MKSAP Quiz: 5-year history of knee pain
A 67-year-old man is evaluated for a 5-year history of right knee pain, with morning stiffness lasting 20 minutes. Following a physical exam, what is the most appropriate initial imaging study?
A 67-year-old man is evaluated for a 5-year history of right knee pain, with morning stiffness lasting 20 minutes.
On physical examination, vital signs are normal. Limitation of flexion and extension of the right knee is noted, with bony enlargement and tenderness to palpation along the medial and lateral joint lines. Crepitus is noted upon range of motion of the right knee. Bony enlargement of a few proximal interphalangeal and distal interphalangeal joints on both hands is present.
Which of the following is the most appropriate initial imaging study?
A. CT
B. MRI
C. Radiography
D. Ultrasonography
MKSAP Answer and Critique
The correct answer is C. Radiography. This content is available to MKSAP 18 subscribers as Question 47 in the Rheumatology section. More information about MKSAP is available online.
Radiography is the most appropriate initial imaging study. Radiography is used to assess inflammatory arthritis and osteoarthritis (OA). Radiography does not visualize soft tissues nearly as well as bone, and due to the two-dimensional nature of the images, not all bone findings are visible on every view. Radiography may not detect early or mild erosive arthritic changes. Despite these limitations, serial radiography can be useful for monitoring arthritis disease progression. Radiography is relatively inexpensive and readily available. Despite low levels of ionizing radiation, radiography is considered safe except for pregnant women. In this case, the most likely diagnosis is OA of the right knee. Weight-bearing views should be obtained to more accurately assess the knee joint on radiographs. Typical radiographic OA features are osteophytes, joint-space narrowing, subchondral sclerosis, and cysts. Erosions are uncommon unless the erosive OA subtype is present, which usually is more aggressive and inflammatory on clinical evaluation.
In contrast to radiography, CT permits multiple views and orientations from a single study. CT is more sensitive for detecting bony abnormalities, such as bone erosions, than radiography or MRI. CT is more expensive than radiography and exposes the patient to more radiation.
MRI is useful in detecting soft-tissue abnormalities, inflammation, and fluid collections, but is less effective than CT in demonstrating bony abnormalities and erosive changes. MRI is more sensitive than radiography in detecting early spine and sacroiliac joint inflammation. MRI is more expensive than radiography and CT and is generally ordered when assessment of soft-tissue imaging is required. Radiography is a better choice than MRI to detect typical changes of OA.
Ultrasonography can detect soft-tissue abnormalities such as synovitis, tendinitis, bursitis, and joint fluid, and Doppler can assess for increased tissue blood flow consistent with synovitis. Ultrasonography can diagnose and monitor disease, and can be used to guide arthrocentesis. Ultrasonography is relatively inexpensive, and there is no ionizing radiation. Because inflammatory disease or joint aspiration is not anticipated and radiography will be better able to detect bony changes of OA, ultrasonography is not indicated.
Key Point
- Radiography is typically used as the initial imaging modality to assess inflammatory arthritis and osteoarthritis.