Working Diagnosis:
Left saphenous nerve neuritis, presumed left saphenous vein injury, and left posteromedial meniscocapsular separation (ramp lesion)

Treatment:
The sonographer performed a sonographically-guided left saphenous nerve hydrodissection at the adductor canal exit for presumed saphenous neuritis from recurrent saphenous vein bleeding. Hydrodissection of the saphenous nerve led resolution of her allodynia. Her medial joint line pain, however, did not improve. A diagnostic anesthetic injection of the semimembranosus tendon bursa was performed to differentiate between semimembranosus and medial meniscus pain. The patient had no improvement in her pain after this injection. The sonographer subsequently performed a sonographically guided platelet rich plasma injection in the left medial meniscocapsular space during a follow-up visit for presumed meniscocapsular separation. This was combined with targeted therapy for meniscal rehabilitation and a knee brace limiting deep flexion.

Outcome:
With these interventions, the patient has had resolution of her pain over 6 months with gradual return to all activities including swimming, soccer, skiing and CrossFit.

Author's Comments:
A ramp lesion is defined as a separation of the peripheral meniscus from the knee joint capsule and can be missed by traditional imaging, such as MRI, that lacks adequate spatial resolution. Sensitivity of MRI may be as high as 77%, but is as low as 0% in some studies. The posteromedial corner is also rarely imaged unless specifically requested.
Ramp lesions typically appear as signal irregularity in the capsular margin of the medial meniscus posterior horn, with T2 GRE sagittal images typically being the most sensitive sequence. Our case shows that ultrasound performed by a skilled sonographer may be helpful in cases missed by MRI. However, arthroscopic evaluation is currently the only reliable method for evaluation.
The patient's neuritis was likely secondary to irritation related to bleeding from greater saphenous vein injury caused by a small medial femoral condylar osteophyte noted during the ultrasound exam. Subsequent hydrodissection permitted delineation of the nerve and meniscal injuries essential to providing this patient with relief. The adductor canal is the most common location of saphenous nerve injury or irritation and can have multiple etiologies. In addition to our case, other examples include direct trauma, repetitive traction (e.g., cyclists and rowers), acute traction (e.g., patellar dislocation), entrapment in scar tissue or compression from masses. Symptoms can include vague anteromedial knee pain exacerbated with activity. It may be reproduced with Tinel sign at the site of entrapment.
The subsequent semimembranosus bursa injection helped delineate semimembranosus from medial meniscus pain given the extremely close proximity of these structures in this area of the knee. The body of the meniscus is attached to the adjacent joint capsule and tibia by meniscotibial ligaments that decrease the mobility of the medial meniscus compared to lateral meniscus and increase susceptibility to injury. Injury is most common in positions of deep flexion with rotation and with valgus stress during tibial external rotation. An injury to one structure in the posteromedial corner should raise suspicion for injury to other structures in the area, including the posterior oblique ligament, semimembranosus tendon (and expansions), oblique popliteal ligament, and posteromedial joint capsule.

Editor's Comments:
Ramp lesions can be difficult to identify as the authors mentioned. In this case it was a very skilled ultrasongrapher that made the diagnosis. Studies on the short and long term outcomes of these lesions is very limited. Treatment include nonsurgical, biologic, and surgical intervention (especially in cases of other needs for surgery, ie ACL tear) can all be considered.

References:
Chahla J, Dean CS, Moatshe G, et al. Meniscal Ramp Lesions: Anatomy, Incidence, Diagnosis, and Treatment. Orthop J Sports Med. 2016;4(7):2325967116657815. Published 2016 Jul 26. doi:10.1177/2325967116657815

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