Posterolateral corner injury diagnosis aids decision to repair or reconstruct

Issue: May 2016

ByFilippo Familiari, MD

ByRoberto Simonetta, MD

Posterolateral corner injuries of the knee account for about 16% of knee ligament injuries and these injuries frequently present with concomitant ACL and PCL injuries. Moreover, the incidence of posterolateral corner injuries is about 7% to 14% in ACL-deficient knees and that incidence is thought by some experts to be underestimated.

This is probably because it is challenging to correctly diagnose a concomitant lesion that occurs on the posterolateral corner, including the fibular collateral ligament (FCL), popliteus tendon (PLT), popliteofibular ligament (PFL), biceps femoris and posterolateral capsule. This type of diagnosis is difficult to make because the anatomy of this area of the knee is complex. Therefore, it has historically been considered the “dark side” of the knee.

It is critical to diagnose these injuries as soon as possible because an early diagnosis may make it possible to repair the disrupted tissues rather than perform a reconstruction, which may require autograft or allograft tissue. Moreover, when these injuries go undetected, recurrent instability in the knee occurs and cruciate ligament reconstructions tend to fail.

Physical examination

According to studies by Fornalski and colleagues and Geeslin and colleagues, the patient usually presents with a history of acute trauma related to motor vehicle accidents or sports injuries. Blunt trauma to the anteromedial aspect of the tibia with a posterolateral directed force and knee hyperextension and external tibial rotation over a fixed foot are the most common injury mechanisms. In acute cases, pain over the joint line, ecchymosis, swelling and inability to walk are the main complaints. In chronic cases, instability with side-to-site activities and limited ability to resume sports activities are the most common complaints.

A detailed physical examination should be performed based on several studies, which indicated that gait must be assessed for varus thrust or hyperextension patterns. Furthermore, limb alignment must be evaluated because this could change the surgical plan for patients with chronic injuries. Several tests have been described for assessing posterolateral instability and include the varus stress test, posterolateral drawer test, reverse pivot-shift test, dial test and external rotation recurvatum test. Both the posterior drawer test and the dial test have been reported to be effective clinical tests to make a diagnosis.

Research has shown that trauma related to isolated and combined posterolateral corner (PLC) injuries can affect the posterior neurovascular bundle. A popliteal artery injury may be present in about one-third of knee dislocations. For this reason, assessment of distal pulses at the foot and ankle are important parts of the initial evaluation. The peroneal nerve also may be injured. Overall, 13% of patients with PLC injuries present with symptoms that must be identified and documented. It is essential to perform a physical exam that records paresthesias or numbness over the dorsum of the foot and the first web space, muscle force grading for ankle dorsiflexion, foot eversion and great toe extension.

Recommended imaging views

A routine radiographic workup with standing anteroposterior (AP), lateral and axial views can help rule out the presence of fractures. Limb alignment and the weight-bearing axis should be evaluated using standing long-leg AP radiographs. Varus and PCL stress radiographs can be used to objectively quantify the extent of lateral compartment varus gapping and a combined PLC and PCL injury, respectively.

MRI aids in the identification of concurrent lesions, such as meniscus tears, cartilage lesions and occult fractures. It has been shown in studies to have 90% sensitivity and specificity for iliotibial band, biceps tendon, FCL and PLT injuries. Moreover, bone bruise patterns can provide added insights into the present injury. Studies show these are found in 81% of PLC injuries and often occur on the anteromedial femoral condyle.

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Repair or reconstruction decision

Although there is strong evidence in favor of PLC reconstruction over repair, in some cases, repair should be considered. The factors that favor repair are typically related to the time from injury.

Repair should be considered for avulsed structures after acute injuries that present within the first 3 weeks. After 3 weeks, the development of scar tissue, tissue retraction and the reduced quality of ligaments and tendons may preclude performing a primary repair. As there is increased likelihood of suture pullout or repair attenuation, primary repair should not be done for a midsubstance FCL or PLT tear. Bony avulsions of the PLT, in the absence of tendon midsubstance tearing or attenuation, can be repaired via a popliteus recess procedure. Avulsion fractures of the fibular attachment of the biceps femoris can be secured with suture anchors. It is also possible to use horizontal mattress sutures to repair tears in the popliteomeniscal fascicles or coronary ligament.

The indications for lateral knee reconstruction include acute grade III midsubstance FCL and PLT tears, and acute and chronic grade III PLC injuries (FCL, PLT and PFL). If a varus axis deformity is seen on long-leg AP radiographs in a patient who has chronic lateral instability, then a staged surgical reconstruction should be performed. The reconstruction should start with a medial opening wedge high tibial osteotomy (HTO) and then include a ligament reconstruction 6 months afterward, if the lateral instability does not resolve with the HTO. In one study, 38% of patients who had chronic PLC knee injuries and underwent a medial opening wedge HTO experienced the resolution of their instability and did not need any subsequent reconstruction.

Various PLC reconstruction techniques have been described by investigators and are categorized as either isometric or anatomic techniques. Anatomic techniques use two femoral tunnels centered on the FCL and PLT attachments, based on published studies about these techniques. The isometric techniques involve a biceps femoris tenodesis, an arcuate complex advancement and a single femoral tunnel reconstruction. In addition to total PLC reconstruction, isolated FCL reconstruction procedures — either anatomic or isometric, are possible.

Timing is critical

Postoperative restrictions include no weight-bearing for the first 6 weeks and the patient is restricted from performing any activity that puts varus or external rotation forces on the knee. Range of motion (ROM) should be initiated on postoperative day 1 from 0° to 90° to minimize the risk of arthrofibrosis. During the first 2 weeks after surgery, quadriceps sets and straight leg raises should be performed four times per day with the patient in a knee immobilizer brace. After 2 weeks, straight leg raises and quadriceps sets can be completed without wearing the immobilizer brace if no extensor lag is present. Gradually, ROM should be increased after 2 weeks, with the goal being for the patient to achieve full ROM at 6 weeks. Controlled weight-bearing is initiated on the surgical leg at 6 weeks postoperatively and it is increased as tolerated. During that time, the use of crutches is progressively discontinued.

After knee ROM reaches 110°, the patient can begin stationary biking. At 12 weeks, the rehabilitation emphasis is transitioned to building muscular strength through low-impact exercises. The goal of those exercises should be to return the patient to full strength by 6 months. During this time, varus stress radiographs should be obtained to determine whether there is any graft attenuation or failure. A patient’s full return to activity should be based on his or her passing a functional test and obtaining physician clearance after subjective and objective assessment of lateral knee stability.

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For more information:
Filippo Familiari, MD, can be reached at Department of Orthopaedic and Trauma Surgery, “Magna Græcia” University of Catanzaro, Campus Universitario “Salvatore Venuta,” Viale Europa - Loc. Germaneto (88100) Catanzaro, Italy; email: filippofamiliari@gmail.com.
Roberto Simonetta, MD, can be reached at Department of Orthopaedic and Trauma Surgery, C.O.T. (Cure Ortopediche Traumatologiche), Via Ducezio,1, 98124 Messina, Italy; email: simonberto@gmail.com.

Disclosures: Familiari and Simonetta report no relevant financial disclosures.