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Year : 2020  |  Volume : 12  |  Issue : 2  |  Page : 107-114

A Comprehensive Review of the Anatomy of Popliteus and Its Clinico-Surgical Relevance

Department of Anatomy, Sri Manakula Vinayagar Medical College and Hospital, Puducherry, India

Date of Submission31-Dec-2019
Date of Acceptance20-Apr-2020
Date of Web Publication28-Dec-2020

Correspondence Address:
Dr. Sudha Ramalingam
Department of Anatomy, Sri Manakula Vinayagar Medical College and Hospital, Puducherry - 605 107
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jotr.jotr_59_19

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An extensive anatomical knowledge of the muscle popliteus and its tendon is indispensable to understand the posterolateral structures of the knee which is prone to injury compared to the medial knee structures. This study describes all the relevant anatomical details of the muscle and its clinical significance. Anatomical and clinical terms regarding the popliteus muscle are searched using databases and search engines for the collection of literature review. Abstracts and articles describing the posterolateral corner (PLC) structures apart from the muscle studied were excluded. Seventy-six articles were adopted using the inclusion and exclusion criteria, among which 62 articles had fulfilled the need. Original articles dealing with morphology and morphometric analysis of popliteus muscle are scarce. Hence, the finer details of the anatomy of the muscle in various populations are unavailable, which is considered as a deficiency of the study. This article deals with the morphology of the popliteus and its clinical and surgical implications pertaining to the PLC of the knee.

Keywords: Popliteofibular ligament, popliteomeniscal fascicles, popliteus muscle tendon unit, popliteus tear, posterolateral corner

How to cite this article:
Somanath D, Ramalingam S. A Comprehensive Review of the Anatomy of Popliteus and Its Clinico-Surgical Relevance. J Orthop Traumatol Rehabil 2020;12:107-14

How to cite this URL:
Somanath D, Ramalingam S. A Comprehensive Review of the Anatomy of Popliteus and Its Clinico-Surgical Relevance. J Orthop Traumatol Rehabil [serial online] 2020 [cited 2021 Jun 17];12:107-14. Available from: https://www.jotr.in/text.asp?2020/12/2/107/305088

  Introduction Top

The intricate anatomy of the posterolateral corner (PLC) of the knee is intriguing. To understand this complexity, the comprehensive structure of the popliteus (PS) muscle and its tendon is a prerequisite [Figure 1]. The PS muscle is a deep muscle of the posterior compartment of the leg on the lower part of the floor of the popliteal fossa. It takes its muscular origin from the medial border of tibia, soleal line, supra-soleal space, part of the bone forming a boundary above the supra-soleal space, and few muscle fibers from the fibula between soleus and tibialis posterior and above the peroneo-tibial band, and all these muscle fibers form the ovoid tendon which grooves the lateral meniscus (LM) [Figure 1]. Then, it runs upward rubbing against the caudal part of the articular surface of the lateral femoral condyle and finally gets inserted into the sulcus in front and just below the fibular collateral ligament (FCL) [Figure 1].[1] The musculo-tendinous junction (MTJ) complex makes up part of the PLC of the knee. Because its main function is to stabilize the lateral rotation between the femur and tibia, in case of its injury or involvement of PLC structures, a thorough knowledge of the PS is necessary to treat such ailments.[2] Hence, this article deals with the anatomy and its clinico-surgical implications.
Figure 1: The structures on the posterior aspect of the knee joint including posterolateral corner: (1) popliteal tendon, (2) popliteofibular ligament, (3) popliteo-meniscal fascicles, (4) popliteus muscle belly, (5) arcuate popliteal ligament, (6) fibular collateral ligament, (7) cut end of semimembranosus muscle, (8) fascia covering popliteus, and (9) lateral meniscus

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  Materials and Methods Top

This article followed PRISMA guidelines, wherein the databases and search engines used for the collection of literature review regarding the popliteus muscle are PubMed, Mendeley, Google Scholar, Google, Cochrane, ProQuest, and Sci-Hub.

Search terms used were popliteus, unlocking muscle, lateral condyle of femur, fibular collateral ligament, popliteo-meniscal fascicles, popliteofibular ligament, popliteus muscle-tendon unit, posterolateral corner, and popliteus tear. Search phrases such as anatomy of the popliteus, morphometric analysis of the popliteus, injuries to the posterolateral corner of knee, and clinical aspects of popliteus were used. Full articles in English regarding the human anatomy, embryology, and morphometric analysis of popliteus as well as comparative anatomy and the clinical and surgical aspects of popliteus during the past 10 years were chosen as the inclusion criteria. Abstracts and articles describing the PLC structures apart from the muscle studied were excluded from the study.

  Results Top

Seventy-six articles were adopted using the inclusion and exclusion criteria, among which 62 articles had fulfilled the need.

  Discussion Top

Gross anatomy

The main femoral origin of PS muscle is from the lateral condyle, anteroinferior to the FCL and inserted into the superomedial part of the posterior tibial surface, which maintains the integrity of the knee joint and acts as a lateral rotator.[3],[4] The PS is a triangular muscle covered by a thick fascia derived from the semimembranosus tendon, and it is innervated usually by two branches from the tibial nerve on its undersurface.[2],[5] These branches ran between the periosteum of the tibia and the PS and entered the muscle 1 cm below its upper border. The entry points of the nerves were located within a rectangle measuring about 2.0 cm × 3.0 cm on the superomedial side of the midline of popliteus fossa.[6]

The PS tendon

Lateral femoral condylar attachment of the PS tendon is intracapsular and partly intrasynovial at the level of the LM with a mean length of 5.45 cm.[7] The commencement of the PS tendon is round near the LM, while the upper part of the tendon is broad [Figure 1].[8] The thicker origin of the tendon from the capsule is found to be longer, and a fibrous attachment of the tendon extended to the posterior aspect of the fibrous capsule of the knee.[9] Very rarely, the PS tendon is divided into superficial and deep parts with the intervening synovial bursa, while the deeper part of the tendon is intra-synovial.[8] It was postulated that when the knee flexion increases, the PS muscle contracts to produce tension on the anterior fibers of the PS tendon, which leads to the tightening of the fibers of the tendon when the tibia is rotated externally.[10]

Further attachments of the PS and popliteomeniscal fascicles

The presence of an additional tendinous origin from the head of the fibula is homologous to the deeper part of the pronator teres in the forearm and inserted into the posterior horn of the LM.[3],[11],[12] The muscular insertion of the PS on the posteromedial aspect of the upper part of tibia acts as an alternative for the deprivement of the attachment of the posterior horn of the LM by the coronary ligaments.[12] The extension between the tendon of PS and the peroneal head is commonly described as the popliteofibular ligament (PFL) [Figure 1]. Usually, the PFL is attached to the posteromedial aspect of the styloid process near the apex which connects to the middle part of FCL and lower part of the tendon of the PS, which becomes loose in medial and taut in lateral rotations of tibia, respectively.[7],[12] The main function of the PFL is to resist the posterior dislocation of the lateral condyle of tibia.[13] In most of the studies, the fusion between PFL and the PS muscle or its tendon is called the PS MTJ. Usually, this ligament is attached either near or far from the junction, but in another study, the PFL is attached to the anterior aspect of the muscle fibers of the PS.[8] The shape of the PFL is commonly found to be ribbon, truncated cone, and very rarely inverted cone. This attachment possesses a protective mechanism by preventing the trapping of the meniscus during external rotation and flexion of the knee joint.[3],[14],[15]

It was thought that the PS did not have an interconnection with the LM. Later, three types of connections were noted. Type I – a slip of fibers from the PS to the upper margin of the dorsal part of LM, Type II – few fibers from the tendinous portion of the PS to the dorsolateral part of the periphery of the LM, and Type III – scanty muscle fibers of the PS attached to the dorsal part of the periphery of the LM. Conversely, few collagenous fibers extended from the proximal margin of the end part of the tendon to the upper margin of the posterior horn of the LM.[16] The most commonly found type was the Type I and the least was the Type III. The PS established attachment with the arcuate, oblique popliteal ligaments, and the posterior capsule of the knee.[17] In yet another study, these fibers are described as the posteroinferior, posterosuperior, and anteroinferior popliteomeniscal fascicles (PMFs), which fix the LM [Figure 1].[12],[18] Among these fascicles, the superior and inferior PMFs form the roof and floor of the popliteal hiatus, respectively. The PS tendon traverses through the normal apertures of the superior and inferior fascicles as it descends from lateral to the medial side through the popliteal hiatus. During such a course, it receives a prolongation from the synovial membrane of the knee joint as the popliteal bursa.[3] During the embryonic stage of the knee development, the head of fibula is exempted from the formation of the joint as the differential growth of tibia is more than the fibula. As a result, the head of the fibula possesses an extension of the posterolateral inferior capsule as it comes out of the joint, which forms the popliteal bursa.[19] Sometimes, these apertures can be mistaken for menisco-capsular detachment.[20] Disruption of these PMFs forms the basis for the mechanical locking of the knee joint. The fewer the fascicles, the greater is the extent of the injury.[17]

The arcuate ligament is considered as a Y-shaped thickening of the tendon of the PS [Figure 1]. An magnetic resonance imaging (MRI) study reported that upper one-third of the ligament maintained the attachment with the lower portion and the inner part of the ligament merge with the outer portion of the tendon of PS, respectively.[21] Paraskevas described it to be made up of the condensation of femoral, peroneal, discal, and capsular origins of the PS. Out of the two arms of the ligament, one arises from the styloid process of the head of the fibula and the other from the lateral articular disc. An aponeurotic extension of PS muscle connects the medial band of the arcuate ligament and capsule of the posterior aspect of the knee joint and posterior horn of the LM. Such an aponeurotic attachment is called the meniscal aponeurosis or posteroinferior PMF.[22]

Function of the PS

The PS acts as a medial rotator of the tibia when the foot is on the ground during the flexion of the knee, supports the posterior cruciate ligament (PCL), and together prevents the anterior displacement of the femur on the tibia while descending stairs.[14],[23] During initial knee flexion, some action potential in the PS was observed, and it showed pronounced action while the flexion is maintained.[14] The stability of the outer side of the knee joint in 90° of flexion is principally contributed by the proximal part of the PS like that of FCL.[23] The maximum activity of the PS and its tendon was recorded during the squat and constant activity of such structures was observed during the extension of the knee from squatting[24] and in contrast, its action potential is minimal during the standing position. The PLC of the knee acts as a fulcrum where the muscle forces are applied during the contraction of the PS because the muscle winds around the posterolateral aspect of the knee just above the MTJ.[25]

The protection of the LM from impingement during flexion of the knee is done by a combined effort of the PS and meniscofemoral ligament than by the sole action of the PS,[26] and the upper and lower PMFs control the inward displacement of the LM. The tear of the PMFs is the deciding factor that determines the level of injury to the LM. The lesions of the entire unit lead to loss of tension on the LM, causing damage rather than the injury of the individual component.[9] In case of anterolateral instability of the knee joint, the active contraction of the PS brings about the anterior displacement of the lateral tibial plateau, and it is called as a pivot-shift syndrome.[23]

In a normal gait cycle, the lower limb swings in the direction of internal rotation from the toe-off stage of the swing phase until the mid-stance. From this stage, the limb moves with external rotation until the next toe-off. The activity of the PS is maximum just before the heel strike and continues throughout the stance phase except for the last stage. It is believed that the PS prevents the foot from rotating in the outward direction in the terminal stage of the swing and in the first three-fourths of stance phases.[6],[27]

The PS muscle acts as a medial rotator of the tibia or lateral rotator of the femur in a packed knee during flexion.[3],[4] However, in contrast, the PS muscle is primarily an extensor and during flexion, its passive lengthening causes rotation of femur or tibia in a weight-bearing or free knee, respectively.[28],[29] During the knee extension, the attachment of the PS tendon is positioned behind the FCL, but it moves anteriorly beneath the FCL in flexion.[8],[12],[16] The PS is considered an important structure contributing to the neutral tibial rotation against the excessive lateral rotation of tibia even in the absence of the posterolateral ligaments, and its tendon is called as the “fifth ligament” which acts as the primary static stabilizer of the knee pertaining to varus angulation and anterior translation near extension, with a minimal stabilizing role in the internal rotation.[7]

Role of the PS in supporting posterior cruciate ligament

The PS muscle is oriented in the sagittal plane as that of the PCL, indicating a supportive function of the ligament. The PS muscle load may decrease the weight transmission forces in the PCL when it carries a load of 44 N, which is sufficient to share with the PCL at 30° of knee flexion. This finding suggests that it is a significant synergist to the PCL, thus reducing the risk of injury. The reduction in the posterior translation of the tibia is produced by the PS load in case of the knee with the PCL injury. This infers that the PCL has a role in stabilizing the posterior tibia by controlling the tension of the capsular and ligamentous complex of the knee during weight transmission. Therefore, the PS can be strengthened with the help of specific exercises in improving the stability of the knee in patients with PCL injury.[25] Inefficiency of the PCL can weaken the posterolateral structures, particularly the PS unit during weight-bearing knee flexion and vice versa. The resultant apparent lengthening of the muscle tendon unit might alter the knee kinematics, leading to instability.[30]

Comparative anatomy

The PS muscle belly and its tendon were independent of each other during development in the lower animals, and it is directly attached to the head of the fibula. These animals had a fibrocartilaginous disc between the femur and the fibula and on evolution, eventually turning into the PS tendon. In lower-order animals, this tendon indented the border of the lateral femoral condyle to produce a groove called the sulcus Sartorius of Fürst. In humans, the sulcus has the same location due to the upright posture.[31] In the lower-grade animals, the tibio-fibular portion of the PS is seen distally, and it does not gain attachment to the femoral condyle. However, in humans, this part ascended to get connected with the lateral femoral condyle. During this process, a few fibers of the PS are attached to the LM.[26] This muscle can be compared to the higher primates as in case of Chimpanzees, there are two rounded tendons. One of the tendons comes from the capsule of the knee joint behind the lateral femoral condyle and the other has a similar origin as in humans, but in case of Orangutans, the tendon from the posterior knee capsule also had an attachment to the superolateral part of the fibular head.[32] The PS muscle is homologous to the deep head of pronator teres, and if the muscle is presented with a superficial slip, then it would arise from the lateral head of gastrocnemius, which is usually seen in Chimpanzees.[11] Taylor and Bonney[11] studied that in domestic cats, the PS had three origins, namely from tibia, fibula, and popliteal fossa, and the lowest and outermost fibers of the PS joined with the muscle flexor tibialis digitorum pedis. In blackface kangaroo, this muscle has a similar origin as in humans with additional slips from a sesamoid bone in its tendon and head of the fibula and get inserted into the upper one-fifths of the tibia, but in case of the sloth bears, they presented an extra origin from the lateral supracondylar ridge of the femur. In case of rabbits, the PS muscle is large and takes its origin from the posteromedial margin of the tibia, and its insertion is similar to that of humans. There is no attachment with the LM, and the PFL is thin with the absence of PMFs. There is an aponeurotic sheath covering the PS tendon completely and the muscle fibers partly.[33]

The presence of sesamoid bone in the PS tendon or in its musculo-tendinous junction (MTJ) is a primitive character of the primates and it is called cyamella. Minor stated that it is always present in the New World monkeys and usually absent in Gorilla and humans. It articulates with the hind part of the articular surface of lateral tibial condyle adjacent to the fibular head if it is present. In rabbits, the presence of cyamella is reported to have a similar articulation with the MTJ as in other primates.[34]

PS complex injury and its surgical treatment with respect to the posterolateral corner

The MTJ unit of the PS, though it is much mobile structure, is prone to injury. The PS injury is rare, and it is mostly associated with the injury of posterolateral structures of the knee. A blow on the anteromedial side of the upper tibia with the externally rotated and hyper-extended knee leads to the PS muscle belly injury rather than the tendon of the PS.[20] The MTJ is the vulnerable point for injury, and the avulsion of the PS tendon may occur at the femoral insertion, and this area is very crucial in diagnosing the injury which can be demonstrated by MRI findings with increased signal intensity in the PS complex when there is a tear of the MTJ.[35]

A number of tests are applied to investigate the pathology of posterolateral knee structures. A specific test to rule out the damage to the PS muscle-tendon unit is the Dial test, which is positive at the earlier flexion of the knee and normal at 90°.[4],[35],[36] In PS tears, the site, its dimensions, presence of avulsed tendon with a bony fragment, the severity of the tendon retraction, and related menisco-ligamentous injury are essential to select the mode of surgery, if applicable.[20]

The surgical sectioning of the PFL does not produce any significant change in the lateral rotation, varus rotation, and posterior translation of the tibia, but along with sectioning of the PS tendon, it results in abnormal external rotation of the tibia. There is an extreme lateral rotation of the tibia in case of sectioning of the PS, especially at 90° to 120° of knee flexion with no significant change in the posterior translation or varus rotation.[13] Similarly, among the transections of the PCL, PFL, FCL, and tendon of PS, division of PS tendon alone increased both the external rotational arc and the external neutral tibial rotation irrespective of the positions of the knee joint.[36] The PFL reconstruction and the PS bypass operations are usually employed to restrain lateral tibial rotation. The utilization of the PS tendon or the PFL to reconstruct PCL and FCL would delineate the excessive anteroposterior laxity and thus regains the normal knee.[37] The posterolateral stability of the knee can be established by the construction of PCL, PFL, and PS tendon than the isolated reconstruction of the PCL itself.[24] Similarly, LaPrade et al.[38] showed that the reconstruction of the PS tendon using autogenous semitendinosus graft is inevitable to restore the external rotational stability of the knee as well as to prevent the concurrent PCL reconstruction graft failure.

The structures stabilizing the posterolateral knee are the PS tendon, PFL, and FCL. An abnormally increased posterolateral rotation shown by positive posterolateral drawer test is commonly applied to evaluate the lesions of PS tendon, PFL, and FCL. The site of the attachment of the PFL is taken into account for performing the reconstruction with a graft for the successful outcome of the knee instability.[8] The mean distance between the site of the femoral attachment of FCL and the PS tendon is 1.85 cm, which is considered being a surgically relevant finding for the reconstruction technique. During MRI investigation in cases of PLC instability and planning for reconstruction, the wider upper part of the PS tendon must be considered as a natural graft (Kurtoglu et al.). On the other hand, the surgical reconstruction of the PS tendon unit had no positive effect on the rotatory and varus stability of the knee, and it did not produce any effect on the posterior stability of the knee in the cases which had PCL reconstruction. However, in case of posterolateral instability, other structural lesions such as meniscal and ligamentous injuries have to be addressed with concomitant PS tenodesis.[39]

Allografts are used in the surgical reconstruction of PLC structures of the knee to give a satisfactory prognosis.[40] Reconstruction of the popliteal unit is achieved by muscle and tendon grafts from the hamstrings, tendo-Achilles, tibialis anterior, semitendinosus, and ilio-tibial tract, and repair of PFLs is accomplished by sutures.[4],[38],[35]

Anterior cruciate ligament (ACL) tear was the most commonly associated injury in 64% of cases with the posterolateral complex injury. The PS MTJ injury in combination with the injury of ACL was seen in cases when the knee was injured when it is flexed from the full extension with internally rotated tibia on the femur. It was observed that there exists an insignificant relationship between the PS and its tendon injury and varus or hyperextension injury mechanisms, and the finding of the PS injury can alert the surgeon to suspect ACL injury.[41] Stannard et al. opined that the anatomical reconstruction can be performed than repair if immediate rehabilitation of the patient is needed, and the injury of the PLC can be treated in avulsion fractures with multiple bony fragments. Further, they added that the quality of soft tissues such as the tendon or ligament is not sufficient to withstand the surgical procedure in case of repair. Most of the cases ended in failure within the tendon or ligament, but not at the site of sutures in repairing avulsion injury.[40] In contrast, Geeslyn et al.[42] recommended that reconstruction of the avulsed PS tendon or FCL can give a better outcome rather than the repair. Surgical repair of the avulsion of PS tendon, FCL, PFL, and reconstruction of mid-substance tears of the other main ligaments can be a choice of treatment in case of Grade-III PLC knee, to restore the functional stability of the knee, and they added that all mended structures should be fixed in the fully extended knee followed by gentle knee exercises postoperatively. Previous studies documented that the surgical outcome in PLC repair is poor when compared to the reconstruction techniques. MCarthy et al.[43] concluded that PLC repair showed improved results and hence, this type of surgical treatment can be an option to select patients with certain types of injury affecting the structures around the knee. In case of tears within the ligament versus avulsion injury, the quality of the tissue and the timing of surgery should be taken into account. Chronic mid-substance tears with low quality can be treated better with reconstruction techniques.

In case of the posterolateral surgical approach of the knee, the neurovascular structures must be identified in relation to the PS muscle. Sometimes, the popliteal artery may pass through the muscle belly of the medial head of gastrocnemius just medial to it. In such cases, the artery may pass in front of the musculature of the PS. Hence, in a muscle-splitting approach, the musculature of the PS can be dissected subperiosteally.[5]

Other injuries of the PS complex

The PS tendon tenosynovitis is a rare clinical condition usually occurring in athletes who are prone to a knee injury. Blake and Trebl[44] showed that this uncommon condition is associated with anterolateral knee pain. The MRI scan image revealed an unusual collection of fluid in relation to the sheath covering the PS with a normal tendon and no other evidence of involvement of other knee structures. The PS tendinitis can be due to downhill running or other deceleration activities. The varus and hyperextension deformities of the knee act as crucial factors for the development of the PS tendinitis. When the hip abductors are weak, the varus knee may strain the PS, while weak knee flexors will strain the muscle when there is genu recurvatum. The activities of the PS may be improved by strengthening exercises, deep tissue massage followed by hold and relax stretch, and also by backward and grapevine running.[45] The presence of cyamella in humans can irritate the PS tendon, leading to tendinitis which can be diagnosed by MRI.[46] Petsche et al.[47] reported a case of a young football player with posterolateral knee tenderness without any further complications and was diagnosed as PS tendinitis. The MRI finding showed a collection of fluid within the synovial bursa covering the proximal PS near the MTJ and further treated with corticosteroid injections. Correspondingly, in case of the PS muscle-tendon unit disorders, the PS tendon sheath injections can be performed as a treatment and diagnostic tool with the guidance of sonography in which the longitudinal approach can be more appropriate rather than the transverse approach.[48]

Cracking sound on the lateral aspect of the knee can be due to the snapping of the PS tendon, which produces pain, which may be spontaneous or due to trauma.[49] In an instance after the total knee arthroplasty, the PS tendon rubbing against the prosthetic femoral condyle on its posterolateral aspect produced popping during the movement of the knee. On such occasions, the surgical release of the femoral attachment of the tendon can relieve the symptom.[50] This type of problem can be tackled by increasing the size of the tibial component, thereby the PS tendon can be shifted from the articular surface during movements if there is impingement by prosthetic tibial condyle. Additionally, the surgical section of PMFs and LM can unfix the tendon in extreme flexion.[51] It is believed that the thickening of the tendon may lead to repetitive cracking sound proximally near the femoral attachment of the PS tendon. Hence, these patients complain about the sound during any activity that requires weight-bearing, which may be attributed to the varus stress applied on the knee producing stretching of the tendon, raising the intensity of the sound.[49]

Undue lateral rotation of the femur can cause tightness of the PS tendon, thereby tightening the lateral flexion gap, which requires the surgical release of the PS tendon in a varus or neutral knee. Such soft-tissue management is necessary to get a symmetrical flexion gap during total knee arthroplasty.[27] A large osteophyte on the lateral condyle of the femur in relation to the PS tendon creates tension in the muscle, and the PS tendon contracture may lead to external subluxation of the tibia. McAllister and Parker[52] studied a young adult with painful popping on the lateral side of the knee with no other symptoms or history of trauma, which was aggravated by active flexion and extension at around 45° of knee flexion on clinical examination. The PS tendon was identified surgically with subluxation out of its groove on the lateral condyle of the femur. Later, the tendon was fixed at its groove with nonabsorbable suture and suture anchor.[27]

Spontaneous rupture of the PS MTJ complex is uncommon. Murray et al.[53] reported a case of an elderly woman with a spontaneous rupture of the PS tendon and presented with pain at the back of the knee, radiating to the calf region with no instability. On arthroscopy, it was found that a bulge protruded into the joint cavity at the PS hiatus followed by the rupture of its contents into the cavity. The prognosis was better 3 weeks after performing the resection of the avulsed PS tendon and its fixation at its anatomical location. Specific rehabilitation protocol can be advised as conservative management in isolated PS tendon rupture. This consists of isometric exercises of quadriceps, strengthening exercises for gastrocnemius, soleus, hamstrings, and graded activity.[54]

Kheir et al.[55] reported a case of spontaneous rupture of PS tendon without knee injury. The symptoms in such a case were a painful locked knee without the involvement of stability. Surgical excision of the ruptured part of the tendon was made following knee arthroscopy. Winje and Phadke[56] reported two young polo players with pain and tenderness of the posterolateral knee after external rotation trauma, and MRI scan revealed PS muscle tear without involving its tendon and with no hemarthrosis. The patient recovered completely after physiotherapy and rest. Usually, the PS tendon rupture is associated with hemarthrosis as it is intra-articular unlike muscular rupture which may be due to the application of thrust on the lateral side during lateral rotation of the tibia in a flexed knee, resulting in pain with posterolateral tenderness. Arthroscopy can confirm the tear of the PS tendon after the removal of the hemarthrosis. The tendon rupture can be managed traditionally with minor surgery such as excision of avulsed bony fragment excluding the repair of the PS tendon, fixation of the bony fragment with screws, and suturing the tendinous intra-substance tear.[57]

Isolated injury of the PS muscle is rare. The part of the PS behind the articular surface of the lateral condyle of the tibia is at risk for strain because the proximal part is fixed by the arcuate popliteal ligament. Therefore, such a strain may be followed by a twist of the knee when the foot is on the ground with posterior knee pain. Treatment modes can aim in injecting the PS and advising stretching exercises for the flexors of the knee to prevent the above condition.[58]

Popliteal dysfunction can be due to the trauma to the muscle itself or knee trauma or as a postsurgical complication, which can be identified by a deficit in the final 5° of extension of knee, leading to lack of screw-home locking movement. Other signs include posterolateral knee pain and tenderness which are treated by the general petrissage technique after the relaxation of the overlying musculature.[59] Forefoot adduction deformity is frequently seen in children with cerebral palsy. One of the common causes is medial tibial torsion, which is due to spasticity of the PS muscle. Such spasticity can be relieved successfully by injecting alcohol if the motor entry point is known precisely.[6]

Arthroscopically, Doral et al.[60] found the PS with three muscle belly at the popliteal hiatus, which formed a single tendon. Such a finding has to be kept in mind to avoid misinterpretation of tendinosis. A MRI study showed an additional PS muscle with a common origin as the lateral head of gastrocnemius muscle from the posterior aspect of the femur above the lateral condyle, and it descended obliquely superficial to the muscle and deep into the popliteal artery. It is inserted into the posteromedial knee capsule proximal to the semimembranosus muscle insertion.[61] Bartonícek[62] documented the bilaterally varied origin of the PS muscle, with the medial part originating from the lateral femoral condyle excluding the posterior knee capsule at the level of the posterior horn of LM. Such variation might pose a difficulty in PLC surgery if the upper margin of the muscle is taken as a landmark. In his study, the reconstruction of the PS tendon did not have a significant effect on the varus and rotatory stability of the knee on physical and radiographic examinations. In addition, it did not affect the posterior stability of the knee of the cases who underwent PCL reconstruction.

  Conclusion Top

The PS trauma is usually associated with other knee injuries, but sometimes it may be an isolated injury or spontaneous in onset. The finding of the PS MTJ injury would alert the surgeon to investigate the injury of the PCL, anterior cruciate ligament, and the LM tear. The surgical reconstruction or repair of the PS unit is significant to avoid knee instability because it acts as a dynamic stabilizer. One of the causes of knee pain is attributed to the PS tendinitis which can be treated conservatively. The lack of final 30° of knee extension is observed to be a salient feature in diagnosing PS tendon tears. Variations such as varied muscle attachments, additional muscle belly, and the presence of duplicated muscle have to be borne in mind, which might be mistaken for other knee pathology.

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  References Top

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