Meniscal ramp lesions are injuries commonly found in the anterior cruciate ligament (ACL)-injured knee. They are tears of the red–red zone of the posterior horn, the meniscocapsular ligament, and/or the meniscotibial ligament [11, 13]. They were originally described by Hamberg et al. [14] in 1983 and later named “ramp lesions” by Strobel in 1988 [31]. Despite knowledge of the strong association between meniscal ramp lesions and ACL tears, they have only recently become the subject of extensive research and discussion in the orthopaedic community. Although more research is still necessary, several recent studies have given us important knowledge about the anatomy, epidemiology, diagnosis, and the biomechanical consequences of these tears, highlighting the importance of the careful and systematic exploration of the posteromedial part of the knee.

Epidemiology and diagnosis

A high degree of suspicion, followed by the systematic exploration of the posteromedial ramp area, is necessary for the diagnosis of meniscal ramp lesions in any case of ACL injury. Over the last few years, several studies have reported a high prevalence of meniscal ramp lesions in the setting of ACL tears [8, 29].

Direct arthroscopic visualisation is generally regarded as the gold standard for the diagnosis of meniscal ramp lesions [22, 29]. However, their visualisation and recognition might not be straightforward. The arthroscopic portals used for their diagnosis, the use of a 30- or 70-degree arthroscope (while viewing through the modified Gillquist view), as well as the debridement of the scar tissue eventually covering the “hidden” lesion, may all affect the ability to recognise these injuries [4, 17, 29, 32]. The different methods (exploration of the ramp area through the modified Gillquist view or the posteromedial portal) employed for the diagnosis of meniscal ramp lesions can also explain their wide variation in prevalence reported in the literature. A recent systematic review and meta-analysis [20] reported a rate of meniscal ramp lesions in the ACL-injured knee ranging from 9.0% to 41.7%. In their study, Sonnery-Cottet et al. [29] found a prevalence of meniscal ramp lesions of 40%. Interestingly, 42% of these tears were only possible to diagnose after the gentle debridement of a superficial tissue layer covering the ramp lesion. These findings may suggest the use of systematic probing of the ramp area through a posteromedial portal during ACL reconstruction.

Magnetic resonance imaging (MRI) is commonly used in the clinical setting to diagnose meniscal ramp lesions. Its use has, however, been criticised, due to the moderate sensitivity reported in several studies [2, 15, 17, 24, 36]. The recent systematic review and meta-analysis by Koo et al. [19] reported that MRI has a specificity of 94% (95% CI 88–97%) but a sensitivity of 71% (95% CI 59–81%) for diagnosing meniscal ramp lesions. Interestingly, the authors found that the use of a 3.0 Tesla MRI scan, positioning the knee in 30 degrees of flexion rather than full extension and interpretation by a musculoskeletal radiologist, increased the sensitivity to 84%. Some authors [3, 34, 36] have theorised that MRI would have moderate sensitivity for the diagnosis of meniscal ramp lesions, because it is generally undertaken in full extension. In this position, there would be an obliteration of the posteromedial recess, thereby reducing the meniscocapsular separation. It should, however, be noted that the radiological criteria used in the previous literature to evaluate the accuracy of MRI with arthroscopy as the gold standard were limited and heterogeneous [2, 18, 21, 36, 38]. Several authors [2, 9, 19, 36] have defined a meniscal ramp lesion on MRI as only a tear at the meniscocapsular junction of the posterior horn. Other authors have not even reported the MRI criteria used for the diagnosis of ramp lesions [3, 24, 34]. In a recent MRI study, Cristiani et al. [8], applying the well-defined radiological criteria reported by Greif et al. [13] (who described seven subtypes of meniscal ramp lesion), found a prevalence of meniscal ramp lesions of 39.5% in ACL tears. The authors highlighted that both the well-defined radiological criteria employed, as well as the short mean time (19.6 ± 15.2 days) from injury to MRI, were important for the diagnosis of meniscal ramp lesions. A short delay from the injury to MRI prevents the post-traumatic oedema from reabsorbing, allowing an accurate diagnosis of the injured structures of the posteromedial ramp area, regardless of the position of the knee at the time of MRI. These findings suggest that the use of MRI, especially in the acute setting, should be reconsidered for the diagnosis of meniscal ramp lesions.

Recent studies have also investigated several factors associated with the presence of meniscal ramp lesions. A detailed knowledge of these factors may facilitate the diagnosis of these important tears. Posteromedial tibial (PMT) bone bruising has been strongly associated with meniscal ramp lesions [20]. Due to their strong association, it has been suggested that PMT bone bruising and meniscal ramp lesions may share the same trauma mechanism [8]. A recent study also reported that contact sport at ACL injury, pivot-shift bone bruising, and a Segond fracture are associated with meniscal ramp lesions [8]. Seil et al. [27] showed that meniscal ramp lesions are associated with contact injuries and complete (rather than partial) ACL tears. The authors therefore suggested that meniscal ramp lesions are caused by a higher energy trauma. In a recent systematic review and meta-analysis, Kunze et al. [20] found that there was strong evidence that meniscal ramp lesions are also associated with age < 30 years and moderate evidence supporting an association with male gender and lateral meniscus tears. Finally, Kim et al. [18] reported that a longer (≥ 3 months) time from injury, varus knee (> 3 degrees), a steeper medial tibial slope, and meniscal slope are all associated with the presence of a meniscal ramp lesion.

Classification

One of the most used classifications of meniscal ramp lesions is the one described by Thaunat et al. [32] in 2016. The authors classified meniscal ramp lesions into five categories. Recently, in 2020, Greif et al. [13] further expanded this classification system into seven categories, depending on the involvement of the different structures of the ramp area. Meniscal ramp lesions were classified as follows: type 1; meniscocapsular ligament tear; type 2, partial superior peripheral meniscal horn tear; type 3A, partial inferior peripheral posterior horn meniscal tear; type 3B, meniscotibial ligament tear; type 4A, complete peripheral posterior horn meniscal tear; type 4B, complete meniscocapsular junction tear; and type 5, peripheral posterior horn meniscal double tear. Knowledge of meniscal ramp lesion subtypes is of clinical relevance, as tears type 1 and 2 are defined as stable, whereas ramp lesion types 3A, 3B, 4A, 4B, and 5 are defined as unstable [13]. Recently, in a study based on 253 patients, Cristiani et al. [8] evaluated the prevalence of the different types of meniscal ramp lesion. Of the 100 patients with a meniscal ramp lesion on MRI, the authors reported that the subtype distribution was as follows: type 1, 13%; type 2, 4%; type 3A, 7%; type 3B, 7%; type 4A, 20%; type 4B, 43%; and type 5, 6%. To date, however, there is a lack of knowledge regarding the natural history and treatment outcomes of the different meniscal ramp lesion subtypes.

Biomechanical consequences

The role of the medial meniscus as a secondary knee stabiliser to anterior tibial translation is well established in the literature [6, 7]. Recent studies have specifically examined the impact of meniscal ramp lesions on knee biomechanics. In a clinical study based on 275 patients, Mouton et al. [25] reported that patients with meniscal ramp lesions have a higher degree of pivot shift compared with patients with an isolated ACL injury at the time of surgery. The authors therefore recommended their repair during ACLR.

Several cadaveric studies have evaluated the biomechanical consequences of meniscal ramp lesions. Stephen et al. [30] showed that anterior tibial translation and external rotation increased significantly in the ACL-deficient knee, following the creation of a posterior meniscocapsular tear. Interestingly, knee biomechanics was not restored by isolated ACLR, but it was only restored after ACLR and meniscocapsular repair. Similarly, Peltier et al. [26] showed that meniscal ramp lesions increased anterior tibial translation and, in particular, meniscotibial ligament tears increased internal and external tibial rotation in the ACL-deficient knee. In another cadaveric study, DePhillipo et al. [10] reported significantly increased anterior tibial translation in the ACL-deficient knee after cutting the meniscocapsular and meniscotibial attachments at the posterior horn of the medial meniscus. Deficiency of these ligaments was also associated with increased internal and external tibial rotation in the ACL-reconstructed knee. In this condition, ACLR was able to restore anterior tibial translation but did not restore external and internal tibial rotation and the pivot shift. Repair of the meniscocapsular and meniscotibial ligament restored the pivot shift, but it was unable to restore internal and external rotation at angles of > 30 degrees.

Treatment and final considerations

Several techniques can be used to repair meniscal ramp lesions and the literature shows that they are safe and effective. Back in 1983, Hamberg et al. [14] showed the good healing potential of meniscal ramp lesions after their repair. The authors reported clinical healing (no meniscal symptoms) in 84% of their patients at a follow-up of 18 months after open repair with interrupted 2–0 vicryl absorbable sutures. In addition, all the patients who underwent a second-look arthroscopy showed healing of the repaired meniscal ramp lesion. More recently, Chen et al. [5], at a second-look arthroscopy, evaluated the healing of meniscal ramp lesions after repair using an all-inside technique. Of the 46 patients who underwent combined ACLR and ramp lesion repair, the authors reported that 40 (86.9%) exhibited complete healing and five (10.8%) partial healing. Only one patient (2.1%) experienced a failure of the repair. Gousopolous et al. [12] and Thaunat et al. [33] reported a significantly lower failure rate and secondary meniscetomy with a suture hook repair through the posteromedial portal in comparison with an all-inside technique. Recently, in a technical note, Siboni et al. [28] proposed a two posteromedial portal approach (one viewing and one working portal), which may aid in improving the visualisation as well as the repair of meniscal ramp lesions.

It is, however, not clear whether there is any clinical benefit in repairing all the meniscal ramp lesions encountered during ACLR. In a randomised controlled trial, Liu et al. [23] allocated patients with a stable ramp lesion to one study group (surgical repair; n = 50) and one control group (abrasion and trephination, n = 41). At a minimum 2-year follow-up, the authors reported no differences in terms of knee laxity (Lachman test, pivot-shift test and KT-1000 arthrometer) and subjective knee outcome (Lysholm knee score and IKDC score) between the groups. Similar results were found in a retrospective study by Yang et al. [37]. The authors evaluated 68 patients with ACLR and meniscal ramp lesions who were divided into two groups depending on the meniscal treatment (arthroscopic margin refreshing, n = 31; arthroscopic margin refreshing + all-inside repair, n = 37). At a minimum 2-year follow-up, there was no difference in terms of Lysholm score, IKDC score, or range of motion. In another study, Albayrak et al. [1] compared 33 patients with ACLR and a stable ramp lesion left untreated with 33 patients with ACLR and no ramp. At a minimum 3-year follow-up, there were no differences in Lachman, pivot-shift test, Lysholm score, IKDC score, and complication rate. The only difference was a longer time to return to sport for the patients with a meniscal ramp lesion. Hatayama et al. [16] compared knee laxity and the healing status (using a 3.0 Tesla MRI) of ramp lesions left untreated or repaired using an all-inside technique through the posteromedial portal. The authors reported a significantly higher healing rate in the repaired group compared with the unrepaired group. However, knee laxity did not differ significantly between the groups.

In a recent study, Tuphé et al. [35] attempted to evaluate the long-term natural history of unrepaired stable ramp lesions. In a minimum 20-year follow-up of 28 patients with an unrepaired, stable ramp lesion, the authors reported that eight patients (28.6%) had meniscal failure. Six (21.4%) were bucket-handle tears and two (7.2%) were vertical tears of the posterior horn. The authors concluded that it may not be wise to leave a stable meniscal ramp lesion unrepaired. It should, however, be noted that the rate of medial meniscal failure/reoperation in the group with no meniscal ramp lesions was not analysed. In addition, the cohort of patients with meniscal ramp lesions was small (28 patients) and the follow-up was very long (minimum 20 years). During such a long follow-up, there could be several confounding factors which could make the interpretation of the results of one study difficult.

In conclusion, there is as yet no clinical evidence to support the systematic repair of all ramp lesions encountered during ACLR. Most of the literature supporting meniscal ramp lesion repair comes from biomechanical, cadaveric studies. Although this literature shows benefits of meniscal ramp lesion repair in terms of knee kinematics, it should be remembered that cadaveric studies have intrinsic limitations, as the biology is not taken into account. Little is still known about the natural (in-vivo) history of meniscal ramp lesions in terms of healing or size progression if left untreated during ACLR. “Absence of evidence” does not mean “evidence of absence” and it is possible that future studies may find clinical benefits in the systematic repair of all ramp lesions. However, to date, with the current evidence, it is recommended always to assess the ramp area thoroughly during ACLR and the repair of unstable ramp lesions should be based on the biomechanical knowledge available, despite the lack of clinical data with a high level of evidence.

Finally, very little is known about the natural course and the implications of meniscal ramp lesions in the ACL-injured knee. Do they progress? Can some heal? Are they a sign of a more severe knee injury? Do they affect the ability to cope with an ACL injury? Could a meniscal ramp lesion per se be an indication for ACLR? There are still many questions to be answered. As is often the case in science, a lot is known, but a lot is also unknown…