A meniscal tear might be removed, repaired, or not treated at all. What might dictate the choice of treatment?
A meniscal tear might cause local pain (likely from the joint capsule, as the meniscus has no pain-sensing nerves), it might provoke swelling in the knee (effusions), and it might cause mechanical symptoms such as catching or locking. Also, a torn meniscal will not provide the shock-absorbing, load-distributing and stabilizing tasks that a normal meniscus would. Then again, some meniscal tears cause no symptoms, and those that are symptomatic might quiet down on their own.
In a young person without arthritis, the goal of treatment for meniscus tears is, foremost, to restore normal meniscal function–absorbing shock and distribution the load of the femoral condyle across a broader surface area. Because the loss of those functions leads to knee arthritis, any meniscal tear in a young patient that is amenable to meniscal repair should be repaired.
The location of a meniscus tear is the major factor to determine if a tear is repairable. Peripheral (so called “red zone”) tears are most likely to heal; central (“white zone”) tears (usually) do not (Figure 1). That is because the blood supply to the meniscus enters it from the capsule at the periphery. That is, the peripherally-located red zone is the most perfused and the centrally-located white zone is the least perfused. The closer the tear is to the capsule, the more suited the tear is for attempted repair.
Figure 1: LEFT An axial view of the medial (red) and lateral (blue) meniscus atop the tibial plateau. The articular cartilage that is not covered by the menisci is shown in yellow, and the (cut) cruciate ligaments are shown in purple. RIGHT: the “red zones” of the menisci are shown (no surprise) in red. (modified from Gray’s Anatomy, https://en.wikipedia.org/wiki/Meniscus_(anatomy)#/media/File:Gray349.png
Another consideration is the configuration of the tear (Figure 2). Meniscal tears are described as radial tears (those that start on the central margin of the meniscus and propagate peripherally), horizontal cleavage tears (those that lie within the meniscal tissue, parallel to the tibial plateau), and longitudinal tears (a top-to-bottom tear in the meniscus, the courses parallel to the capsule, perpendicular to the plateau).
Figure 2: A radial tear is highlighted in red, a horizontal cleavage tear is highlighted in blue, and a longitudinal tear is highlighted in green. (Courtesy: modified drawing courtesy of Dr. Matt Skalski, Radiopaedia.org, rID: 55569.)
A bucket handle tear (Figure 3) is a specific form of a large longitudinal tear in which a large fragment is still tethered anteriorly and posteriorly, with the central piece flipped (like a bucket handle) into the intercondylar notch.
Figure 3: A bucket handle tear of the meniscus: the displaced fragment, tethered to the anterior and posterior aspects of the intact meniscus, is said to resemble the “bail handle” of a bucket, resulting in a loop that moves freely within two fixed mounts on the rim. (Courtesy: drawing courtesy of Dr. Matt Skalski, Radiopaedia.org, rID: 55569. Photo courtesy Wikipedia)
Bucket handle tears are notorious for blocking motion and thus are more likely to need surgery. Because excision will lead to a loss of a large amount of tissue, a repair is usually attempted even if the edge is not in the optimal location in the red zone.
The larger the meniscus tear, the more motivated we’d be to try to save it, as more meniscus will be lost if it fails to heal. Also, very small peripheral tears are apt to heal on their own. If a radial tear is to be treated, (Figure 4) it almost always must be excised, not repaired as these tears, by definition, involve the most central aspect of the white zone. (It is not possible to be further from the capsule!)
Figure 4: An arthroscopy photo of a radial meniscal tear: a metal probe is seen coursing from roughly the 7 o’clock position towards 1 o’clock to displace the free edge of the torn meniscus into the joint space. This displacement, which can occur during normal knee motion, is thought to be the source of symptoms. The displaced fragment can cause a catching sensation, but also by tugging on the remaining meniscus can irritate the (very sensitive) capsule to which the meniscus is attached at the periphery. (The red arrow indicates the force applied on the probe, which is displacing the beak of the meniscal tear and making its extent more apparent.)
Another final consideration is the “quality” of the tissue. If the torn piece of meniscus is badly damaged or macerated, excision is chosen, as the tissue is not likely to function even if the suture line were to heal.
If the patient is older, and presumed to have at least some arthritis, treatment is dictated by the presence and severity of symptoms. Most surgeons would offer surgery sooner if there are so-called mechanical symptoms, such as catching, locking or blocked motion. In those case, partial meniscectomy is performed. (This is likely the most common operation in orthopaedic surgery in the US.)
Another reason surgery may be chosen is the presence of recurrent effusions. Typically, surgery is selected if the patient remains in too much pain despite a course of non-operative treatment.
Note that if the joint is presumably not pristine and if there are no mechanical symptoms, it is certainly reasonable to defer operative treatment, as symptoms very well may resolve. For those patients, the treatment offered is usually some combination of physical therapy, pharmacologic therapy (e.g. NSAIDs) or benign neglect. Physical therapy is thought to be helpful to prevent stiffness and atrophy and a motivate a patient to more willingly accept a non-operative approach.
Additional Points to Consider
For many years, the menisci were thought to be vestigial, serving no specific function; thus, surgeons routinely removed them. In 1948, Thomas John Fairbank published a paper, "Knee Joint Changes After Meniscectomy" in the Journal of Bone and Joint Surgery reporting that total meniscectomy produced squaring of the femoral condyles, peaking of the tibial spines ridging, and joint space narrowing. This form of arthritis is now known as “Fairbank’s changes.”
Because a meniscal tear can cause arthritis, it’s common to see a patient present with both arthritis and meniscal tear. In those cases, it can difficult to determine if the pain associated with a meniscus tear is from the tear itself, is part of an overall arthritic process, or is an incidental finding.