A dial test performed at 90 degrees of flexion is most indicative of which instability pattern?

• A. ACL tear
• B. PLRI with PCL
• C. Meniscal Lesion
• D. IT Band Friction Test

Answer: (B)

The dial test looks at rotatory instability of the knee by measuring how much the tibia twists externally relative to the femur when the knee is flexed at two angles. At about 30 degrees of flexion, the posterolateral corner (the structures that resist external rotation on the outside of the knee) plays the major role, so an abnormal or increased external rotation at this angle points toward posterolateral corner injury and posterolateral rotatory instability.

When the knee is flexed to 90 degrees, the posterior cruciate ligament (PCL) and the associated structures become the limiting restraints. If there is a deficiency here, you’ll see more external rotation at 90 degrees. If both the posterolateral corner and the PCL are involved, the abnormal external rotation tends to be pronounced when the knee is at 90 degrees.

So a dial test done at 90 degrees of flexion that shows excessive external rotation indicates a combined pattern of posterolateral rotatory instability with PCL involvement. That coexisting instability explains why this angle is most indicative of that particular pattern.