CHAPTER 10 The knee

Fig. 10.A.

Anatomical Features

The knee joint (Fig. 10.A) combines three articulations (medial tibiofemoral (M), lateral tibiofemoral (L) and patellofemoral (P)), which share a common synovial sheath; anteriorly, this extends a little to either side (1) of the patella and an appreciable amount proximal to its upper pole (2). This portion, the suprapatellar pouch, lies deep to the quadriceps muscle.

There is little congruency between the articular surfaces of the tibia and femur; as a result, there is a well developed system of ligaments to give the knee stability, and an arrangement of intra-articular menisci to reduce the contact loadings between femur and tibia.

Ligaments

During the last 10° or so of knee extension the ligaments of the joint are twisted taut as a result of medial rotation (8) of the femur on the tibia; at the start of flexion, this tightening is undone by lateral rotation of the femur, aided by contraction of the popliteus muscle.

Menisci

In plan view the medial (m) and lateral (l) menisci are C-shaped; they are triangular in cross-section, and formed from dense avascular fibrous tissue. Their extremities (horns) (9) are attached to the upper surface of the tibia on which they lie; the posterior horn of the lateral meniscus has an additional attachment (10) to the femur, whereas both anterior horns are loosely connected (11). The concave margin (12) of each meniscus is unattached; the convex margin of the lateral meniscus is anchored to the tibia by coronary ligaments (13), whereas the corresponding part of the medial meniscus is attached to the joint capsule (14) and thereby loosely united to both femur and tibia.

During extension of the knee (15) the menisci slide forwards (16) on the tibial plateau and become progressively more compressed, adapting in shape to the altering contours of the particular portions of the femur and tibia between which they come to lie.

Only the peripheral edges of the menisci have an appreciable blood supply, so that meniscal tears that involve the more central portions have a poor potential for healing.

Bursae

Numerous bursae have been described round the knee, but from the practical point of view only a few are of any real significance.

At the front:

At the back:

Bursal enlargements may be encountered in the popliteal fossa, and these are generally referred to as Baker’s cysts or enlarged semimembranosus bursae. Some are found to communicate with the knee joint (sometimes with a valve-like mechanism), and tend to keep pace in terms of distension with any effusion in the knee.

Others are quite unconnected with the joint. The anatomical explanation is that although the semimembranosus bursa (SM) itself never communicates with the knee, it is often connected to the bursa (G) under the medial head of gastrocnemius, which does.

Swelling of the Knee

The knee may become swollen as a result of the accumulation within the joint cavity of excess synovial fluid, blood or pus (synovitis, haemarthrosis, pyarthrosis). Much less commonly, the knee swells beyond the limits of the synovial membrane. This is seen in soft tissue injuries of the knee, when haematoma formation and oedema may be extensive. It is also a feature of fractures, infections and tumours of the distal femur, where confusion may result either from the proximity of the lesion to the joint or because it involves the joint cavity directly. Although primary tumours of the knee are rare, in malignant synovioma there is striking swelling of the joint, and this often extends beyond the limits of the synovial cavity.

Synovitis, Effusion

The synovial membrane secretes the synovial fluid of the joint; excess synovial fluid indicates some affection of the membrane. Joint injuries cause synovitis by tearing or stretching the synovial membrane. Infections act directly by eliciting an inflammatory response which causes the synovial membrane to secrete more fluid. The membrane itself becomes thickened and its function disturbed in rheumatoid arthritis and villonodular synovitis; both conditions are usually accompanied by large effusions. In long-standing meniscus lesions and in osteoarthritis of the knee the synovial membrane may not be directly affected, and consequently no effusion may be present in either of these conditions. Minor injuries of the knee which do not materially damage any of the main structural elements are in some cases followed by rather persistent effusions (traumatic synovitis). In spite of these exceptions, the recognition of fluid in the joint is of great importance. Effusion indicates damage to the joint, and the presence of a major lesion must always be eliminated. A tense synovitis may be aspirated to relieve discomfort.

Haemarthrosis

Blood in the knee is seen most commonly following acute injuries where there is tearing of vascular structures. The menisci are avascular, and there may be no haemarthrosis when a meniscus is torn. Bleeding into the joint will take place, however, if the meniscus has been detached at its periphery, or if there is accompanying damage to other structures within the knee (e.g. the cruciate ligaments). In injuries of the medial ligament, a haematoma may track distally without involvement of the joint cavity. Nevertheless, the presence of a haemarthrosis generally indicates a substantial injury to the joint and is a serious finding. Its physical presence alone may give rise to great discomfort and make diagnosis of its underlying cause rather difficult. In view of this a tense, painful haemarthrosis should be aspirated.

Pyarthrosis

Infections of the knee joint are rather uncommon, and usually bloodborne. Sometimes the joint is involved by direct spread from an osteitis of the femur or tibia; rarely the joint becomes infected following surgery or penetrating wounds.

In acute pyogenic infections the onset is usually rapid and the knee very painful; swelling is tense, tenderness is widespread, and movement resisted. There is pyrexia and general malaise. Pyogenic infections occurring in patients already suffering from rheumatoid arthritis often have a much slower onset. Although the joint is invariably swollen, other inflammatory changes are often suppressed, especially if the patient is receiving steroids.

Tuberculous infections of the knee, now uncommon in the UK, have a slow onset spread over weeks. The knee appears small and globular, with the associated profound quadriceps wasting contributing to this appearance.

In gonococcal arthritis, great pain and tenderness, often apparently out of proportion to the local swelling and other signs, are the striking features of this condition.

When pus is suspected in a joint, aspiration should always be carried out to empty it and obtain specimens for bacteriological examination. If tuberculosis is suspected, synovial biopsy to obtain specimens for culture and histology is required. All knee infections are treated by splintage and an appropriate antibiotic regimen.

Extensor Mechanism of the Knee

Extension of the knee is produced by the quadriceps muscle acting through the quadriceps ligament, patella, patellar ligament and tibial tubercle. Weakness of extension leads to instability, repeated joint trauma and effusion. There is often a vicious circle of pain → quadriceps inhibition → quadriceps wasting → knee instability → ligament stretching and further injury → pain. Loss of full extension also leads to instability, as there is failure of the screwhome mechanism which tightens the ligaments of the joint at terminal extension.

Rapid wasting of the quadriceps is seen in all painful and inflammatory conditions of the knee. Weakness of the quadriceps is also sometimes found in lesions of the upper lumbar intervertebral discs, as a sequel to poliomyelitis, in multiple sclerosis and other neurological disorders, and in the myopathies. Difficulty in diagnosis is common when the wasting is the presenting feature of a diabetic neuropathy or secondary to femoral nerve palsy from an iliacus haematoma. Maintenance of good quadriceps tone and breaking the quadriceps vicious circle is an essential part of the treatment of virtually all conditions affecting the knee joint.

Disruption of the extensor mechanism of the knee is seen in a number of conditions. Fractures of the patella seldom give difficulty in diagnosis provided the appropriate radiographs are taken. Ruptures of the quadriceps tendon or patellar ligament result from sudden, violent contraction of the quadriceps and are seen in the middle-aged when there has been some accompanying degenerative change in the structures involved. Avulsion of the tibial tuberosity may also be seen as a result of a sudden muscle contraction. All these acute conditions are generally treated surgically.

There are a number of conditions short of disruption which may affect the patellar ligament and its extremities, with the generic title of jumper’s knee. In the Sinding–Larsen–Johansson syndrome, seen in children in the 10–14-year age group, there is aching pain in the knee associated with X-ray changes in the distal pole of the patella. Osgood–Schlatter’s disease (which is often thought to be due to a partial avulsion of the tuberosity) occurs in the 10–16 age group. There is recurrent pain over the tibial tuberosity, which becomes tender and prominent. Radiographs may show partial detachment or fragmentation of the tuberosity. Pain usually ceases with closure of the epiphysis, and the management is usually conservative. In an older age group (16–30) the patellar ligament itself may become painful and tender. This almost invariably occurs in athletes, and there may be a history of giving—way of the knee. CT scans may show changes in the patellar ligament, which becomes expanded centrally. Exploration and incision of the patellar ligament is usually advised. Rarely, pain and tenderness may occur proximal to the upper pole of the patella in quadriceps tendinitis.

Ligaments of the Knee

The cruciate, collateral, posterior and capsular ligaments, and the menisci, form an integrated stabilising system which prevents the tibia from shifting or tilting under the femur in an abnormal fashion. The pathological movements that may occur after ligamentous injury are (a) tilting of the knee into varus or valgus, (b) shifting of the tibia directly forwards or backwards (anterior or posterior translation), and (c) rotation of the tibia under the femur so that the medial or lateral tibial condyle subluxes forwards or backwards.

Ligament injuries are important to detect as they may account for appreciable disability, in the form of incidents of giving way of the joint, recurrent effusion, lack of confidence in the knee, difficulty in undertaking strenuous or athletic activities, and sometimes trouble in using stairs or walking on uneven ground.

The diagnosis and interpretation of instability in the knee is difficult and somewhat controversial, for the following reasons:

The Medial Ligament and Capsule

The medial ligament stretches between the femur and the tibia and has both superficial and deep layers. Considerable violence (usually in the form of a valgus strain or a blow on the lateral side of the knee) is required to damage the medial ligament. When the forces are moderately severe a few fibres only may be torn, usually near the upper attachment (sprain of the medial ligament). Then, when the knee is examined clinically, no instability will be demonstrated, but stretching the ligament will cause pain. Minor tears of the medial ligament may be followed eventually by calcification in the accompanying haematoma, and this may give rise to sharply localised pain at the upper attachment (Pellegrini–Stieda disease).

With greater violence the whole of the deep part of the ligament ruptures, followed in order by the superficial part, the medial capsule, the posterior ligament, the posterior cruciate ligament, and sometimes finally the anterior cruciate ligament. Acute complete tears give rise to serious instability in the knee, which can move or be moved into valgus. They are usually dealt with by immediate surgical repair. Partial tears do well by immobilisation for 6 weeks in a pipe-stem plaster. Chronic lesions may be accompanied by tibial condylar subluxation (see later), although there is some doubt as to whether this is indeed possible without there being some additional damage to the anterior cruciate ligament. Surgical treatment may be indicated for such instability. Medial ligament tears may accompany fractures of the lateral tibial table, which will require additional attention.

The Lateral Ligament and Capsule

This ligament may be damaged by blows on the medial side of the knee, throwing it into varus. It most frequently tears at its fibular attachment. As in the case of the medial ligament, increasing violence will lead to tearing of the posterior capsular ligament and the cruciates. In addition, the common peroneal nerve may be stretched and sometimes irreversibly damaged. These injuries are usually treated by operative repair and, where applicable, exploration of the common peroneal nerve. Again, any associated fracture of the medial tibial table may require attention. Chronic lesions may be associated with tibial condylar subluxations.

The Anterior Cruciate Ligament

Impaired anterior cruciate ligament function is seen most frequently in association with tears of the medial meniscus. In some cases this is due to progressive stretching and attrition rupture of the ligament. (This may occur if an attempt is made to obtain full extension in a knee blocked by a meniscal fragment.) In others, the anterior cruciate ligament tears at the same time as the meniscus, and in the most severe injuries the medial ligament may also be affected (O’Donoghue’s triad).

Isolated ruptures of the anterior cruciate ligament are uncommon and are not usually treated surgically unless accompanied by avulsion of bone at the anterior tibial attachment, or if there is a strongly positive pivot shift test.

When the tear is acute and accompanies a meniscal lesion, the meniscus is preserved if at all possible to reduce the risks of tibial subluxation and secondary osteoarthritic change, although the damage may be such that excision cannot be avoided. After attention to the meniscus, many would then advocate direct repair of the anterior cruciate ligament, supplemented by a ligament reinforcement or a reconstruction procedure (e.g. using part of the patellar ligament and its bony attachments). When an acute anterior cruciate tear is associated with damage to the medial or, less commonly, the lateral collateral ligament, a similar approach may be employed.

Chronic anterior cruciate ligament laxity generally results from old injuries, and may cause problems from acute, chronic or recurrent tibial subluxations. There may be a history of giving way of the knee, episodic pain and functional impairment. There is often quadriceps wasting and effusion, and secondary osteoarthritis may develop. Intense quadriceps and hamstring muscle building is usually advised as a first measure. In resistant cases, a ligament reconstruction may be advocated. There is no doubt that these procedures are often initially very successful, but in some the long-term results are disappointing.

The Posterior Cruciate Ligament

Posterior cruciate ligament tears are produced when in a flexed knee the tibia is forcibly pushed backwards (as, for example, in a car accident when the upper part of the shin strikes the dashboard). Most advise immediate surgical repair if the injury is seen at the acute stage, as persisting instability and osteoarthritis are common sequelae in the untreated case.

Rotatory Instability of the Knee: Tibial Condylar Subluxations

In this group of conditions, when the knee is stressed the tibia may sublux forwards or backwards on either the medial or lateral side, giving rise to pain and a feeling of instability in the joint. The main forms are as follows:

1. The medial tibial condyle subluxes anteriorly (anteromedial rotatory instability). In the most severe cases this occurs as a result of tears of both the anterior cruciate ligament and the medial structures (medial ligament and capsule). The medial meniscus may also be damaged and contribute to the instability. In the less severe cases there is some controversy regarding which structures may be spared. Clinically, the condition should be suspected on the evidence of the anterior drawer and Lachman tests, and the demonstration of instability on applying a valgus stress to the joint.

2. The lateral tibial condyle subluxes anteriorly (anterolateral rotatory instability). In the more severe cases the anterior cruciate ligament and the lateral structures are torn, and there may be an associated lesion of the anterior horn of the lateral meniscus. It may be diagnosed from the results of the anterior drawer and Lachman tests, and by demonstrating instability on applying a varus stress to the knee, although a number of specific tests may afford additional confirmation.

3. The lateral tibial condyle subluxes posteriorly (posterolateral rotatory instability). This may follow rupture of the lateral and posterior cruciate ligaments, and be recognised by the presence of instability in the knee on applying varus stress, in combination with eliciting an abnormal posterior drawer test. There are also specific tests for this instability.

4. Combinations of these lesions (particularly 1 and 2, and 2 and 3) may be found, especially where there is major ligamentous disruption of the knee.

Where symptoms are demanding, and when a firm diagnosis has been established, the stability of the joint may be restored by an appropriate ligamentous reattachment or reconstruction procedure.

Lesions of the Menisci

Congenital Discoid Meniscus

This abnormality, most frequently involving the lateral meniscus, commonly gives rise to presenting symptoms in childhood. The meniscus has not its usual semilunar form but is D-shaped, with its central edge extending in towards the tibial spines. It may produce a very pronounced clicking from the lateral compartment, a block to extension of the joint, and other derangement signs. It is usually treated by excision.

Meniscus Tears in the Young Adult

The commonest cause is a sporting injury, when a twisting strain is applied to the flexed, weightbearing leg. The trapped meniscus commonly splits longitudinally, and its free edge may displace inwards towards the centre of the joint (bucket-handle tear). This prevents full extension (with physiological locking of the joint), and if an attempt is made to straighten the knee a painful elastic resistance is felt (’springy block to full extension’). In the case of the medial meniscus, prolonged loss of full extension may lead to stretching and eventual rupture of the anterior cruciate ligament.

The aim in treating meniscal tears is to correct the mechanical problems that they have created within the joint, while if at all possible preserving as much of each meniscus as is possible; this, it is thought, will reduce the risks of instability and the onset of secondary osteoarthritis. In many cases the torn part of the meniscus (e.g. the handle of a bucket-handle tear) only is excised, but some major meniscal tears may require total meniscectomy. In peripheral detachments and certain other lesions, particularly those near the periphery of the meniscus, repair by direct suture or other measures is sometimes attempted. Many surgical procedures are performed arthroscopically, thereby facilitating early recovery.

Degenerative Meniscus Lesions in the Middle-Aged

Loss of elasticity in the menisci through degenerative changes associated with the ageing process may give rise to horizontal cleavage tears within the substance of the meniscus; these tears may not be associated with any remembered traumatic incident, and sharply localised tenderness in the joint line is a common feature. In an appreciable number of cases symptoms may resolve without surgery, although this may sometimes be required.

Cysts of the Menisci

Ganglion-like cysts occur in both menisci, but are much more common in the lateral. Medial meniscus cysts must be carefully distinguished from ganglions arising from the pes anserinus (the insertion of sartorius, gracilis and semitendinosus). In true cysts there is often a history of a blow on the side of the knee over the meniscus. They are tender, and as they restrict the mobility of the menisci they render them more susceptible to tears. They are generally treated by excision, and sometimes simultaneous meniscectomy may be required, especially if there are problems with recurrence. Some workers believe that all meniscal cysts have an associated tear, and prefer to deal with the problem by arthroscopic resection of the tear and simultaneous decompression of the cyst through the substance of the meniscus.

Patellofemoral Instability

The patella has always a tendency to lateral dislocation as the tibial tuberosity lies lateral to the dynamic axis of the quadriceps (Fig. 10.B); any tightness in the extensor mechanism (e.g. from quadriceps contractions or fibrosis) generates a lateral component of force that tends to displace the patella laterally. Normally, at the beginning of knee flexion the patella engages in the groove separating the two femoral condyles (the trochlea), and this keeps it in place as flexion continues. This system may be disturbed in a number of ways. The side thrusts that tend to cause the patella to sublux laterally may be increased by an abnormal lateral insertion of the quadriceps, tight lateral structures, or by increases in the angle between the axis of the quadriceps and the line of the patellar ligament (e.g. as a result of knock-knee deformity, or by a broad pelvis). The lateral condyle which supports and guides the patella may be deficient, or the patella itself may be small and poorly formed (hypoplasia). If the patella is highly placed (patella alta) it may fail to engage in the condylar groove at the beginning of flexion. (This condition is often associated with genu recurvatum.) Medial to the patella the soft tissues that would normally help prevent an abnormal lateral excursion of the patella may be deficient, sometimes as a result of stretching from previous dislocations.

Fig. 10.B. Some factors relating to patellar instability. Because the quadriceps and the patellar ligament meet at an angle (Q angle) there is a lateral component of force when the quadriceps contracts, and this tends to dislocate the patella laterally (a). This is resisted by the femoral sulcus in which the patella lies, and the prominence of the lateral femoral condyle (b). This mechanism may be interfered with by an abnormal lateral insertion of the quadriceps (c), or an increase in the Q angle (e.g. in knock knee) (d). The lateral femoral condyle may be hypoplastic and the condylar sulcus shallow (e); or the patella itself may be hypoplastic (f). The patella may be highly placed, especially in genu recurvatum (g), so that it fails to engage in the condylar gutter.

There are a number of conditions characterised by loss of normal patellar alignment.

Retropatellar/Anterior Knee Pain Syndromes/Chondromalacia Patellae

These are characterised by chronic ill-localised pain at the front of the knee, often made worse by prolonged sitting, or walking on slopes or stairs. It is commonest in females in the 15–35-year age group, and the pathology is often uncertain. In some there is softening or fibrillation of the articular cartilage lining the patella (chondromalacia patellae), and some of these cases progress to develop clear patellofemoral osteoarthritis.

Those suffering from retropatellar knee pain (anterior knee pain) may be divided into two groups: in one no significant cause can be found, whereas in the other there is evidence of patellar malalignment. In this latter group some of the factors responsible for recurrent dislocation may be found to be present (even although there may be no history of frank dislocation). Although symptoms are often prolonged, they are usually not severe and may be dealt with by restriction of the activities known to aggravate the symptoms, and by physiotherapy. In some cases, where symptoms are particularly severe and unresponsive, and where there is evidence of malalignment, lateral release and patellar debridement procedures are often practised. Where the articular surface of the patella is seriously involved, patellectomy is sometimes advocated. Anterior knee pain was once thought to be associated with excessive foot pronation, but this is no longer considered to be the case.

Osteochondritis Dissecans

This occurs most frequently in males in the second decade of life, and most commonly involves the medial femoral condyle. Possibly as a result of impingement against the tibial spines or the cruciate ligaments, a segment of bone undergoes avascular necrosis, and a line of demarcation becomes established between this area and the underlying healthy bone. Complete separation may occur so that a loose body is formed. The symptoms are initially of aching pain and recurring effusion, with perhaps locking of the joint if a loose body is present. Good results generally follow conservative treatment with quadriceps exercises and continued weightbearing if the condition is found before epiphyseal closure. If the fragment becomes loose, it should be fixed surgically. If the lesion is long standing, with a fragment smaller than its crater, it should be excised. The cavity may be drilled in an attempt to encourage vascularisation of its base. In all cases the damaging effects of a loose body must be prevented.

Fat Pad Injuries

The infrapatellar fat pads may become tender and swollen and give rise to pain on extension of the knee, especially if they are nipped between the articulating surfaces of femur and tibia. This may occur as a complication of osteoarthritis, but is seen more frequently in young women when the fat pads swell in association with premenstrual fluid retention. Excision of the pads may be required to relieve the symptoms.

Loose Bodies

Loose bodies are seen most frequently as a sequel to osteoarthritis or osteochondritis dissecans. Much less commonly, numerous loose bodies are formed by an abnormal synovial membrane in the condition of synovial chondromatosis. Loose bodies are treated by excision, but synovectomy may be required in synovial chondromatosis if massive recurrence is to be avoided.

Affections of the Articular Surfaces

Osteoarthritis (Osteoarthrosis)

The stresses of weight-bearing mainly involve the medial compartment of the knee, and it is in this area that primary osteoarthritis usually first occurs. This is an exceedingly common condition, arising without any obvious previous pathology in the joint. Overweight, the degenerative changes accompanying old age, and overwork are common factors. Secondary osteoarthritis may follow ligament and meniscus injuries, recurrent dislocation of the patella, osteochondritis dissecans, joint infections and other previous pathology. It is seen in association with knock-knee and bow-leg deformities, which throw additional mechanical stresses on the joint.

In osteoarthritis the articular cartilage undergoes progressive change, flaking off into the joint and thereby producing the narrowing that is a striking feature of radiographs of this condition. The subarticular bone may become eburnated, and often small marginal osteophytes and cysts are formed. Exposure of bone and free nerve endings gives rise to pain and crepitus on movement. Distortion of the joint surfaces is one cause of progressive loss of movement and fixed flexion deformities. Treatment is generally conservative, by quadriceps exercises, short-wave diathermy, analgesics and weight reduction. Surgery may be considered in severe cases. The procedures available include joint replacement, osteotomy (especially in cases of genu varum and valgum) and arthrodesis.

Rheumatoid Arthritis

Characteristically the knee is warm to touch, there is effusion, limitation of movements, muscle wasting, synovial thickening, tenderness and pain. Fixed flexion, valgus and (less commonly) varus deformities are quite common. Generally other joints are also involved, although the monoarticular form is occasionally seen. Active cases are often treated by synovectomy in an attempt to avoid or delay the progress of the condition. An acute flare-up of symptoms may be treated by temporary splintage. Either joint replacement, osteotomy or arthrodesis may be considered in well selected cases.

Reiter’s Syndrome

This usually presents as a chronic effusion accompanied by discomfort in the joint. It is often bilateral, with an associated conjunctivitis. There is often a history of urethritis or colitis.

Ankylosing Spondylitis

The first symptoms of ankylosing spondylitis are generally in the spine, but occasionally the condition presents at the periphery, with swelling and discomfort in the knee joint. Stiffness of the spine and radiographic changes in the sacroiliac joints are nevertheless almost invariably present.

Disturbances of Alignment

Genu Varum (Bow Leg)

This commonly occurs as a growth abnormality of early childhood, and usually resolves spontaneously. Rarely genu varum is caused by a growth disturbance involving both the tibial epiphysis and the proximal tibial shaft (tibia vara), and treatment by osteotomy may be required. In adults this deformity most frequently results from osteoarthritis, where there is narrowing of the medial joint compartment. It also occurs in Paget’s disease and rickets. It is less common in rheumatoid arthritis unless secondary osteoarthritic changes supervene in that condition.

Genu Valgum (Knock Knee)

This is seen most often in young children, where it is usually associated with flat foot. Nearly all cases resolve spontaneously by the age of 6. It is also seen in the plump adolescent girl, and it may be a contributory factor in recurrent dislocation of the patella. In adults it most frequently occurs as a result of the bone softening and ligamentous stretching accompanying rheumatoid arthritis. It occurs after uncorrected depressed fractures of the lateral tibial table, and as a sequel to a number of paralytic neurological disorders where there is ligament stretching and altered epiphyseal growth. Selected cases may be treated by corrective osteotomy.

Genu Recurvatum

Hyperextension at the knee is seen after ruptures of the anterior cruciate ligament and in girls where the growth of the upper tibial epiphysis may be retarded from much pointe work in ballet classes or from the wearing of high-heeled shoes in early adolescence. In the latter cases there is corresponding elevation of the patella (patella alta) contributing to a tendency to recurrent dislocation. More rarely, the deformity is seen in congenital joint laxity, poliomyelitis and Charcot’s disease.

Bursitis

Cystic swelling occurring in the popliteal region in both sexes is usually referred to as enlargement of the semimembranosus bursa. In fact, several of the bursae known to the anatomist may be involved, either singly or together. The swelling sometimes communicates with the knee joint and may fluctuate in size. Rupture may lead to the appearance of bruising on the dorsum of the foot, and this may help to distinguish it from deep venous thrombosis or cellulitis. If there is any doubt about the diagnosis, or if the swelling is persistent and producing symptoms, excision is advised.

Fluctuant bursal swellings may also occur over the patella (prepatellar bursitis or housemaid’s knee) or the patellar ligament (infrapatellar bursitis or clergyman’s knee). Chronic prepatellar bursitis, with or without local infection, is common in miners, where it is referred to as ‘beat knee’; it is also associated with other occupations where prolonged kneeling is unavoidable (e.g. it is common in plumbers and carpet layers). If the swelling is bulky or tense it is aspirated; recurrent swellings, if troublesome, are excised.

How to Diagnose a Knee Complaint

1. Note the patient’s age and sex, bearing in mind the following important distribution of the common knee conditions (Table 10.1).

Table 10.1

Infections are comparatively uncommon and occur in both sexes in all age groups.

Reiter’s syndrome occurs in adults of both sexes; ankylosing spondylitis nearly always occurs in adult males. Both are comparatively rare.

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