As you may be aware, knee injuries are a strong clinical interest of mine. To increase my understanding of this very important joint, I sat down with Orthopedic Surgeon Dr Chris Raynor to find out more information on the menisci (AKA the “shock absorbers” of the knee).
For those who don’t know Chris, Chris is an orthopaedic surgeon specializing in sports medicine. He is staff at the Cornwall Community Hospital, and runs clinics at the University of Ottawa, and at his brand-new integrated healthcare facility in Ottawa’s southeast end – Human 2.0.
He completed his residency in orthopaedic surgery at the University of Ottawa, and he did a fellowship in sports medicine and arthroscopy at the University of Western Ontario’s renowned Fowler/Kennedy Clinic. Dr. Raynor’s patients have included amateur and competitive athletes from a variety of sports, CIS varsity athletes, MMA fighters, rodeo athletes, and professional CFL players. He believes that movement is medicine, and he wants to help people inject as much physical activity into their lives as possible.
So without further ado, here’s our discussion on meniscus injuries. I hope you enjoy our chat and learn something new!
Mick: Thanks for your time today Chris! Can I start off with this one - What are the menisci in the knee, and what is their function?
Chris: No problems at all Mick. Within the knee there are two menisci – one medial and one lateral, and they have three primary functions. Number one, their role is to act as a shock absorber. Number two, they provide a force distribution mechanism within the knee so that there are not any areas where force in the knee can be loaded in one particular area. And lastly, they serve to help maintain some form of stability within the knee outside of the knee ligaments. Much in the same way a chock block would function if you were trying to stop a car from rolling downhill and you put a wedge behind the back wheels. The menisci function in that same way, so that when the knee is moving into flexion, they prevent the femoral condyles rolling off the back of the tibial surface.
Mick: Interesting to hear they are more than just a “shock absorber”. How would you injure your menisci and what could happen as a result in the short and long terms?
Chris: There are a number of ways in which you can injure the menisci, either individually or in pairs, and typically you're going to have one of two mechanisms. Firstly, you can have direct loading of the meniscus so that the femoral condyle is basically loaded directly onto the tibial surface and compresses the meniscus. Think compression injury from landing on a stiff straight knee. The more common mechanism however is going to be when the meniscus is exposed to a shear force. In this case, the femoral condyle is sliding across the surface of the tibia with the meniscus in between. And what happens is that as the bone slides across the meniscus, the meniscus gets pulled one way by the femoral condyle and another way by the tibia. This would be common in pivoting or change of direction movement.
Now in the short term, you're likely to have pain in the knee, and you're going to have the development of fluid and swelling in the knee, which will basically stretch the capsule of the knee until it is taut adding to the pain state. Then you're likely to have short term stiffness in the knee and a loss of range of motion - an inability to straighten or bend the knee. Depending on the pain, swelling and loss of range of movement, you may also have decreased ability to walk.
In the long term, however, this is where you can sometimes see the real detrimental effects of an injured meniscus. Because of their role in force distribution and force absorption at the knee, the loss of a functioning menisci results in degenerative changes to the knee.
Mick: Not all meniscus injuries are created equally are they Chris? Can you take us through the different types of meniscus injuries that one could sustain?
Chris: Sure. So there are a number of different types of meniscal injury. Some may be more severe than others. First you can have meniscal tears that are only partial, as opposed to complete or full meniscal tears. And what we mean by that is that the tear does not extend all the way through from top to bottom. So that's the broad headings.
But then when you look at the specific types of meniscus tears, you can have something that we call a horizontal meniscus tear, which is usually a simple tear that follows the circumferential fibres of the meniscus. It usually does not involve a significant part of the meniscus, and it is usually close to the edge, the inside edge. It only extends over a very short distance and is the most benign or the simplest meniscus tear that you could have.
Then if you allow that to progress and one end of that breaks off, you can have what we call a radial tear that runs perpendicular to the circumferential fibres of the meniscus. Sometimes, these may progress to become a “parrot-beak” tear, which is basically a radial tear that has extended further across, and then into, the meniscus body. These types of tears are considered full-thickness tears, as they've gone into the substance of the meniscus.
Next you can have what we call a bucket handle tear, which is a full thickness tear that follows the curvature of the meniscus. It’s called a bucket handle because if you kind of look at it from the side, the large portion of the meniscus looks like a bucket, and when the inner part flips onto itself into the notch, it looks like the handle of a bucket. With a bucket handle tear, it is considered a more severe tear, and often cause the knee to “lock”.
Finally, you can have something that we call a complex tear, which is a tear that has several different planes to it. It may have a horizontal component, but it may also have a vertical component or a parrot-beak component or a radial component.
Aside from the specific types of tears, the other thing that we need to consider is the location of these tears. If you were to look at the meniscus from the top down, the meniscus is divided into three zones based on the vascularity of the meniscal segment. The outermost edge of the meniscus, the portion of the meniscus that's closest to the capsule, is called the “red-red” zone. And this is the zone of the most abundant vascularity (blood supply), and is the part of the meniscus which is most likely to heal. Conversely, the innermost edge is what's called the “white-white” zone, which is the least vascular part of the meniscus, and this is the part that is unlikely. Then In between the two zones, we have the “red-white” zone. And this is intermediate vascularity. And so as long as we provide an ideal milieu for healing meniscal tears in that zone could possibly heal themselves if appropriately stabilized and we give them the appropriate time to do so. Location of tears can also be defined by where the tear occurs in relation to the meniscus itself. Locations of tears may include the body of the meniscus, the anterior horn, the posterior horn, the anterior root, or the posterior root.
Mick: Very good. You mentioned before that a person may experience “locking” sensations when they injure their meniscus. The “locking” sensations that people describe; are they a consistent “locking” or can it be transient?
Chris: The “locking” is typically related to a specific knee position or angle, and it can certainly be transient in nature. Usually patients will say to me that they were doing a particular movement when locking occurred. They pivoted or they were in deep knee flexion, and they were able to get into that position, but then suddenly when they tried to get out of that position and then tried to straighten the leg, it would “lock”. And usually that would be at about 10 to 15 degrees of extension, and they were unable to get it straight for all that they tried to do. But then over the next day or so, after they were relaxed, they would feel a little click or a clunk or something move. And then all of a sudden, they'd be able to straighten their leg again. So it's something that is transient, and in some cases unpredictable.
Sometimes people, when they describe “locking”, they will say, "Oh yeah, my knee locks," but the knee actually doesn’t lock. They'll mean that they heard a click, or that it was painful, so they didn't want to extend it, but that extension was still possible. So I'll specifically say to them, "When you bend your knee, are you able to bend it freely?”. I also ask “When you go to straighten your knee, is there something mechanically stopping you from fully extending it?". I specifically use those words just so that there's clarity. I don't say locking. I just ask them if there's a mechanical block, because from a surgical perspective, that's what we surgeons think of as “locking”.