Diagram of a meniscus tear

Knee Cartilage Tears

There are two type of cartilage within the knee joint, Hyaline or articular cartilage and meniscal or Fibrocartilage.  In order to understand how I treat each tear 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. 

Microscopic photographs of Fibrocartilage (left) and Hyaline cartilage (right)

It is a very highly organized structure with numerous cells and hyaline cartilage repair and healing is one of the holy grails of orthopaedic scientific inquiry. Fibrocartilage, conversely, is mostly fibrous tissue with few cells and resembles a tendon under the microscope.  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 incogruence 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.

Diagram showing types of meniscus tears

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 mensicus without serious consequence to the joint long term.  Removing the entire meniscus can lead to degeneration, but I rarely remove the entire meniscus for a tear and 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.  I probably see at least 5 patients per day in clinic with meniscus tears.

Diagram showing articular (hyaline) cartilage and meniscus (fibrocartilage)

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.  The meniscus can be excised without much consequence but the hyaline cartilage cannot.  So the treatment follows this basic premise:  I remove torn menisci to protect and prevent damage to the hyaline cartilage. I 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, I treat this with joint replacement (either partial or total).

Appearance of normal menisci on MRI, notice they are uniform, dark triangular structures

So to review, meniscus tears are one of the most common conditions which bring patients into the office for evaluation.  Most patients do not remember a specific activity which precipitates the pain but rather describe a more insidious (gradual) 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.  Many are caused by inconspicuous activity such as bending down to pick up and object. Unlike arthritic pain, patients with meniscus tears often complain of fairly sharp pain in the knee with a sudden onset.  Most do not have prodromal symptoms (mild symptoms before the tear occurs). 

MRI scans showing tears of the mensicus

I 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 I 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 1/3 will respond well to the injection and won't need further work-up.  A number of other inflammatory conditions can mimick meniscal tears so an MRI is not always automatically ordered.  In patients that fail to improve with corticosteroid injection or who have relief of pain for a short periof of time and then have the pain return,  I will usually order an MRI which is a specialized imaging study that allow me to evaluate the cartilage and ligaments around the knee to assess the size and character of the tear. Smaller tears can often be managed without surgery and I treat these with a combination of physical therapy, anti inflammatory medications and occasionally, corticosteroid injection.

Intra-operative photos showing normal Articular and meniscus cartilage (probe under the normal meniscus)

Larger tears are often 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.  These symptoms are explained by a large tear of the cartilage that becomes displaced, wedged inside the joint and then frees up again and gets pushed "back into its normal postion".  In patients with large tears or mechanical symptoms such as locking or recurrent effusion (fluid in the joint) I will recommend surgical debridement 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 does not have a blood supply, that is it 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 which is the gliding cartilage that covers the end of the bones.  Loss of hyaline cartilage is irreparable and can lead to premature osteoarthritis.  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.  For these reasons I recommend removal of the torn fragment of meniscus as soon as possible; delaying the surgery can lead to irreparable damage to the gliding cartilage in the knee joint.

Drawing showing how arthroscopy is performed

Mensicus Surgery:

This is done as a brief (20-30 minute) outpatient procedure and recovery is very quick. Most patients are able to walk comfortably within 10 days of surgery although I ask patient to limit their activity and not engage in sports for the first 4 weeks after surgery. I use two small incisions in the front of the knee (about 5mm in length) for the arthroscopic clean out.  Most patients do not require physical therapy after surgery. Recovery is rapid and most patients are able to resume light aerobic activity after 4 weeks and full exercise at 8 weeks.

Arthroscopy photos of normal meniscus (left) and torn meniscus (right)

The only exception is in cases of mensicus tear with extensive damage to the hyaline cartilage in the same area.  I find this is a common presentation for heavier patients in their 50's who are referred over for treatment of a meniscus tear.  The MRI is very sensitive for mensicus tears but its ability to visualize hyaline cartilage damage is very limited.  In these cases the MRI does not show the extensive hyaline cartilage damage and this is discovered at the time of surgery.  Unlike isolated meniscal tears, recovery from extensive hyaline cartilage tears is very protracted.  I would estimate that roughly 1/3 of patients with this presentation will have poor control of pain after arthroscopy and have a partial knee replacement to treat the loss of hyaline cartilage.  So in patients in their 50's with meniscus tears I always discuss the possibility of finding hyaline cartilage damage at the time of surgery and that if I find this to be the case the arthroscopy will not help their symptoms a great deal.

Arthroscopy photo showing normal hyaline cartilage (L) and torn hyaline cartilage with exposed bone (R)