Tips from Other Journals

Previous | Next

Evaluating Patients with Acute Knee Pain: A Review

Knee pain is a common problem in adults, and acute knee pain often brings patients to the physician's office. Although plain knee radiographs are the most common test ordered, most radiographs are normal. Decisions about diagnostic testing in patients with acute knee pain and when to refer the patient to an orthopedist are often difficult. Jackson and associates reviewed the literature about the evaluation of acute knee pain to determine when diagnostic testing is necessary.

The authors attempted to answer the following questions about acute knee pain beginning less than one week before the clinical visit: (1) How useful are clinical decision rules in managing possible knee fractures? (2) How accurate is the physical examination in diagnosing cartilage and ligament injuries? (3) How sensitive and specific is magnetic resonance imaging (MRI) for cartilage and ligament injury? and (4) What is the utility of plain knee radio-graphs in patients with suspected osteo-arthritis and pseudogout? The literature search showed that osteoarthritis was the most common diagnosis in patients with acute knee pain, followed by meniscal injuries, collateral and cruciate ligamentous injuries, gout, and fracture. Strains and sprains also were commonly diagnosed. Rheumatoid arthritis, infectious arthritis, and pseudogout were rare.

Five articles reported on four decision rules that may be useful. The Ottawa knee rules of when to order a radiograph in adults with acute knee pain have excellent sensitivity and a specificity of 49 to 54 percent, and are the only decision rules that have been validated in repeated studies. Other decision rules-the Pittsburgh knee rules, Weber and colleagues' rule, and Fagan and Davies' rule-have not been as well validated. Even with plain radiography, some fractures will be missed, and follow-up is recommended in patients with acute knee pain.

Meniscal injuries often accompany twisting leg injuries that occur while full weight is on the foot. Swelling occurs after several hours, and walking up and down stairs becomes painful. Ligamentous injury, which results in almost immediate swelling, usually is caused by direct stress or a blow to the knee while weight is on that leg. The ligament involved varies depending on the direction of the stress. The history often is not as helpful as the physical examination in distinguishing meniscal from ligamentous injury.

Physical examination by a knowledgeable examiner can detect meniscal, anterior cruciate ligament, and posterior collateral ligament injury with reasonable accuracy. The Lachman maneuver is the most sensitive test for a ligamentous tear, but the pivot test appears to be more specific. A negative physical examination by a competent examiner makes the likelihood of these injuries very low. Positive test results indicate that follow-up MRI has a moderate sensitivity and specificity for meniscal, ligamentous, and cartilaginous injuries.

The authors conclude that the history is not useful in evaluating an acute knee injury except as an adjunct to the physical examination. The latter is specific and moderately sensitive. Patients with a negative examination can be followed carefully without further evaluation. If the examination is positive, referral to an orthopedist may be a better strategy than MRI because of the latter's relatively low specificity. A plain radiograph may be helpful when there is a high suspicion of osteoarthritis or fracture, but because clinical criteria probably perform better in the diagnosis of osteoarthritis, radiography should be reserved for suspected fractures. Plain films can reveal markers for pseudogout, but their sensitivity and specificity in patients with acute pain is low. An algorithm, when used by clinicians with excellent knee examination skills, may lead to the correct diagnosis most efficiently (see the accompanying table).

Algorithmic Approach to Acute Knee Pain Step Question Action 1 Has there been a recent injury and at least one of the following predictors of fracture? Age > 55 years Tenderness at head of fibula or isolated to the patella Inability to bear weight for at least four steps of walking Inability to flex knee >90 degrees Plain films 2 Is there effusion? Arthrocentesis (especially to rule out infectious or crystalline arthritis) 3 Does the physical examination suggest meniscal or ligamentous injury, or a history of locking or giving-way sensation? Orthopedic referral (for examination and decision on need for magnetic resonance imaging or arthroscopy) 4 Are there clinical criteria suggesting osteoarthritis? At least three of the following: History Age > 50 years Morning stiffness lasting > 30 minutes Physical examination Crepitus Bony enlargement No palpable warmth Symptomatic treatment, including: Analgesics (such as acetaminophen or nonsteroidal anti-inflammatory drugs) Exercise Plain films may be considered, although evidence for their utility is weak. 5 Is there evidence of a systemic rheumatologic disorder (such as rheumatoid arthritis, seronegative inflammatory arthropathy, or reactive arthropathy)? Polyarticular involvement, especially the hands Morning stiffness lasting > 30 minutes Serum rheumatologic assays Rheumatoid arthritis: rheumatoid factor Systemic lupus erythematosus: antinuclear antibody 6 Does the pain persist or remain undiagnosed despite symptomatic treatment and clinical follow-up? Rheumatology or orthopedic referral Reprinted with permission from Jackson JL, O'Malley PG, Kroenke K. Evaluation of acute knee pain in primary care. Ann Intern Med 2003;139:582.

richard sadovsky, m.d.

Jackson JL, et al. Evaluation of acute knee pain in primary care. Ann Intern Med October 7, 2003;139:575-88.

editor's note: Guidelines for the use of radiologic investigation in evaluating acute knee injury in all persons except infants also have been compiled by the American College of Radiology.1 These guidelines review indications for radiologic evaluation in a variety of circumstances. Radiographic studies are not indicated for patients who fall, have no focal tenderness or effusion, and are able to walk. If focal tenderness, effusion, or inability to bear weight is noted, the first study should be plain films. For patients who have had significant trauma or in whom posterior knee dislocation is suspected, plain films and angiography/ magnetic resonance arthrography/Doppler studies are considered most appropriate. Soft tissue injuries are best evaluated by magnetic resonance imaging or single-photon emission computed tomography.-r.s.

REFERENCE

1. American College of Radiology (ACR) appropriateness criteria. Acute trauma to the knee. Accessed March 10, 2004 at: http://www.acr.org/cgi-bin/fr?tmpl:appcrit,pdf:0365-374_acute_trauma_to_ knee_ac.pdf.

Previous | Next