Radiology Teaching Files > Case 5473143

Contributed by: Radiology Residency Program Faculty & Staff.
Patient: female
History: Elderly female with sudden onset knee pain.

Fig. 1: MRI Right Knee

Fig. 1:
Coronal Fat Sat T2: There is diffuse marrow edema in the medial femoral condyle with a crescentic linear fracture line at the subchondral bone.
Sagittal Fat Sat T2 and Sagittal Proton Density: Subchondral fracture is at the weight bearing surface of the medial femoral condyle.  A tear of the posterior horn of the medial meniscus is also present.


Spontaneous Osteonecrosis of the Knee (SONK)


Spontaneous Osteonecrosis of the Knee (SONK)

- syn: Ahlbäck disease
- Necrosis of the weight-bearing portion of the femur or tibia with associated subchondral fracture and collapse
- Epidemiology: Middle-aged and elderly patients, F>M
- can be associated with meniscal tears

Etiology: (controversial)
- Traumatic theory: osteoporotic patient suffers insufficiency fracture following trivial trauma, bone subsequently becomes necrotic
- Vascular theory: thrombotic venous occlusion leading to venous hypertension and hypoxic death - recently less accepted in the knee

Radiographic Findings:
- (+/-) Subchondral sclerosis
- (+/-) Articular surface collapse
- Effusion

MR Findings:
- Necrosis: discrete area of subchondral decreased signal intensity
- Surrounded by intermediate signal (combination of fat and edema)
- Focus of low signal intensity ischemia or fracture surrounded by diffuse increased signal intensity edema
- (+/-) Linear often serpiginous low signal abnormality adjacent to the edema (probable fracture)
- (+/-) Articular surface collapse

Nuclear Medicine Findings:
Bone Scan: Positive after 72 hours

Differential Diagnosis:
Subchondral Fracture
Osteochondritis Dissecans (OCD)
Stress Response/Fracture


Stoller, David W. ... [et al.] Diagnostic Imaging: Orthopaedics. Amirsys, 2004.

Resnick, D., Kransford, MJ. Bone and Joint Imaging. 3rd Edition. Elsevier Saunders, 2005.

Submitted by:
Aakash D. Singh, M.D. – PGY-V Radiology Resident
Marshall L Chalfant, M.D. - Radiologist
Aultman Hospital

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Additional Details:

Case Number: 5473143Last Updated: 08-02-2006
Anatomy: Skeletal System   Pathology: Trauma
Modality: MRExam Date: 07-20-2006Access Level: Readable by all users
Keywords: spontaneous osteonecrosis, sonk, ahlback diseaseACR: 451.44

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