OSTEOARTHRITIS OF THE KNEEOSTEOARTHRITIS OF THE KNEE

OSTEOARTHRITIS OF THE KNEE

The knee is affected by osteoarthritis more often than any other joint. The condition is particularly common in elderly, fat women.

CausesIt is caused by wear and tear; but nearly always

some factor is present that has caused the joint to wear out sooner than usual.

Overweight is the commonest factor: for some reason it seems to impose a harmful stress upon the knee whereas it does not adversely affect the hip or ankle.

Other important predisposing factors are: 1-Previous fracture causing irregularity of the joint

surfaces; 2-Previous disease with damage to articular cartilage

(especially old rheumatoid arthritis or infective arthritis);

3-Previous intra articular mechanical damage, as from a torn meniscus or from osteo chondritis dissecans; and

4-Mal-alignment of the tibia on the femur (as in long-established bow-leg or knock-knee deformity from any cause).

Pathology.

The articular cartilage is worn away and the underlying bone becomes eburnated. There is hypertrophy of bone at the joint margins, with the formation of osteophytes. The changes may affect predominantly the femorotibial joint or the patellofemoral joint; but usually the whole joint is affected.

Clinical features. The patient is commonly an elderly, heavy woman, in

whom both knees may be affected. In another group, mostly in men, there is a history of previous mechanical derangement from a sports injury. There is slowly increasing aching pain in the joint, worse after unusual activity, and 'grating' may be felt or heard on movement. The symptoms 'are often exacerbated by a slight strain or twist. There is usually evidence of one of the predisposing factors mentioned above.

On examination the knee is slightly thickened from hypertrophy of bone at the joint margins, where a rim of osteophytes may be palpable. Effusion of fluid into the joint is unusual, except after much activity. Movement is moderately restricted and is accompanied by coarse crepitation. The quadriceps muscle is wasted. In severe cases there is a tendency to varus (bow-leg) deformity (less often a valgus (knock-knee) deformity), often with inability to straighten the knee fully.

Radiographic features. Narrowing of the cartilage space, which is the

first sign of osteoarthritis in most joints, is often not discernible until a later stage in the case of the knee. The first clear sign of osteoarthritis in the knee is sharpening or 'spiking' of the joint margins, especially of the patella (Fig. 308) and tibia. Later, narrowing of the cartilage space is obvious osteophytes form at the joint margins, and the subchondral bone may become sclerotic (Fig. 309). Opacities that appear to be loose bodies are often seen; most are not in fact loose but are attached to the synovial membrane

Advanced osteoarthritis of the knee. Note the narrowing of the cartilage space, especially on the medial side and in the patello-femoral compartment. Note also the sclerosis of the subchondral bone, and osteophytes at the joint margins.

Treatment. In the usual case of moderate severity,

conservative treatment is often successful in relieving the symptoms, although the structural changes in the joint are clearly irreversible. The most effective method is by physiotherapy. Intensive active exercises are carried out to strengthen the wasted quadriceps muscle. Local heat therapy is often also given, but it is less important than the exercises. The knee is largely dependent upon the quadriceps for its stability, and if a powerful muscle can be developed symptoms may remain in abeyance despite marked osteoarthritis.

Intra-articular injections of hydrocortisone have been tried, but the results are uncertain. Repeated injections are not recommended because they seem sometimes to accelerate the degenerative process.

Operative treatment. In the worst cases, with severe persistent

pain, especially when associated with deformity, operation may be advisable. Its nature will depend upon the circumstances of each case. The following are the operations most used:

1)Removal of loose bodies; 2)Upper tibial osteotomy; 3)Excision of patella; 4)Arthroplasty; 5)Arthrodesis.

Figure 310—Bow-leg deformity from uneven - destruction of articular cartilage, that of the medial compartment being much thinner than that of the lateral. Body weight is now transmitted mainly through the diseased medial half of the joint. Interrupted line shows wedge of bone to be removed for correction of deformity. Figure 311—After corrective osteotomy and fixation with staples the line of weight transmission is shifted towards the more healthy lateral –coni-partment.

Removal of hose bodies. When loose bodies cause recurrent locking of the joint they should be removed. This is a simple operation, usually carried out by an arthroscopic technique, that gives good results. Any evident irregularities or excrescences of the articular surfaces may be trimmed at the same time.

Upper tibial osteotomy. Tibial osteotomy aims to relieve pain and "to correct deformity. It is especially-valuable when wear of articular cartilage and bone has proceeded more in one half of the joint than in the other. For instance, if the medial half of the joint is markedly narrowed whereas the lateral compartment remains relatively healthy, there will be obvious bow-leg deformity and pain is likely to be prominent in the degenerate medial compartment, which is forced by the mal-alignment to take most of the weight (Fig. 310).

Correction of the mal-alignment by removal of a wedge of bone based laterally (Fig. 311) transfers the weight-bearing thrust towards the more healthy lateral compartment and is often effective in relieving pain. Likewise if the lateral compartment is worn more than the medial, with con sequent genu valgum, a medially based wedge may be excised.. The osteotomy is done about 1.5 centimetres below the upper articular surface of the tibia, and to permit early walking the fragments are usually fixed together at operation by metal staples (Fig. 311)

Excision of patella. This is appropriate only when the arthritic process is largely confined to the patello-femoral joint, the femoro-tibial joint being relatively healthy.

Arthroplasty (Figs 304-306). This is undertaken less often for osteoarthritis than for rheumatoid arthritis, because the disability is seldom severe enough to justify' an operation that is still unpredictable in its results and particularly in its durability. Methods of replacement arthroplasty were outlined on page 335.

Arthrodesis. This is now seldom undertaken, but is may be appropriate in a severe case, especially when other operations have failed and when the other knee and the hips are normal.

PREPATELLAR BURSITIS

The bursa that lies in front of the lower half of the patella and the upper pan of the patellar tendon is prone to inflammation.

Types. There are two types of prepatellar bursitis: 1) irritative; and 2) infective or suppurative.

IRRITATIVE PREPATELLAR BURSITISThis is caused by repeated friction; it

occurs especially in those who do much kneeling. There is fibrous thickening of the wall of the bursa, which is distended with fluid.

Clinical features. There is a softly fluctuant swelling in front of the lower part of the patella ('housemaid's knee'). The swelling is clearly demarcated. It is manifestly confined to a plane in front of the joint, and the joint itself is unaffected.

Treatment. A trial may be made of aspiration under local anaesthesia, but the effusion tends to recur unless further friction can be avoided. The risk of recurrence may possibly be reduced if hydrocortisone is injected into the emptied sac. Operative excision of tire bursa affords a more certain permanent cure.

SUPPURATIVE PREPATELLAR BURSITIS

This is caused by infection of the bursa with pyogenic organisms which reach the bursa directly through a puncture wound, or through the lymphatics from an infected lesion on the leg. The wall of the bursa is acutely inflamed and the sac is distended with pus.

Clinical features. There are pain and swelling in front of the knee. There may be mild constitutional disturbance, with pyrexia. The swelling is confined to the site of the prepatellar bursa. It is acutely tender on palpation, and the overlying skin is hot and reddened. The inguinal lymphatic glands are often enlarged and tender. The knee joint itself is unaffected, but the patient is unwilling to bend it fully, because flexion increases the pain by tensing the skin over the bursa.

Treatment. Appropriate antibiotic therapy should be instituted and the bursal abscess should be drained by incision.

POPLITEAL CYSTS

Cystic swellings are not infrequently found in the popliteal fossa. Most are examples of irritative bursitis, usually of the semimembranosus bursa. A few are caused by herniation of the synovial cavity of the knee (Baker's cyst).Care must be taken to distinguish popliteal cysts from other, more serious swellings in this region, such as aneurysm of the popliteal artery and synovial sarcoma.

SEMIMEMBRANOSUS BURSITISThe semimembranosus bursa lies between

the medial head of the gastrocnemius and the semimembranosus. The bursa may become distended with fluid to form an elongated sac that bulges backwards between the muscle planes. Clinically, there is a soft cystic swelling at the back of the knee, close to the medial condyle of the femur.

Treatment is not always required. In children particularly, operation may usually be avoided because the cyst may disappear spontaneously. Nevertheless if the swelling becomes uncomfortably large the sac should be excised.

BAKER'S CYSTA Baker's cyst is simply a herniation of the synovial

cavity of the knee, with the formation of a fluid-filled sac extending backwards and downwards (Fig'. 333). It is not a primary condition but is always secondary to a disorder of the knee with persistent synovial effusion, such as rheumatoid arthritis or osteoarthritis. In long-standing cases the hernial sac is much elongated, and may extend a considerable distance down the calf.

Clinically there is a soft cystic bulge near the midline behind the knee or in the upper calf. The underlying abnormality of the knee, with synovial effusion, will usually be obvious. Treatment. In most cases treatment should be directed towards the underlying condition of the knee rather than to the cyst itself. Nevertheless if the cyst is extensive it is sometimes advisable to excise it.

Fig.333To show how a Baker's cyst isformed as a herniation of thesynovial membrane.