The most important findings of the present study were that an isolated meniscal tear deteriorated from the injury to surgery in 48.3% (28/58) of patients ≥ 40 years old, and the duration from injury to MRI (OR, 1.031, p < 0.001) and that from MRI to surgery (OR, 1.024, p < 0.001) were independent predictors of worsening of an isolated meniscal tear at the time of surgery.
Many previous studies have demonstrated an increased incidence of meniscal tears with delayed ACLR in pediatric and adult patients [5-9, 27, 29, 30]. Recurrent episodes of instability in the ACL-deficient knee could cause displacement or enlargement of the already-torn meniscus [31]. However, in the present study the deterioration of the meniscal tear was confirmed in nearly one-third of the patients with ACL-intact knees. Many authors have demonstrated the role of the meniscus, especially the medial meniscus, as an important restraint for anterior tibial translation in the ACL-deficient knee [32, 33]. However, the influence of isolated meniscal tear on knee stability still remains controversial, because few studies have investigated this issue. It was reported that a meniscal tear developed during screw-home mechanism (0-30° flexion) and ascent from a squatting position (120-60° flexion) [34]. Kedgley et al. showed that the stress distribution on the meniscal tear surface under weight-bearing differed depending on the tear pattern and tear location, according to a finite element analysis [35]. They showed that differences in the stresses across the tear surfaces were greater for the LM than for the MM in longitudinal tear samples. In addition, they found that only the posterior segment of the LM was compressed throughout the range of knee flexion (0-30°). In the present study, there was not significant difference in the rate of worsening of the tear of the MM or LM between the Group A and Group B (p = 0.22). The deterioration of the meniscal tear in our study was assessed using the grading system reported by Guenther et al. [27]. This grading method did not consider the morphology of the meniscal tear. Furthermore, the majority of tear locations in this study population were in the middle to posterior segments of the meniscus. Therefore, the influence of the morphology and/or location of the tear on the development of isolated meniscal tear was not evaluated in this study. However, the present study was the first, to the best of our knowledge, to evaluate the development of an isolated meniscal tear from injury to surgery in the clinical setting, demonstrating the worsening of the tear in a half of patients ≥ 40 years old. It was speculated that activities under weight bearing between the injury and surgery might cause the enlargement of the torn meniscus or the development of a new meniscal tear, suggesting that patients with an isolated meniscal tear may benefit from early surgical treatment if indicated for the surgery in older patients. Cannon et al. reported a superior success rate in patients who underwent meniscal repair acutely (within 2 weeks from the onset) in comparison to those who received it chronically (88% vs. 79%) [19]. Noyes et al. found better results in the acutely repaired meniscal tear group (within 10 weeks from the injury) than in the chronically repaired group (success rate: 90% vs. 85%) [21]. Tengrootenhuysen et al. also reported better results in the acutely treated group (within 6 weeks of injury) compared with the chronically treated group (success rate, 83% vs. 52%) [36]. However, why the early surgical group had better clinical results than the delayed surgical group remains unclear. The worsening of the isolated meniscal tear before surgery may be a factor associated with worse clinical outcomes in the delayed surgical group. Future studies are needed to clarify whether or not the development of a meniscal tear in the ligament-intact knee affects the surgical results.
In the treatment for an isolated meniscal tear, conservative or surgical treatment is selected depending on the clinical setting. Many factors, such as tear stability, length, morphology, segment and vascularity were reported to be considered for the suitability of conservative treatment [37]. If conservative treatments fail, preservation of the meniscus, by meniscal repair or left in situ, is recommended as the clinical and radiological outcomes are worse after partial meniscectomy [10, 11, 38]. Based on the 2019 European Society for Sports Traumatology, Knee Surgery and Arthroscopy (ESSKA) meniscus consensus, preservation of the meniscus should be the first line of treatment whenever possible, regardless of the age, BMI, tear size, or tear location [38]. Several authors demonstrated favorable clinical results of meniscal repair performed in patients who were 40 years and older [16, 17, 21]. However, patient’s age and radiographic findings (KL grade) could become a bias to clinicians when evaluating the cause of knee pain, which may result in a delayed decision to perform MRI to evaluate meniscal tears in middle-aged or elderly patients with radiographically OA knee. However, Englund et al. reported that meniscal tears on knee MRI were detected in 35% of persons > 50 years old, and two-thirds of those tears were asymptomatic [39]. Therefore, it is not appropriate to make a diagnosis of a meniscal tear in aged patients using only MRI findings [24, 25]. All patients in the present study had a history of the sudden onset of knee pain, and individuals whose onset of meniscal tear could not be identified were not included in order to exclude cases of incidental meniscal tears detected on MRI. With increased age, the vascular supply to the meniscus is decreased [40]. Furthermore, the meniscus of patients with OA knee is more degenerative and sensitive to minor injury than in patients without OA knee, implying more easily worsening of the tear after an injury in OA knee patients. In order to prevent the development of meniscal tear after the injury, it is recommended to consider performing MRI at an early stage in middle-aged or elderly patients suspected of having a traumatic meniscal tear. This will decrease the rate of worsening of the meniscal tear, which may lead to better clinical results after meniscal repair in such populations. The avoidance of preoperative deterioration of the meniscal tear may result in performing meniscal repair rather than meniscectomy. However, the purpose of the present study was to evaluate whether or not an isolated meniscal tear deteriorates before surgery, and it was beyond the scope of this study to assess the differences in surgical outcomes or procedures between subjects with and without worsening of the meniscal tear at surgery. Further prospective studies will be required to investigate the influence of preoperative deterioration of the meniscal tear on surgical procedures and surgical results.
The current study has several limitations. First, patients who did not undergo surgery were not evaluated in this study. Therefore, the presence or absence of worsening of an isolated meniscal tear in patients treated conservatively could not be described. Second, MRI is the most commonly performed diagnostic imaging modality in the diagnosis of meniscal tear [41]. However, the sensitivity and specificity of MRI for medial meniscal tear are 89% (95% CI, 83%-94%) and 88% (95% CI, 82%-93%), respectively, and those for the lateral meniscal are 78% (95% CI, 66%-87%) and 95% (95% CI, 91%-97%), respectively [42]. Therefore, the accuracy of the evaluation of meniscal tear by MRI could affect the results of the present study. Third, as mentioned in the discussion, the grading system of the meniscal tear used in this study was unable to evaluate the morphology of the tear. Furthermore, the length of the meniscal tear was not evaluated using a probe at surgery. Therefore, the detailed measurement of the tear length was not performed. Fourth, due to the retrospective study design, the patient activities from the injury to surgery were not completely evaluated. However, all subjects had knee pain that limited their preoperative activity level, therefore the activity level was not high. Finally, young patients and patients with severe OA-knee (KL 3 or KL 4) were not identified in the study population. Therefore, preoperative worsening of meniscal tears in these cohorts was not evaluated.