ACUTE OSTEOMYELITIS (General description of acute osteomyelitis, p. 85)

The femur is one of the bones most commonly affected by pyogenic osteomyelitis. The infection is carried to the femur either through the blood stream (haematogenous osteomyelitis), when it usually affects the lower metaphysis; or it is introduced through an external wound, especially in cases of compound fracture. The clinical features and treatment are the same as those of osteomyelitis elsewhere (p. 89).

CHRONIC OSTEOMYELITIS (General description of chronic osteomyelitis, p. 90)

Chronic pyogenic osteomyelitis is nearly always a sequel to acute infection that has been neglected or has responded poorly to treatment. As with the acute disease, the lower end of the femur is affected more often than the upper; but in many cases the infection spreads to involve a large part of the femoral shaft. Clinical features and treatment are like those of chronic osteomyelitis elsewhere (p. 91).

BONE TUMOURS IN THE THIGH

The femur is one of the commonest sites of the important bone tumours.

Malignant tumours (General description of malignant bone tumours, p. 112)

The femur is a common site for all of the main types of malignant bone tumour occurring in younger patients. Three require mention – namely osteosarcoma, Ewing’s sarcoma, and chondrosarcoma, though others such as lymphoma, malignant fibrous histiocytoma, and myeloma should be considered in the differential diagnosis of destructive femoral bone lesions. However, it should be remembered that metastatic tumours are much more common than any of the primary malignant tumours, particularly in patients over the age of 50.

Osteosarcoma (osteogenic sarcoma)

This is usually a tumour of childhood or early adult life: when it occurs in patients beyond middle age it is usually a complication of Paget’s disease. Typically it arises in the metaphysis of a long bone, and the lower metaphysis of the femur is the favourite site. The tumour is highly malignant, with a mortality still in the region of 40% or more despite recent advances in treatment. Treatment is discussed on page 117.

Ewing’s tumour

This also occurs mainly in children or adolescents. Unlike most bone tumours, it usually affects the shaft of the bone, which it expands in a fusiform manner. Over it, layer upon layer of new bone is laid down, giving a typical ‘onion-peel’ appearance as seen in the radiographs. Although the tumour responds dramatically to chemotherapy, usually in combination with radiotherapy or surgical excision, the prognosis remains poor, with a mortality in the region of 50 per cent from blood-borne metastases. Treatment is discussed on page 121.

Chondrosarcoma

This tumour occurs more commonly in middle age and elderly patients suggesting that it represents a malignant change in a pre-existing chondroma. Clinically it presents with local pain and swelling and may reach a large size because of slow growth. Imaging shows an expanding lytic lesion with characteristic patchy calcification and cortical destruction. Treatment is entirely surgical since no chemotherapy is effective on the relatively avascular tumour.

Metastatic (secondary) tumours

The femur is commonly invaded by metastatic tumours, especially in its proximal half (Fig. 18.6).

Fig. 18.6 Metastatic tumour in the femur – a common site. A Pathological fracture has occurred. B The later radiograph shows the bone after internal fixation of the fragments by an intramedullary device. The primary tumour was in the lung.

Pathology. The tumours that metastasise most readily to bone are carcinomas of the lung, breast, prostate, kidney, and thyroid. The bone structure is usually destroyed by the tumour and pathological fracture is common (Fig. 18.6A).

Clinical features. Pain is the predominant symptom, but sometimes the tumour causes little disturbance until a pathological fracture occurs.

Treatment. The principles of treatment of metastatic tumours in bone were described on page 126. Most pathological fractures of the femur lend themselves well to internal fixation with a long modified intramedullary nail, though sometimes this requires the addition of acrylic bone cement to achieve stability (Fig. 18.6B). Where massive bone destruction has occurred in the proximal or distal femur, it may be necessary to replace this with a custom prosthesis. This facilitates nursing and greatly increases the quality of life because external splintage can be dispensed with and the patient mobilised.

PYOGENIC ARTHRITIS OF THE KNEE (General description of pyogenic arthritis, p. 96)

Pyogenic arthritis is commoner in the knee than in most other joints, partly because the knee is so exposed to injury and partly because of the close relationship of the joint cavity to the lower metaphysis of the femur, which is one of the commonest sites of acute osteomyelitis. The onset is acute or subacute, with pain, swelling, and loss of function. Radiographs do not show any abnormality in the early stages.

Treatment. Appropriate antibiotic therapy must be started immediately (see p. 98). Local treatment: The joint is rested in a plaster splint in a position of 20 ° of flexion. The purulent effusion is removed daily by aspiration so long as it re-forms or by arthrotomy. Rest is continued until the infection has been overcome; thereafter active movements are encouraged.

TUBERCULOUS ARTHRITIS OF THE KNEE (General description of tuberculous arthritis, p. 98)

After the hip, the knee is the limb joint most often affected by tuberculosis, usually in children or young adults. It is now an uncommon disease in Britain and other Western countries, though seen more often in developing countries and occasionally in immigrants to Britain. The knee is painful, diffusely swollen from thickening of the synovial membrane, and warm. Movements are restricted, the thigh muscles are wasted, and an abscess or sinus is sometimes apparent.

Radiographic features. The earliest change is diffuse rarefaction throughout the area of the knee (Fig. 18.7). Later, unless the disease is arrested, there is narrowing of the cartilage space and erosion of the underlying bone.

Fig. 18.7 Tuberculous arthritis of right knee in a child. The normal left knee is shown for comparison. Note the rarefaction, the diminution of cartilage space, and the small area of erosion near the lateral margin of the tibial joint surface. Destruction is only moderate, and a reasonably good result may be achieved with conservative treatment.

Treatment. Constitutional treatment, by antituberculous drugs, is the same as that for other tuberculous joints (p. 102). Local treatment is at first by rest in a splint or plaster, generally for two to three months in the first instance, depending on severity and progress. Subsequent management depends upon the response to treatment and the state of the joint at the end of this period of immobilisation. If the articular cartilage and bone are still intact, if the general health is good and the local signs have subsided, and if the erythrocyte sedimentation rate has steadily improved, it is likely that the disease has been aborted. In that event active joint movements are encouraged and walking is gradually resumed.

On the other hand, if the review at the end of the initial period of immobilisation shows that the disease is still active and that articular cartilage or bone has been destroyed, sound bony fusion should usually be the ultimate aim, though arthroplasty may sometimes be considered. Immobilisation is therefore continued until the disease becomes quiescent. Arthrodesis may then be undertaken, provided the growth epiphyses have closed. In children still growing it is better to defer arthrodesis lest growth be disturbed, and in the meantime to protect the knee in a walking caliper or splint.

RHEUMATOID ARTHRITIS OF THE KNEE (General description of rheumatoid arthritis, p. 134)

The knees are among the joints most frequently affected by rheumatoid arthritis, and they often suffer severe permanent disability. Both knees are often affected simultaneously with several other joints.

The knees are painful, swollen from synovial thickening, and warm to the touch. Bow-leg, knock-knee, or flexion deformity may occur. Movement is impaired, and painful if forced.

Imaging. Radiographs do not show any abnormality at first. Later there is diffuse rarefaction of the bone in the area of the joint. In long-established cases destruction of articular cartilage leads to narrowing of the joint space (Fig. 18.8), and there may be clear-cut erosions of bone, characteristically at the articular margins. Radioisotope bone scanning shows increased uptake of isotope in the region of the joint.

Fig. 18.8 A and B AP and lateral radiographs showing rheumatoid arthritis of the knee. The bone is porotic and there is complete loss of the medial joint space with irregularity of the articular surface indicating an underlying erosive process.

Course and prognosis. The inflammation dies down after months or years, but the knee is seldom restored to normal. The joint surfaces are usually damaged and wear out sooner than those of a normal joint. Thus in the late stages osteoarthritis is liable to be superimposed upon the original rheumatoid condition.

Treatment. In the active stage the treatment is that for rheumatoid arthritis in general and requires coordinated care by a multi-disciplinary team (p. 137). Local treatment for the knees depends upon the severity of the inflammatory reaction. If it is severe, rest in bed or even temporary immobilisation with moulded plaster or polythene splints is advisable. When it is moderate or slight, activity within the limits of pain is encouraged. Physical treatment is worth a trial. The most effective methods are exercises to preserve muscle power and joint movement, and local heat in the form of short-wave diathermy. Injections of hydrocortisone into the joint have sometimes given relief, but repeated injections are inadvisable because they may accelerate the destructive process.

Operative treatment. Three types of operation may be employed in treating more advanced stages of joint disease:

In deciding between them each case must be considered on its merits, and no hard-and-fast rules can be laid down.

Synovectomy. When there is persistent boggy thickening of the synovial membrane, but the articular cartilage is well preserved, the operation of synovectomy (excision of the synovial membrane) is worth considering. Comfort may be much improved and the advance of the disease is possibly slowed by the removal of the tissue producing the proinflammatory cytokines and enzymes responsible for cartilage destruction. This operation alone has no place in the later stages of the disease and is now used less frequently since the introduction of better drugs for the medical control of inflammatory disease.

Replacement arthroplasty. Replacement arthroplasty of the knee now gives as good results as have been achieved at the hip. Excellent and durable results are now being achieved in over 90 per cent of patients after ten years. In a favourable case pain is well relieved and good function is restored, with perhaps 90 ° or more of flexion movement. Replacement arthroplasty of the knee is particularly valuable for patients with severe disorganisation of the joint, and especially for elderly patients with involvement of several other joints.

Several techniques of knee arthroplasty are available: all of them rely upon replacement of the articular surfaces by a metal or plastic (polyethylene) prosthesis. Most of the earlier devices took the form of a hinge, but such devices are now seldom used because they do not mimic normal knee movement, and consequently there may be early implant loosening with bone destruction.

The present trend is to provide gliding articular surfaces rather than a pivoted hinge. Thus the femoral condyles may be replaced by a metal prosthesis cemented in place, and the tibial condyles by a matching polyethylene prosthesis, usually with a metal backing (total condylar replacement, Fig. 18.9A). When badly damaged, the patella may also be resurfaced with a matching polyethylene bearing. In unicompartmental arthritis, the medial or the lateral femoral condyle may be replaced alone (Fig. 18.9B). However, this is only suitable for osteoarthritis and in most cases of inflammatory arthritis, bicondylar replacement is preferred (Fig. 18.10). Many different types of total knee prosthesis are now available, including designs that incorporate artificial menisci, but medium’term results show no obvious advantages over the excellent results obtained with the original condylar replacements.

Fig. 18.9 A Condylar total knee replacement arthroplasty. A biconvex metal prosthesis is used to resurface both femoral condyles and articulates with a flatter biconcave metal-backed polyethylene tibial component. B Unicondylar knee arthroplasty to replace a single tibio-femoral compartment. The curved femoral resurfacing prosthesis articulates with either a fixed, or mobile, polyethylene tibial component.

Fig. 18.10 A and B AP and lateral radiographs showing a total replacement arthroplasty of the knee. The metal prosthesis resurfacing both femoral condyles articulates with a polyethylene tibial prosthesis, which is not visible, but is supported by the metallic tibial stemmed implant.

Arthrodesis. This is a reliable operation for the total abolition of pain and good stability, but it is appropriate only if the other joints of the lower limbs are healthy – a condition that is seldom met in rheumatoid disease. The joint is usually fused in about 20 ° or 25 ° of flexion, a position that is more convenient than the fully straight position, though a stiff knee is, of course, an awkward handicap.

OSTEOARTHRITIS OF THE KNEE (General description of osteoarthritis, p. 140)

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

Cause. It is caused by a degeneration of the articular cartilage of uncertain aetiology; but nearly always some factor is present that has caused the joint to wear out sooner than usual. Obesity 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: previous fracture causing irregularity of the joint surfaces; previous disease with damage to articular cartilage (especially old rheumatoid arthritis or infective arthritis); previous intra-articular mechanical damage, as from a torn meniscus or from osteochondritis dissecans; and 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 thickened and eburnated. There is hypertrophy of bone at the joint margins, with the formation of marginal osteophytes. The changes may affect predominantly the medial compartment of the femoro-tibial joint, or the patello-femoral 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. An earlier sign in many cases is sharpening or ‘spiking’ of the joint margins, especially of the patella (Fig. 18.11) and tibia. Later, narrowing of the cartilage space is obvious, osteophytes form at the joint margins, and the subchondral bone may become sclerotic (Fig. 18.12). Opacities that appear to be loose bodies are often seen; most are not in fact loose but are attached to the synovial membrane.

Fig. 18.11 Spiking of the articular margins of the patella, as seen in the lateral radiograph, is an early sign of osteoarthritis. The normal state (right) is shown for comparison.

Fig. 18.12 A and B Radiographs of a knee with advanced osteoarthritis. There is marked narrowing of the medial joint space and the patello-femoral joint. However the bony cortex of tibia and femur remain clearly defined with subchondral sclerosis and numerous marginal osteophytes, some of which may have become loose bodies posteriorly.

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 a substantial degree of arthritis.

Intra-articular injections of hydrocortisone have been tried for pain relief, but the results are uncertain and any improvement is usually temporary. In general, steroid injections are not recommended because they have sometimes led to acceleration of the degenerative process. More recently injection of hyaluronan preparations has become popular, to provide viscosupplementation by increasing the viscosity of the synovial fluid, but the results have proved inconclusive.

Operative treatment. In advanced arthritis, with severe persistent pain, especially when associated with deformity and stiffness, operation may be advisable. Its nature will depend upon the circumstances of each case. The following are the operations most used:

Arthroscopic washout. Washout of the joint, often coupled with an arthroscopic debridement, has been used to treat early osteoarthritis in younger patients. However, its use in randomised controlled trials has indicated that its benefit may be doubtful and shortlasting.

Removal of loose 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 affected one half of the tibio-femoral joint more than the other. Commonly 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. 18.13A). Correction of the mal-alignment by removal of a wedge of bone based laterally (Fig. 18.13B) 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 consequent genu valgum, a medially based wedge may be excised. The osteotomy is done about 1.5 cm 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. 18.13B).

Fig. 18.13 A 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. B After corrective osteotomy and fixation with staples the line of weight transmission is shifted towards the more healthy lateral compartment.

Excision of patella. This is only appropriate in the unusual situation when the arthritic process is largely confined to the patello-femoral joint, the femoro- tibial joint being relatively healthy. With the introduction of successful techniques for patello-femoral arthroplasty this operation is now seldom performed.

Arthroplasty (see Fig. 18.10). This has now become established as the surgical treatment of choice for advanced osteoarthritis of the knee. It will correct deformity, relieve pain, and restore mobility in over 90% of patients, with results extending out for 10–15 years. Methods of replacement arthroplasty were outlined for the treatment of rheumatoid arthritis on page 392. Most commonly the same techniques of total replacement arthroplasty of both the tibio-femoral and patello-femoral joints are used in osteoarthritis. However, unicompartmental tibio-femoral arthroplasty is now being increasingly used as an alternative to upper tibial osteotomy in younger active patients to restore more movement when the arthritis is at an early stage and confined to one compartment. A curved metal prosthetic replacement is fixed to the affected femoral condyle and articulates with a polyethylene tibial component, either directly, or through a gliding polyethylene meniscal bearing to provide more physiological movement (Fig. 18.14). The results in appropriately selected cases are as good as those from total joint replacement and still allow later revision to the full procedure if required at a later stage.

Fig. 18.14 A and B Radiographs of unicompartmental tibio-femoral arthroplasty with a metal resurfacing of one femoral condyle articulating with a polyethylene tibial prosthesis supported by a metal backing fixed to the bone.

Arthrodesis. This is now seldom undertaken, but it may occasionally be appropriate in a severe case, or as a salvage procedure when other operations have failed and where the other knee and the hips are normal.

HAEMOPHILIC ARTHRITIS OF THE KNEE (General description of haemophilic arthritis, p. 145)

Haemophilic arthritis affects the knee more often than any other joint. It is uncommon because haemophilia itself is encountered only rather rarely.

Pathology. Initially there is simply a haemorrhage into the joint (haemarthrosis). With rest, this is slowly absorbed into the hypertrophic synovial membrane. But further bleeding usually occurs, and this leads eventually to degenerative changes in the articular cartilage and to fibrous thickening and contractures of the synovial membrane.

Clinical features. The findings on examination vary according to the phase and duration of the disease. After each fresh episode of bleeding the knee is swollen, partly from contained blood and partly from synovial thickening caused by interstitial extravasation of blood. The overlying skin is abnormally warm. Joint movements are restricted, and painful if forced.

In a quiescent phase between episodes of haemarthrosis there is some thickening of the joint from synovial fibrosis, movements are slightly or moderately impaired, and often there is moderate flexion deformity.

Investigations. The clotting time of the blood is increased.

Diagnosis. Because of the synovial thickening, increased warmth of the skin and restriction of knee movements, haemophilic arthritis is easily mistaken for chronic inflammatory arthritis. A history of previous bleeding incidents and the increased clotting time of the blood are the important distinguishing features. Biopsy should be avoided because it may cause further bleeding. A history of haemophilia in other male family members also provides a clue.

Treatment. In centres where the necessary haematological facilities are available the ideal treatment for acute haemarthrosis is to aspirate the knee under the temporary cover of antihaemophilic factor (factor VIII) as if it were an ordinary traumatic haemarthrosis. The leg should be elevated and ice packs should be applied to the knee, which should be rested in a polythene or plaster splint until the acute symptoms subside. With the increasing availability of recombinant factor VIII, many haemophilic patients retain their own supply at home and are able to initiate treatment by intravenous injection at the onset of symptoms of bleeding. This can be repeated for several days to manage the acute episode and reduce the need for hospital admission and delay the development of chronic joint changes. If antihaemophilic factor is not available the outlook for the future of the knee is much less favourable. Aspiration should usually be avoided. Instead, the knee should be bandaged and immobilised on a Thomas’s splint or in a plaster backslab. After 2–4 weeks the residual blood is absorbed and cautious activity may be resumed under physiotherapy supervision.

The chronic degenerative arthritis that results from multiple repeated haemarthroses may have to be controlled by the permanent use of a polythene knee splint. Operative treatment to reduce this risk – such as arthroscopic synovectomy – is practicable, but only under the cover of adequate doses of antihaemophilic factor. When joint contractures or deformities develop, they may require tendon release or lengthening, or even corrective osteotomies. Advanced haemophiliac arthropathy (see Fig. 9.7, p. 147) may necessitate replacement arthroplasty of the joint to restore mobility. This is now possible under factor VIII cover, which needs to be continued for 2–3 weeks after surgery. The majority of patients get good results, but there is a greater risk of complications, particularly infection as many patients have acquired HIV from contaminated blood transfusions.

NEUROPATHIC ARTHRITIS OF THE KNEE (General description of neuropathic arthritis, p. 147)

Neuropathic arthritis (Charcot’s osteoarthropathy) of the knee is now seen very seldom in Britain because of the rarity of tabes dorsalis, formerly the most prevalent underlying cause. Other occasional causes include denervation of the joint from a lesion of the cauda equina or from other neurological disease.

The pathological changes may be regarded as a much exaggerated form of osteoarthritis. The articular cartilage and parts of the underlying bone are worn away, but at the same time there is often considerable hypertrophy of bone at the joint margins. The ligaments become lax and the joint is unstable.

Clinically there is marked lateral laxity, often allowing severe bow-leg deformity. Pain is slight or absent.

Radiographs show marked destructive changes, usually with some new bone formation at the joint margins.

Treatment may be required if there is marked deformity or gross instability demanding some form of protective appliance (orthosis), such as a moulded plastic splint or a caliper. Arthrodesis is practicable but because of the absence of severe pain operation should usually be avoided.

ANTERIOR KNEE PAIN (Including chondromalacia of the patella)

Anterior knee pain is a generic term that almost certainly includes more than a single clinical entity. The non-specific nature of the label implies, correctly, that the pathogenesis of the pain is not always well understood. The clinical syndrome characteristically occurs in adolescents, especially girls, though it also affects athletes, particularly runners. The description that follows relates to one well-recognised type of lesion, namely chondromalacia of the patella. Similar symptoms may occur in the absence of demonstrable patellar changes, and their causation is often conjectural. Chondromalacia may represent part of a spectrum of conditions associated with patellar instability or malalignment. These also include the more severe disorders of recurrent or habitual dislocation (see p. 409).

TEARS OF THE MENISCI

Injuries of the menisci (semilunar cartilages) are common in men under the age of 45. A tear is usually caused by a twisting force with the knee semiflexed or flexed. It is usually a football injury, but it is also common among men who work in a squatting position. Thus it was common among coal miners excavating shallow seams, before the advent of mechanisation. The medial meniscus is torn much more often than the lateral.

Pathology. In patients of athletic age there are three types of meniscus tear, but all begin as a longitudinal split (Fig. 18.15A) which must be distinguished from the iatrogenic transverse tear resulting from operative trauma (Fig. 18.15B). If the split extends throughout the length of the meniscus it becomes a bucket-handle tear, in which the fragments remain attached at both ends (Fig. 18.16A). This is much the commonest type. The ‘bucket handle’ (that is, the central fragment) is displaced towards the middle of the joint, so that the condyle of the femur rolls upon the tibia through the rent in the meniscus (Fig. 18.16A). Since the femoral condyle is so shaped that it requires most space when the knee is straight, the chief effect of a displaced ‘bucket-handle’ fragment is that it limits full extension (= ‘locking’).

Fig. 18.15 A A tear of a meniscus nearly always takes the form of a longitudinal split, which may extend throughout the length of the meniscus or may emerge at the concave border. A transverse tear B is nearly always an artefact, produced at the time of operation.

Fig 18.16 The three types of meniscus tear. A Bucket-handle tear, the commonest type. B Posterior horn tear. C Anterior horn tear.

If the initial longitudinal tear emerges at the concave border of the meniscus a pedunculated tag is formed. In posterior horn tear the fragment remains attached at its posterior horn (Fig. 18.16B); in anterior horn tear it remains attached at its anterior horn (Fig. 18.16C). The peripheral part of the meniscus is vascular and tears in the peripheral third can sometimes be sutured as they have some capacity for healing. The inner part is avascular and does not heal, tears in the inner third therefore need to be excised.

As the inner parts of the meniscus are almost avascular, when they are torn there is not an effusion of blood into the joint. Instead there is an effusion of clear synovial fluid, secreted in response to the injury.

Clinical features of torn medial meniscus. The patient is usually male and 18–45 years old. The history is characteristic, especially with ‘bucket-handle’ tears. In consequence of a twisting injury the patient falls and has pain at the antero-medial aspect of the joint. He is unable to continue what he was doing, or does so only with difficulty. He is unable to straighten the knee fully. The next day he notices swelling of the whole knee. He rests the knee. After about 2 weeks the swelling lessens, the knee seems to go straight, and he resumes his activities. Within weeks or months the knee suddenly gives way again during a twisting movement; there are pain and subsequent swelling as before. Similar incidents occur repeatedly.

Locking. By ‘locking’ is meant inability to extend the knee fully. It is not a true jamming of the joint because there is a free range of flexion. Locking is a common feature of torn medial meniscus, but the limitation of extension is often so slight that it is not noticed by the patient. Persistent locking can occur only in ‘bucket-handle’ tears: tag tears cause momentary catching but not true locking in the accepted sense.

On examination in the recent stage the typical features are effusion of fluid, wasting of the quadriceps muscle, local tenderness at the level of the joint antero-medially, and (characteristically in ‘bucket-handle’ tears) limitation of the last few degrees of extension by a springy resistance, with sharp antero-medial pain if passive extension is forced.

In the ‘silent’ phase between attacks there are often no signs other than wasting of the quadriceps.

Clinical features of torn lateral meniscus. The features are broadly similar, but the clinical picture is often less clearly defined. The history may be vague. Pain is at the lateral rather than the medial side of the joint, Instead it is often poorly localised.

Imaging. Plain radiographs are usually normal, whether the tear be of the medial or of the lateral meniscus, but in untreated cases of long duration signs of early degenerative arthritis may be noted in the affected compartment. Arthrography will often demonstrate meniscal tears, but it is now seldom undertaken because MRI is even more reliable in demonstrating the various types of tear and is non-invasive (Fig. 18.17).

Fig. 18.17 A Coronal MR scan of knee showing that the lateral meniscus has a bucket handle tear with a large meniscal fragment displaced centrally into the joint (arrow). B Sagittal T2 weighted MR scan of the knee with a vertical tear of the posterior horn of the medial meniscus (arrow).

Arthroscopy. On arthroscopic examination a meniscal tear can be seen whatever its site, except sometimes at the posterior end of the lateral meniscus (Fig. 18.18).

Fig. 18.18 Arthroscopic photograph showing tear of medial meniscus.

Diagnosis. In the ‘silent’ phase clinical diagnosis often depends largely upon the history. The surgeon should be very cautious in diagnosing a torn meniscus unless there is a clear history of injury and unless there have been recurrent incidents, each followed by synovial effusion. If one is relying on clinical diagnosis alone a period of observation may be required before the diagnosis becomes reasonably certain. MRI, or arthroscopy if this is not available, should establish the nature of the lesion conclusively.

Late effects. Long-continued internal derangement from a torn meniscus predisposes to the later development of degenerative arthritis. Arthritis is also liable to develop many years after a meniscus has been removed.

Treatment. Once the diagnosis is established the standard treatment is to excise either the whole meniscus or, more appropriately in most cases, the displaced ‘bucket-handle’ fragment alone. This operation is usually best carried out by the arthroscopic technique without formal opening of the joint – though of course the joint may be opened by incision if difficulty arises during the course of arthroscopic surgery. In selected cases of peripheral tear, repair by suture is sometimes undertaken using a semi-closed arthroscopic technique.

HORIZONTAL TEAR OF DEGENERATE MEDIAL MENISCUS

The meniscal tears described above are uncommon in patients over the age of 50, when the menisci begin to show degenerative changes. But a degenerate meniscus is liable to suffer a different type of lesion. The medial meniscus in particular may split horizontally at a point often near the middle of its convexity (Fig. 18.19). Such a split is usually of small dimensions, and since there is no separation of the fragments natural healing can occur.

Fig. 18.19 Horizontal tear of medial meniscus, seen in plan and on section.

Clinically there is troublesome and persistent pain at the medial aspect of the knee at the joint level. The pain may be noticed after a minor injury, but often an injury has not been remembered. In the early stages there is usually a small effusion of fluid into the joint.

Treatment should be expectant at first, by bandaging and quadriceps exercises. In most cases the symptoms resolve in the course of several months. In the occasional case in which they fail to do so, excision of the torn meniscal fragment by arthroscopic surgery should be advised.

CYSTS OF THE MENISCI

A cyst of a meniscus (semilunar cartilage) forms a tense, almost solid swelling at the level of the joint, usually on the lateral side.

Cause. Cysts arise spontaneously, but there is often a previous history of direct injury at the site of the cyst.

Pathology. The swelling is formed by a proliferation of fibrous tissue, which is honeycombed with small cystic cavities containing small quantities of clear gelatinous fluid.

Clinical features. The lateral meniscus is affected much more often than the medial. There is visible swelling, most obvious when the knee is held slightly flexed, at the level of the joint and usually anterior to the lateral (or medial) ligament (Fig. 18.20). The swelling tends to be painful at night and it is usually tender on firm pressure. The swelling is so tense that fluctuation can seldom be elicited – indeed it is sometimes mistaken for bone.

Fig. 18.20 Cyst of lateral meniscus.

Imaging. Radiographs may show an indentation of the side of the tibial condyle where the cyst has been in contact with it. MRI scanning will confirm the origin of the cyst from the meniscus (Fig. 18.21) and exclude more serious soft’tissue tumours.

Fig. 18.21 Sagittal T2 weighted MR scan of knee. There is a cyst lying adjacent to the anterior horn of the lateral meniscus. The adjacent meniscus has a horizontal tear. Meniscal cysts are always associated with a meniscal tear.

Treatment. If the disability justifies operation the cyst should be excised together with the meniscus from which it arises. Very occasionally, it may be practicable to excise the cyst arthroscopically while leaving the meniscus intact.

DISCOID LATERAL MENISCUS

Rarely the lateral meniscus (semilunar cartilage) fails to assume its normal crescentic form during development, but persists in its embryonic form as a thick disc-like mass interposed between the lateral condyles of the femur and tibia.

A discoid meniscus may cause recurrent discomfort in the knee, with a tendency to giving way. Usually a loud ‘clonk’ can be demonstrated on flexion–extension movements. These symptoms often become prominent during childhood or adolescence. If the disability becomes troublesome the meniscus should be removed. There is a risk of the development of degenerative arthritis in later life.

OSTEOCHONDRITIS DISSECANS OF THE KNEE (General description of osteochondritis dissecans, p. 153)

Osteochondritis dissecans is characterised by local ischaemic necrosis of a segment of the articular surface of a bone and of the overlying articular cartilage, with eventual separation of the fragment to form an intra-articular loose body. The knee is affected much more often than any other joint.

Cause. This is unknown. Impairment of the blood supply to the affected segment of bone by thrombosis of an end artery has been suggested. Injury is possibly a predisposing factor. There is also a constitutional predisposition to the disease, because it may affect several members of a family or several joints in the same patient.

Pathology. The lesion nearly always affects the articular surface of the medial condyle of the femur (Fig. 18.22). The size of the affected segment varies – it is often about 2 cm in diameter. Within the area of the lesion the subchondral bone is avascular and the overlying cartilage softens. A clear line of demarcation forms between the avascular segment and the surrounding normal bone and cartilage (Fig. 18.22A). After many months the fragment separates as a loose body (sometimes two or three), leaving a shallow cavity in the articular surface which is ultimately filled with fibrocartilage (Fig. 18.22B&C). The damage to the joint surface predisposes to the later development of osteoarthritis, especially when the fragment is large.

Fig. 18.22 The evolution of osteochondritis dissecans. A A segment of the articular surface dies. B A line of demarcation forms around it. C The fragment breaks away and lies loose in the joint, leaving a cavity in the femoral condyle.

Clinical features. The patient is an adolescent or a young adult, who complains of discomfort or pain in the knee after exercise, a feeling of insecurity, and intermittent swelling. The condition is commoner in males and may affect both knees in 15–20% of patients. When a loose body has already separated within the joint the predominant symptom is recurrent sudden locking. On examination there is a fluid effusion. The quadriceps muscle is wasted. Movements are not usually impaired.

Imaging. Radiographs show a clear-cut defect of the bone at the articular surface of the medial femoral condyle (Fig. 18.23). At first the cavity is occupied by the separating fragment of bone; but later the cavity may be empty, and a loose body will then be seen elsewhere in the joint. The lesion is shown best in tangential postero-anterior projections with the knee semiflexed (Fig. 18.23B). The advent of MRI has provided more valuable information on the state of the overlying articular cartilage and whether this is healing or liable to separate (Fig. 18.24).

Fig. 18.23 Osteochondritis dissecans. A Routine antero-posterior radiograph. B Tangential postero-anterior projection with knee semiflexed – the so-called intercondylar view. This shows clearly the large crescentic cavity in the medial femoral condyle, with the separating fragment in situ. Inset shows the loose fragment after removal.

Fig. 18.24 A Coronal MR scan of knee showing early osteochondritis dissecans. The arrow points to a defect of the cortex of the medial femoral condyle, which is the commonest site for this condition. B Coronal MR scan of knee. In this case the area of osteochondritis has become separated from the underlying bone and can potentially become displaced forming an intra-articular loose body.

Arthroscopy. The osteochondritic lesion in the medial femoral condyle will be clearly evident in the later stages. Initially, however, the defect is concealed by articular cartilage that looks normal, though if it is probed an area of softening may be apparent.

Treatment. In the developing stage treatment should be expectant: the knee is supported with a crepe bandage and strenuous activities are curtailed. Sometimes in these early cases the lesion will heal spontaneously, especially in young adolescents, and can be monitored by repeat MRI.

When the lesion shows a clear line of demarcation between the separating fragment and the surrounding normal bone – the loose piece should usually be removed, especially if it is small. This may be done arthroscopically. A shallow cavity is left in the femoral condyle, but this gradually fills with fibrocartilage and adequate function is usually restored.

Because of the risk of the later development of osteoarthritis if a large part of the femoral condyle has been excavated, some surgeons recommend that the loose fragment be replaced in position and fixed with a pin or pins. It has been shown that the fragment may unite again with its bed, but it is by no means certain yet that the incidence of late osteoarthritis will be reduced by this method of treatment. Attempts are now being made to use chondrocyte or osteochondral grafting of the defect for cases in which the separated fragment is large, but as yet the long-term results are uncertain.

LOOSE BODIES IN THE KNEE

The knee is the joint most commonly affected by the formation of loose bodies. There are four main causes:

Pathology. Osteochondritis dissecans was described on page 153. A loose body may be formed by spontaneous separation of a fragment of bone and cartilage from the articular surface of the medial femoral condyle. The loose body lies free in the joint, and a shallow cavity remains in the condyle.

Osteoarthritis was described on page 393. Some of the loose bodies that may be found in osteoarthritis are probably formed by detachment of marginal osteophytes. Most separated osteophytes, however, retain a synovial attachment and do not cause trouble: although they appear loose in radiographs they should not be regarded as such unless symptoms of locking indicate that they are moving freely within the joint. True loose bodies may possibly form from flakes of articular cartilage shed into the joint that gradually enlarge, nourished by synovial fluid.

Chip fracture of joint surface (osteochondral fracture) is an infrequent cause of intra-articular loose bodies. There is a clear history of the causative injury. A flake of bone with overlying articular cartilage is detached, always from a convex surface.

Synovial chondromatosis (osteochondromatosis) is a rare disease of the synovial membrane (p. 152). It is characterised by the formation of numerous small villous processes, which become pedunculated. Later their bulbous extremities become cartilaginous and they are detached to lie free in the joint. Finally, some or all of the numerous loose bodies become calcified.

Whatever the cause of a loose body, its repeated jamming between the joint surfaces will predispose to osteoarthritis after a long latent period, or will aggravate existing osteoarthritis.

Clinical features. The characteristic symptom of a loose body in the knee is recurrent locking of the joint from interposition of the loose piece between the joint surfaces. Suddenly, without warning, the knee becomes jammed during movement. Locking is accompanied by severe pain. After a variable interval the patient is usually able, by manoeuvring the limb, to disengage the loose body and free the joint. The next day the knee is found to be swollen with fluid. In many cases the patient is able to feel the mobile body through the soft tissues when it lies in a superficial part of the joint. It is common for such a body to lodge in the suprapatellar pouch.

On examination the findings are often slight, for a patient is seldom seen when the knee is locked. If he is seen soon afterwards a fluid effusion is present. Between attacks there may be no objective signs other than perhaps slight wasting of the quadriceps. Sometimes the loose body can be palpated, especially if it has migrated to the suprapatellar pouch. The features of an underlying condition such as osteoarthritis may be present.

Radiographic features. With few exceptions, loose bodies are shown radiographically. They often lie in the suprapatellar pouch (Fig. 18.25A). Care should be taken not to mistake the fabella (a seasmoid bone in the lateral head of the gastrocnemius) (Fig. 18.25B) for a loose body. The position of the fabella is constant: it lies slightly above the level of the joint well behind the femur and towards the lateral side, and it is always oval in shape with its long axis vertical.

Fig. 18.25 A Loose body in the knee. As in this case, loose bodies often lie in the suprapatellar pouch. B The fabella, a sesamoid bone in the lateral head of the gastrocnemius, is present in many normal persons. It is sometimes mistaken for a loose body in the joint.

Treatment. In general the treatment for an intra-articular loose body is to remove it, when possible by an arthroscopic technique. Removal should always be advised if the loose body is causing recurrent locking. If there are no symptoms of locking operation is not essential. In such cases the fragment, though appearing loose in the radiographs, is often attached to the synovial membrane and is kept out of harm’s way. This applies particularly to detached osteophytes in cases of osteoarthritis.

RECURRENT DISLOCATION OF THE PATELLA

The patello-femoral joint is one of the three joints that are most liable to recurrent displacement, the others being the shoulder and the ankle. In the case of the patello-femoral joint, unlike the other two, the instability is often caused by congenital factors rather than by an initial violent injury.

Pathological anatomy. In dislocations of the patella the displacement is always lateral, the patella slipping over the lateral condyle of the femur while the knee is flexed. Four factors, all of which may be inborn, predispose to recurrent dislocation:

This last factor is seldom an important one.

Clinical features. Recurrent dislocation of the patella is more common in girls than in boys. Often both knees are affected. Trouble usually begins during adolescence. Dislocation occurs while the patient is engaged in some activity that entails flexing the knees – not necessarily a violent exertion. Suddenly, while the knee is flexed or semiflexed, there is severe pain in the front of the knee, and the patient is unable to straighten it. Often the displacement of the patella is recognised and reduced on the spot, either by the patient herself or by an onlooker.

On examination in the dislocated state the knee is swollen, and the patella is seen and felt upon the lateral side of the lateral femoral condyle. After reduction the main signs are an effusion of fluid (usually blood-stained), and tenderness over the medial part of the quadriceps expansion, which is usually strained or torn. One of the minor anatomical anomalies mentioned above may be observed. In particular, generalised ligamentous laxity is often found, as evidenced by the patient’s ability to hyperextend the knee (genu recurvatum) or other joints such as the wrists or the joints of the fingers and thumb; this double-jointedness may be present also in parents or other relatives. The patella is often found to lie higher than normal, and it may be unduly small.

Imaging. Radiographs are seldom obtained in the state of dislocation. After reduction the knee may appear normal radiographically, but commonly the patella is small and is seen at a slightly higher level than usual, often in both knees (‘patella alta’).

MRI scans may be more informative and may demonstrate damage to the articular surface of the patella and any defects or tears in the medial soft’tissue structures (Fig. 18.26).

Fig. 18.26 Axial MR scan of knee in a patient following a recent acute dislocation of the patella. The large arrow indicates bone oedema where the patella has struck the condyle at the moment of dislocation. The star indicates the reciprocal bone oedema seen within the medial patellar facet. The small arrow indicates disruption of the medial patello-femoral ligament.

Course. Dislocation of the patella does not always become recurrent: some patients have no further trouble after an initial dislocation. But in most cases dislocations recur with ever-increasing ease and frequency, so that the patient may become seriously handicapped. Oft-repeated dislocations predispose to the later development of osteoarthritis.

Treatment. Treatment should be expectant at first. After a dislocation the patient should receive a course of physiotherapy designed to strengthen the quadriceps muscle, and especially the vastus medialis.

If the dislocations recur with such frequency that the patient is seriously disabled, operation should be advised. The method often recommended is to detach the bony insertion of the patellar tendon and transpose it to a new bed in the tibia, medial and distal to the original insertion (Fig. 18.27). In this way the patella is drawn lower into the deeper part of the intercondylar groove of the femur, and the line of pull of the quadriceps mechanism is transferred more to the medial side. This operation is often criticised on the grounds that it may be followed, after an interval of many years, by the development of degenerative arthritis. But such arthritis is an in-built complication of recurrent dislocation of the patella and cannot be ascribed solely to the operation. Other operations include release of tight soft tissues at the lateral side of the joint, reefing of the quadriceps expansion, and repair of the soft tissues on the medial side.

Fig. 18.27 Transposition of the insertion of the patellar tendon downwards and medially re-aligns the pull of the quadriceps and draws the patella down to lie in the intercondylar groove of the femur.

GENU VARUM AND GENU VALGUM

Genu varum (bow leg) and genu valgum (knock knee) occur commonly in childhood. In the vast majority of instances there is no underlying disease, and the deformity need not cause anxiety because it is gradually corrected spontaneously as the child grows.

Genu varum or genu valgum may also occur, either in children or in adults, as a consequence of injury or disease. The commonest causes are:

In assessing a case of genu varum or genu valgum the surgeon must always be careful to exclude such underlying organic disorders by full clinical examination, and if necessary by radiography, before diagnosing the benign childhood affections described in the following sections.

Benign genu varum of toddlers

The knee and leg are bowed outwards (Fig. 18.28A). A mild degree of this deformity is so common as to be almost normal in children aged 1 to 3 years. It does not require treatment unless it persists into later childhood. Care should be taken to exclude the possibility of rickets or other underlying bone disease.

Fig. 18.28 A Typical genu varum in a toddler. Slight bowing is common in infants but it is usually corrected spontaneously as the child grows. B Genu valgum. Deformity of this degree in young children is usually corrected spontaneously during growth.

RUPTURE OF THE QUADRICEPS APPARATUS

The quadriceps muscle gains insertion into the tibia through the medium of the patella (enclosed within the quadriceps expansion) and the patellar tendon. Complete rupture may occur at three points (Fig. 18.29):

Fig. 18.29 The three points at which the quadriceps apparatus may rupture. 1. At insertion of quadriceps into patella. 2. Through the patella. 3. At insertion of patellar tendon into tibial tubercle.

In all cases the injury is caused by an unexpected flexion force, resisted automatically by a sudden contraction of the quadriceps.

Avulsion from patella

Avulsion of the quadriceps tendon from the upper pole of the patella occurs mainly in elderly men, in whom the quadriceps tendon is often degenerate. It is not a common injury. The clinical diagnosis is seldom in doubt, but can be confirmed by ultrasound or MR scanning (Fig. 18.30). The tendon should be re-attached to the bone by strong non-absorbable sutures passed through drill holes near the upper border of the patella.

Fig. 18.30 Sagittal T2 weighted MR scan of knee showing a degenerate tear of the quadriceps tendon (arrow).

¹ Robert Osgood (1873–1956) was a famous American orthopaedic surgeon, but was working as a radiologist in Boston Children’s Hospital when he described the condition in 1903. He worked with Robert Jones in England during the First World War and helped him found the British Orthopaedic Association.

Carl Schlatter (1864–1934) was a Swiss general surgeon who also reported the condition in 1903, he later became Professor of Surgery in Zurich in 1924.

Apophysitis of the tibial tubercle is a childhood affection in which the tibial tubercle becomes enlarged and temporarily painful. Often known as Osgood–Schlatter’s disease, it was formerly regarded as an example of osteochondritis juvenilis (p. 130), but it is now generally agreed that it is nothing more than a strain of the developing tibial tubercle, from the pull of the patellar tendon.

Clinical and radiographic features. The patient is a child or adolescent aged 10 to 16 years, usually a boy, and often active in athletic pursuits. The complaint is of pain in front of and below the knee, worse on strenuous activity. On examination the tibial tubercle is unduly prominent, and tender on palpation. Pain is increased when the quadriceps is tensed, as in raising the leg against resistance with the knee held straight. The symptoms and signs are confined to the region of the tibial tubercle, and the knee joint itself is normal.

Radiographs show enlargement and sometimes fragmentation of the tibial tubercle (Fig. 18.31).

Fig. 18.31 Lateral radiograph of knee. The tibial tuberosity is fragmented. The normal appearance of the tibial tuberosity in adolescents is very variable. Diagnosis of Osgood–Schlatter’s syndrome is principally clinical based on localised pain and tenderness. Many patients with radiographs similar to this are asymptomatic.

Course. The disorder is usually self-limiting, and normal function is almost always restored by the time the apophysis of the tibial tubercle is fused to the main body of the bone.

Treatment. In most cases treatment is not required. If local pain and tenderness are severe and the symptoms persist into late adolescence, it may be necessary to rest the knee for a few weeks in an extension brace.

PREPATELLAR BURSITIS

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

Types. There are two types of prepatellar bursitis:

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. This can be achieved by appropriate imaging using ultrasound or MRI scans.

Baker’s cyst¹

A 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. 18.32A). 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. Occasionally this may rupture and the resultant pain and local tenderness may be mistaken for a deep vein thrombosis.

Fig. 18.32 A To show how a Baker’s cyst is formed as a herniation of the synovial membrane. B Sagittal T2 weighted MR scan of knee showing the typical appearance of a large popliteal or Baker’s cyst. The large high’signal lesion in the popliteal fossa is often associated with extensive degenerative changes in the knee joint, as seen here.

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.

Imaging. Where there is any uncertainty as to the diagnosis, it may be necessary to use ultrasound or MRI scanning to establish the nature and extent of the lesion (Fig. 18.32B).

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, with routine histological examination of the removed sac to confirm the diagnosis.

¹ Augusto Pellegrini (1877–1958), who was Professor of Surgery in Florence and later Perugia, described post-traumatic ossification of knee ligaments in 1905. He was also a pioneer in the development of powered prostheses for the upper limb.

Alfred Stieda (1869–1945) was a German surgeon and Professor in Konigsberg who also reported the condition in 1905.

Pellegrini–Stieda’s disease is the name sometimes used to describe ossification in the subligamentous haematoma after partial avulsion of the medial ligament from the medial condyle of the femur. Clinically there is persistent discomfort at the medial side of the knee after an injury to the medial ligament. There are thickening and slight tenderness over the site of attachment of the ligament to the medial femoral condyle. Radiographs show a thin plaque of new bone close to the medial condyle.

Treatment is by active mobilising and muscle-strengthening exercises.