The Active External Rotation Sign: A Physical Exam Technique for Detecting Posterolateral Corner Injury in Chronic...

The posterolateral corner (PLC) of the knee comprises important static and dynamic stabilizers, including the lateral collateral ligament, popliteus tendon, biceps femoris tendon, the popliteofibular ligament, and the posterolateral capsule. These structures are disrupted in many knee injuries, yet may be overlooked due to the complex anatomy, subjective clinical diagnostic exams, and poorly defined imaging techniques. Complete PLC lesions rarely heal with non-operative treatment, and can lead to significant instability and poor outcomes, and are therefore most successfully treated surgically.

A thorough physical examination and a high index of suspicion is necessary when evaluating the knee to identify these occult injuries. Current physical exam testing for PLC injuries typically includes side to side comparisons of the varus stress test, dial test, and heel-to-table distance. However, these injuries continue to be under-diagnosed as global clinical consensus for PLC injury identification remains elusive.

In these videos, we show the "active external rotation sign" where chronic posterior cruciate ligament-PLC deficient patients are positioned in 90° of knee flexion and are instructed to actively contract their hamstrings. Verbal cues given to the patient include "contract your hamstrings" and "dig the back of your heel into the ground." This can result in dynamic external rotation of the tibia with simultaneous posterior tibial translation on the femur. The biceps femoris pulls on the fibula and without the PLC to stabilize the knee, tibiofibular external rotation and posterior translation occurs. The biomechanics are similar to the dial test, but this detection tool utilizes active motion instead of passive motion, and presents with this abnormal and asymmetric knee motion.

The purpose of this presentation is to describe and demonstrate an important clinical sign that may be seen with chronic PLC injuries and that may be used as a new test for diagnosis.

Detection of PLC injuries with the active external rotation sign may assist in the clinical detection of incompetent PLC function, which can put cruciate reconstruction surgery at risk of failure if not simultaneously addressed.

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.