Subchondral insufficiency fracture of the medial femoral condyle treated conservatively with early non-weightbearing

Abstract

Spontaneous osteonecrosis of the knee (SONK) is a poorly understood but debilitating disease, that is a common cause of unilateral acute knee pain and swelling. The term "SONK" has been replaced by the term "subchondral insufficiency fracture" in the latest pathology and imaging literature. Few studies investigated the pathogenesis of SONK by examining the histological changes of the tissues. Very recently, the development of SONK was associated with a meniscal root tear. In terms of the preferred imaging, plain radiographs can confirm the diagnosis in late stages; however, magnetic resonance imaging (MRI) scan is often required. Regarding the treatment, conservative management is usually the treatment of choice in early stages, including a period of non-weightbearing or the use of medications, such as nonsteroidal anti-inflammatory drug (NSAIDS) or bisphosphonates. However, when SONK progresses, often a surgical intervention is required, such as knee replacement, but also minimally invasive techniques, such as arthroscopic intervention, have been described. We present a case of early SONK and discuss the possible pathogenesis of SONK, the clinical presentation, the radiological findings, and we focus on the importance of early diagnosis and early off-load period that is required to prevent further progression of the disease.

Keywords: Atraumatic knee pain; Early stage; Nonweightbearing; Spontaneous osteonecrosis of the knee; Therapy.

Fig. 1

Lateral radiograph of the knee. There is a small suprapatellar knee effusion. No lipohaemarthrosis. No bony injury is identified.

Fig. 2

Sagittal PD fluid sensitive MRI sequence. There is a small knee effusion with intact menisci. There is florid high signal within the medial femoral condyle in keeping with extensive marrow oedema. There is irregularity of the subchondral bone plate.

Fig. 3

Axial (A) and coronal (B) PD fluid sensitive MRI sequences. There is indentation of the articular cartilage at the medial femoral condyle with irregularity at the subchondral bone plate, in keeping with chondral injury. There is intense oedema at the medial femoral condyle which appears out of proportion to the degree of chondral defect. Findings are suggestive of subchondral insufficiency fracture.