Biomechanics of the Lateral Side of the Knee

<div style="text-align: justify;"> <div class="separator" style="clear: both; text-align: center;"> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-9uoBG_62gpEQ3hNCutTU04bFzHEBt74JwjPWnX5-A60gZTM8Y6G9lXnoCLW8wYLArLPVMuh3abnxuG-Nh18zmeoJrSOS5OpM8GGf5Q5IOojEPZBTD8F1j228Xi2zXSWbGQj6CojxOgI/s1600/KNEE_BIOMECHANICS.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-9uoBG_62gpEQ3hNCutTU04bFzHEBt74JwjPWnX5-A60gZTM8Y6G9lXnoCLW8wYLArLPVMuh3abnxuG-Nh18zmeoJrSOS5OpM8GGf5Q5IOojEPZBTD8F1j228Xi2zXSWbGQj6CojxOgI/s320/KNEE_BIOMECHANICS.jpg" width="277" /></a></div> <a href="http://imedicalcenter.blogspot.com/2015/06/biomechanics-of-lateral-side-of-knee.html"><b><span style="color: blue;">BIOMECHANICS</span></b></a>. The primary function of the structures of the lateral and posterolateral knee are to resist varus rotation, external tibial rotation, and, to a lesser extent, posterior tibial translation. Several biomechanical studies have shown the FCL, popliteus tendon, and popliteofibular ligament to be the most important stabilizing structures of the posterolateral knee.12,17,22–25  The posterolateral structures act in concert with the PCL in providing overall stability of the knee. The complex anatomy of the knee does not allow pure rotational or translational motions to occur.  Normal biomechanics of the knee, and abnormal pathomechanics, are the result of complex coupled rotations and translations. This section discusses posterolateral biomechanics, including anterior-posterior translation, varus-valgus rotation, and internal-external rotation. In addition, the role of intra-articular pressures, osseous configurations, and meniscal configurations will also be addressed.<br /> <br /> <b>OSSEOUS AND MENISCI</b><br /> In the majority of the population, the normal mechanical axis of the lower extremity lies slightly medial to the center of the knee. To achieve balance in the stance phase of gait, compressive forces are transmitted through the medial compartment of the knee whereas the lateral structures are under significant tension. During the normal gait cycle, the lateral ligamentous structures of the knee are subjected to greater forces than the medial ligamentous structures and are appropriately more substantial and stronger.11<br /> Likewise, the bony anatomy of the lateral compartment of the knee is quite different from the medial compartment. The medial femoral-tibial compartment has an inherently stable ‘‘cup’’ formation. The convex medial femoral condyle rests in the concavity of the medial tibial plateau. On the contrary, the lateral compartment of the knee is inherently unstable as the convex lateral femoral condyle articulates with a convex lateral tibial plateau. Without additional support these 2 convex surfaces would have minimal surface contact, high contact stresses, and very little stability. The inherently unstable bony geometry of the lateral compartment allows greater motion than the medial compartment, but relies on the posterolateral soft tissue structures to provide the required stability. The roles of the medial and lateral menisci parallel the roles of the medial and lateral osseous compartments. Both menisci add stability to their respective compartments, but the lateral meniscus must do so when accommodating the relatively greater range of motion of the lateral compartment. The lateral meniscus contributes to lateral knee stability by adding concavity to the lateral tibial plateau. To preserve its increased motion across the tibial plateau, it has less restraining static meniscotibial attachments than the medial meniscus, and is dynamically stabilized by a branch of the popliteus tendon. <br /> Because the lateral meniscus is less restrained, it is also less stable than the medial meniscus. This permits it more motion across the tibial plateau with flexion and extension of the knee. The increased excursion of the lateral meniscus limits its ability to compensate for the unstable bony geometry of the lateral tibiofemoral compartment. Therefore, the remaining soft tissues of the PLC must provide significant stability to the lateral side of the knee.25<br /> <br /> <b>ANTERIOR-POSTERIOR TRANSLATION</b><br /> The primary restraint to anterior translation of the tibia relative to the femur is the ACL. It accounts for about 86% of the total resistance to anterior tibial translation.11 Although the posterior horn of the medial meniscus provides some support to this role, especially in the ACL-deficient knee, it is easily injured when the ACL<br /> is compromised. This indicates the minimal amount of support the ACL receives in this role and the necessity of reconstructing it when it is deficient. Several studies have demonstrated that the posterolateral structures do not prevent primary anterior tibial translation.26,27 However, like the posterior horn of the medial meniscus, the PLC helps prevent anterior tibial translation in the ACL-deficient knee. The role of the PLC seems to be more prominent near extension, whereas the role of the posterior horn of the medial meniscus is<br /> more noticeable in flexion. This can be demonstrated on physical examination. Typically, an ACL-deficient knee, with an intact posterior horn of the medial meniscus and a torn PLC, will have a markedly positive Lachman test (greater than +2) and a subtle (grade 1) anterior drawer. Conversely, an ACL-deficient knee, with a torn posterior horn of the medial meniscus and an intact PLC, will have a positive anterior drawer and positive Lachman test. However, in the later example, the Lachman test may not be as prominent. Clinically, if an ACL is reconstructed in a knee with a PLC injury, the reconstructed graft will be at higher risk of failure unless the PLC injury is addressed. This underscores the need to thoroughly exam the PLC in all ACL-deficient knees, before reconstruction.</div> <div style="text-align: justify;"> Resistance to posterior tibial translation is far more complex. The stout and centrally located PCL is the primary static stabilizer of the knee and plays a strong role in resisting posterior tibial translation. It provides<br /> 95% of the total restraint to posterior tibial displacement forces at all flexion angles.11,22 With the knee in near full extension, isolated sectioning of the posterolateral structures results in increased posterior translation of the lateral tibial plateau. As the knee is flexed to 90 degrees, there is minimal posterior translation. In PCL-deficient knees with transected posterolateral structures, posterior tibial translation of the medial and lateral tibial plateaus is appreciated at 30 and 90 degrees of flexion. Thus, the posterolateral structures are important in resisting posterior tibial translation at small flexion angles (eg, 30 degrees). The PCL and PLC structures work in concert, and injury to both of these structures results in a significant increase in posterior translation of the knee at all flexion angles.23,24<br /> <br /> The popliteus is a dynamic stabilizer that assists the PCL by resisting posterior tibial translation. In the intact knee, loading the popliteus has been shown to reduce the in situ forces in the PCL by 9% and 36%, at 90 and 30 degrees of flexion, respectively.28 In the PCL-deficient knee, loading the popliteus has been shown to reduce posterior tibial translation by up to 36%. This amounts to a reduction of posterior translation by approximately 2 to 3 mm. The results of this study confirm that the popliteus muscle complements the PCL in resisting posterior tibial loads and can contribute to knee stability when the ligament in absent.27,28 In a combined PCL and PLC injury model, Harner et al29 demonstrated that a deficiency of the PLC increased posterior tibial translation, in the PCL reconstructed knee, by 4.6 to 6.0 mm. They found a corresponding increase in the in situ forces in the PCL graft of 22% to 150%, if the posterolateral structures were not<br /> repaired or reconstructed. These results demonstrate that an isolated PCL graft reconstruction is rendered ineffective and may be overloaded if the posterolateral structures are deficient. Although the PCL provides the greatest contribution to resisting posterior tibial translation, both biomechanical and clinical studies have shown that it cannot function appropriately in a knee with a deficient PLC. Conversely, clinical studies have demonstrated that many individuals can function with an isolated rupture of the PCL, although their biomechanics may not be identical to that of a healthy knee. These studies demonstrate the importance of a fully functional PLC in resisting posterior tibial translation, and the necessity of repairing or reconstructing the PLC when it is compromised.<br /> <br /> VARUS-VALGUS ROTATION<br />The FCL is the primary restraint to varus stress at all flexion angles of the knee. LaPrade et al30 found that varus forces on the FCL had loading responses from 0 to 90 degrees of flexion, with the greatest being at 30 degrees (12 N/J). Although other soft tissues provide additional support in this function, the FCL receives the least support at 30 degrees of flexion. This makes the FCL most susceptible to injury at 30 degrees of flexion. It has been shown that approximately 300N of force is required to cause failure of this ligament.17 The PCL is considered a secondary restraint to varus rotation; however, sectioning of this structure with an intact FCL does not affect varus rotation. Conversely, when the PLC is deficient and the PCL is intact, the PCL will provide some resistance to varus stress, but it is not as effective in this role as an intact PLC. In a combined PCL and PLC injury model, Harner et al29 demonstrated that a deficiency of the posterolateral structures after PCL reconstruction increased varus rotation up to 7 degrees. Grood et al23 and Veltri et al31 reported that an increase in varus rotation (as much as 19 degrees) can be appreciated with the combined sectioning of the PCL and posterolateral structures. This varus rotation occurred throughout all angles of knee flexion, with the maximal increase observed at 60 degrees. The posterolateral structures act as the primary restraint to varus rotation especially at lesser degrees of knee flexion (maximal restraint at 30 degrees). The PCL acts as secondary restraint that is most noticeable when the PLC is compromised. The PCL is more effective at resisting varus stresses at greater degrees of knee flexion (60 degrees). To a lesser degree, dynamic resistance to varus rotation is provided by the iliotibial band, biceps femoris muscle tendon complex, and lateral gastrocnemius.9<br /><br />INTERNAL-EXTERNAL ROTATION<br />The popliteus complex is usually considered the primary restraint to external rotation of the knee. However, recent studies have shown that this function is shared by the FCL. In selective cutting studies, several authors have demonstrated that sectioning of the FCL, popliteus tendon, and deep ligaments of the lateral knee created increases in external rotation at all angles of knee flexion.22,28 Further studies have identified the specific roles of the FCL and the popliteus complex in resisting external rotation. In a recent cadaveric study, LaPrade et al30 found that the FCL resisted greater external rotation forces in the early range of knee flexion (0 to 30 degrees) when compared to the popliteus complex. The external rotation moment responses for the FCL were fairly constant from 0 to 60 degrees of knee flexion, averaging approximately 10 N/J. The mean load response peaked at 30 degrees of flexion (20 N/J) before falling to 8.1 N/J at 90 degrees of flexion. The popliteus tendon and popliteofibular ligament became more highly loaded by an external rotation torque with higher amounts of knee flexion. The popliteus tendon and the popliteofibular ligament had similar loading patterns to an external rotation torque, from 0 to 90 degrees of knee flexion. Their mean load response generally increased with increasing knee flexion, peaking to approximately 13 N/J at 60 degrees of knee flexion (FCL 10 N/J) before slightly declining to 10 N/J at 90 degrees.30 Therefore, the FCL is the primary restraint to external rotation from 0 to 30 degrees, whereas the popliteus complex (popliteus tendon and popliteofibular ligament) assumes a more important primary role in resisting external rotation at knee flexion angles greater than 60 degrees. The PCL is a secondary stabilizer in resisting external rotation of the tibia. Isolated sectioning of the PCL does not increase external tibial rotation when the PLC is intact. The role of the PCL as a secondary stabilizer becomes significant when the PLC is compromised. In a PCL-intact knee, isolated sectioning of the posterolateral structures increased external rotation of the lateral tibial plateau, with maximal external rotation (average 13 degrees) demonstrated at 30 degrees of knee flexion. At 90 degrees of flexion, a smaller amount (average 5.3 degrees) of external rotation was observed. Combined sectioning of the PLC and the PCL results in an increase in external rotation of the lateral tibial plateau at all angles of knee flexion, with a maximal increase noted at 90 degrees. As much as 20 degrees of increased external rotation can be appreciated at this degree of knee flexion.22,23 This is the basic science behind the external<br />tibial rotation test (or Dial test) commonly used to distinguish between isolated PLC injuries and combined PCL/PLC injuries.<br /><br /> Thus, the fibular collateral ligament is the primary restraint to external rotation at small degrees of knee flexion (30 degrees) and the popliteus complex is the primary restraint against external rotation at greater degrees of knee flexion (60 degrees). The PCL serves as a secondary restraint when the PLC is injured and is most effective at knee flexion angles of 90 degrees. These basic science studies have important clinical applications. Because isolated sectioning of the PCL does not increase external tibial rotation, any increased tibial external rotation should make a clinician suspicious of a PLC injury. In a combined PCL and PLC injury model, Harner et al29 biomechanically demonstrated that a deficiency of the posterolateral structures after PCL reconstruction increased external rotation up to 14 degrees. If the PLC is not reconstructed when the PCL is reconstructed, this resulting increased external rotation places the patient at increased risk of reinjury. Therefore, it is important to reconstruct the posterolateral complex in addition to the PCL to restore normal external tibial rotation restraints. The posterolateral structures play a small role in preventing primary internal rotation of the knee.31 Because there is a large amount of variability in internal rotation changes within ACL-intact and ACL-deficient knees, this particular knee instability has not demonstrated much clinical significance.<br /><br />ARTICULAR CONTACT PRESSURES<br />The structures of the PLC are important in maintaining joint stability, which can have significant effects on articular contact pressures. Abnormal joint loading patterns and contact pressures can predispose a joint to degeneration. Sectioning the PCL and posterolateral structures has been shown to increase medial, lateral, and patellofemoral compartment contact pressures. 32 In a cadaveric biomechanical model of the knee, Skyhar et al,32 demonstrated that sequentially sectioning the PCL and then the posterolateral structures resulted in a significant increase in patellofemoral contact pressure at all angles of flexion. This finding is a result of 2 interrelated factors. First, with the loss of these structures, posterior tibial translation increases, thus, diminishing the moment arm of the patellar tendon. The angle between the quadriceps and patellar tendon decreases and creates an increase in the reaction force of the patellofemoral joint. This phenomenon is known as the ‘‘reverse Maquet’’ effect. Second, the quadriceps must exert a greater force because it is acting through a diminished lever arm. This increases articular contact pressures even more. The loss of ligamentous support creates instability so that the pressure is less likely to be distributed over the articular surface in a normal pattern. A combined PCL and PLC injury induces external rotation of the tibia on the femur, which creates aberrant medial and lateral contact pressures that are already elevated owing to the increase in quadriceps force. Several authors have postulated that this combined injury shifts the center of rotation further into the medial compartment, increasing shear and/or changing contact areas within these compartments during knee motion, ultimately, resulting in a varus-thrust gait pattern.32,33 The abnormal contact pressures seen in this combined injury may lead to premature degeneration of the joint and underscore the importance of the PLC in maintaining a healthy knee.<br /><br />GRAFT RECONSTRUCTIONS<br />From a clinical standpoint, the PLC can have a significant effect on the survival of the native ACL and PCL. Studies have shown that sectioning of the FCL and surrounding posterolateral structures resulted in increased<br />stresses on the ACL with internal rotation and on the PCL with external rotation.24 Similar to the native ACL or PCL, the reconstructed ACL or PCL is at increased risk of failure in a knee with a deficient PLC. Studies have shown that sectioning the FCL and surrounding posterolateral structures results in increased<br />stresses on reconstructed ACL and PCL grafts.34,35 LaPrade et al34,35 have shown that coupled loading of varus and internal moments, at 0 and 30 degrees of flexion, significantly increased ACL graft forces. Furthermore, significantly increased forces were demonstrated within PCL grafts with varus and/or coupled external rotation at 30, 60, and 90 degrees of flexion. These studies affirm the recommendation to reconstruct the PLC in both isolated and combined injuries.</div>

BIOMECHANICS . The primary function of the structures of the lateral and posterolateral knee are to resist varus rotation, external tibia...

FCL (Fibular Collateral Ligament)

<div style="text-align: justify;"> <span style="color: blue;"><b>FCL (Fibular Collateral Ligament). </b></span>The FCL, also known as the <a href="http://imedicalcenter.blogspot.com/2015/06/fcl-fibular-collateral-ligament.html">lateral collateral ligament</a>, is the primary static stabilizer to varus opening of the knee in the initial 0-degree to 30-degree arc of knee flexion. With knee flexion beyond 30 degrees, the FCL<br />becomes slightly lax.4 In addition, this ligament provides resistance to external rotation of the tibia, primarily near extension. The femoral origin of the FCL is extracapsular and easily identified by palpating the lateral epicondyle. LaPrade et al9 have shown that the femoral insertion of the FCL consistently lies 1.4mm proximal and 3.1mm posterior to the lateral epicondyle.  This location may be palpated as a small bony depression formed between the lateral epicondyle and the supracondylar process. The FCL is approximately 70mm long and its primary distal insertion site is the lateral aspect of the fibular head. <br /> </div> <table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody> <tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi2HJPw4aS4LxZHSIVQM9G63k1qsm33H4LKE7Mxz6BMa36DsXg5N_iSiHDqQWzIoIE5EOnM_fu_9ui91UoKn_Tjr5NxFGNNb8FfH7gFyUt8UaY4r4Gsf6iefx9FCNRHCokTBL_dx88nFBM/s1600/FCL.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="271" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi2HJPw4aS4LxZHSIVQM9G63k1qsm33H4LKE7Mxz6BMa36DsXg5N_iSiHDqQWzIoIE5EOnM_fu_9ui91UoKn_Tjr5NxFGNNb8FfH7gFyUt8UaY4r4Gsf6iefx9FCNRHCokTBL_dx88nFBM/s400/FCL.jpg" width="400" /></a></td></tr> <tr><td class="tr-caption" style="text-align: center;">FIGURE 3. Removal of the long head of the biceps femoris tendon reveals components of the short head of the biceps<br />(SHB): capsular arm (Cap arm), direct arm (Dir arm), anterior arm (Ant arm), and lateral aponeurosis (LatAp). F, femur; FCL, fibular collateral ligament; LM, lateral meniscus; M 1/3, the midthird lateral capsular ligament; T, tibia. Reprinted with permission.16</td></tr> </tbody></table> <div style="text-align: justify;"> During a surgical approach, the FCL can be easily identified through a small 3-cm incision made parallel to the fibers of the long head of the biceps femoris tendon. This incision is made superficial to the proximal extent of the fibular head and should release the insertion of the anterior arm of the long head of the biceps femoris tendon.6 This incision should readily expose the biceps bursa, which forms an inverted ‘‘J’’ shape around the anterior and anteromedial portions of the FCL. The biceps bursa encapsulates the distal 25% of the FCL. <br />The long head of the biceps femoris tendon forms the lateral border of the biceps bursa.8 The fibular insertion of the FCL lies 8.2mm posterior to the anterior border of the fibula, and 28.4mm antero-inferior to the proximal tip of the fibular styloid.17,23 On average, this comprises 38% (13.9 mm) of the total width of the fibular head, which measures 36.6mm anterior to posterior.6,9</div>

FCL (Fibular Collateral Ligament). The FCL, also known as the lateral collateral ligament , is the primary static stabilizer to varus openi...

BICEPS FEMORIS

<div style="text-align: justify;"> <span style="color: blue;"><b>BICEPS FEMORIS.</b></span> The biceps femoris is a fusiform muscle that contains 2 heads, long and short. The long head of the biceps femoris muscle originates from the ischial tuberosity and is part of the common hamstring origin. It is innervated by the tibial division of the sciatic nerve. The short head of the biceps femoris muscle originates just medial to the linea aspera of the distal femur, and is innervated by the peroneal division of the sciatic nerve. Both heads flex the leg at the knee joint and laterally rotate the leg when it is flexed.7 The long head of the biceps has 5 major insertions at the knee. It divides into 2 tendinous components called the direct and anterior arms, and 3 fascial components called the reflected arm and, anterior and lateral, aponeurotic expansions. The most important of these structures are the direct and anterior arms, and the lateral aponeurotic expansion. The direct arm inserts onto the lateral aspect to the fibular styloid. </div> <div style="text-align: justify;"> <br /></div> <div style="text-align: justify;"> The anterior arm courses lateral to the fibular collateral ligament (FCL) and inserts onto the lateral tibial plateau.6 A small biceps femoris bursa separates this arm from the FCL.8 The lateral aponeurotic expansion connects the long and short heads of the biceps femoris to the posterolateral aspect of the FCL.5,6 The short head of the biceps femoris muscle divides into 6 components. These components consist of direct,<br /> capsular, and anterior tendinous arms, along with 3 nontendinous insertions. The 3 nontendinous attachments<br /> insertions include a muscular insertion onto the long head of the biceps femoris tendon, a lateral aponeurotic expansion attaching both the short and long heads to the postero-medial aspect of the FCL, and a third insertion, just lateral to the capsular arm, forming a confluence with the capsulo-osseous layer of the iliotibial<br /> tract. This confluence with the capsulo-osseous layer forms an intimate attachment between the fascia of the<br /> iliotibial band and the biceps femoris5,6 (Fig. 2).<br /> </div> <div style="text-align: justify;"> The most important insertions of the short head of the <a href="http://imedicalcenter.blogspot.com/2015/06/biceps-femoris.html">biceps femoris</a> are the 3 tendinous arms. They are most easily identified at the level of the fibular head. The direct arm is the least important of the 3 and attaches to the posterolateral aspect of the fibular styloid. </div> <div style="text-align: justify;"> <br /></div> <table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody> <tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglIUjGAq8kYAbGdt5go-Kug6RVB-5RyYJb91YbaWDEyYyxcJyXFKbnVSDWRbPNoJ_yS75pdJhs1lYUUJc3ki6jbP3H4CGmeiCt0DHpTlKWlIP-R7AlblxK2V2hjpyVxJoEfzGMYda_WzA/s1600/FCL.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="270" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEglIUjGAq8kYAbGdt5go-Kug6RVB-5RyYJb91YbaWDEyYyxcJyXFKbnVSDWRbPNoJ_yS75pdJhs1lYUUJc3ki6jbP3H4CGmeiCt0DHpTlKWlIP-R7AlblxK2V2hjpyVxJoEfzGMYda_WzA/s400/FCL.jpg" width="400" /></a></td></tr> <tr><td class="tr-caption" style="text-align: center;">FIGURE 2. Retraction of the superficial layers of the iliotibial tract reveals the capsulo-osseous layer (COITT), short head of the biceps tendon (SHB), short head of biceps-capsuloosseous layer confluens (CON), long head of biceps tendon<br /> (LHB), fibular collateral ligament (FCL), lateral capsular incision (Cap Inc), and iliotibial tract insertion (I). Reprinted with<br /> permission.16</td></tr> </tbody></table> <div style="text-align: justify;"> <br /></div> <div style="text-align: justify;"> The capsular arm extends from the main tendon of the short head of the biceps to the posterolateral aspect of the capsule, and inserts just lateral to the tip of the fibular styloid. It provides a stout attachment between the posterolateral capsule, lateral gastrocnemius tendon, and capsulo-osseous layer of the iliotibial band. The most distal edge of the capsular arm is the fabellofibular ligament.5,6 The anterior arm passes medial to the FCL and inserts with the meniscotibial portion of the midthird lateral capsular ligament onto the proximal-lateral tibia. In association with ACL injuries, the anterior arm of the short head of the biceps, along with the meniscotibial component of the midthird lateral capsular ligament, is frequently found to be avulsed off the anterolateral aspect of the tibia. This may occur with a small bony avulsion called a Segond fracture4 (Fig. 3). The peroneal nerve lies deep and posterior to the biceps femoris tendon, and should be the first structure identified during dissection of the PLC. It is located approximately 1.5 to 2 cm distal to the fibular styloid as it travels along the lateral aspect of the fibular head.7</div>

BICEPS FEMORIS. The biceps femoris is a fusiform muscle that contains 2 heads, long and short. The long head of the biceps femoris muscle ...

Anatomy and Biomechanics of the Lateral Side of the Knee

<div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;"><span style="color: blue;"><b>Anatomy and Biomechanics of the Lateral Side of the Knee.</b></span> The posterolateral corner (PLC) of the knee is a critical element for a functional lower extremity. It consists of an array of complex ligamentous and musculotendinous structures. The primary function of the PLC is to resist varus and external rotation and posterior translation of the tibia. Injuries to these structures can cause significant disability and compromise activities of daily living and work, recreational, and sporting activities. A thorough understanding of the complex anatomy and biomechanics of the PLC will aid the clinician in this challenging diagnostic and therapeutic problem. The first section of this paper describes the anatomy of the PLC of the knee focusing on the intricate insertion sites of the individual structures. The second section discusses how the anatomy influences the biomechanics of the PLC.</span></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;"><i>(Sports Med Arthrosc Rev 2006;14:2–11)</i></span></div> <div style="text-align: justify;"> <br /></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;"><a href="http://imedicalcenter.blogspot.com/2015/06/anatomy-and-biomechanics-of-lateral.html">The posterolateral corner (PLC) of the knee</a> is a critical element for a functional lower extremity. It consists of an array of complex ligamentous and musculotendinous structures. The primary function of the PLC is to resist varus and external rotation and posterior translation of the tibia. Injuries to these structures can cause significant disability and compromise activities of daily living and work, recreational, and sporting activities. A thorough understanding of the complex anatomy and biomechanics of the PLC will aid the clinician in this challenging diagnostic and therapeutic problem. The first section of this paper describes the anatomy of the PLC of the knee focusing on the intricate insertion sites of the individual structures. The second section discusses how the anatomy<br />influences the biomechanics of the PLC. </span></div> <div style="text-align: justify;"> <br /></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;">ILIOTIBIAL BAND</span><br /> <span style="font-family: Georgia,"Times New Roman",serif;"></span><span style="font-family: Georgia,"Times New Roman",serif;">The iliotibial band is a thick fascial sheath extending over the tensor fasciae latae muscle along the lateral aspect of the thigh. This structure originates from the anterior superior iliac spine and the anterior part of the external lip of the iliac crest. It inserts onto the anterolateral aspect of the lateral tibial plateau. Its insertion on the tibia was originally described by Gerdy and later popularized by Segond as the ‘‘tubercle of Gerdy.’’ Today it is referred to as ‘‘Gerdy tubercle.’’1 The iliotibial band is divided into superficial, deep, and capsulo-osseous layers. The superficial layer is first encountered after dissecting through the subcutaneous tissues on the lateral aspect of the leg. After splitting the first fascial layer (superficial layer) of the iliotibial band, deeper fibers intimately adhere to the lateral supracondylar tubercle of the femur and blend into the lateral<br />intramuscular septum. These layers, now called the deep and capsulo-osseous layers of the iliotibial band, are commonly known as ‘‘Kaplan fibers’’ (Fig. 1). An anterior portion of the iliotibial band, known as the iliopatellar band, curves anteriorly to insert onto the lateral aspect of the patella.1,2 The deep layer of the iliotibial band is visualized beginning 6 cm proximal to the lateral femoral epicondyle, at the termination of the lateral intermuscular septum. It covers a triangular-shaped area over the lateral supracondylar face of the distal femur. It connects the medial border of the superficial iliotibial layer to the distal termination of the lateral intermuscular septum of the distal femur.3 Medial and distal to the deep layer, the capsuloosseous layer originates from the region of the lateral intermuscular septum and the fascia over the posterolateralaspects of the lateral gastrocnemius and plantaris  </span><span style="font-family: Georgia,"Times New Roman",serif;">muscles.</span></div> <div style="text-align: justify;"> <br /></div> <table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody> <tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNbWqxopsyZbLkommO1XPKzGtE_YIs0T9q7tjf3xSupMilVoU_n0AXJv7fjMT3mZaTNG3GrXbzLQ8XkRNzN21Zr8bPdkEBDs566CBUMHToKKB1eKmHR3Mos5-HiaiWPFWEQO3SjKKAzGA/s1600/Retraction-of-the-superficial-layer.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img alt="Anatomy and Biomechanics of the Lateral Side of the Knee" border="0" height="270" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiNbWqxopsyZbLkommO1XPKzGtE_YIs0T9q7tjf3xSupMilVoU_n0AXJv7fjMT3mZaTNG3GrXbzLQ8XkRNzN21Zr8bPdkEBDs566CBUMHToKKB1eKmHR3Mos5-HiaiWPFWEQO3SjKKAzGA/s400/Retraction-of-the-superficial-layer.jpg" title="Anatomy and Biomechanics of the Lateral Side of the Knee" width="400" /></a></td></tr> <tr><td class="tr-caption" style="text-align: center;">FIGURE 1. Retraction of the superficial layer of the iliotibial<br /> tract reveals the deep (DITT) and capsulo-osseous (COITT)<br /> layers. G, Gerdy tubercle. Reprinted with permission.16</td></tr> </tbody></table> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;"> Along the lateral aspect of the knee, this structure blends with the short head of the biceps femoris in a region known as the confluence of the short head of the biceps femoris and the capsulo-osseous layer. The capsulo-osseous layer functions as an anterolateral ligament of the knee, as it forms a sling over the lateral femoral condyle.2–5 Distally, it inserts onto the lateral tibial tuberosity, just posterior and proximal to Gerdy tubercle.1,6 This layer, reinforced by the deep layer, tethers the superficial layer to the distal-lateral aspect of the femur, forming a sling behind the lateral femoral condyle. Historically, this lateral sling of tissue is what most surgeons attempted to reconstruct in extra-articular anterior cruciate ligament (ACL) reconstructions.</span></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;"><br /></span></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;">Source : Anthony R. Sanchez, II, MD,* Matthew T. Sugalski, MD,* and Robert F. LaPrade, MD, PhD*w</span></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;"><br /></span></div> <div style="text-align: justify;"> <span style="font-family: Georgia,"Times New Roman",serif;">From the *TRIA Orthopaedic Center, 8100 Northland Drive,<br />Bloomington, MN 55431; and wDivision of Sports Medicine,<br />University of Minnesota, 2512 South 7th Street, Suite 200,<br />Minneapolis, MN 55454.<br />Reprints: Robert F. LaPrade, MD, PhD, Division of Sports Medicine,<br />University of Minnesota, 2512 South 7th Street, Suite 200,<br />Minneapolis, MN 55454 (e-mail: lapra001@umn.edu).</span></div>

Anatomy and Biomechanics of the Lateral Side of the Knee. The posterolateral corner (PLC) of the knee is a critical element for a function...