Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 52-year-old man is evaluated for a 5-year history of gradually progressive left knee pain. He has 20 minutes of morning stiffness, which returns after prolonged inactivity. He has minimal to no pain at rest. He reports no clicking or locking of the knee. Over the past several months, the pain has limited his ambulation to no more than a few blocks.

On physical examination, vital signs are normal. BMI is 25. The left knee has a small effusion and some fullness at the back of the knee; the knee is not erythematous or warm. Range of motion of the knee elicits crepitus. There is medial joint line tenderness to palpation, bony hypertrophy, and a moderate varus deformity. There is no evidence of joint instability on stress testing.

Radiographs of the knee reveal bone-on-bone joint-space loss and numerous osteophytes.

Which of the following is the most appropriate next diagnostic step for this patient?

A: CT of the knee
B: Joint aspiration
C: MRI of the knee
D: No diagnostic testing

MKSAP Answer and Critique

The correct answer is D: No diagnostic testing. This item is available to MKSAP 16 subscribers as item 3 in the Rheumatology section.

No additional diagnostic testing is indicated for this patient who has osteoarthritis, which is a clinical diagnosis. According to the American College of Rheumatology’s clinical criteria, knee osteoarthritis can be diagnosed if knee pain is accompanied by at least three of the following features: age greater than 50 years, stiffness lasting less than 30 minutes, crepitus, bony tenderness, bony enlargement, and no palpable warmth. These criteria are 95% sensitive and 69% specific but have not been validated for clinical practice. Additional diagnostic testing is not appropriate, because it has no impact on the management of advanced disease.

CT of the knee is very sensitive for pathologic findings in bone and can be used to look for evidence of an occult fracture, osteomyelitis, or bone erosions. However, none of these are suspected in this patient.

Small- to moderate-sized effusions can occur in patients with osteoarthritis, and the fluid is typically noninflammatory. Joint aspiration in this patient without evidence of joint inflammation and evident osteoarthritis is not useful diagnostically but is often done in the context of intra-articular corticosteroid injection or viscosupplementation.

MRI is useful to evaluate soft-tissue structures in the knee such as meniscal tears. Patients with meniscal tears may report a clicking or locking of the knee secondary to loose cartilage but often have pain only on walking, particularly going up or down stairs. Patients with degenerative arthritis often have MRI findings that indicate meniscus tears. These tears are part of the degenerative process but do not impact management; arthroscopic knee surgery for patients with osteoarthritis provides no clinical benefit. The one exception may be in patients with meniscal tears that result in a free flap or loose body, producing painful locking of the joint. These symptoms are not present in this patient.

Key Point

• Osteoarthritis is diagnosed clinically and does not require advanced imaging to establish the diagnosis.

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