What is a Knee Meniscus? What happens when you tear it?

What is a Knee Meniscus?

Your knee meniscus is a fibrocartilage that separates thigh bone (femur) from your shin bone (tibia). It is commonly referred to as your "cartilage". Each knee joint has two menisci: a medial and lateral meniscus.

The menisci of the knee have unique shape. They are a wedged, kidney shape. The menisci act like a wedge to assist with the rotational stability created by the anterior cruciate ligament.

The menisci also act as a shock absorber. As we walk, run, and jump the knee absorbs tremendous forces. The menisci help to absorb these forces so that the bone surfaces are not damaged. The amount of force increases exponentially as the speed of movement increases from walking to running to jumping. The menisci disperse the compressive forces over the entire knee rather than isolating them.

How Do You Injure Your Meniscus?

In the younger population, your knee meniscus is usually torn traumatically, by a twisting on a slightly flexed knee.

The traumatic type of meniscal injuries are most often sports-related. The meniscus can be torn anterior to posterior, radially (parrot beak), or can have a bucket handle appearance.

In the older adult, the tear may be due to a natural age-related degeneration of the meniscus or a rough arthritic femoral bone surface tearing into the softer meniscus. In this case, surgery may be required to attend to both the meniscal repair and to repair the damaged joint surface.

Depending on the type of tear, meniscus repair be complicated. Large meniscal tears that are inadequately treated may cause premature degenerative bony (arthritis) changes.

Signs and Symptoms of a Meniscus Tear

The history of a painful twist occurring on a slightly flexed knee will indicate the likelihood of a meniscal tear. You may also experience clicking, popping, or locking of the knee. These symptoms are usually accompanied by pain along the knee joint line and a joint swelling.

Clinical examination may reveal tenderness along the knee joint line. You will usually notice it is painful to squat.

Your physiotherapist or doctor will use McMurray's test and other clinical tests to confirm a meniscal tear diagnosis.

X-rays or MRI?

A MRI scan is the most accurate non-invasive test to confirm a meniscal tear. X-rays do not show meniscal tears.

Do Meniscal Tears Heal?

Meniscal blood supply is limited: the menisci get nutrition from blood and synovial fluid within the joint capsule. Your meniscus has two distinct regions that affect their ability to heal. We call these the Red Zone and the White Zone.

The red zone has blood supply, whereas the the white zone doesn’t have a blood supply and won’t heal naturally.

Red Zone: The outside of the meniscus has a blood supply from the synovial capsule. Lateral meniscal tears may heal without the need for surgery.

White Zone: The inside of the meniscus gets its nutrition from the synovial fluid. Due to this, tears of the inner meniscus do not usually heal due to a lack of blood supply to trigger an inflammatory response. These injuries often require surgery.

Treatment Options for a Knee Meniscus Tear

A small meniscal tear, or a tear in the red zone, will usually respond quickly to physiotherapy treatment. One of the major roles of your meniscus is shock-absorption. Luckily, the other vital shock absorbers around your knee are your muscles. Researchers have discovered that if you strengthening your leg muscles, your bone stresses will reduce as your muscle strength improves and your knee becomes more dynamically stable.

Your physiotherapy treatment will aim to:

Reduce pain and inflammation.
Normalise joint range of motion.
Strengthen your knee: esp quadriceps (esp VMO) and hamstrings.
Strengthen your lower limb: calves, hip and pelvis muscles.
Improve patello-femoral (knee cap) alignment.
Normalise your muscle lengths Improve your proprioception and balance Improve your technique and function eg walking, running, squatting, hopping and landing.
Minimise your chance of re-injury.

Meniscal injuries are commonly associated with other knee injuries, which need to be treated in conjunction with your meniscal tear.

How Long Does Meniscal Healing Take?

Your meniscal tear will commonly take up to six or eight weeks to fully heal. As mentioned previously, some meniscal tears will require surgery.

Your physiotherapist will guide you as to what is most likely for your knee injury. It is important to avoid activities and exercises that place excessive stress through your meniscus and further delay your healing. In some cases, your physiotherapist may advise you to keep weight off your knee. In this instances, crutches may be recommended.

Everyone is different, so be guided by your physiotherapist.

Will You Require Surgery for a Meniscus Injury?

Most surgeons will recommend a few weeks of physiotherapy treatment prior to contemplating surgery.

Pre-operative physiotherapy has two main benefits:

Successfully rehabilitating your knee injury without the need for surgery.
Strengthening your knee to better prepare you for your post-operative rehabilitation.

If surgery is required, surgery is usually performed arthroscopically (via a fibre-optic camera about the size of a pencil) to either resect (remove) the torn fragment or repair (stitch) a tear in the outer zone.

Generally, the best treatment option is to repair the torn meniscus and save as much of the shock absorber as possible. This will leave you with near "normal" structures and decrease the likelihood of degenerative arthritic changes in later life.

Post-Surgical Physiotherapy for Meniscal Injuries

Resected Meniscal Tears

Physiotherapy rehabilitation for resected meniscal tears can normally be reasonably aggressive, targeting early return to function. You will be progressed through rehabilitation as your pain and swelling allow. Most arthroscopic patients can return to normal function within 3 to 6 weeks.

Post-Meniscal Repair

Rehabilitation after a meniscus repair is usually different than a resection due to healing time require where a meniscus has been stitched. Most surgeons will have you non-weight bearing for 4 to 8 weeks to allow the meniscus to heal before commencing weight-bearing exercises. Physiotherapy rehabilitation should focus on early mobilisation of the knee (tibiofemoral) and kneecap (patellofemoral) joints, plus strengthening of your quadriceps, hamstrings and leg muscles.

Your treatment guidelines will be similar to the nonoperative approach taking into consideration the findings and operative procedures performed. For more specific information, please ask your physiotherapist.

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