Knee Problems: Preliminary Examination of Injured or Arthritic Patients

ABSTRACT: Ascertain specifics of the patient’s knee pain, including its location, mechanical components (instability, locking, effusion, and catching), circumstances of onset, severity, and association with sports. Observe the patient’s gait, degree of discomfort while walking on the affected leg, and linear and rotational alignment of both legs. Check for hip and spinal problems that might refer pain to the knee. Only then begin a focused examination of the knee. The ballottement test and loss of the normal concavity distal and medial to the patella confirm the presence of effusion. Atrophy of the vastus medialis muscle results in problems with patellofemoral stabilization.

Key words: knee, pain, physical examination

The knee is the largest joint in the body. It is also one of those most commonly injured, because it is relatively unprotected by layers of fat or muscle and thus is vulnerable to direct trauma. Moreover, as a modified hinge joint at the end of two long levers, it is subjected to maximal stresses, predisposing it to indirect trauma.¹

Because painful or dysfunctional knees are so common, it is well worthwhile for all primary care physicians to hone their skills in knee examination. Fortunately, you can easily palpate its anterior, medial, and lateral aspects, and abnormal motions and instabilities are readily detectable.

In this article on examining the injured or arthritic knee, we will review its anatomy and explain the interrelation of the normal structure and injury. We will describe details to be obtained from the patient’s history and will conclude with the initial observations from physical
examination.

CLINICAL ANATOMY

The tibiofemoral joint consists of the round distal femoral condyles articulating on the relatively flat tibial plateaus. Each load-bearing surface is covered by articular cartilage on top of thick subchondral bone and is vulnerable to direct trauma and ischemic events. Such trauma can lead to osteochondral fractures that may not be detectable on plain
radiographs.

Osteochondral fracture usually leads to hemarthrosis; aspiration shows the presence of fat globules, which confirms the diagnosis. These fractures often result in loose bodies that may cause mechanical symptoms, or they may become trapped in the synovium and therefore be asymptomatic, despite radiographic visibility.

The subchondral bone may also undergo avascular necrosis, with subsequent loose body formation. This condition is known as osteochondritis dissecans in teenagers and young adults (Figure 1), and it has a more favorable prognosis than the osteonecrosis that occurs in older patients.

Figure 1 – The radiographs show an osteochondral defect in the lateral aspect of the medial femoral condyle with intra-articular loose bodies(A and B). MRI of the knee reveals an unstable, stage 4 osteochondral defect that involves the distal medial femoral condyle with at least 3 intra-articular loose bodies (C). Osteochondritis dissecans was diagnosed in this patient, a 16-year-old boy who had presented with recurrent right knee pain.
(Courtesy of Roli Agrawal, MD and Sarah Kizilbash, MD.)

The two C-shaped menisci, located on either joint line, significantly increase the contact area between the two bones. The medial meniscus is firmly attached to the joint capsule and therefore is more susceptible to injury than the mobile lateral meniscus. Meniscal tears are a relatively common problem, leading to joint-line pain and tenderness, effusion, locking, catching, and instability. Symptoms are often exacerbated by squatting or twisting.

The knee is supported by a thick joint capsule, four major ligaments, and the structures of the posterolateral corner. The centrally located anterior and posterior cruciate ligaments (ACL and PCL) are not palpable. Injury to these ligaments is suggested by a history of severe trauma accompanied by acute hemarthrosis, symptoms of instability, and positive results of provocative tests for instability. Even in the absence of demonstrable clinical laxity, 72% of knee injuries associated with acute hemarthrosis and normal-appearing radiographs prove to be ACL tears.^2,3

The medial collateral ligament (MCL) is composed of two structures: the superficial MCL (tibial collateral ligament), which plays the primary role in preventing valgus instability, and the deep MCL (part of the medial joint capsule). The origin of the superficial MCL is at the medial femoral epicondyle, and it inserts distally at the proximal medial tibial metaphyseal flare. The deep MCL arises from the medial epicondyle and inserts onto the medial meniscus.

The fibular collateral ligament (FCL) originates from the lateral femoral epicondyle and inserts onto the fibular head. It resists varus stress to the knee and acts in conjunction with the posterolateral corner (the popliteus tendon complex and arcuate ligament) in resisting posterolateral rotational instability. Because both the MCL and FCL are subcutaneous, they are easily palpated.

Patellofemoral pressures of up to seven times body weight occur during normal daily activities. Consequently, this articulation is a significant source of injury. The retropatellar surface consists of the medial and lateral facets. The extensor mechanism fans out on either side of the patella to form medial and lateral retinacula, which continue posteriorly to merge into the soft tissue layers of the knee.

These retinacula provide static medial and lateral support to the patella to keep it centered in the trochlear groove of the distal femur. Tears or excessive tightness of the retinaculum can predispose susceptible persons to patellofemoral disorders.

The patellofemoral articulation also has a number of dynamic stabilizers (the vastus medialis obliquus and vastus lateralis muscles and the iliotibial band) that contribute to normal patellofemoral function. The extensor mechanism inserts into the tibial tubercle, which is easily palpable on the anterior surface of the proximal tibia.

OBTAINING AN OPTIMAL HISTORY

Characterizing pain. The patient’s chief complaint usually is pain. Start by defining this symptom.

Location. First, ask for the location of the pain. Should the patient respond by placing a hand over the entire anterior surface of the knee, suspect a patellofemoral problem. A finger pointing to the medial or lateral joint line commonly indicates meniscal tears, whereas pain along the course of the MCL or the LCL may represent injury to these structures.

Posterior pain may represent posterior capsular stretching caused by forced posterior tibial translation or hyperextension, popliteal tendinitis, or hamstring tendinitis; or this pain may be referred from the patellofemoral joint. Poorly localized pain may occur with severe injuries (eg, to the ACL or PCL), leading to effusion.

Association with activity. Determine whether the pain is activity-related, and find out what specific activities exacerbate it. Patellofemoral pain is often accentuated by prolonged sitting with bent knees, as in a bus or movie theater (the “theater” sign); on rising from a chair; while descending stairs (due to eccentric loading of the extensor mechanism); or while squatting (which can also exacerbate meniscal symptoms). Pain that increases while the patient ascends stairs is less specific and can result from various pathologic conditions of the knee.

Association with time of day. Knee pain that is worse in the morning and improves with activity may be related to inflammatory disease, such as rheumatoid arthritis or arthritis associated with seronegative spondyloarthropathy. Severe, unrelenting pain suggests infection. Pain that is relatively dormant during the day but awakens the patient during the night should cause you to suspect malignancy. Note, however, that malignancy can also present with activity-related pain.

Mechanical complaints. Always query patients about mechanical symptoms (instability, locking, catching, and effusions).

Instability. The differential diagnosis of instability includes ligament injury, meniscal tears, loose bodies, and extensor mechanism failure. Virtually anything that causes knee pain can lead to reflex inhibition of the quadriceps mechanism, with subsequent knee instability due to muscle dysfunction or weakness. Therefore, note whether pain precedes the instability or whether the knee just “gives way without warning.” The history is far more specific for a mechanical problem if instability is not preceded by pain.

Locking. When the history is of extension block following acute injury, the cause is usually a meniscal tear—although it can also be caused by a tense effusion, an osteochondral fragment, another loose body, or an ACL tear. The history is more specific for meniscal injury if the extension block can be resolved by a reduction maneuver (such as twisting or manipulation of the knee). True locking, when the knee can be neither extended nor flexed, is usually caused by a tear of the posterior horn of the lateral meniscus. Chronic blocking of full knee extension may be caused by intercondylar notch stenosis in association with osteoarthritis.

Catching. This is a nonspecific symptom. It may be related to chondromalacia patellae (the breakdown of articular cartilage), a loose flap of articular cartilage, a meniscal tear, a plica, or a loose body.

Effusions. These should be characterized by frequency and relation to activity. Activity-related effusions may be due to chondromalacia, a loose meniscal fragment, or other mechanical problems (eg, a pathologic synovial plica). Effusions that are not related to activity may be caused by inflammatory conditions.

Direct versus indirect injury. If the patient experienced an acute injury, determine whether the mechanism was direct (eg, a blow to the tibial tubercle or patella) or indirect (eg, a twisting motion). Indirect trauma more commonly leads to ligament or meniscal injuries, whereas direct trauma causes contusions, patellofemoral cartilage injury, or posterior cruciate ligament injuries (from a blow to, or a fall onto, the tibial tubercle).

Severity. In a sports-related injury, was the patient able to continue playing or forced from the game? Was the leg able to bear weight? Did an effusion occur? An acute effusion within an hour or two of injury indicates a hemarthrosis, which may be caused by an ACL injury, an osteochondral fracture, a peripheral meniscal tear, or a patellofemoral dislocation.

PCL tears may cause a hemarthrosis or may be associated with such extensive capsular tearing that the hemarthrosis extravasates. Thus, such tears may or may not lead to an effusion.⁴ A delayed effusion (occurring more than 12 hours after injury) indicates a synovial effusion, which may be due to a meniscal tear in its avascular central region, a mild patellofemoral subluxation, or a sympathetic effusion caused by periarticular trauma.

History of knee injury or other problems. This information helps determine the condition of the knee at the time of the current injury and also alerts you to the likelihood of ongoing muscle weakness. A classic scenario is the patient with a chronic ACL tear who suffers
a meniscal tear following an episode of instability.

If the patient has had no acute injury, look for a history of overuse or training error. Was there a recent increase in activity (eg, escalated running mileage, attendance at a football camp)? Was there a change in the normal routine? For example, running on hills or on a curved track may lead to a functional leg-length discrepancy and possibly predispose the patient to iliotibial band friction syndrome.⁵ Or has this patient been engaging in bursts of intense activity without proper conditioning (the infamous “weekend warrior” syndrome)?

Onset of pain. Did the pain start insidiously (eg, osteoarthritis), or was the onset acute? Older patients with osteonecrosis often can remember the exact moment the pain began.

After you have taken a thorough history, you should be able to start formulating a differential diagnosis to guide the physical examination.

INITIAL OBSERVATION

Gait. The physical examination starts as soon as the patient enters the room. Observe the gait, which should be smooth, symmetric, and painless. An uninjured person should neither limp nor experience discomfort. The knee should extend fully at midstance. If a flexion contracture is detectable by visual observation, it is usually greater than 15 degrees. Lesser degrees of flexion contracture are difficult to observe without formal measurement.

Loss of extension. This may be due to swelling or mechanical blockage, including osteoarthritis. Reluctance to extend the knee fully during stance, always keeping it in 15 to 20 degrees of flexion, occurs in association with posterolateral rotational instability. In knees with this instability pattern, extension causes the joint to give way.⁶

Medial or lateral thrust. This sideways motion of the knee during the stance phase of gait usually indicates skeletal erosion due to arthritis, with ligamentous laxity of the opposite side of the knee. For example, medial compartment erosion due to arthritis coupled with lateral ligamentous laxity leads to a lateral thrust.

Ability to bear weight and degree of pain elicited by walking. If the examination follows an acute injury, these factors give an indication of its severity. Inability to bear unilateral weight while walking or hopping suggests a major problem. Often, the most reliable physical examination is immediately after the injury, before swelling and inflammation cause the patient discomfort, leading to apprehension, guarding, muscle spasm, and difficulty in assessment.

If a thorough examination is prevented by these effects, immobilize the patient’s knee for a day or two. This will often decrease the pain and inflammation, enabling you to do a better examination. Alternatively, aspirate any effusion and inject a local anesthetic into the joint to relieve the pain.

Linear and rotational alignment. Observation of the alignment of the entire leg can reveal much, but too often it is rushed through in pursuit of the more involved tests. Have the patient standing, disrobed from the waist down except for undergarments.

The knee is usually in slight (6 to 8 degrees) valgus (internal rotation). Excess genu valgum (knock knee) may be associated with generalized ligamentous hyperlaxity or patellofemoral disorders. Genu varum (bowleg) can result from, or contribute to, degenerative knee conditions.

Inspect the feet, looking for pes planus (flatfoot) that may contribute to genu valgum and its related problems. Excess femoral anteversion may cause the patellas to rotate inward; yet, because of compensatory external tibial torsion, the feet may still point straight ahead. This combination of compensatory rotational mal-alignments predisposes to development of patellofemoral problems, especially if the knee is also in valgus (the so-called miserable malalignment syndrome).

Baker’s cyst. This swelling behind the knee is often most visible and most easily palpated when the patient is standing with the knee extended. Among children, a Baker’s cyst may occur and resolve spontaneously (Figure 2). In adults, however, it is usually associated with an intra-articular effusion that is often caused by meniscal injury.

Spine and hip. Check these before becoming focused on the knee. Hip pain is often referred to the knee, as are radicular symptoms. More than once, knee arthroscopy has been performed, with normal findings, before the patient received the appropriate diagnosis of slipped capital femoral epiphysis (in adolescents) or osteoarthritis of the hip (in adults).

Suspect hip injury if the patient’s pain is reproduced by hip rotation, especially forced internal rotation. If symptoms are reproduced by straight leg raising or reversed prone straight leg raising, look for a radicular source of the pain.

Leg length. Should your patient be a long-distance runner with lateral knee pain, you might measure the leg length. Despite controversy in the orthopedic literature, some investigators have found that increased leg-length discrepancy predisposes to iliotibial band friction syndrome in the shorter leg. This syndrome may also be associated with increased forefoot varus and an increased Q angle.⁵

Figure 2 – A 17-year-old boy presented with a fluctuant, cystic mass on the posterior aspect of the left knee. Popliteal cyst (also known as Baker cyst) was diagnosed after clinical examination of the mass. (Courtesy of Alexander K. C. Leung, MD.)

KNEE EXAMINATION

Once you have checked the patient’s gait, standing alignment, and other possible sources of disease, begin a focused examination of the knee. Examine the contralateral leg first, for two reasons: first, to gain the patient’s confidence (this may cause relaxation, thus simplifying your examination of the injured knee) and second, to have a comparison for the focused exam.

Always ask for a history of injury to the contralateral knee. Do not automatically assume that it is free from trauma.

Perform most of the knee examination with the patient sitting or supine on the examining table. Again, observation is the first step. Look for effusion, atrophy, ecchymosis, or any obvious deformity. The presence of the last two help point you toward the area of injury.

Ecchymosis may be misleading, however, because the direct trauma to the bruised area may have resulted in indirect trauma and ligament injury to other areas of the knee. Thus, look for concomitant injury to other, less obvious damaged areas of the leg.

Effusion. If your practice encompasses sports medicine, you should be able to pick up subtle effusions. When a patient’s knee symptoms have been of long duration, examination results are often relatively normal. A small effusion may be the only sign to warn of internal derangement. The red flag presented by subtle effusion is important in heightening your index of suspicion for the remainder of the examination, because any effusion—no matter how small—is abnormal.

If the patient’s knee is not too obese, a small effusion is best recognized by loss of the normal concavity just distal and medial to the patella, at the level of the joint line.⁷ Compare this area with that of the opposite leg, because some persons have less concavity than others. By milking the effusion distally from the suprapatellar pouch, you may increase the sensitivity of this observation.

The ballottement test is also very useful for detecting the presence of effusion. As above, milk any fluid in the suprapatellar pouch distally, under the patella; then compress the patella against the distal femur. If the patella rebounds off the femur, this is consistent with an effusion.¹

Subsequent to acute trauma, a large effusion with palpably increased warmth suggests hemarthrosis rather than effusion of synovial fluid. The effusion of hemarthrosis is also firmer to the touch. When palpated, the swelling of synovial effusion should feel smooth and may exhibit a fluid wave. Synovial thickening, which is usually lumpy and more rubbery, does not exhibit a fluid wave. Combinations of hemarthrosis and synovial fibrosis may be more difficult to define and may require confirmation by aspiration.

Localized collections of fluid may also occur extra-articularly, because the collateral ligaments are extrasynovial. When they are injured, swelling may develop outside the knee joint. Fluid may also collect in the prepatellar bursa, pes anserine bursa, superficial and deep infrapatellar bursas, and the bursa over the MCL. Do not confuse these extra-articular fluid collections with an intra-articular effusion.

Atrophy. The distal end of the vastus medialis obliquus muscle (an important dynamic patellofemoral stabilizer) should be more distal than the distal end of the vastus lateralis. If this relationship is reversed, the vastus medialis has atrophied and may be contributing to problems referable to this articulation. Compare both legs for symmetry, and confirm your findings by measuring the circumference of the leg 15 cm above the superior patellar pole of the extended knee. This distance is proximal to the suprapatellar pouch, and thus you avoid falsely enlarged measurements due to effusion or synovitis. A 1.25-cm (0.5-inch) difference is significant.n

REFERENCES:

1. Hoppenfeld S. Physical Examination of the Spine and Extremities. Norwalk, Conn: Appleton-Century-Crofts; 1976.

2. DeHaven KE. Diagnosis of acute knee injuries with hemarthrosis. Am J Sports Med. 1980;8:9-14.

3. Noyes FR, Bassett RW, Grood ES, Butler DL. Arthroscopy in acute traumatic hemarthrosis of the knee. J Bone Joint Surg. 1980;62:687-695.

4. Hughston JC, Andrews JR, Cross MJ, Moschi A. Classification of knee ligament instabilities: the
medial compartment and cruciate ligaments. J Bone Joint Surg (Am). 1976;58:159-172.

5. Schwellnus MP. Lower limb biomechanics in runners with the iliotibial band friction syndrome. Med Sci Sports Exerc. 1993;25(suppl):S68.

6. Hughston JC, Norwood LA. The posterolateral drawer test and external rotational recurvatum test for posterolateral rotatory instability of the knee. Clin Orthop. 1980;147:82-87.

7. Hughston JC, Walsh WM, Puddu G. Patellar Subluxation and Dislocation. Philadelphia: WB Saunders Co; 1984.