By Emily Delzell
The anterolateral ligament (ALL) of the knee, a structure not well documented or consistently reported before the 2013 publication of a Belgian study, is a key stabilizer of internal rotation—though only when the knee is flexed at high angles—and may be an appropriate target for surgical reconstruction in certain patients, according to research from the University of Washington in Seattle epublished in January.
“Our study found that, once the knee has flexed more than thirty five degrees, the ALL is actually the most important structure that resists internal rotation,” said Peter Cavanagh, PhD, DSc, coauthor of the study assessing the ALL’s biomechanical function under internal rotation and anterior drawer knee flexion.
“It was always known there were some strong fibers in the anterolateral region of the knee joint capsule,” Cavanagh said. “The clue was the existence of the Ségond fracture—an avulsion fracture that sometimes pulled off a small piece of bone from the tibia in a severe knee injury where the ACL is damaged. Something more substantial than just the joint capsule was attached—and that something turned out to be the ALL.”
Cavanagh, professor and vice chair for research in University of Washington’s Department of Orthopedics and Sports Medicine, and his colleagues identified the ALL in 11 cadaveric knees using descriptions of its insertions from the 2013 study.
The researchers used a robotic testing system to apply 134 N of anterior drawer force at flexion angles between 0˚ and 90˚ and separately applied 5 Nm of internal rotation at the same angles. They also determined in situ forces on the ALL, anterior cruciate ligament (ACL), and lateral collateral ligament (LCL).
In all but one knee, the ALL attached just anterior to the insertion of the LCL on the femoral epicondyle, with the tibial attachment located posterior to the Gerdy tubercle and anterior to the tip of the fibular head on the ridge of the tibial plateau, the authors wrote. They also noted a convergence of the ALL with the LCL insertion on the femur proximally and confluent with the anterolateral joint capsule and the deeper lateral meniscus.
During internal rotation the ALL’s biomechanical contribution increased significantly with increasing flexion, while the ACL’s work significantly decreased. The ALL’s contribution outstripped the ACL’s when knee flexion angles exceeded 30˚.
During anterior drawer, ALL forces were significantly lower than ACL forces at all flexion angles. For both anterior drawer and internal rotation at all flexion angles, LCL forces were significantly lower than those of the ACL or ALL.
The American Journal of Sports Medicine epublished the study on January 2.
For a number of years, Cavanagh said, surgeons have suggested that structures that are both internal and external to the joint capsule should be repaired after serious knee injuries such as an ACL rupture.
“Our finding that the ALL is an important stabilizer of internal rotation again puts the emphasis on the need for an extra-articular repair when the ALL has been damaged, which is likely to be caused by excessive internal rotation and knee varus,” he said.
Robert F. LaPrade, MD, PhD, an orthopedic surgeon at The Steadman Clinic and chief medical officer at the Steadman Philippon Research Institute in Vail, CO, also agreed that ALL reconstruction is probably indicated in some patients.
“I believe that for patients in whom the ALL is found to be torn and who have significant rotatory instability, an attempt at a reconstruction based upon anatomic principles is reasonable, but definitely more study is necessary,” LaPrade told LER.
Cavanagh noted that, even after ACL repair, a damaged ALL could cause rotational knee instability at higher flexion angles that may be resolved by extra-articular repair of the ruptured ALL.
Claes S, Vereecke E, Maes M, et al. Anatomy of the anterolateral ligament of the knee. J Anat 2013;223(4):321-328.
Parsons EM, Gee AO, Spiekerman C, Cavanagh PR. The biomechanical function of the anterolateral ligament of the knee. Am J Sports Med 2015 Jan 2. [Epub ahead of print]