Grade 0: | The screw is entirely inside the cancellous bone without contact with the internal surface of the cortical lamina. |
Grade 1: | The screw penetrates the internal cortical lamina but not its external surface. |
Grade 2: | The screw partially penetrates the external cortical lamina, with less than 3 mm; furthermore, the tip of the screw ends within the cancellous bone. |
Grade 3: | The screw penetrates the external cortical lamina in a range between 3 and 6 mm, with the tip of the screw ending within the soft tissues. |
Grade 4: | The screw penetrates the external cortical lamina with more than 6 mm. |