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    Interspinous Ligament
    Spinal ligament between adjacent vertebral spinous processes.
    Gluteus Maximus
    Largest muscle in the buttocks responsible for hip extension.
    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.
    Gastrocnemius
    Calf muscle responsible for plantarflexion of the foot.
    Gliding (Plane) Joints
    e.g., between carpals
    Femur
    Thigh bone, the longest and strongest bone in the body.
    Lacrimal Bones
    Bones forming part of the eye socket and housing the tear ducts.
    Lumbar Vertebrae (L1 - L5)
    Vertebrae in the lower back (L1-L5).
    Ellipsoidal (Condyloid) Joints
    e.g., wrist
    Hyoid Bone
    U-shaped bone in the neck that supports the tongue.
    Inferior Nasal Conchae
    Bones inside the nasal cavity that filter and humidify air.
    Facial Bones
    Bones forming the structure of the face.
    Mandible
    Lower jawbone that houses the teeth.
    Patella
    Knee cap, protecting the knee joint.
    Occipital Bone
    Bone forming the back and base of the skull.
    Thoracic Vertebrae (T1 - T12)
    Vertebrae in the upper and mid-back (T1-T12).
    Palatine Bones
    Bones forming part of the hard palate and nasal cavity.
    Humerus
    Upper arm bone connecting the shoulder to the elbow.
    Annular Ligament
    The annular ligament is a strong fibrous band encircling the head of the radius, stabilizing the proximal radioulnar joint and allowing smooth rotation of the forearm.
    Fibula
    Smaller bone in the lower leg, located alongside the tibia.
    Pubis
    Part of the pelvis that joins with the opposite side to form the pubic symphysis.
    Abductor Digiti Minimi Muscle
    The abductor digiti minimi muscle is a hypothenar muscle that abducts and flexes the little finger, aiding grip and precision in hand movements.
    Temporal Bones
    Bones forming the lower sides of the skull and housing the ears.
    Tarsals (7 bones)
    7 ankle bones.
    Clavicle
    Collarbone connecting the arm to the body.

    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? Bones are constantly producing new cells in the bone marrow.