The deleterious effect of a medial meniscal tear on cartilage thickness loss was not uniform across the medial compartment. Meniscal body tear was associated with cartilage loss in external tibial and femoral subregions and in adjacent central and anterior tibial subregions. Meniscal posterior horn tear was associated specifically with cartilage loss in the posterior tibial and no other subregion. These relationships were independent of age, gender, BMI, and tears in the other two meniscal segments and persisted in the tibial subregions after further adjustment for meniscal extrusion. In the lateral compartment, meniscal body tear was associated with cartilage loss in the external and adjacent central, anterior, and posterior tibial subregions and meniscal posterior horn tear with cartilage loss in the external tibial subregion. These lateral compartment relationships were attenuated by further adjustment for meniscal extrusion. Cartilage loss in the internal subregions, which are not covered by the meniscus, was not associated with any meniscal segment tear. These findings demonstrate the significance of meniscal damage for subsequent subregional cartilage thickness loss and suggest that at least some of the meniscal tear effect is experienced locally.
Our findings are in keeping with previous reports in which meniscal damage was associated with knee OA progression at the larger joint surface (15
) and some early subregional findings. Lynch et al found that, in knees with or at higher risk of developing knee OA, medial cartilage score worsening associated with medial meniscal tear appeared to be more frequent in the central subregions (21
). In the BOKS study, Niu et al used an M:N matched case-control design including knees with 6 tibial subregions eligible for cartilage score worsening and with worsening in one subregion at follow-up (20
). In the 37 knees examined, compared to tibial subregions without meniscal damage in identical locations, the OR of cartilage worsening in sites with such damage was significantly increased.
In contrast, we examined quantitative cartilage thickness loss within tibial and femoral subregions and were thereby not vulnerable to potential bias associated with grading menisci and cartilage subregions together in the same session. Crema et al also measured cartilage thickness, but studied women with or without knee OA (22
). As their goals and analytic methods differed from ours, it is difficult to derive answers to the questions we posed directly from their report. In contrast to all of these previous studies, we adjusted not only for extrusion, but addressed potential confounding from tears in the other two meniscal segments, a key step in the examination of a local effect.
In our study, isolated meniscal tear occurred most frequently in the medial meniscal posterior horn, in agreement with previous reports (29
). The reduced mobility from soft tissue attachments and greatest load transmitted through this region during knee flexion makes this meniscal segment particularly vulnerable (30
). The most common medial pattern
, however, was concurrent body and posterior horn tear. The most common lateral meniscal tear pattern (involving all three segments) may relate to its greater mobility and more even between-segment sharing of load (31
The finding that baseline medial meniscal body tear had the strongest association with subsequent cartilage loss in the external tibial subregion where the body segment overlies supports some local impact of meniscal damage on cartilage health. Baseline posterior horn tear had an isolated effect in the posterior tibial subregion. The small number of knees with anterior horn tear may have limited our ability to detect relationships involving tears in this segment. The relationship between body tear and anterior tibial cartilage loss may relate to the proximity of anterior and external subregions ().
The effects of baseline lateral meniscal body tear were less confined to the anatomical mapping proposed in our hypotheses. During knee flexion, the lateral meniscus experiences nearly twice the magnitude of antero-posterior translation as the medial meniscus (32
). With this movement, the lateral meniscal body segment may overlie the anterior, external, central, and posterior tibial cartilage subregions and the posterior horn may overlie the posterior and external tibial subregions. The associations between lateral meniscal tear and cartilage loss were attenuated by adjustment for meniscal extrusion. In theory, extrusion of the more mobile lateral meniscus could itself contribute to a more diffuse tear pattern, and less matching between tear site and subregion of cartilage loss.
It is important to acknowledge that some knees without longitudinal data came from persons whose BMI was greater than the persons we analyzed; it is uncertain how this may have affected results. While the WORMS system is commonly applied to assess meniscal tears in knee OA, it does not include tear type or location in relation to vascular supply. Further, efforts to match meniscal segment to cartilage subregion are inherently imperfect: optimal meniscal grading and cartilage segmentation require different sets of MR images; knees vary in meniscal and articular cartilage shape; and the match may be altered by meniscal movement and/or extrusion during activity.
In summary, the detrimental effect of meniscal tears is not spatially uniform across the tibial and femoral cartilage surfaces, and at least some of it is experienced locally. These results support a focal protective role of meniscal tissue on articular cartilage integrity in knee OA.