Abstract
Background:
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.
Indications:
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.
Technique Description:
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.
Results:
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.
Discussion/Conclusion:
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.
Patient Consent Disclosure Statement:
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.
This is a visual representation of the abstract.
Keywords
Video transcript
In this video, we are going to present the use of the “active external rotation sign” as a physical exam tool for diagnosing chronic posterolateral corner (PLC) injury in patients with chronic multiligament knee injuries (MLKIs).
We have no disclosures to report.
Background
The PLC is an important complex of structures that help provide restraint to varus forces and posterolateral rotation of the tibia relative to the femur with a secondary function of resisting anterior and posterior tibial translation. 6 The static stabilizers of the PLC include the lateral collateral ligament (LCL), the posterolateral capsule, and popliteofibular ligament (PFL), while the dynamic structures include the biceps femoris insertion, the popliteus muscle and tendon, and iliotibial (IT) band. It's important to understand the relationship between the anatomic structures of the PLC to properly assess for PLC injuries during the physical exam.
PLC injuries are often a result of combined hyperextension and excess varus forces on the knee or combined posterior and posterolaterally directed forces. Up to 70% of PLC injuries are missed during the initial injury presentation, which often delays acute surgical intervention necessary for restoring functional stability. 4 Furthermore, PLC injuries commonly occur in the setting of MLKIs, making it challenging to properly assess and isolate PLC injury.4,5 Since magnetic resonance imaging (MRI) does not provide sufficient information regarding the functional competence of the tissue, a thorough physical exam is necessary to fully understand the extent of injury. 8
Common physical exams assess the integrity of the LCL, posterior cruciate ligament (PCL), and PLC. The LCL is the most commonly injured structure within the PLC and is best assessed using varus stress radiographs.1,2 Lateral gapping of 2.7 mm or more is suggestive of a complete LCL injury, while a gap of 4 mm or more suggests a grade III PLC injury. 5
The posterior drawer test can be used to test for PCL injury.1,4 In this test, the patient is supine and then while the knee is at 90° of flexion, the examiner grasps the proximal lower leg and attempts to translate it posteriorly. In this video we show a grade 0 in a normal knee where there is no posterior translation. Not shown, is the grade 1 where there is 0-5 mm of increased posterior translation compared to the normal knee, but the tibial plateau still remains anterior to the femoral condyles. And we show here in the video a grade 2 posterior drawer, which has 6 to 10 mm of increased translation, where the tibial plateau becomes even with the femoral condyles. When performing a posterior drawer test in patients with combined PCL and PLC injuries, the medial plateau will translate posteriorly beyond the medial femoral condyle, consistent with a grade 3 posterior drawer test with increased translation of 11 to 15 mm. 10
For specific evaluation of the PLC, the dial test and supine heel-to-table distance are often utilized.1,4 The goal of the dial test is to identify abnormal and asymmetric external rotation of the tibia while the knees are in 30° and 90° of flexion. While viewing the foot positioning with the tibio-talar joint locked in neutral position, more than 10° of increased external rotation in the injured knee when at 30° suggests a PLC injury, while more than 10° of increased external rotation of the injured knee at 90° indicates a combined PCL and PLC injury. 4 This test is best performed in the prone position to eliminate the posterior translation of the tibia on the femur and to compare the positioning of the feet, without having to support the contralateral limb. In the supine heel-height test, the distal thigh is stabilized to the exam table while the foot is lifted up, and if there is injury to the PLC structures or capsule, or there are combined injury patterns, the limb may demonstrate increased hyperextension, creating an asymmetric increased heel height difference. 4
Technique Description
In this video, we will present a new physical exam technique for diagnosing PLC injuries called the “ active external rotation sign.” During the active external rotation sign, the hamstring contraction results in external rotation of the tibia with simultaneous posterior tibial translation on the femur. The biomechanics are similar to the passive motions elicited on the dial test, but this detection tool utilizes active motion. In a positive test, the biceps femoris pulls on the fibula and without the PLC to stabilize the knee, tibiofibular external rotation and posterior translation occurs. This is able to happen since the essential static stabilizers of the PLC, such as the LCL, popliteus, and PFL, are injured. And as implied by the discussion on the biomechanics of the exam, this test cannot be utilized if the patient also has an avulsed biceps femoris tendon, which can be seen in PLC injuries. This is an important clinical sign that can be used as a new test for diagnosing PLC injury and may correlate with some of the patient's symptomatology. There is not yet a grading system available for this test given limited case numbers.
Similar to the passive motion dial test, this active motion external rotation test should also be done at both 30° and 90° of knee flexion in order to distinguish between isolated PLC injuries versus combined PLC and PCL injuries. The patient can be either in a sitting position or in a supine position, as long as their knee is at either 30 or 90°, and the patient is given verbal instructions to “contract your hamstring” and “dig the back of your heel into the ground.” At 90° of knee flexion, the patient contracts their hamstring, and if the tibia externally rotates and posteriorly translates, then that indicates that there is combined PCL and PLC injury. At 30° of knee flexion, the patient contracts their hamstring, and if the tibia externally rotates, but does not posteriorly translate, then that indicates there is isolated PLC injury.
As demonstrated in this negative test at 30°, in a healthy knee, the PLC complex acts to restrain varus gapping of the knee and resist external rotation of the tibia relative to the femur.
And as shown here in the negative test at 90°, the intact PCL acts to resist posterior translation of the tibia relative to the femur and the PLC acts to resist external rotation.
In this patient with chronic PLC and PCL injury, we demonstrate a positive active external rotation test at 90°. Since this patient has PLC injury, when the biceps femoris tendon pulls on the fibula, there is insufficient resistance to prevent external rotation of the tibia relative to the femur.
And again, as another example, this is a different patient with chronic PLC and PCL injury who has a positive active external rotation test at approximately 90° of knee flexion.
Discussion
PLC injuries should be treated surgically in a timely and organized manner to avoid complications. In the setting of a MLKI, PLC injury significantly increases the risk of common peroneal nerve (CPN) and popliteal artery injuries. 9 Although all MLKIs warrant a careful neurovascular assessment, there should be an increased index of clinical suspicion for CPN injury when the PLC is involved. 3 Long-term, PLC injuries can lead to development of arthrofibrosis, less consistent results with cruciate ligament reconstruction and earlier progression to osteoarthritis.6,9
Return-to-sports guidelines for PLC injuries remain a controversial topic in the orthopedic literature with respect to residual muscular strength, movement pattern deficits, and the effectiveness of return-to-play testing. 9 Patients recovering from PLC injuries or surgery typically follow a staged rehabilitation program that progresses from range of motion to muscular endurance to strength training, with the timing and rigor based on the degree of injury and type of surgery performed. 1 Hamstring exercises and knee hyperextension should be avoided for the first 4 months after surgery, while light quadricep exercises, such as a stationary bicycle, can be started at 6 to 8 weeks. 7 Generally, athletes can resume progressive strengthening exercises at about 4 to 6 months postoperative and return-to-sports at least 9 months postoperative.1,7
Here are our references.
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Footnotes
Submitted September 17, 2023; accepted February 28, 2024.
One or more of the authors has declared the following potential conflict of interest or source of funding: M.J.M. is a consultant and lecturer for Smith & Nephew. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
