Table 1.
University of Pennsylvania Classification of OST
| Stage | Criteria | |
|---|---|---|
| 0 | Normal or nondiagnostic radiograph, bone scan, and MRI | |
| I | Normal radiograph: abnormal bone scan and/or MRI | |
| A ‒ Mild | (<15% of head affected) | |
| B ‒ Moderate | (15%-30%) | |
| C ‒ Severe | (>30%) | |
| II | Lucent and sclerotic changes in femoral head | |
| A ‒ Mild | (<15%) | |
| B ‒ Moderate | (15%-30%) | |
| C ‒ Severe | (>30%) | |
| III | Subchondral collapse (crescent sign) without flattening | |
| A ‒ Mild | (<15% of articular surface) | |
| B ‒ Moderate | (15%-30%) | |
| C ‒ Severe | (>30%) | |
| IV | Flattening of femoral head | |
| A ‒ Mild | (<15% of surface and <2-mm depression) | |
| B ‒ Moderate | (15%-30% of surface or 2- to 4-mm depression) | |
| C ‒ Severe | (>30% of surface or >4-mm depression) | |
| V | Joint narrowing and/or acetabular changes | |
| A ‒ Mild |  | |
| B ‒ Moderate | ||
| C ‒ Severe | ||
| VI | Advanced degenerative changes | |
| Stage | Criteria | |
|---|---|---|
| 0 | Normal or nondiagnostic radiograph, bone scan, and MRI | |
| I | Normal radiograph: abnormal bone scan and/or MRI | |
| A ‒ Mild | (<15% of head affected) | |
| B ‒ Moderate | (15%-30%) | |
| C ‒ Severe | (>30%) | |
| II | Lucent and sclerotic changes in femoral head | |
| A ‒ Mild | (<15%) | |
| B ‒ Moderate | (15%-30%) | |
| C ‒ Severe | (>30%) | |
| III | Subchondral collapse (crescent sign) without flattening | |
| A ‒ Mild | (<15% of articular surface) | |
| B ‒ Moderate | (15%-30%) | |
| C ‒ Severe | (>30%) | |
| IV | Flattening of femoral head | |
| A ‒ Mild | (<15% of surface and <2-mm depression) | |
| B ‒ Moderate | (15%-30% of surface or 2- to 4-mm depression) | |
| C ‒ Severe | (>30% of surface or >4-mm depression) | |
| V | Joint narrowing and/or acetabular changes | |
| A ‒ Mild | | |
| B ‒ Moderate | ||
| C ‒ Severe | ||
| VI | Advanced degenerative changes | |
Reprinted from Lee et al17 with permission.