**Abstract**

The anterolateral ligament (ALatL) of the knee is an under investigated soft tissue structure of the knee with its existence within the body mostly unknown to the layperson. It was determined that the ALatL has a femoral origin which is either anterior and distal, or posterior and proximal to the origin of the lateral collateral ligament, varying depending on the specimen being investigated. While there have been several studies recently conducted investigating the function of the ALatL of the knee through analysing a number of different factors including origin and insertion along with both physical and mechanical properties, there is still much mystery surrounding this ligament. Hence, further research should be conducted to accurately quantify the importance of the anterolateral ligament to internal tibial rotation stability, and the effect that a damaged anterolateral ligament can have on the stresses experienced by surrounding soft tissue structures of the knee.

**Keywords:** anterolateral ligament, knee, biomechanics, anterior cruciate ligament

## **1. Introduction**

In late 2013, the world at large was told of a "new ligament" that had been discovered in the human knee, for example by ScienceDaily [1], the New York Times [2] and the British Broadcasting Corporation [3]. The subject of these stories was an anatomical paper by Claes and co-workers [4] that described the anterolateral ligament (ALatL) of the knee.

Looking at the interest generated by this paper does suggest some novelty in this description. At the time of writing, this paper had been cited by 172 other papers on PubMed. **Figure 1** shows the number of papers listed on PubMed, by year, that resulted from a search for the terms "anterolateral ligament" and "knee". The results of this search show a tremendous amount of interest by the scientific community for one small ligament.

Claes and colleagues' study was anatomical, and although it was hypothesised (not tested) that the ALatL is a restraint to internal rotation of the tibia, it could only point to the ligament's "suggested role" in anterior cruciate ligament (ACL) injury-associated instability, highlighting the need for further kinematic evidence.

Two of the reasons for this interest in the anterolateral ligament included (1) a "close association" of anterolateral and anterior cruciate ligament injuries, and (2) residual rotatory instability following anterior cruciate ligament reconstruction [5].

#### **Figure 1.**

*Number of papers listed on PubMed, by year, that resulted from a search for the terms "anterolateral ligament" and "knee".*

It is unclear just how close the association is between the ALatL and ACL injuries [5], although this is not the forum for an in depth analysis. Magnetic Resonance Imaging (MRI) is used to diagnose ALatL injuries, e.g., Claes et al. [6], but MRI analysis has yet to consistently describe the complex anatomy of the lateral side of the knee [7]. Although identification of the ligament itself on MRI appears to be a reliable process, identifying an injury to the ALatL is much less reliable [8].

Thus, it remains to be seen whether it can be established how often the ALatL is injured at the same time as the ACL, or whether an ACL-deficient knee also has an ALatL deficiency.

#### **1.1 Background**

The knee of the human body is often considered the most complex joint in the body. Major functions of the knee joint are to provide movement of the lower limb and weight bearing, distributing forces from the femur to tibia. The knee joint provides a range of movements between the femur and tibia through a number of soft tissue structures that articulate motion about the medial and lateral condyles of the two bones. The knee is capable of providing movement in six degrees of freedom with the major movement being flexion/extension with a general range of motion of 0–140°. The joint is most stable when it is in the locked, extended position, however is not mobile. Therefore, this can be the cause of many soft tissue injuries when an external force acts on the knee while it is in this extended position.

Depending on the location, magnitude and direction of the external force applied, damage to different ligaments will occur. This generally occurs when they become taut and overloaded with force. There are essentially eight major ligaments that make up the knee including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL), patellar ligament, oblique popliteal ligament, arcuate popliteal ligament and the "new" anterolateral ligament (ALatL). All of these ligaments provide stability to the knee depending on their attachment and insertion sites, along with their physical and mechanical properties.

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*The Biomechanics of the Anterolateral Ligament DOI: http://dx.doi.org/10.5772/intechopen.92055*

with the anterior cruciate ligament.

**2. Literature review**

**2.2 Origin and insertion**

disregarded [4].

This chapter will therefore investigate the properties of the anterolateral ligament of the knee to determine the main functionality it provides. The focus of the chapter will take a biomechanical approach to investigating the anterolateral ligament through the analysis of the physical and mechanical properties. The chapter will conclude with a discussion on its possible injury mechanism and its association

Initial research has been conducted to analyse the findings of research papers investigating a number of different features of the ALatL. Firstly, the presence of the ligament is discussed with existing speculation about the existence of the anterolateral ligament in all specimens. Research presenting data about both the physical dimensions of the ligament as well as the mechanical properties will be

The anterolateral ligament of the knee is a recently defined ligament in the scheme of anatomical history [4], with it only recently being fully recognised as a ligament [9]. There is still confusion surrounding the existence of the ALatL in all specimens with some studies reporting the ligament being found in all subjects, while others have reported discoveries in only as little as 50% of those investigated. The contradiction between studies continues with some demonstrating the ALatL is a capsular structure which has attachment below the lateral meniscus, while others

A study conducted by Claes et al. [4] investigated 41 specimens with an ALatL able to be located in 40 of the 41 samples. In all specimens the major origin of the ligament was located to be fixed to the lateral femoral epicondyle, anterior to the origin of the LCL and proximal and posterior to the insertion of the popliteus tendon. The insertion on the anterolateral tibia was most commonly located midway between Gerdy's tubercle and the fibular head. Within this investigation, all specimens with deficiencies were excluded and knees with a damaged ACL also

Kennedy et al. [5] conducted an anatomic dissection of 15 non-paired freshfrozen cadaveric knees to investigate the ALatL. Some major findings from the study included that the ALatL femoral attachment was consistently located posterior and proximal to the attachment of the LCL and the lateral femoral epicondyle. The anterolateral tibial attachment was located approximately midway between the

A later study conducted by Kosy et al. [9] investigated the presence of the ALatL in 11 specimens to investigate its role within the knee structure. In this study they were able to identify the ALatL in 10 of the 11 specimens. The one specimen, which the ALatL was not able to be identified was also the only specimen which did not have the ACL intact, indicating the ALatL may have been damaged simultaneously in this example. Of the 10 specimens investigated, there was slight variation in the

centre of the Gerdy's tubercle and the anterior margin of the fibular head.

have stated it is extra-capsular, with no such attachment at this site [9].

investigated to determine the functionality of the ligament.

**2.1 Presence of the anterolateral ligament**

**1.2 Aim**

*The Biomechanics of the Anterolateral Ligament DOI: http://dx.doi.org/10.5772/intechopen.92055*

### **1.2 Aim**

*Recent Advances in Biomechanics*

It is unclear just how close the association is between the ALatL and ACL injuries [5], although this is not the forum for an in depth analysis. Magnetic Resonance Imaging (MRI) is used to diagnose ALatL injuries, e.g., Claes et al. [6], but MRI analysis has yet to consistently describe the complex anatomy of the lateral side of the knee [7]. Although identification of the ligament itself on MRI appears to be a reliable process, identifying an injury to the ALatL is much less

*Number of papers listed on PubMed, by year, that resulted from a search for the terms "anterolateral ligament"* 

Thus, it remains to be seen whether it can be established how often the ALatL is injured at the same time as the ACL, or whether an ACL-deficient knee also has an

The knee of the human body is often considered the most complex joint in the body. Major functions of the knee joint are to provide movement of the lower limb and weight bearing, distributing forces from the femur to tibia. The knee joint provides a range of movements between the femur and tibia through a number of soft tissue structures that articulate motion about the medial and lateral condyles of the two bones. The knee is capable of providing movement in six degrees of freedom with the major movement being flexion/extension with a general range of motion of 0–140°. The joint is most stable when it is in the locked, extended position, however is not mobile. Therefore, this can be the cause of many soft tissue injuries when an external force acts on the knee while it is in this extended position. Depending on the location, magnitude and direction of the external force applied, damage to different ligaments will occur. This generally occurs when they become taut and overloaded with force. There are essentially eight major ligaments that make up the knee including the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL), patellar ligament, oblique popliteal ligament, arcuate popliteal ligament and the "new" anterolateral ligament (ALatL). All of these ligaments provide stability to the knee depending on their attachment and insertion sites, along with

**94**

their physical and mechanical properties.

reliable [8].

**Figure 1.**

*and "knee".*

ALatL deficiency.

**1.1 Background**

This chapter will therefore investigate the properties of the anterolateral ligament of the knee to determine the main functionality it provides. The focus of the chapter will take a biomechanical approach to investigating the anterolateral ligament through the analysis of the physical and mechanical properties. The chapter will conclude with a discussion on its possible injury mechanism and its association with the anterior cruciate ligament.

### **2. Literature review**

Initial research has been conducted to analyse the findings of research papers investigating a number of different features of the ALatL. Firstly, the presence of the ligament is discussed with existing speculation about the existence of the anterolateral ligament in all specimens. Research presenting data about both the physical dimensions of the ligament as well as the mechanical properties will be investigated to determine the functionality of the ligament.

#### **2.1 Presence of the anterolateral ligament**

The anterolateral ligament of the knee is a recently defined ligament in the scheme of anatomical history [4], with it only recently being fully recognised as a ligament [9]. There is still confusion surrounding the existence of the ALatL in all specimens with some studies reporting the ligament being found in all subjects, while others have reported discoveries in only as little as 50% of those investigated. The contradiction between studies continues with some demonstrating the ALatL is a capsular structure which has attachment below the lateral meniscus, while others have stated it is extra-capsular, with no such attachment at this site [9].

#### **2.2 Origin and insertion**

A study conducted by Claes et al. [4] investigated 41 specimens with an ALatL able to be located in 40 of the 41 samples. In all specimens the major origin of the ligament was located to be fixed to the lateral femoral epicondyle, anterior to the origin of the LCL and proximal and posterior to the insertion of the popliteus tendon. The insertion on the anterolateral tibia was most commonly located midway between Gerdy's tubercle and the fibular head. Within this investigation, all specimens with deficiencies were excluded and knees with a damaged ACL also disregarded [4].

Kennedy et al. [5] conducted an anatomic dissection of 15 non-paired freshfrozen cadaveric knees to investigate the ALatL. Some major findings from the study included that the ALatL femoral attachment was consistently located posterior and proximal to the attachment of the LCL and the lateral femoral epicondyle. The anterolateral tibial attachment was located approximately midway between the centre of the Gerdy's tubercle and the anterior margin of the fibular head.

A later study conducted by Kosy et al. [9] investigated the presence of the ALatL in 11 specimens to investigate its role within the knee structure. In this study they were able to identify the ALatL in 10 of the 11 specimens. The one specimen, which the ALatL was not able to be identified was also the only specimen which did not have the ACL intact, indicating the ALatL may have been damaged simultaneously in this example. Of the 10 specimens investigated, there was slight variation in the

femoral origin of the ALatL, with it found to be posterior and proximal to the LCL attachment in six knees, anterior and distal in three knees, and at the same site in one knee. The tibial attachment was more consistent in location, and was found to be a mean 17.7 (±2.95) mm from Gerdy's tubercle and 12.3 (±3.55) mm from the fibular head.

Helito et al. [10] stated that there is some controversy regarding the femoral attachment site of the ALatL around whether it is anterior and distal or posterior and proximal to the LCL attachment site. Despite this, the tibial attachment site is however consistently defined as being between the Gerdy's tubercle and the fibular head.

In conclusion, studies conducted by Claes et al. [4], Kennedy et al. [5] and Kosy et al. [9] found some discrepancy between the femoral origin of the ALatL and Helito et al. [10] stated that this was a common trait. Claes et al. [4] found the origin to be located anterior and distal to the origin of the LCL, compared to research conducted by Kennedy et al. [5] and Kosy et al. [9] who agreed that the most

#### **Figure 2.**

*Sketch of the anterolateral aspect of the knee showing the anterolateral ligament relative to other soft tissue structures. ALatL = anterolateral ligament; GT = Gerdy's tubercle; LCL = lateral collateral ligament; LFE = lateral femoral epicondyle; LM = lateral meniscus; PrTFJ = proximal tibiofibular joint; and TibT = tibial tubercle.*

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*The Biomechanics of the Anterolateral Ligament DOI: http://dx.doi.org/10.5772/intechopen.92055*

the lateral side of the knee.

**2.3 Physical dimensions**

ently during measurement.

**3. Mechanical properties**

extensional stiffness of 2.60 (±0.93) N.

the various studies discussed.

stance tear and bony avulsion of the tibial attachment.

common origin site was posterior and proximal to the LCL attachment. Kosy et al. [9] did however define the origin, in three of the 10 specimens, to be anterior and distal to the ALatL, which agreed with the Claes et al. [4] findings. Hence, it must therefore be concluded that there is variance in the origin of the ALatL in different knee specimens. All four sources however agreed the anterolateral tibial insertion of the ALatL was roughly midway between Gerdy's tubercle and the fibular head [4, 5, 9, 10]. **Figure 2** shows an image that highlights the position of the ALatL on

Claes et al. [4] found that the measured mean length of the ALatL while in neutral rotation at a flexion angle of 90° was 41.5 (±6.7) mm and in extension was 38.5 (±6.1) mm. This therefore shows that there is some tension in the ALatL during flexion of the knee. Further testing found that the ALatL was mostly in tension while the knee was in a flexed position with an internal rotation applied. The mean width of the ALatLs' investigated by Claes et al. [4], was 6.7 (±3.0) mm and thickness 1.3 (±0.6) mm. Kosy et al. [9] found that of the 10 specimens that the ALatL was able to be located and for a knee flexion angle of 30° and neutral rotation, the mean dimensions were length 40.1 (± 5.53) mm, width 4.63 (±1.39) mm and thickness 0.87 (±0.18) mm. Hence, the values found by Claes et al. [4] and Kosy et al. [9] were similar while also taking into consideration the knee was positioned differ-

Zens et al. [11] conducted a biomechanical analysis of the ALatL to determine its mechanical properties allowing for a better understand of its role. Four specimens were investigated in the study. When a load was applied, it was found that all four specimens showed an inter-ligamentous failure at approximately one third of the ALatL's length, distal from the femoral insertion site. The mean ultimate

mean ultimate extension distance of 11.89 (±1.56) mm, hence, resulting in a mean

Helito et al. [10] also investigated the strength and stiffness of the ALatL of the knee through completing a biomechanical study. The methodology of testing involved 14 knee specimens of which the ALatL was tested for its tensile strength. Throughout testing the strength at the maximum resistance limit, deformation and stiffness were all measured. The mean maximum strength of the ALatL was found to be 204.8 (±114.9) N. The stiffness was 41.9 (±25.7) N/mm and the deformation of the ALatL was 10.3 (±3.5) mm [10]. **Table 1** shows a summary of the findings from

The mean maximum strength of the ALatL varied quite significantly between studies with Zens et al. [11] recording a much smaller strength value compared to other sources. Helito et al. [10] had a large variance in strength values from 89.9– 319.7 N outlining how much it can vary between specimens. Zens et al. [11] however detailed that the ACL has been proven to have a higher ultimate tensile strength in

Results from a study conducted in 2015 discovered that the average maximum load that the ALatL was able to handle during a pull-to-failure test was 175 N with a mean stiffness of 20 N/mm [5]. Failure of the ligament occurred through several mechanisms including ligamentous tear at the femoral or tibial origin, mid-sub-

and the

load to failure was 49.90 (±14.62) N, ultimate tension of 32.78 N/mm2

#### *The Biomechanics of the Anterolateral Ligament DOI: http://dx.doi.org/10.5772/intechopen.92055*

common origin site was posterior and proximal to the LCL attachment. Kosy et al. [9] did however define the origin, in three of the 10 specimens, to be anterior and distal to the ALatL, which agreed with the Claes et al. [4] findings. Hence, it must therefore be concluded that there is variance in the origin of the ALatL in different knee specimens. All four sources however agreed the anterolateral tibial insertion of the ALatL was roughly midway between Gerdy's tubercle and the fibular head [4, 5, 9, 10]. **Figure 2** shows an image that highlights the position of the ALatL on the lateral side of the knee.
