IMAGING IN PRACTICE MONICA KOPLAS, MD JEAN SCHILS, MD MURALI SUNDARAM, MD, MBBS Imaging Institute, Cleveland Clinic Head, Section of Emergency Radiology Section of Musculoskeletal Radiology, Imaging and Musculoskeletal Radiology, Imaging Institute, Cleveland Clinic, and Professor of Institute, Cleveland Clinic Radiology, Cleveland Clinic Lerner School of Medicine of Case Western Reserve University The painful knee: Choosing the right imaging test ■ ABSTRACT ADIOGRAPHY PLAYS A KEY ROLE in the ini- R tial evaluation of acute knee pain in The initial evaluation of acute knee pain should include adults. Yet conflicting studies and the absence plain radiography, which is a quick and cost-effective way of clear guidelines may leave the primary care to identify a wide range of problems, including fracture, physician uncertain as to which imaging test degenerative changes, osteochondral defects, and to order—ie, whether radiography is suffi- effusions. Computed tomography (CT) is the test of choice cient, and when computed tomography (CT) to better delineate fractures in patients who have knee or magnetic resonance imaging (MRI) is trauma. If the history and physical examination point to needed. This article reviews the indications damage of the cartilage, the menisci, and the cruciate for radiologic examination of the knee and and collateral ligaments and arthroscopy is contemplated, discusses indications for cross-sectional imag- ing studies. Imaging in oncology patients is then magnetic resonance imaging (MRI) is useful for not discussed here. evaluating these structures. ■ ACUTE KNEE PAIN: A TYPICAL SCENARIO ■ KEY POINTS In the emergency department, most patients undergo A 47-year-old woman presents to the emer- gency department with left knee pain after a plain radiography to assess for fracture, yet more than motor vehicle accident that occurred the day 90% of these studies do not show a fracture. before. The car she was driving hit a tree, and she hit her knee on the dashboard. She was CT is useful in patients with knee trauma but normal wearing a seatbelt at the time of the accident. radiographs. She says she was unable to walk immediately after the accident because of knee pain. MRI is the imaging modality for internal derangement of The initial examination in the emergency the knee. room reveals swelling and pain throughout the range of motion. The anterior drawer test and Ultrasonography’s role in the evaluation of acute knee the Lachman test are negative (see below). pain is generally limited to assessment of the extensor Initial radiographs (FIGURE 1) reveal no mechanism, joint effusion, and popliteal cyst. acute fracture or effusion, but focal ossifica- tion adjacent to the proximal medial femoral condyle may indicate a past injury to the medial collateral ligament. The patient is discharged home with a knee immobilizer, pain medication, and crutches, with instructions for a follow-up visit in the orthopedics clinic. Five days later, she returns to the emer- gency department complaining of continuing CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 75 • NUMBER 5 MAY 2008 377 Downloaded from www.ccjm.org on September 24, 2021. For personal use only. All other uses require permission. IMAGING IN PRACTICE KOPLAS AND COLLEAGUES Based on the physical examination and the patient’s complaints, she receives a diag- nosis of medial collateral ligament strain and injury. She is given a hinged brace and is instructed to undergo a physical rehabilitation program. Three weeks after the initial evaluation, she returns to the orthopedics clinic with con- tinuing knee problems. Mild knee effusion persists, but she has less pain and swelling, allowing a more complete examination. The examination reveals less limitation of range of motion and a hint of positivity on the Lachman test. The knee is diffusely tender, and the pain seems out of proportion with the maneuvers used during the examination. She requests more pain medication. You suspect internal derangement of the knee. Which imaging test should you order to further eval- uate this patient? ■ A SYSTEMATIC AND COST-EFFECTIVE APPROACH IS NEEDED The case presented above represents a typical scenario for the presentation of acute knee pain and illustrates the diagnostic challenges. Knee pain Knee pain is a common reason for emer- accounts for 1.9 gency room visits, and it accounts for approxi- mately 1.9 million visits to primary care clinics million visits to annually.1 In the emergency department, most primary care FIGURE 1. This anteroposterior radiograph patients undergo plain radiography to assess for clinics annually of a 47-year-old woman who was in a fracture, yet approximately 92% of radiograph- motor vehicle accident shows focal ic studies do not show a fracture.2 Clearly, the ossification adjacent to the medial femoral evaluation of knee pain requires a systematic, condyle (arrow) but no evidence of acute accurate, and cost-effective approach. fracture. Key elements of the physical examination knee pain. She says the knee gives way when In acute knee pain, accurate diagnosis begins she puts weight on it. The physical findings with a detailed history and physical examina- are unchanged, and she is discharged home tion. with a follow-up appointment with orthope- The anterior drawer test is done to eval- dics in 3 days. uate the anterior cruciate ligament. With the At the follow-up visit, she complains of relaxed knee flexed to approximately 80˚ and persistent knee pain in the medial aspect of the foot stabilized in a neutral position, the the knee joint. Physical examination is diffi- examiner grasps the proximal tibia in a firm cult because of pain and swelling, and it yet gentle grip, and then applies anterior force, reveals mild joint effusion with no gross insta- noting the degree of anterior displacement bility. She has pain on the medial side with compared with the other knee. valgus stress, but there appears to be a hard The Lachman test, a variation of the end point. There is no posterior sag, and the anterior drawer test, is more definitive for the Lachman test is negative. anterior cruciate ligament and is carried out 378 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 75 • NUMBER 5 MAY 2008 Downloaded from www.ccjm.org on September 24, 2021. For personal use only. All other uses require permission. with the knee in 15˚ of flexion and external concern is whether he or she has a fracture. rotation, in order to relax the iliotibial band. The Ottawa knee rules9 for when to order The upper hand grasps the distal thigh, and radiography in adults with knee pain are high- the lower hand, with the thumb on the tibial ly sensitive for detecting a clinically impor- tubercle, pulls the tibia forward. The degree of tant fracture. If any one of the five Ottawa cri- anterior motion in millimeters is noted and teria applies—ie, the patient is age 55 or older, compared with that on the other side, and the has tenderness at the head of the fibula, has end point is graded as “soft” or “hard.” An end patellar tenderness, is unable to flex the knee point is considered hard when a ligament to 90˚, or is unable to bear weight—then radi- abruptly halts the motion of the bone being ography is indicated. tested against the stabilized bone. An end While studies have validated the ability of point is considered soft when the ligament is the Ottawa rules to detect important fractures disrupted and the restraints are the more elas- in acute knee injury,2,10 fracture is the cause of tic secondary stabilizers. only a small percentage of knee complaints in the primary care setting. More common caus- Debate continues es include osteoarthritis, meniscal injury, liga- Some authors contend that in skilled hands a mental injury, and crystal arthropathy, and thorough history, physical examination, and these account for approximately half of all radiographic examination are sufficient to diag- diagnoses. Sprain and strain account for most nose trauma-related intra-articular knee disor- of the rest of knee injuries.1 ders.3 Others contend that MRI plays a key role in the initial evaluation. A number of stud- Acute exacerbations of osteoarthritis ies4–8 have shown that using MRI in the initial Osteoarthritis is a chronic problem, yet it is evaluation not only identifies key lesions, but not unusual for a patient to present to the pri- also may eliminate the need for an invasive mary care physician with an acute exacerba- diagnostic procedure (ie, arthroscopy). tion of joint pain. The clinical hallmarks For example, MRI can reveal fracture, include age over 50, stiffness lasting less than stress fracture, insufficiency fracture, and tran- 30 minutes, bony enlargement and tender- Osteoarthritis sient patellar dislocation—conditions that ness, and crepitus. The radiographic hall- is a chronic may satisfactorily explain knee symptoms. marks, according to the Kellgren-Lawrence grading scale, are joint space narrowing, problem, yet it ■ PLAIN RADIOGRAPHY STILL THE FIRST osteophytes, subchondral cysts, and sclerosis. often presents STEP IN KNEE EVALUATION These radiographic findings correlate well with clinical findings in these patients.11 as an acute Radiography is the first step in the evaluation exacerbation of knee pain. It is quick and inexpensive and Situations in which radiography of joint pain can yield many diagnostic clues. It can readily is less helpful reveal fractures, osteochondral defects, bony In some cases the radiographic findings may lesions, joint effusions, joint space narrowing, not explain the patient’s clinical signs and and bone misalignment. symptoms. For example, in suspected crys- In patients with knee trauma, supine talline and septic arthritis, the clinical presen- anteroposterior and cross-table lateral radi- tation may include warmth, erythema, and ographic images are generally obtained. In effusion. Arthrocentesis would be indicated in patients whose knee pain is not due to trauma, such a patient.