Subchondral insufficiency fracture of the knee: review of current concepts and radiological differential diagnoses

Subchondral insufficiency fracture of the knee (SIFK) is a common cause of knee joint pain in older adults. SIFK is a type of stress fracture that occurs when repetitive and excessive stress is applied to the subchondral bone. If the fracture does not heal, the lesion develops into osteonecrosis and results in osteochondral collapse, requiring surgical management. Because of these clinical features, SIFK was initially termed “spontaneous osteonecrosis of the knee (SONK)” in the pre-MRI era. SONK is now categorized as an advanced SIFK lesion in the spectrum of this disease, and some authors believe the term “SONK” is a misnomer. MRI plays a significant role in the early diagnosis of SIFK. A subchondral T2 hypointense line of the affected condyle with extended bone marrow edema-like signal intensity are characteristic findings on MRI. The large lesion size and the presence of osteochondral collapse on imaging are associated with an increased risk of osteoarthritis. However, bone marrow edema-like signal intensity and osteochondral collapse alone are not specific to SIFK, and other osteochondral lesions, including avascular necrosis, osteochondral dissecans, and osteoarthritis should be considered. Chondral lesions and meniscal abnormalities, including posterior root tears, are also found in many patients with SIFK, and they are considered to be related to the development of SIFK. We review the clinical and imaging findings, including the anatomy and terminology history of SIFK, as well as its differential diagnoses. Radiologists should be familiar with these imaging features and clinical presentations for appropriate management.

A TRIATHLETE WITH MEDIAL MENISCUS TEAR AND SUBCHONDRAL INSUFFICIENCY FRACTURE

Subchondral insufficiency fracture of the knee (SIFK) is an important differential diagnosis for knee pain. If diagnosed early, SIFK can be treated conservatively with non-weight bearing ambulation. If left untreated, this disease may lead to catastrophic complications such as subchondral fragment detachment and fragmentation or subchondral collapse which will warrant the need for surgical intervention. The author reports a 44-year-old triathlete that presented with complaint of a trivial left anteromedial knee pain for one-year duration. This disease presented at an unusual site of the medial tibial condyle. Moreover, the patient is a healthy triathlete that does not have any predisposing factors for SIFK. Magnetic resonance imaging showed subchondral insufficiency fracture of the medial tibial condyle with a complex multi-directional medial meniscus tear in the same knee. Could the undiagnosed medial meniscus injury be the causation leading to the development of SIFK? Here, the author will summarize the literature on various clinical features, work-up and management of SIFK.