KNEE SYNDROMES & ARTHROSCOPIC KNEE PROCEDURES

R.L.Morgan-Jones, M.J.Cross O.A.

There are many knee operations that can be performed using an arthroscope. Most operations can be done as a day-case procedure although many patients require a period of muscle strengthening afterwards to obtain the best outcome. Below is an outline of the commonest “knee syndromes” and the arthroscopic procedures used to treat them.

Medial meniscal syndrome 1, 2 & 3
1. Locked knee
A torn meniscus can displace into the knee joint causing a mechanical block to extension and resulting in pain and muscle spasm. The classic type of meniscal tear producing a locked knee is the “Bucket Handle” tear. The torn meniscus remains attached front and back allowing the central torn portion to flip into the knee joint like the handle of a bucket. As the pain and spasm reduce the displaced meniscus can drop back allowing the knee to move freely again. This mechanical “locking” of the knee can be an intermittent feature with symptomless periods of in-between episodes.
2. Medial pain syndrome
The gradual onset of pain aggravated by twisting, squatting and catching your toe; as well as pain at night when you sleep on the side with legs together. This is typical of a cleavage tear of the medial (inner) meniscus which can intermittently be “pinched” by the knee joint as it flexes or twists suddenly. In-between episodes the torn portion of meniscus can fold away under the untorn meniscus and the knee become pain free.
3. Lateral pain syndrome
The triad of pain in the lateral (outer) joint line, radiation up into the thigh and down into the lower leg, and exacerbation on ascending stairs are all associated with a torn lateral meniscus. The clinical sign of a meniscal ‘pseudocyst’ is a lump in the lateral joint line, tender to touch and varying in prominence according to the degree of flexion of the knee. The ‘pseudocyst’ results from the torn meniscus folding in on itself.

Meniscectomy
There are two menisci in every knee, the medial (inside) and the lateral (outside).  Menisci can be damaged acutely when the knee sustains a sudden forced flexion and twisting strain, or chronically as part of degenerate changes within the knee (‘wear & tear’). The meniscus has little blood supply, except along the periphery where it attaches to the joint capsule, and therefore is unlikely to heal. A torn meniscus causes mechanical interference in the knee joint. This may result in the knee ‘locking’, preventing full extension. Recurrent displacement of a torn meniscus can produce damage to the smooth articular surface of the knee resulting in long-term degeneration.

Torn menisci can be removed by arthroscopy leaving the undamaged, stable portion behind. Occasionally a meniscus is torn along its peripheral attachment where there is a reasonable blood supply. This type of tear can sometimes be repaired allowing the meniscus to heal.

Anterior knee pain
Many people, of all ages and sporting activity, have pain generally located to the front (anterior) of the knee. This is caused by a relative weakness of the Quadriceps muscles in front of the thigh and tightness of the Hamstring muscles behind the thigh. In biomechanical terms this has the effect of walking on a permanently bent (flexed) knee. This increases the pressure on the patella and produces anterior knee pain. Occasionally this is precipitated by a minor injury, which results in residual Quadriceps weakness after the original injury has healed. Often however there is no prior accident or injury.

The solution to this problem is Quadriceps strengthening and Hamstring stretching. Quadriceps strengthening is best achieved by repetitive straight leg raising. Quadriceps exercises, which involve knee flexion, should be avoided, as flexion exercises will aggravate the pain. Hamstring stretching is equally important to reduce the flexion force around the knee. These exercises take at least 6 to 12 weeks to work and thereafter should be part of a patient’s daily routine.

Lunge lesions
The “lunge lesion” is an isolated injury to the femoral articular cartilage in the groove (Trochlea) through which the patella runs during knee flexion. It is the result of high shear and compressive forces produced by deceleration of the flexed knee, with co-contraction of the hamstrings and quadriceps muscle groups. Classically during a lunging motion as often occurs in sports such as squash, tennis, and netball. This roughened articulating area produces a painful, grinding sensation as the flexes leading to joint irritation and swelling. In severe cases this damaged area requires an arthroscopic chondroplasty to smooth the roughened articular cartilage. All patients however will require an exercise programme of Quadriceps strengthening and Hamstring stretching to protect against further injury.

Chondroplasty
The weight-bearing surface of the knee joint is covered in a highly specialised articular hyaline cartilage. This surface allows near friction free movement and absorbs the normal loading that occurs with daily activities. If an acute injury or chronic degeneration damages this surface, the cartilage roughens and causes local irritation. Sometimes a crackling sound or sensation may be present. As the cartilage deteriorates the knee itself can become swollen as the synovial joint lining produces increased amounts of synovial fluid to try and lubricate the knee.

These rough areas of articular cartilage can be smoothed by using an arthroscopic ‘shaver’. This removes any loose or roughened areas leaving a smooth articulating surface, thus reducing the local irritation.

Microfracture
When the articular hyaline cartilage is damaged to the extent that the underlying bone is exposed chondroplasty by itself is insufficient. In these cases we need to promote new cartilage formation in the damaged area. This is done by breaking through the exposed bone, using a bone awl, to the underlying blood supply (microfrature). The bleeding bone surface will ‘heal’ by the formation of a new cartilage layer. This new cartilage is called fibrocartilage and forms a new smooth surface, although it lacks some of the special properties of the original hyaline cartilage.

Notchplasty
In knees, which already have osteoarthritis, the joint forms new bone called osteophytes. These can often be felt on the edge of the knee joint as a bony lump. If osteophytes form in the middle of the knee joint they can prevent full knee extension, which in turn prevents muscle strengthening around the knee. In some patients it is possible to remove these central osteophytes arthroscopically and improve knee extension.

Removal of loose bodies
A piece of bone or cartilage can be broken off during an injury or as part of a more general degeneration and form a ‘loose body’ within the knee. Loose bodies can remain symptomless for long periods but can cause sudden attacks of pain and locking. Usually the locking is only momentary and the knee can be ‘wriggled’ free.

Loose bodies can be removed at arthroscopy although they can often be difficult to find.