Notch width index

Last revised by Leonardo Lustosa on 20 Oct 2023

The notch width index (NWI) is a measurement that has been proposed as a possible indicator of the risk of anterior cruciate ligament injuries 5.

The NWI is assessed on the tunnel view radiograph of the knee as the ratio between the width of the intercondylar notch and the width of the femur. These measurements are made at the level of the popliteal groove and parallel to the joint line 1,2.

Alternatively, the measurement can be performed on a coronal MRI sequence 4-8.

There are many conflicting reports regarding the actual relevance of the NWI as a predictor of ACL injuries. While some studies suggest that a narrower NWI is associated with a higher risk of ACL injuries 1,2, others have concluded that the NWI alone is not a reliable predictor for such injuries 3,4.

The most extensive meta-analysis to date (c.2023) has found that NWI was lower in ACL injury cases among men 5.

A proposed limit for which the NWI would be considered a critical indicator of risk for ACL injuries has been <0.20 (males) and <0.18 (females) 2.

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