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Fig. 1 Illustration demonstrating posterior (A) and lateral (B) view of an isolated fibular collateral ligament (FCL) reconstruction procedure demonstrating the reconstructed FCL using a semitendinosus graft. PLT, popliteus tendon; PFL, popliteofibular ligament Reproduced with permission from Coobs B, LaPrade RF, Griffith C, Nelson BJ: Biomechanical analysis of an isolated fibular (lateral) collateral ligament reconstruction using an autogenous semitendinosus graft. Am J Sports Med 2007;35(9):1521-1527.

AAOS Now

Published 2/1/2013
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Terry Stanton

Shedding Light on the “Dark Side”of the Knee

OREF award winner summarizes years of research on the knee’s posterolateral corner

For years, Robert F. LaPrade, MD, PhD and colleagues, have sought to advance knowledge of the posterolateral corner of the knee (PLC) and find more effective treatment strategies for injuries to this challenging anatomic site. Their efforts were recognized with the 2013 Orthopaedic Research and Educational Foundation (OREF) Clinical Research Award.

The award recognizes Dr. La-Prade’s work in unraveling many of the mysteries surrounding “the dark side” of the knee, including insight into anatomy, biomechanics, reconstruction techniques, magnetic resonance imaging (MRI) protocols and clinical outcome assessments.

Many mysteries
According to Dr. LaPrade, complex knee surgeon at the Steadman Clinic in Vail, Colo., the PLC gained its “dark side” reputation from several factors.

“The anatomy was poorly understood, clinical diagnostic exams were mainly subjective, imaging techniques were not defined, and most surgical reconstruction procedures were not anatomically based or biomechanically validated,” he said. Yet few institutions were studying PLC injuries.

Developing an optimal surgical approach that would allow less traumatic identification of injuries was one of the initial goals of the research. Through anatomic studies, the researchers found that access to the main posterolateral knee structures could be obtained using the following incisions:

  • Laterally based hockey stick-shaped skin incision
  • A splitting incision of the superficial layer of the iliotibial band
  • Deeper dissection concurrent with a common peroneal nerve neurolysis
  • An incision through the biceps bursa

Seeking to define landmarks, attachment sites, and quantitative anatomical relationships, they identified 28 separate PLC component structures.

Study findings
The following points are among their findings:

The femoral attachment of the fibular collateral ligament (FCL) is not to the lateral epicondyle but to a small depression 1.4 mm proximal and 3.1 mm posterior to the lateral epicondyle. This suggests that variations in outcomes for surgery may be the result of use of nonanatomic attachment sites on the femur.

The FCL is most readily identified and accessed through a small horizontal incision into the biceps bursa, providing an access point for reconstruction.

The popliteus tendon is an essential primary stabilizer against external knee rotation, with both dynamic and static roles, essentially making it the “fifth ligament” of the knee.

The average distance between the femoral attachment sites of the FCL and the popliteus tendon is 18.5 mm—important for developing anatomic-based surgical reconstructions.

Reconstruction techniques that attempt to reconstruct both the FCL and the popliteus tendon with one femoral-based graft are at a high risk for failure or overconstraint, similar to what had been encountered for nonanatomic cruciate ligament reconstructions.

The iliotibial band, which is rarely damaged in PLC injuries, is a primary superficial landmark in the approach to the PLC.

Examination and imaging
Clinical examination for suspected PLC injuries should include the following:

  • External rotation recurvatum test (Positive findings suggest combined ACL and PLC injury.)
  • Varus stress test
  • Dial test (posterolateral rotation) at 30° and 90° of flexion
  • Posterolateral drawer test
  • Lachman test (Increased anterior translation in an anterior cruciate ligament [ACL]-deficient knee and increased posterior translation in a posterior cruciate ligament [PCL]-deficient knee indicate possible PLC injuries.)

They also found that the oblique popliteal and fabellofibular ligaments were primary ligamentous restraints to knee hyperextension, and they were able to develop a test to identify tears of the popliteomeniscal fascicles in patients with vague lateral knee pain.

To improve imaging of the area, the researchers developed an MRI technique that uses a high-field scanner with slices 2 mm thick and inclusion of the entire fibular head and styloid. The use of a coronal oblique imaging technique, angled along the course of the native popliteus tendon, was found to provide the best view of these structures and has been widely adopted.

In addition, arthroscopic evaluation of grade 3 PLC injuries is an effective adjunct and especially useful (and superior to the open method) for identifying injuries to the popliteus tendon femoral attachment, coronary ligament of the posterior horn of the lateral meniscus, the mid-third capsular ligament, and the popliteomeniscal fascicles.

Understanding the injury
The researchers next embarked on a series of animal and human studies to develop an in vivo model of PLC injuries. Animal models of posterolateral instability confirmed that grade 3 posterolateral injuries did not heal, although medial injuries often do.

“We believe this occurred secondary to the difference in the bony anatomy between the medial and lateral compartments of the knee,” they write. “The two convex opposing surfaces of the femur and tibia in the lateral compartment have an inherent bony instability, which is likely a major contributing factor for the lack of soft-tissue healing with posterolateral knee injuries in both the rabbit and canine models and human clinical experience.”

They also confirmed that instability due to an injured PLC led to early onset arthritis in the medial compartment.

The studies led to a number of important clinical advancements in the treatment of complex knee injuries. For example, patients who need either a ACL or PCL reconstruction should be carefully assessed for posterolateral knee injuries, because not treating the posterolateral injury concurrent with the reconstruction increases the risk for failure.

From their anatomic and biomechanical studies, the researchers developed anatomic techniques for reconstructing the FCL, popliteus tendon, and popliteofibular ligament using an Achilles tendon allograft, divided into two limbs with two separate bone plugs (Fig. 1). Biomechanical testing showed that the technique restored static stability to the knee for all applied loads.

Finally, they noted that in some PCL tears, the FCL remains intact, but the popliteus tendon needs to be reconstructed. The anatomic reconstruction they developed uses a semitendinosus autograft and restores stability to knees with this injury.

In summarizing the clinical lessons of their work, Dr. LaPrade and his coauthors wrote that “proper treatment of grade 3 PLC injuries requires a comprehensive understanding of the anatomy and clinically relevant biomechanics to synthesize the various clinical exams utilized to diagnose these injuries.” Stress radiographs, MRI scans, and arthroscopy may also be indicated.

In patients with chronic posterolateral knee instability and varus alignment, the varus alignment should be corrected before soft tissue reconstruction to prevent graft failure. For acute injuries, outcomes are best when intervention is performed in the first few weeks following injury; a combined hybrid repair of the biceps or lateral capsule, along with anatomic reconstructions of the FCL and/or popliteus tendon, provides excellent patient clinical and objective outcomes. For chronic PLC injuries, an anatomic PLC reconstruction restores objective stability to the knee and significantly improves patient outcomes.

Dr. LaPrade’s coauthors include Steinar Johansen, MD; Lars Engebretsen, MD, PhD; Chad J. Griffith, MD; Benjamin R. Coobs, MD; and Andrew G. Geeslin, MD.

Disclosure information: Dr. LaPrade—Arthrex; Knee Surgery; Sports Traumatology; Arthroscopy; American Journal of Sports Medicine; Dr. Engebretsen—DePuy, Arthrex, Nycomed, Smith & Nephew, British Journal of Sports Medicine, Acta Orthopaedica, Knee; Knee Surgery, Sports Traumatology, Arthroscopy, Journal of Bone and Joint Surgery–American. The other authors report no conflicts.

Terry Stanton is senior science writer at AAOS Now. He can be reached at tstanton@aaos.org

Bottom Line

  • A poor understanding of the anatomy of the PLC of the knee led to treatment failures due to the use of nonanatomic reconstruction techniques.
  • MRI studies should capture the entire fibular head and styloid region; bone bruises over the anteromedial knee should alert the clinician to a possible PLC injury.
  • Patients needing an ACL or PCL reconstruction should be assessed for PLC injury to reduce risk of reconstruction graft failure.
  • An autogenous semitendinosus graft will most closely reproduce the native strength of the FCL.

Additional Information
Kappa Delta/OREF Clinical Research Awards