Aetiology and pathogenesis of bone marrow lesions and osteonecrosis of the knee

Abstract

Bone marrow lesions (BML) of the knee are a frequent MRI finding, present in many different pathologies including trauma, post-cartilage surgery, osteoarthritis, transient BML syndromes, spontaneous insufficiency fractures, and true osteonecrosis.Osteonecrosis (ON) is in turn divided into spontaneous osteonecrosis (SONK), which is considered to be correlated to subchondral insufficiency fractures (SIFK), and avascular necrosis (AVN) which is mainly ascribable to ischaemic events.Every condition has a MRI pattern, a different clinical presentation, and specific histological features which are important in the differential diagnosis.The current evidence supports an overall correlation between BML and patient symptoms, although literature findings are variable, and very little is known about the natural history and the progression of these lesions.A full understanding of BML will be mandatory in the future to better address the different pathologies and develop appropriately-targeted treatments. Cite this article: Marcacci M, Andriolo L, Kon E, Shabshin N, Filardo G. Aetiology and pathogenesis of bone marrow lesions and osteonecrosis of the knee. EFORT Open Rev 2016;1:219-224. DOI: 10.1302/2058-5241.1.000044.

Keywords: MRI; bone marrow lesions; bone marrow oedema; knee; osteonecrosis; subchondral insufficiency fractures; subchondral pathology.

Fig. 1

Bone marrow oedema-like signal related to anterior cruciate ligament tear. On a sagittal fluid-sensitive image (PD with fat suppression) oedema around the sulcus of the lateral femoral condyle is visible (white arrows). On sagittal PD without fat suppression, there are subchondral impaction fractures in addition to bone contusions (black arrows).

Fig. 2

Typical contusions related to spontaneously reduced lateral patellar dislocation. On axial fluid-sensitive sequence (T2 fat suppression) there is oedema in the medial patella (arrow), and in the anterior aspect of the lateral femoral condyle (dotted arrows).

Fig. 3

Oedema-like signal on coronal and sagittal PD fat suppression (white arrows) in the medial femoral condyle of a patient, ten years after a hyaluronan-based matrix-assisted autologous chondrocyte transplantation. The implant presents a cartilage-like signal, and only a few signs of the initial procedure are still present (white arrowhead).

Fig. 4

Advanced osteoarthritis. On the coronal PD fat suppressed image (a) there is subchondral bone marrow oedema-like signal at the periphery of the medial femoral condyle, and also the medial tibial plateau (white arrow). Other components of osteoarthritis including cartilage loss and osteophytes are also seen. There is medial meniscus extrusion (arrowhead). On the coronal T1WI (b) there are low-signal intensities (black arrows). At this point it is hard to determine whether these are insufficiency fractures or early cyst formation.

Fig. 5

Coronal PD fat suppression image of the knee demonstrates reversible bone marrow oedema-like signal in the medial femoral condyle. The oedema-like signal is extensive and demonstrates indistinct margins (see arrow).

Fig. 6

Progression of an insufficiency fracture over ten months. Coronal PD fat suppression (a) and T1WI (b) at the acute stage show a bone marrow oedema-like signal in the medial femoral condyle (see arrow) and a linear hypo-intensity on T1 with a thickness of < 4 mm (black arrow). Flattening of the articular surface is already present. After ten months (c and d) the oedematous signal has nearly resolved, but there is a subchondral area of low signal on all sequences > 4mm thick representing osteonecrosis (arrowhead). Medial meniscus extrusion is also seen (dotted arrow).