Microstructural and Mechanical Properties of the Anterolateral Ligament of the Knee

Background: The variable anatomy and controversy of the anterolateral ligament (ALL) reflect the complex relationship among the anterolateral knee structures. Purpose/Hypothesis: The purpose was to quantify the microstructural and mechanical properties of the ALL as compared with the anterolateral capsule (ALC) and lateral collateral ligament (LCL). The primary hypotheses were that (1) there is no difference in these properties between the ALL and ALC and (2) the LCL has significantly different properties from the ALL and ALC. Study Design: Descriptive laboratory study. Methods: The LCL, ALL, and ALC were harvested from 25 cadaveric knees. Mechanical testing and microstructural analyses were performed using quantitative polarized light imaging. The average degree of linear polarization (AVG DoLP; mean strength of collagen alignment) and standard deviation of the angle of polarization (STD AoP; degree of variation in collagen angle orientation) were calculated. Results: Linear region moduli were not different between the ALC and ALL (3.75 vs 3.66 MPa, respectively; P > .99). AVG DoLP values were not different between the ALC and ALL in the linear region (0.10 vs 0.10; P > .99). Similarly, STD AoP values were not different between the ALC and ALL (24.2 vs 21.7; P > .99). The LCL had larger modulus, larger AVG DoLP, and smaller STD AoP values than the ALL and ALC. Of 25 knee specimens, 3 were observed to have a distinct ALL, which exhibited larger modulus, larger AVG DoLP, and smaller STD AoP values as compared with nondistinct ALL samples. Conclusion: There were no differences in the mechanical and microstructural properties between the ALL and ALC. The ALC and ALL exhibited comparably weak and disperse collagen alignment. However, when a distinct ALL was present, the properties were suggestive of a ligamentous structure. Clinical Relevance: The properties of the ALL are similar to those of a ligament only when a distinct ALL is present, but otherwise, for the majority of specimens, ALL properties are closer to those of the capsule. Variability in the ligamentous structure of the ALL suggests that it may be more important in some patients than others and reconstruction may be considered in selective patients. Further study is needed to better understand its selective role and optimal indications for reconstruction.

Paediatric knee anterolateral capsule does not contain a distinct ligament: analysis of histology, immunohistochemistry and gene expression

ObjectivesThe presence of a discrete ligament within the knee anterolateral capsule (ALC) is controversial. Tendons and ligaments have typical collagens, ultrastructure, transcription factors and proteins. However, these characteristics have not been investigated in paediatric ALC. The purpose of this study was to characterise the paediatric ALC in terms of tissue ultrastructure and cellular expression of ligament markers scleraxis (SCX)—a basic helix-loop-helix transcription factor—and the downstream transmembrane glycoprotein tenomodulin (TNMD), as compared with the paediatric lateral collateral ligament (LCL) and paediatric quadriceps tendon (QT). We hypothesised that, in comparison to the LCL and QT, the ALC would possess poor collagen orientation and reduced SCX and TNMD expression.Methods15 paediatric ALCs (age 6.3±3.3 years), 5 paediatric LCLs (age 3.4±1.3 years) and 5 paediatric QTs (age 2.0±1.2 years) from fresh cadaveric knees were used in this study. Fresh-frozen samples from each region were cryosectioned and then stained with H&E to evaluate collagen alignment and cell morphology. Expression of SCX and TNMD was determined by gene expression analysis and immunohistochemistry.ResultsThe histological sections of the paediatric LCL and QT showed well-organised, dense collagenous tissue fibres with elongated fibroblasts, while the ALC showed more random collagen orientation without clear cellular directionality. The aspect ratio of cells in the ALC was significantly lower than that of the LCL and QT (p<0.0001 and p<0.0001, respectively). The normalised distribution curve of the inclination angles of the nuclei in the ALC was more broadly distributed than that of the LCL or QT, indicating random cell alignment in the ALC. SCX immunostaining was apparent in the paediatric LCL within regions of aligned fibres, while the comparatively disorganised structure of the ALC was negative for SCX. The paediatric LCL also stained positive for TNMD, while the ALC was only sparsely positive for this tendon/ligament cell-surface molecule. Relative gene expression of SCX and TNMD were higher in the LCL and QT than in the ALC.ConclusionIn this study, a distinct ligament could not be discerned in the ALC based on histology, immunohistochemistry and gene expression analysis.Level of evidenceControlled laboratory study.

Biomechanical Assessment of a Distally Fixed Lateral Extra-articular Augmentation Procedure in the Treatment of Anterolateral Rotational Laxity of the Knee

Background: Most lateral extra-articular tenodesis (LET) procedures rely on passing a strip of the iliotibial band (ITB) under the fibular (lateral) collateral ligament and fixing it proximally to the femur. The Ellison procedure is a distally fixed lateral extra-articular augmentation procedure with no proximal fixation of the ITB. It has the potential advantages of maintaining a dynamic element of control of knee rotation and avoiding the possibility of overconstraint. Hypothesis: The modified Ellison procedure would restore native knee kinematics after sectioning of the anterolateral capsule, and closure of the ITB defect would decrease rotational laxity of the knee. Study Design: Controlled laboratory study. Methods: Twelve fresh-frozen cadaveric knees were tested in a 6 degrees of freedom robotic system through 0° to 90° of knee flexion to assess anteroposterior, internal rotation (IR), and external rotation laxities. A simulated pivot shift (SPS) was performed at 0°, 15°, 30°, and 45° of flexion. Kinematic testing was performed in the intact knee and anterolateral capsule–injured knee and after the modified Ellison procedure, with and without closure of the ITB defect. A novel pulley system was used to load the ITB at 30 N for all testing states. Statistical analysis used repeated measures analyses of variance and paired t tests with Bonferroni adjustments. Results: Sectioning of the anterolateral capsule increased anterior drawer and IR during isolated displacement and with the SPS (mean increase, 2° of IR; P < .05). The modified Ellison procedure reduced both isolated and coupled IR as compared with the sectioned state ( P < .05). During isolated testing, IR was reduced close to that of the intact state with the modified Ellison procedure, except at 30° of knee flexion, when it was slightly overconstrained. During the SPS, IR with the closed modified Ellison was less than that in the intact state at 15° and 30° of flexion. No significant differences in knee kinematics were seen between the ITB defect open and closed. Conclusion: A distally fixed lateral augmentation procedure can closely restore knee laxities to native values in an anterolateral capsule–sectioned knee. Although the modified Ellison did result in overconstraint to isolated IR and coupled IR during SPS, this occurred only in the early range of knee flexion. Closure of the ITB defect had no effect on knee kinematics. Clinical Relevance: A distally fixed lateral extra-articular augmentation procedure provides an alternative to a proximally fixed LET and can reduce anterolateral laxity in the anterolateral capsule–injured knee and restore kinematics close to the intact state.

The Anterolateral Complex of the Knee

The objective of this study was to clarify the layer-by-layer anatomy of the anterolateral complex of the knee. Twenty fresh-frozen human cadaveric knees (age range 38 - 56 yrs.) without any history of knee injury or surgery were used for this dissection study. After skin and subcutaneous tissue removal, the ITB was incised in its most anterior part and reflected posteriorly followed by blunt dissection of its deeper layers. Subsequently, an incision was made between the ITB and the short head of the biceps muscle with consecutive evaluation of the insertion site of the biceps tendon and its extensions. Once the deep layers of the ITB were identified, the connections to the lateral intermuscular septum and Kaplan fibers were cut. The superficial ITB was then reflected distally in order to assess the geographical relationship between the superficial and deep ITB as well as the distal anteromedial aspect of the biceps muscle. Finally, the anterolateral capsule was incised to evaluate its connections to the surrounding anatomic structures. The anterolateral aspect of the knee consists of three distinct layers. Superficially, the ITB with its insertion to Gerdy’s tubercle and extensions to the patella (iliopatellar band) was appreciated. Posterior reflection of the superficial ITB revealed a firm distinct connection of Kaplan fibers to the distal femoral metaphysis. The deep layer of the ITB runs from the Kaplan fibers in a distal direction and forms a functional arc. This arc is reinforced by the capsulo-osseous layer of the ITB, which originates from an area distal to the Kaplan fibers, the fascia of the lateral gastrocnemius and plantaris muscles. The distal half of the capsulo-osseous layer merges posteriorly with the fascia of the biceps muscle. The three layers of the ITB become confluent distally. Its insertion spanned from Gerdy’s tubercle to an area just posteriorly, with the capsulo-osseous layer forming the posterior part. The biceps muscle has fascial and aporoneurotical extensions, which insert to the proximal tibia together with the capsulo-osseous layer of the ITB. Layer 3 consists of the anterolateral capsule. In 7/20 (35%) specimens the mid-third capsular ligament was observed as a thickening within, but not separate from the anterolateral capsule. The anterolateral complex of the knee consists of the ITB with its three layers, the functional arc formed by the fibers between the distal femoral metaphysis and Gerdy’s tubercle, and the anterolateral capsule. In 35% of specimens a capsular thickening (mid-third capsular ligament) was identified. Surgeons should consider the complex anatomy of this functional unit, i.e. the anterolateral complex, when considering lateral extra-articular procedures.

The Anterolateral Complex of the Knee

Background: Significant controversy exists regarding the anterolateral structures of the knee. Purpose: To determine the layer-by-layer anatomic structure of the anterolateral complex of the knee. Study Design: Descriptive laboratory study. Methods: Twenty fresh-frozen cadaveric knees (age range, 38-56 years) underwent a layer-by-layer dissection to systematically expose and identify the various structures of the anterolateral complex. Quantitative measurements were performed, and each layer was documented with high-resolution digital imaging. Results: The anterolateral complex of the knee consisted of different distinct layers, with the superficial and deep iliotibial band (ITB) representing layer 1. The superficial ITB had a distinct connection to the distal femoral metaphysis and femoral condyle (Kaplan fibers), and the deep layers of the ITB were identified originating at the level of the Kaplan fibers proximally. This functional unit, consisting of the superficial and deep ITB, was reinforced by the capsulo-osseous layer of the ITB, which was continuous with the fascia of the lateral gastrocnemius and biceps femoris muscles. These 3 components of the ITB became confluent distally, and the insertion spanned from the Gerdy tubercle anteriorly to the lateral tibia posteriorly on a small tubercle (lateral tibial tuberosity). Layer 3 consisted of the anterolateral capsule, in which 35% (7/20) of specimens had a discreet mid-third capsular ligament. Conclusion: The anterolateral complex consists of the superficial and deep ITB, the capsulo-osseous layer of the ITB, and the anterolateral capsule. The anterolateral complex is defined by the part of the ITB between the Kaplan fibers proximally and its tibial insertion, which forms a functional unit. A discrete anterolateral ligament was not observed; however, the anterolateral ligament described in recent studies likely refers to the capsulo-osseous layer or the mid-third capsular ligament. Clinical Relevance: The anterolateral knee structures form a complex functional unit. Surgeons should use caution when attempting to restore this intricate structure with extra-articular procedures designed to re-create a single discreet ligament.