Q: I fell down the stairs and tore my left ACL. Since I didn't go in right away for surgery, I ended up with an unusual tear of my meniscus called a "ramp" tear. How often do these happen and why did I get one?

A: A ramp lesion involves the medial meniscus, a C-shaped piece of thick cartilage inside the knee. There are two of these protective liners: medial (side closest to the other knee) and lateral (side away from the other knee).

A ramp lesion occurs when one particular edge of the medial meniscus (near the posterior or back portion of the cartilage) comes loose. The tear is located where the meniscus meets the synovium (lining of the knee joint). It is usually a lengthwise or longitudinal tear.

It occurs most likely as a result of increased torsional (twisting) and shear forces of the tibia (lower leg bone) as it moves against the femur (thigh bone). Anytime the ACL is torn or stretched too much, the tibia can slip and slide more than it should underneath the femur. That's when the back edge of the meniscus is most likely to crack, tear, and/or pull away from the bone.

You may not be so unusual or alone with your ramp lesion. Here's why we say that. In a recent study of 868 patients with ACL injuries, there were 16.6 per cent who had a ramp lesion of the medial meniscus. This was determined through arthroscopic examination.

And from the data collected in that study, it looks like the longer the ACL injury goes untended, the more likely it is that a ramp lesion will develop. At least that was true up to 24 months after the injury. Beyond two years, the number of ramp tears that developed later leveled off.

Two additional risk factors for ramp lesions were identified: age (younger than 30) and sex (male). Three-fourths of the group only had one ramp lesion (no other tears in the meniscus). But the remaining one-fourth had a ramp tear plus one other meniscal tear -- either of the same meniscus or of the lateral meniscus.

Reference: Xin Liu, MD, et al. Arthroscopic Prevalence of Ramp Lesion in 868 Patients with Anterior Cruciate Ligament Injury. In The American Journal of Sports Medicine. April 2011. Vol. 39. No. 4. Pp. 832-837.