History

The history is of particular importance in the diagnosis of disorders of the knee. In a case of torn meniscus, for instance, the history is often the most important factor in the clinical diagnosis. When there has been a previous injury to the knee, the exact sequence of events at the time of the injury and afterwards must be ascertained. Enquiry is made into the mechanism of the injury; what the patient was doing at the time; whether he was able to carry on afterwards. Was he able to finish the game? If not, was he carried from the field or was he able to walk? How soon after the injury did the knee swell? Was he able to straighten the knee fully? If not, how did he eventually get it straight? Was he able to bend it? These and many other details must be elicited by careful questioning because they are so important in building up a picture of what exactly happened to the knee. Caution is necessary in accepting the patient’s story of ‘locking’ at its face value. Many patients speak of ‘locking’ when the knee simply feels stiff and painful, or when it causes momentary jabs of pain on movement. Locking from a torn meniscus means simply that the knee cannot be straightened fully; it can usually be flexed freely. In locking from a loose body within the joint the knee may be jammed so that it will neither flex nor extend, but this is rather uncommon and the knee usually unlocks itself after an interval, or can be freed by judicious manoeuvring.

Exposure

For proper examination the whole length of the limb must be uncovered. It is impossible to examine a knee adequately when the thigh is half covered by tightly rolled trousers or underpants. The sound knee must also be exposed for comparison. For proper examination of the knee the patient must always be recumbent upon a couch.

Steps in clinical examination

A suggested routine for clinical examination of the thigh and knee is summarised in Table 18.1.

Table 18.1 Routine clinical examination in suspected disorders of the thigh and knee

Determining the cause of a diffuse joint swelling

The knee exemplifies better than any other joint the different types of diffuse articular swelling. That the joint is in fact swollen should be obvious from inspection: comparison of the two knees will show that the concavities present at each side of the patella have been filled out on the affected side.

A diffuse swelling of the knee can arise only from three fundamental causes:

Determination of the particular cause or combination of causes in a given case depends entirely on careful palpation, as follows:

Thickening of bone. Thickening of bone is detected without difficulty by deep palpation if the affected side is compared with the normal. There may be a general enlargement, caused perhaps by a bone infection or by an expanding tumour or cyst; or there may be simply a local prominence, caused usually by osteophytes at the joint margin or by an exostosis.

Fluid within the joint. A fluid effusion is best detected by the fluctuation test. The palm of one hand is placed upon the thigh immediately above the patella – that is, over the suprapatellar pouch. The other hand is placed over the front of the joint, with the thumb and index finger just beyond the margins of the patella (Fig. 18.1A). Pressure of the upper hand upon the suprapatellar pouch drives fluid from the pouch into the main joint cavity, where it bulges the capsule at each side of the patella and imparts an easily detectable hydraulic impulse to the finger and thumb of the lower hand (Fig. 18.1B). Conversely, by pressure of this finger and thumb the fluid can be driven back into the suprapatellar pouch, the hydraulic impulse being clearly received by the upper hand. In this way an unmistakable sense of fluctuation can be elicited between the two hands. With practice it is easy to detect even a small effusion in this way. The ‘patellar tap’ test (Fig. 18.1C), in which the patella is tapped backwards sharply so that it strikes the femur and rebounds, though still used, is less reliable. The test is negative in the presence of fluid in two circumstances: first, when there is insufficient fluid to raise the patella away from the femur; and secondly, when there is a tense effusion. If used at all, the ‘patellar tap’ test should be used only as a supplementary method.

Fig.18.1 A Fluctuation test for fluid in the knee joint. One hand compresses the suprapatellar pouch, B while the thumb and finger of the other hand detects the fluid impulse on either side of the patella. C In the patellar tap test the finger pushes the patella onto the front of the femoral condyle through the fluid resistance.

Distinction between effusions of blood, serous fluid, and pus is made partly from the history, partly from the clinical examination. An effusion of blood (haemarthrosis) appears within an hour or two of an injury and rapidly becomes tense and therefore painful. An effusion of clear fluid develops slowly (12–24 hours) and is never as tense as an effusion of blood (haemarthrosis). An effusion of pus is associated with general illness and pyrexia.

Thickening of synovial membrane. A thickened synovial membrane is always a prominent feature of chronic inflammatory arthritis. The thickening is often most obvious above the patella, where the reduplicated membrane forms the suprapatellar pouch. It has a characteristic boggy feel on palpation, rather as if a sheet of warm sponge-rubber had been placed between the skin and the underlying bone. It is worth emphasising that since it is highly vascular, a thickened synovial membrane is always associated with increased warmth of the overlying skin.

Movements

Accurate assessment of the range of movement is particularly important in the knee, because even a slight impairment of movement is significant. It is important to note also whether movement is painful and whether it is accompanied by crepitation.

Flexion. The normal range varies with the build of the patient. Thin patients can flex more than fat patients – usually enough to bring the heel in contact with the buttock. The range of the sound knee should always be taken as the normal for the individual.

Extension. There is a fairly wide variation in the normal range of extension: it is wrong to accept 0 ° as the starting-point of movement (0 ° = the anatomical position, with the knee straight). Many normal women can hyperextend their knees whereas some normal men cannot extend quite to the straight position. Variations are only of small magnitude but they may be significant. It is important to detect even a slight impairment of knee extension: therefore the range on the sound side must be taken as the yardstick of normal extension and a very careful comparison must be made between the two sides.

Tests for stability

The integrity of each of the four major ligaments is tested in turn.

Testing the medial and lateral ligaments. For this test the joint must be in a position just short of full extension, so that the posterior part of the joint capsule is relaxed: with the knee fully extended even marked laxity of the collateral ligaments can be masked by the intact posterior capsule, held taut. It must be remembered, however, that with the knee slightly flexed the medial and lateral ligaments are normally somewhat slack and allow a little side-to-side wobble. Technique: Support the limb by a hand gripping the ankle region and by the other hand behind the knee, flexing it slightly. Instruct the patient to relax the muscles. Using the more proximal hand as a fulcrum on the appropriate side of the knee, apply first an abduction force to test the medial ligament (Fig. 18.2A) and then an adduction force to test the lateral ligament. If the ligament is torn, the joint will open out more than in the normal knee when stress is applied.

Fig. 18.2 A Testing the medial ligament. The knee is held slightly flexed (see text). B Testing the cruciate ligaments. The patient’s foot is steadied by sitting upon it. Pulling the tibia forwards tenses the anterior ligament; pushing it backwards tenses the posterior ligament.

Testing the anterior and posterior cruciate ligaments. The anterior cruciate ligament prevents anterior glide of the tibia on the femur; the posterior cruciate ligament prevents posterior glide. First the ligaments are tested with the knee flexed 90 °. Technique: The patient’s knee being flexed to a right angle and the foot placed firmly on the couch, sit lightly on the foot to prevent it from sliding (Fig. 18.2B). With the interlocked fingers of the two hands form a sling behind the upper end of the tibia, and clasp the sides of the leg between the thenar eminences. Place the tips of the thumbs one upon each femoral condyle. Ensure that the patient has relaxed the thigh muscles. Alternately pull and push the upper end of the tibia to determine the amount of antero-posterior movement. Normally there is an antero-posterior glide of up to half a centimetre; but since the normal is variable it is wise to use the patient’s sound limb for comparison. Excessive glide in one or other direction indicates damage to the corresponding cruciate ligament.

In a second test the ligaments are examined with the knee flexed only 15 ° or 20 ° (Lachman test). One hand supports the thigh just above the knee, gripping the femoral condyles, while the other hand grasps the upper end of the tibia (Fig. 18.3). While the patient relaxes the muscles the extent of any anterior or posterior glide of the tibial condyles upon the femur is determined by push-and-pull movements of the tibia.

Fig. 18.3 In the Lachman test the amount of anterior or posterior glide of the tibia upon the femur is assessed with the knee flexed only about 20 °.

Lateral pivot shift. The test for lateral pivot shift is supplementary to the tests described above for deficiency of the anterior cruciate ligament: it may be positive when the foregoing test is equivocal. The test depends on the fact that when the anterior cruciate ligament and the lateral ligament are deficient or lax the pivot between the lateral condyle of the femur and that of the tibia may be unstable. In that event the lateral tibial condylar surface may be displaced forwards in relation to the femoral condyle when the tibia is rotated medially with the knee straight. When the knee is then flexed the subluxation is spontaneously reduced with a visible or palpable ‘jerk’. The test is thus an indication of antero-lateral instability.

Technique. The leg on the affected side is lifted by the examiner’s corresponding hand (the right foot is lifted by the right hand; the left leg by the left hand) so that the knee drops into full extension with the muscles relaxed. The limb is supported under the arm, and with the other hand the examiner then presses against the outer aspect of the limb just below the knee, imparting a valgus strain (Fig. 18.4). At the same time the tibia is rotated medially upon the femur. The knee is now flexed slowly from the straight position. If the test is positive the lateral tibial condyle becomes spontaneously relocated on the femoral condyle when the knee reaches 30 ° or 35 ° of flexion. The relocation is evidenced by a visible or palpable jerk (hence the term ‘jerk test’ sometimes used for the manoeuvre).

Fig. 18.4 Test for lateral pivot shift. The test depends upon first rotating the tibia medially to provoke subluxation of the lateral condyle of the tibia upon the lateral femoral condyle, and then correcting the subluxation by flexing the knee (see text).

Rotation test for pedunculated tag of meniscus

The object of this test, often known as McMurray’s test and used only for suspected tears of the menisci, is to demonstrate a pedunculated tag of meniscus by causing it to be momentarily jammed between the joint surfaces: when the knee is then straightened a loud click may be heard and felt as the tag is disengaged.

The manoeuvre is carried out by repeatedly:

A loud click, distinct from the normal patellar click and usually associated with pain, suggests a tag tear (not a ‘bucket-handle’ tear) of a meniscus. Caution: Loud clicks can often be produced in normal knees. Most of them arise from movements of the patella, and they are not accompanied by pain. Discretion must be used in interpreting a click as an abnormal finding.

Extrinsic causes of pain in the thigh and knee

In most cases symptoms felt in the knee have their origin locally in or near the joint; but there are exceptions that may trap the unwary. Most importantly, pain in the knee may be the predominant feature of a disorder of the hip, such as arthritis or slipped upper femoral epiphysis. Less commonly sciatic pain, perhaps from a prolapsed intervertebral disc, has its greatest intensity at the level of the knee. In the investigation of pain in the knee we must therefore recognise the possibility that it may be referred from the spine or hip, and extend the examination to those regions if a satisfactory explanation for the trouble is not found on local examination.

Imaging

Radiographic examination. In a straightforward case antero-posterior and lateral films are sufficient. They should always include a reasonable length of the femur and of the tibia and fibula. Tangential projections of the femoral condyles with the knee flexed are sometimes helpful, especially when osteochondritis dissecans is suspected. Tangential (‘sky-line’) views of the patella may also be required.

When it is suspected that the knee symptoms might be referred from a lesion of the hip or spine appropriate radiographs of those regions should be obtained.

Radioisotope bone scanning. Occasionally this may be useful in the diagnosis of inflammatory or neoplastic lesions.

Magnetic resonance imaging. When adequate information cannot be obtained from plain radiography, magnetic resonance imaging may be helpful as a non-invasive alternative to arthroscopy.

Arthroscopy

Arthroscopy can be a useful adjunct to clinical and radiographic examination in the diagnosis of knee complaints (Fig. 18.5). Its use for diagnostic purposes has been largely replaced by MRI, but it is a well’established method of treating a number of intra-articular disorders by minimally invasive operation.

Fig. 18.5 Arthroscopic photograph showing normal appearance of medial meniscus. The medial femoral condyle is seen above, and the upper surface of the tibia is at the lower right. The concave edge of the meniscus is seen clearly lying upon the tibia.

Arthroscopy is usually carried out with the patient anaesthetised, the joint cavity is filled with saline through a hollow needle, and a cannula and telescope are entered at the appropriate site – usually antero-laterally or antero-medially, depending upon whether the surgeon is concerned to inspect mainly the medial or the lateral compartment. By correctly manoeuvring and rotating the arthroscope, and if necessary by the use of alternative sites of entry, almost the whole extent of the interior of the joint can be brought into view with the possible exception of the postero-lateral recess. The information gained can be enhanced by probing the menisci and other intra-articular structures with an instrument introduced at a site away from the arthroscope.

Benign tumours (General description of benign bone tumours, p. 106)

Of the four main types of benign bone tumour – osteoid osteoma, chondroma, osteochondroma, and giant-cell tumour – only the giant-cell tumour requires further consideration here, because of the special treatment requirements when it occurs close to the knee.

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.

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.