Overview Of Knee Arthroscopy

Conditions in the knee which are commonly treated with an arthroscopic technique include:

• Injury to the meniscal cartilage
• Injury to the articular cartilage
• Removal of loose ‘bodies’ from within the knee joint
• Injury to the anterior and posterior cruciate ligaments
• Excision of diseased tissue from the knee joint
• Fixation of some types of fracture (including osteochondral lesions)

Meniscal cartilage injury

Injury to the meniscus is common in activities of everyday living and in sporting or athletic events. As one gets older the substance of the meniscus gets stiffer and more brittle with the result that relatively minor twisting injury may result in a tear of the meniscus. Much greater force is required to injure the more pliable meniscus of a child or young adult.

The cardinal symptoms of a torn meniscus are of pain and swelling. The location of the pain usually corresponds to the location of the torn meniscus, being felt on either the medial (inner) or lateral (outer) aspect of the knee. The pain is often localised to a very specific area which may in addition be tender to the touch. Pain is often brought on during twisting and bending movements of the knee. Swelling of the knee characteristically comes on a day or so after the injury. A torn meniscus will not as a rule repair itself and, if symptoms persist, arthroscopic surgery may be required. Not everyone with a torn meniscus will need surgery.

Post-meniscectomy osteoarthritis occurs some years (up to 20) after surgery to remove the entire meniscus. Modern practice is to preserve as much of the meniscus as possible at the time of any arthroscopic surgery. Removing the entire meniscus alters the biomechanics of the knee and causes increased wear and tear.

Articular cartilage injury

Articular cartilage is the smooth, low friction substance which covers the end of the bones thus forming the joint. It has an exceptionally low coefficient of friction when uninjured meaning that joint surfaces are very slippery and glide over each other with great ease. When one or both of these surfaces is injured the friction increases exponentially and further wear of the joint is inevitable. The rate of progression of this wear (osteoarthritis) depends on a number of factors including the stability of the affected joint and the mechanical alignment of the forces going through the joint.

Following ligament injury (e.g. Anterior Cruciate Tears) the knee may become unstable and consequently any episodes of the knee giving way will put the meniscus at risk of tearing resulting again in osteoarthritic change. It is worth noting that at the time of a significant ligament injury to the knee there is, by definition, some damage caused to the articular surfaces. This has only really been appreciated since the advent of MRI scanning which often shows swelling in the bone deep to the area of articular injury.  In acute ACL injury this is most commonly seen in the lateral (outer) side of the knee.

Loose bodies in the knee joint

In the osteoarthritic process, osteophytes are formed and these are bone outgrowths from the edge of the joint. These can become detached and are then known as ‘loose bodies’. As well as the symptoms of osteoarthritis, a patient may well experience the loose body catching or jamming in the knee joint which produces severe pain as well as locking of the knee. There may in addition be some swelling of the knee.  These loose bodies are easily removed from the joint using an arthroscopic technique. Other loose bodies may arise from areas of the knee where osteochondritis has occurred such as in the active adolescent with osteochondritis dessicans.

Cruciate ligament injury

Techniques for reconstructing the cruciate ligaments are continually evolving. Today’s operations are highly successful and use arthroscopic (keyhole) methods to ensure that a reconstructed cruciate ligament is not only in the exactly correct position but also that it is securely fixed to the bone. This has meant that the size of any incision is minimal and hospital stay is short (can be done as a day case).

Other tissues in the knee

There are some folds of soft tissue in the joint called plicae which we all have. Following injury these folds can become thickened and fibrotic and cause symptoms. A symptomatic plica is easily addressed with arthroscopy. The lining of the joint is called the synovium. This tissue is responsible for the nutrition of the tissues within the knee (meniscus and articular cartilage) and also produces the lubrication. Several conditions can affect the synovium and the arthroscope is often used to biopsy such tissues to make a diagnosis and can also be used to excise the diseased tissue in some cases.

Trauma

Traumatic fracture of the tibia or femur extending into the joint damages the articular surfaces. This type of injury is treated by accurate fixation of the bone involved and restoring the continuity of the articular surfaces. Post traumatic osteoarthritis may ensue many months/years later and depends to a large extent upon how well the joint surfaces are realigned following treatment for the fracture. Arthroscopic methods are used to help ensure that the fixation of the joint surface is accurate. In the knee a common injury of this type involves the lateral tibial plateau which if neglected results in a valgus (knock-knee) alignment and subsequent instability and osteoarthritis. Osteochondritis dissecans is a condition affecting children and adolescents. An area of articular cartilage with its underlying bone becomes unstable within the knee and if separation occurs the child may present with a ‘loose body’. Arthroscopic methods are used to help with the diagnosis and assessment of this condition and in some cases the fragment can be pinned back using a keyhole technique.