软骨下功能不全骨折 (SIF) 和膝关节骨坏死 (SIF-ON)（以前被误称为自发性膝关节骨坏死 (SONK)）是在没有先前创伤、肿瘤或炎症事件的情况下出现的骨病变。这两种情况的特征在于MRI 上的骨骺骨髓水肿 (BME) 样信号可显示早期阶段。然而，虽然 SIF 通常会自发愈合，但它们也可能演变成骨坏死（即 SIF-ON），这可能会发展为关节面不可逆的塌陷。仔细分析其他 MRI 征象可能有助于在早期区分这两种情况。在 SIF 中，BME 水肿样信号延伸到紧邻软骨下板的区域，而在 SIF-ON 中，由于骨髓改变，该软骨下区域在液体敏感 MR 图像上显示出低信号强度。具有低流体敏感信号强度的软骨下区域的厚度和长度是决定SIF-ONs预后的重要因素。如果厚度超过 4 毫米或长度超过 14 毫米，则预后较差。 SIF 和 SIF-ON 的鉴别诊断包括与“复杂区域疼痛综合征”(CRPS) 相关的骨病变、全身性骨骺骨坏死以及与软骨病理相关的骨病变。临床相关性声明影像学在诊断软骨下功能不全方面发挥着重要作用骨折 (SIF) 与伴有骨坏死 (SIF-ON) 和塌陷的软骨下不全骨折 (SIF-ONs) 和塌陷，以及将其与其他表现为骨髓水肿样信号的自发性膝关节软骨下骨病变区分开来。要点• 软骨下不全骨折可能会影响膝关节，特别是在老年人中。• 软骨下功能不全骨折通常会自发愈合。• 有时，软骨下骨坏死和塌陷可能使软骨下功能不全骨折复杂化。• 骨髓样水肿是所有这些病变中常见的非特异性体征。• 骨折并发的骨坏死中的骨髓退化在液体敏感序列上呈低信号。© 2023。欧洲放射学会 (ESR)。

Subchondral insufficiency fractures (SIFs) and SIFs with osteonecrosis (SIF-ONs) of the knee (previously misnamed spontaneous osteonecrosis of the knee (SONK)) are bone lesions that appear without prior traumatic, tumoral, or inflammatory event.Both conditions are characterized in the early stages by epiphyseal bone marrow edema (BME)-like signal at MRI. However, while SIFs usually heal spontaneously, they can also evolve to osteonecrosis (i.e., SIF-ON), which may progress to an irreversible collapse of the articular surface. Careful analysis of other MRI signs may help differentiate the two conditions in the early phase. In SIFs, the BME edema-like signal extends to the area immediately adjacent to the subchondral plate, while in SIF-ONs, this subchondral area shows low signal intensity on fluid-sensitive MR images due to altered bone marrow. The thickness and length of subchondral areas with low fluid-sensitive signal intensity are important factors that determine the prognosis of SIF-ONs. If they are thicker than 4 mm or longer than 14 mm, the prognosis is poor. The differential diagnosis of SIFs and SIF-ONs include bone lesions associated with the "complex regional pain syndrome" (CRPS), epiphyseal osteonecrosis of systemic origin, and those related to cartilage pathology.Clinical relevance statement Imaging plays an essential role in diagnosing subchondral insufficiency fractures (SIFs) from subchondral insufficiency fractures with osteonecrosis (SIF-ONs) and collapse, as well as in distinguishing them from other spontaneous knee subchondral bone lesions presenting with bone marrow edema-like signal.Key points• Subchondral insufficiency fractures may affect the knee, especially in older adults.• Subchondral insufficiency fractures usually heal spontaneously.• Sometimes, subchondral osteonecrosis and collapse may complicate subchondral insufficiency fractures.• Bone marrow-like edema is an aspecific sign seen in all these lesions.• Degraded marrow in osteonecrosis complicating fractures is hypointense on fluid-sensitive sequences.© 2023. European Society of Radiology (ESR).