The influence of the steep medial posterior tibial slope on medial meniscus tears in adolescent patients: a retrospective case-control study

Meniscal tears, occurred in adolescent patients, are common injuries concomitant with anterior cruciate ligament (ACL) ruptures during athletic activity. If left untread, meniscal tears are thought to carry potential sequelae, resulting in abnormal stress distribution within the tibiofemoral joint; therefore, accelerating the deterioration of the articular cartilage and early post-traumatic osteoarthritis [1, 2]. Overall, risk factors for meniscal tears are considered to be extrinsic and intrinsic. Extrinsic risk factors for meniscal tears is multifactorial, including neuromuscular forces, injury mechanisms, delay of surgery, untreated ligamentous injuries, and landing biomechanics during physical activity [3‐5], while the intrinsic risk factors, including age, sex, lower limb alignment, high body mass index (BMI), and geometry of the tibial plateau [6‐8]. Identification of these intrinsic anatomical factors, such as posterior tibial slope (PTS), may help orthopedic surgeons better recognize risk factors of meniscal tears in susceptible individuals.

In recent years, several studies have been conducted on the risk factors between the PTS and meniscal injuries in ACL-deficient knees [6, 8‐12]. The bony morphology of the proximal tibia, especially a steep tibial slope, is known to have a negative effect on the biomechanics and kinematics of the knee [13, 14]. Furthermore, increased PTS is associated with the magnitude of the shear force in tibial platform and influences the biomechanics of the tibiofemoral joint, which may increase the risk of meniscal injuries in adults [10]. Actually, medial meniscal tears (MMT) are more frequently occurred due to the role in transmitting shear force with compressive force. Furthermore, medial meniscus also plays an important role in maintenance of knee stability [15‐17]. Until now, however, potential anatomical risk factors for MMT in adolescents remain unclear. As is well known, meniscus is a critical regulator within the tibiofemoral joint with various functions, such as shock absorption, load diffusing, and enhancement of stability [18]. In addition, the medial meniscus is an important component that distributes compressive loading force across the knee and is subjected to anteroposterior shear forces. Walker et al. [19] reported that the medial meniscus delivers the higher percentage of shear force compared to lateral meniscus. Using knee radiographs and magnetic resonance imaging (MRI), Markl et al. [12] showed a statistically significant association between a steep PTS and MMT in adults, regardless of sex. Nevertheless, limitations of these studies are they focused on the relationship between the PTS and meniscal tears in adults. In clinical practice, it is also important for orthopedic surgeons to investigate the association between the PTS and MMT in adolescents.

Therefore, it is necessary to suppose that the morphology of the tibial may act as an important role in MMT because increased PTS would lead to higher shear force in the medial meniscus during compressive loading. To the best of our knowledge, however, there is a paucity of literatures regarding the relationship between the PTS and MMT in adolescents, despite their potential clinical importance. The purpose of this study was (a) to investigate the association between the PTS and MMT, and (b) to determine the optimal cut-off values of PTS for discriminating between the MMT and the control groups. It was hypothesized that an increased PTS may serve as a potential risk factor for MMT in this population.

Twenty-two patients in the isolated MMT group were excluded due to ligamentous injuries, cartilage defects, lateral meniscal tears, and previous trauma or knee surgery. A total of seventy-two patients who met the inclusion and exclusion criteria were enrolled in the final analysis (36 with isolated MMT, and 36 controls). All cases in the MMT group sustained sprots-related meniscal tears. Each group consisted 21 males and 15 females. As shown in Table 1, the ICCs for the MPTS was 0.912 (95% CI, 0.875–0.954) for the intra-observer reliability and 0.894 (95% CI, 0.834–0.937) for the inter-observer reliability, and the ICCs for the LPTS was 0.878 (95% CI, 0.847–0.921) for the intra-observer reliability and 0.851 (95% CI, 0.804–0.913) for the inter-observer reliability, indicating an excellent inter- and intra-reliabilities.

The patients’ demographic characteristics and PTS measurements of the two groups were shown in Table 2. No significant difference was observed between the two groups in terms of age (p = 0.566) and genders (p = 1.000). The MPTS was higher in the knees with isolated MMT than that of the controls (10.7° ± 2.1° vs 8.8° ± 1.7°, p<0.001). However, there was no significant difference regarding the LPTS between the isolated MMT and controls (11.5 ± 3.4 vs 10.9 ± 2.6, p = 0.403). To clarify the exact tear location of the MM, the meniscus was divided into three parts: the anterior horn (AH), the body, and the posterior horn (PH). In our study, the most common tear location of the MM was the posterior horn, followed by the tears involving the body. In addition, tears of the anterior parts of the menisci were seen least frequently. The distribution of meniscal tears in different anatomical location was shown in Fig. 4. According to the ROC analysis, the calculated optimal cut off value of MPTS with an increased risk for isolated MMT was 10.3°, with a sensitivity of 73.3% and specificity of 78.9% (Fig. 5).

The most important finding of the present study was that increased MPTS is associated with an increased risk for isolated MMT, whereas the LPTS appears to have less of an influence. These findings are similar with existing studies involving the adult population [22]. In addition, our results showed that the cut-off values of MPTS discrimination between the groups in adolescent patients was 10.3°, with a sensitivity of 73.3% and a specificity of 78.9%. This association may be originated from the biomechanical change and higher shear force in tibial plateau under the condition of a steep tibial slope. It has been reported that the tibial slope was an anatomical factor which have a great influence on the kinematics of tibiofemoral joint [23]. A large number of biomechanical studies have also shown a liner relationship between steep tibial slope and anterior translation of the tibia during weightbearing activities, which subsequently increased shear forces on ACL and meniscus [14, 24, 25]. Therefore, a steep tibial slope, leading to an increased anterior tibial translation, may predispose adolescent patients to MMT.

Actually, multiple literatures have shown that an association between increased PTS and meniscal tears in adults [11, 22, 26]. Kolbe et al. [11] identified that increased LPTS is a potential risk factor for posterolateral meniscal root tears in ACL-deficient knees. Moreover, Moon et al. [22] demonstrated that patients with medial meniscal posterior horn tears had significantly greater PTS than controls. Alici et al. [26] utilized both knee radiographs and MRI scans to measure PTS values in 212 meniscal tears patients, and they reported that the lateral meniscal tears group had increased LPTS when compared to the control group, whereas there is no association between the increased PTS values and MMT. These abovementioned published results provided some evidences that MMT are associated with increased tibial slope.

Despite the growing interests in PTS and its relationship with meniscal tears in adults [22, 27], this intrinsic anatomic factor remains unclear in adolescent patients. An increased demand to attain athletic activities and peak performance in adolescent patients may result in higher incidence of meniscal tears, especially in patients with increased tibial slope. The current study showed significant difference in MPTS values between the isolated MMT group and control group. Also, these findings were consistent with the results of Moon et al. [22], who demonstrated significant differences in MPTS between medial meniscal posterior horn tears patients and matched controls. Similarly, we assumed that this phenomenon may be partially explained by the function of medial meniscus, sustaining higher shear force and compressive loading forces in the presence of physiologic activities [28]. Therefore, anterior translation of the tibial that originate from a steep tibial slope may have a greater influence on medial meniscus. Of note, the main clinical significance of this study may have profound effects in the establishment of identification risk factors of MMT in a plain radiograph without using MRI.

The optimal cut-off value of MPTS was determined with the ROC curve analysis, which showed that the MPTS greater than 10.3° is associated with an increased risk for isolated MMT in adolescent patients. Recently, Moon et al. [22] identified that increased PTS (≥6.6°) was considered as an anatomical predictor for medial meniscal posterior horn tears with sensitivity of 55.3% and specificity of 75.0%. The reason for this discrepancy may be explained by the difference of patient selection. Dare et al. [29] revealed that PTS was tend to decrease or flatten with age, which may explain that the cut-off PTS values of the study was significantly higher than previously reported in adults. Another reason for this discrepancy may be attributed to the racial differences. Taken together, we considered that the adverse effect by increased tibial slope on MMT should not be overlooked in adolescents.

Several limitations should be noted in the present study. First, it was a retrospective study with the usual limitations and bias inherent to single center. To minimize bias, all observers who measured MPTS and LPTS on radiographs were blinded to the arthroscopic findings of meniscal status. Second, the number of patients enrolled in our study was relatively small and the location of meniscal tears were not evaluated in this study. However, the results of the presents study are meaningful in clinical significance, as the cut-off values of MPTS found in our study may be helpful for surgeons to consider intrinsic anatomical risk factors for MMT, especially with increasing number of meniscal tears in adolescents. Despite these limitations, there were important strengths associated with this study. To our knowledge, this is the first study to investigate the relationship between MPTS and MMT in adolescent patients. Also, these characteristics should be assessed by orthopedic surgeons using plain radiographs when suspect MMT in the adolescent patients.

In conclusion, this study demonstrated that increased MPTS is associated with MMT, and MPTS≥10.3° was identified to be a risk factor for MMT in adolescents. This finding places an emphasis on the identification of risk factors for MMT, that is, if we recognize the steep MPTS in a plain radiograph, we can strongly suspect risk of MMT with using MRI.