What imaging features help distinguish acute osteomyelitis vs osteoarthritis on MRI?

What imaging features help distinguish acute osteomyelitis vs osteoarthritis on MRI?

• A. Osteomyelitis: marrow edema with post-contrast enhancement and possible fracture; OA: joint space narrowing, osteophytes, subchondral sclerosis; edema is minimal.
• B. Osteomyelitis shows no edema; OA shows marrow edema.
• C. OA shows post-contrast enhancement; Osteomyelitis has no enhancement.
• D. Osteomyelitis is limited to soft tissue with no bone involvement.

Answer: (A)

On MRI, the main distinction comes from what tissue is primarily affected and how it appears with edema and contrast. Acute osteomyelitis involves bone marrow, so you see marrow edema (bright on T2/STIR, dark on T1) and post-contrast enhancement of the marrow and surrounding inflamed tissue. There may also be periosteal reaction and even fracture risk as the infection weakens bone. Osteoarthritis, by contrast, is a degenerative process of the joint surfaces, so the hallmark features are joint space narrowing from cartilage loss, osteophyte formation at the joint margins, and subchondral sclerosis. Edema within the bone marrow is not a defining feature of OA and, if present, is typically mild and not accompanied by the robust marrow enhancement seen in infection. Thus, the imaging pattern of marrow edema with post-contrast marrow enhancement and possible fracture aligns with acute osteomyelitis, while the pattern of joint space narrowing, osteophytes, and subchondral sclerosis without prominent marrow edema fits osteoarthritis.

On MRI, the main distinction comes from what tissue is primarily affected and how it appears with edema and contrast. Acute osteomyelitis involves bone marrow, so you see marrow edema (bright on T2/STIR, dark on T1) and post-contrast enhancement of the marrow and surrounding inflamed tissue. There may also be periosteal reaction and even fracture risk as the infection weakens bone. Osteoarthritis, by contrast, is a degenerative process of the joint surfaces, so the hallmark features are joint space narrowing from cartilage loss, osteophyte formation at the joint margins, and subchondral sclerosis. Edema within the bone marrow is not a defining feature of OA and, if present, is typically mild and not accompanied by the robust marrow enhancement seen in infection. Thus, the imaging pattern of marrow edema with post-contrast marrow enhancement and possible fracture aligns with acute osteomyelitis, while the pattern of joint space narrowing, osteophytes, and subchondral sclerosis without prominent marrow edema fits osteoarthritis.