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    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
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    e.g., thumb joint
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    Ligaments connecting the sacrum to the iliac bones.
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    Cartilaginous joints where bones are connected by fibrocartilage.
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    Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.
    Biceps Brachii
    Muscle responsible for elbow flexion.
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Acetabulum
    The acetabulum is the pelvic socket that connects with the femoral head to form the hip joint, vital for stability, movement, and weight-bearing.
    Ilium
    Uppermost and largest part of the hip bone.
    Occipital Bone
    Bone forming the back and base of the skull.
    Clavicle
    Collarbone connecting the arm to the body.
    Ligamentum Flavum
    Spinal ligament connecting the laminae of adjacent vertebrae.
    Vomer Bone
    Bone forming the nasal septum.
    Skull
    Bony structure of the head that encases the brain.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Biceps Tendon
    Tendon that attaches the biceps muscle to the bone.
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    Fibrous joints between skull bones.
    Brachioradialis
    Muscle responsible for forearm flexion.
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
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    Muscle that raises the corners of the mouth.
    Zygomatic Bones
    Cheekbones that form part of the orbit.
    Ethmoid Bone
    Bone forming part of the nasal cavity and the orbit.
    Ribs (12 Pairs)
    12 pairs of bones that form the sides of the thoracic cage.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    Pivot Joints
    e.g., atlanto-axial joint

    Achilles Tendon

    Reviewed by our medical team

    Tendon connecting the calf muscle to the heel bone.

    1. Overview

    The Achilles tendon, also known as the calcaneal tendon, is the largest and strongest tendon in the human body. It connects the calf muscles to the heel bone and plays a pivotal role in walking, running, and jumping. Despite its strength, it is a common site for injury, especially in athletes and active individuals. The tendon is named after the Greek mythological hero Achilles, whose only vulnerable spot was his heel.

    2. Location

    The Achilles tendon is located in the posterior compartment of the lower leg:

    • Proximally: It originates from the merging of the gastrocnemius and soleus muscles (collectively known as the triceps surae).

    • Distally: It inserts into the posterior surface of the calcaneus (heel bone).

    • It runs superficially down the back of the ankle and is easily palpable above the heel.

    3. Structure

    The Achilles tendon is composed primarily of dense regular connective tissue:

    • Collagen fibers (Type I):

      • Provide tensile strength; fibers are arranged longitudinally for maximum load-bearing capacity.

    • Paratenon:

      • A thin, flexible sheath surrounding the tendon, facilitating movement and supplying blood vessels.

    • Fascicles and tenocytes:

      • The tendon is organized into fascicles, maintained by tenocytes (specialized fibroblasts).

    The Achilles tendon lacks a true synovial sheath and instead relies on the paratenon for nutrition and lubrication.

    4. Function

    The Achilles tendon serves several essential biomechanical functions:

    • Force transmission: Transmits contraction force from the gastrocnemius and soleus muscles to the calcaneus, producing plantarflexion of the foot.

    • Shock absorption: Acts as a spring during locomotion, storing and releasing elastic energy to minimize muscular workload.

    • Postural support: Helps maintain balance and posture when standing and walking.

    5. Physiological role(s)

    Beyond basic movement, the Achilles tendon supports a range of physiological and functional roles:

    • Gait mechanics: Essential for push-off during walking and running cycles.

    • Energy efficiency: Stores mechanical energy during dorsiflexion and releases it during plantarflexion, aiding in efficient movement.

    • Neuromuscular coordination: Works in coordination with proprioceptive receptors and lower leg muscles to respond to dynamic changes in terrain.

    • Adaptation to stress: Adapts to physical activity through remodeling and hypertrophy with appropriate mechanical loading.

    6. Clinical Significance

    The Achilles tendon is commonly involved in orthopedic and sports-related conditions:

    • Achilles tendinitis:

      • Inflammation of the tendon, usually due to overuse or improper footwear. Presents with pain, swelling, and stiffness.

    • Tendinosis:

      • Degenerative changes in the tendon without significant inflammation, often due to chronic microtrauma.

    • Achilles tendon rupture:

      • Partial or complete tear, typically occurring during explosive activities like sprinting or jumping. Patients may report a sudden "pop" with loss of plantarflexion.

      • Requires surgical or conservative treatment followed by prolonged rehabilitation.

    • Insertional Achilles tendinopathy:

      • Pain at the point where the tendon inserts into the calcaneus, commonly seen in runners and older individuals.

    • Haglund’s deformity:

      • Excessive bony enlargement of the heel that irritates the Achilles tendon, often resulting in bursitis and discomfort.

    • Post-surgical considerations:

      • Rupture repair requires careful rehabilitation to avoid re-rupture and ensure return to full function.

    Did you know? The pelvic girdle consists of the ilium, ischium, and pubis.