Meniscal ramp lesion, defined as peripheral detachment lesion of posterior horn of medial meniscus, usually occurs at the time of acute ACL rupture and in knees with following chronic ACL laxity after ACL rupture, which significantly increases with time until 24 months after initial ACL injury. Patients younger than 30 years of age and male patients were more susceptible[3].
ACL rupture will increase tibial anterior translation and internal rotation, which make medial meniscus to ‘‘engage’’ the posteromedial femoral condyle and act as a wedge against the postero- medial tibia[6,7,8]. On the other hand, Hughston[9]suggested that semimembranosus muscle contraction with wedge effect of PHMM would produce great stress at the meniscocapsular junction and possibly result in a peripheral meniscocapsular longitudinal tear (Ramp lesion).
But in our clinic, isolated meniscal ramp lesion without obvious ACL rupture were observed in some patients. ACL longitudinal splits or minor laxity were observed arthroscopically in these patients. An important suspicious finding during probe examination is probe insertion into menicsocapsular junction despite the lack of a visible lesion in the posterior horn of medial meniscus.
During intraoperative ACL integrity assessment, there are maybe following conditions: a. normal (synovium intact) b. synovium damaged c. longitudinal splits d. partial rupture e. complete rupture. ACL longitudinal splits or minor laxity were observed intraoperatively with probe tensioning in these patients. ACL longitudinal splits will cause minor anterior and internal rotation instability. To resist the minor instability, semimembranosus muscle will contract. Minor instability and semimembranosus muscle contraction may cause wedge effect of PHMM and stress increase in meniscocapsular junction of PHMM and gradually result in isolated ramp lesion without obvious ACL rupture. The mechanism of isolated meniscal ramp lesion without obvious ACL rupture is similar to ramp lesion with following chronic laxity after acute ACL rupture.
In young patients, ACL longitudinal splits may be caused by daily knee pivot activity or hyperextension. In older patients, ACL longitudinal splits may be caused by degenerative osteoarthritis, such as impingement and attrition of ACL by intercondylar fossa osteophyte.
PHMM is known to have secondary effect of limiting anterior translation of tibia[10]. Ramp lesion repairing significantly increases postoperative knee function following ACL reconstruction[11]. Peltier[12]concluded Ramp lesions appear to play a significant role in knee stability and also increase the forces in the ACL. Numerous other investigators have demonstrated that isolated ACL reconstruction fails to restore normal joint kinematics and results in residual laxity in the presence of a ramp lesion.[5,12,13] Furthermore, it has been demonstrated that repair of Ramp lesions abolishes [13,14,15] the pathologic increase in laxity and therefore provides a biomechanical rationale for identifying and repairing these lesions.
Isolated ramp lesion without obvious ACL rupture also need to be repaired to increase postoperative knee function. Pre-operative identification of isolated ramp lesions may aid surgeon in surgical planning and patient education to improve postoperative knee function, which may have otherwise been missed. The patient with posteromedial knee pain and limitation of flexion or squatting will give surgeon suspicion of ramp lesion. If physical examination shows negative lachman test or anterior drawer test, isolated ramp lesion without obvious ACL rupture should be considered. Pre-operative MRI is necessary to detect ACL integrity and isolated ramp lesion. Combined with patient symptom, physical examination and MRI examination, isolated ramp lesion without obvious ACL rupture may not be missed preoperatively.
Arner et al reported that Sensitivity of detecting a ramp lesion on MRI ranged from 53.9 to 84.6%, while specificity was 92.3-98.7%. Negative predictive value was 91.1-97.4%, while positive predictive value was 50.0-90.0%. MRI studies investigating Ramp lesions suggested the presence of posteromedial tibial edema, and detachment between medial meniscus and joint capsule as the most significant indicator of a Ramp lesion[16].
According to Sonnery-Cottet classification[17], isolated ramp lesion without obvious ACL rupture is meniscocapsular rupture without meniscotibial ligament disruption (Type1). These lesions are very peripherally located in the synovial sheath of posteromedial capsule. Their mobility at probing is very low. These characteristics make it possible to perform all-inside isolated ramp lesion repair with Omnispan meniscal repairing system through routine anterolateral and anteromedial portal. Because of longitudinal rupture of isolated ramp lesion, horizontal mattress suture can be performed to restore good stability. After 3 months, these patients can acquire healing of isolated ramp lesion (Figure 1) because of good blood supply in Ramp region and good repairing stability.
Arthroscopy is considered gold standard for diagnosis of ramp lesions[18]. However, it is not without pitfalls[19]. 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[17,18].
Improved visualization through intercondylar view is key to (1) improved diagnosis of Ramp lesion[20], (2) better diagnosis through probing and debridement from posteromedial portal before repairing, and (3) better control of the complete closure of the Ramp lesion[21], all of which lead to a better healing rate for these lesions. After diagnosis confirmation through intercondylar visualization, debridement from posteromedial portal before repairing is important. Then horizontal mattress all-inside suture of meniscocapsular rupture can be performed through anteromedial portal with routine anterolateral view[22]. For longitudinal ACL spilt, we utilize radiofrequency to shrink ACL and increase ACL tension. Together with all-inside meniscal ramp lesion repair, the instability was well decreased.
Postoperatively 3 months later, MRI was used to confirm meniscocapsular rupture healing with improved knee function score and no posteromedial knee pain or flexion/squatting limitation. MRI signal of healing meniscocapsular rupture manifests as low signal meniscocapsular attachment. Because of unwillingness for surgery of Chinese patients, we can not acquire second-look arthroscopic examination to confirm meniscocapsular rupture healing.