Knee Arthroscopy Surgery
The knee joint has two different types of cartilage in it. There is the Articular cartilage, which covers the ends of the bone and allows smooth movement of the joint surfaces past one another. The second type is the meniscus cartilage. These are cushioning shock absorbers of the knee. They are mostly attached to the tissue that surrounds the knee, with only fairly small direct bone attachments at the front and back. There is one meniscus on the inner side of the knee and another on the outer side. They are able to shift position within the joint to a limited degree, and help stabilise the joint and spread the forces evenly across the bone surfaces. When viewed from the top they are “C” shaped.
The meniscus can experience injuries, and broadly these can be broken into 5 broad types:
- A previously healthy meniscus can have an injury, and this is what we commonly see in patients in their teens, twenties and thirties after a sporting or work injury. Sometimes this occurs in combination with injuries to other parts of the knee, such as the cruciate ligaments (the ACL). We call these Traumatic tears.
- A meniscus can tear after an injury, in the context of some degeneration that was present before the injury but which was not causing any symptoms beforehand. This will often occur in patients in their forties or fifties after a workplace injury or following a social sporting or recreational injury. Often this is a relatively minor twist that brings on the symptoms. We call these “Degenerate” or “Complex” tears.
- Menisci can develop symptoms without a specific injury. An MRI will show a tear, often combined with some relatively mild wear of the articular cartilage, but an xray won’t show clear features of arthritis yet. This most commonly is found on the back inner edge of the knee.
- Sometime patients are born with a meniscus that covers the entire space between the thigh bone and the shin bone, rather than just sitting around the edge of that space. These are called Discoid Meniscus, and are a normal anatomical variant. They are most common on the outer half of the knee. Discoid menisci will often become degenerate and painful in middle age without a specific injury.
- Finally, in patients with arthritis of the knee the articular cartilage wears away and the meniscus wears along with it. When a knee replacement is performed we remove the meniscus, both because they are not needed for the knee replacement to work but also because they are usually partly or completely torn and missing due to the arthritis.
Meniscal Tears Patterns
The meniscus can tear in a variety of patterns, and each tear type has different options for surgical treatment.
- In traumatic tears the attachment of the outer rim of the meniscus to the knee capsule can completely separate and the main section of the meniscus can become unstable. Sometimes the torn segment will move into the gap in the middle of the knee and cause the knee to “lock”, being unable to fully bend or straighten because the displaced meniscus is mechanically jamming it. This pattern is called a Bucket-handle tear and is commonly surgically repaired with surgical anchors and stitches done in a keyhole manner.
- Sometimes the meniscus will tear at one of the points where it attaches to the bone. This is called a meniscal Root tear, and most often effects the attachments at the back of the knee. This can be repaired by roughening the bone where the meniscus is meant to attach, and then drilling a small tunnel in the bone so that stitches can be passed to pull the meniscus back down onto the attachment point so it will heal.
- The most common tear pattern involves a section of the underside or central edge of the meniscus tearing. It becomes unstable and flicks in and out of the space between the bones, causing sudden stabbing pain, knee instability or giving-way, ache, and joint inflammation. Sometimes these sections can break off and move around the knee as a loose body that can cause jamming, and can sometimes be felt under the skin.
The best treatment for each tear is based on the type of tear, the mechanism of injury, the symptoms, and how long the symptoms have been present for.
Most bucket handle tears, and tears that have occurred in combination with injury to other knee ligaments will need surgery.
Many degenerate tears will resolve by themselves without needing surgery. This process is often assisted by physiotherapy, and generally if a knee is going to resolve it will do so over a 3-4 month period.
For tears that are either causing regular mechanical instability of the knee, ongoing ache or intrusive stabbing pain then arthroscopic keyhole surgery may be best.
When to have a knee arthroscopy
A knee arthroscopy is a routine and successful operation, but it is still surgery with rare but serious potential complications, and should not be done until the expected benefits outweigh the risks.
As with all surgical procedures, if a good outcome can be achieved while avoiding an operation, even if it takes a little longer, then an operation should be avoided.
If the meniscus injury is producing symptoms that either clearly are not going to resolve with non-surgical treatment, or have failed to respond to non-surgical care then that is when knee arthroscopy should be considered.
The knee arthroscopy experience
For most patients a knee arthroscopy is a day surgery procedure, meaning you come in to hospital on the day of surgery and go home a couple of hours after the operation, once the nurses have determined that you are safe. For most patients it is a general anaesthetic, so you go completely to sleep. A tourniquet is applied to the thigh and inflated during the surgery to minimise bleeding, so that I can see clearly inside the knee. The leg is painted sterile, and wrapped with surgical drapes. For most cases there are two keyholes, which are each about 1cm long. From these keyholes I can view all of the inner sections of the knee joint, and can usually pass instruments to do whatever treatments are required. Sometimes one or two additional holes are required, if I need to pass instruments into less common regions of the joint, but this does not change the recovery. Sterile fluid is pumped into the knee to allow a clear view, and to help removed any trimmed sections of cartilage or other tissue. Once the procedure is complete I put local anaesthetic into the keyhole sites, and into the knee joint as well. Sometimes some steroid is included, to provide longer acting anti-inflammatory effect if I think it would be beneficial. The keyhole are closed with adhesive dressings – most of the time no stitches are required. Bandages are applied. Typically this operation will take 20-30 minutes.
Most people can walk on the knee straight away, and go home once the nurses assess you as being safe. The outer bandages can be removed 2 days after the surgery, and the adhesive skin dressings left in place if possible until you see me for the post surgery review. This usually is scheduled 10-14 days after the procedure. For patients who had longer operations, more complex problems, are not walking on the leg well, or have specific risk factors then I may prescribe medications to prevent clots in the veins for a period of time after the operation.
What are the risks?
As with any surgery, knee arthroscopy has risks which we cannot always prevent or avoid.
Serious complications are rare but include events like heart attacks or strokes during the surgery, infections in the knee joint or even unexpected sudden death during or after the operation.
More minor complications are more common but also temporary or fixable and include things like:
- Shallow infection at the surgical scars.
- Clots in the veins of the legs or clots that form on the lungs.
- More advanced arthritis being found at operation than what was suggested on any pre-operative scans. This can be a reason for persisting knee pain despite a successful operation on the meniscus.
- Ongoing pain from the meniscus.
- Failure of any meniscal repairs to heal, resulting in symptoms recurring, and sometime requiring further surgery.
- Development or progression of arthritis in the knee in the future.
- A scar that is over-sensitive or which is raised or discoloured after healing.
- Altered skin sensation near the scar that can be temporary or permanent.
- Injuries to arteries that require repair. These are extremely uncommon but at their most serious can require amputation of the leg if the blood supply cannot be restored.
- Injuries that cause nerves to stop working normally, temporarily or permanently
- Pneumonia, stomach ulcer, or temporary bowel obstruction in response to the surgery.