Knee Pain

Clinical appearance

Knee pain may be intrinsic or it may radiate from a proximal structure such as the hip or the lumbar plexus. If knee motion is free and painless while the patient is lying on the contralateral side, knee disease can be safely ruled out. While in the same position, if hip hyperextension, but not rotation or flexion, reproduces the pain, the source of the pain may be in the lumbar plexus or the femoral nerve. However, if all 4 motions reproduce the "knee pain," the source of pain is the hip. Intrinsic knee pain may affect the front, the medial side, the lateral side, or the posterior aspect of the joint (Table 13). Knee examination should include inspection, range of passive motion, patellofemoral function, stressing of the medial and lateral compartments, and an assessment of joint stability. Inspection may reveal swelling at the suprapatellar pouch and parapatellar gutters indicative of a synovial effusion, prepatellar swelling from prepatellar bursitis, and patellar tendon region swelling caused by pretendinous bursitis, tendon inflammation, fat pad hyperplasia/inflammation (Hoffa's disease), or infrapatellar bursitis. Swelling at the medial or lateral articular lines usually represents a meniscal cyst. A bulge in the popliteal fossa may be caused by a Baker's cyst (Figure 5) should be excluded.

Palpation is used to confirm or refute the above findings, because fat and synovial proliferation can cause bulges around the knee joint. Identification of focal tenderness may be critical for diagnosis. Classic findings include tenderness at the medial or lateral articular lines in meniscal disease; patellar or tibial insertion of the patellar tendon in calcific enthesopathy and patellar tendon enthesitis, respectively; tibial insertion of the pes anserinus in the anserine bursitis syndrome; and lateral femoral condyle in patients with the iliotibial band syndrome. Valgus and varus stress while flexing and extending the joint will identify unicompartmental abnormalities, such as lateral and medial meniscal lesions. The Lachman test, which can be described as a drawer sign elicited by pulling forward the upper tibia with the knee flexed 20 degrees, is positive in anterior cruciate ligament tears.

Differential diagnosis

Anterior pain.

Pain in the anterior knee (29) may be caused by one or more of the lesions listed in Table 13. The "shrug sign" is particularly useful in the diagnosis of patellofemoral syndrome (chondromalacia patella). To perform this test the supine patient is asked to relax the quadriceps. The patella, firmly held between the observer's index and thumb, is displaced distally and kept in a firm posterior contact. The patient is then asked to contract the quadriceps, and a positive test result is the occurrence of pain, often excruciating, as the roughened patella slides proximally against the roughened femoral condyle. A tender, inflamed medial plica (a vestigial synovial fold that has become swollen by inflammation and fibrosis) will jump under the examining finger in a medial parapatellar location during flexion and extension movements of the joint. Prepatellar bursitis is evident as a tender, soft tissue lump in front of the patella. Conditions affecting the quadriceps-tendon-patella-patellar ligament-tibia unit result in pain on resisted extension and display tenderness over the patella or at the tibial insertion of the patellar ligament. By actively elevating the straight leg, one can distinguish pretendinous bursitis, which still bulges, from deep infrapatellar bursitis, which tends to get buried under the taut ligament. Osgood-Schlatter's disease in pediatric cases results in a tender, hard lump at the tibial tuberosity. Successful treatment of anterior knee pain requires consideration of these potential causes.

Medial pain.

Pain over the medial aspect of the knee is usually caused by a meniscal tear in a younger patient and medial compartment osteoarthritis in patients past the age of 50 years. However, there are other considerations. Anserine bursitis (not truly a bursitis in most instances) hurts on pressure 3-5 cm distal to the medial articular line (30). Medial collateral ligament bursitis, which overlaps the articular line, hurts more on pressure in flexion when the bursa is exposed than in extension when the sac gets covered by the medial collateral ligament. Meniscal cysts characteristically soften and may become undetectable in full flexion and full extension, while they are hard and prominent when the knee is flexed 30-40 degrees.

Lateral pain.

Pain in the lateral knee is seen in the iliotibial band syndrome (31), a condition that results from the excessive friction of a tight iliotibial band on the lateral femoral condyle. Patients with this syndrome report lateral knee pain while running, going up or downstairs, and bicycling. On examination with the knee in semiflexion, a tender spot is found on the lateral femoral condyle anterior to the band. Tenderness decreases or disappears when the knee is fully extended. Other conditions affecting the lateral knee include meniscal tears and cysts, as well as the biceps femoris tenosynovitis in which there is tenderness in the posterolateral corner of the joint.

Posterior pain.

Pain in the posterior knee may be caused by popliteal (Baker's) cysts, various lesions affecting the popliteal artery, venous thrombosis, hematomas, ganglia, and soft tissue tumors including sarcomas (32). Foucher's maneuver is very useful in distinguishing popliteal cysts from other mass lesions. When the knee is flexed 30-40 degrees, Baker's cysts become soft or undetectable (a positive Foucher's sign) while other popliteal masses remain unchanged (33). Echography, with Doppler, is particularly helpful in the analysis of posterior knee pain. Venous disease, popliteal artery aneurysms, solid tumors, and ganglia can be reliably identified by this method.

Treatment

Painful knee conditions lead to quadriceps weakness, and quadriceps weakness alters patellar biomechanics and results in further pain. Thus, in addition to specific measures for the diagnosed condition, all patients with a painful knee should be instructed on isometric quadriceps exercises. The use of a cane on the opposite side helps relieve pain and provides stability and safety while the condition improves. Depending on the cause of the pain, local or systemic analgesics or NSAIDs may be used. Both warm packs and cold compresses are analgesic, the effect varying with the individual patient. Prepatellar bursitis is treated in a similar fashion as olecranon bursitis, although it is generally more problematic. Septic cases often require hospitalization, catheter or surgical drainage, and parenteral antibiotics for a few days until the process is controlled. At this point, oral antibiotics may be started and continued to complete 2-3 weeks of therapy.

In some of the regional syndromes, one or more corticosteroid infiltrations will eventually be required. Anserine bursitis, medial collateral ligament bursitis, and the iliotibial band syndrome respond particularly well to corticosteroid infiltrations. Technical aspects of this procedure are discussed in the accompanying article. On the other hand, the medial plica syndrome, tight lateral retinaculum, and meniscal pathology including ruptured menisci and meniscal cysts are amenable to arthroscopic surgery. Baker's cysts almost always reflect intraarticular pathology that results in excess synovial fluid production and distention of a pre-existent communicating gastrocnemius-semimembranous bursa. They are best treated by addressing the knee problem that causes the bursal distention. Provided that infection has been ruled out, knee drainage followed by intraarticular corticosteroids is an effective method to reduce a symptomatic Baker's cyst and avert the risk of rupture. Long-term treatment is aimed at the underlying knee process.

Role of the primary care physician

Primary care physicians should be able to diagnose and treat anserine bursitis, patellofemoral syndrome, and prepatellar bursitis. Other causes of knee pain may require referral to a rheumatologist or orthopedist. Primary care providers should educate patients about the importance of the correct technique of quadriceps strengthening exercises. A well-integrated program of analgesics, anti-inflammatory drugs (including corticosteroid infiltrations), and physical therapy, including a cane when needed, provides interim comfort to patients with knee pain.

Key issues

Many of the knee conditions are within the field of primary care medicine, including anserine bursitis, prepatellar bursitis, patellofemoral syndrome, and early tibiofemoral osteoarthritis. Primary care physicians should learn to identify and treat patients with these conditions and refer others to the appropriate specialists.