Evaluating Acutely Injured Patients for Internal Derangement of the Knee (2024)

Nearly one-half of adults will experience knee pain at some point in their lives.¹ Primary care physicians in the United States evaluate knee pain during approximately 4 million office visits each year, and knee symptoms are the 10th most common reason for outpatient visits.² Although most episodes of knee pain in primary care patients are caused by osteoarthritis, many patients have acute injuries. Approximately 9 to 10 percent of patients with acute knee pain who are treated by family physicians have meniscal tears, 7 percent have collateral ligament injury, and about 4 percent have a cruciate ligament injury ^2,3 (Figure 1⁴ ).

Because approximately one-third of patients with knee pain seek care from their primary care physician,¹ it is important to be aware of the signs and symptoms associated with internal derangement of the knee (i.e., fracture, ligamentous injury, or meniscal tear). The primary role of the family physician in early evaluation of knee injury is to identify patients in need of referral for possible surgical intervention. If internal derangement and other acute external knee injuries (e.g., patellar subluxation, patellar tendon rupture) can be ruled out, the patient can be reassured that symptoms will likely resolve with conservative treatment (i.e., rest, ice, compression, elevation, and pain control).

A 52-year-old woman presents to the emergency department for evaluation of knee pain that began after a car crash. Her right knee struck the dashboard during a head-on collision. She was not able to walk immediately after the crash. Examination reveals a large effusion. The patient is not able flex the knee to 90 degrees, and she cannot bear weight on the leg. Radiography reveals a depressed tibial plateau fracture.

It is essential to accurately diagnose knee fractures while simultaneously using resources judiciously. Knee radiography is the most common imaging modality performed for trauma in the emergency department setting, but it has the lowest yield for diagnosing clinically significant fractures.⁵

The Ottawa Knee Rule can guide appropriate use of radiography at the point of care based on easily obtainable clinical information⁶ (Table 1^5–7 ). It has been repeatedly validated^8–11 and decreases radiography utilization by 28 to 35 percent.^9,10 The rule is 98.5 to 100 percent sensitive (i.e., it will detect almost all patients with fracture), and it has a specificity of 49 percent.⁹ If the prevalence (pretest probability) of fracture is 11 percent in the emergency department setting, the likelihood of fracture in a patient with any of the Ottawa Knee Rule criteria is approximately 20 percent, whereas in those with none of the Ottawa criteria, fracture can be ruled out based on clinical findings alone (approximately 1 percent chance of fracture).⁹ In the outpatient primary care setting, where the prevalence of fracture is only 2 percent, the probability of fracture in patients with a negative Ottawa Knee Rule evaluation is extremely low.

The American College of Radiology has published recommendations for use of knee radiography in patients who have acute knee trauma.⁵ Although the recommendations have not been prospectively validated, they are similar to the Ottawa Knee Rule criteria. They recommend against radiography in patients (excluding infants) who can walk without a limp or who have a twisting injury and no effusion. The Pittsburgh Knee Rule criteria include blunt trauma or fall as the mechanism of injury, age younger than 12 years or older than 50 years, and inability to walk as independent predictors of fracture.⁷ A prospective validation trial comparing the Ottawa and Pittsburgh criteria showed that each rule is sensitive (97 to 100 percent of fractures found), but that the Pittsburgh rule is more specific (60 versus 27 percent for the Ottawa rule).¹²

An 18-year-old high school basketball player presents the morning after sustaining a left knee injury during a game. An opposing player fell while rebounding the ball, striking the anterior aspect of the patient's tibia and forcing the femur to slide posteriorly on the tibia. The patient reports that he heard a pop, and that the knee immediately became swollen. He was unable to bear weight after the injury and is not able to take four steps in your office. Knee radiography is negative for fracture. Anterior drawer and Lachman tests are positive; the patient cannot tolerate a pivot shift test. Arthrocentesis reveals a large hemarthrosis.

No systematic review has addressed the diagnostic accuracy of physical examination findings in patients with collateral ligament injuries.^3,13 Tenderness along the course of the ligament with reproduction of pain with valgus or varus force may be helpful. Visual inspection for differences in appearance between symptomatic and asymptomatic knees may also be revealing.

Historically, patients with ligamentous injury often have forceful stresses applied to the joint while bearing weight. They may hear or feel a popping sensation, and often note immediate swelling. Anterior cruciate ligament (ACL) injury accounts for more than 70 percent of acute hemarthroses in young athletes.¹⁴

The Lachman, anterior drawer, and pivot shift tests are common maneuvers used to examine the knee for internal derangement from ligamentous injury (Table 2^3,15,16 and Table 3^3,15–17 ). The acute swelling that can accompany injuries may make the initial physical examination difficult, so repeated examination may be necessary. The pivot shift test has a greater positive predictive value (i.e., a positive test is helpful for ruling in injury), whereas the Lachman test has a better negative predictive value (i.e., a negative test is helpful for ruling out injury).³

Magnetic resonance imaging (MRI) is highly accurate in diagnosing injury to the ACL and posterior cruciate ligament.¹⁸ It can be used when historical and physical examination findings are equivocal. Although the use of MRI has been advocated to confirm clinical suspicions before proceeding to arthroscopy,¹³ the American Academy of Orthopaedic Surgeons states that it is usually not required to diagnose an ACL tear.¹⁹ It has been suggested that MRI is better used to rule out internal derangement than to rule it in, because clinical findings are often sufficient for diagnosis.²⁰ Internal derangement is unlikely (less than 2 percent) and MRI typically unnecessary if physical examination maneuvers are negative.³

A 42-year-old man presents two days after injuring his right knee while playing tennis. He twisted his body with the right leg planted on the court surface. He felt a sharp pain and could not continue playing. He reports mild swelling and a sense of clicking in the medial knee with episodes of locking, which prevent full range of motion. Examination reveals medial joint line tenderness, a positive ballottement test, pain with full flexion of the knee, and positive McMurray and Thessaly tests.

Several systematic reviews have examined the diagnostic accuracy of physical examination maneuvers in patients with meniscal tears.^3,13,21–26 Although the individual studies have been of varying quality and have had inconsistent results, there is agreement that composite findings from the history and physical examination are more clinically helpful than any examination maneuver alone, and that a thorough examination can be nearly as accurate as magnetic resonance imaging^3,20 (Table 4¹³ ).

Family physicians must have proficient physical examination skills and must be able to assess how much each finding increases or decreases clinical suspicion of meniscal injury. Some patients will be unable to fully extend the knee, indicating a possible “bucket-handle” meniscal tear.¹³ Tenderness on the joint line is fairly sensitive (76 percent) for meniscal tear, but is not specific (29 percent).³ The positive and negative likelihood ratios for joint line tenderness are approximately 1.0, so this finding does not provide useful information. A positive McMurray test substantially increases the probability of a meniscal tear; this test has high specificity (97 percent) but low sensitivity (52 percent).³ The Thessaly test is a validated method to assess for meniscal injury and is a valuable tool in the physical examination of patients with an acutely injured knee^15,27 (Figure 2). It has been proven more accurate than the McMurray test or the finding of joint line tenderness.¹⁵

A combination of historical features and examination findings will help alert physicians to the possibility of meniscal tear more than the results of any one test.¹⁷ Features found to be most predictive of meniscal tear include age older than 40 years (odds ratio [OR] = 4.1), weight bearing during trauma (OR = 3.4), pain with passive flexion during examination (OR = 2.7), and inability to continue activity (OR = 2.2).¹⁷ The presence of all four of these features significantly increases the likelihood of meniscal tear; if the pretest probability of meniscal tear was 10 percent, the presence of all four factors increases that probability to 39 percent. The absence of all of these factors would decrease the probability to 1 percent.¹⁷

The presence of effusion is a predictor of internal derangement; 74 to 91 percent of patients with traumatic injury and effusion have internal derangement of the knee.^16,28 The combination of patients reporting swelling and having a positive ballottement test is helpful for detecting effusion (positive likelihood ratio = 3.6 when both are present; negative likelihood ratio = 0.4 when both are absent).¹⁶ Although ultrasonography is not routinely necessary for determining the presence of effusion, it can be diagnostic. Compared with MRI, ultrasonography may provide a more convenient, accessible, and cost-effective method of diagnosing effusion.²⁸