Symptomatic tensor fasciae suralis muscle as accessory muscle at popliteal fossa in young soldier: a case report

Abstract

Introduction

The tensor fasciae suralis is an aberrant muscle frequently identified in cadaveric studies and MRI studies; however, it has been rarely reported in clinical studies. We present a case of recurrent popliteal pain in a young adult male and our experience with its diagnosis and treatment.

Case presentation

A 20-year-old active-duty soldier presented with recurrent right popliteal pain, initially triggered by intense physical activity during military training. Pain subsided with rest but recurred after strenuous exercises, such as soccer. Examination revealed a palpable soft mass with mild tenderness and swelling in the popliteal region. Ultrasonography identified an aberrant tensor fasciae suralis muscle with perifascial edema, originating from the semimembranosus muscle and attaching to the fascia of the medial gastrocnemius. MRI confirmed the findings with edema at its boundary. Conservative management led to symptom improvement. A follow-up ultrasound six months later showed resolution of swelling.

Conclusion

This case highlights the importance of recognizing the TFS muscle to avoid misdiagnosis and unnecessary interventions.

Introduction

The tensor fasciae suralis(TFS) muscle, known as ischioaponeuroticus, since it was first discovered in an anatomical cadaver laboratory [1]. The TFS muscle exhibits various morphological and morphometric characteristics, originating from the long head or short head of the biceps femoris or the semitendinosus muscle, and inserting into the Achilles tendon, sural fascia, or the medial head of the gastrocnemius [2,3,4,5]. This muscle has no symptoms or symptoms of swelling have been reported [6,7,8,9]. However, clinical experiences of swelling and pain due to tensor fascia are rarely reported [10]. In particular, if the muscle is located in the center of the popliteal fossa, excessive exercise may cause pain and swelling.

Case report

The patient is a 20-year-old active-duty soldier who began experiencing pain in the right popliteal region during military training after enlisting. Intermittent pain would occur in the popliteal area following intense physical activity but subsided with rest without requiring any specific treatment. He visited our hospital during military leave due to recurrent pain following a recent soccer game. On initial examination, there were no signs of swelling, effusion, patellar compression test, or joint line tenderness, and the range of motion was normal. However, swelling was observed in the popliteal area, and a soft mass measuring approximately 10.5 cm in length and 1 cm in thickness was palpated in the subcutaneous tissue. The mass exhibited mild tenderness, and the patient experienced mild pain around the popliteal area when in a squatting position. Blood laboratory tests revealed no significant abnormalities.

Ultrasonography using a linear 12–5 MHz array transducer (EPIQ 7G, Philips Medical Systems, Bothell, WA, USA) of the popliteal region revealed an abnormal TFS muscle compared to the healthy side. The TFS muscle was elongated beneath the subcutaneous fat layer, with hypoechoic perifascial edema observed between the TFS muscle and the medial head of the gastrocnemius muscle. The TFS muscle originated from the semimembranosus muscle and was attached to the fascia over the medial head of the gastrocnemius muscle, which appeared slightly swollen. (Figs. 1 and 2)

Fig. 1

On the right leg, the transverse ultrasound image shows the TFS muscle (arrow) located posterior, superficial to the gastrocnemius medial head (asterisk). But TFS muscle could not be seen from the normal left leg

Fig. 2

On the right leg, the longitudinal ultrasound image shows the TFS muscle (arrow) located posterior, superficial to the gastrocnemius medial head (asterisk). Hypoechoic perifascial edema is present between the TFS muscle and medial head of gastrocnemius muscle. But TFS muscle could not be seen from the normal left leg

Magnetic Resonance Imaging (MRI) [3.0T, Skyra, Siemens Healthcare, Erlangen, Germany] was performed to evaluate the entire length of the TFS muscle, from its origin at the semitendinosus muscle to its attachment at the fascia of the medial head of the gastrocnemius muscle, and findings were compared with the healthy side. A 12 × 7 × 1.2 cm aberrant muscle was identified in the superficial area of the popliteal region. Slightly increased signal intensity, suggestive of edema, was observed at the boundary with the semitendinosus muscle. (Figs. 3, 4 and 5)

Fig. 3

Axial T1-weighted image shows an anomalous muscle (arrow) is superficially located in popliteal region

Fig. 4

Sagittal T1-weighted image shows an anomalous muscle (white arrow) originating from the semitendinosus muscle (gray arrow), this muscle located superior and posterior to the gastrocnemius muscle fascia (black arrow)

Fig. 5

Axial T2-weighted image shows an anomalous muscle (arrow) is located in the right leg, but it could not be seen from the normal left leg

In his past medical history, the patient visited our outpatient clinic two years ago with right popliteal pain following intense exercise. Symptoms improved with conservative treatment after radiographic examination. Additionally, when similar symptoms occurred during his time in the military, an MRI study was conducted at a military hospital, where he was informed that the MRI showed nonspecific findings. However, upon reevaluation of the MRI images taken at that time, the presence of the TFS muscle was identified.

After being diagnosed with the presence of the accessory TFS muscle, the patient was transferred to a department within his military unit that required minimal training and exercise. Restriction of physical activity, adequate rest, and the use of non-steroidal anti-inflammatory drugs resulted in significant pain improvement. A follow-up ultrasound examination conducted six months later confirmed that the swelling of the TFS muscle had subsided.

This muscle is located superficially near the popliteal crease, where its swelling during excessive exercise can cause popliteal pain. Additionally, it may be mistaken for a mass, as it is abnormally palpable compared to the healthy leg. However, it can be easily identified using ultrasound or MRI. Without an understanding of the TFS muscle as an accessory muscle, diagnosing symptoms caused by this aberrant muscle may be challenging. Furthermore, the TFS muscle is prone to swelling following intense exercise involving the knee joint, but symptoms typically resolve with rest.

Discussion

The TFS muscle is an anatomical variation found in the popliteal region. Since its first description by Kelch in 1813, various shapes and forms have been reported by several authors based on anatomical displacements observed during cadaver dissections [1]. Recently, subtypes of the TFS muscle have been classified based on differences in muscle origin and insertion, as analyzed in previously published studies [2, 3].

The TFS muscle is a type of accessory muscle that has been reported to occur symmetrically in both legs, although this is rare. It most commonly occurs in one leg and is predominantly found in men [3]. The TFS muscle typically originates from the long head of the biceps femoris muscle, the short head of the biceps femoris muscle, or the semitendinosus muscle. Its insertion points include the Achilles tendon, sural fascia, or the medial head of the gastrocnemius muscle. The muscle is primarily innervated by the tibial nerve, although in some cases, it may be innervated by the sural nerve [2, 3].

Bale et al. analyzed several previously reported cases and classified 38 TFS muscles (32 from cadaver studies and 6 from radiologic reports) into six subtypes based on differences in muscle origin and insertion [3]. Gonera et al. proposed renaming the muscle as the “popliteofascial muscle,” arguing that this term more accurately reflects its anatomical characteristics. The accessory muscle, traditionally referred to as the TFS muscle, originates from the popliteal surface of the femur and is most commonly inserted into the deep fascia surrounding the gastrocnemius, with some cases inserting into the Achilles tendon [2].

In 1995, Chason reported a 40-year-old male athlete who presented with swelling and a palpable mass after running. This case was the first to describe MRI findings of the TFS muscle. Since then, ultrasound findings [7, 8] and MRI findings [6,7,8,9,10] related to the TFS muscle have been reported only rarely. Differential diagnoses based on MRI findings include Baker’s cyst, soft tissue tumors, aneurysms of the popliteal artery, popliteal abscesses, blood clots in superficial vessels such as the lesser saphenous vein, and protruding pathological changes in superficial nerves.

The accessory soleus muscle is a common type of accessory muscle, typically located between the Achilles tendon and the soleus muscle. Other examples include the peroneus quartus muscle in the foot, the accessory lumbricalis muscle, and the extensor digitorum manus muscle in the hand. These muscles are usually asymptomatic; however, the accessory lumbricalis muscle can sometimes cause symptoms such as numbness or tingling due to nerve compression in the carpal tunnel. Accessory muscles around the knee joint, such as accessory slips in the medial or lateral head of the gastrocnemius muscle, are relatively common findings on MRI and can occasionally cause popliteal artery entrapment. In contrast, the TFS muscle is rarely observed. However, due to its superficial location in the popliteal region, it can be mistaken for a soft tissue tumor.

Ultrasound is a low-cost, noninvasive diagnostic tool that can easily assess the relationship between muscles and surrounding structures, such as fascia, and differentiate between solid and liquid structures. Given that the TFS muscle is a superficial muscle, it can be readily diagnosed using ultrasound [7, 9, 10].

MRI can also aid in the diagnosis of the TFS muscle. However, if the field of view is not adequately set during the MRI examination, it may be challenging to determine the muscle’s origin, insertion, and overall shape. In such cases, an additional ultrasound examination can provide valuable supplementary information [7,8,9,10].

The TFS muscle is a rare aberrant accessory muscle that is typically asymptomatic. While there are occasional reports of swelling accompanied by pain, no cases of recurring symptoms have been documented to date.

If symptoms such as swelling and pain are associated with this muscle, ultrasound or MRI can be valuable diagnostic tools to avoid unnecessary surgical intervention. However, without awareness of the TFS muscle as an accessory muscle, interpreting these symptoms as being caused by an aberrant muscle may be challenging.

When the TFS muscle is not located at the exact center of the popliteal crease, it usually does not cause pain or swelling and may resemble a popliteal mass or Baker’s cyst. However, when the TFS muscle is located at the center of the popliteal fossa, repeated flexion or physical activity can irritate the popliteal crease, leading to pain or swelling. Recognizing the rare aberrant muscle, TFS muscle, during clinical practice and utilizing MRI or ultrasonography can be beneficial for diagnosis and treatment.

The tensor fasciae suralis is an aberrant muscle frequently identified in cadaveric studies and MRI studies; however, it has been rarely reported in clinical studies. The authors report the findings of ultrasound and MRI of TFS muscles accompanied by pain due to excessive exercise with a review of the literature compared to the health side.