MRI is considered the examination modality of choice in the assessment of MMPRT through several characteristic radiological features .
To our knowledge, this is the first study to have developed a new MRI technique with varus stress position to address the challenges encountered by previous studies with regard to the measurement of the accurate degree of true MME in MMPRT in MRI scans at the supine position. This study included 70 patients who presented with an episode of medial or posteromedial knee pain with or without popping sensation.
According to the demographic data, the mean age of patients was 49.09 ± 8.50 years, with more predominance within female patients, and the ratio of women to men with MMPRT was 4:1. The mean BMI was 31.67 ± 4.95 kg/m2, and 60% of patients were overweight, and the majority of the patients (55.7%) were in the chronic stage. This is consistent with the findings of Kim et al. , who found that MMPRT was more often observed in a chronic stage, especially in middle-aged or elderly female patients (> 40 years of age) with mild symptoms, degenerative changes, and commonly no clear history of trauma.
Regarding the risk factors of MMPRT, Hwang et al.  found that many factors may be related to MMPRTs, such as high BMI of > 30 kg/m2, increased age, female gender, and varus malalignment. The results of this study were consistent with this finding, as it was found about 90% of cases had a history of osteoarthritis (OA), 54.3% were elder than 50 years, the majority of patients (80%) were female gender, and 58.6% were obese.
Based on the patients’ clinical presentation, approximately 65.7% of the studied patients presented with posterior knee pain associated with popping sensation, which was a good indicator in the diagnosis. This is in line with the study by LaPrade et al. ] and Lee et al.  which revealed that the remember of time of painful popping sounds is so important to identify the duration of onset and treatment plan of MMPRT. On the other hand, it has not been investigated whether a single event of painful popping is a typical clinical symptom of other meniscal tears.
The diagnosis of meniscal root tears is considerably difficult, with a reported detection rate of 73% to 89%, even if it is based on characteristic MRI findings [2, 21]. The current results indicated that approximately 90.0% of the studied patients had positive MRI signs of MMPRT.
The evaluation of MRI and arthroscopic procedures is essential to reach a proper definite MMPRT diagnosis. In this study, MRI showed 95.24% sensitivity, 80.0% specificity, 95.2% positive predictive value, 80.0%negative predictive value, and 92.31% accuracy in diagnosing MMPRT. This is consistent with a systematic review published by Oei et al. , who concluded that MRI demonstrates sensitivity and specificity rates of 93% and 88%, respectively, considering arthroscopy being the gold standard reference in the diagnosis of a medial meniscal tear.
In the present study, several characteristic MR findings have indicated the presence of MMPRT. It was reported that the highest detection rate of approximately 97.1% was observed in the MME sign. However, Choi et al.  reported a lower detection rate of MRI-based MME (≥ 3 mm) in MMPRT patients (83.3%). The higher detection rate in the current study was attributed to the varus stress position. Overall, 88.6% of the studied patients had the cleft sign, 82.9% had the giraffe neck sign, 87.1% had ghost sign, and 65.7% had radial tear sign. The results of this study are consistent with those of another similar study conducted by Furumatsu et al.  who illustrated that the cleft, ghost, giraffe neck, and radial tear signs were detected in 81.7%, 80%, 81.7%, and 69.6% of the MMPRT MRI images, respectively. Although the medial extrusion sign was most commonly observed in MMPRT (90%), it was found to be an indirect sign and not specific for meniscal root tears. Furumatsu et al.  detected that the coexistence of any two characteristic MRI signs, except for the medial extrusion sign, was observed in 91.7% of MMPRT patients. This result is consistent with that of the present study, which indicated a high detection rate of approximately 90.0%.
Although the presence of extruded meniscus of more than 3 mm was considered an indirect sign in meniscal root tears as reported by Bhatia et al. , it could be utilized as a further guide in MMPRT diagnosis as recommended by Koo et al. .
In the present study, MRI technique with varus stress position was performed on 35 patients. In this new technique, we measured the true MME amount in MMPRT patients as they were exposed to postural load caused by the stress varus position technique that was relatively simulating weight-bearing MRI and standing plain X-ray.
Moreover, it was observed that approximately two-thirds of studied patients (62.9%) had positive MME (MME ≥ 3) at pre-varus assessment, whereas all patients (100.0%) showed positive MME at post-varus assessment, with a statistically significant difference between pre-varus MME (3.75 ± 1.30 mm) and post-varus MME (5.89 ± 1.52 mm). This finding is consistent with that of a study by Lerer et al.  who found meniscus extrusion could be considered a diagnostic sign for MMPRT in MRI. According to the duration of onset or the chronicity of MMPRT, the MME measurements in the present study illustrated that the degree or amount of MME was highest in the chronic cases, followed by the subacute and acute cases, with a statistically significant difference in both the pre and post-stress varus position techniques.
In the comparison between pre- and post-varus stress amount of MME in all three stages of MMPRT, it was found that statistically significant differences were observed between pre- and post-varus MME amount in each stage of chronicity. The findings of Furumatsu et al.  are also consistent with pre-varus stress results of the MME measurement in the current study. One of the positive findings of the present study was mentioned by Chung et al. , who found that decreased MME (3.5 ± 1.4 mm) at 1 year after arthroscopic repairs of MMPRT had more appropriate clinical scores and radiographic features at 5-year follow-up compared with increased MME (5.1 ± 1.4 mm) at 1 year after MMPRT pullout repairs.
Concerning MRI-based associated findings of MMPRT, the current study showed that 30.0% of the studied patients of MMPRT had associated ACL tear, whereas only 2.9% of them had PCL tear, which is consistent with the findings of Lee et al.  and Ra et al. , who stated that acute medial meniscal root tears could occur as a result of multiligamentous injuries in the knee joint, such as ACL and PCL tears.
On the other hand, 54.3% of patients showed positive subchondral bone marrow edema based on current results, which is consistent with the findings of a previous study by Bhatia et al. , who found that ipsilateral tibiofemoral compartment bone marrow edema is more common when MMPRT is present.
Regarding the treatment of MMPRTs, the current results showed that the majority of patients underwent valgus HTO, only 10.0% in the acute stage underwent arthroscopy, 27.1% underwent both valgus HTO and meniscal arthroscopic repair, and 20% underwent conservative therapy. That is why only a small part of the study group had an arthroscopic reference standard. This finding is consistent with that of Chung et al. , who demonstrated that in the case of MMPRT associated with varus misalignment, osteotomy should be performed either alone or with another surgical intervention.
The present study has strength points, including the prospective design, confirmatory arthroscopic reference, and information on the new MRI technique with varus stress position in measuring the true MME amount that could solve the problem related to inadequate extrusion measurement performed via supine non-weight-bearing MRI.
However, this study has several limitations, such as the limited number of cases that are screened via MRI and confirmed arthroscopically because the majority of the cases in the current study were in the chronic stage who underwent either osteotomy or conservative treatment, as well as the unavailability of weight-bearing upright MRI to compare it with the results of MME measurements performed using the MRI technique with varus stress.