Charles B. Eaton
Knee pain is a very common condition, ranking number seven in the National Ambulatory Care survey. It has been suggested that 90% of knee pain in patients can be diagnosed after an appropriate history and knee examination.
Key clinical questions include: What is the possibility of internal derangement or fracture? Does this patient need an imaging study? Are the history, physical examination, and time spent with the patient sufficient to make the most cost-effective diagnosis and treatment plan? Does this patient need specialist referral?
A. Causes of knee pain. Dividing the onset of knee pain according to the time course of symptoms (acute—minutes to hours; subacute—hours to days; or intermittent and chronic—weeks to months) helps to differentiate the common causes of knee pain. (Table 12.4). In addition, referred knee pain can develop from hip or back problems.
A. Age and etiology. The patient’s age is an important factor in determining the likelihood of certain knee problems. Because of stronger ligaments, avulsion fracture (anterior intercondylar eminence of the tibia, tibia tubercle) is more common in younger age groups, whereas ligamentous rupture occurs in older persons. Patellar dislocations and apophysitis are more likely in growing adolescents.
B. Trauma. Understanding the mechanism of injury and estimating the acceleration or deceleration and torsional forces across the knee joint, predict the likelihood of occult fractures and internal derangement. Patients describing a popping sensation during a rotational or twisting injury, followed by an immediate swelling, usually have internal derangement of either meniscal or ligamentous components, or both. Locking of the knee suggests a “bucklehandle” meniscal tear obstructing normal hingejoint activity of the femoraltibial joint.
C. Alleviating or exacerbating factors. Patellofemoral syndrome (PFS) or chrondromalacia patella is associated with anterior knee pain that worsens going up or down stairs or with prolonged sitting. Morning stiffness that improves with mild activity, but worsens as the day progresses, is typical of degenerative arthritis (osteoarthritis). The stiffness of rheumatoid arthritis (RA) generally does not improve with activity. Patients with multiple joint pains should be questioned about fever or skin rash to rule out infectious or inflammatory joint disease.
Both knees, as well as the hip, ankle, and foot on the affected side, should be examined. The knees are inspected for symmetry, signs of quadriceps or calf wasting, and any obvious swellings, discoloration, or pallor. Thigh, knee, calf circumference, and leg length are measured to document any asymmetry. Measurement of the quadriceps or Q angle (normal <15°) is important to evaluate anterior knee pain. Inability to perform full knee flexion and extension will highlight any effusion. Neurovascular supply should also be evaluated.
In nonacute circumstances, the suprapatellar bursa is milked to determine if effusion is present. The patellar apprehension test may detect patellar dislocation; the patellar grind test is used to detect PFS. Evaluation of patellofemoral tracking within the femoral groove also helps make the latter diagnosis as the patella will track laterally in PFS, leading to the characteristic “jockey cap” patella. The knee should be carefully palpated for tenderness of the patellotibial insertion (Osgood-Schlatter’s disease), the body of the infrapatellar tendon (tendinitis), the insertion of the tendon on the patella (Sinding-Larsen-Johannson disease), medial and lateral joint line (potential meniscal pathology), pes anserine bursa (bursitis), or iliotibial band insertion. Plica, a painful, thickened band of exuberant synovium, can also be diagnosed by palpitation of the medial and lateral joint lines.
Ligamentous testing is done next. Test the posterior cruciate ligament through the posterior drawer sign. Use the Lachman test for the anterior cruciate ligament, or, in obese patients, the anterior drawer sign. The medial collateral ligament is tested in zero and 15° of flexion by applying a valgus stress to the knee. The lateral collateral ligament is tested similarly using a varus stress. McMurray’s test may detect a meniscal tear. A duck walk test can also be used to look for a posterior meniscal tear. The patient’s gait is observed, specifically looking for forefoot varus and heel valgus, Morton’s foot deformity, and femoral anteversion, all of which can accentuate valgus stress on the knee and lead to a painful overuse syndrome.
Most diagnoses can be made without an x-ray study or expensive diagnostic test.
A. Ottawa rules. For acute injuries, the Ottawa knee rules are highly sensitive, but less specific, in determining the need for a plain knee x-ray study in adults (1). This decision rule has not been tested in children. The Ottawa rules recommend an x-ray study if any of the following are found: age 55 years or older, tenderness at the head of the fibula, isolated patellar tenderness, inability to flex the knee to 90°, or inability to bear weight immediately after the trauma (1).
B. Radiographs and procedures. Testing depends on the diagnosis suspected, medicolegal requirements, and response to therapy. Knee films are important when surgical treatment of degenerative arthritis is considered, or if chondrocalcinosis, gout, RA, osteomyelitis, or osteochondritis dissecans should be ruled out. Magnetic resonance imaging (MRI) of the knee is a sensitive and specific test for detecting meniscal or ligament injury; however, it is no better than a consistent history, a positive McMurray’s or Lachman’s test, and medial joint line tenderness (2). MRI is indicated when a patient has a good history for internal derangement and a normal clinical examination, or fails to improve despite adequate conservative therapy. A bone scan is warranted when a stress fracture or cancer is suspected. Computed tomography may define bony pathology and, with arthrography, detect meniscal and ligamentous pathology when an MRI is contraindicated. Duplex ultrasound will rule out a deep venous thrombosis or detect a Baker’s cyst. Arthrocentesis can be used to diagnose gout, pseudogout, or septic arthritis, and to relieve pain and allow corticosteroid instillation. Arthroscopy is helpful when internal derangement is suspected and the probability of arthroscopic treatment is high.
Clinical information may trigger further immediate diagnostic workup. Hemarthrosis could indicate internal derangement or fracture. Knee pain and a limp in a child with a normal knee examination suggests hip disease (Legg-Calvé-Perthes, slipped femoral capital epiphysis). Bony swelling and night pain suggest tumor; fever and joint swelling, infectious or inflammatory arthritis. A knee effusion with rash suggests gonorrhea, Reiter’s syndrome, or collagen vascular disease.
Of nontraumatic anterior knee pain, 70% is related to patellofemoral syndrome. Meniscal tears can develop in older patients without a trauma history. Knee pain in a growing adolescent is jumper’s knee (patellar tendinitis) or traction apophysitis until proved otherwise.
References
1. Steil IG. Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med 1995;26:405–413.
2. Gelb HJ, Glasgow SG, Sapega AA, Torg JS. Magnetic resonance imaging of knee disorders. Clinical value and cost-effectiveness in a sports medicine practice. Am J Sports Med 1996;24:99–103.
Read excerpts from these other book chapters related to Knee pain:
Copyright Details: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter, Copyright © 2008 Williams & Wilkins.
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More About This Book:
Title: The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter Authors: Robert B. Taylor (editor) Publisher: Lippincott Williams & Wilkins Copyright: 2000 ISBN: 0-78172-094-X 
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