811.BJBJR Follow us @BoneJointRes Freely available online OPEN ACCESS BJR KNEE The anterolateral ligament is a secondary stabilizer in the knee joint A VALidated COMPUtatiONAL MODEL OF THE BIOmechanicaL EFFects OF A DEFicient ANTERIOR crUciate LIGAMENT AND ANTEROLateraL LIGAMENT ON KNEE JOINT Kinematics K-T. Kang, Objectives Y-G. Koh, The aim of this study was to investigate the biomechanical effect of the anterolateral liga- K-M. Park, ment (ALL), anterior cruciate ligament (ACL), or both ALL and ACL on kinematics under C-H. Choi, dynamic loading conditions using dynamic simulation subject-specific knee models. M. Jung, Methods J. Shin, Five subject-specific musculoskeletal models were validated with computationally predicted S-H. Kim muscle activation, electromyography data, and previous experimental data to analyze effects of the ALL and ACL on knee kinematics under gait and squat loading conditions. Department of Orthopedic Surgery, Results Arthroscopy and Joint Anterior translation (AT) significantly increased with deficiency of the ACL, ALL, or both Research Institute, structures under gait cycle loading. Internal rotation (IR) significantly increased with defi- Yonsei University ciency of both the ACL and ALL under gait and squat loading conditions. However, the defi- ciency of ALL was not significant in the increase of AT, but it was significant in the increase College of Medicine, of IR under the squat loading condition. Seoul, South Korea Conclusion The results of this study confirm that the ALL is an important lateral knee structure for knee joint stability. The ALL is a secondary stabilizer relative to the ACL under simulated gait and squat loading conditions. Cite this article: Bone Joint Res 2019;8:509–517. Keywords: Anterolateral ligament, Anterior cruciate ligament, Computational analysis Article focus Computational analysis study was carried Assessment and comparison of the ante- out without clinical data. rolateral ligament (ALL), anterior cruciate ligament (ACL), or both ALL and ACL on Introduction kinematics under dynamic loading Injury of the anterolateral complex in the conditions. knee joint is often accompanied by anterior cruciate ligament (ACL) rupture.1-3 This is Key messages usually treated surgically using standard pro- ALL is a secondary stabilizer relative to the cedures that have improved over several dec- ACL under simulated gait and squat load- ades.4-7 However, residual anterolateral ing conditions. rotational instabilities (ALRI) negatively cor- ACL and ALL work independently and relate with functional outcomes and remain synergically in the knee joint under gait challenging to treat.4,8,9 Despite the inherent and squat loading conditions. limitations of biomechanical studies, it has Correspondence should be sent to S-H. Kim; email: been suggested that the ALL may contribute [email protected] Strengths and limitations to the anterolateral stability of the knee joint doi: 10.1302/2046-3758.811. Our simulation was performed using five as a secondary stabilizer by preventing ante- BJR-2019-0103.R1 different models, rather than using a sin- rolateral subluxation of the proximal tibia on Bone Joint Res 2019;8:509–517. gle representative model. the femur.4,8,10 Several studies have reported VOL. 8, NO. 11, NOVEMBER 2019 509 510 K-T. KANg, Y-G. KOH, K-M. PARk, C-H. CHOI, M. JUNG, J. SHIN, S-H. KIM that the ALL is a well-defined and distinct ligamentous ACL, deficient ALL, or deficient ACL and ALL under gait structure of the knee joint.4,11,12 Histological examination and squat loading conditions. We hypothesized that the revealed that the ALL consists of compact collagen fibres ALL is an important lateral knee structure for knee joint in a parallel orientation, compatible with ligamentous or stability during daily dynamic activity. tendinous tissues.12 The presence of the ALL in previous anatomical studies varied from 83% to 100%,13 but it Patients and Methods should be noted that the ALL designation has been used Experimental procedures. After receiving approval from inconsistently with regard to its precise insertions.4,14,15 the hospital’s institutional review board (3-2016-0271) A correlation between ALL injuries and ACL ruptures and written informed consent from all subjects, subject- has been postulated to underlie anterolateral rotatory specific data were used to develop subject-specific MSK instability, leading to a positive pivot-shift test result.4,8 In models, and EMG sensors were used for motion capture. a previous biomechanical study, ALL damage led to knee Four male subjects and one female subject who had no instability at high flexion. Furthermore, other studies sug- previous medical history of lower limb problems partici- gested that the ALL is responsible for the Segond avulsion pated in this study. The mean age, height, and weight of fracture, a well-known radiological sign of an ACL tear.16-18 subjects were 33.0 years (sd 4.4; 26 to 36), 175 cm (sd Simultaneous ALL and ACL tears have been theorized to 7.4; 163 to 182), and 75.6 kg (sd 6.7; 65 to 83), respec- occur due to a common mechanism of injury involving tively. The subjects performed gait and squatting activi- excessive internal rotation (IR) torque.2 Parsons et al16 ties, and ground reaction forces were measured using a performed a biomechanical study to investigate the func- force plate. In addition, tracks of marker locations were tion of the ALL. They reported that the ALL made a large measured using a 3D motion capture system (Vicon, contribution to IR stability in flexion, but contributed Oxford, United Kingdom) (Fig. 1). EMG signals were minimally to anterior tibial translational stability from 0° recorded from the following muscles using an EMG sen- to 90° of flexion.16 Saiegh et al19 found that dissection of sor (Delsys, Boston, Massachusetts): gluteus maximus, the ALL in an ACL-deficient knee did not increase instabil- rectus femoris, vastus lateralis, biceps femoris, semimem- ity in a cadaveric model. Schon et al20 suggested that an branosus, gastrocnemius medialis, tibialis anterior, and anatomical ALL reconstruction in conjunction with an soleus medialis. Raw data from the EMG signals were ACL reconstruction resulted in joint overconstraint. transformed into muscle activation data by root mean Therefore, the ability of combined ACL and ALL recon- square analysis.22 structions to safely restore native joint kinematics without Computational model. The five subject-specific models causing joint overconstraint is unclear.20 However, Thein were developed using AnyBody version 6.0.5 (AnyBody et al,21 based on a biomechanical study, found that the Technology, Aalborg, Denmark), a commercial software ALL carried minimal load during the pivot shift, Lachman, package for MSK simulation analysis. The generic lower and anterior drawer tests. Furthermore, Tavlo et al11 limb MSK model is based on the Twente Lower Extremity found that ALL was a significant stabilizer of tibial inward Model anthropometric database.23 The MSK model is rotation. Reconstruction of a torn ALL in ACL-reconstructed actuated by approximately 160 muscle units. It has been knees significantly improved inward rotational stability. previously validated for predicting muscle and joint reac- As can be seen from the above review of previous tion forces in human lower limbs during locomotion.24-26 research, the biomechanical effects of the ALL are still 3D bone and soft-tissue models were reconstructed controversial. However, to the best of our knowledge, from CT and MRI scans in our previous study.27-29 By the literature has seldom investigated the kinematic using 3D femoral and tibial models of the five subjects, changes in response to deficiency of the ALL, ACL, or the femur and tibia in AnyBody were scaled with non- both ligaments during daily dynamic activities such as linear radial basis functions as scaling laws. The remain- walking and squatting. ing parts were scaled using an optimization scheme that The objective of this study was to develop and vali- minimizes the difference between the model markers and date a subject-specific musculoskeletal (MSK) model recorded marker positions. The knee joint in this study with 12-degrees-of-freedom motion at both the tibio- was considered to have 12 degrees of freedom (TF, six; femoral (TF) and patellofemoral (PF) joints based on data PF, six). The hip and ankle joints were considered to have from four healthy male subjects and one healthy female three and two degrees of freedom, respectively. subject. First, to validate the computational model, pre- Ligament insertion points were also observed in the MRI dicted muscle activation and corresponding electromyo- sets and descriptions can be found in the literature. Two graphy (EMG) recordings were compared. In addition, experienced orthopaedic surgeons (YGK and SHK) deter- the anterior drawer test results for an intact condition, mined the locations of the ligaments independently.30-36 and for both ACL and ALL deficiency, were compared The attachment points in AnyBody model were modified with previous experimental results. Second, kinematics using the subject-specific attachment sites. As shown in were compared for anteroposterior (AP) translations and Figure 2, the following 21 ligament bundles were mod- internal-external (IE) rotations with respect to a deficient elled: the ACL (anteromedial bundle of the ACL (aACL), BONE & JOINT RESEARCH THE ANTEROLATERAL LIGAMENT IS A SECONDARY STABILIZER IN THE KNEE JOINT 511 z 4 x 3 x 3 z 1 3 y 2 2 x 1 4 2 x 1 y y y x 2 y y z z z z Fig. 1a Fig. 1b Schematic of subject-specific musculoskeletal models during a) gait and b) squat loading conditions. posterolateral bundle of the ACL (pACL)); posterior cruci- Where f(ε) is the current force, k is the stiffness, ε is the ate ligament (PCL; anterolateral bundle of the PCL (aPCL), strain, and ε1 was assumed to be constant at 0.03.