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Does the anterolateral ligament play a biomechanical role in the function of the knee?
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Secondary stabilizer
To answer the main question posed, the anterolateral ligament (ALL) does have a biomechanical role in the function of the knee, acting as a secondary stabilizer to internal rotation and potentially anterior translation. This has been clearly demonstrated in a number of well-done biomechanical investigations. Thein and colleagues used a robotic manipulator to simulate pivot shift (PS) and anterior stability testing in cadavers with the ACL intact, sectioned and with the ACL and ALL sectioned. They reported significant increases in anterior translation and internal rotation between the ACL sectioned state and the ACL/ALL sectioned state. In addition, the load borne by the ALL was minimal in the ACL intact state but increased up to six-fold when the ACL was sectioned. Samuelson and colleagues similarly found that transecting the anterolateral structures in ACL-deficient cadaveric knees increased anterior translation and internal rotation, particularly at high flexion angles.
They also reported that reconstructing the ACL alone in knees with combined ACL and anterolateral structure sectioning did not return internal rotation values to the intact state. Another investigation reported small but significant differences in internal rotation and anterior translation between native cadaveric knees and ACL-reconstructed/ALL-sectioned knees undergoing simulated PS and anterior instability testing. Lastly, Rasmussen and colleagues concluded, “the ALL [is] an important lateral knee structure” after reporting that additional sectioning of the ALL after ACL transection leads to significant increases in axial plane translation as well as internal rotation, with reconstruction of the ALL resulting in a return of native knee stability. In summary, the literature concludes the ALL plays an important biomechanical role as a secondary stabilizer of internal rotation and likely also anterior translation of the knee.
Given these findings, there is an increasing body of literature evaluating the role of ALL reconstruction on knee motion. In general, a number of biomechanical investigations have reported that ALL reconstruction leads to a small amount of over-constraint in internal rotation, particularly at higher flexion angles, with only a few authors reporting otherwise. This has led to debate on whether surgeons should be performing concomitant ALL reconstructions at the time of ACL surgery. It is clear that in the presence of an ACL tear without ALL injury, a well-performed ACL reconstruction is capable of recreating native knee biomechanics. When there is damage to the anterolateral structures, however, biomechanical studies have demonstrated that even a well-performed ACL reconstruction may lead to a small amount of additional rotatory, and potentially anterior, motion. It is unknown, however, if these small residual deficits translate into clinical significance. Interestingly, Sonnery-Cottet and colleagues reported an approximately three-fold decrease in the rate of ACL graft re-rupture for those undergoing concomitant ACL and ALL reconstruction vs. isolated ACL reconstruction at a minimum of 2 years postoperatively. The decision for ALL reconstruction, however, must be weighed against the potential for over-constraint, which may limit physiologic motion and the screw-home mechanism, therefore potentially increasing the risk for joint arthrosis.
In summary, there should be little debate that the ALL plays a biomechanical role in knee stability, albeit as a secondary stabilizer. Controversy still exists regarding the indications for ALL reconstruction, but it may be appropriate for certain chronic or revision ACL reconstruction circumstances in patients with significant (grade 3 PS) instability in order to restore native knee motion and unload some forces from the ACL graft.
- References:
- Nitri M, et al. Am J Sports Med. 2016;doi:10.1177/0363546515620183.
- Rasmussen MT, et al. Am J Sports Med. 2016;doi:10.1177/0363546515618387.
- Samuelson M, et al. Am J Sports Med. 1996;24:492-497.
- Schon JM, et al. Am J Sports Med. 2016;doi:10.1177/0363546516669314.
- Sonnery-Cottet, et al. Am. J. Sports Med. 2017;doi:10.1177/0363546516686057.
- Spencer L, et al. Am J Sports Med. 2015;doi:10.1177/0363546515589166.
- Thein R, et al. J Bone Joint Surg Am. 2016;doi:10.2106/JBJS.15.00344.
Geoffrey D. Abrams, MD, is an assistant professor in the Department of Orthopedic Surgery and director of Stanford University Sports Medicine at Stanford University School of Medicine in Stanford, Calif.
Disclosure: Abrams reports no relevant financial disclosures.
More research needed
In my career, few knee “ligaments” with such a “wispy” anatomical makeup have received as much attention as the anterolateral ligament (ALL). In part, this has to do with our difficulty in defining the anatomic intricacies of the anterolateral knee. In addition, the large size and close proximity of the iliotibial band to the ALL also makes it hard to distinguish its relative contribution to knee stability. This is reflected in cadaveric biomechanical studies that have been done where some have shown significant contributions and others have not. In addition, we lack high-level clinical studies (ie, Level 1, Level 2) comparing ACL reconstructions with and without lateral extra-articular tenodesis (LET). Most of these studies suffer from being retrospective chart and survey reviews, lack comparison groups, have inconsistent definitions of the grade of pivot shift (PS) and lack sufficient clinical follow-up, including relevant physical exam findings and well-done radiographic and MRI images to assess degenerative changes over time. Until a randomized, controlled clinical trial with long-term follow-up is performed, it will be difficult to justify adding a LET to the knee treatment for most patients undergoing an ACL reconstruction.
That being said, I do believe that LET may have a selective role in certain settings. For example, I will perform a LET (modified Lemaire technique) when there is a true grade 3 PS in the setting of primary or revision ACL reconstruction. Nevertheless, I am still concerned about the potential to over-constrain the lateral compartment and the potential consequence of loss of motion (ie, extension) and/or lateral compartment arthritis. For me, an absolute contraindication to performing LET is any meniscal or articular cartilage deficiency in the lateral compartment. In this setting, I would consider combined lateral meniscus transplant with ACL reconstruction. Certainly, at this time, we cannot justify performing LET in most primary or revision ACL reconstructions until more convincing evidence is presented.
- References:
- Daggett M, et al. Am J Sports Med. 2014;doi:10.1177/0363546516638069.
- Kittl C, et al. Am J Sports Med. 2016;doi:10.1177/0363546516638070.
- Slette EL, et al. Arthroscopy. 2016;10.1016/j.arthro.2016.04.028.
- Song GY, et al. Arthroscopy. 2016;doi:10.1016/j.arthro.2015.08.038.
- Sonnery-Cottet, et al. Am J Sports Med. 2016;doi:10.1177/0363546515625282.
Christopher D. Harner, MD, is professor and vice chair of the Department of Orthopaedic Surgery at University of Texas Health Science Center, McGovern Medical School in Houston.
Disclosure: Harner reports no relevant financial disclosures.