure rates and of the possibility of requiring additional surgery in the future.

Noyes et al. evaluated their transplants objectively with the use of magnetic resonance imaging in twenty-nine patients and arthroscopy in thirteen patients. I believe that such direct evaluation of the transplant is an important step in the critical assessment of the outcome of this procedure for two principal reasons: 1) a meniscal transplant may have failed but may be "clinically silent" (this has been well-established in follow-up evaluations of other reconstructive procedures such as meniscal repair and rotator cuff repair); and 2) other procedures, such as ligament reconstruction and osteochondral autograft transfer, are often performed concomitantly, making it difficult to determine if the clinical improvement is the result of the meniscal transplant or the associated procedure. Magnetic resonance imaging is currently the best modality for postoperative evaluation of a meniscal transplant. With appropriate pulse sequence modification to magnetic resonance imaging, metallic artifact from the surgical procedure can be minimized and the meniscus, hyaline cartilage, and subchondral bone can be carefully evaluated.

Noyes and associates found that most of the transplants had abnormally increased signal intensity on follow-up magnetic resonance images. These findings provide insight into the biologic changes that occur in the transplant. The authors believed that the signal intensity changes reflected the remodeling process that was occurring as the native collagen architecture of the meniscal transplant was replaced with newly synthesized, poorly organized collagen. I believe that these changes reflect the differences in water mobility as a function of altered structure (collagen-fiber architecture) and composition (proteoglycan and water content) of the tissue that occurs not only as a result of remodeling but also as a consequence of degenerative changes in the meniscus and the inability of the tissue to repair microscopic damage. The cells that repopulate the meniscal transplant do not assume a normal meniscal-cell phenotype and likely do not synthesize and maintain the appropriate matrix molecules.

When confronted with a full-thickness chondral defect (a relative contraindication to meniscal transplantation), should a surgeon consider performing a cartilage resurfacing procedure in conjunction with meniscal transplantation? Currently, it remains unresolved whether a concomitant cartilage resurfacing procedure will "convert" an otherwise unsuitable knee into a suitable candidate for meniscal transplant. Another unresolved question is whether corrective osteotomy will make the "relieved" compartment suitable for meniscal transplantation. It is not known how osteotomy affects load transmission in flexion versus extension. The meniscus transmits greater loads in the flexed knee, whereas osteotomy is performed with the leg in extension. Additional studies are required to examine this important question.

Another important question pertains to the proper timing of performing meniscal transplantation in an asymptomatic knee that has undergone a total or a subtotal meniscectomy. Noyes et al. state that meniscal transplantation "should be performed earlier than was typically done in the patients in this study." Because the results of this procedure appear to be the best in knees with the least degenerative changes, perhaps meniscal transplantation should be performed immediately after meniscectomy, even in the absence of symptoms. At this time, however, we do not have evidence of the long-term chondroprotective effect of meniscal transplantation, and this technically complex procedure is associated with risks (such as transmission of disease) that are inherent to human allograft tissue. Noyes et al. recommend that meniscal transplantation should be performed in the asymptomatic knee if degeneration of the articular cartilage has occurred, but not if the knee is asymptomatic and there is no degeneration of the articular cartilage. I would agree with this recommendation. I recommend a careful follow-up, including a clinical examination and magnetic resonance imaging, of asymptomatic patients who have undergone total or subtotal meniscectomy. In my opinion, meniscal transplantation should be considered as soon as the articular cartilage begins to undergo degenerative change or when recurrent effusions develop, as long as other indications are appropriate. Newer imaging techniques that detect the early matrix changes that occur in cartilage before the loss of morphology will likely prove efficacious in guiding the optimal timing of meniscal transplantation.

In summary, this paper illustrates the efficacy of meniscal transplantation for short-term relief of symptoms. These results also point out the value of direct, objective evaluation of the transplanted tissue with the use of either arthroscopy or magnetic resonance imaging, rather than the sole reliance on subjective questionnaires. Lastly, it is clear that continued follow-up is necessary to determine if a meniscal transplant can provide long-term chondroprotection.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.