Meniscal ramp lesions occur much more frequently than was previously considered, and particularly so in ACL-injured knees. The historically high rate of missed diagnoses is a result of unfamiliarity with this injury pattern within the orthopedic community, and also the difficulty in diagnosis. A systematic exploration of the posteromedial compartment of the knee is mandatory to reliably identify ramp lesions. Failure to recognize and repair these injuries is associated with persistent anterior and posteromedial instability. Understanding their nature, biomechanics, and epidemiology is essential in allowing orthopedic surgeons to suspect their presence and adequately treat these lesions.
Meniscal ramp lesions are a “hot topic” because of increasing recognition that they have important biomechanical consequences and also that they occur much more frequently than was previously understood.
Historically, ramp lesions have been underdiagnosed because of the low sensitivity of MRI and inadequate visualization through standard arthroscopic anterior viewing portals.
A systematic exploration of the posteromedial compartment of the knee via a trans-notch approach is needed to confirm or refute the presence of a meniscal ramp lesion.
If left untreated, meniscal ramp lesions may contribute to residual anteroposterior instability in the anterior cruciate ligament–reconstructed knee and may also result in failure of meniscal repair.
Recent epidemiologic data and definition of risk factors helps to inform an appropriate index of suspicion, identification, and adequate treatment of ramp lesions.
Meniscal ramp lesions were studied by Hamberg and colleagues in the 1980s but at that time were described only as “injuries of the posterior aspect of the medial meniscus.” Later, Strobel introduced the term ramp lesion and characterized the injury as a longitudinal tear, 2.5 cm in length, located at the meniscocapsular junction. In 1991, Morgan described a surgical technique for arthroscopic repair of ramp lesions using a suture hook through a posteromedial portal, and in 2004 Ahn and colleagues reported a series providing clinical outcomes of repair.
Despite this long history of recognition of ramp lesions, the topic has been infrequently studied over the past few decades, until a recent resurgence in interest. This lack of prior importance attributed to the topic is likely a consequence of an underestimation of their incidence due to a high rate of missed diagnoses, insufficient knowledge about their biomechanical consequences, and an intuitive sense that these lesions could heal spontaneously. The recent interest in these injuries heralds an increasing recognition of their importance and an emerging concept of their association with posteromedial knee instability. The contemporary literature describes these injuries as tears at the posterior meniscocapsular junction and/or tears of the posterior meniscotibial ligament. The expression “hidden lesion,” also has been recently used to describe this injury, and the term refers to the difficulty in identifying ramp lesions from standard anterior arthroscopic portals, and also with preoperative MRI, which has low sensititvity.
Ramp lesions are hypothesized to occur through a number of possible mechanisms. The most simple is as a result of high forces transmitted through the posteromedial capsule during valgus strain, internal rotation of the tibia, and axial loading at the time of an anterior cruciate ligament (ACL) injury. The contrecoup injury mechanism, a compensatory varus alignment and internal rotation of the femur after the initial pivot-shift mechanism, also offers a potential mechanism because it results in impaction between the medial femoral condyle and the medial aspect of the tibial plateau, thus trapping the meniscus. Similarly, Hughston also suggested these lesions could occur as a result of the meniscus becoming trapped between the femur and tibia, but attributed this to the increased anterior tibial translation that occurs as a result of an ACL injury. Hughston and others have also suggested a potentially important role for the semimembranosus muscle-tendon complex, which in cadaveric study has been found to have a firm attachment to the medial meniscocapsular area in most specimens (86%). This close anatomic relationship between the semimembranosus tendon and the meniscocapsular region often can be visualized at the time of ramp repair ( Fig. 1 ). It is hypothesized that contraction of the semimembranosus, secondary to excessive anterior translation of the tibia during an ACL tear or the subsequent contrecoup mechanism may stress this posteromedial area, resulting in a meniscocapsular tear ± meniscotibial ligament injury and posteromedial instability.
The emerging concept of ramp lesions representing a posteromedial instability is based on increasing recognition of the potentially important role of these injuries in knee stability. Ahn and colleagues and Peltier and colleagues have demonstrated an increase in anteroposterior instability in ACL-deficient cadaveric knees on creation of ramp lesions and others have also demonstrated significant increases in both internal and external rotation laxity at all knee flexion angles on creation of ramp lesions ± meniscotibial ligament injuries. Peltier and colleagues concluded that these lesions appear to play a significant role in knee stability and also that ramp lesions increase the forces in the ACL. These reports are further supported with the work of numerous other investigators who have demonstrated that isolated ACL reconstruction fails to restore normal joint kinematics and results in residual laxity in the presence of a ramp lesion. Furthermore, it has been demonstrated that repair of these lesions abolishes the pathologic increase in laxity and therefore provides a biomechanical rationale for identifying and repairing these lesions.
Ramp lesions are reported to occur frequently (9.3%–24.0%) in ACL-deficient knees, including in children and adolescents, but Seil and colleagues identified an even higher rate of 41% in those with a contact rather than noncontact mechanism of injury. Additional previously reported risk factors for the occurrence of ramp lesions in ACL-deficient knees include male gender, patients younger than 30 years, revision ACL reconstruction, chronic injuries, preoperative side-to-side anteroposterior laxity difference of 6 mm or more, and the presence of concomitant lateral meniscal tears. The presence of any of these factors should raise the index of suspicion for the existence of a ramp lesion.
The accurate detection and treatment of these lesions is essential for restoring knee kinematics and abolishing residual knee laxity. When ramp lesions are overlooked in an ACL reconstruction, anteroposterior and rotational instabilities persist, increasing the risk of failure of the reconstruction. Because of the high incidence of ramp lesions, surgeons must be highly suspicious of this diagnosis when evaluating a patient with ACL rupture and be aware that there are no specific physical examination tests for ramp lesions.
MRI can be helpful in the detection of a ramp lesion, but it is important to note that it has low to moderate sensitivity and a recognized rate of missed diagnoses. Recently, a broad range of sensitivities of both 1.5T and 3T MRI for the detection of ramp lesions has been reported by DePhillipo and colleagues (48%), Hatayama and colleagues (71.7%), and Arner and colleagues (53.9%–84.6%), with a high specificity (>90%). The most specific sign in the MRI evaluation of ramp lesions is the hyperintense signal that can be observed between the meniscus and the capsule ( Fig. 2 ). However, most acute knee MRI evaluations are performed with the knee in full extension, which reduces the meniscocapsular gap, and can lead to false-negative tests. The MRI detected presence of bone bruising in the postero-medial tibial plateau has also been associated with ramp lesions, at a rate that varies from 38.5% for Hatayama and colleagues, 66.3% for Kumar and colleagues, and 72.0% for DePhillipo and colleagues.
Arthroscopy is considered gold standard for diagnosis of ramp lesions. However, it is not without pitfalls. Forty percent of ramp lesions are not identified through standard anterior portal visualization and inspection of the posterior compartment via a trans-notch view, and posteromedial probing is required to identify them. This is of particular importance, because these missed tears are repairable.
Ramp lesions may be classified into 5 types according to their morphology ( Fig. 3 ):
Type 1 : Meniscocapsular lesions. These lesions are very peripherally located in the synovial sheath. Mobility at probing is very low.
Type 2 : Partial superior lesions. These lesions are stable and can be diagnosed only by a trans-notch approach. Mobility at probing is low.
Type 3 : Partial inferior or hidden lesions. The lesions are typically subtle or not immediately visible even with trans-notch visualization but can be strongly suggested by significant mobility on probing and also by identification of abnormal tissue quality on needling.
Type 4 : A complete tear of the red-red zone. Mobility at probing is very high.
Type 5 : A double tear involving the meniscocapsular junction and a second more anterior tear of the posterior horn.
As these lesions occur, by definition, in a well-vascularized zone, isolated tears that are small (less than 10 mm) and stable may amenable to conservative treatment. If these conditions are not met, suture of the tear is recommended. One of the most popular surgical techniques for treating meniscal ramp lesions is the use of a posteromedial portal suture hook device. This is used to pass a suture through the injured area, which is then tied with sliding knots (described later in this article). More recently, some investigators have proposed alternative treatments like a classic all-inside suture technique or even abrasion and trephination of stable lesions (without repair), when they measure less than 1.5 cm, at the time an ACL reconstruction. Although these studies provide important information, they do not provide sufficient evidence to guide optimal treatment. In contrast, some surgeons have suggested that acute repair is necessary for ramp lesions because the capsular portion of the torn meniscus has a tendency to retract inferiorly, away from the tibial plateau, making it less likely for the tissue to heal spontaneously, thus requiring a specific posteromedial approach for the repair.
An important characteristic of the ramp lesion and one of the reasons why it has been underdiagnosed over the years is the difficulty in observing the tear via classic anterior portals, because the medial femoral condyle is located between the arthroscope and the posterior meniscocapsular junction, where it occurs. This is particularly true in varus knees and in those knees with a tight medial compartment. Some strategies have been proposed to improve visualization of the posteromedial aspect of the knee, including the use of a leg holder for joint distraction along with a large inflow cannula ; or pie crusting of the medial collateral ligament. Despite application of these techniques, the view of the peripheral area of the meniscus remains restricted. To better assess this region, a trans-notch approach is recommended because it provides better visualization of the posterior meniscocapsular junction. Although a ramp lesion may be suspected by increased mobility of the meniscus, it is essential to perform a direct visualization of the posterior meniscocapsular junction, because some of these tears (types I and II) may seem stable when inspected through anterior portals, even after probing. Observing this scenario, Sonnery-Cottet and colleagues have proposed a systematic arthroscopic exploration of the knee joint, using a 30° scope, which includes 4 steps:
Step 1: Standard arthroscopic exploration
Step 2: Exploration of posteromedial compartment and probing the meniscocapsular junction with a needle
Step 3: Creation of a posteromedial portal
Step 4: Meniscal repair procedure
Step 1: Standard Arthroscopic Exploration
The patient is positioned supine on the operating table with a tourniquet applied high on the thigh. A foot support is used to maintain the knee at 90° of flexion during the procedure, while allowing it to be manipulated through full range of motion, as needed ( Fig. 4 ). A standard high lateral parapatellar portal is created for visualization with the arthroscope, while a medial parapatellar portal is created for instrumentation.