There are two type of cartilage within the knee joint, Hyaline or articular cartilage and meniscal or Fibrocartilage. IIn order to understand each tear is treated, it is important to understand what each type of cartilage does. Hyaline cartilage is a very smooth material that coats the ends of the bones and allows them to glide past each other with very little friction.
It is a very highly organized structure with numerous cells. Hyaline cartilage repair and healing is one of the holy grails of orthopaedic scientific inquiry. Any injury to the joint (fractures, ligament tears, infection) can cause damage to the hyaline cartilage. Once the damage is done, it is irreparable and mature hyaline cartilage lacks the ability to remodel. There are several surgical interventions to transplant hyaline cartilage into an area of damage, but this technology is very expensive, poorly understood and very limited in its ability to provide long term healing. Because of this surgeons are very careful to minimize the potentially damaging effects of various insults to the hyaline cartilage. For example, any fracture that enters into a joint and has any residual incongruence is reduced (lined up) and fixed to minimize the ongoing damage to the hyaline cartilage. Damage and loss of the hyaline cartilage leads to osteoarthritis of the joint.
Fibrocartilage is mostly fibrous tissue with few cells and resembles a tendon under the microscope. The meniscus is a ribbon of fibrocartilage that runs along the periphery of the weight bearing surface of the joint. Like hyaline cartilage it is avascular (meaning it has no ability to heal itself and remodel) but unlike hyaline cartilage, we can safely excise torn portions of the meniscus without serious short term consequence to the joint. Removing the entire meniscus can lead to degeneration but this is rarely necessary. Removing small portions has not been shown to be detrimental in the long term. Think of the meniscus as a shock absorber cartilage that helps to protect the hyaline cartilage. Tears of the meniscus, especially the medial meniscus are very common.
Isolated tears in the hylaine cartilage are unusual and these tears are usually associated with some other condition such as a fracture or large meniscus tear. Unlike meniscal tears which can be debrided and the torn portions excised, when hyaline cartilage is lost it leaves behind exposed bone which is very sensitive to pain. Loss of articular or hyaline cartilage is also referred to as osteoarthritis. So the treatment follows this basic premise: We remove torn menisci to protect and prevent damage to the hyaline cartilage. We transplant hyaline cartilage into defects to arrest the degeneration of the joint and prevent further arthritis from developing. If arthritis and cartilage loss have already taken place and are extensive, a joint replacement operation may be indicated (either partial or total).
So to review, meniscus tears are one of the most common conditions that bring patients into the office for evaluation. Patients may not remember a specific activity that precipitated the pain but rather describe a more insidious (gradual) onset. Many tears are caused by inconspicuous activity such as bending down to pick up and object. Others remember a fairly sharp pain in the knee with a sudden onset. Regardless of the cause, most patients describe stiffness in the knee, pain in a fairly specific location around the tear, clicking and some have fluid collection in the joint.
We generally start with an x-ray to make sure there are no other potential causes of the pain such as arthritis. In patients with mild symptoms and an otherwise normal x-ray we may try an injection of corticosteroid to relieve the inflammation prior to proceeding with an MRI. In patients without mechanical symptoms (locking and catching), about one out of three will respond well to the injection and will not need further work-up. A number of other inflammatory conditions can mimic meniscal tears so an MRI is not always automatically ordered. In patients who fail to improve with corticosteroid injection or who have relief of pain for only a short period of time, we will usually order an MRI. This will allow us to evaluate the cartilage and ligaments around the knee and to assess the size and character of the tear. Smaller tears can often be managed without surgery, namely with a combination of physical therapy, anti inflammatory medications and occasionally, corticosteroid injection.
Larger tears may be associated with mechanical clunking or locking in the joint as the fragment of cartilage binds inside the joint and prevents it from moving properly. This “locking” is often sporadic in nature and patients will have periods of minimal symptoms mixed with periods of severe pain and limited range of motion. In patients with large tears or mechanical symptoms such as locking or recurrent effusion (fluid in the joint), surgical debridement is advised for a couple of reasons. The most obvious is that removing the torn fragment provides rapid relief of pain essentially immediately after the surgery. Patients with large, displaced tears (also referred to as bucket handle tears) often describe dramatic relief of pain after removal of the torn fragment. Second, the meniscus tissue itself is avascular. The consequence is that the meniscus has no ability to repair or remodel after a tear. Therefore, if you have a large meniscus tear, it cannot heal itself over time. Finally, the larger tears can cause damage to the hyaline cartilage. Loss of hyaline cartilage is irreparable and can lead to premature osteoarthritis.Delaying the surgery can lead to irreparable damage to the gliding cartilage in the knee joint.
This is done as a brief outpatient procedure and recovery is very quick. Most patients are able to walk comfortably within 10 days of surgery. Patients should limit their activity and not engage in sports for the first 4 weeks after surgery. We use two small incisions in the front of the knee (about 5mm in length) for the arthroscopic clean out. Recovery is rapid and most patients are able to resume light aerobic activity after 4 weeks and full exercise at 8 weeks.
A common exception is in cases of mensicus tear with extensive damage to the hyaline cartilage in the same area. This is a common presentation for heavier patients in their 50s. The MRI is very sensitive for mensicus tears but its ability to visualize hyaline cartilage damage is limited. Extensive hyaline cartilage damage may only be discovered at the time of surgery. Unlike isolated meniscal tears, recovery from extensive hyaline cartilage tears is very protracted. Roughly 1/3 of patients with this presentation will have poor control of pain after arthroscopy and will require some sort of knee replacement to treat the loss of hyaline cartilage.
For more information about the surgery and what to expect during and after your knee surgery look at the link below for knee arthroscopy surgery instructions. It has additional information about when, where and how that you may forget to ask in clinic.