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A Different Type of Knee Meniscus Tear

In this study, orthopedic surgeons from the Shelbourne Knee Center in Indianapolis, Indiana take a look at the results of treatment for a different type of knee meniscus tear. Their focus is on the posterior lateral meniscus root (PLMR).

This type of meniscal tear occurs most often when traumatic force is generated that is strong enough to rupture the anterior cruciate ligament (ACL) inside the knee. Along with the ACL tear, a posterior lateral meniscus root (PLMR) tear occurs.

With a PLMR type of meniscal injury, the main body of the meniscus (cartilage) is torn away from the root or its attachment to the bone. The tear is either straight across the C-shaped meniscus called a radial tear or at an angle (oblique tear).

As the name suggests, this type of tear occurs in the back portion of the knee along the outside edge. The more common meniscal tear is on the medial side (closest to the other knee). Medial meniscal tears are usually linked with degenerative changes in the knee rather than the traumatic ligamentous injuries associated with posterior lateral meniscus root (PLMR) tears.

What happens if the PLMR meniscal tear isn't repaired at the time that the ACL tear is surgically reconstructed? Are the long-term results the same as, similar, or different from results for medial meniscal root tears? Those are the questions these researchers attempted to answer by comparing results five years after injury in two groups of patients.

The first group had a complete posterior lateral meniscus root (PLMR) tear. The second group was the control group -- they had an ACL tear but without any involvement of the meniscus and especially no tears of the PLMR. Results were measured based on X-rays (showing joint space), level of pain, knee range-of-motion, and function.

Ten years after treatment, they found no statistically significant differences between the two groups. Yes, the patients with a PLMR tear had narrowing of the joint space along the lateral side. But this change did not seem to make any difference in function or activity for the PLMR group.

The results of this study do not answer the question of whether or not PLMR tears should be repaired at the time of reconstructive surgery for ACL tears. At the 10-year mark, it looks like leaving the PLMR tear alone is an acceptable treatment option. But what we don't know is what happens after 15 years? or 20 years? Do these patients eventually develop osteoarthritis?

The authors note that PLMR tears are difficult to repair. There are nerves and blood vessels close by that could be injured during a repair procedure. Because of the location of the posterior lateral meniscus, the risk of further cartilage damage or damage to the opposing bone (femoral condyle) is high just trying to get the arthroscopic instruments into the area.

For these reasons, until there is clear evidence that PLMR tears should be routinely repaired, surgeons are advised to leave them alone. PLMR repair should be done only when it is clear that leaving the PLMR tear will yield a worse result than fixing it.

The results of this study will be held as a baseline. Patients will be remeasured routinely and results reported again. In time, it may become clearer just what the role of surgical repair for PLMR tears really is and when to recommend leaving the injury versus repairing it.

Reference: K. Donald Shelbourne, MD, et al. Long-term Evaluation of Posterior Lateral Meniscus Root Tears Left In Situ at the Time of Anterior Cruciate Ligament Reconstruction. In The American Journal of Sports Medicine. July 2011. Vol. 39. No. 7. Pp. 1439-1443.