Morphological variability of the leg muscles: potential traps on ultrasound that await clinicians.

BACKGROUND: Although muscles and their tendons are not considered the most morphologically variable structures, they still manifest a substantial diversity of variants. The aim of this study is to increase awareness of some of the many possible variants found during ultrasound imaging of one lower limb compartment, the leg, that could potentially mislead clinicians and lead to misdiagnosis. MATERIALS AND METHODS: PubMed was used for a comprehensive literature search for morphological variations. Relevant papers were included, and citation tracking was used to identify further publications. RESULTS: Several morphological variants of muscles of the leg have been described over many years, but this study shows that the occurrence of further variations in ultrasound imaging requires further investigations. CONCLUSIONS: The incidence of additional structures including muscles and tendons during ultrasound examination can cause confusion and lead to misinterpretation of images, misdiagnosis, and the introduction of unnecessary and inappropriate treatments.

The subpopliteal fat body.

INTRODUCTION: The knee is likely to get hurt due to its excessive weight-bearing, for which it is surrounded by strongly tensioned ligaments, connectives and muscles. These highly active structures are imbedded in fatty tissue. The Fatty and loose connective tissue of the knee recently gained a renaissance in research. While the Hoffa fat body in the ventral knee attracted attention over the last years, we have investigated a smaller, dorsal fat body, ventral to the popliteus muscle. This fat body has not been described before. MATERIALS AND METHODS: 11 knees of 11 fresh specimens were investigated. All muscles but the popliteus muscle were removed. The popliteus was released from its tibial origin and dissected towards its tendinous insertion. Thereby, a subpopliteal fat body (SFB) was shown. The related vessels and nerves were evaluated. The size of the body was measured. Examples of histological slices were stained with HE and immunostained against neurofilament. RESULTS: The SFB lies ventral of the popliteus muscle at the concave posterior tibia and attaches to the periosteum and the popliteus muscle. It is not attached to the posterior cruciate ligament. It is separated from the subpopliteal recess by a lamella deriving from the fibular head. Arterial and venous vessels are seen entering the SFB, deriving from the popliteal artery or the anterior tibial artery. A subbranch of the tibial nerve was seen to reach the SFB. The SFB could be identified in MRI scans and in plastinations. DISCUSSION: Primarily, the SFB provides a gliding space for the mobile part of the popliteus muscle over the tibia. The SFB lies within the tibial concavity, ventral to the popliteus muscle. This is exactly where embryologically, the popliteal artery passes through, before its involution in later stages. Therefore, the SFB may show the former perivascular autonomic nerves which encompass the embryologically created arteries, from which we have seen the arterial remnants. The nerves seen here form neurovascular bundles which could be a source of pain, when compressed. This anatomy may explain the autonomic component of pain in the deep lateral region of the knee. The SFB is functional fat, comparable to the Hoffa's fat pad in the ventral knee.

Characterastics of muscle architectural parameters for early knee osteoarthritis in middle-aged and elderly women / 中国康复理论与实践

ObjectiveTo observe the architectural parameter changes of the muscles around the knee in middle-aged and elderly women with early knee osteoarthritis (KOA) by musculoskeletal ultrasound, and to clarify the indicators of muscles that affect early KOA. MethodsFrom January to August, 2022, 20 healthy middle-aged and elderly healthy women (controls) and 20 middle-aged and elderly women with unilateral early KOA (KOA group) were recruited through Beijing Bo'ai Hospital, to measure muscle thickness of the popliteus muscle, the muscle thickness and the pennation angle of the quadriceps, as rectus femoris, vastus intermedius, vastus lateralis, vastus medialis longus and vastus medialis oblique. ResultsCompared with the healthy limb of KOA group, and the controls, the muscle thickness of vastus medialis longus, vastus medialis oblique and popliteus muscle of the affected limb of KOA group became thinner (t > 2.133, P < 0.05); the proportion of thickness of vastus medialis oblique to thickness of vastus lateralis became smaller (t > 3.660, P < 0.05). The pennation angle was smaller in the affected limb of KOA group than in the matched dominant side of the controls (t = 3.101, P < 0.05). Logistic regression analysis showed that the muscle thickness of vastus medialis oblique (OR = 0.235, 95%CI 0.068 to 0.805, P = 0.021) and popliteus muscle (OR = 0.387, 95%CI 0.152 to 0.980, P = 0.045) were related to the onset of early KOA. ConclusionThe thickness of vastus medialis longus, vastus medialis oblique and popliteus muscle decrease, and the balance of the strength of vastus medialis oblique and vastus lateralis weakens in the affected limbs of the middle-aged and elderly women with early KOA. The thickness of vastus medialis oblique and popliteus muscle are protective factors for onset of KOA.

Classification of the popliteofibular ligament.

The purpose of this study was to characterize the morphological variations in the distal attachment of the popliteofibular ligament (PFL) and create an accurate classification for use in planning surgical procedures in this area and in evaluating radiological imaging. One hundred and thirty-seven lower limbs of body donors fixed in 10% formalin solution were examined for the presence and course of the PFL. The PFL was present in 88.3% of cases. We propose the following three-fold classification: type I (72.3%), the most common type, characterized by the attachment onto the apex of the head of the fibula, type II (8.7%), characterized by a bifurcation, with the dominant band inserting on the anterior slope of the styloid process of the fibula and the smaller band onto the posterior surface of the styloid process of the fibula and type III (7.3%), characterized by a double PFL: the first PFL (main) originated from the popliteus tendon and inserted onto the anterior slope of the styloid process of the fibula, while the second originated from the musculotendinous junction of the popliteus muscle and inserted on the posterior surface of the styloid process of the fibula. The PFL was characterized by high morphological variation, as reflected in our proposed classification. This variation may present clinical and biomechanical issues for both medical personnel and researchers. Our proposed classification may be valuable for clinicians who evaluate and perform surgical procedures within the knee joint area.

Current concepts on the morphology of popliteus tendon and its clinical implications.

In this review we described the anatomy and biomechanics of popliteus muscle and its tendon. Furthermore, we combined the anatomy with clinics and discussed a wide spectrum of disorders regarding the popliteus and its musculotendinous complex. There are three main anatomical regions of the popliteus musculotendinous complex: the proximal origin, the mid-portion, the distal part on the tibia. The unique localisation and various origins of the tendon, connected with structures such as fibular head, Wrisberg, Humphrey and posterior cruciate ligament, lateral meniscus, medial collateral ligament, give an implication to diagnosis and treatment. Popliteus dysfunction is often overlooked, that is the reason why diagnosis and treatment of its injuries is mostly insufficient. Repetitive or acute direct varus forces, when the tibia is in external rotation, and knee hyperextension or flexion with forced external rotation of the tibia, are the main mechanisms of trauma. Popliteus injuries mainly affect the athletic population and lead to severe activity limitations. Chronic disorders of the popliteus tendon, less known, are often described as tendinopathy and are frequently seen in runners. Their symptoms can mimic the lateral meniscal tears. On the other hand, high-energy traumatic injuries of the popliteus tendon often accompany complex, multi ligamentous injuries seen in competitive sports. We also presented the implication of popliteus tendon in knee arthroplasty, due to its particular exposition to iatrogenic trauma during surgery. The issues such as proper tibial component location and well-designed cut systems are crucial to avoid the popliteus impingement and preserve its structure.

Positional changes in tendon insertions from bone to fascia: development of the pes anserinus and semimembranosus muscle insertion in human foetuses.

Development of a long muscle belly in foetal extremities generally requires a definite bony insertion of the long tendon. However, in adults, the pes anserinus and the semimembranosus tendon (SMT) are inserted into fasciae. Development of fascial insertions in foetuses was investigated by examining serial histological sections obtained from 7 foetuses at 8-9 weeks and 8 foetuses at 14-16 weeks. The presence of matrix substances and macrophages was also examined by immunohistochemistry. At 8 weeks, the tendons of the semitendinosus, gracilis, sartorius and semimembranosus muscles were straight and inserted into the initial shaft-like proximal end of the tibia on the proximal side of the popliteus muscle. At 9 weeks, however, the medially extending popliteus muscle appeared to push the pes anserinus tendons superficially, with a loss of cartilage insertions. The SMT obtained an attachment to the popliteus muscle. At 14-16 weeks, the SMT divided into thick and thin bundles: the former contained abundant macrophages and inserted into the tenascin-positive perichondrium of the enlarged proximal tibia, while the later without macrophages ended at the joint capsule. The pes anserinus tendons, negative for both versican and tenascin-c, took highly tortuous courses toward the fascia cruris. Because the medial extension of the popliteus muscle was associated with the enlargement of the proximal tibia, the topographical relationship of the popliteus muscle with these 4 tendons changed drastically, resulting in a loss of cartilage insertion of the pes anserinus tendons as well as the division and reconstruction of the SMT.

Neurovascular Compression Caused by Popliteus Muscle Enlargement Without Discrete Trauma.

Popliteal entrapment syndrome caused by isolated popliteus muscle enlargement is very rare, although its occurrence has been reported after discrete trauma. However, popliteal artery stenosis with combined peroneal and proximal tibial neuropathy caused by popliteus muscle enlargement without preceding trauma has not been reported. A 57-year-old man presented with a tingling sensation and pain in his left calf. He had no previous history of an injury. The symptoms were similar to those of lumbosacral radiculopathy. Calf pain became worse despite treatment, and the inability to flex his toes progressed. Computed tomography angiography and magnetic resonance imaging of the lower extremity showed popliteal artery stenosis caused by popliteus muscle enlargement and surrounding edema. An electrodiagnostic study confirmed combined peroneal and proximal tibial neuropathy at the popliteal fossa. Urgent surgical decompression was performed because of the progressive neurologic deficit and increasing neuropathic pain. The calf pain disappeared immediately after surgery, and he was discharged after the neurologic functions improved.

In vivo ultrasound imaging of the popliteus muscle: investigation of functional characteristics.

[Purpose] The aim of this study was to use ultrasound imaging equipment for in vivo observation of the popliteus muscle thickness during rest and exercise to examine its functional characteristics and to establish a training method for this muscle. [Subjects and Methods] The subjects included 30 healthy adults (15 men and 15 women). The measurement tasks, consisting of isometric knee flexion and extension and internal rotation of the lower leg were performed in an arbitrary order. The popliteus muscle thickness was measured using an ultrasound. [Results] The popliteus muscle thickness significantly increased in the internal rotation in 27 subjects (90%), whereas, it remained unchanged in the remaining three subjects (10%). [Conclusion] This study differed from most of the previous studies because it involved in vivo observation of the popliteus muscle. We found that ultrasound was an effective method for the measurement of popliteus muscle thickness. The results suggest that internal rotation of the lower leg is the most effective exercise for working the popliteus muscle.

Is it safe to reconstruct the knee Anterolateral Ligament with a femoral tunnel? Frequency of Lateral Collateral Ligament and Popliteus Tendon injury.

PURPOSE: This study sought to determine the safety limits for performing a femoral bone tunnel to reconstruct the knee anterolateral ligament (ALL) by establishing its distance from the lateral collateral ligament (LCL) and the popliteus muscle tendon (PT) on the lateral femoral condyle. METHODS: Anatomic study on 48 knee cadaveric specimens. The femoral attachments of the studied structures were isolated, and the distance between them was measured. For each cadaver, the percentage of cases in which at least 50 % of the LCL and PT would be injured when using 4- to 12-mm-diameter drills in an ALL reconstruction procedure was evaluated. RESULTS: The LCL and PT were 3.8 mm and 10.2 mm distant from the ALL, respectively. A 4-mm tunnel would cause LCL injury in 8.3 % of cases, with increasing incidence of injury up to 87.5 % with a 12-mm drill. Injury to the PT would start with the 10-mm drill, causing injury in 2.0 % of cases. CONCLUSIONS: Performing a tunnel in the center of the ALL may cause an iatrogenic injury to the LCL origin. No cases of PT injury are expected to occur with drills smaller than 10 mm.

Neurovascular Compression Caused by Popliteus Muscle Enlargement Without Discrete Trauma

Popliteal entrapment syndrome caused by isolated popliteus muscle enlargement is very rare, although its occurrence has been reported after discrete trauma. However, popliteal artery stenosis with combined peroneal and proximal tibial neuropathy caused by popliteus muscle enlargement without preceding trauma has not been reported. A 57-year-old man presented with a tingling sensation and pain in his left calf. He had no previous history of an injury. The symptoms were similar to those of lumbosacral radiculopathy. Calf pain became worse despite treatment, and the inability to flex his toes progressed. Computed tomography angiography and magnetic resonance imaging of the lower extremity showed popliteal artery stenosis caused by popliteus muscle enlargement and surrounding edema. An electrodiagnostic study confirmed combined peroneal and proximal tibial neuropathy at the popliteal fossa. Urgent surgical decompression was performed because of the progressive neurologic deficit and increasing neuropathic pain. The calf pain disappeared immediately after surgery, and he was discharged after the neurologic functions improved.

Neurovascular Compression Caused by Popliteus Muscle Enlargement Without Discrete Trauma

Popliteal entrapment syndrome caused by isolated popliteus muscle enlargement is very rare, although its occurrence has been reported after discrete trauma. However, popliteal artery stenosis with combined peroneal and proximal tibial neuropathy caused by popliteus muscle enlargement without preceding trauma has not been reported. A 57-year-old man presented with a tingling sensation and pain in his left calf. He had no previous history of an injury. The symptoms were similar to those of lumbosacral radiculopathy. Calf pain became worse despite treatment, and the inability to flex his toes progressed. Computed tomography angiography and magnetic resonance imaging of the lower extremity showed popliteal artery stenosis caused by popliteus muscle enlargement and surrounding edema. An electrodiagnostic study confirmed combined peroneal and proximal tibial neuropathy at the popliteal fossa. Urgent surgical decompression was performed because of the progressive neurologic deficit and increasing neuropathic pain. The calf pain disappeared immediately after surgery, and he was discharged after the neurologic functions improved.

Popliteus muscle hemorrhage as a rare cause of a proximal tibial neuropathy.

Proximal tibial neuropathy is an uncommon focal mononeuropathy that is most often caused by trauma, ischemia, or neoplastic infiltration or compression of the tibial nerve. We report a patient who presented with a tibial neuropathy following a leg injury, which initially mimicked a lumbosacral radiculopathy but which was the result of a proximal tibial neuropathy. Electrophysiologic studies confirmed a proximal tibial neuropathy and MRI revealed a popliteus muscle hemorrhage with mass effect on the tibial nerve. Following conservative management the patient had little recovery of function after 15 months.

Shape and innervation of popliteus muscle.

The aim of this study was to delineate the shape of the popliteus muscle and determine the correct motor point site for treating spasticity. A total of 22 legs from 13 fresh Korean cadavers were evaluated. The x-axis was set as a transverse line across the lateral and medial epicondyle of the femur and the y-axis as a vertical line at the midpoint of the medial malleolus of the tibia and lateral malleolus of the fibula. The popliteus muscle is an obtuse triangle in shape. Superior, medial, and inferior angles were 27.2±4.3°, 114.8±19.8°, and 38.0±18.8° respectively. The lengths of the superior, medial, and lateral sides of the triangle were 7.6±1.0 cm, 6.2±1.0 cm, and 11.9±1.5 cm respectively. Nerve branches ran superficially on the periosteum of the tibia and entered the popliteus on its superficial surface. The diverging point of the nerve branch entered the popliteus from the tibial nerve located at the midline of the popliteal fossa and 17% of the leg length above the intercondylar line. Most nerve entry points (83.3%) were within a 2.0×3.0 cm rectangle with the center located at -1.0 cm (-7%) on the x-axis and -3.3 cm (-9%) on the y-axis.

Shape and innervation of popliteus muscle / 대한해부학회지

The aim of this study was to delineate the shape of the popliteus muscle and determine the correct motor point site for treating spasticity. A total of 22 legs from 13 fresh Korean cadavers were evaluated. The x-axis was set as a transverse line across the lateral and medial epicondyle of the femur and the y-axis as a vertical line at the midpoint of the medial malleolus of the tibia and lateral malleolus of the fibula. The popliteus muscle is an obtuse triangle in shape. Superior, medial, and inferior angles were 27.2+/-4.3degrees, 114.8+/-19.8degrees, and 38.0+/-18.8degrees respectively. The lengths of the superior, medial, and lateral sides of the triangle were 7.6+/-1.0 cm, 6.2+/-1.0 cm, and 11.9+/-1.5 cm respectively. Nerve branches ran superficially on the periosteum of the tibia and entered the popliteus on its superficial surface. The diverging point of the nerve branch entered the popliteus from the tibial nerve located at the midline of the popliteal fossa and 17% of the leg length above the intercondylar line. Most nerve entry points (83.3%) were within a 2.0x3.0 cm rectangle with the center located at -1.0 cm (-7%) on the x-axis and -3.3 cm (-9%) on the y-axis.