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    From Musculoskeletal System

    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Buccinator
    Muscle that helps with chewing and blowing air out.
    Saddle Joints
    e.g., thumb joint
    Nasal Bones
    Bones forming the bridge of the nose.
    Tibialis Anterior
    Muscle that dorsiflexes and inverts the foot.
    Rotator Cuff Muscles
    Supraspinatus, Infraspinatus, Teres Minor, Subscapularis.
    Tibia
    Shin bone, the larger bone in the lower leg.
    Maxillae
    Upper jaw bones that house the teeth and form part of the orbit.
    Carpals (8 bones)
    8 wrist bones.
    Skull
    Bony structure of the head that encases the brain.
    Rectus Abdominis
    Abs muscle that flexes the trunk.
    Deltoid
    Shoulder muscle responsible for arm abduction.
    Posterior Longitudinal Ligament
    Spinal ligament running along the back of the vertebral column.
    Trapezius
    Muscle responsible for moving, rotating, and stabilizing the scapula.
    Adductors
    Muscles that bring the thighs toward the midline.
    Syndesmoses
    Fibrous joints where bones are connected by ligaments.
    Sternum
    Breastbone located in the center of the chest.
    Scapula
    Shoulder blade providing attachment for muscles of the upper limb.
    Acromioclavicular Ligament
    Ligament that connects the acromion to the clavicle.
    Anterior Scalene Muscle
    The anterior scalene muscle is a deep neck muscle that elevates the first rib during inspiration and aids in neck flexion and stability, located between key neurovascular structures.
    Hamstrings
    Biceps Femoris, Semitendinosus, Semimembranosus.
    Pubis
    Part of the pelvis that joins with the opposite side to form the pubic symphysis.
    Ulna
    Forearm bone on the pinky side.
    Radius
    Forearm bone on the thumb side.
    Fibula
    Smaller bone in the lower leg, located alongside the tibia.

    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? Each human hand has 27 bones.