Anatomy of the #Soleus Muscle

Courtesy: Prof Nabile Ebraheim, University of Toledo, Ohio, USA

GENERAL ANATOMY

• The soleus is a broad, flat muscle located beneath the gastrocnemius muscle.

• It lies within the superficial posterior compartment of the leg.

• The soleus is a major contributor to the triceps surae muscle complex.

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COMPARTMENTS OF THE LEG

The leg is divided into four anatomical compartments:

1. Anterior compartment

2. Lateral compartment

3. Deep posterior compartment

4. Superficial posterior compartment

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ORIGIN

• Arises from the upper one-third of the posterior surface of the tibia.

• Originates from the middle one-third of the medial border of the tibial shaft.

• Also arises from:

  • The posterior surface of the head of the fibula

  • The upper one-third of the posterior surface of the fibular shaft

• Additional origin from a fibrous arch between the tibia and fibula, known as the soleal arch.

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INSERTION

• The soleus muscle joins the gastrocnemius muscle.

• Together, they form the Achilles tendon.

• The Achilles tendon inserts into the posterior surface of the calcaneus.

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INNERVATION

• Supplied by the tibial nerve, with nerve roots S1 and S2.

• The tibial nerve passes through the fibrous arch of the soleus muscle.

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FUNCTION

• Primary plantar flexor of the ankle joint.

• Plays a crucial role in:

  • Standing posture

  • Walking and running

  • Preventing forward sway of the body during stance

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CLINICAL CORRELATIONS

1. Compartment Syndrome

• A surgical emergency.

• Characterized by increased pressure within a closed muscle compartment.

• Leads to compromised microcirculation and tissue ischemia.

• If untreated, may result in muscle necrosis and permanent disability.

Fasciotomy

• Performed using a posteromedial incision, placed approximately 2 centimeters posterior to the medial border of the tibia.

• Allows decompression of:

  • The superficial posterior compartment

  • The deep posterior compartment

• Access to the deep posterior compartment is achieved by releasing the soleus muscle from its tibial attachment.

• Care must be taken to protect the saphenous nerve.

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2. Achilles Tendinitis

• Caused by overuse and repetitive microtrauma.

• Results in:

  • Pain

  • Swelling

  • Degenerative changes within the Achilles tendon

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3. Retrocalcaneal Bursitis

• Inflammation of the bursa located between the anterior surface of the Achilles tendon and the posterior calcaneus.

• A common cause of posterior ankle pain, especially in athletes.

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4. Achilles Tendon Rupture

• Rupture commonly occurs proximal to the calcaneal insertion.

• Blood supply is derived from:

  • Posterior tibial artery

  • Peroneal artery

Watershed Zone

• A region with relatively poor blood supply.

• Located approximately 2 to 6 centimeters proximal to the calcaneal insertion.

• This zone is particularly prone to tendon rupture.

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Clinical Test

Thompson Test

• The examiner squeezes the calf muscle.

• Normal response: plantar flexion of the foot.

• Complete Achilles tendon rupture:

  • Absence of ankle movement during calf squeeze

  • Indicates loss of tendon continuity

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DIFFERENTIATING TIGHTNESS

Gastrocnemius Tightness

• Ankle dorsiflexion is limited when the knee is extended.

• Gastrocnemius spans the knee joint.

• Knee flexion relaxes the muscle and improves ankle dorsiflexion.

• Increased dorsiflexion with knee flexion indicates gastrocnemius tightness.

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Achilles Tendon Tightness

• Ankle dorsiflexion remains equally restricted with:

  • Knee extension

  • Knee flexion

• Indicates contracture or tightness of the Achilles tendon.

• Degree of dorsiflexion does not change with knee position.

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CLINICAL IMPORTANCE

• The soleus muscle is essential for ankle stability and endurance activities.

• Pathology involving the soleus or Achilles tendon significantly affects gait and athletic performance.

• Understanding its anatomy is critical in managing compartment syndrome, tendon injuries, and posterior leg pain.