Popliteus Muscle/Popliteus Complex. The popliteus is an obliquely oriented muscle that originates from the postero-medial aspect of the proximal tibia. It forms the floor of the inferior part of the popliteal fossa and is innervated by the tibial nerve. The muscle gives rise to the popliteus tendon at the lateral one-third of the popliteal fossa in the PLC. The average length of the popliteus tendon is 54.5 mm.5 The tendon continues proximally, through the popliteal hiatus in the coronary ligament, at which point it becomes intra-articular, and inserts onto the lateral femoral condyle. This popliteal hiatus is also known as the ‘‘bare area of the lateral mensicus.’’10
The popliteus is a dynamic internal rotator of the tibia and is believed to contribute to the dynamic stability of the lateral meniscus. To facilitate these functions, it has multiple insertions on the posterolateral aspect of the knee. The popliteus muscle-tendon unit and its multiple ligamentous connections from the tendon to the fibula, tibia, and meniscus are known as the popliteus complex.11 Each of these ligamentous connections have been further clarified. The ligamentous insertion on the fibula is comprised of the anterior and posterior popliteofibular ligaments. Historically, these 2 ligaments were collectively known as the arcuate ligament. The popliteal insertion onto the tibia is known as the muscular aponeurotic attachment. The popliteal connections to the lateral meniscus are known as the 3 popliteomeniscal fascicles. This complex provides dynamic and static stability to the knee primarily in response to external tibial rotation.5,9
The popliteus is a dynamic internal rotator of the tibia and is believed to contribute to the dynamic stability of the lateral meniscus. To facilitate these functions, it has multiple insertions on the posterolateral aspect of the knee. The popliteus muscle-tendon unit and its multiple ligamentous connections from the tendon to the fibula, tibia, and meniscus are known as the popliteus complex.11 Each of these ligamentous connections have been further clarified. The ligamentous insertion on the fibula is comprised of the anterior and posterior popliteofibular ligaments. Historically, these 2 ligaments were collectively known as the arcuate ligament. The popliteal insertion onto the tibia is known as the muscular aponeurotic attachment. The popliteal connections to the lateral meniscus are known as the 3 popliteomeniscal fascicles. This complex provides dynamic and static stability to the knee primarily in response to external tibial rotation.5,9
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| FIGURE 4. A and B, Photograph (A) and illustration (B) demonstrating the isolated fibular collateral ligament, popliteus tendon, popliteofibular ligament, and lateral gastrocnemius tendon (lateral view of a right knee). Reprinted with permission.23 |
The femoral insertion of the popliteus tendon is intra-articular and requires an arthrotomy for clear identification. During a surgical approach, the arthrotomy should begin just distal to the lateral epicondyle, run parallel to the FCL, and end at around the level of the lateral meniscus. The popliteus should be easily identified in the popliteal sulcus of the femur. The insertion of the popliteus is consistently found at the most anterior 1/5 and proximal 1/2 of the sulcus. The average crosssectional area of the popliteus sulcus is 3.4 cm2; 0.59 cm2 of the popliteal sulcus is used for the footprint of the popliteus tendon.9
Numerous researchers have found that the popliteus tendon insertion site was consistently anterior to the FCL along the lateral aspect of the lateral femoral condyle9,12–14 (Fig. 4). Specifically, LaPrade et al9 located the popliteus insertion site 18.5mm distal and anterior to the femoral insertion of the FCL, and 15.8mm distal and anterior to the lateral epicondyle of the femur (Fig. 5). Furthermore, they noted that the popliteus tendon did not completely enter the confines of the popliteal sulcus until the knee was flexed to an average of 112 degrees. In knee flexion less than 112 degrees, the tendon subluxed anteriorly out of the sulcus (Fig. 6). As the popliteus tendon courses proximal and laterally, it gives off 3 branches which contribute to the dynamic stability of the lateral meniscus. These are known as the popliteomeniscal fascicles.4,14
Numerous researchers have found that the popliteus tendon insertion site was consistently anterior to the FCL along the lateral aspect of the lateral femoral condyle9,12–14 (Fig. 4). Specifically, LaPrade et al9 located the popliteus insertion site 18.5mm distal and anterior to the femoral insertion of the FCL, and 15.8mm distal and anterior to the lateral epicondyle of the femur (Fig. 5). Furthermore, they noted that the popliteus tendon did not completely enter the confines of the popliteal sulcus until the knee was flexed to an average of 112 degrees. In knee flexion less than 112 degrees, the tendon subluxed anteriorly out of the sulcus (Fig. 6). As the popliteus tendon courses proximal and laterally, it gives off 3 branches which contribute to the dynamic stability of the lateral meniscus. These are known as the popliteomeniscal fascicles.4,14
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| FIGURE 5. Attachment sites of the fibular collateral ligament (FCL) on the femur and fibula and the popliteus tendon (PLT) in the popliteus sulcus of the femur (lateral view of a right knee). In addition, the average distance between the femoral attachment sites is noted. Reprinted with permission.23 |
The first meniscal fascicle is the popliteus muscle’s aponeurotic attachment. This meniscal aponeurosis is an attachment of the popliteus muscle to the posterior capsule and lateral meniscus. This structure, initially described by Last,15 was termed the posteroinferior popliteomensical fascicle by Staubli and Birrer.14 Located medial to the popliteus tendon, this popliteomeniscal fascicle provides a posterior tibial attachment for the lateral meniscus. The postero-superior popliteomeniscal fascicle arises from the medial superior surface of the popliteus tendon as it penetrates the posterior capsule. It blends into the posterior horn of the lateral meniscus and the meniscofemoral portion of the posterior capsule of the joint.4,14
The postero-inferior popliteomeniscal fascicle forms from the popliteus muscle aponeurosis, just medial to the tendon, whereas the postero-superior popliteomensical fascicle forms from the popliteus tendon. The ligament of Wrisberg bisects these 2 posterior popliteomeniscal fasicles as it connects the posterior horn of the lateral meniscus to the medial femoral condyle, providing additional stability to the lateral meniscus.5 The last fascicle, the antero-inferior popliteomeniscal fascicle, originates the furthest distally along the popliteus tendon. From the anterior edge of the popliteus tendon, it blends into the middle third of the lateral meniscus forming the anterior boundary of the popliteal hiatus.4,5,14
The biomechanical significance of each of the 3 individual popliteomeniscal fascicles is not completely understood. However, it is known that together they stabilize the lateral meniscus and prevent medial entrapment of the meniscus during varus forces on the knees.16 These functions are complicated by the need to permit the large excursion of the lateral meniscus over the chondral surfaces.
The postero-inferior popliteomeniscal fascicle forms from the popliteus muscle aponeurosis, just medial to the tendon, whereas the postero-superior popliteomensical fascicle forms from the popliteus tendon. The ligament of Wrisberg bisects these 2 posterior popliteomeniscal fasicles as it connects the posterior horn of the lateral meniscus to the medial femoral condyle, providing additional stability to the lateral meniscus.5 The last fascicle, the antero-inferior popliteomeniscal fascicle, originates the furthest distally along the popliteus tendon. From the anterior edge of the popliteus tendon, it blends into the middle third of the lateral meniscus forming the anterior boundary of the popliteal hiatus.4,5,14
The biomechanical significance of each of the 3 individual popliteomeniscal fascicles is not completely understood. However, it is known that together they stabilize the lateral meniscus and prevent medial entrapment of the meniscus during varus forces on the knees.16 These functions are complicated by the need to permit the large excursion of the lateral meniscus over the chondral surfaces.
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| FIGURE 6. The position of the popliteus tendon (PLT) to the popliteus sulcus with the knee in full extension and at an average of 112 degrees of knee flexion (ghosted view) (lateral view of the right knee). PFL, popliteofibular ligament. Reprinted with permission.23 |
The popliteofibular ligament is the second most prominent structure in the PLC, with the most prominent being the popliteus tendon. The anatomy and function of the popliteofibular ligament is becoming more defined. The popliteofibular ligament consists of anterior and posterior divisions. These divisions originate from the popliteus tendon at its musculotendinous junction.9 They form a ‘‘Y’’ configuration, providing a firm connection between the popliteus tendon and fibula (Fig. 7).
The anterior division, attached to the proximallateral musculotendinous junction, inserts just anterior to the posterior division and medial to the FCL. On average, it attaches 2.8mm distal to the anteromedial aspect of the tip of the fibular styloid process.9 The stouter posterior division of the popliteofibular ligament, which is typically reconstructed in PLC injuries, originates from the popliteus tendon and inserts 1.6mm distal to the tip of the fibular styloid process on its posterior medial downslope.9 A small longitudinal groove may be palpated on this downslope, identifying its course. It inserts on the fibular styloid just anterior to the fabellofibular ligament.
The popliteofibular ligament is a static stabilizer of the lateral and posterolateral knee, resisting varus, external rotation, and posterior tibial translation.4,11 A force of 298N is required to cause failure of this structure.17 Alternatively, rather than an intrasubstance tear, the posterior division may avulse a fragment of the fibular head in what is known as an arcuate fracture. Arcuate fractures are often associated with cruciate ligament injuries.18 Due to their roles as both static and dynamic restraints, the popliteus and popliteofibular ligaments are vital components of any posterolateral reconstructive procedure. Directly posterior to the popliteofibular ligament courses the inferior lateral geniculate artery. This artery originates off the popliteal artery and courses along the posterior joint capsule just proximal to the superior aspect of the lateral meniscus. As it courses laterally, it bisects the popliteofibular ligament and the fabellofibular ligament (capsular arm of the short head of the biceps femoris) as they attach to the fibular styloid. The popliteofibular ligament lies anterior and the fabellofibular ligament lies posterior to the inferior lateral geniculate artery where it crosses the posterior aspect of the fibular styloid.7,10
The final component of the popliteus complex is its popliteotibial insertion. This is a direct attachment extending from the anterior surface of the popliteus muscle to an area just lateral to the fovea of the posterior cruciate ligament (PCL). It inserts on the inferior surface of the lateral meniscus and on the posterior capsule. The insertion on the posterior capsule lies medial to the popliteal tendon, an area devoid of a coronary ligament attachment.4,9
The anterior division, attached to the proximallateral musculotendinous junction, inserts just anterior to the posterior division and medial to the FCL. On average, it attaches 2.8mm distal to the anteromedial aspect of the tip of the fibular styloid process.9 The stouter posterior division of the popliteofibular ligament, which is typically reconstructed in PLC injuries, originates from the popliteus tendon and inserts 1.6mm distal to the tip of the fibular styloid process on its posterior medial downslope.9 A small longitudinal groove may be palpated on this downslope, identifying its course. It inserts on the fibular styloid just anterior to the fabellofibular ligament.
The popliteofibular ligament is a static stabilizer of the lateral and posterolateral knee, resisting varus, external rotation, and posterior tibial translation.4,11 A force of 298N is required to cause failure of this structure.17 Alternatively, rather than an intrasubstance tear, the posterior division may avulse a fragment of the fibular head in what is known as an arcuate fracture. Arcuate fractures are often associated with cruciate ligament injuries.18 Due to their roles as both static and dynamic restraints, the popliteus and popliteofibular ligaments are vital components of any posterolateral reconstructive procedure. Directly posterior to the popliteofibular ligament courses the inferior lateral geniculate artery. This artery originates off the popliteal artery and courses along the posterior joint capsule just proximal to the superior aspect of the lateral meniscus. As it courses laterally, it bisects the popliteofibular ligament and the fabellofibular ligament (capsular arm of the short head of the biceps femoris) as they attach to the fibular styloid. The popliteofibular ligament lies anterior and the fabellofibular ligament lies posterior to the inferior lateral geniculate artery where it crosses the posterior aspect of the fibular styloid.7,10
The final component of the popliteus complex is its popliteotibial insertion. This is a direct attachment extending from the anterior surface of the popliteus muscle to an area just lateral to the fovea of the posterior cruciate ligament (PCL). It inserts on the inferior surface of the lateral meniscus and on the posterior capsule. The insertion on the posterior capsule lies medial to the popliteal tendon, an area devoid of a coronary ligament attachment.4,9
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