Uncommon Rupture of the Lateral Meniscus ‘RAMP-Like’ Type Associated with ACL Tear: Literature Review and Case Report

Abstract

We present a case of a rare incidence of a RAMP-type tear of the external meniscus in a 21-year-old male patient, in which a repair with vertical meniscal sutures was performed. This is a scarcely described tear in the literature that is associated with anterior cruciate ligament (ACL) injuries.

We report our experience with a case treated at our center, where we identified this distinct injury of the posterior horn of the external meniscus. Although Magnetic Resonance Imaging may reveal fluid posterior to the posterior horn of the lateral meniscus in a longitudinal configuration, the definitive diagnosis is made through arthroscopy. The chosen treatment was to close the defect with vertical meniscal sutures. We believe that more studies are needed to determine the ideal management.

 

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Keywords

RAMP lesion - ACL reconstruction - lateral meniscus - meniscal tear

Introduction

Over time, the approach to meniscal injuries has undergone significant evolution. Initially, the common practice was to perform total meniscectomies; however, over the years, there has been a shift toward a more conservative approach aimed at preserving as much meniscal tissue as possible, given its crucial role in knee biomechanics and function.

The recognition and description of RAMP-type lesions have marked an important milestone in the management of meniscal tears. These injuries, which might have gone unnoticed in the past, are now valued for their significant impact on knee stability and function. Early identification and appropriate treatment of RAMP lesions have become essential to achieving optimal recovery outcomes for patients.

RAMP-type lesions were originally defined as tears of the peripheral attachment of the posterior horn of the medial meniscus at the meniscocapsular junction.[1] It has been observed that these injuries have an incidence that varies between 9% and 17% in patients with rupture of the anterior cruciate ligament (ACL),[1] [2] which underlines the importance of their detection and treatment in the context of ligamentous injuries associated.

A crucial aspect to consider is the role of the meniscotibial ligament in knee stability, especially in the context of chronic ACL injuries. Biomechanical studies have shown that menisco-capsular and meniscotibial injuries of the posterior horn of the medial meniscus can significantly alter the kinematics of the knee, increasing anterior translation, internal and external rotation, as well as the pivot shift in knees with ACL tear.[3]

Recently, an injury has been identified in the lateral meniscus, known as a RAMP-type tear ([Fig. 1]). Although the posterior union of the lateral meniscus has received less attention, in the literature these injuries are described as Wrisberg rip or zip lesion-type tears, which are characterized by presenting a longitudinal tear in the posterior horn of the lateral meniscus (PHLM). This represents a lesion that originates anterior to the meniscus-femoral junction and extends medially, compromising the posterior horn of the meniscus.[4]

Fig. 1 Description of a RAMP-type lateral meniscus tear. The lesion is located posterior to the posterior horn of the lateral meniscus.

The RAMP-type meniscal tear that we describe in this case is characterized by a detachment of the capsule-synovial junction at the level of the PHLM, unlike the Wrisberg rip or zip tear that compromises the external meniscus. This type of injury can involve the posterior meniscus-tibial ligaments and even extend beyond, being a continuum that compromises the popliteo-meniscal region, which represents a detachment of the PHLM from the synovial tissue.

To our knowledge, there are no studies that report on the incidence of this particular type of injury, much less the percentage associated with ACL tears.

Our objective is to report an unusual case, perform a review of the literature, and describe the surgical technique that we have used.

 

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Case Report

The ethics committee of our center granted approval for the study. The selected patient gave consent to participate in this study.

We present the case of a 21-year-old male patient who suffered a traumatic twisting mechanism of his right leg during a soccer game. The patient described the traumatic event as a mechanism in which his foot remained fixed on the ground and his body experienced external rotation. After this, he could not continue and had to consult the emergency service of our center due to pain that did not subside, a feeling of instability, and an increase in volume in relation to his knee.

Physical examination revealed a knee effusion with a painful range of motion in flexion and extension. The patient had positive tests for anterior-posterior instability. In addition, positive meniscal tests were observed for the lateral meniscus.

The x-ray showed no fractures or dislocations. Magnetic resonance imaging (MRI) revealed a complete ACL tear with bone edema on the posterolateral tibial plateau. Although no clear lesions were observed in the meniscus and the meniscal tissue appeared intact, fat-suppressed T2 sequences revealed fluid behind the PHLM in a longitudinal arrangement ([Fig. 2]). These findings justified surgical intervention and planning for ACL reconstruction using a technique with bone – tendon – bone autograft and eventual meniscal suture.

Fig. 2 T2-weighted MRI with fat suppression of the reported patient. Sagittal image (A) shows bone edema in the posterior region of the lateral plateau with disruption of the capsuloligamentous junction. Sagittal image (B) displays a complete ACL tear. Axial image (C) reveals synovial fluid at the capsuloligamentous junction. Coronal image (D) shows synovial fluid related to the root of the lateral meniscus.

 

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Surgical technique

Under general anesthesia, the patient was placed in a supine position with the affected leg on the table and supported by a support that allows us to take it from flexion to extension. Initially, bone-patellar tendon-bone (BTB) autograft extraction was performed to prepare the plasty to reconstruct the ACL.

Conventional arthroscopic portals (anterolateral and anteromedial) facilitated diagnostic arthroscopy, confirming the complete ACL tear and revealing a RAMP-type lateral meniscus tear ([Fig. 3]).

Fig. 3 Arthroscopic image of a RAMP-type lateral meniscus tear.

A scraping and debridement of the lesion were performed to promote greater bleeding and healing. Subsequently, two vertical sutures were planned (due to the size of the defect), both using an "all-inside" system, taking care to protect the neurovascular structures. Finally, closure of the defect was confirmed with the probe, along with the resulting stability of the meniscus ([Fig. 4]). Care was taken during suture placement to avoid excessive tension, aiming to prevent potential tears caused by the application of excessive force.

Fig. 4 Arthroscopic images showing how the defect is closed with two vertical meniscal sutures. Both “all-inside” sutures are installed (A and B). The final tensioning of the sutures is demonstrated (C).

After this, the ACL footprint is identified, a tibial tunnel is made and then a femoral tunnel with a modified transtibial technique, a BTB autograft plasty is performed, and it is fixed in the femur and tibia with metal screws. A satisfactory plasty was observed. Then, an anterolateral plasty is performed according to the modified Lemaire technique, fixing it with an anchor in the corresponding position.

Postoperative management included immobilization of the knee with a brace between 0° and 60°, and the immediate start of rehabilitation following a non-weight bearing protocol for a period of four weeks, with the purpose of promoting healing of the tear and the care of meniscal sutures.

After the first month, an increase in the Brace to 0–90° for 2 more weeks was indicated. After these 2 weeks, the use of the splint was suspended and a physical therapy protocol focused on achieving a full range of motion, strengthening muscles, and recovering joint balance was initiated.

This comprehensive approach to postoperative recovery aims to not only promote proper healing of the meniscal injury but also facilitate the restoration of functionality and strength in the affected knee.

The patient completed a rehabilitation protocol focused on protecting the repair of the meniscal injury and recovering functionality after the ACL injury. In our center, generally, nine months after surgery, an MRI is performed to evaluate the ligamentization of the graft and specific tests are applied to determine fitness for return to sports. Once this process has been successfully completed, the patient is authorized to resume his or her sporting activity.

 

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Anatomy

One of the most notable differences that distinguishes the external meniscus from the internal meniscus is its greater mobility, which is attributed in part to the hiatus through which the popliteus tendon passes, allowing a wider range of motion compared to the medial meniscus, which is why is more exposed to injuries.

The posterior root of the lateral meniscus is precisely positioned, located 1.5 mm posterior and 4.2 mm medial to the lateral tibial eminence, in addition to being positioned 12.7 mm in front of the posterior cruciate ligament.[5]

Unlike the medial meniscus, the lateral meniscus does not have the insertion of the semimembranosus or the posterior oblique ligament, which gives it a different structure and a greater capacity for movement. In addition, it has a hiatus for the popliteus tendon, with a width between 12 and 15 mm, located approximately 36% of the length of the meniscus from the posterior root.[6]

In the region medial to the popliteus hiatus, there are structures such as the meniscotibial and posterior meniscofemoral ligaments, fascicles that go from the popliteus tendon to the meniscus, and also insertion of the meniscal tissue into the synovium,[7] all of these structures are essential for maintain the stability of the PHLM.

 

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Discussion

Strobel et al.[8] first introduced the term RAMP lesion in 1988 to describe tears involving the meniscocapsular junction in the posterior zone of the medial meniscus. In recent years, various authors have identified an injury occurring in the lateral meniscus, which suggests a similar configuration to that described by Strobel and has been termed RAMP lesion. However, unlike the medial meniscus injury, this is characterized by a disruption in the posterior horn of the lateral meniscus at the capsule-synovial junction.

Although the pathophysiology and optimal treatment have not yet been fully elucidated due to the rarity and infrequency of this tear, diagnostic confirmation is usually made during arthroscopy. Frequently, this type of tear may go unnoticed in imaging, particularly in MRI. Therefore, it is essential to examine this area with the probe during arthroscopy, especially if there is suspicion.[9]

The RAMP lesion that we describe in the case of the reported patient is characterized by a capsular-synovial detachment or rupture at the level of the PHLM, which entails destabilization of the meniscus. This injury may be part of a continuum of conditions, potentially progressing to a zip-type injury, involving the posterior meniscotibial ligament or extending through the meniscus-popliteal complex.[10] The involvement of these posterolateral structures could go unnoticed, so it is very necessary to perform an arthroscopic diagnosis of the stability in this area.[11]

In [Figure 5] we detail the configuration of the different PHLM breakage patterns described in our article, mainly highlighting the differences between a zip-type lesion and a RAMP lesion. In the first, the PHLM is affected; In the second, it is characterized by a posterior detachment of the meniscal tissue, separating the posterior horn from the synovial tissue.

Fig. 5 In image (A), the red line corresponds to a RAMP-like lesion. In the image (B), the red line represents a tear involving the posterior horn of the lateral meniscus (“zip” type lesion). In the image (C), the red line describes a lesion affecting the menisco-popliteal complex.

Although there is little information in the literature about this type of injury and some articles have described similar injuries, such as posterolateral meniscocapsular tear, in the recently published article by Gil Noriega et al.[10] this injury was described and differentiated from other injuries that involve PHLM using histological tissue samples. More research is still needed on this type of injury to understand the biomechanical repercussions and conclude the ideal management.

Another cause of increased mobility of the lateral meniscus is injuries to the popliteomeniscal fascicles, which together with the popliteus tendon, form a ring-shaped peripheral junction around the lateral meniscus in the popliteal hiatus.[12] The popliteal complex has, at least in part, the function of providing additional stability through the popliteomeniscal fascicles to the section of the lateral meniscus that would not otherwise be anchored within the popliteal hiatus.[13] By providing both a static and dynamic connection between the lateral meniscus and the popliteus tendon, the popliteomeniscal fascicles are important in controlling the movement of the lateral meniscus during knee flexion and extension.

Stäubli y Birrer[14] reported that increased movement of the lateral meniscus, as well as loss of its lateral retraction under varus stress, occur when these fascicles are torn. Biomechanical studies carried out by Simonian et al.[15] confirmed these clinical observations, demonstrating that the movement of the lateral meniscus is almost doubled when the posteroinferior and anteroinferior popliteomeniscal fascicles are injured, compared to a meniscus whose fascicles are intact. Therefore, they are an important part of the posterolateral region of the knee and provide stability to it.

Although there are no biomechanical studies on this type of injury, we believe that lateral meniscus RAMP tears could significantly alter knee biomechanics due to their role in rotational stability. Therefore, further biomechanical and clinical studies are needed to better understand this uncommon injury.

As a surgical team, our suggested treatment approach involves clearly identifying the synovial tissue zone and the meniscal tissue zone and closing the defect with all-inside meniscal sutures, ideally in a vertical configuration. It is important to avoid leaving the repair too tight to prevent future radial tears; in this way, we provide stability to the defect and prevent the progression of the tear.

In conclusion, it is crucial to distinguish between a tear of the lateral meniscus posterior horn and a RAMP tear to achieve an accurate diagnosis and effective treatment planning. This entails performing a repair that considers the tissue being repaired, the suture configuration, the number of sutures to use, and always addressing concomitant injuries.

 

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Conflicto de Interés

Los autores no tienen conflictos de interés que declarar.

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Publication History

Received: 08 September 2024

Accepted: 29 November 2024

Article published online:
20 May 2025