Medial Collateral Ligament (MCL)

The medial (tibial) collateral ligament (MCL) consists of a deep and a superficial band. It attaches proximally to the medial femoral epicondyle immediately below the adductor tubercle and inserts distally into the medial tibial condyle (deep band) and into the medial surface of the tibia (superficial band or long band). The long, superficial band attaches to the tibia as a large fascial extension 7 to 10 cm below the joint line, deep to the pes anserinus tendons (Figure 6-8). The deep ligament band has attachments to the peripheral margin of the medial meniscus.

FIGURE 6-8 THE KNEE: MEDIAL ASPECT.

Lateral Collateral Ligament (LCL)

The relatively small-diameter lateral (fibular) collateral ligament extends from the lateral femoral epicondyle proximally to attach onto the fibular head distally (Figure 6-9).

FIGURE 6-9 THE KNEE: LATERAL ASPECT.

Anterior Cruciate Ligament (ACL)

The anterior and posterior cruciate ligaments, so named for the position of their attachment to the tibia, are situated centrally between the two tibiofemoral articulations (Figure 6-10). The cruciates provide a strong mechanical tie between the femur and the tibia, providing the main resistance to sagittal displacement; they also assist the collateral ligaments in resisting lateral bending of the joint. The anterior cruciate ligament (ACL) provides strong resistance to anterior displacement and excessive internal rotation of the tibia on the femur. The ACL attaches distally on the tibia in a relatively large expanse just in front of and lateral to the tibial spine (intercondylar eminence). It spirals upward and laterally to attach onto the posteromedial corner of the lateral femoral condyle, posterior to the longitudinal axis of the femur. The ACL twists around the posterior cruciate ligament (PCL) with internal rotation of the tibia on the femur, and it may be injured either with excessive anterior translation of the tibia on the femur or with excessive internal tibial rotation. The ACL has been described as consisting of three distinct bundles; although this is a somewhat oversimplified representation of the ligament in vivo, it is nonetheless useful when dealing with partial ACL tears. The anteromedial fibers are taut in flexion, whereas the larger, posterolateral fibers are tight in extension. The intermediate fibers remain relatively taut throughout knee range of motion.

FIGURE 6-10 THE KNEE: CRUCIATE LIGAMENTS AND THEIR TIBIAL ATTACHMENTS.

Posterior Cruciate Ligament (PCL)

The tibial attachment of the PCL is extraarticular, extending down the back of the tibial plateau over 1 or 1.5 cm distal to the joint line (see Figure 6-6) and blending with the posterior horn of the lateral meniscus. On the femoral side, the ligament attaches onto the anterolateral aspect of the medial femoral condyle in the intercondylar notch on the opposite side of, and anterior to, the ACL (see Figure 6-10). The anterior fibers of the PCL are taut in flexion, whereas the posterior fibers are taut in extension.

During the open-packed position (knee flexion), the collateral and cruciate ligaments are lax, and flexion is not checked until the leg contacts the thigh. During the close-packed position (full extension), the cruciate ligaments become taut, preventing further extension. The collateral ligaments also prevent hyperextension as a result of their posterior attachment to the tibia and fibula.

Medial Meniscus

The medial meniscus is C-shaped and has a larger radius than the lateral meniscus. The anterior horn of the medial meniscus is firmly attached to the tibia, just anterior to the ACL attachment. The posterior horn attaches adjacent to the PCL.

Lateral Meniscus

The lateral meniscus is more circular in shape, more mobile, and covers a larger portion of the articular surface than the medial meniscus. It is attached to the tibia between the tibial spines, between the tibial attachments of the medial meniscus. It is separated from the posterolateral joint capsule by the tendon of the popliteus muscle.

The Synovial Membrane

The knee synovium is the largest in the body. It lines the inner surface of the capsule, suprapatellar pouch, cruciate ligaments, and free borders of the menisci. The suprapatellar pouch extends proximally about 6 cm above the patella.

Blood and Nerve Supply

The knee derives its blood supply from a number of genicular branches from the femoral, profunda femoris, popliteal, and anterior tibial arteries. Its nerve supply is from the femoral, obturator, tibial, and common peroneal nerves.

Knee Movements

The knee is not a true hinge joint, because the axis of movement is not a fixed one. Instead, the axis shifts forward during extension and backward during flexion. Also, the commencement of flexion and the end of extension are accompanied by rotatory movements. Therefore, movements of the knee from full flexion to full extension consist of three components: 1) a simple rolling movement of the tibia on the femur; 2) a gliding movement of the tibia on the femur superimposed on rolling, in which the axis of movement through the medial and lateral femoral condyle gradually shifts forward during extension (opposite to what occurs during flexion); and 3) a rotatory movement at the end of extension, consisting of external rotation of the tibia on the femur through contraction of the biceps femoris and tensor fascia lata. This rotary movement is referred to as the locking movement of the joint or the screw-home movement. At the commencement of knee flexion, the converse occurs: the tibia internally rotates on the femur through contraction of the popliteus, semitendinosus, sartorius, gracilis, and semimembranosus, thereby “unlocking” the joint.

The screw-home position on full extension contributes significantly to knee stability, particularly when standing erect. It allows the patient to maintain knee extension over prolonged periods of standing without relying on continuous quadriceps contraction; therefore, it is an energy-conserving mechanism. The presence of a knee flexion deformity abrogates this stabilizing mechanism, causing quadriceps muscle fatigue.

Clicking, Snapping, and Clunking Noises and Sensations

Normal knees often make painless, high-pitched clicking sounds during squatting. Patients with arthritis or an inflamed synovium may note a crackling sound or sensation with knee movement. Low-pitched clunks may be caused by a loose body, a meniscus, or a cartilage fragment that is getting caught in the joint mechanism during movement. A patient may experience an audible snap or pop during rupture of a ligament or capsular structure or as a bone fractures.

Swelling

Diffuse knee-joint swelling is a nonspecific symptom that suggests knee synovitis and joint effusion. Knee swelling that occurs immediately after an injury is often caused by bleeding into the joint from a ligament or capsular rupture or by an intraarticular fracture. Such bleeding is usually accompanied by bruising. Swelling that arises hours or days after an injury is more likely to be caused by inflammation rather than bleeding (e.g., acute synovitis). Swelling of the knee that occurs without injury suggests an inflammatory arthritis with synovitis and effusion.

Heat and Redness

Swelling, heat, and redness are all signs of inflammation in the knee joint or periarticular tissues.

Stiffness

Stiffness may accompany knee swelling, or it may be an independent symptom. With a large effusion, the knee is more comfortable in slight flexion, and patients have difficulty with both full extension and full flexion. They describe the knee as feeling “tight.” Arthritis and periarticular contractures can cause decreased range of motion that is not due to fluid in the knee joint. A sense of stiffness in the morning is common with both rheumatoid arthritis and osteoarthritis.

Deformity

Acute deformity after trauma suggests a major muscular, ligamentous, or bony injury that is accompanied by loss of integrity of the knee joint or the surrounding musculature sufficient to cause the deformity. For example, the patient may report noticing a lump at the lateral aspect of the knee that jumped back into place later on, suggesting a patellar dislocation that spontaneously reduced. The insidious onset of deformity often accompanies knee arthritis. Varus deformity of the knee is particularly common in medial compartment osteoarthritis.

Giving Way and Instability

The knee collapses when the patient bears weight if the extensor mechanism is disrupted or inhibited by pain or muscle weakness. Patellofemoral problems often cause a sense of the knee’s giving way, especially when descending stairs, because the quadriceps muscle is contracting eccentrically with controlled lengthening of the muscle. Disruption of the ACL can cause collapse of the knee with certain maneuvers that result in femoral translation into an abnormal position on the planted tibia.

Pivoting

An ACL disruption allows the tibia to slide forward on the femur, especially on the lateral side of the knee. The patient may notice that this happens when the body is swung around to the outside of a planted leg during cutting sports. This movement rotates the femur around the tibia, and, because of the incompetent ACL, the femur rides back excessively on the lateral side. Patients often describe what happens by using their fists to indicate how the knee pivots. Pivoting is often accompanied by painful collapse as the knee joint gives way.

Locking

True locking of the knee refers to sudden or recurrent inability to flex or to extend the knee. It can occur because of a mechanical block to knee-joint motion, such as a loose body, meniscus flap, cruciate ligament stump, cartilage flap, or scar tissue that interferes with knee flexion or extension by its interposition between the joint surfaces. True locking must be distinguished from pseudolocking, which is caused by knee-joint stiffness or lack of movement due to pain inhibition, as opposed to a mechanical block. Asking the patient whether the knee “jams up” or “gets stuck” because something seems to be caught in it may be helpful in differentiating true locking from pseudolocking.

Safety Considerations

In complex knee revision surgery, the extensor mechanism or the collateral ligaments may be compromised. The examiner should avoid undue force when examining for passive range of motion or when testing the integrity of the ligaments in these situations. Certain types of knee implants may click, especially during testing for stability in flexion, as the artificial components move apart a few degrees and then back together. This usually is not a sign of pathology. Some numbness around the incision site is common, but a painful trigger point near the incision may indicate the presence of a neuroma.

Pain after Total Knee Arthroplasty

Mechanical failure. Knee dislocation and periprosthetic distal femoral fractures or proximal tibial fractures generally result in severe functional impairment, usually with complete inability to walk, severe pain, and an often characteristic deformity. Knee dislocation is extremely rare early on, but it can occur after significant wear of the components has rendered the interface unstable or with subsidence or loosening of one or more implant components. A thorough neurovascular examination is essential in these situations, considering the proximity of the vascular trifurcation and the common peroneal nerve. The patellofemoral joint should be evaluated after total knee replacement surgery for possible patellar maltracking related to implant position, quadriceps muscle imbalance, and soft-tissue contractures. This entails an assessment of alignment that includes the Q angle, the relative height of the patella, and quadriceps muscle bulk and strength, as well as a dynamic impression of patellar tracking as the patient flexes and extends the knee. Problems with patellofemoral function may severely impair walking ability, because the knee gives way during loading.

Neurovascular Pain and Dysfunction

The common peroneal nerve is particularly at risk for injury when a preoperative fixed valgus deformity is corrected at the time of knee replacement, resulting in lengthening of the lateral side of the knee and stretching of the peroneal nerve. Complaints of pain and paresthesia should be evaluated with a complete neurological examination. The most obvious motor abnormality with complete loss of common peroneal nerve function is a dense foot drop.

Deep Vein Thrombosis

Patients are at significant risk for deep vein thrombosis (DVT) after total knee replacement surgery. Most surgeons use thromboprophylaxis for a variable period after surgery, and the patient should be questioned about the specifics of this treatment. The clinician should have a high index of suspicion for the possibility of DVT, especially if the patient has gone 8 to 12 weeks since the surgery and is no longer receiving thromboprophylaxis. Physical examination is poor at determining whether DVT is present, and diagnostic tests, such as ultrasound or venography, should be used liberally if DVT is suspected.

Implant Loosening and Infection

Mechanical loosening of the implant–bone interface may be associated with pain. Important causes of loosening include trauma, osteolysis due to implant wear, and infection. The examiner should inquire about recent falls or other injuries and the relationship of these events to the onset of pain. Information regarding how long the knee replacement has been in situ can provide clues regarding the possibility of implant wear. Finally, potential sources of infection should be sought. Low-grade infections may go undetected for many months before implant loosening or systemic manifestations are noted. Typically, pain due to infection is always present and is not relieved with rest, whereas mechanical loosening may result in intermittent pain, usually with activity. If infection is suspected, knee aspiration and fluid culture are indicated. Early postoperative infection can sometimes be managed with debridement with successful retention of the implants.

Other Causes

Bursitis around the knee can be a potential cause of knee pain after prosthetic implantation. For example, medial overhang of the tibial component may cause pes anserine bursitis. Referred knee pain from the hip joint or lumbar spine is another potential source of pain.

Genu Varum and Genu Valgum

Normally, the center of the knee joint lies on a line that connects the center of the hip and the center of the ankle joint (see Figure 6-2). In an individual with genu varum, or bowleg deformity, the center of the knee joint falls lateral to the axis connecting the centers of the hip and ankle joints (Figure 6-11). Although accurate assessment of bony alignment requires radiographic imaging, a patient with more than 3 cm of space between the medial femoral condyles when standing with the feet together probably has genu varum. Conversely, genu valgum, or knock-knee deformity, occurs when the center of the knee joint is medial to the biomechanical axis of the lower extremity (Figure 6-12). Clinically, an individual with more than 3 cm between the medial malleoli likely has genu valgum. Inspection for varus or valgus misalignment is best performed with the knee in a weight-bearing (standing) position.

FIGURE 6-11 GENU VARUM.

FIGURE 6-12 GENU VALGUM.

Genu Recurvatum and Genu Procurvatum

When the knee is examined from the side, the patient should be able to fully straighten it. A few degrees of hyperextension can be normal, especially in patients with generalized ligamentous laxity; but more than 10° of hyperextension, or genu recurvatum (“back knees”), generally indicates pathology such as hypermobility syndrome or a cruciate ligament laxity or injury (Figure 6-13). A fixed flexion deformity (genu procurvatum) or the inability to achieve full extension is always pathological and may be caused by arthritis, a large joint effusion, or a mechanical block to extension resulting from a meniscus tear or loose body.

FIGURE 6-13 GENU RECURVATUM.

Squinting and Frogeye Patellae

Squinting patellae, patellae that are facing toward each other when the patient walks toward the examiner with feet pointing forward, suggest an internal rotational deformity of the femur or an external rotational deformity of the tibia (Figure 6-14). External femoral rotation or internal tibial rotation gives the appearance of patellae that face away from each other (frogeye patellae; Figure 6-15).

FIGURE 6-14 SQUINTING PATELLAE.

FIGURE 6-15 FROGEYE PATELLAE.

Knee Swelling

A diffuse, generalized knee swelling usually indicates either a joint effusion or a diffuse inflammatory synovitis with synovial thickening. By contrast, an asymmetric, localized swelling often suggests a bursitis or tendon lesion. Medial swelling can be caused by a small knee-joint effusion. A popliteal cyst located behind the medial compartment of the knee is often caused by a distended, communicating medial gastrocnemius-semimembranosus bursa. Less commonly, a cyst behind the lateral compartment suggests a swollen, communicating popliteus bursa. In the setting of inflammation, the skin overlying the knee may appear erythematous.

What Is the Vascular Status of the Limb?

It is essential to assess the vascular status of both lower extremities as part of a knee evaluation. Some examiners are in the habit of performing the vascular examination as the very first or very last part of the overall evaluation to ensure that it is not missed inadvertently. In addition to inspecting for vascular skin compromise, palpation of the pedal pulses (dorsalis pedis and posterior tibial) can be used as a quick screening test. If the distal vascular status is intact, this suggests that there is no compromise to the arterial circulation of the entire extremity. In the absence of pedal pulses, palpation of the popliteal and femoral pulses is required. Circulatory problems are a potential cause of leg pain and may also increase the risk of surgical complications, if an operation is required.

Is the Knee Joint Inflamed?

The normal knee should be slightly cooler to the touch than the adjacent anterior thigh, which is surrounded by a well-perfused muscle layer. A knee that feels as warm as or warmer than the thigh is likely to be inflamed. Other signs of knee synovitis include redness, swelling, and a joint effusion. Synovitis of the knee is characterized by synovial thickening and diffuse joint-line tenderness, both along the medial and lateral compartments. The synovium is best palpated along the joint line with the knee 90° flexed. Normally, the synovial membrane is quite thin and difficult to palpate. Chronic synovitis, caused by rheumatoid or other inflammatory arthritis, is often associated with significant synovial thickening, with more soft tissue intervening between the palpating thumbs and the joint line (Figure 6-16).

FIGURE 6-16 PALPATION OF THE MEDIAL AND LATERAL TIBIAL PLATEAUS AND JOINT LINES.

Is There Fluid in the Knee Joint?

Rapid fluid accumulation in the knee after an injury suggests that bleeding from a vascular structure, such as the ACL, has occurred. Osteoarthritic, inflammatory, or infectious conditions cause more gradual accumulation of a knee effusion.

Bulge sign. In the brush, stroke, or wipe test, fluid is pushed up into the suprapatellar pouch by sliding the hand from the distal aspect to the proximal along the medial aspect of the knee joint with the patient in the supine position and the knee relaxed in extension. The fluid is then milked back down by sliding the hand from the superior aspect to the inferior along the lateral aspect of the knee (Figure 6-17). A medial fluid bulge indicates free fluid within the knee joint (bulge sign). The test can be used to demonstrate small to moderate effusions (less than 30 mL), but it may be difficult to detect a bulge with a large or tense effusion, because in this situation, the fluid cannot be milked out of one compartment and into the other.

FIGURE 6-17 BULGE SIGN FOR KNEE EFFUSION.

Balloon test or cross-fluctuance test. The examiner places one hand over the suprapatellar pouch and the thumb and fingers of the other hand on the medial and lateral sides of the joint line, just distal to the margins of the patella. By pressing down with one hand and then the other, the examiner may feel cross-fluctuance of the fluid under the hands (Figure 6-18). The balloon test is particularly useful for patients in whom the patellar tap (Figure 6-19) is difficult to perform due to a large, tense effusion or the presence of a fixed knee-flexion deformity.

FIGURE 6-18 BALLOON TEST.

FIGURE 6-19 PATELLAR TAP TEST FOR KNEE EFFUSION.

Is There Pathology Involving Soft Tissues?

Palpation of muscles and tendons is helpful in determining whether the structure is inflamed or partially or completely torn, and it helps to determine atrophy, especially if one side is asymmetric compared to the opposite side. Soliciting active contraction and passively stretching the painful muscle or tendon is required to complete the evaluation.

Quadriceps muscle and tendon. Disuse atrophy of the quadriceps muscle, especially the vastus medialis component, is a common finding in patients with knee pathology. The vastus medialis is palpated for its bulk and firmness bilaterally, with the knee in extension, during voluntary contraction of the muscle. Normally, the underlying femur bone cannot be palpated through the vastus medialis muscle without the application of extraordinary pressure. The girth of the quadriceps is measured and compared bilaterally by tape measure at a defined distance (approximately 15 cm above the tibial tubercle) with the knee in extension and the muscle contracted (Figure 6-20). The vastus medialis obliquus (VMO) contributes to both medial stability of the patella and the screw-home movement of the tibia on the femur in the last 10° of extension.

FIGURE 6-20 MEASURING QUADRICEPS MUSCLE BULK.

The quadriceps tendon is palpated for tenderness, defects, or swelling along the central tendinous portion and over the insertion into the proximal patellar pole. The medial and lateral patellar insertions of the vastus medialis and vastus lateralis, respectively, in association with the patellar retinacula, should also be palpated if pathology in the extensor mechanism is being considered (Figure 6-21).

FIGURE 6-21 QUADRICEPS TENDON.

Infrapatellar ligament (patellar tendon). Because this structure connects two bones, it is sometimes referred to as the infrapatellar ligament. Others consider the patella to be a large sesamoid bone and therefore refer to the structure as the patellar tendon. The infrapatellar ligament is palpated for tenderness, swelling, or defects along its length, from the inferior pole of the patella to its insertion into the tibial tubercle. The infrapatellar fat pad is situated immediately posterior to the patellar tendon at the level of the joint line. It can be readily palpated by curling the fingers around the tendon from either side (see Figure 6-8).

Pes anserinus. The pes anserinus—the conjoint tendon of the sartorius, gracilis, and semitendinosus muscles—inserts into the medial surface of the proximal tibia about 5 cm below the joint line and at the same level as the tibial tuberosity (see Figure 6-8). It is best palpated during resisted knee flexion of less than 90° (Figure 6-22). The fingers are placed around the medial aspect of the knee, just above the joint line. The two sharp, cordlike structures are the gracilis (more anterior and lateral) and the semitendinosus (more posterior and medial). Between these two structures, the bulky semimembranosus tendon (not part of the pes anserinus) can be palpated. More proximally, the semimembranosus muscle bulk is evident medial to the semitendinosus tendon. The fleshy bulk anterior to the gracilis tendon is the sartorius muscle.

FIGURE 6-22 THE ILIOTIBIAL BAND.

Iliotibial tract. The iliotibial tract is attached proximally to the iliac crest. The tensor fascia lata muscle inserts into it anteriorly, and the bulk of the gluteus maximus muscle inserts into it posteriorly (Figure 6-23). Distally, the iliotibial band attaches to the Gerdy tubercle on the anterolateral aspect of the proximal tibia. A band from the iliotibial tract also attaches to the lateral upper patella (superior patellar retinaculum). It is easy to palpate the iliotibial band distally by moving the fingers from the posterior to anterior aspect, just anterior to the biceps femoris tendon, while the knee is flexed 30° with an ipsilateral single-leg stance or during resisted abduction of the hip (see Figure 6-23).

FIGURE 6-23 THE ILIOTIBIAL BAND.

Is the Iliotibial Band Inflamed?

A tight iliotibial band can be associated with iliotibial band syndrome, inflammation of the band as it crosses over the lateral femoral epicondyle. This can be assessed with the Ober test (described in Chapter 5) and by one of the following two tests.

Renne test. The iliotibial band is directly over the lateral femoral epicondyle when the knee is in approximately 30° of flexion. The patient stands with the knee extended, and the examiner’s fingers are placed over the lateral femoral epicondyle. The patient is then asked to slowly flex the knee down into a squatting position (Figure 6-24). Pain at the epicondyle at about 30° of knee flexion is suggestive of iliotibial band friction syndrome.

FIGURE 6-24 RENEE TEST.

Noble test. This test is analogous to the Renne test but with the patient supine on the examining table. The knee is passively flexed and extended with one hand around the ankle and the thumb of the other hand placed over the lateral femoral epicondyle. Pain over the epicondyle at about 30° of knee flexion is suggestive of iliotibial band friction syndrome.

Semimembranosus. The biceps femoris, the semimembranosus, and the semitendinosus together make up the hamstring muscles. The semimembranosus muscle can be palpated between the gracilis and semitendinosus tendons during resisted knee flexion in the supine or prone position. The bulky part of the muscle is medial to the semitendinosus proximally, but distally the tendon comes to lie deep to the pes anserinus as the tendon inserts more proximally onto the posteromedial tibial plateau (see Figure 6-22). It can be difficult to distinguish between semimembranosus tendinitis and posteromedial joint-line tenderness caused by meniscus pathology.

Biceps femoris. The biceps femoris tendon can be readily palpated in the supine or prone position, with the knee flexed, by curling the fingers around the proximal fibula and then moving them proximally around the cordlike biceps femoris tendon, which attaches to the fibular head. Resisted knee flexion makes the tendon more prominent. The common peroneal nerve can be palpated just below the biceps femoris tendon insertion, as it winds around the fibular head. The nerve is quite superficial at this level, and the patient may experience some discomfort with palpation.

Gastrocnemius. With the patient in the prone position and the knee flexed against resistance, the insertions of the gastrocnemius into the back of the medial and lateral femoral condyles may be palpated. Tendinitis may develop at either insertion point. The muscle belly is readily palpable more distally. The medial head of the gastrocnemius is torn more commonly than the lateral head during sports.

Knee bursae. A bursa is a potential space with very little fluid that facilitates movement of adjacent soft tissues. It is usually not palpable unless bursitis with fluid distension has developed. Bursae are compressible but may be quite firm to palpation. Chronic bursitis may lead to loculation of the bursa, making it difficult to aspirate. There are at least 14 bursae about the knee joint, but some are more commonly associated with clinical problems. For example, a popliteal cyst (Baker cyst) is readily visible and palpable with the patient standing. It is located between the medial gastrocnemius insertion and the semimembranosus tendon. This cyst typically arises due to chronic knee-joint inflammation with persistent joint fluid that enters into and distends the semimembranosus bursae. The popliteal cyst usually maintains a connection with the knee joint, which is why aspiration usually results in recurrence unless the underlying joint pathology is also addressed. The prepatellar bursa lies between the patella and the overlying skin. The deep infrapatellar bursa, which lies distal to the infrapatellar fat pad, separates the patellar tendon from the proximal tibia. The superficial infrapatellar bursa is situated more superficially, between the patellar tendon and the overlying skin. Medially the pes anserine bursa separates the tendons of the sartorius, gracilis, and semitendinosus from the underlying tibia.

Synovial membrane. The synovial membrane can be palpated for tenderness and synovial swelling (thickening) in a similar fashion. The thumbs of both hands palpate the medial and lateral joint lines, with the fingers placed behind the knee for counterpressure (see Figure 6-16).

Infrapatellar fat pad. The infrapatellar fat pad lies immediately behind the patellar ligament at the level of the joint line. Contusion of the pad is associated with local pain, tenderness, and swelling.

Is There Pathology Involving Bony Structures?

Patellar pathology and tests. The patella is readily palpable in the supine patient. The main body may be tender to palpation with traumatic contusions or fractures. Occasionally there is a bipartite patella, with a groove between the superolateral portion and the main patellar fragment (Figure 6-25). This can be a variant of normal. If it is associated with tenderness to palpation, swelling, or crepitus, a patellar fracture must be ruled out. Unless the patient has ligamentous laxity, the undersurface of the patella is difficult to palpate. The lateral facet can best be palpated for retropatellar tenderness or defects by sliding the patella laterally with the knee relaxed and extended. The medial surface can be palpated if the patella can be flipped up to face the examiner medially. The margins of the trochlear groove of the femur can be palpated with the knee flexed and the patella displaced to either side.

FIGURE 6-25 A BIPARTITE PATELLA.

The patella is subject to lateral displacement during flexion and extension because the femur meets the tibia at an angle (see Figure 6-2). Because the quadriceps pulls along the femur, and the patellar tendon is anchored along the proximal tibia, this angle tends to force the patella laterally during active extension with muscle contraction. The vastus medialis resists this lateral translation, and the distal femoral anatomic groove further prevents patellar displacement. Normally the distance between the tibial tubercle and the lower pole of the patella is approximately the same distance as the distance from the lower to the upper pole of the patella (the patellar length). A high riding patella (patella alta) is one in which the length from the tendon to the lower patellar pole is greater than the patellar height, causing the patella to lie above the deep part of the femoral groove. In this position the patella is more prone to lateral displacement. Patella baja denotes a low-lying patella. The Q angle represents the relationship between the quadriceps muscle line of pull through the patella onto the tibial tubercle. As noted previously, a large Q angle has significant implications for patellar stability and may be associated with a patellofemoral syndrome (pain in the anterior aspect of the knee related to the extensor mechanism). The combination of generalized ligamentous laxity, a large Q angle, and a high-riding patella places the individual at high risk for the development of patellofemoral syndrome.

Chondromalacia patellae is a pathological diagnosis of cartilage damage or softening. It may be associated with the clinical entity of patellofemoral syndrome, but the two terms are not synonymous. The line of quadriceps muscle pull is approximated by drawing a line from the anterior superior iliac spine (see Chapter 5) to the center of the patella in a supine patient with the hips and knees fully extended. The angle between this line and a line from the center of the patella to the tibial tubercle constitutes the Q angle (see Figure 6-4).

Patellar Tests

Patellar apprehension (instability) test. Because of the Q angle, patellar dislocation is almost always to the lateral side. Spontaneous reduction is common before the patient presents to the examiner. With the patient in the supine position and the knee in a comfortable position of a few degrees of flexion, the patella is gently pushed laterally from its medial border. Patient apprehension and pain are evidence of previous patellar dislocation and are often accompanied by quadriceps muscle contraction. A modification of this test, known as the moving patellar apprehension test (MPAT), is associated with greater diagnostic accuracy. It is performed with the knee in full extension and the patella displaced laterally as far as possible by the examiner’s thumb. The knee is then flexed to 90° and brought back into full extension with the lateral force maintained. The test is then repeated, but with force directed medially. For the MPAT to be considered positive, the patient must display apprehension with a laterally directed force but not with a medially directed force.

Patellofemoral grinding test (Clarke sign). With the patient supine, the knee extended, and the leg relaxed, the patella is pushed distally in the trochlear groove by the examiner. The patient is then asked to tighten the quadriceps while the examiner palpates, compresses, and resists proximal movement of the patella. Normally, patellar movements are smooth and painless; but in patients with patellofemoral osteoarthritis or patellar contusion, the movements are rough and painful. The maneuver can be very painful, even in normal subjects. The patellar grinding test is neither sensitive nor specific and adds little useful information.

Is There a Pathological Plica Causing Anterior Knee Pain?

A synovial plica is a band of synovial tissue that is present in most normal knees. With repeated trauma or irritation, these plicae can become thickened and painful (pathological plica). A pathological plica often manifests as anterior knee pain that may be associated with popping or snapping sensations and may need to be considered in the differential diagnosis of anterior knee pain. A pathological plica is more common on the medial side. Rarely, a thick cord and popping of the plical band can be palpated medially by internally rotating the tibia while flexing and extending the knee joint (Hughston plica test). The patient may also experience apprehension as the patella is pushed medially in the supine position with the knee flexed to approximately 30°. The apprehension is caused by pain that occurs as the plica is compressed between the patella and the underlying medial femoral condyle.

Tibial tuberosity. The tibial tubercle is readily palpable at the inferior attachment of the patellar ligament, a few centimeters below the joint line. It may be quite prominent in individuals with a history of tibial tubercle apophysitis (Osgood-Schlatter disease).

Medial femoral condyle and epicondyle. The medial femoral condyle can be palpated in the flexed knee medial to the patellar ligament, from the joint line distally to the proximal extent of the condyle medial to the patella. Full knee flexion is required to palpate the inferior part of the condyle. The proximal part can best be palpated with the knee in extension and the patella displaced laterally. The medial femoral epicondyle is readily palpable a few centimeters above the joint, the most prominent medial bony landmark of the distal femur, where the MCL attaches proximally (see Figure 6-5).

Lateral femoral condyle and epicondyle. The lateral femoral condyle is less prominent than the medial condyle but can be palpated in an analogous manner. The lateral epicondyle is easily identified as the most prominent lateral bony landmark on the distal femur, where the fibular collateral ligament is attached proximally (see Figure 6-5). Either epicondyle may be tender if it is inflamed (epicondylitis). Inflammation of the iliotibial band may cause tenderness in this area, which can be differentiated from epicondylitis using Ober, Renne, and Noble tests as described earlier.

Medial tibial plateau. Beginning from the joint line adjacent to the medial side of the patellar ligament, the fingers are moved medially to palpate the prominent medial tibial plateau (see Figure 6-16). The posterior muscular attachments prevent bony palpation of the posteromedial plateau in most patients. Osteoarthritis may lead to osteophyte formation around the knee joint, which may be readily palpable as enlargements that may or may not be tender.

Lateral tibial plateau. The joint line and plateau are palpated beginning at the lateral margin of the patellar ligament and moving laterally along the lateral tibial plateau (see Figure 6-16). As on the posteromedial side, the posterolateral plateau is difficult to palpate because of the muscular and tendinous structures overlying it.

Lateral tibial (Gerdy) tubercle. The iliotibial tract inserts into the Gerdy tubercle just below the joint line, between the fibular head laterally and the patellar ligament medially (see Figure 6-1). It is quite distinct in some individuals.

Fibular head. The fibular head is readily palpated by following the biceps femoris tendon distally, from behind the lateral aspect of the femur to its insertion into the fibular head. The fibular head becomes more distinct with internal rotation of the tibia on the femur. The fibular head may be grasped between the thumb and fingers to test for stability and inflammation of the proximal tibiofibular joint by attempting to displace the fibula forward and backward. The common peroneal nerve can be palpated by moving the fingers distally along the proximal fibula until a cordlike structure is noted crossing the bone obliquely. The nerve can be rolled and palpated gently with the fingers; firm palpation may cause pain and paresthesia.

Is There Joint Instability or Pathology Involving the Ligaments?

The medial and lateral collateral ligaments are the main structures that resist varus and valgus forces across the knee joint, whereas the anterior cruciate ligament resists primarily anterior translation of the tibia relative to the femur, and the posterior cruciate ligament primarily resists posterior translation of the tibia relative to the femur. The collateral ligaments can be assessed by palpation and other maneuvers, but the cruciate ligaments cannot be directly palpated and are evaluated indirectly through various specific maneuvers.

Medial and Lateral Collateral Ligament Palpation

When palpating the MCL, it may be difficult to differentiate meniscal tenderness in the medial joint line from MCL tenderness, given the intimate relationship between these two structures (see Figures 6-6 and 6-9). It is important to assess the entire extent of the ligament by slowly moving from the medial femoral epicondyle down to the tibial insertion point. The area of maximal tenderness should be sought. Maximal tenderness over the ligament, away from the joint line, is less likely to be related to meniscus pathology.

The LCL is easily isolated by placing the leg into the figure-four position. The ligament can then be palpated as it runs from the lateral femoral epicondyle to the fibular head. It is situated anterior to the biceps femoris tendon distally (Figure 6-26).

FIGURE 6-26 PALPATION OF LATERAL COLLATERAL LIGAMENT.

Joint Stability

In most slightly flexed, normal knees, some laxity allows a few degrees of angulation in varus/valgus testing and a few millimeters of glide in the anteroposterior plane. When examining a patient with an acute injury, laxity may be difficult to detect due to muscle spasm. The patient should be made as comfortable as possible to facilitate muscle relaxation, especially of the hamstring and quadriceps muscles.

Severity of ligament injury. Ligament injuries are graded from first degree to third degree. First-degree injuries involve microscopic tearing of the ligament that results in mild swelling and pain with palpation and stressing but no joint instability. Second-degree injuries involve microscopic tears of a portion of the ligament with pain on palpation and stressing of the ligament, along with moderate swelling and bruising and a slight instability of a firm end point. A third-degree tear is a complete tear of the ligament that involves considerable swelling and bruising with gross instability but may actually be associated with less pain on palpation and stressing of the ligament than a lesser, second-degree injury.

Pseudolaxity and fixed deformity. Care must be taken to consider the neutral, varus/valgus, and anterior/posterior positions of the knee in relation to the start and end positions of the ligament test. Loss of articular cartilage and collapse of a knee compartment due to arthritis may result in increased movement with varus/valgus testing, as the knee is brought from its deformed position to a normal position. This phenomenon is observed when the ligament retains its normal length in the presence of collapse of the corresponding joint compartment, known as pseudolaxity. If the collapse is long-standing, the corresponding ligament may contract, resulting in a fixed deformity. Similarly, a rupture of the PCL results in posterior sag of the tibia and an apparent increased anterior translation of the tibia in a forward direction. If the examiner does not appreciate that the start position is abnormal, anterior laxity may be mistakenly diagnosed.

Medial stability. The MCL and the posteromedial capsule provide the major static medial support to the knee joint. At 30° of flexion, the MCL is isolated, whereas the posteromedial capsule and cruciate ligaments contribute to the resistance of valgus force in full-knee extension. The medial joint line is palpated while the leg is supported. With the knee at 30° of flexion, a valgus force is applied by the examiner’s arms (Figure 6-27). Joint opening and the patient’s pain response during valgus stressing of the joint are noted. Repeating the test with the knee in full extension evaluates both the MCL and the posterior capsule. If there is laxity in both flexion and full extension, both structures, and possibly one or more cruciate ligaments, are torn. If there is laxity only at 30° of flexion, the posterior capsule is intact.

FIGURE 6-27 TESTING MCL.

Lateral stability. The LCL and the posterolateral knee-joint capsule provide the major static resistance to varus forces at the knee joint. Isolated injury to the LCL is rare, and associated tests for the posterior capsular structures (see Posterolateral Instability, p. 86) should always be performed when considering lateral-sided knee instability. The capsule and the cruciate ligaments provide strong resistance to varus force in knee extension, whereas the LCL acts more in isolation with knee flexion. To isolate the LCL, the knee is flexed to 30°, the lateral joint line is palpated, and a varus force is applied using the leg tucked under the examiner’s arm as a fulcrum. The tibia should be kept in neutral rotation. The test is repeated in full-knee extension to evaluate the integrity of the posterior capsule. Laxity in both flexion and extension suggests disruption of the posterior capsule, and possibly of one or more cruciate ligaments, along with the LCL. The patient’s pain response is assessed during ligament stress testing. A grade 1 ligament tear will exhibit no laxity, but the patient will experience pain with stressing.

Anterior stability. The ACL prevents forward displacement of the tibia on the femur. It is taut with internal tibial rotation. This structure may be injured during running, when the foot is planted and the individual pivots to the same side, resulting in strong internal tibial rotation on the femur. The ACL may also be injured with hyperextension, as the tibia is forced forward on the femur, or with a direct blow to the tibia from behind.

Lachman test. After an acute injury, hamstring spasm will prevent the examiner from appreciating laxity of the ACL with the knee in flexion. Moreover, it may be difficult for the patient to flex the knee due to pain. A Lachman test can be performed supine or prone with the knee in a comfortable position of slight flexion (about 30°). The femur is stabilized with one hand, while the other is used to pull the proximal tibia forward. It is important for the patient to try to relax the hamstring muscles during this test, but it is less critical; the hamstrings are at a mechanical disadvantage, because the examiner’s force is being applied roughly perpendicular to the muscle line of pull (Figure 6-28).

FIGURE 6-28 LACHMAN TEST.

Anterior drawer test. The anterior drawer test is performed with the knee flexed 90° and the hip flexed 45°. The passive anterior drawer test involves placing the examiner’s fingers up the proximal tibia and fibula into the hamstrings, to make sure that these are relaxed. An anterior force is then applied to the proximal tibia, in an attempt to displace it forward on the femur, while the foot is stabilized on the examination table (Figure 6-29). Hamstring spasm can yield a false-negative result. The active anterior drawer test can be performed with the knee in the same position. It involves stabilizing the foot and asking the patient to contract the quadriceps to try to extend the leg against resistance. The quadriceps muscles pull the tibia forward if the ACL is disrupted. The active anterior drawer test is unlikely to yield useful information in an acutely painful injury because of quadriceps inhibition due to pain.

FIGURE 6-29 ANTERIOR DRAWER TEST.

Anteromedial and Anterolateral Rotatory Instability

Pivot shift (MacIntosh) test and jerk test of Hughston. The pivot shift test (MacIntosh test) is a test for anterolateral rotatory instability caused by both an anterior cruciate tear and a posterolateral capsular tear. With the knee in full extension, the tibia internally rotated, and a valgus force applied, the tibia and the fibular head will sublux forward on the femur laterally in the presence of a complete ACL tear combined with a posterolateral capsule tear. As the knee joint is flexed beyond 30° to 40°, the iliotibial band comes to lie posterior to the lateral femoral epicondyle, and the tibia is seen to jump backward into position due to traction from the iliotibial band and other secondary restraints pulling the tibia back into place (Figure 6-30). The degree of instability is increased with hip abduction, because it relaxes the iliotibial tract. With severe disruption of the posterolateral corner of the knee joint, the tibia may jam up against the femoral condyle and not reduce until the valgus stress is relaxed, allowing further knee flexion. In the presence of medial joint instability, the pivot shift test cannot be performed, because the essential medial fulcrum is lost. After the tibia is reduced with flexion, the examiner can extend the knee again, while maintaining the valgus and internal rotation force at the knee. The tibia is seen and felt to jerk anteriorly, as it displaces once more at about 30°. This maneuver is sometimes called the jerk test of Hughston. It is less sensitive than the pivot shift test.

FIGURE 6-30 PIVOT SHIFT TEST.

Slocum test. ACL disruptions are commonly associated with anterior rotatory instability because of disruption of both the ACL and the posteromedial capsule (anteromedial rotatory instability) or the posterolateral capsule (anterolateral rotatory instability). Testing for posterior capsular injury with the Slocum test involves performing the anterior drawer test with the hip flexed 45° and the knee flexed 90° with the tibia either in external rotation, to tighten the posteromedial capsule, or in internal rotation, to evaluate the integrity of the posterolateral capsule (Figure 6-31). The tibia should be rotated no more than 15° to 20° to avoid excessive tightening of multiple secondary restraints that might lead to a false-negative test. If the capsule is intact, the drawer should be greater in the neutral position than when the capsule is tightened in internal or external rotation. Anterolateral rotatory instability exists if the amount of anterior laxity in internal rotation is similar to that of the anterior drawer test done in the neutral position. Anteromedial rotatory instability exists if the amount of anterior laxity in external rotation is similar to that of the anterior drawer test done in the neutral position (see Figure 6-31).

FIGURE 6-31 SLOCUM TEST.

Posterior Stability

The PCL prevents posterior displacement of the tibia on the femur; however, the PCL can be disrupted during sports, when an individual falls onto a hyperflexed knee, or when the tibia is forced posteriorly while the leg is planted. The latter mechanism may also occur during a motor vehicle collision, as the engine and dash impact against the proximal tibia, forcing it posteriorly relative to the femur. The PCL may also be injured with the knee in hyperextension, although this mechanism usually results in combined injuries. Knee hyperextension first disrupts the ACL, followed by the posterior capsule and ultimately the PCL.

It is important to remember that examination of the patient in the supine position subjects the PCL-deficient knee to the forces of gravity, with the result that the tibia may be in the displaced position when the knee is first evaluated. It is not uncommon for junior clinicians to mistakenly diagnose ACL deficiency in a PCL-deficient knee.

Posterior sag (gravity drawer test) and quadriceps active test. Normally, the tibial plateau is visible and palpable in front of the medial and lateral femoral condyles with the knee in 90° of flexion. With the patient supine, the hip flexed 45°, and the knee flexed 90°, the tibia will sag backward due to gravity if the PCL is incompetent (Figure 6-32). When looking for posterior sag, care should be taken to position the tibia in neutral rotation to avoid involving the secondary restraints of the knee, which could lead to a false-negative test. The examiner can look for a posterior sag of the tibia by lifting the patient’s heel until the hip and knee are in 90° of flexion, taking into consideration the neutral position of the tibia in relation to the femur. A sagging tibia can be lifted forward to the neutral position. Alternatively, the patient may be asked to contract the quadriceps muscle to lift the tibia forward to the neutral position. This maneuver is sometimes referred to as the quadriceps active test (Figure 6-33). Care should be taken to avoid misinterpreting the anterior translation observed as a positive active anterior drawer sign (see the earlier discussion of the anterior drawer sign), which indicates disruption of the ACL. The key is to note whether the tibia begins in a posteriorly displaced position (PCL rupture with posterior sag due to gravity) or in a normal position (normal or ACL rupture) before the anterior translation is noted, and whether it lies in a normal position (PCL rupture reduced by quadriceps) or in an anteriorly displaced position (ACL rupture) when the quadriceps muscle is actively pulling the tibia forward.

FIGURE 6-32 POSTERIOR SAG TEST.

FIGURE 6-33 QUADRICEPS ACTIVE TEST.

Reverse Lachman test. The concept is the same as for the Lachman test, except that the force is directed posteriorly, beginning with the knee flexed 30° and the tibia in a neutral position. In practice, the Lachman and reverse Lachman tests are performed at the same time by alternately applying an anterior force and then a posterior force, taking care to note the neutral position of the tibia on the femur and to interpret any translation in relation to this position.

Posterior drawer test. The posterior drawer test can be performed actively and passively, as with the anterior drawer test, except that the force is directed posteriorly. Comparison is always made with the normal side. As with the anterior drawer test, the knee is flexed 90° with the tibia in neutral rotation. With the fingers palpating the tibial plateau and femoral condyles anteriorly to assess their relative position, the proximal tibia is pulled forward until the tibia is in the normal relationship to the femur (tibial plateau palpable about 1 cm in front of the femoral condyles). A posteriorly directed force is then applied to the proximal tibia, and the degree of posterior translation is noted. Translation of the tibial plateau to a position posterior to the femoral condyles indicates complete disruption of the PCL (Figure 6-34). In practice, the anterior and posterior drawer tests are usually performed at the same time.

FIGURE 6-34 POSTERIOR DRAWER TEST.

The active posterior drawer test can be performed with the knee in the same position. The foot is stabilized on the examination table, and the patient attempts to flex the knee. The hamstrings will pull the tibia posteriorly into a maximally displaced position in a PCL-deficient knee. The examiner must recognize that the tibia usually starts from a displaced position already, due to gravity. A positive result will be more evident if the tibia is passively reduced to a neutral position before hamstring contraction.

Posteromedial and Posterolateral Rotatory Instability

PCL disruptions are commonly associated with posterior rotatory instability because of concomitant disruption of the posteromedial capsule (posteromedial rotatory instability) or, more commonly, the posterolateral capsule (posterolateral rotatory instability). Although these rotatory tests are analogous to those discussed earlier for anterior rotatory instability, the junior clinician may be confused by the fact that the opposite tibial rotation is required to test the posterolateral (or posteromedial) corner. Consideration of the force to be applied will remind the examiner of the correct rotation for each test: If anterior stability is to be tested, by applying an anteriorly directed force, external rotation of the tibia will slacken the posterolateral structures and tighten up the posteromedial structures. If posterior stability is to be tested, by applying a posteriorly directed force, external tibial rotation will tighten up the posterolateral structures and slacken the posteromedial ones once the force is applied.

Testing for posterior capsular injury involves performing the posterior drawer test with the tibia either in external rotation, to tighten the posterolateral capsule, or in internal rotation, to evaluate the integrity of the posteromedial capsule. The tibia should be rotated no more than 15° to 20° to avoid excessive tightening of multiple secondary restraints, which might lead to a false-negative test. If the capsule is intact, the drawer should be greater in the neutral position than when the capsule is tightened in internal or external rotation. Posterolateral rotatory instability exists if the amount of posterior laxity in external rotation is similar to that of the posterior drawer test done in the neutral position. Posteromedial rotatory instability exists if the amount of posterior laxity in internal rotation is similar to that of the posterior drawer test done in the neutral position.

Reverse pivot shift test. This is a test of posterolateral rotatory instability; it follows the same concept as the pivot shift test but for the PCL. With the knee flexed 70° to 80° and the patient in the supine position, an external rotation and valgus force are applied to the tibia. This forces the tibia into a subluxed position if the PCL and posterolateral corner of the knee are disrupted. While the valgus and external tibial rotation are maintained, the knee is extended. Visible and palpable reduction of the tibia occurs as the knee nears full extension. The test can also be performed with the patient in the prone position, and it can be performed with the knee reduced in full extension; the subluxation is observed as the knee is flexed upward, analogous to the jerk test.

Tibial external rotation (dial) test. Disruption of the posterolateral corner of the knee results in excessive external tibial rotation. With the patient in the prone position, and the knees in 30° of flexion, both feet are passively externally rotated by lifting the great toes (Figure 6-35). More than 10° of excess external rotation indicates the presence of a torn posterolateral knee capsule and surrounding structures. The test should then be repeated with 90° of knee flexion. An isolated posterolateral capsular injury is associated with less side-to-side difference in rotation at 90°, because the intact PCL provides stability in 90° of knee flexion. If the posterolateral capsular injury is associated with a PCL disruption, the test will be equally or more positive with the knee flexed 90°, compared with 30° of flexion. A negative test in 30° of flexion implies that no significant injury is present to the posterolateral corner, and the 90° test is not required.

FIGURE 6-35 TIBIAL EXTERNAL (DIAL) TEST.

External rotation recurvatum test. With the patient in the supine position, the legs are lifted off the examining table by the great toes. The amount of external tibial rotation and knee recurvatum are noted. Excessive lateral rotation is indicative of a posterolateral capsular injury. Excessive rotation combined with recurvatum suggests a combined injury to the posterolateral corner of the knee and one or more of the cruciate ligaments. The examiner should be aware that external rotation may give the appearance of genu varum (Figure 6-36).

FIGURE 6-36 EXTERNAL ROTATION RECURVATUM TEST.

Is There Pathology Involving the Menisci?

The menisci are situated between the femur and tibia, allowing the outer edge to be palpated along the medial and lateral joint line. Joint-line tenderness alone is not very specific, as it may be related to other problems, such as arthritic involvement of the medial or lateral compartment. Several specific maneuvers have been described that aim to detect meniscus pathology.

Medial and Lateral Meniscus Palpation

Palpation along the medial and lateral joint lines is performed with the patient in the supine or sitting position with the knee flexed 90° and the muscles relaxed. Palpation proceeds from the patellar ligament anteriorly to the biceps femoris tendon laterally and the semitendinosus medially. The posterior horn of the meniscus is easier to palpate with the patient prone. The posterior horn of the lateral meniscus is palpated posteromedial to the biceps femoris tendon, and the posterior horn of the medial meniscus can be palpated posterolateral to the semimembranosus tendon.

Meniscal Tests

McMurray test. The basic premise of the McMurray test is that meniscus tears are trapped during certain knee movements, with resultant pain and clunking. The test is easy to demonstrate but difficult to describe. It can be properly performed only if the patient has a reasonably full and relatively pain-free range of motion. The knee is flexed to 90°, and an external rotation and varus force are applied to the joint. The applied forces are maintained while the knee is flexed smoothly to a position of maximum flexion, and then the force is smoothly changed from a varus and external rotation force to an internal rotation and valgus force while the knee is extended from the fully flexed position. The process is then reversed and is usually repeated several times in smooth succession, until the examiner is satisfied that the entire range has been thoroughly assessed. It may be helpful to consider that the heel describes a large “U,” with the toes always pointing toward the center of the “U.” During the test, the fingers of the examiner’s free hand are placed along the medial and lateral joint lines to palpate any abnormal snapping or clicking that might be caused by meniscus pathology. A positive test is indicated by pain in association with a clunk, as the torn meniscus fragment is manipulated between the femur and tibia. It is possible to trap a meniscus fragment and cause the knee to lock completely. Although it is generally thought that the medial meniscus is assessed during the valgus and internal rotation position of the tibia, and the lateral meniscus during the opposite phase of the test, this is probably an oversimplification. The area of pain and clunking is more reliable in pointing out the location of pathology in conjunction with other signs and symptoms (Figure 6-37).

FIGURE 6-37 McMURRAY TEST.

Apley distraction and grinding (compression) tests. Joint-line tenderness can be associated with meniscus or collateral ligament injury. The concept behind the Apley test is that ligaments usually are painful when stressed in distraction, whereas pain involving the meniscus is felt with compression. With the patient in the prone position, the knee flexed 90°, and the femur stabilized with one hand, distraction is applied with the other hand by pulling upward on the ankle while rotating medially and laterally. A varus and valgus force may also be applied to further delineate whether the MCL or the LCL might be the source of pain (Apley distraction test). Once the distraction portion of the test has been completed, compression is applied to alternately grind the medial and lateral meniscus between the tibia and femur, with gentle varus and valgus force applied, while internally and externally rotating and compressing the ankle downward (Apley grinding or compression test; Figure 6-38).

FIGURE 6-38 APLEY TEST.

Duck walk test (Childress sign). The squatting position places great stress on the posterior horns of both menisci and is painful if the posterior horn is torn. The patient is asked to squat and “walk like a duck.” Pain in combination with a clunk suggests a posterior horn meniscus tear.

Flexion, Extension, and Rotation

Besides flexion and extension, the normal knee joint allows for internal and external rotation of the tibia on the femur, especially during knee flexion. Active and passive range-of-motion testing can be quickly screened by asking the patient to fully flex the knee and then extend it. The limits of motion are probed with further passive maneuvers after the maximal active range is established. Flexion and extension can be evaluated with the patient supine, prone, or standing, by asking the patient to squat. Any loss of full extension is abnormal. The range of flexion is somewhat variable, and the two sides should be compared. Lack of active full extension that can be corrected passively is usually caused by quadriceps weakness, loss of mechanical advantage, adhesion formation, effusion, or reflex inhibition. This is referred to as extension or quadriceps lag. Passive knee extension requires that the femur be stabilized on the examining table in the supine position, while the examiner attempts to lift the heel off the table. Although an extension lag can be passively corrected, it is not possible to correct a fixed knee-flexion deformity. Up to 5° of hyperextension at the knee is not uncommon. More than 10° of hyperextension is abnormal and suggests a cruciate ligament injury or a connective tissue disorder. Most patients are able to flex to the point of touching the heel to the buttock (approximately 135°).

Tibial rotation on the femur is best tested with the patient in the sitting position and the lower leg over the edge of the examining table. The patient is asked to internally rotate the lower leg and then to externally rotate it. Normally, approximately 30° internal rotation and 20° external rotation are possible. Passive manipulation is again used after the limit of active range has been observed (Figure 6-39). Normally, in full extension the tibia externally rotates on the femur into a stable position (the screw-home mechanism).

FIGURE 6-39 PASSIVE LATERAL AND MEDIAL ROTATION OF THE KNEE.

With the knee flexed 90°, any tibial torsion is noted. Normally, the forefoot points straight forward. With medial tibial torsion, the feet point toward each other (“pigeon-toed” foot deformity); this is often associated with genu varum. In excessive lateral tibial torsion, the feet point outward, and there is often a valgus deformity.