Meaurement: imaging of the knee with femur vertical
Point of measurement: horizontal line through the femoral condyles at the apex of the popliteal groove (see Figure 4, van Eck et al).
Measurements:
(1) bicondylar width (distance between external points of medial and lateral condyles along line)
(2) notch width (distance between internal points of medial and lateral condyles along line
notch width index = NWI =
= (notch width in mm) / (bicondylar width.
Interpretation:
• The NWI mean and standard deviation (SD) are determined for a population.
• The NWI distribution needs to be controlled for gender.
• Notch stenosis is diagnosed when the NWI is less than 1 SD below the mean for the population.
• The NWI of patients with bilateral anterior cruciate ligament ruptures tend to be smaller than others in the population.
• The significance may be greater in certain populations such as the skeletally immature.
Performance:
• Some authors may measure the bicondylar and notch widths at different levels rather than using the popliteal notch for reference.
