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Journal of the Anatomical Society of India

An anomalous muscle in the region of the popliteal fossa: A case report

Author(s): Gupta Roopam Kumar, Bhagwat S.S.

Vol. 55, No. 2 (2006-07 - 2006-12)

Gupta Roopam Kumar, Bhagwat S.S.
Government Medical College & Hospital, Surat, Gujarat.

Abstract:

The present case report is regarding the incidental finding of an anomalous muscle, 27.5 cm long, in the popliteal region during routine dissection of a male, middle aged cadaver. The muscle was shaped like the letter ‘Y’. The upper slips were attached to the semitendinosus and the long head of the biceps femoris at the mid thigh level. The lower slip was attached at the junction of the two heads of gastrocnemius muscle.

The two upper slips meet the one lower slip at a ‘w’ shaped tendinous intersection at the middle of the muscle. The innervation of the upper part of the muscle was via the tibial component of the sciatic nerve. No other anomalies were noted in this specimen.

This is considered to be a case of Tensor Fascia Suralis muscle and the third head of gastrocnemius muscle present in the same specimen.

Key words: Anomalous muscle, Tensor Fascia Suralis, Third head of Gastrocnemius, Semitendinosus, Biceps Femoris

Introduction:

Variations in muscle arise primarily due to our genetic composition, an inheritance carried over from our ancient origins. Many or most variations are totally benign; some are errors of embryologic developmental timing or persistence of an embryologic condition. Some of these variations may seriously compromise parts of the muscular, vascular, nervous, skeletal and / or other organ systems.

It was the notion of Galen that the human body has been created in the best possible way, reflecting the perfection of the Creator, and that variations are the result of imperfect or unnatural development. The variations, according to Galen and Vesalius, must be unnatural, the handiwork of the Devil. (Straus et al 1943)

Tensor fasciae suralis or ischioaponeuroticus is a slip that leaves the belly of the semitendinosus (it may also be one of the other hamstrings) and ends in a tendon that joins the fascia of the leg (Ronald et al 1995)

Case reports of Tensor fasciae suralis muscle have been published time and again. (Somayaji S.N. et al 1998; Miyauchi R. 1985; Frey H. 1913; Barry D. et al 1924; Montet X et al 2002; Seema S.R. & Balakrishna 2001 & Parsons FG ,1920)

Text books of Anatomy also describe the more frequent variations. (Schaeffer 1947 & Henry W.1962). The Third head (Caput tertium) is the most common variation of the gastrocnemius muscle (Bergman R.A et al 1995 & William et al 1995).

Material & Method:

During routine dissection of a male cadaver of approximately 40 years age and muscular build, a muscle variation was found in the Right popliteal fossa region. The muscle was carefully cleaned, preserving the attachments, relative position and neurovascular connections. Careful dissection was carried out in the whole limb and all other structures were found to be normal. This muscle was studied & photographed. The leg was preserved in formalin in the museum for future reference.

Case Report:

The surface anatomy of the right popliteal fossa region of the cadaver being dissected was apparently normal. The skin, superficial fascia and deep fascia were removed along with the cutaneous nerves and superficial veins of the area which were normal. On exposing and clearing the boundaries of the popliteal fossa, abnormal muscular tissue was found in the popliteal fossa close to the roof of the fossa. This muscle was cleaned and studied. (Fig. 1).

The muscle was shaped like the letter ‘Y’ which was attached by two upper slips to the semitendinosus and the long head of the biceps femoris at the mid thigh level. The lower slip was attached at the junction of the two heads of gastrocnemius muscle. The upper part seems to be a variant of the rare tensor fascia suralis muscle, and the lower part seems to be a variant of the third head of gastrocnemius. It could be described as having four parts, a proximo-lateral part, a proximo-medial part, a middle part and a distal part.

Fig. 1: The anomalous muscle in the region of right popliteal fossa.

The total length of the muscle from the most proximal point to the most distal point was 27.5cm, the average width was 2.3 cm and the average thickness was 0.5 cm.

The proximo-lateral part was fleshy, flat, and was attached to the middle of the medial side of the long head of Biceps femoris muscle, where a tendinous intersection was present. The length of attachment was 4.0 cm and the part was 8.0 cm long and 4 cm wide with average thickness of 0.5 cm. The direction of muscle fibers were downwards and medially continuing with the fibers of the middle part and medially with the fibers of the proximo-medial part. The proximo medial part of the muscle was fleshy and flat and was attached to the lateral side of the middle of the semitendinosus. The length of the attachment was 8.0 cm, and this part was 2 cm long, 8 cm wide and 0.5 cm thick. The direction of muscle fibers were downwards and laterally continuing with the fibers of the middle part and medially with the fibers of the proximo-lateral part.

The middle part of the muscle was lying in the middle of the popliteal fossa, and was made of the muscle slips from the upper two parts which tapered downwards, and another slip from the distal part joined in the middle of these two slips forming a ‘w’ shaped tendinous intersection.

The dimensions of the middle part were 10 cm long, 2 cm wide and 0.5 cm thick. There was no nerve or vessel entering this part.

The distal part of the muscle was fleshy and attached to the junction of the two heads of the gastrocnemius muscle at the upper fleshy part. The length of the attachment was 5 cm vertically. The muscle received a branch from the tibial nerve on its deep aspect at the proximo lateral part. A vascular bundle entered from the 4th perforator of the profunda femoris artery, at the deeper aspects at the proximomedial part. (Fig. 2).

Fig. 2

Discussion:

The anomalous muscle found could be a variant of the semitendinosus, or the biceps femoris or the gastrocnemius or a combination of these. It must be a very rare muscle because the common standard text books of anatomy do not mention it, even as a variant. The variations found and reported for the semitendinosus mention a rare muscle named Tensor fasciae suralis or ischioaponeuroticus, as a slip that leaves the belly of the semitendinosus (it may also be one of the other hamstrings) and ends in a tendon that joins the fascia of the leg. (Ronald et al, 1995). According to Straus et. al (1943) Semitendinosus may be fused with neighboring muscles and a muscle fasciculus may extend from the body of the muscle to the fascia of the back of leg.

The Third head (Caput tertium) is the most common variation of the gastrocnemius muscle (Bergman, R.A et al, 1995;Williams et al (1995) and it has been studied extensively over a period of almost 200 years. Kelch (1813) is generally cited as the first to report the third head. It may arise from the long head of biceps femoris or the third head may “split” and arise from more than one location or divide near its termination to join both heads of gastrocnemius. The third head may or may not cross popliteal neurovascular structures or some portions of the neurovascular component before insertion into one head, or the other, of gastrocnemius or its tendon. It has an overall frequency of 2.9 to 5.5%. Mori reported it’s presence in 2.8% of his cases (Ronald et al, 1995). According to Straus et al (1943) A slip from the biceps may join the triceps and give rise to ‘Quadriceps surae’.

The normal attachment of the Biceps femoris muscle to the crural fascia represents an extension to the leg that is found in some mammals. The crural extension may be seen as muscular slips (tensor fasciae suralis) attached to the fascia, gastrocnemius, or Tendo Achilles. Macalister (1875) reported the variations of biceps flexor cruris (biceps femoris) as it may have a third head arising in common with a middle head of gastrocnemius. A slip from the long head to the Tendo Achilles has been described by Macalister (1875) who said this reminded him of the insertion of the rectus in many animals, as for example, in the lion.

According to Straus et al (1943), in the mammals below man the insertion of the biceps, gracilis and the semitendinosus takes place chiefly into the fascia of the back of the leg, and extends more distally than in man. This insertion of the flexor muscles is associated with a permanent position of flexion at the knee. In the human embryo likewise the muscles are inserted more distally than in adult. The tensor fascia suralis is a muscle fasciculus that may take the place of fibrous prolongations from the tendon of the biceps femoris to the into the sural fascia. This may extend to the tendon of Achilles.

According to Henry W.(1962), variations in the hamstring muscle is not common. There may be variable amount of fusion of the muscles and there may be an accessory slip of origin and insertion of these muscles. Most anomalous slips are apparently associated with the biceps. Sometimes a slip of insertion of the biceps inserts to the fascia of the leg called as tensor fascia suralis. Instances in which a part of the biceps is inserted into the superficial muscle of the calf (Gastrocnemius) or its tendon has been reported.

Somayaji SN et al (1998) described an anomalous muscle (tensor fascia suralis?) in the popliteal fossa as a muscle arising by 2 thin tendinous slips, one from biceps and the other from semitendinosus and inserting into the tendo calcaneus.

Barry D et al (1924) and Parsons FG (1920), have reported the Tensor fascia suralis muscle. Montet X et al (2002) have reported the Sonographic and MRI appearance of tensor fasciae suralis muscle.

Conclusion:

Having considered the literature available and on comparing this case, we come to the conclusion that this case may be a ‘Tensor fascia Suralis’ or a case of ‘Third Head’ of gastrocnemius, or a combination of both, found in the same specimen.

The upper part of this muscle above the tendinous intersection, exactly matches the definition of Tensor fascia suralis muscle, but it does not join the fascia of the leg, or the Achilles tendon either. The lower part of this muscle below the tendinous intersection matches the description of the third head of the gastrocnemius, but it does not arise from the popliteal surface of femur, as discussed above.

We find well defined tendinous intersection of the upper two muscle slips (tensor fascia suralis part) with the lower slip (third head of gastrocnemius part) in the middle part of the muscle. On tracing the muscle fibers carefully we found the fibers coming from the semitendinosus and biceps ending at this intersection, and the fibers beginning at this intersection could be traced clearly till their attachment at the junction of the heads of gastrocnemius.

A tendinous intersection signifies embryological development from different myotomes.

Therefore this anomalous muscle is a rare case of ‘Tensor Fascia Suralis’, giving origin to the ‘Third Head’ of gastrocnemius muscle instead of joining the sural fascia, and the ‘Third head’ originating from this muscle instead of the popliteal surface of the femur. Both variations present in combination in the same specimen. It may also be an altogether new muscle anomaly found.

References:

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  2. Bergman, R.A., Walker, C.W. and G.Y. El-Khoury . The third head of Gastrocnemius in CT images; Annals Anat. (1995); 177:291-294
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