Meniscal tear (Knee Cartilage)
What is the meniscus?
The meniscus is basically a set of two half-moon shaped
pieces of cartilage in the knee joint. They sit on the tibial plateau, which is
the top of the shin bone. They are triangular in cross section and there is one
each side of the joint: The outside one is called the lateral meniscus and the
inner one the medial meniscus. The lateral one is more circular and the medial
one is more open and it also attaches to the medial collateral ligament (MCL).
The Meniscus has limited vascularity and the nerve supply it has is for
proprioception not pain and these are in the outer third of the meniscus. It’s
just as well really, otherwise you’d be walking around in agony and bleeding
inside you knee joint, especially considering that it is considered that walking
produces about 3 times your body weight in your knee!
What does it do?
It helps with shock absorption, it makes the joint surfaces
fit together better so it therefore spreads the load out better, which also helps
with synovial sweep. This is spreading the lubricating nutrition filled fluid
in the joint. It is very slippy (200 times that of ice!) and so it does a great
job of reducing friction. It is involved in the locking mechanism of the knee and the
weight distribution is 55% lateral and 45% medial. So pretty impressive really!
So what is a meniscal tear?
Tears are described by how they look, where the tear occurs and
how it is caused.
How they look:
Longitudinal, flap, bucket handle, transverse, horn.
Where they occur:
Medial, lateral, posterior or anterior. Meniscal tears
present twice as much in the medial compartment of the knee and 80% are
posterior tears (Campbell et al 2001).
How it is caused:
There are either traumatic or degenerative types of tears. Traumatic are as they sound, from a one off event usually sporting in nature with a weight bearing twisting motion in a
flexed knee. A degenerative tear occurs gradually over time and is more related
to ageing. This is because the articular cartilage becomes thinner & less
elastic & blood supply is reduced. A review of 3,000 meniscectomies found
that 50% of tears were degenerative (Smillie 1968).
Interestingly one piece of research found that kneeling
occupations are found to increase the risk of meniscal tears (McMillan &
Nichols 2005).
What are the symptoms of a meniscal tear?
Sometimes you can feel a "pop" but you can often
still walk or even play on with it. Swelling and stiffness will occur over a
few days and not instantly. You can often get clicking inside your knee;
obviously you will get pain and limited range of movement. If the pain is high then your knee will give way on
you and if a piece of the tear breaks off, then you can get locking of the knee. If
this happens then you will almost certainly need to have surgery to remove the
loose piece.
How do you diagnose a tear?
A good clinical examination of the knee is up to 90%
accurate in diagnosis of a meniscal tear (Mohan & Gosal 2007).
The mechanism of injury is useful as the absence of weight
bearing during trauma may help rule out a meniscal tear (Cleland &
Koppenhaver 2005).
There is usually swelling but this doesn’t appear instantly
if the injury is purely the meniscus. If you have injured ligament then they
bleed and therefore the swelling is instant.
The McMurrays test is 16%-58% sensitive & 77%-98%
specific for diagnosing meniscal tears (Malanga et al 2003).
The Thessaly test is excellent for detecting & ruling out
meniscal tears and has a 90% sensitivity & a 98% specificity (Harrison et
al 2009).
Imaging:
Incidental findings of meniscal tears on MRI are found in 1
in 3 middle aged or elderly asymptomatic knees (Cyteval 2008), but an MRI has a
diagnostic accuracy of around 70-80% in detecting meniscal tears (McDermott 2011).
Often the diagnosis is confirmed by actually performing an arthroscopy, which involves putting a camera into the knee via keyhole. If a
tear is found they can sort it while they are inside.
So how do you treat a meniscal tear?
There is conservative treatment and there is surgery.
Conservative treatment:
For a traumatic tear conservative treatment may not work if
the tear is large and in the non-vascular portion of the meniscus. Surgery is
very likely if the tear has broken off as it will not heal in this case.
Overall if you can get some improvement in the first few weeks then it is worth
trying to treat it conservatively.
A partial meniscectomy is not recommended as a first
treatment for degenerative tears (Beaufils et al 2009). This is due to the fact
that you are losing the cartilage in your knee anyway so ideally you don’t want
to remove anymore as loss of cartilage is essentially osteoarthritis. In fact
89% of patients experience osteoarthritis following meniscectomy (Rangger et al
1997).
Generally conservative treatment is about rehabilitation
which involves strengthening, stretching, proprioceptive exercises as well as
settling pain, swelling and restoring range of movement. This piece of research
found that Quadriceps strengthening exercises & orthotics had encouraging
results for patients with knee cartilage damage (Arroll et al 1996).
The most common surgery is a meniscectomy.
This is when they go inside via keyhole and they essentially
trim and remove a piece of meniscus.
Meniscectomy vs. strengthening: No differences in relief of
knee pain, improved function, or increased satisfaction (Yim et al 2013).
Patient satisfaction was 84% following partial medial
meniscectomy & 73% following partial lateral meniscectomy (Salata et al
2010).
Risk of osteoarthritis is significantly higher after lateral
meniscectomy than after medial meniscectomy (Allen et al 1984).
Physiotherapy with home exercises improves knee function
& range of motion in patients post-arthroscopic meniscectomy (Dias et al
2013).
Other surgery:
Microfracture:
This is when they create small holes in the bone. The
surface layer of bone is hard and lacks good blood flow. By penetrating this
hard layer, this allows the deeper, more vascular bone to access the surface
layer with the aim of stimulating cartilage growth.
Meniscus repair:
Some meniscal tears can be repaired by stitching the torn
pieces back together. Success depends upon the type of tear, where it is and the
overall condition of the injured meniscus. Recovery time is much longer than
from a meniscectomy as it has to heal and this is slow.
Mosaicplasty:
A mosaicplasty moves round 'plugs' of cartilage and
underlying bone to damaged areas. The plugs are each a few millimeters in
diameter, and when multiple plugs are moved into a damaged area the result is a
mosaic appearance--the multiple small plugs of cartilage look like mosaic
tiles.
OATS:
OATS stands for 'osteochondral autograft transfer system,'
and the technique is very similar to mosaicplasty. In the OATS procedure the
plugs are usually larger, and therefore only one or two plugs are needed to
fill the area of cartilage damage.
Meniscal transplant:
A meniscal transplant replaces the damaged meniscus with
donor cartilage. This is usually done with a donor meniscus but there are
synthetic types and now they can even grow your cartilage for you outside of
your body in a lab. However between 21% and 55% of transplants fail within 10
years so there is a lot more to be done with this option for a meniscal tear.
Great information shared on meniscal tears with pictures . Thanks for sharing such a nice article.
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