Knee Pain: Do you (or your dog) need a Meniscus Replacement?

its-all-fun-and-games-until-you-tear-your-meniscus-b8e07I was standing watching a knee arthroscopy in theatre this week with one of the local knee guys, we were looking at a cartilage in the knee which had been squashed and torn.  This particular injury was a simple tear of the meniscus repaired with great dexterity through keyhole surgery; all while the surgeon explained that hours of Xbox games lead to the fine tuning of this skill.  I’ll leave the virtues of computer games for another post but it did however get me thinking about what to do with a meniscus that has been almost destroyed.

Menisci from above

The menisci are two pieces of tissue that add cushioning to the knee joint.  They sit between the two major bones that make up the knee – the tibia and the femur.  They are made up of fibrocartilage and shaped like crescents when looked at from above and like a wedge when looked at from the front.  This shape is important as it increases the contact area between the femur and tibia within the joint.  They are present in all mammals with varying anatomical forms.  As an interesting aside, arthroscopy is performed in dogs in some specialist vet practices but it’s still strange to think that my cat could tear a meniscus if she ever got up off the couch.  Menisci are important in distributing forces through the knee during activity.  Initially thought to be shock absorbers it is now though that in addition to this they also help keep the bones of the knee in position and provide lubrication to the joint. The fibrocartilage that makes up the meniscus is 3/4 water with the rest being collagen and then small amounts of other substances such as elastin and proteogylcans (good scrabble score on that word).  Only the outer quarter of each meniscus has a blood supply therefore tears that are closer to the inner border of the meniscus are less likely to heal by themselves.

dog meniscus
Canine Menisci 

How do I know if I have a meniscal tear? Meniscal tears are very common with two types identified.  If you are young you may have injured your meniscus when you compress and rotate the knee especially if the leg is in a straight position such as when playing netball when catching the ball a player will plant one foot and pivot around this leg making it a prime target for meniscal injury.  If you are over 40, the second type of injury is with degeneration of the cartilage and may appear without incident.  Someone with a meniscal tear will have swelling of the knee which will come on over 24hrs.  The knee can also catch and lock or conversely may collapse with pain.   Your GP or specialist will be able to identify a tear usually on clinical examination and can be confirmed on MRI scanning.

Initial treatment involves resting the knee, ice, compression and elevation, physiotherapy, simple analgesia and a slow return to exercise.  Not all tears require surgical intervention, however the moment a knee has mechanical symptoms of locking or giving way, especially when a patient is young, many orthopaedic surgeons are of the opinion that physiotherapy may further tear and damage the cartilage leading to increased difficulty of repair with poorer outcomes and increased risk of osteoarthritis in the joint.  Certain tears are even considered to be urgently in need of treatment  this being a ‘bucket handle’ type tear.

Bucket Handle Tear as demonstrated using fruit in season

  So if you have failure of conservative management, ongoing pain, locking or giving way in the knee with an MRI demonstrating a tear then referral to a surgeon would be the next step.  In the past surgeons would perform a complete removal of the meniscus although today the buzz words are ‘meniscal preservation’ aiming to remove as little as possible to still have a stable meniscus.  Repair is another option for the surgeon with around 15% of tears being repairable where the tear is repaired through the use of darts and suture material.

The experts think that around 1.7 million patients have meniscal surgery each year world wide.  While previously most tears were associated with wear and tear in older individuals, many more acute tears are now presenting sustained in a younger population associated with playing sports.  Because of the blood supply problems, resection, or removal of part or all of the meniscus, is often the best way to proceed in an operation.  This procedure is known as total or subtotal meniscectomy.  While this is often the only surgical option its important to note prior to the decision to proceed with surgery that loss of this cartilage has been associated with osteoarthritis.  One systematic review showed after 5 years 50% knees following meniscectomy will demonstrate arthritic changes.  Its important to note that a meniscal tear alone is correlated with osteoarthritic changes however with complete removal of the meniscus the stresses through the knee are doubled, meaning that total meniscectomy may actually increase the risk of osteoarthritic changes more than the tear itself.  Luckily in most situations only the damaged part of the meniscus needs to be removed and sometimes the structure can even be repaired.  So if you damage your meniscus it is likely you will need a camera in the joint to assess exactly what is going on.  MRI’s are good but don’t give the real time image of an arthroscopy.   The main intervention will be either resection of the damaged part of the meniscus or repair of the tear depending on the complexity of the tear and its position.

How the meniscus arrives to theatre for implantation

Knowing that repairing a large complex tear is difficult, and that cutting out the majority of the meniscus will leave a patient prone to early onset osteoarthritis, some surgeons on the coast are now performing meniscal replacement.  The first meniscal replacement was performed in 1984 and by 2003 there had been over 4000 US operations with 800 being performed each year using grafts from cadavers.   The main reason to do this operation is to combat pain in an area where the meniscus has been previously removed.   Some clinical studies have shown that meniscal graft may copy normal meniscal function almost completely, may reduce pain and improve knee function.  The surgery is not without its risks however and while in some patients the grafts will last 10-15 years there is a complication rate of between 6-11% of cases.   Disease spread is theoretically possible but reported to be very unlikely.  Rejection of the graft is exceptionally rare to the point where the tissues is thought to not cause immune concerns unlike other organs.  This has been correlated in some animal studies which have shown complete replacement of donor cells by host cells meaning foreign material was no longer present.

So if you are young and have ongoing pain in your knee following arthroscopic repair or resection of a meniscus a good option may be replacement of the meniscus with a graft.  Obviously more long term research needs to be done but this is a slowly growing field in orthopaedics.

  • GPearls on the GC
    • avoid a straight leg with compression and twisting forces to avoid damage to your meniscus
    • the moment a knee has mechanical symptoms of locking or giving way see your doctor
    • more computer games your surgeon has played prior to the operation apparently the greater the success of the operation.
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