July 18, 2024

Spontaneous Osteonecrosis of Knee (SONK) is a result of vascular arterial insufficiency to the medial femoral condyle resulting in necrosis and destruction of bone.

Spontaneous Osteonecrosis of Knee (SONK)
Spontaneous Osteonecrosis of Knee (SONK)


More in elderly women (> 55 years)

M: F=1:3

Risk factors

  • Corticosteroid use
  • SLE
  • Alcoholism
  • Pancreatitis
  • Sickle cell disease
  • RA
  • Cassion disease
  • Gaucher disease


  • No predisposing factors
  • Speculation includes (Sub-chondral insufficiency fracture, which may be caused by meniscal root tear)

Clinical features

  • Sudden onset of severe knee pain, increases at night and with activities
  • Effusion
  • Limited ROM, Tenderness @ medial femoral condyle


X-ray features

  • Standing AP and Lateral view
  • Tunnel View (long axis of the femur at 60 degrees to the long axis of the tibia)
  • Flattening of the weight-bearing portion
  • Radiolucent area forms in subchondral bone surrounded by a rim of sclerosis
  • Later collapse: Varus deformity

Tech-99m Scan: Localized area of increased uptake

MRI: (diagnostic study of choice)


Stage 1Normal x-ray, MRI, and bone scan shows changes
Stage 2Flattening of the weight-bearing portion
Stage 3The radiolucent area surrounded by sclerosis
Stage 4Sub chondral collapse + sequestrum/ fragments
Stage 5Narrowing of joint spaces, osteophytes formations, and tibial changes (Subchondral sclerosis)

Treatment Options:

Treatment outlines for Spontaneous Osteonecrosis of Knee are explained below.


  • Braces
  • Strengthing exercises (Quadriceps and hamstrings)
  • Lifestyle and activity modifications


Prognosis: >5 cm2: Bad prognosis (related to the site)

See also: Panner’s Disease of Elbow

See also: