The classical test for fluid is the patellar tap (figure 94a,b). With your left hand, compress the lower thigh and slide the hand down towards the patella, pushing fluid out of the suprapatellar pouch. Maintain this hand in position above the patella and use your right hand to push the patella back onto the femoral condyle. If fluid is present, the patella is separated from the condyle and the pressure produces a bony tap as the patella hits the underlying femur.
If only a small amount of fluid is present, empty the medial side of the joint by gently sweeping the fluid upwards into the suprapatellar pouch. Use one hand to press above the medial side of the patella to prevent backflow on this side, and with the other hand, sweep down the lateral side of the patella (figure 94c,d). Small amounts of fluid pass back into the medial side of the joint, producing a bulge behind the patella. If the joint is tensely swollen, pressure on one side behind the patellar can be felt transmitted to the other.
Active knee flexion is 0–135 degrees; a few extra degrees can be obtained by passively compressing the calf against the thigh muscles (figure 95a,b). Up to 5 degrees of passive extension may be present (figure 95c,d). Look for hyperextension (figure 96); this may indicate ligament abnormality, as in injury or Marfan’s syndrome. Listen for clicks and creaks. Place your left hand on the patella to feel for crepitus during passive movements produced with your right (figure 97). This may also be detected by sliding the patella from side to side across the femoral condyles (figure 98a,b).
The medial ligament is tested for pain and laxity by placing your left fist on the lateral side of the extended knee. Grip the ankle with your right hand and attempt to abduct the tibia on the femur (figure 99a). The lateral ligament is tested similarly by placing your fist against the medial side of the joint and attempting adduction (figure 99b). In the normal knee, neither of these movements should be present and the test should be pain free.
Cruciate ligament function is assessed by the draw test. Flex the knee to 90 degrees, with the foot resting on the couch. Sit on the forefoot and grip the upper end of the calf with both hands and pulls forward and push backwards (figure 100a,b). There should be no gliding movement. Anterior movement suggest laxity of the anterior cruciate ligament and the reverse the posterior.
Loose bodies within the knee, and damage to the menisci, can cause locking of the joint. This can be assessed by sitting, squatting and standing movements and by the McMurray test. In the latter, hold the ankle with your right hand and the flexed knee with your left. Use the right hand to rotate the foot, first in one direction and then the other. In each case use both hands to apply abduction across the knee and gradually extend the knee from the flexed position (figure101a–d). In the presence of an abnormal cartilage this manoeuvre may produce pain, a click or the protrusion of a lump along the joint margin.
Complete the examination of the knee by asking the patient to stand; look for valgus (knock knees) and varus (bow legs) deformities, and observe the gait.