Knee arthroscopy is keyhole surgery for the knee. Knee arthroscopy can successfully manage a wide range of knee conditions, and is especially useful for managing meniscal tears. It is typically performed as day surgery (no need to stay in hospital overnight) and most people can walk without crutches within a few days. Complications can occur as a result of knee arthroscopy, but they are very uncommon; most people have a return to nearly normal knee function within a couple of weeks.
Knee Anatomy
The knee is a complex modified hinge joint. In addition to hinging, as the knee flexes it slides and rotates. This complex motion is facilitated by the shape of the bones and by the associated soft-tissues and ligaments within and around the knee. The round ends of the thigh bones (femoral condyles) move on the flat upper end of the shin bone (tibial plateau). These bone surfaces are covered in very smooth joint cartilage (articular cartilage), which allows pain-free knee movement. Cushioning cartilages (the medial and lateral meniscus) increase the congruency between the round femoral condyles and the relatively flat tibial plateau. The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) help the knee to move normally as it flexes and, along with the medial and lateral collateral ligaments (MCL and LCL), provide stability for the knee during activity.
Common reasons for needing knee arthroscopy
Mensical Tears: Meniscal resection and repair
Tears in the medial or lateral meniscus (meniscal tears) are one of the most common reasons for needing knee arthroscopy. Meniscal tears may cause knee pain, clicking and/or swelling. A torn meniscus may become caught between the bones in the knee joint and cause clicking. Nerves in the torn meniscus are commonly irritated, causing pain. A meniscal tear may act as a one-way valve during knee movements, forcing fluid from the knee joint into the tissues behind the knee and causing a bakers cyst. A bakers cyst is therefore best managed by treating the underlying cause (usually a meniscal tear) rather than drawing fluid from (aspirating) the cyst. Meniscal tears are usually managed by removing (resecting) the torn part of the meniscus. While this does result in some loss of congruity between the bones in the knee, the remaining part of the meniscus continues to function normally. Sometimes meniscus tears can be successfully repaired during knee arthroscopy, and where possible this is performed. However, because of the poor blood supply to the meniscus, which further deteriorates with age, most tears are not amenable to repair.
Joint cartilage injury
Microfracture
Discrete areas of damage to the articular cartilage can be addressed with knee arthroscopy. My preference is usually to manage discrete areas of articular cartilage damage by intentionally causing bleeding from the underlying bone (microfracture). This creates scar cartilage (fibrocartilage) formation in the defect. Other (not necessarily arthroscopic) procedures are available that result in formation of joint cartilage (hyaline cartilage) in the injured area, but the hyaline cartilage that forms is not structured like articular cartilage and the objective results of these procedures have not demonstrated any clinical benefit over microfracture. Similarly, cartilage transplantation procedures, which may be appropriate in some limited situations, have not been shown to have significant advantages over microfracture for managing modest and contained cartilage defects. Results of microfracture are satisfactory in approximately two thirds of cases. Recovery from microfracture is longer than recovery from other arthroscopic procedures; crutches are required for six weeks and abstaining from sport and sporting-like activities is required for three months following surgery. Because of the slower recovery following microfracture, the risk of some complications, such as deep venous thrombosis (DVT), may be more common than following other arthroscopic procedures; I usually recommend patients use appropriate DVT prophylaxis for at least 2 weeks following arthroscopic microfracture.
Chondroplasty
Wide spread thinning of articular cartilage (chondromalacia) with associated flap-tears and/or fraying may cause knee pain as well as mechanical symptoms such as knee locking and clicking. These larger and less discrete areas of articular cartilage damage that are not amenable to microfracture or other cartilage salvage procedures may benefit from being smoothed off during knee arthroscopy (chondroplasty). Chondroplasty works fairly well at reducing mechanical symptoms related to unstable areas of articular cartilage, but does not reliably reduce knee pain, especially if there are areas of full thickness cartilage loss (arthritis). Results of chondroplasty are usually much less predictable than the results of managing meniscal pathology.
Inflamed tissue within the knee
Tissue may become inflamed within the knee (synovitis) as a result of an injury or because of a more general problem such as inflammatory arthritis. Synovitis results in knee pain and swelling. A discrete area of local synovitis resulting from an injury is reasonably well addressed with knee arthroscopy. Generalised synovitis as a result of inflammatory arthritis is becoming less common as medical management of inflammatory arthritis improves, but if required can be addressed with knee arthroscopy (arthroscopic synovectomy). Most patients stay in hospital overnight after an arthroscopic synovectomy.
Knee arthritis
Knee arthroscopy may be used as an adjunct in the management of knee arthritis, particularly in younger patients who may not be suitable for more invasive operations. Knee arthroscopy can address symptomatic meniscal tears associated with arthritis (although not all meniscal tears are symptomatic), and is able to remove loose bits of bone and cartilage (loose bodies) from the knee. It therefore addresses the mechanical problems associated with knee arthritis reasonably well. It does not, however, manage the pain associated with arthritis particularly well, and some patients with predominantly mechanical arthritis symptoms find that knee arthroscopy stirs up the pain component of their arthritis. I think an arthroscopic debridement is a reasonable option in patients with severe knee arthritis who are too young to seriously consider total joint replacement, but I do not usually recommend knee arthroscopy as a treatment for older patients with end-stage knee arthritis.
Diagnostic knee arthroscopy
Knee arthroscopy allows a look into the knee with low risk and low morbidity. For this reason is may be used to help diagnose conditions within the knee when other diagnostic tools (such as x-ray and MRI) have not been helpful or cannot be performed.