Appendicular Skeleton – Anatomy and Name Of Bones

A single upper extremity includes 14 phalanges (proximal, intermediate, and distal), five metacarpals?, eight carpal bones, two forearm bones (radius? and ulna?), the humerus?, and the shoulder girdle (scapula? and clavicle?).[rx] A single lower extremity contains 14 phalanges (proximal, intermediate, and distal), five metatarsals?, seven tarsal bones, two leg bones (fibula?, tibia?), the femur?, and the hip bone or coxal bone (ilium?, ischium, and pubis).[rx][rx] These bones articulate with each other and are joined by a multitude of ligaments?, cartilage?, and tendons? to form the appendicular skeleton. There are also bony prominences and protuberances that serve as muscle attachment sites on the surfaces of these bones. The appendicular skeleton is structured for a greater range of motion and locomotion generation when compared to the axial skeleton.[rx]

Structure and Function of Appendicular Skeleton

There are 126 named bones of the appendicular skeleton (all bones exist in pairs) [rx]:

Upper Limb

• Shoulder girdle:
  • Clavicle
  • Scapula

• Arm
  • Humerus
• Forearm
  • Radius
  • Ulna

• Wrist or carpal bones
  • Scaphoid
  •  Lunate
  •  Triquetrum
  •  Pisiform
  •  Trapezium
  •  Trapezoid
  •  Capitate
  • Hamate
• Hand
  • Metacarpals x5
  • Phalanx x14

• Pelvic girdle (hip or coxal bone)
  • Ilium
  •  Ischium
  • Pubis
• Thigh
  • Femur
• Leg
  • Tibia
  • Fibula
• Tarsal bones
  • Talas
  • Calcaneus?
  •  Cuboid
  • Medial, intermediate, and lateral cuneiform
  • Navicular
• Foot
  • Metatarsals x5
  • Phalanx x14

There are also various sesamoid bones not included in the list, such as the largest of the sesamoid bones, the patella?, that protects the knee joint, and important attachment points for the ligaments that allow for the extension of the knee.[rx][rx]

There are two bilateral? joints where the appendicular skeleton directly articulates with the axial skeleton. The first of these articulations is the sternoclavicular joint, where the sternum? of the axial skeleton articulates with the clavicle of the appendicular skeleton. The sternoclavicular joint is a synovial joint.[rx] The second point where the appendicular skeleton directly articulates with the axial skeleton is the sacroiliac joint, where the sacrum? articulates with the ilium. The sacroiliac joint is both a synovial joint and a syndesmosis. The connection between the sacrum and the ilium is important to transfer the load of the axial skeleton to the lower limb of the appendicular skeleton.[rx]

The thoracoscapular articulation is a second articulation between the upper limb of the appendicular skeleton and the axial skeleton. This articulation is not an actual joint and does not have a synovial membrane. The thoracoscapular articulation forms between the anterior surface of the scapula and the posterior ribs 2-7.[10]

The bones of the foot function to form a base where the skeleton contacts the ground while standing. During the gait cycle, the articulations between the bones of the foot combined with the fascia? and ligaments allow for deformation of the arches, which create spring-like properties in the foot that are utilized during walking and running.[11]

Blood Supply and Lymphatics of Appendicular Skeleton

The blood supply to the lower extremity of the appendicular skeleton originates from the common iliac arteries?, which are the terminal branches of the descending aorta?. The common iliac artery? branches into the internal and external iliac arteries, supplying all the structures of the pelvis and the lower extremities.[rx] The external iliac artery continues into the lower extremity to become the femoral artery as it passes under the inguinal ligament?.[rx] A major branch of the femoral artery is the deep femoral artery. The deep femoral artery supplies blood to the femur. The medial femoral circumflex artery and lateral femoral circumflex artery are early branches of the deep femoral artery that vascularize the hip joint?.[rx] The femoral artery continues posteriorly to the knee as the popliteal artery, then continues into the lower leg where it divides into the anterior tibial artery and the posterior tibial artery. The posterior tibial artery then bifurcates into the posterior tibial and fibular arteries, which distally contribute to the vasculature of the foot.[rx][rx][rx]

The blood supply to the upper extremity of the appendicular skeleton comes from the subclavian artery. The subclavian artery is a branch of the brachiocephalic trunk on the right or a branch directly off the aortic arch on the left. The clavicle receives vascular supply from the suprascapular artery, thoracoacromial artery, and the internal thoracic? artery.[rx] The subclavian artery becomes the axillary artery after the lateral edge of the first rib. It then becomes the brachial artery after passing the inferior border of the teres minor muscle. The brachial artery bifurcates near the elbow into the radial and ulnar arteries, which distally contribute to the vasculature of the hands.[rx][rx]

The lymphatics of the upper and lower limb primarily follow the major blood vessels.[rx]

Nerves Supply of Appendicular Skeleton

The upper extremity nerves originate from the brachial plexus. The brachial plexus is composed of roots, trunks, divisions, cords, and ultimately the five named branches. Spinal nerve roots C5 to T1 contribute to the brachial plexus. The terminal branches of the brachial plexus include the musculocutaneous, axillary, median, radial, and ulnar nerves. These named branches provide innervation to the upper limb.[rx]

The lower extremity innervation originates from the lumbar? plexus and the sacral plexus, which is formed by spinal nerve roots T12 to S3.[rx] Part of the lumbosacral plexus forms the sciatic nerve, which contributes the majority of the innervation to the lower limb. The sciatic nerve divides into the tibial and fibular nerves, which continue distally to innervate the lower limb.[rx]

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