Evaluation of the reliability and accuracy of MRI for the diagnosis of meniscal ramp lesions

Abstract

Background

Meniscal ramp lesions are a special type of meniscal injury that affects the periphery of the posterior horn of the medial meniscus and/or its meniscocapsular attachments, strongly associated with anterior cruciate ligament (ACL) tears. Due to their location, these lesions can be missed arthroscopically so it is essential to diagnose them on preoperative magnetic resonance imaging (MRI).

Purpose

To evaluate the accuracy of MRI in detecting meniscal ramp lesions in patients with ACL tears using arthroscopy as the reference standard.

Material and Methods

Two musculoskeletal radiologists, blinded to the surgical findings, retrospectively and independently evaluated 106 knee MRI scans for the presence of meniscal ramp lesions in non-consecutive patients who underwent arthroscopic ACL reconstruction between January 2019 and July 2022 by a single surgeon at one institution. Having arthroscopy as reference, the diagnostic sensitivity and specificity as well as the positive and negative predictive values (PPV/NPV) of the MRI scans were calculated. Cohen's kappa coefficient was used to test inter-observer reliability. A P value <0.05 was considered statistically significant.

Results

In the study group of 106 patients (72 men, 34 women; mean age = 33.84 ±13.12 years), 76 had an arthroscopy-confirmed meniscal ramp lesion, while 30 did not. The sensitivity and specificity of MRI for the detection of meniscal ramp lesion were 88% and 87%, respectively. The PPV and NPV were 94% and 74%, respectively. Inter-rater reliability was excellent (k = 0915).

Conclusion

This study demonstrates that MRI can accurately detect meniscal ramp lesions.

Keywords

Ramp lesion meniscocapsular ligament meniscotibial ligament knee instability magnetic resonance imaging

Introduction

The term meniscal ramp lesion was first used by Strobel in 1988 to describe a special type of meniscal injury involving the peripheral attachment of the posterior horn of the medial meniscus (PHMM) typically associated with an anterior cruciate ligament (ACL) deficiency (1). Today it is known that there are two posterior meniscal attachments merged at a common attachment on the PHMM: the meniscocapsular ligament and the meniscotibial ligament (2) (Fig. 1). Although there is still no clear consensus on its definition, in recent literature, the term ramp lesion includes injuries of any of these two ligaments as well as peripheral longitudinal tears in zone 1 (the red-red zone) of the PHMM (3,–7), because both the PHMM and its meniscoligamentary transition zone are considered to be a functional unit (8) with an important biomechanical involvement of the knee (9,–12). Several studies have shown that these lesions may be responsible for knee instability (2,11,13–), predisposing the knee to meniscal (12) and articular damage (12,14) and ultimately to the failure of the ACL graft (15) if they remain unrepaired during ACL reconstruction.

Fig. 1.

This is an example of the normal anatomy of the ramp zone. A sagittal proton density magnetic resonance image show the normal ligaments that conform the posterior meniscocapsular junction of the posterior horn of the medial meniscus: the meniscocapsular ligament (arrow) and the meniscotibial ligament (curved arrow), extending from the joint capsule (arrowhead) to the posterior horn (*).

Due to the significant role that ramp lesions have in ACL-deficient knee stability, it is important to detect and treat them during arthroscopic ACL repair surgery. However, due to their location, they can be missed arthroscopically when using only anterior standard portals (5,16,17). For this reason, it is essential to identify these lesions on preoperative MRI to aid surgical planning (7,18).

The aim of the present study was to analyze the diagnostic accuracy of MRI in detecting meniscal ramp lesions using arthroscopy as the reference standard. Our hypothesis is that MRI is useful for the diagnosis of these lesions, with sensitivity and specificity values of more than 80% using the criteria we have developed.

Material and Methods

Study population

Patients who underwent arthroscopic ACL reconstruction between January 2019 and July 2022 by a single surgeon (AM) at one institution were retrospectively screened to be included in our study group.

The inclusion criteria were the presence of an arthroscopically proven meniscal ramp lesion and having a preoperative MR study performed within 3 months before surgery, obtaining a total of 85 patients. Patients with previous medial meniscus surgery (n = 2) or extensive tear of the medial meniscus (n = 5), such as a bucket handle tear, were excluded. Poor MRI quality was also an exclusion criterion (n = 2).

There was also a control group, including 30 patients with an ACL tear confirmed arthroscopically without evidence of ramp lesion.

The study protocol was approved by our institutional review board and there was no requirement for informed consent.

MRI protocol

Among the 106 patients, 65% underwent preoperative MRI in our institution while the rest of the patients provided images of the MRI scans performed in other medical centers. At our institution, every MRI scan was performed on a 1.5-T MRI unit (Vantage Elan; Canon Medical Systems SA, Zoetermeer, the Netherlands). Proton density-weighted (PD) fat-suppressed sequences in the three planes of space and PD sequences in the sagittal plane were obtained using a dedicated knee coil with the knee in full extension with these parameters: repetition time (TR)/echo time (TE) = 2710–2900/30–36 ms; section thickness = 3.5 mm; intersection gap = 0.5 mm; matrix size = 512 × 512–640 × 640; and field of view = 16 cm.

All externally conducted studies were also performed on a 1.5-T MRI unit and included the sequences described above.

Image interpretation

Two trained musculoskeletal radiologists with extensive experience in musculoskeletal MRI (PG and SE, with 25 and 9 years, respectively) were blinded to the surgical findings and to the prevalence of meniscal ramp lesions in the study group. They retrospectively and independently evaluated 106 preoperative knee MR studies to assess the presence or absence of meniscal ramp lesions.

The authors considered a meniscal ramp lesion to be any vertical/oblique tear that affects the outer third (zone 1) of the PHMM as well as any tear of the meniscocapsular or meniscotibial ligaments, either mid-substance or in its common meniscal insertion. The radiological signs used to diagnose a ramp lesion were as follows: the presence of a hyperintense vertical or oblique line in zone 1 of the PHMM extending to at least one articular surface in PD fat sat sequences; and/or the presence of a high PD fat-saturated signal in mid-substance or in the meniscus attachments of meniscotibial and/or meniscocapsular ligaments.

In cases where a ramp lesion was diagnosed, radiologists also classified it into seven different types according to the classification proposed by Greif et al. (7), which was based on Thaunat's (6) and was published in 2020. According to Greif, a meniscal ramp lesion type 1 consists of a meniscocapsular ligament tear; type 2 is a partial superior peripheral PHMM tear; type 3A, a partial inferior peripheral PHMM tear; type 3B, a meniscotibial ligament tear; type 4A, a complete peripheral PHMM tear; type 4B, a complete meniscojunction tear; and type 5 is a peripheral PHMM double tear. Fig. 2 shows MR images and graphic illustrations of each type. The radiological signs used for the diagnosis of each of them are as follows:

Type 1: a vertical linear fluid signal in the meniscocapsular ligament;

Type 2: a linear vertical fluid signal reaching the superior articular surface of zone 1 of the PHMM;

Type 3A: a linear vertical oblique fluid intensity signal reaching the inferior articular surface of the PHMM;

Type 3B: disruption of the meniscotibial ligament with high signal;

Type 4A: a linear fluid intensity signal extending from the superior to the inferior articular surface of the PHMM in zone 1;

Type 4B: a linear fluid signal intensity extending from the superior to the inferior articular surface with disruption of the capsular ligaments;

Type 5: two parallel linear fluid intensity signal areas extending from the superior to the inferior articular surface within zone 1 of the PHMM and its meniscocapsular attachments.

Fig. 2.

Greif et al.'s classification of meniscal ramp lesions, represented with sagittal proton density magnetic resonance images and graphic illustrations. Meniscal ramp lesions: (a1, a2) type 1; (b1, b2) type 2; (c1, c2) type 3A; (d1, d2) type 3B; (e1, e2) type 4A; (f1, f2) type 4B; and (g1, g2) type 5.

Image interpretation was performed on a workstation using worklist in random order with anonymized images.

After the first reading and analysis of inter-observer reliability, a second evaluation was carried out for cases upon which the radiologists disagreed and a consensus was reached between the two radiologists when analyzing the MR diagnostic performance.

Arthroscopy

All ACL reconstructions were performed by a single orthopedic surgeon (AM) with more than 25 years of experience in knee surgery. Before starting this study, radiologists reviewed the recent literature on meniscal ramp lesions with him to unify concepts.

During surgery, the patient was positioned supine on the operating table with the knee in 90° of flexion and the standard lateral parapatellar portal was used for viewing. A systematic and complete evaluation was performed through standard anterior portals. To better visualize the posteromedial compartment, a 30° or 70° scope was placed through the intercondylar notch space and the meniscocapsular junction was tested with a probe. In case of high suspicion of injury, a posteromedial portal was created to detect the possible ramp lesion and repair it.

A ramp lesion was defined as a longitudinal tear affecting the peripheral insertions of the PHMM at both the meniscocapsular junction and meniscal zone 1.

Statical analysis

Cohen's kappa (k) coefficient was used to test inter-observer reliability. Kappa values >0.8 were considered excellent, values of 0.6–0.8 were considered good, values of 0.4–0.6 were considered moderate, values of 0.2–0.4 were considered fair, values <0.2 were considered poor.

Having arthroscopy as the reference standard, the diagnostic sensitivity, specificity and positive and negative predictive values (PPV/NPV) of MRI for detecting meniscal ramp lesions were calculated.

A P value <0.05 was considered statistically significant.

Data analysis was performed using SPSS version 26 (IBM Corp., Armonk, NY, USA).

Results

A total of 106 patients (72 men [68%], 34 women [32%]; mean age = 33.84 ± 13.12 years; age range = 12–66 years) were included in the study group. Of these patients, 76 (52 men, 14 women; mean age = 34.32 ± 13.06 years) had an arthroscopy-confirmed meniscal ramp lesion, while 30 did not (22 men, 8 women; mean age = 32.63 ± 13.40 years). The prevalence of each of the types of meniscal ramp lesions is shown in Table 1.

Table 1.

Prevalence of meniscal ramp lesion types found in our sample.

Meniscal ramp lesions	n (%)
1	4 (5.3)
2	0 (0)
3A	32 (42.1)
3B	4 (5.3)
4A	21 (27.6)
4B	13 (17.1)
5	2 (2.6)
Total	76 (100)

In the inter-observer statistical analysis, the agreement between the two radiologists was excellent before the consensus step of the methods. The calculated kappa was 0.915 (>0.8 defined as excellent).

The sensitivity of MRI for the detection of meniscal ramp lesion was 0.88 (range = 0.81–0.95) and the specificity was 0.87 (range = 0.75–0.99). PPV was 0.94 (range = 0.89–1.00) and NPV was 0.74 (range = 0.6–0.89). There were 67 true positives, four false positives, 26 true negatives, and nine false negatives.

Discussion

Our hypothesis has been confirmed: the study demonstrated that MRI is a reliable technique for the diagnosis of meniscal ramp lesions, with a sensitivity of 88%, specificity of 87%, PPV of 94%, and NPV of 74%.

The results are consistent with a meta-analysis (19) published in 2019 that included only eight articles but that examined the role of MRI in the diagnosis of these lesions (20,–27), which showed excellent pooled specificity (94%) and moderate pooled sensitivity (71%), which raised to 84% when using a 3.0-T MRI with the patient's knee in the neutral position (30° of flexion) and the involvement of musculoskeletal radiologist for MRI interpretation.

In the last 4 years, more articles have been published evaluating the performance of the MRI in the diagnosis of meniscal ramp lesions. Most of them obtained good results, similar to ours. The study that obtained the best results was carried out by Okazaki et al. (28), with a sensitivity and specificity of 98.8% and 85.2%, respectively, using as a diagnostic criterion the irregularity of the posterior margin of MM, and 87.5% and 100% using the presence of complete fluid filling between the PHMM and the capsule, conducting the MRI scans with the knee at 90° of flexion. Others who also obtained positive results were Laurens et al. (29), with a sensitivity of 75% and specificity of 75% using the presence of complete fluid hyperintensity between the PHMM and the capsule as radiological criteria.

However, there have also been published studies with poor results. In a large study of 2156 patients, Thaunat et al. (30) obtained a lower sensitivity, of 68.4%, but without specifying the diagnostic criteria used. An article about meniscal ramp lesions in the pediatric population was also published (31), with worse MRI results (sensitivity = 57%, specificity = 68.5%, PPV = 40%, and NPV = 80%), although with a higher sensitivity than the only pediatric study that had been published previously, by Malatray et al. (23%) (25). These two studies obtained poor results, perhaps because meniscal vascularization in children can generate false-positive results.

Many different MRI features were used to describe meniscal ramp lesions in the literature, and the presence of a complete fluid filling between the PHMM and the capsule (20,21,23,25–33) and the irregularity of the posterior margin of the PHMM (21,27,28,32,34) were the most widespread. The authors of this article agree with the literature, that the presence of fluid interposed between the PHMM and the capsule is a valid sign for the diagnosis of meniscal ramp lesion, as it corresponds to a type 4B lesion. However, we consider that this radiological finding alone is not sufficient to make the diagnosis; we must also detect a clear meniscocapsular junction lesion. Fig. 3 shows one of the four false-positive cases, which was diagnosed as a type 4B lesion, since radiologists clearly observed the presence of fluid interposed between the PHMM and the capsule, but they did not notice during the lecture the integrity of the meniscocapsular and meniscotibial ligaments in the next slice. On the other hand, we do not agree that the irregularity of the posterior margin of the PHMM is a reliable criterion on its own, if we do not see a clear meniscal or meniscocapsular junction tear. We did not use this sign during the interpretation of the images and the false-negatives cases that we reviewed later did not present this feature on MRI.

Fig. 3.

This is one of the false-positive cases, which was diagnosed as a type 4B lesion. (a) A sagittal proton density with fat sat MR image shows the presence of fluid interposed between the posterior horn of the medial meniscus and the capsule (arrowhead), which is one of the radiological signs described to diagnose a meniscal ramp lesion. (b) However, in the next slice, the integrity of the meniscocapsular (arrow) and meniscotibial (curved arrow) ligaments can be appreciated, which rules out the presence of a ramp lesion, as described in the arthroscopic findings.

The remaining three false positives were two cases diagnosed as type 3B lesions (Fig. 4), which, given that they are called “hidden lesions” due to their location, could have gone unnoticed at arthroscopy, as well as another 4B case (Fig. 5), in which we clearly see the absence of both the meniscocapsular and meniscotibial ligament and even a slight meniscocapsular separation; however, at surgery, there was no evidence of meniscal ramp lesion.

Fig. 4.

These are the two false-positive cases diagnosed as type 3B lesions on MRI. Sequences with PD fat-saturated weighting in the sagittal plane showing perimeniscal fluid occupying the posterior aspect of the medial meniscus and the upper surface of the medial tibial plateau (arrowhead), without evidence of a clear meniscotibial ligament. Note the normal meniscocapsular ligament (arrow).

Fig. 5.

Another example of a false-positive case on MRI. In this sagittal PD fat-saturated image, radiologists clearly saw the absence of both the meniscocapsular and meniscotibial ligament and even a slight meniscocapsular separation and soft tissue edema between the PHMM and the capsule (arrow); however, there was no evidence of meniscal ramp lesion at surgery. PHMM, posterior horn of the medial meniscus.

Regarding the nine false-negative cases, two were type 4B ramp lesions. One of them was an interesting case shown in Fig.6 in which radiologists observed a slight meniscus-capsular separation but a clear integrity of the meniscocapsular and meniscotibial ligaments, so it was considered a kind of ligamentous laxity; however, the surgeon at arthroscopy considered it to be a true ramp lesion. The other 4B lesion missed on MRI is the case shown in Fig. 7, in which the meniscocapsular and meniscotibial ligaments are unaltered; however, the surgeon observed a meniscocapsular junction tear arthroscopically. The other seven false-negatives cases were two type 1 cases, which corresponds to a meniscocapsular ligament tear, and five type 3A cases, which are partial inferior meniscal tears. Of these five lesions, two were interpreted as horizontal tears and the rest were missed on imaging. This is in line with the study published by Thaunat et al. in 2021 (30), in which they state that the lesion most likely to be missed on preoperative MRI was type 3.

Fig. 6.

This is one of the false-negative cases, which was diagnosed arthroscopically as a type 4B lesion. A proton density with fat-saturated MR image in the sagittal plane showed a slight meniscus-capsular separation but both the meniscocapsular ligament (arrow) and the meniscotibial ligament (arrowhead) appeared to be intact, so radiologists considered it to be a kind of ligamentous laxity; however, the surgeon at arthroscopy diagnose a true ramp lesion.

Fig. 7.

Another example of a false-negative case on MRI. On arthroscopy, the surgeon observed a clear tear at the meniscocapsular junction; however, on this sagittal plane proton density with fat-saturated MR image, the meniscocapsular (arrow) and meniscotibial ligaments (arrowhead) appear to be intact.

The good results obtained in our study in terms of sensitivity and specificity as well as inter-observer concordance demonstrate that the classification and description of radiological signs proposed by Greif for each of the types of meniscal ramp lesions is valid. This is in agreement with an earlier study published by the same authors that also demonstrates that this classification has a good degree of reproducibility on MRI (35), as well as with Chagas-Neto et al. (36) who showed in their study that Thaunat et al.'s arthroscopic classification on which Greif's is based has also good reproducibility when applied by trained musculoskeletal radiologists.

Regarding the prevalence of each of the types of meniscal ramp lesion in our sample, the most frequent was type 4 (4A and 4B) as described previously by us (35) and by Chagas-Neto et al. (36); the least frequent were type 2 (of which we did not observe any) and type 5, as in our last study (35) and in the sample of Thaunat et al., which is composed of 2156 patients (30). Among the 76 ramp lesions of our study, only 5.3% were stable (types 1 and 2) while the remaining 94.7% were unstable (types 3A, 3B, 4A, 4B, and 5) according to the criteria proposed in both Thaunat et al.'s (6) and Greif's classifications (7), which are based on the integrity or rupture of the meniscotibial ligament. However, DePhillipo et al. (2) in a recent laboratory study of 14 cadavers, found that there were no histological differences observed between the meniscocapsular and meniscotibial ligament in their attachments in the PHMM; therefore, they concluded that these classification systems may not be appropriate for surgical planning, since type 1 lesions, consisting of a meniscocapsular ligament tear, would also have to be considered unstable. Arthroscopically, a ramp lesion is considered unstable if the surgeon can displace the meniscus with probing, which is quite subjective. We therefore consider it necessary, as Thaunat et al. in their last article (30), to validate a system for both arthroscopy and MRI that determines when a ramp lesion is stable and when it is unstable, because this differentiation is of great importance, as there are authors who consider that only unstable lesions should be repaired (37,38).

The epidemiological characteristics of meniscal ramp lesions in ACL-deficient knees are still incompletely defined. Its incidence has varied widely in the literature, ranging from 9% (27,39) to 42% (40), probably secondary to the fact that there are authors that include in the definition of meniscal ramp lesion the peripheral longitudinal tears of PHMM, while others consider ramp lesions just tears limited in the meniscocapsular junction. The incidence reported in the only three studies involving more than 1000 patients was 15.5% (30), 15.8% (26), and 23.9% (3). Young age, male sex, and increased time from injury were the first risk factors described (3,4,41), to which concomitant lateral meniscus tear (3,40,42), contact sports (40,42,43), increased medial meniscal slope (26,34), and presence of posterior medial tibial plateau bone contusion in MRI (24,34,40,41) were also described. Although in this study we did not statistically analyze possible associations with other radiological findings, the typical individual with a meniscal ramp lesion was a 35-year-old man, as in the literature.

The present study has some limitations. First, the design was retrospective. Perhaps a prospective evaluation would have improved the results, since we believe that some of the false-positive ramp lesions (type 3B) may have been undetected at arthroscopy. Another limitation is that not all MR studies were performed at the same institution: 35% were carried out in other hospitals. However, only those studies of good quality and with appropriate sequences for meniscal assessment were included in the sample. On the other hand, our study's greatest strength is the number of patients studied, as it is the largest of the articles published so far on meniscal ramp lesions in radiology journals. In addition, all the arthroscopies performed, which were taken as a reference in the study, were performed by a single surgeon who always used the same protocol to detect meniscal ramp lesions.

In conclusion, this study demonstrates that MRI can reliably detect meniscal ramp lesions in patients with an ACL tear. This is very good news because to diagnose them preoperatively allows surgeons to plan surgery and treat them during ACL reconstruction, because if they remain unrepaired, the stability of the knee will not be restored, and this could cause meniscal and articular damage and also lead to the failure of the ACL graft.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Sara Escoda Menéndez

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, et al. Ramp lesions associated with ACL injuries are more likely to be present in contact injuries and complete ACL tears. Knee Surg Sports Traumatol Arthrosc 2018;26:1080–1085.