Rediscovering the Posteromedial Corner of the Knee

You might not realize it, but the knee actually has corners. It may look like your leg is round on the outside but inside are complex bony and soft tissue structures in a location referred to as a corner. Injury to any of these "corners" that goes untreated can create a painful, unstable knee even after surgery for the presenting knee problem.

There are two corners in the front (anterior) and two in the back (posterior. Then add one from each side: medial (side closest to the other knee) and lateral. Combining front and side and back and side gives us corners named anteromedial, anterolateral, posteromedial, and posterolateral.

The corners of the knee are made up of a very complex system of soft tissues woven together. The way in which they share the load makes an injury of one ligament likely to affect the function of others as well. Sometimes where one ligament ends and another begins is impossible to tell. Likewise, many of the ligaments are attached to the joint capsule surrounding the joint (or to the joint itself) in very unique ways. Connective tissue called fascia is also part of the soft tissue structures that helps hold everything together at each corner.

In this article, the posteromedial corner (PMC) of the knee is the area of interest. In this corner are the posterior oblique ligament (POL), part of the hamstring muscle/tendon, the oblique popliteal ligament (OPL), and the back curved corner of the meniscus. Injuries to the PMC may go unrecognized and untreated. Often, an injury severe enough to damage the soft tissue structures of the PMC means there are other ligaments and soft tissue structures damaged as well.

For example, it's usually pretty obvious if either of the main ligaments that criss-cross inside the joint are injured (posterior cruciate ligament or anterior cruciate ligament). Reconstructive surgery for either of these ligaments without repairing damage to the posteromedial corner may fail to take care of the problems (pain and instability). That's when the surgeon goes looking for a multiligament and/or medial-sided problem to account for the ongoing symptoms. If the joint doesn't line up as it should, then uneven forces applied to the joint can wear down the graft tissue used in the reconstructive procedure. The result may be a failed surgery.

As mentioned, traumatic force from an injury strong enough to tear one ligament is often enough to rip adjoining soft tissues. Identifying all areas of damage and injury is important in restoring normal biomechanics and function. How is this done? Surgeons rely on several tools. First, there is the patient history (how the injury happened) and the injury pattern (what was injured -- muscles, tendons, ligaments, bone).

Then comes the examination. All of the physical findings are considered. Joint motion, areas of ligament laxity or looseness and any results from imaging studies (X-rays, MRIs) are reviewed. The final diagnosis and full extent of the injury/damage may not be clear until an arthroscopic examination is performed. With the patient relaxed under the influence of anesthesia, there's no painful muscle guarding so the injury can be probed thoroughly. The surgeon checks for any movement that should not be there in the knee meniscus, tibial plateau, tibia, or femur.

Treatment depends on the diagnosis. Many problems are still handled conservatively with rest, support, medications, and activity modification. Mild medial-sided knee injuries (labeled grade I) affecting the corners usually don't require surgery. The medial collateral ligament (MCL) has a healing capacity of its own. In fact, when there is a mild MCL tear along with a cruciate ligament tear, the surgeon may decide to postpone reconstruction of the cruciate ligament until the MCL has healed first.

Moderate-to-severe medial-sided injuries combined with other ligament injuries may not recover without surgical intervention. Whenever pain and limitations are still present six months later, surgical repair or reconstruction may be required. How does the surgeon put it all back together with everything woven together like in the natural knee? Is it possible to restore the natural biomechanics of the knee? Should everything be repaired at once? How long can surgery be delayed to allow natural healing but not compromise the structures that don't heal on their own?

The authors conclude by saying these are all questions that are heavily debated in the literature. The main point is to make sure knee injuries are examined carefully enough to identify damage to the corners. The most common techniques for reconstructing the posteromedial corner of the knee are reviewed. Details are discussed regarding type of graft material to use (e.g., taken from the patient or from a donor bank) and fixation method (e.g., bioabsorbable screws). Photos taken during arthroscopic examination and open surgery are provided to guide the surgeon making repairs to this area of the knee.

Reference: Lisa M. Tibor, MD, et al. Management of Medial-Sided Knee Injuries, Part 2. In The American Journal of Sports Medicine. June 2011. Vol. 39. No. 6. Pp. 1332-1340.

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