“Too much of a good thing can be taxing.”—Mae West
It is well known that an insufficiency of meniscal tissue predisposes to arthritic changes of the knee1. Meniscal resection in adolescents has been reported to cause three times as many radiographic changes that are consistent with osteoarthritis after thirty years as compared with the findings in the contralateral, unaffected knee2. However, it is questionable whether meniscal injury in adolescent or younger patients truly poses the same treatment dilemma as it does when found in middle-aged patients.
An appreciation of the essential role that the meniscus plays in prolonging the longevity of the knee has persuaded surgeons to preserve this important tissue, insofar as possible, rather than to resect it. As such, meniscal transplantation has gradually evolved to become a standard procedure for the treatment of the meniscus-deficient knee, although it is seldom a reliable solution for middle-aged patients. The artificial meniscus has been suggested as a viable alternative. However, unconvincing long-term data and restrictive inclusion criteria make this procedure unfeasible for the majority of patients requiring additional meniscal tissue. So, why is it that too much of a good thing can actually be a bad thing?
The discoid meniscus is essentially a vestigial soft-tissue interposition graft. Its position, between the articulation of the femoral condyle and the tibial plateau, renders it susceptible to injury. In 1979, Watanabe et al., in the Atlas of Arthroscopy, classified the lateral discoid meniscus on the basis of the degree of coverage of the lateral tibial plateau and the presence or absence of the normal posterior meniscotibial ligament3. Employing this classification, Aichroth et al. recommended that patients with a Wrisberg-ligament-type discoid meniscus should undergo a total meniscectomy because of the absence of a stabilizing posterior meniscal ligament attachment4; partial meniscectomy was recommended for complete and incomplete discoid menisci. Interestingly, the authors reported that, after a total meniscectomy, a “pseudomeniscus” was formed in a number of cases and stated that “the pliability of immature tissue may allow adaptation of the knee to the stresses of activity.” Kim et al., in their analysis of the long-term prognosis following the arthroscopic treatment of lateral discoid meniscus tears, determined that clinical and radiographic outcomes were related to the volume of meniscus removed, with less resection being associated with improved results5.
Although discoid lateral meniscus is commonly thought to produce symptoms at an early age, some patients are not symptomatic until middle age. The current study by Kim et al. explored the long-term effects a torn discoid meniscus in the middle-aged patient. The study revealed that the torn lateral discoid meniscus contributed to the development of varus knee malalignment and arthritic change.
It has been well documented that the discoid lateral meniscus occurs more frequently in the Asian population6. Therefore, clinical follow-up from this region, as provided in the current study, offers a valuable insight into the natural history of this condition. It should also be considered that tears of a discoid meniscus are different from other meniscal injuries as they typically occur as a result of minor trauma and are not necessarily related to sporting activities or heavy labor. For that reason, patients with a discoid meniscus are unable to protect their knees to avoid rupture. The real question is whether, as knee surgeons, we should intervene early to reshape this oversized meniscus (which admittedly is more prone to rupture anyway) or just leave it alone, let nature take its course, and deal with it later? Or are we damned if we do and damned if we don’t?
The current study goes some way to answering this question. The comparison between the control group of seventy-four patients with a torn “normal” lateral meniscus and the study group of eighty-four patients with a torn discoid lateral meniscus suggested that it is preferable to have a torn normally shaped lateral meniscus in middle age. However, who is to know whether reshaping a discoid lateral meniscus in early life ever creates a “normal” lateral meniscus that possibly could be torn in later life? Nonetheless, the current study has a number of strengths, including the large number of patients with the condition in addition to the inclusion of a control group; the use of radiographic measurement evaluations of osteoarthritis, with a relatively high correlation coefficient for Kellgren-Lawrence grading; and the use of a knee score to evaluate knee function. Furthermore, the study was performed in a region in which this specific knee abnormality is commonly seen and treated and is not a rare occasional finding as it is in many areas. Admittedly, a weakness of the study is the retrospective design; however, given the frequency of condition and the long-term follow-up reported, it would have been extremely difficult to gather these data prospectively. In addition, all procedures were performed by a single surgeon over the course of a career, which offers a consistency of treatment. The study expands our current knowledge and highlights the role of the discoid lateral meniscus as a vestigial nuisance and troublemaker in the knee. It is important that this study is followed by further prospective studies, perhaps in a multicenter registry, to include younger patients to further elucidate the long-term effect of modern treatment methods.