Occasionally a firm diagnosis cannot be made on the basis of the history and clinical examination alone. The following additional investigations are often helpful.
(a) Arthroscopy may give much useful information, and in conjunction with the clinical examination will permit a firm, accurate diagnosis to be made in the majority of cases. Incorrect diagnoses are most common in lesions involving the menisci in their posterior thirds. An increasing number of conditions are amenable to arthroscopic surgery, which can often follow diagnostic arthroscopy in the same session.
(b) MRl scans These can be useful in diagnosing lesions of the menisci and ligaments, but it has been suggested that they should only be used if there is diagnostic uncertainty. An accuracy of 90% is claimed. However, there is often an increase in the signal intensity in the region of the posterior third of the medial meniscus (from the myxoid degeneration that may occur in the ageing process, or after previous surgery), and this can lead to false interpretations.
(c) Arthrography may be helpful, although the interpretation of the radiographs is specialized and often difficult.
(d) Examination under anaesthesia If pain prevents full examination (e.g. by preventing flexion) anaesthesia may be helpful. This is frequently followed by arthroscopy.
(e) Provocative exercises These are carried out under the supervision of a trained physiotherapist. They aim to throw considerable stress on the menisci by applying torsional stresses to the weightbearing knee. If the meniscus has been damaged, the exercises are likely to be followed by localized pain, swelling, and sometimes even locking, so that any doubtful meniscus lesion is likely to declare itself.
Suspected acute infections
(a) Aspiration and culture of the synovial fluid.
(b) Blood culture.
(c) Full blood count, including differential white count, and estimation of the sedimentation rate and C-reactive protein.
Suspected tuberculosis of the knee
(a) Chest radiograph.
(b) Synovial biopsy, with specimens of synovial membrane being sent for both histological and bacteriological examination. At the same time, synovial fluid specimens are also sent for bacteriology and sensitivities.
(c) Mantoux test.
Suspected rheumatoid arthritis
(a) Examination of other joints.
(b) Estimations of rheumatoid factor.
(c) Full blood count and sedimentation rate.
(d) Serum uric acid.
Further investigation of poor mineralization, bone erosions etc.
(a) Estimation of serum calcium, phosphate and alkaline phosphatase.
(b) Estimation of rheumatoid factor.
(c) Serum uric acid.
(d) Full blood count and differential count.
(e) Skeletal survey and chest radiograph.
(f) Radioisotope scan.
Further investigation of chronic effusion, aspirate negative
(a) Tests as for suspected rheumatoid arthritis.
(b) Brucellosis agglutination tests.
(c) Radiography of the chest and sacroiliac joints.
(d) Exploration and synovial biopsy.
Further investigation of severe undiagnosed pain
(a) Radiography of the chest, pelvis and hips.
10.1. Swelling (1): Note the presence of swelling confined to the limits of the synovial cavity and suprapatellar pouch, suggesting effusion, haemarthrosis, pyarthrosis or a space-occupying lesion in the joint.
10.2. Swelling (2): Note whether the swelling extends beyond the limits of the joint cavity, suggesting infection (of the joint, femur or tibia), tumour or major injury.
10.3. Lumps: Note presence of localized swellings, e.g. (A) prepatellar bursitis (housemaid's knee). (B) infrapatellar bursitis (clergyman's knee). (C) meniscus cyst (in joint line). (D) diaphyseal aclasis (exostosis, often multiple and sometimes familial). In beat knee (a common affliction in miners) there is chronic anterior bursal enlargement, often with thickening of the overlying skin.
10.4. Discoloration: Note any bruising which suggests trauma to the superficial tissues or knee ligaments. Note that bruising is not usually seen in meniscus injuries. Note any redness suggesting inflammation.
10.5. Skin marks: Note (A) scars due to previous injury or surgery: the relevant history must be obtained. (B) Sinus scars are indicative of previous infections, often of bone, and with the potential for reactivation. (C) Evidence of psoriasis, with the possibility of psoriatic arthritis.
10.6. Temperature (1): Note any increased local heat and its extent, suggesting in particular rheumatoid arthritis or infection. There may also be increased local heat as part of the inflammatory response to injury, and in the presence of rapidly growing tumours. Always compare the two sides.
10.7. Temperature (2): A warm knee and cold foot suggest a popliteal artery block. Always make allowance for any warm bandage the patient may have been wearing just prior to the examination, and check the peripheral pulses.
10.8. The quadriceps (1): Inspect the relaxed quadriceps muscle. Slight wasting and loss of bulk are normally apparent on careful inspection.
10.9. The quadriceps (2): Examine the contracted quadriceps. Place a hand behind the knee and ask the patient to press the leg against the hand. Feel the muscle tone with your free hand.
10.10. The quadriceps (3): Repeat the last test, this time asking the patient to dorsiflex the inverted foot. This demonstrates the important vastus medialis portion of the quadriceps, which may be involved in recurrent dislocation of the patella.
10.11. The quadriceps (4): Substantial wasting, especially in the fat leg, may be confirmed by measurement, assuming the other limb is normal. This test, being objective, may be valuable for repeat assessments and in medicolegal cases. Begin by locating the knee joint (see later for details) and marking it with a ballpoint pen. Make a second mark on the skin 18 cm above this. Repeat on the other leg.
10.12. The quadriceps (5): Compare the circumference of the legs at the marked levels. Wasting of the quadriceps occurs most frequently as the result of disuse, generally from a painful or unstable lesion of the knee, or from infection or rheumatoid arthritis.
10.13. Extensor apparatus (1): Loss of active extension of the knee (excluding paralytic conditions) follows (1) rupture of the quadriceps tendon, (2) many patellar fractures, (3) rupture of the patellar ligament, (4) avulsion of the tibial tubercle.
10.14. Extensor apparatus (2): With the patient sitting with his legs over the end of the examination couch, ask him to straighten the leg while you support the ankle with one hand. Feel for quadriceps contraction and look for active extension of the limb.
10.15. Extension apparatus (3): Note the position of the patella in relation to the joint line and the tibial tuberosity. If its upper border is high, this suggests that it is proximally displaced and that you should suspect lesions 2, 3 or 4.
10.16. Extensor apparatus (4): If the patella is normally placed, lay a finger along its upper border. Loss of normal soft tissue resistance is suggestive of a rupture of the quadriceps tendon (I).
10.17. Extensor apparatus (5): Look for gaps and tenderness at the other levels to help differentiate between lesions 2. 3 and 4. Radiographs of the knee are essential.
10.18. Effusion (1): Small effusions are detected most easily by inspection. The first signs are bulging at the sides of the patellar ligament and obliteration of the hollows at the medial and lateral edges of the patella.
10.19. Effusion (2): With greater effusion into the knee the suprapatellar pouch becomes distended. Effusion indicates synovial irritation from trauma or inflammation.
10.20. Effusion (3): Patellar tap test (ballottement test) (1): Squeeze any excess synovial fluid out of the suprapatellar pouch with the index and thumb, slid firmly distally from a point about 15 cm above the knee to the level of the upper border of the patella. This will also 'float' the patella away from the femoral condyles.
10.21. Effusion (4): Patellar tap test
(2): Place the tips of the thumb and three fingers of the free hand squarely on the patella, and jerk it quickly downwards towards the femur. A click as the patella strikes the condyles indicates the presence of effusion. Note that if the patella is not properly steadied as described it will tilt, giving a false negative. Note too that if the effusion is slight or tense, the tap test will be negative.
10.22. Effusion (5): Fluid displacement test (1): Small effusions may be detected by this manoeuvre. Evacuate the suprapatellar pouch as in the patellar tap test before.
10.23. Effusion (6): Fluid displacement test (2): Stroke the medial side of the joint to displace any excess fluid in the main joint cavity to the lateral side of the joint.
10.24. Effusion (7): Fluid displacement test (3): Now stroke the lateral side of the joint while watching the medial side closely. Any excess fluid present will be seen to move across the joint and distend the medial side. This test will be negative if the effusion is gross and tense.
10.25. Effusion (8): Palpable fluid wave test: This can be useful in testing for larger effusions, especially in fat knees. With the thumb on one side of the joint and the fingers on the other (a), compress the knee to empty the hollows at the side of the joint. Now, with the other hand attempt to force fluid from the suprapatellar pouch distally into the knee (b). The force of any fluid being transmitted should be picked up by the compressing hand.
10.26. Haemarthrosis: A haemarthrosis is a sign of major joint pathology, is usually obvious within half an hour of injury, and gives a doughy feel in the suprapatellar region. A tense haemarthrosis should be aspirated to relieve pain and permit a more thorough clinical (and usually) arthroscopic examination.
10.27. Pyarthrosis: Tenderness in pyarthrosis is usually widespread. There is generally a severe systemic upset, and quadriceps wasting. If pyarthrosis is suspected, the knee should always be aspirated to relieve painful and destructive joint pressure, and to obtain pus for elucidating the infecting agent and establishing antibiotic sensitivities.
10.28. Synovial membrane: Pick up the skin and the relaxed quadriceps tendon to assess the thickness of the synovial membrane in the suprapatellar pouch. The synovial membrane is thickened in inflammatory conditions, e.g. rheumatoid arthritis, and in villonodular synovitis.
10.29. Tenderness (1): It is first essential to identify the joint line quite clearly. Begin by flexing the knee and looking for the hollows at the sides of the patellar ligament; these lie over the joint line. Then confirm this by feeling with the fingers or thumb for the soft hollow of the joint. When the examining finger is moved proximally it should rise out of the joint hollow on to the femoral condyle; similarly, when moved distally it should ride over the eminence of the tibia.
10.30. Tenderness (2): joint line structures: Begin by palpating carefully from in front back along the joint line on each side. Localized tenderness here is commonest in meniscus, collateral ligament and fat pad injuries.
10.31. Tenderness (3): collateral ligaments: Now systematically examine the upper and lower attachments of the collateral ligaments. Associated bruising and oedema are a feature of acute injuries.
10.34. Tenderness (6): Femoral condyles: suspected osteochondritis dissecans (1 ): Flex the knee fully and look for tenderness over the femoral condyles. Osteochondritis dissecans most frequently involves the medial femoral condyles, and particular attention should therefore be paid to the medial side.
10.32. Tenderness (4): tibial tubercle: In children and adolescents, tenderness is found over the tibial tubercle (a), which may be prominent in Osgood-Schlatter's disease, and after acute avulsion injuries of the patellar ligament and its tibial attachment. Tenderness over the lower pole of the patella (b) and proximal patellar ligament is found in Sinding-Larsen-Johansson disease. Tenderness over the quadriceps tendon (c) is found in quadriceps tendinitis.
10.35. Suspected osteochondritis dissecans (2): Wilson's test: The aim of the test is to cause pressure between the anterior cruciate ligament and the lateral aspect of the medial femoral condyle. Flex the knee (a) and internally rotate the foot (b). Now extend the knee fully (c). If pain occurs at full extension and is relieved by external rotation of the foot, then the test is positive.
10.33. Tenderness (5): Patellar ligament: Where in an athletic patient a problem with the patellar ligament is suspected, look for patellar ligament tenderness while the patient is attempting to extend the leg against resistance. This test is best performed with the leg over the end of the examination couch.
10.36. Movements (1): Extension: First make sure that the knee can be fully extended. If in doubt, lift both legs and sight along the good and affected leg. Full extension is recorded as 0°. Loss of full extension may be recorded as 'The knee lacks X° of extension'.
10.37. Movements (2): Extension: If there is still some doubt, examine the patient in the prone position, fully relaxed, and with his legs hanging over the edge of the examination couch. Any loss of extension on one side should be obvious from the position of the heels.
10.38. Movements (3): Extension: Try to obtain full extension if this is not obviously present. A springy block to full extension is very suggestive of a bucket-handle meniscus tear. A rigid block to full extension (commonly described as a fixed flexion deformity) is often present in arthritic conditions affecting the knee.
10.39. Movements (4): Hyperextension (genu recurvatum): This is present if the knee extends beyond the point when the tibia and femur are in line. Attempt to demonstrate this by lifting the leg while at the same time pressing back on the patella. If severe, look for other signs of joint laxity, particularly in the elbow, wrist and fingers, keeping in mind the rare Ehlers-Danlos syndrome.
10.40. Movements (5): Hyperextension.
if present, is recorded as 'X° hyperextension'. It is seen most frequently in girls, and is often associated with a high patella, chondromalacia patellae, recurrent dislocation of the patella, and sometimes tears of the anterior cruciate, medial ligament, or medial meniscus.
Measure the range of flexion in degrees, starting from the zero position of normal full extension. Flexion of 135° and over is regarded as normal, but compare the two sides. There are many causes of loss of flexion, the commonest of which are effusion and arthritic conditions.
Alternatively, measure the heel-to-buttock distance with the leg fully flexed. This can be a very accurate way of detecting small alterations in the range (1 cm = 1.5° approximately) and is useful for checking daily or weekly progress. Note that obviously flexion can never be greater than when the heel contacts the buttock, and that inability to bring the heel to the buttock is not necessarily an indicator of flexion loss (135° is less than this).
10.43. Movements (8): Recording: The range of movements in the examples illustrated would be recorded as follows: (A) 0-135° (normal range); (B) 5° hyperextension - 140° flexion; (C) 10-60° (or 10° fixed flexion deformity with a further 50° flexion).
10.44. Genu valgum (knock knee) in children (1): Note whether unilateral or bilateral; the latter is more common. The severity of the deformity is recorded by measuring the intermalleolar gap. Grasp the child by the ankles and rotate the legs until the patellae are vertical.
10.45. Genu valgum in children (2):
Now bring the legs together to touch lightly at the knees, and measure the gap between the malleoli. (Normally the knees and malleoli should touch). Serial measurements, often every 6 months, are used to check progress. Note that with growth a static measurement is an angular improvement. In the 10-16-year age group < 8 cm in females and < 4 cm in males is regarded as normal.
10.46. Genu valgum in adults (1): In adults the deformity is seen most often in association with rheumatoid arthritis. It is also common in teenage girls. It is best measured by X-rays, and the films should be taken with the patient taking all his weight on the affected side.
10.47. Genu valgum in adults (2): The degree of valgus may be roughly assessed by measuring the angle formed by the tibial and femoral shafts. Allow for the 'normal' angle, which is approximately 6° in the adult. The shaded area represents genu valgum. (Note that the tibiofemoral angle is virtually the same as the Q angle used in the assessment of patellar instability.)
Measure the distance between the knees, using the fingers as a gauge. Ideally the patient should be weightbearing, and it is essential that both patellae should be facing forwards to counter any effect of hip rotation. In the 10-16-year age group, < 4 cm in females and < 5 cm in males is regarded as being within normal limits.
10.49. Genu varum (2): An assessment of the deformity may also be carried out with X-rays, as in genu valgum, with the patient weightbearing during the exposure of the films. The deformity is seen most commonly in osteoarthritis and Paget's disease. It may occur in rheumatoid arthritis, although genu valgum is commoner in that condition.
10.50. Genu varum (3): In children, radiography may be helpful. In (A) rickets, note the wide and irregular epiphyseal plates. In (B) tibia vara, note the sharply downturned medial metaphyseal border. Note that radiological varus is normal till a child is 18 months old.
10.51. Instability (1): The following potential deformities may be looked for: (A) valgus (when the medial ligament is torn: severe when the posterior cruciate is also damaged); (B) varus (when the lateral ligament is torn: severe when the posterior cruciate is also torn); (C) anterior displacement of the tibia (anterior cruciate tears: worse if medial and/or lateral structures torn); (D) posterior displacement of the tibia (posterior cruciate ligament tears).
The medial tibial condyle subluxes anteriorly (anteromedial instability): this is usually due to combined tears of the anterior cruciate and medial structures; (2) the lateral condyle subluxes anteriorly (anterolateral instability): this is usually due to tears of the anterior cruciate plus the lateral structures; (3) the lateral tibial condyle subluxes posteriorly (posterolateral instability) or (4) the medial tibial condyle subluxes posteriorly (posteromedial instability). (3) and (4) are due mainly to tears of the posterior cruciate and lateral or medial structures. (5) Combinations of these instabilities.
10.53. Valgus stress instability (1):
Begin by examining the medial side of the joint, and the medial ligament in particular. Tenderness in injuries of the medial ligament is commonest at the upper (femoral) attachment and in the medial joint line. Bruising may be present after recent trauma, but haemarthrosis may be absent. (Where the medial ligament has been injured and displays tenderness without laxity it may be classified as a grade 1 injury.)
10.54. Valgus stress instability (2):
Extend the knee fully. Use one hand as a fulcrum, and with the other attempt to abduct the leg. Look for the joint opening up and the leg going into valgus. On release of the valgus force a confirmatory clunk may be felt. Moderate valgus is suggestive of a major medial and posterior ligament rupture (grade 2 injury). Severe valgus may indicate additional cruciate (particularly posterior cruciate) rupture (grade 3 injury).
10.55. Valgus stress instability (3): If in doubt, use the heel of the hand as a fulcrum and use the thumb or index, placed in the joint line, to detect any opening up of the joint as it is stressed. If there is still some uncertainty, compare the two sides.
10.56. Valgus stress instability (4): stress films (1): If there is still some doubt, then radiographs of both knees should be taken while applying a valgus stress to each joint.
10.57. Valgus stress instability (5): stress films (2): The films of both sides are then compared. Any instability should be obvious.
10.58. Valgus stress instability (6): If no instability has been demonstrated with the knee fully extended, repeat the tests with the knee flexed to 20° and the foot internally rotated. Some opening up of the joint is normal, and it is essential to compare the sides. Demonstration of an abnormal amount of valgus suggests less extensive involvement of the medial structures (e.g. partial medial ligament tear, still classified as a grade 2 injury).
10.59. Valgus stress instability (7): If the knee is very tender and will not permit the pressure of a hand as a fulcrum, attempt to stress the ligament with this crossover arm grip, with one hand placed over the proximal part of the tibia just distal to the knee joint to avoid any local pressure over the joint and its ligaments.
10.60. Valgus stress instability (8): If a haemarthrosis is present (and this is not always the case) preliminary aspiration may allow a more meaningful examination of the joint.
10.61. Valgus stress instability (9): If the knee remains too painful to permit examination, the joint should be fully tested under anaesthesia; there should be provision to cany on with a surgical repair should major instability be demonstrated (i.e. where several major structures are involved), or with an arthroscopy.
10.64. Varus stress instability (3):
Again, for a more sensitive assessment of 'give', the thumb can be placed in the joint line. If there is varus instability in extension as well as flexion, it suggests tearing of the posterior cruciate ligament as well as the lateral ligament complex.
10.62. Varus stress instability (1): Begin by examining the lateral side of the joint. Tenderness is most common over the head of the fibula or in the lateral joint line in acute injuries of the lateral joint complex (lateral ligament and capsule).
10.65. Varus stress instability (4): As in the case of valgus stress instability stress films may be taken, and if examination is not possible even after aspiration, arrange to examine the knee under general anaesthesia.
10.63. Varus stress instability (2):
Attempt to produce a varus deformity by placing one hand on the medial side of the joint and forcing the ankle medially. Carry out the test as in the case of valgus stress instability, first in full extension and then in 30° flexion, and compare one side with the other. Note that when testing the lateral ligament, in the normal knee there is a little more 'give' than with the medial.
10.66. Varus stress instability (5):
Always cheek that the patient is able to dorsiflex the foot, to ensure that the motor fibres in the common peroneal nerve (lateral popliteal) have escaped damage.
10.67. Varus stress instability (6): In addition, test for sensory disturbance in the distribution of the common peroneal nerve.
10.68. The anterior drawer test (1): Flex the knee to 90°, with the foot pointing straight forwards, and steady it by sitting close to it. Grasp the leg firmly with the thumbs on the tibial tubercle. Check that the hamstrings are relaxed, and jerk the leg towards you. Repeat with the knee flexed to 70° and compare the sides. Note: significant displacement (i.e. the affected side more than the other) confirms anterior instability of the knee. Note also that in tears the endpoint of the anterior translation is usually softer and less clearly defined than the firm endpoint when the ligament is intact. When the displacement is marked (say 1.5 cm or more) then the anterior cruciate is almost certainly torn, and there is a strong possibility of associated damage to the medial complex (medial ligament and medial capsule) and even the lateral complex. If the displacement is less marked, and one tibial condyle moves further forward than the other, then the diagnosis is less clear: it may suggest an isolated anterior cruciate ligament laxity or a tibial condylar subluxation (rotatory instability).
10.69. The anterior drawer test (2):
Repeat the test with the foot in 15° of external rotation. Excess excursion of the medial tibial condyle suggests a degree of anteromedial (rotatory) instability, with possible involvement of the medial ligament as well as the anterior cruciate ligament.
10.70. The anterior drawer test (3):
Now turn the foot into 30° of internal rotation and repeat the test. Anterior subluxation of the lateral tibial condyle suggests some anterolateral rotational instability, with possibly damage to the posterior cruciate and the posterior ligament as well as the anterior cruciate ligament.
10.71. The anterior drawer test (4):
Beware of the following fallacy: a tibia already displaced backwards as a result of a posterior cruciate ligament tear may give a false positive in this test. This also applies to the Lachman tests described in the following frames. Check by inspecting the contours of the knee prior to testing.
Lachman tests are also used to detect anterior tibial instability. In the manipulative Lachman test, the knee should be relaxed and in about 15° flexion. One hand stabilizes the femur while the other tries to lift the tibia forwards. The test is positive if there is anterior tibial movement (detected with the thumb in the joint), with a spongy endpoint. The test is sometimes easier to perform with the patient prone (see next frame).
10.73. The Lachman tests (2): The prone test (Feagin and Cooke): This is especially useful where the patient has large thighs which are difficult to grasp. With the patient prone, encircle the tibia with both hands, placing the index fingers and thumbs in the joint line. Flex the knee to 20° and attempt to push the tibia forwards. Anterior translation should be readily detected by the fingers, and the firmness of the endpoint should be noted.
10.74. The Lachman tests (3): In the active Lachman test the relaxed knee is supported at 30° and the patient asked to extend it. If the test is positive, there will be anterior subluxation of the lateral tibial plateau as the quadriceps contracts, and posterior subluxation when the muscle relaxes. It is considered that this is best seen from the medial side. Repeat, resisting extension by applying pressure to the ankle.
10.75. Radiological analysis of anterior cruciate function (1): Anterior subluxation of the tibia in extension may also be demonstrated with X-rays. The lower thigh is supported by a sandbag, and the leg extended against the resistance of a 7 kg weight. The limb should be in the neutral position, with the patella pointing upwards, and the X-ray film cassette placed between the legs.
10.76. Radiological analysis (2): On the films, draw two lines parallel to the posterior cortex of the tibia, tangential to the medial tibial plateau and the medial femoral condyle. Measure the distance between them. Normal = 3.5 mm ± 2 mm. Ruptured anterior cruciate = 10.2 mm ± 2.7 mm. The latter is slightly increased if the medial meniscus is also torn. The diagnostic reliability is high.
10.77. Posterior tibial instability: testing the posterior cruciate ligament (1): the gravity test: Rupture, detachment or stretching of the posterior cruciate ligament may permit the tibia to sublux backwards, frequently giving rise to a striking deformity of the knee which allows the diagnosis to be made on inspection alone. The knee should be flexed to 20°, with a sandbag under the thigh.
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