Inspection is only possible with adequate exposure. Begin by placing the patient in shorts or tying the gown up above the knee. The patient’s gait should be observed first. Pay attention to the positioning of the knee on both the medial/lateral plane (valgus vs. varus) and the anterior/posterior plane (extension lag vs. knee recurvatum). Also, observe the joint above and below. Be sure to note any restrictions in the hip or ankle motion. Look at the foot for evidence of pes cavus (high arch) or pes planus (flat footed). The patient should then sit or lie on a table.
It is important to next look at the joint for any gross evidence of effusion or discoloration. Any changes can be evaluated further as the examination proceeds. Next, the examiner should assess for any muscle atrophy or fasciculations. If there is atrophy, the thigh or calf circumference should be measured and compared with the unaffected side. Finally, check the skin for any evidence of scarring from previous surgery of trauma.
Palpation of the knee should be done systematically. Begin either medially or laterally, and work across the knee. Address the skin, soft tissue, and bony aspects of the joint. Begin the examination by laterally palpating the overlying skin, which should move freely over the soft tissue and bones. The lateral collateral ligament can be palpated next. Palpate along the length of the ligament from the lateral femoral condyle to the insertion on the fibula. Have the patient cross the leg (FABER—Flexion of the knee to 90 degrees, ABduction and External Rotation of the hip) to better palpate the ligament. Moving more proximally, the biceps femoris tendon can be palpated as it comes down to its insertion on the fibular head.
Bony palpation should include the lateral tibial plateau, fibular head, and the lateral femoral condyle. All should be felt for tenderness or palpable osteophytes. In addition, the anterior portion of the lateral meniscus lies on the lateral tibial plateau and may be tender after an injury. This should be checked with the knee in 90 degrees of flexion. Moving across, the anterior portion of the knee should be palpated. Palpate over the prepatellar bursa (above the patella) and the superficial infrapatellar bursa (overlying the infrapatellar ligament). Next in the region is the patella. All four poles of the patella should be palpated, in addition to the undersurface of the medial and lateral aspects. Palpation of the medial and lateral facets of the patella can be performed with the patient lying supine and the knee completely relaxed. Tenderness or hypersensitivity is indicative of patellofemoral pathology. Furthermore, one should palpate the lateral retinacula for the presence of a synovial plica (Fig. 2-11). Proximally, the quadriceps muscle should be palpated for any discomfort of defects. Distally, the infrapatellar tendon should be palpated to its insertion on the tibia at the tibial tubercle.
FIGURE 2-11. Palpation of the lateral retinacula of the knee for synovial plica.
The medial portion of the knee is addressed in a similar fashion. Palpate the skin, and palpate in the region of the pes anserine bursa (medial to the tibial tubercle and just above the insertion of the tendons of the sartorius, gracilis, and semitendinosus). Next, palpate the medial collateral ligament from its origin on the medial femoral condyle to the medial tibia. Moving proximally, the tendons of the sartorius, gracilis, and semitendinosus should be followed from their insertion to the muscle tendon junction.
Bony palpation medially should include the medial femoral condyle and the medial tibial plateau. As with the lateral tibial plateau, the medial meniscus can be palpated. This is made possible by internally rotating the tibia with the knee at 90 degrees and palpating between the tibial plateau and femoral condyle. Palpate for joint line tenderness medially and for any palpable osteophytes.
Before turning the patient, the joint should be checked for an effusion. With the patient in the supine position, with the leg in full extension, place the examiner’s thumb on the medial side below the patella. Compress the suprapatellar pouch and lateral knee to accumulate fluid on the lateral side. Compression medially should give a sense of fullness laterally. In addition, the patellar ballottement test can be performed. Using both hands, the proximal hand starts 10 cm above the patella with the thumb lateral and fingers medial. The distal hand starts 5 cm below with the same orientation. While compressing the tissues, the hands are slowly brought toward each other. When they are just above and below the patella, the index finger from the distal hand taps the patella. Without an effusion, the patella will be in the femoral condyles and there will be no findings. With an effusion, the patella will “tap” onto the femur and the examiner will feel the sensation.
The last region to be inspected is the posterior aspect of the knee. This is done best with the patient in the prone position. Palpate for the boundaries of the popliteal fossa, which include medially the semitendinosus and semimembranosus muscles. Laterally palpate for the biceps femoris muscle and inferiorly the two heads of the gastrocnemius. Within the region of the popliteal artery are the popliteal vein and posterior tibial nerve. Palpate for any popliteal cysts, which is best done with the knee in extension.
Range of Motion
Range of motion of the knee should be approximately 135 degrees of flexion and 0 degrees of extension. Both internal and external rotation should be approximately at 10 degrees. Loss of range of motion can be of traumatic or degenerative causes. It is important to check both active range of motion and passive range of motion. A patient with quadriceps weakness may be unable to achieve full active extension but with the examiner’s assistance has full range of motion.
The testing can be performed with the patient seated on the edge of the examination table to start. Check the active and passive extensions (this can be incorporated into the manual muscle testing). Watch the patella during extension for its position in the trochlear groove. Active flexion can also be tested in this position, but passive flexion is better tested with the patient in the supine position. Loss of terminal flexion and extension can also be attributed to a joint effusion.
The neurologic examination should consist of manual muscle testing, sensation, and reflexes. The manual muscle testing is performed to test quadriceps strength by extending the knee. Hamstring testing should be performed with the patient flexing the knee while sitting. Another useful test is a step down test. Watch the patient step down from a foot stool in the room to assess his or her control descending and the amount of increase in the Q angle. Table 2-10 lists what should be included in manual muscle testing (24).
Reflexes can be addressed next. Table 2-11 lists what should be included in reflex testing (24).
Finally, sensation can be tested for both pinprick (lateral spinothalamic tract) and light touch (dorsal columns). Table 2-12 lists what should be included in sensation testing (24).
Stability of the ligaments should be tested with the patient relaxed and in a supine position. Beginning with the collateral ligaments, the examiner should firmly grasp the distal leg and provide a valgus (laterally applied) force to the knee. This will test the medial collateral ligament. The test should be completed with the knee in 20 to 30 degrees of flexion and also with the knee in full extension to test medial capsular integrity (Fig. 2-12). Remember to apply three points of pressure, one being distal lateral leg, the next lateral knee, and finally distal medial knee to maintain control of the leg. If possible, palpate around the knee, and palpate the ligament for a defect during the application of a valgus force.
FIGURE 2-12. Evaluation of the stability of the collateral ligaments of the knee.
In a similar fashion, apply a varus (medially applied) force to the knee to check the lateral collateral ligament. Again, it is helpful to place a finger on the ligament during the maneuver. It is also important to apply three points of pressure. As with the medial side, check in full extension and in 20 to 30 degrees of flexion.
The anterior and posterior cruciate ligaments should be examined next. The Lachman’s maneuver is the most sensitive test for injury to the anterior cruciate ligament (ACL). The test is performed by firmly grasping the distal lateral thigh with the outside hand in a supine patient. The knee is then placed in slight flexion, approximately 30%. Next, the proximal medial leg is grasped by the examiner’s inside hand and slightly laterally rotated. A quick upward force is then applied to the tibia by the inside hand while the thigh remains stabilized by the outside hand. The examiner is feeling for a sharp end point of the ACL. This examination maneuver is difficult and must be practiced many times before it can be done correctly (Fig. 2-13), but this is the most accurate method of judging the integrity of the ACL (25).
FIGURE 2-13. Evaluation of the stability of the ACL of the knee.
With the patient in a supine position and the hip flexed at 45 degrees while the knee is in 90 degrees of flexion, the examiner can test both the posterior and the anterior cruciate ligaments. The foot is stabilized when the examiner sits on the patient’s foot. To test the ACL, the examiner grasps around the proximal tibia and places the thumbs on the medial and lateral tibial plateaus. The tibia is then pulled anteriorly with respect to the femur. The amount of anterior movement should be minimal and equal to the opposite side. The movement is compared with the opposite knee.
Testing of the posterior cruciate ligament is completed just after the ACL. With the patient supine, the hip is flexed to 45 degrees and the knee flexed to 90 degrees. The foot is immobilized by the examiner sitting on the foot. The examiner then gives a posteriorly directed force to the tibia with the thumbs on the tibiofemoral junction. As with the anterior drawer test, the laxity is compared with the opposite side. Another indication of a posterior cruciate tear is hyperextension of the knee joint. This can be observed with the patient supine and the hip and knee flexed at 90 degrees. The examiner elevates the leg by lifting the heel with all muscles relaxed. Again, both sides should be tested for comparison.
The posterolateral complex of the knee includes the posterolateral capsule, the popliteus muscle, and the lateral collateral ligament. When one or more of these structures are injured, particularly in the setting of a posterior cruciate ligament deficiency, the knee becomes susceptible to rotatory instability. Posterolateral complex laxity can be demonstrated by examining the tibial external rotation with the knee flexed at 90 degrees and comparing it with the contralateral side.
Medial and Lateral Menisci
The medial and lateral menisci may account for the second most commonly injured structures in the knee, second only to the patellofemoral joint (PFJ) as a source of knee pain in the younger patient groups. Rotatory motion, particularly when combined with compression, is felt to be the common biomechanical factor leading to injury. An aging and degenerative meniscus is probably more susceptible to this type of trauma. Commonly, injury to the meniscus will result in an effusion, making the detection of an effusion an important clinical test when looking for meniscal injury. Joint line tenderness is sensitive for meniscal injury but not specific. The posterior horns are loaded during flexion so that simultaneous knee flexion and rotation will be sensitive for pain secondary to a posterior horn meniscal tear. Pain associated with the internal tibial rotation tends to be more indicative of injury of the lateral meniscus, whereas external rotation may be more suggestive of the medial meniscus.
A test for meniscal injury would be the McMurray’s test (26). McMurray’s test is performed with the patient supine.
The knee is brought into full flexion, and the tibia is internally rotated and then extended to 90 degrees while being held internally rotated. An audible pop, click, or locking is considered a positive McMurray’s test and felt to be specific for posterior horn bucket handle lateral meniscal tear. Externally rotating the tibia and performing the same motion will detect injury to the posterior horn of the lateral meniscus (Fig. 2-14).
FIGURE 2-14. Evaluation for meniscal injury or McMurray’s test of the lateral meniscus for the knee.
Biomechanics of the Knee
The knee appears to function primarily as a hinge joint, but with closer observation, its biomechanics are more complex. Rotatory motion also occurs and, although very limited, may play an important role for many of the acute traumatic and chronic overuse injuries. The primary static stabilizers include the anterior cruciate and posterior cruciate ligaments, the posterolateral complex, the remaining capsular structures, and, to a lesser extent, the medial and lateral menisci. The role of the dynamic stabilizers of the knee in controlling rotatory motion has not been well studied. However, it does appear that the medial hamstrings, lateral hamstrings, and popliteus muscles play a role here in dynamic rotary stabilization. Although knee muscle kinesiology has been extensively studied, the great majority of work has been looking at the biomechanics of the PFJ (27-33). This is not surprising, considering that patellofemoral syndrome is the most common knee disorder causing pain and limiting function.
There is no other musculoskeletal disorder in which the kinetic chain plays a greater role or requires a more thorough analysis than with patellofemoral-related pain. It is widely believed that the relative position of the patella in the PFJ, how it sits at rest, and how it travels during dynamic activities can contribute to patellofemoral syndrome and be a risk factor for patellofemoral subluxation/dislocation (26,34). The quadriceps muscles are the primary knee extensors, with a small contribution coming from some fibers of the adductor magnus (35). Three muscles of the PFJ—the vastus lateralis (VL), the vastus medialis, and the vastus intermedius—cross only the knee joint and are relatively fixed in their line of pull. Tightness in the lateral or medial retinacular structures can somewhat alter this. The hip joint is the primary rotator of the lower limb, and the degree of rotation may play an important role in patella tracking disorders. The fourth quadriceps muscle, the rectus femoris, is a two-joint muscle that crosses the hip in addition to the knee joint. It originates from the anterior superior iliac spine (ASIS), and calculating the Q angle reflects its line of pull. The Q angle is measured by extending a line from the ASIS to the midpoint of the patella. One measures the angle created by the intersection of the second line that connects the midpoint of the patella to the tibial tubercle. The normal Q angle is 10 to 14 degrees, and any significant deviation from this may lead to improper patella tracking and subsequent PFJ pain. External rotation of the hip decreases the Q angle, whereas internal rotation increases it. During normal gait mechanics, ankle pronation occurs simultaneously with hip internal rotation; conversely, supination occurs with hip external rotation. Therefore, hyperpronation can increase the Q angle, whereas hypersupination can decrease it.
EMG has been used to study knee muscle function, primarily looking at the balance and relationship among the VL, vastus medius (VM), and vastus medialis oblique (VMO), and to better understand patellofemoral maltracking syndromes (27,36-39). Sczepanski et al. (38) compared VMO and VL EMG activity during concentric and eccentric isokinetic exercises in asymptomatic individuals and found a greater VMO/ VL ratio only during concentric contractions at 120 degrees per second. Reynolds et al. (37) studied asymptomatic women and found no difference in the VMO/VL relationship through full range of motion. In a study that looked at the effect of Q angles, Boucher et al. (27) found no significant differences in VMO/VL EMG ratio between asymptomatic volunteers and patients with patellofemoral maltracking syndromes. They did find a decrease in the VML/VL ratio in a subset of patellofemoral syndrome (PFS) patients with Q angles greater than 22 degrees at 15 degrees of knee extension. Voight and Wieder (39) compared the reflex response times of the VMO and VL EMG following a tendon tap. There was an increase in the VL response times in patellofemoral maltracking syndrome patients. These studies are far from conclusive, and the debate about the relationship between the VMO and the VL as contributing factors for patellofemoral disorders continues, while conventional clinical management remains based on these principles.
Kinesiological work has also been done to better understand muscle mechanics as it pertains to patients who have torn their ACLs and to help determine the most effective methods of managing these patients both nonsurgically and postoperatively. The ACL restrains anteromedial rotation of the tibia. An EMG study by Limbard et al. (40) on ACLdeficient patients found an increase in biceps femoris activity with a simultaneous decrease in quadriceps activity during swing-to-stance transition at normal walking speeds. At this point in gait, the hamstring may have been firing to prevent anteromedial tibial rotation. The hamstrings were less active in these patients from midstance to terminal stance. Branch et al. (41) found an increase in EMG activity of the lateral hamstrings in ACL-deficient patients during swing phase and an increase in medial hamstring and a decrease in quadriceps activity during stance phase. Tibone et al. (42) had reported similar findings. Solomonow et al. (43) stressed that an intact ACL led to excitement of the hamstrings and inhibition of the quadriceps. Baratta et al. (44) studied coactivation patterns. Hypertrophy of the quadriceps impaired hamstring coactivation, and strengthening of the hamstrings reduced this. Lutz et al. (45) demonstrated a greater ability to perform cocontractions of the hamstrings and quadriceps during closed kinetic chain exercises, thus conferring more stability to the knee. Weresh et al. (46) studied the popliteus muscle and found no difference in activation between ACL-deficient patients and controls.
Based on these EMG studies, one can now look for some of the muscle imbalances and other anatomic factors for patellofemoral maltracking syndromes such as hyperpronation or excessive hip internal rotation during the physical examination. Once these findings have been identified, they can then be more specifically addressed with physical therapy or some other form of a structured exercise program.