Dial Test at 30° and 90°: Posterolateral Corner (PLC) vs Isolated PCL Guide
In short
Missed posterolateral corner (PLC) knee injuries lead to failed ACL and PCL reconstructions. Learn how the Dial test at 30 and 90 degrees of flexion differentiates isolated PLC tears from combined PCL ruptures.
In this guide (7 sections)
Anatomy of the Posterolateral Corner (PLC)
The Posterolateral Corner (PLC) of the knee consists of the fibular collateral ligament (FCL/LCL), popliteus tendon, and popliteofibular ligament (PFL). These structures form the primary restraint against external tibial rotation and varus stress.
Overlooking a PLC injury during cruciate ligament reconstruction is the leading cause of graft failure due to persistent rotational shear.
How to Perform the Dial Test Step-by-Step
The Dial test is ideally performed with the patient lying prone on an examination table:
- Testing at 30° Knee Flexion: The clinician flexes both knees to 30 degrees, places hands on the soles of both feet, and applies maximal external rotation torque to both tibias, observing the thigh-foot angle bilaterally.
- Testing at 90° Knee Flexion: The clinician flexes both knees to 90 degrees and repeats the external rotation torque, measuring the bilateral difference.
- Positive Threshold: A difference in external rotation of greater than 10 to 15 degrees compared to the normal contralateral side indicates significant ligamentous disruption.
Clinical Interpretation: 30° vs 90° Difference
Differentiating between isolated PLC injuries and combined PCL/PLC tears depends entirely on the angle of laxity:
| Knee Flexion Angle | Pathological Finding | Anatomical Structure Involved | |
|---|---|---|---|
| Increased Rotation at 30° Only | >10° increased external rotation at 30°, but normal at 90° | Isolated Posterolateral Corner (PLC) injury | |
| Increased Rotation at Both 30° and 90° | >10° increased external rotation at both 30° and 90° | Combined PCL and Posterolateral Corner injury | |
| Normal Rotation at Both Angles | Symmetrical rotation (<10° difference) | Intact posterolateral structures and PCL |
Frequently Asked Questions
Can the Dial test be performed in supine if prone is uncomfortable?
Yes. The Dial test can be performed in supine with legs dangling over the edge of the plinth, though prone positioning stabilizes the femur more effectively.
Why does PCL involvement increase rotation specifically at 90 degrees?
At 90 degrees of knee flexion, the PCL tightens and serves as a secondary restraint against external rotation. If the PCL is torn alongside the PLC, rotational laxity increases at 90 degrees.
The Anatomy of the Posterolateral Corner (PLC)
The posterolateral corner consists of the fibular collateral ligament (FCL), popliteus tendon, and popliteofibular ligament (PFL). These static and dynamic stabilizers work in synergy to resist knee varus opening, tibial external rotation, and posterior tibial translation.
Interpreting 30 Degrees vs 90 Degrees Rotational Differences
A rotational increase exceeding 10 degrees at 30 degrees of flexion that normalizes at 90 degrees confirms an isolated PLC tear (since the intact PCL secondary restraint engages at 90 degrees). An increase in external rotation exceeding 10 degrees at both 30 and 90 degrees confirms a combined, highly unstable PCL and PLC tear requiring surgical reconstruction.
Gait Instability and Dynamic Knee Bracing
Patients with unrecognized PLC tears present with a characteristic varus thrust gait during the stance phase of walking. Fitted with a hinged knee brace locked to prevent hyperextension, early physiotherapy retrains quadriceps and gastrocnemius co-contraction to stabilize the lateral knee.
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