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Figure 1. Anteroposterior radiograph of the left knee.
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Figure 2. Coronal magnetic resonance imaging of the knee.
An 82-year-old woman presents with a 4-month history of left knee pain. She denies a known injury or precipitating event. She has tried intra-articular steroid and hyaluronic acid injections over the last few months with only minimal relief. On physical examination, the patient has pain over the medial joint line that is made worse with weight-bearing and varus stress to the knee. A radiograph is taken of the knee (Figure 1). Coronal magnetic resonance imaging (Figure 2) reveals bone marrow edema over the medial femoral condyle and tibial plateau.
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Bone marrow edema is a common finding on magnetic resonance imaging (MRI) in patients with advanced osteoarthritis. Bone marrow edema is more common in patients with knee pain compared with patients with asymptomatic arthritic knees. Edema is associated with an acceleration of cartilage loss over time. Patients who present with arthritis-associated bone marrow edema are 8 times more likely to have knee replacement compared with similar patients with no edema.1,2
The loss of articular cartilage increases subchondral bone stress leading to arthritic progression. As the arthritic cascade progresses, the overloading of subchondral bone causes microdamage that outpaces repair of the bone. The differential diagnosis for bone marrow edema includes osteonecrosis, bone marrow edema syndrome, osteochondritis dissecans, bone contusion, stress fracture, and tumors.1,2
Bone marrow edema caused by arthritis is often confused with a stress fracture on MRI. Both have similar histopathology with findings of bone marrow necrosis, fibrosis, and trabeculae abnormalities. Bone marrow edema associated with arthritis is generally found in the knee compartment with the most arthritis, usually the medial compartment.1,2
Treatment of bone marrow edema involves resting the joint so bone repair can catch up to subchondral damage of weight-bearing. An unloader brace has not been shown to improve symptoms or reduce bone marrow edema. Intravenous zoledronic acid has been shown to help reduce bone marrow edema and improve symptoms by reducing resorption of the subchondral bone. A subchondroplasty procedure, which includes an injection of a polymerizable calcium phosphate bone substitute in the subchondral bone at the location of the bone marrow edema, has recently been used to help restore healing and strengthen subchondral bone in these patients.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopaedics for Physician Assistants.
References
1. Hofmann S, Kramer J, Vakil-Adli A, Aigner N, Breitensher M. Painful bone marrow edema of the knee: differential diagnosis and therapeutic concepts. Orthop Clin North Am. 2004;35(3):321-333, ix. doi:10.1016/j.ocl.2004.04.005
2. Sharkey PF, Cohen SB, Leinberry CF, Parvizi J. Subchondral bone marrow lesions associated with knee osteoarthritis. Am J Orthop. 2012;41(9):413-417.
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