Posterolateral corner injuries
Posterolateral corner injuries of the knee are injuries to a complex area formed by the interaction of multiple structures. Injuries to the posterolateral corner can be debilitating to the person and require recognition and treatment to avoid long term consequences. Injuries to the PLC often occur in combination with other ligamentous injuries to the knee; most commonly the anterior cruciate ligament and posterior cruciate ligament. As with any injury, an understanding of the anatomy and functional interactions of the posterolateral corner is important to diagnosing and treating the injury.
Signs and symptoms
Patients often complain of pain and instability at the joint. With concurrent nerve injuries, patients may experience numbness, tingling and weakness of the ankle dorsiflexors and great toe extensors, or a footdrop.Complications
Follow-up studies by Levy et al. and Stannard at al. both examined failure rates for posterolateral corner repairs and reconstructions. Failure rates repairs were approximately 37 – 41% while reconstructions had a failure rate of 9%.Other less common surgical complications include deep vein thrombosis, infection, blood loss, and nerve/artery damage. The best way to avoid these complications is to preemptively treat them. DVTs are typically treated prophylactically with either aspirin or sequential compression devices. In high risk patients there may be a need for prophylactic administration of low molecular weight heparin. In addition, having a patient get out of bed and ambulate soon after surgery is a time honored way to prevent DVTs. Infection is typically controlled by administering 1 gram of the antibiotic cefazolin prior to surgery. Excessive blood loss and nerve/artery damage are rare occurrences in surgery and can usually be avoided with proper technique and diligence; however, the patient should be warned of these potential complications, especially in patients with severe injuries and scarring.
Causes
The most common mechanisms of injury to the posterolateral corner are a hyperextension injury, direct trauma to the anteromedial knee, and noncontact varus force to the knee.Mechanism
Structures found in the posterolateral corner include the tibia, fibula, lateral femur, iliotibial band, the long and short heads of the biceps femoris tendon, the fibular collateral ligament, the popliteus tendon, the popliteofibular ligament, the lateral gastrocnemius tendon, and the fabellofibular ligament. It has been reported that among these, the 3 most important static stabilizers of the posterolateral corner are the FCL, popliteus tendon, and popliteofibular ligament Studies have reported that these structures work together to stabilize the knee by restraining varus, external rotation and combined posterior translation with external rotation to it.Bones
The bones that make up the knee are the femur, patella, tibia, and fibula. In the posterolateral corner, the bony landmarks of the tibia, fibula and femur serve as the attachment sites of the ligaments and tendons that stabilize this portion of the knee. The patella plays no significant role in the posterolateral corner. The bony shape of the posterolateral knee, with the two convex opposing surfaces of the lateral femoral condyle and the lateral tibial plateau, makes this portion of the knee inherently unstable compared to the medial aspect. Thus, it has a much higher risk of not healing properly after injury than the medial aspect of the knee.Ligaments
The fibular collateral ligament connects the femur to the fibula. It attaches on the femur just proximal and posterior to the femoral lateral epicondyle and extends approximately 70 mm down the knee to attach to the fibular head. From 0° to 30° of knee flexion, the FCL is the main structure preventing varus opening of the knee joint.The popliteofibular ligament connects the popliteus muscle at the musculotendinous junction to the posterior and medial portion of the fibular styloid. It has two divisions, anterior and posterior, and acts to stabilize the knee during external rotation.
The mid-third lateral capsular ligament is made of a part of the lateral capsule as it thickens and extends along the femur, attaching just anterior to the popliteus attachment at the lateral epicondyle, and extends distally to the tibia attaching slightly posterior to Gerdy's tubercle and anterior to the popliteal hiatus. In addition, it has a capsular attachment at the lateral meniscus. It has two divisions, the meniscofemoral component and the meniscotibial component named for the areas they span, respectively. Studies suggest that the mid-third capsular ligament functions as a secondary varus stabilizer in the knee.
Tendons and muscles
The long and short heads of the biceps femoris each branch off into 5 attachment arms as they course distally in the knee. In the posterolateral corner, the long head has 3 important anatomic attachments. The direct arm attachment is on the posterolateral fibular styloid, the anterior arm lateral to the FCL and the lateral aponeurotic arm on the posterior and lateral portion of the FCL. The short head of the biceps also has 3 important arms in the posterolateral corner. The capsular arm attaches to the posterolateral capsule as well as the fibula, just lateral to the styloid and provides a strong attachment to the capsule, lateral gastrocnemius tendon, and capsuloosseus layer of the IT band. The fabellofibular ligament is actually a thickening of the capsular arm of the biceps femoris as it runs distally to the fibula. The direct arm attaches to the posterior and lateral aspect of the fibular styloid. The anterior arm attaches to the tibia at the same site as the mid-third lateral capsular ligament and is often injured in Segond fractures. Injuries to the biceps femoris tendons have been reported in patients with anterolateral-anteromedial rotatory instability.The popliteus tendon's main attachment is on the femur at the proximal portion of the popliteus sulcus. As the tendon runs posteriorly and distally behind the knee, it gives off 3 fascicles that attach to and stabilize the lateral meniscus. The popliteus tendon provides static and dynamic stabilization to the knee during posterolateral rotation.
The iliotibial band is mainly divided into two layers, the superficial and capsuloosseus layers. The superficial layer runs along the lateral knee and attaches to Gerdy's tubercle and sends a deeper portion that attaches to the lateral intermuscular septum. The capsuloosseus layer extends from the IM septum and merges with the short head of the biceps femoris attaching with it at the anterolateral aspect of the tibia. The IT band stabilizes the posterolateral corner by helping to prevent varus opening.
The lateral gastrocnemius tendon inserts on the supracondylar process of the femur slightly posterior to the FCL. Injuries involving this tendon are typically associated with severe traumas and are not often seen.
Diagnosis
The majority of posterolateral knee injuries occur in combination with another ligamentous injury, such as a cruciate ligament tear. This can make the diagnosis difficult and calls for the use of plain film radiographs and MRI to aid in the diagnosis. During the physical exam, it is imperative to assess a patient for signs of nerve injury as up to 15% of PLC injuries have associated nerve damage. Numbness, tingling, and/or dorsiflexor/great toe extensor muscle weakness all may suggest possible nerve damage.Radiographs
Normal antero-posterior radiographs are useful to look for Segond fractures and fibular head avulsion fractures. Bilateral varus stress AP radiographs comparing the injured leg to the normal side are useful in assessing the lateral joint space for opening after a potential injury. More than a 2.7 mm increase between sides indicates a fibular collateral ligament tear, while greater than 4.0 mm indicates with a grade III posterolateral knee injury. Posterior stress radiographs taken with the patient kneeling show the amount of posterior tibial translation in both knees and are helpful to diagnose PCL insufficiency and combined injuries. Between 0–2 mm increased posterior translation between the affected and healthy knees is normal, 2–7 mm indicates a partial tear, 8–11 mm suggests a complete tear and greater than 12 mm suggests a combined PCL and PLC injury.MRI
High quality MRI images of the knee can be extremely useful to diagnose injuries to the posterolateral corner and other major structures of the knee. While the standard coronal, sagittal and axial films are useful, thin slice coronal oblique images should also be obtained when looking for PLC injuries. Coronal oblique images should include the fibular head and styloid to allow for evaluation of the FCL and popliteus tendon.Specialized tests
In addition to a complete physical examination of the lower extremity, there are a set of specialized tests that must be synthesized to specifically check for injuries to the posterolateral corner. It is always important when evaluating an extremity for injury to compare it with the normal side to make sure you are not seeing a normal variation within that patient:- External Rotation Recurvatum Test - One of the first tests developed to assess the PLC, the external rotation recurvatum test is performed with the patient lying supine. The practitioner stabilizes the distal thigh with one hand while lifting the great toe with the other. The injured side is compared to the healthy one and a positive test is indicated by an increased amount of recurvatum, or hyperextension, in the affected knee. Increased recurvatum indicates possible combined injuries to the posterolateral corner and cruciate ligaments. The increase on recurvatum is best reported as the heel height off the examining table.
- Varus stress test at 0° and 30° - Varus stress testing is accomplished while the patient is lying supine on an examination table. The physician supports the thigh against the side of the exam table and applies a varus force to the knee joint while holding the ankle or foot, first at 0°of flexion and then at 30°. As the knee is stressed, the practitioner should feel for increased gapping at the lateral joint space. Gapping can be graded based on the amount the joint opens under stress; grade I causes pain, but with no gap present, grade II causes some gapping, but a definite endpoint is present, and grade III causes significant gapping with no definite endpoint felt. A negative varus stress test shows no difference between either knee at 0° or 30°. Increased gapping at 0° of flexion typically reflects a serious posterolateral injury with a high probability of accompanying cruciate ligament involvement. Lower grades at 30° are more suggestive of partial tears of the FCL or mid-third lateral capsular ligament, while higher grades indicate complete tears of the FCL and damage to other posterolateral structures.
- Dial Test - The dial test can be performed with a patient lying supine or prone. With the patient supine and the knees flexed 30° off the table, stabilize the thigh and externally rotate the foot. As the foot rotates, watch for external rotation of the tibial tubercle of the affected knee compared to the healthy one. A difference of greater than 10-15° indicates a positive test and likely injuries to the posterolateral knee. Next, repeat the test with the patient's knees flexed at 90°. Increased rotation at 90° indicates a combined PCL and posterolateral knee injury. If the rotation decreases compared to 30°, then an isolated PLC injury has occurred. Beware of a possible medial knee injury in the face of a positive dial test.
- Posterolateral Drawer Test - The posterolateral drawer test is similar to the commonly known posterior drawer test for PCL stability. Have the patient lie on their back with the knee flexed at 90° and externally rotate the foot to approximately 15°. While stabilizing the foot, apply a posterolateral rotation force to the tibia and watch for the amount of posterolateral rotation. Increased mobility and posterolateral rotation compared to the contralateral normal side usually indicates an injury to the popliteus complex.
- Reverse Pivot Shift Test - The reverse pivot shift test is almost exactly as its name implies, a reverse of the pivot shift test. The patient lies on their back with their knee flexed to between 45° and 60° and their foot externally rotated. The practitioner applies a valgus force while slowly extending the knee. A clunk will be felt around 30° of knee flexion if the subluxed or dislocated joint has reduced. This occurs as the iliotibial band changes from a knee flexor to extensor around 30°. Again, the affected knee should be compared the normal side to rule out a false positive test.
- Lachman & Posterior drawer tests - Increased anterior translation on the Lachman test is found when the patient has had a combined ACL and PLC injury. Increased posterior translation on the posterior drawer test indicates a combined posterior cruciate ligament tear with the PCL injury.
- Figure 4 Test - The patient lies supine and flexes their affected knee to approximately 90° then crosses it over the normal side with the foot across the knee and the hip externally rotated. The practitioner applies a varus stress on the joint by pushing the affected knee towards the exam table. This places tension on the posterolateral structures of the knee, especially the popliteus complex and popliteomeniscal fascicles. If these structures have been disrupted by injury, there is no tension to stabilize the lateral meniscus and the lateral meniscus can displace medially into the joint causing the patient pain and reproducing their symptoms at the lateral joint line. As always, the injured knee should be compared to the contralateral normal side.