The thigh and knee

18 The thigh and knee


The knee depends for its stability upon its four main ligaments and upon the quadriceps muscle. The importance of the quadriceps cannot be overemphasised. So efficiently can a powerful quadriceps control the knee that it can maintain stability despite considerable laxity of the ligaments. In many injuries and diseases of the knee the quadriceps wastes strikingly, and to some extent the condition of the muscle is an index of the state of the knee: if it is wasted it is probable that there is a significant abnormality within the joint.


Apart from its vulnerability to injury, the knee is also particularly prone to almost every kind of arthritis. Moreover, it is the joint most commonly affected by osteochondritis dissecans and intra-articular loose body formation.


The region of the knee is the zone of most active bone growth in the lower limb (contrast the upper limb, where most growth occurs towards the shoulder and the wrist rather than towards the elbow). Perhaps partly for this reason the metaphyses near the knee are common sites of osteomyelitis and of primary malignant bone tumours.


The knee is, in fact, a region where nearly every kind of orthopaedic disorder may be represented.


In the diagnosis of knee complaints arthroscopy has secured for itself a role in investigation for any suspected intra-articular lesion although MRI has usurped this position. Arthroscopic techniques of surgery have become routine for such common disorders as meniscal tears and intra-articular loose bodies. Arthroscopic surgery has the advantages that formal opening of the knee is avoided and that recovery and convalescence are greatly accelerated. Stay in hospital is reduced, or increasingly the operation is performed as a ‘day case procedure’ without the need for admission.


In recent years total replacement arthroplasty of the knee has become established as the routine operation for the relief of disabling arthritis, whether rheumatoid or degenerative. The newer operation of unicompartmental arthroplasty is now producing results that allow it to be considered as an alternative to tibial osteotomy for the treatment of arthritis confined to a single tibio-femoral compartment.



SPECIAL POINTS IN THE INVESTIGATION OF THIGH AND KNEE COMPLAINTS







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.



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.




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.



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.



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).








DISORDERS OF THE THIGH





BONE TUMOURS IN THE THIGH


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



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.







ARTICULAR DISORDERS OF THE KNEE




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.



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.



Course and prognosis

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Jun 5, 2016 | Posted by in ORTHOPEDIC | Comments Off on The thigh and knee

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