Is the anterolateral ligament the smoking gun to explain rotational knee laxity or just vaporware?

Since the publication of the ‘discovery’ of a new knee ligament in 2013, coined as anterolateral ligament (ALL), the scientific research into this ‘new’ anatomical structure has grown exponentially in the past years. The Journal of ISAKOS (JISAKOS) publishes in this issue three studies on the anatomy of the anterolateral capsule (ALC) of the knee and the biomechanics of the combined reconstruction of the anterior cruciate ligament (ACL) and the ALL. 4 The history of the ALL takes us more than one century back to Segond’s works, as well as to some other reports (earlier than 2013) of this structure. Despite much controversy and conflicting findings on the macroscopic anatomical, histological and MRI of the ALL, a consensus paper by international knee experts has characterised the ALL as a structure within layer 3 of the ALC. Nonetheless, if the ALL is really a distinct ligament structure or a thickening of the ALC remains open for debate. To better understand the phenotype of the ALC, Iseki et al evaluated the histology, immunohistochemistry and genetic expression of the ALC from paediatric specimens to investigate if there are any ligamentlike characteristics. They found no discernible histological and immunohistochemical characteristics consistent with a ligament phenotype and that the ligament genetic markers (scleraxis and tenomodulin) were largely absent and poorly expressed in the ALC. Their methodology still needs to be replicated in adult specimens, but their findings suggest that the ALC does not display ligamentlike characteristics and do not support the belief that there is a distinct ligament at the ALC. In a recent systematic review of MRI studies, high variability was found in the identification of the ALL, which appeared in 51%–100% of all assessed knees (with a very high intraobserver and interobserver reliability rates), and the entire portion of the ligament was often not seen. These findings suggest that the ALL may not really exist as a distinct ligament, which goes in line with several other publications. Being the case that the ALL was not a defined ligament, performing an anterolateral ligament reconstruction (ALLR) does not recreate the native anatomy of the knee, but should rather be considered as a lateral nonanatomical augmentation procedure. Lateral extraarticular tenodesis (LEAT) is being performed since the 1980s but has recently gained renewed interest. Lateral augmentation procedures—either LEAT or ALLR—are performed in the ACLdeficient knee in patients with highrisk profile of reinjury and aim to better control the knee internal rotation and decrease the risk of graft tear. The ALL strength varies between 49.9 N and 204.8 N, which is lower compared with the strength of the iliotibial band (487.9 N), ALC (319.7 N) or the distal iliotibial tract (769 N). The strength of the iliotibial band (as compared with the ALL) suggests that this structure would be more fitted to withstand the high rotational torques. Indeed, adding a LEAT significantly decreases the forces at the ACL graft, 29 but an ALLR produces only a modest decrease. The role of ALLR is still not well established and is currently not being broadly used in daily clinical practice, and thus, the biomechanical studies are still an important step to investigate the effect of adding an ALLR on the knee stability and contact pressures. Two of the studies published in this JISAKOS issue explore the biomechanics of anterolateral augmentation procedures in the setting of an ACLdeficient knee. 4 Neri et al performed a cadaveric biomechanical study comparing ACL reconstruction isolated and combined with five different anterolateral augmentation procedures—ALLR and modified versions of Ellison, deep Lemaire, superficial Lemaire and MacIntosh LEAT procedures. They found that in the setting of an anterolateraldeficient knee, only the ALLR and Ellison procedures restored internal rotation laxity to the native intact state over the full range of knee flexion. The deep and superficial Lemaire and MacIntosh, although better controlling internal rotation, overconstrained the knee. The same group performed a pilot biomechanical study on the tibiofemoral lateral compartment contact pressures after ACL reconstruction combined with the same five anterolateral procedures described in Neri and colleagues. They found that the ACL reconstruction combined with ALLR or with the Ellison procedure did not change the contact pressures, while the Lemaire (either deep or superficial) and MacIntosh procedures increased the contact pressure during tibial internal rotation. However, this study only includes four specimens which highly increases the risk of type II error,and this should be taken into account when interpreting their findings. In opposition to their findings, conflicting evidence has shown no significant increase in the tibiofemoral compartment after ACL reconstruction with LEAT and, despite that the findings from Neri et al that suggest an increased risk of knee overconstrain and subsequent risk of cartilage wear after ACL reconstruction with Clínica do Dragão, EspregueiraMendes Sports Centre FIFA Medical Centre of Excellence, Porto, Portugal Dom Henrique Research Centre, Porto, Portugal School of Medicine, University of Minho, Braga, Portugal ICVS/3B’sPT Government Associate Laboratory, Braga/ Guimarães, Portugal 3B’s Research GroupBiomaterials, Biodegradablesand Biomimetics, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, University of Minho, AvePark, Parque de Ciência e Tecnologia, Zona Industrial da Gandra, Barco, Guimarães, Portugal