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Appendicular skeleton

The appendicular skeleton is the peripheral portion of the human skeletal system, comprising the bones of the upper and lower limbs along with the pectoral and pelvic girdles that attach these limbs to the . The term "appendicular" derives from the Latin appendicula, a diminutive of appendix, meaning a small or addition. It consists of 126 bones in total, forming a specialized for , locomotion, grasping, and manipulation of objects. The pectoral girdle, also known as the , includes the clavicles and scapulae, which anchor the upper limbs to the and provide attachment sites for muscles that enable movement. Each contains 30 bones: the in the , the and in the , eight carpals in the , five metacarpals in the hand, and 14 phalanges in the fingers. These structures facilitate precise dexterity and reach, essential for activities like tool use and object handling. In contrast, the pelvic girdle unites the two hip bones (each formed by the fusion of the ilium, , and pubis) and connects to the , supporting the weight of the upper body and serving as a sturdy base for lower limb attachment. The lower limbs, with 30 bones each, include the (thigh), and (leg), (kneecap), seven tarsals in the ankle, five metatarsals in the foot, and 14 phalanges in the toes, enabling bipedal walking, running, and balance. Overall, the appendicular skeleton's design emphasizes flexibility and strength, differing from the more rigid by prioritizing functional adaptation for dynamic movement.

Overview

Definition and Etymology

The appendicular skeleton constitutes the portion of the skeletal comprising the bones of the upper and lower limbs along with their associated girdles, which attach the limbs to the . This division contrasts with the , which forms the central core of the body including the , , and . In adult humans, the appendicular skeleton accounts for 126 of the total 206 bones in the body. Of these, the upper appendicular skeleton includes 64 bones, with 32 bones per upper limb including the pectoral girdle. The lower appendicular skeleton comprises 62 bones, consisting of 30 bones per lower limb plus the two bones of the pelvic girdle. These components are organized into the pectoral and pelvic girdles supporting the respective limbs. The term "appendicular" derives from the Latin appendicula, a diminutive form of appendix meaning "small appendage" or "that which hangs from." It entered English in the 1650s and anatomical contexts in the 19th century (first recorded 1839), underscoring the oppositional pairing with the "axial" skeleton. The nomenclature gained prominence in 19th-century anatomical texts.

Components and Organization

The appendicular skeleton is divided into two primary divisions: the upper appendicular skeleton, consisting of the pectoral girdle and the bones of the upper limbs, and the lower appendicular skeleton, comprising the pelvic girdle and the bones of the lower limbs. The upper division facilitates manipulation and reaching movements, enabling precise control of objects through flexible and articulations, while the lower division supports weight-bearing and , providing stability for upright and bipedal . The upper appendicular skeleton connects to the solely through the pectoral girdle at the sternoclavicular joint, where the medial end of each articulates with the manubrium of the , allowing significant mobility while maintaining attachment to the trunk. In contrast, the lower appendicular skeleton attaches more robustly via the pelvic girdle at the sacroiliac joints, where the auricular surfaces of the (part of the ) form synovial articulations with the ilia of the two hip bones, reinforced by strong ligaments to transmit forces from the lower limbs to the . These attachment points ensure the appendicular components integrate with the central body axis for coordinated movement. Within each division, the bones form a serial chain of connections that promote segmented mobility. In the upper limb, the articulates proximally with the glenoid cavity of the at the glenohumeral , followed by distal connections to the and at the , and further linkages through the carpal, metacarpal, and phalangeal bones of the hand. Similarly, in the lower limb, the connects proximally to the of the at the , then articulates distally with the and at the , extending to the tarsal, metatarsal, and phalangeal bones of the foot. This hierarchical arrangement of girdle-to-limb and intra-limb articulations creates a scaffold for leverage and . The appendicular skeleton exhibits bilateral symmetry, with nearly all of its 126 bones occurring in pairs—one on the left side and one on the right—to mirror the body's overall architecture and support balanced function. The pectoral girdles and upper limbs are fully paired, as are the pelvic girdles (two hip bones) and lower limbs, though the anterior pubic symphysis unites the hip bones midline without altering their paired origins. This organization ensures symmetrical load distribution and coordinated bilateral actions.

Upper Appendicular Skeleton

Pectoral Girdle

The pectoral girdle, also known as the , forms the skeletal framework that connects the upper limbs to the , consisting of the paired clavicles and scapulae. This structure provides attachment points for muscles that enable a wide range of upper body movements while maintaining flexibility. Unlike the more rigid pelvic girdle, the pectoral girdle is designed for mobility rather than weight-bearing stability. The , or collarbone, is a slender, S-shaped that lies horizontally across the superior , serving as the sole bony connection between the and the . It features a medial sternal end, which is triangular and articulates with the manubrium of the , and a lateral acromial end, which is flattened and connects to the . The central shaft of the clavicle is curved, with the medial two-thirds convex anteriorly and the lateral third concave anteriorly, providing leverage for muscle attachments and protection for underlying neurovascular structures. In terms of , the male clavicle is typically longer, thicker, and more curved than the female counterpart, reflecting broader width in males, though these differences are minimal overall. The , or , is a flat, triangular located on the posterior , contributing to the posterior aspect of the pectoral girdle. Its key features include the prominent , a ridge on the posterior surface that divides the supraspinous and infraspinous fossae; the , a lateral extension of the that forms a bony shelf; the , an anteriorly projecting hook-like structure for muscle and attachments; and the , a shallow oval depression on the lateral border that serves as the socket for the . The lacks direct bony articulation with the , instead relying on muscular suspensions such as the and serratus anterior for positioning. Articulations of the pectoral girdle include the sternoclavicular joint, where the meets the , and the , linking the to the scapula's , forming an incomplete bony ring that enhances mobility. This open-ring configuration, combined with the scapula's ability to glide over the via the scapulothoracic articulation, permits extensive shoulder movements, including up to 180 degrees of arm circumduction. The girdle's design prioritizes over stability, allowing independent function while transmitting forces from the arms to the .

Upper Limb Bones

The upper limb bones form a serial chain from the through the to the hand, enabling precise and reach. These 30 bones per limb (excluding the pectoral girdle) articulate to support mobility, with the connecting proximally to the via the . The is the single bone of the , extending from the to the . Its proximal end features a smooth, rounded head that articulates with the glenoid cavity of the . Immediately distal to the head lies the surgical neck, a narrowed region prone to fractures. Along the mid-shaft on the lateral side is the , a roughened V-shaped . At the distal end, the medial projects prominently, while the smaller lateral sits opposite. The distal includes the pulley-shaped trochlea medially, which articulates with the , and the rounded capitulum laterally, which articulates with the to form part of the . The consists of two parallel bones: the laterally and the medially. The has a disc-shaped head proximally that articulates with the humerus's capitulum and the 's radial notch, forming the proximal radioulnar joint. This joint, along with the distal radioulnar joint where the 's head pivots against the 's ulnar notch, allows for pronation and supination of the . The features the process proximally, a hook-like projection that inserts into the humerus's fossa during elbow extension and serves as a site for attachment. Distally, the tapers to a rounded head. These bones enable both hinge-like flexion/extension at the and rotational movements. The hand contains 27 bones organized into the , , and fingers. The includes eight arranged in two rows: the proximal row comprises the scaphoid, lunate, triquetrum, and pisiform, while the distal row includes the , , capitate, and hamate. These short bones articulate with the at the radiocarpal joint, where the distal meets the scaphoid, lunate, and triquetrum. The is formed by five , numbered 1 to 5 from to little finger, each with a proximal base, elongated shaft, and distal head. The fingers consist of 14 phalanges: the has two (proximal and distal), while each of the other four digits has three (proximal, middle, and distal). This arrangement provides the dexterity essential for grasping and fine motor tasks.

Lower Appendicular Skeleton

Pelvic Girdle

The pelvic , also known as the hip girdle, consists of two innominate bones, or os coxae, one on each side of the body, which together form a robust bony structure that connects the to the lower limbs. Each innominate bone is formed by the fusion of three primary bones: the ilium superiorly, the posteriorly and inferiorly, and the pubis anteriorly. The ilium is the largest and most superior portion, featuring a broad, fan-shaped body with a prominent superior margin called the and a posterior indentation known as the . The forms the posteroinferior part, including the , a roughened projection that supports body weight during sitting. The pubis constitutes the anteromedial section, with its bodies meeting at the midline , a fibrocartilaginous reinforced by an interposed disc. Laterally, the three bones converge to form the , a deep, cup-shaped cavity that serves as the socket for articulation with the head of the . The pelvic girdle articulates with the primarily through the sacroiliac joints, which are bilateral compound joints between the auricular surfaces of the ilium and the , combining synovial and syndesmotic elements for limited motion. These joints are stabilized by strong ligaments, such as the anterior and posterior sacroiliac ligaments, enabling the transfer of upper body weight to the lower limbs while maintaining stability. The provides midline connection between the two pubic bones, contributing to the overall rigidity of the structure. The complete bony ring formed by the two innominate bones, the , and the enhances this stability, distinguishing the pelvic girdle from the more mobile pectoral girdle and supporting upright posture in bipedal humans. The is divided into the false pelvis (or greater pelvis) superiorly, which is broader and lies above the , and the true pelvis (or lesser pelvis) inferiorly, which is narrower and encloses pelvic organs below the brim. This division underscores the girdle's role in weight-bearing and enclosure. Sex differences in pelvic morphology are pronounced, with the female generally wider to accommodate ; for instance, females exhibit a broader and outlet, a subpubic angle greater than 80 degrees, and a wider compared to males, who have a narrower with a subpubic angle less than 70 degrees and a deeper sciatic notch. These adaptations reflect evolutionary pressures balancing bipedal locomotion with reproductive needs.

Lower Limb Bones

The lower limb bones form the skeletal framework of the , , and foot, comprising 30 bones per limb excluding the , which collectively support , propulsion, and balance during . These structures are adapted for enduring compressive forces, with robust proximal elements transitioning to more flexible distal segments to facilitate efficient and terrain adaptation. In the thigh, the serves as the longest and strongest in the , extending from the to the and providing leverage for powerful movements. Its proximal end features a rounded head that articulates with the of the pelvic girdle at the acetabulofemoral , connected by a narrowed vulnerable to fractures under torsional stress. Laterally, the forms a prominent projection for attachment of , while the medial lesser trochanter anchors the ; posteriorly, the runs as a roughened along the shaft for adductor and muscle origins. Distally, the medial and lateral condyles articulate with the , enabling flexion and stability during weight transfer. The , or kneecap, is a small, triangular embedded in the of the femoris muscle anterior to the . It articulates with the patellar surface of the 's distal end, protecting the from direct compression and increasing the leverage of the during extension. The leg consists of the and , two parallel that articulate proximally with the and distally with the foot, distributing forces while allowing subtle movements for shock absorption. The , the larger medial weight-bearing , features a proximal tibial plateau with medial and lateral condyles that receive the femoral condyles at the , supported by the tibial tuberosity for attachment. Its distal end expands into the medial , forming the medial ankle prominence and articulating with the talus. The , a slender lateral , primarily stabilizes the ankle without direct weight-bearing; its proximal head articulates with the at the proximal tibiofibular , and the distal lateral extends inferiorly to brace the ankle laterally. These tibiofibular joints permit slight rotation to accommodate foot inversion and eversion during . The foot's skeletal components include seven tarsal bones, five metatarsals, and 14 phalanges, forming a resilient platform for balance and propulsion. The tarsals, located in the posterior foot, consist of the talus (articulating superiorly with the and at the ankle , covered by about 60% for smooth motion), the (the largest tarsal, bearing approximately 50% of body weight and serving as the heel's attachment for ), the navicular (medial, articulating with the talus and three cuneiforms), the (lateral, connecting to the and fourth/fifth metatarsals), and the three cuneiforms (medial, intermediate, and lateral, wedged between navicular and metatarsals). These bones form flexible like the subtalar and transverse tarsal to adapt to uneven surfaces. The five metatarsals, numbered 1 to 5 from medial to lateral, are elongated bones with bases articulating to tarsals, shafts for muscle attachments, and heads forming the ball of the foot; the first metatarsal includes sesamoid bones for enhanced stability during push-off. The phalanges include 14 toe bones: two in the hallux (proximal and distal) and three in each of the other four toes (proximal, middle, distal), enabling fine grip and flexion. The foot's arches—medial longitudinal (supported by the talus, , navicular, three cuneiforms, and first three metatarsals for shock absorption), lateral longitudinal (formed by the , , and fourth/fifth metatarsals for rigidity), and transverse (along the for lateral stability)—collectively distribute weight, store , and enhance propulsion efficiency during walking and running.

Functions and Clinical Relevance

Role in Locomotion and Manipulation

The upper appendicular skeleton plays a pivotal role in enabling prehensile and precise object handling through coordinated movements at its key s. The shoulder complex, formed by the glenohumeral , facilitates wide and adduction (up to 180° and 50°, respectively), allowing the arm to reach and position objects in , while the supports flexion (approximately 150°) and extension for bringing items close to the . circumduction, combining flexion, extension, , and adduction (ranges of 70-80°, 70°, 20-30°, and 30-50°), enhances dexterity for rotational adjustments, and finger opposition—particularly the thumb's ability to oppose the other digits—enables secure gripping and fine motor tasks like tool use. The serves as a primary in these actions, amplifying force during activities such as , where rapid extension and rotation generate high velocities for . In contrast, the lower appendicular skeleton is optimized for bipedal locomotion, supporting efficient weight transfer and forward propulsion during . Hip extension (up to 20° beyond neutral) at the acetabulofemoral , driven by , propels the body forward from heel strike, while knee flexion (peaking at 60° during swing phase) and extension maintain stride length and . Ankle plantarflexion (about 20°) during push-off generates the primary propulsive , complemented by dorsiflexion (10-20°) to clear the foot and absorb at initial contact, ensuring smooth progression. is achieved through compressive forces along the (up to 3-4 times body weight in stance) and precise tibial alignment with the , which minimizes lateral deviation and distributes loads axially for endurance in upright walking. The appendicular skeleton integrates these functions to balance and , with the upper limbs exhibiting near-360° rotational at the for versatile manipulation, compared to the lower limbs' approximately 180° sagittal-plane dominance at the for controlled bipedal support. This dichotomy reflects an evolutionary transition from quadrupedal locomotion in early , where limbs were symmetrically load-bearing, to human bipedalism, which emphasized (anterior rotation of 10-15°) to reposition the center of gravity over the hips, freeing the upper extremities for manipulative tasks while adapting the lower for efficient, energy-saving .

Common Disorders and Injuries

The appendicular skeleton is susceptible to various disorders and injuries due to its role in supporting movement and bearing weight. In the upper appendicular skeleton, fractures are among the most common, accounting for up to 10% of all fractures and often occurring in the midshaft region. These fractures typically result from falls onto the shoulder or outstretched arm, sports-related collisions, or traffic accidents, with diagnostic confirmation via imaging showing displacement or comminution. Risk factors include younger age in active individuals and, for complications, advanced age, female gender, and smoking. injuries, involving tears or in the muscles and tendons stabilizing the , frequently arise from scapular stress due to repetitive overhead motions or acute trauma, leading to pain and reduced mobility. Diagnosis involves physical exams like the empty can test and MRI for tear extent, with risk factors encompassing age over 40, occupations involving overhead work, and biomechanical imbalances such as scapular dyskinesis. , caused by compression of the within the formed by the wrist's , often stems from repetitive wrist flexion or prior fractures altering tunnel space. Symptoms include numbness and tingling, diagnosed through and nerve conduction studies, with risk factors like female sex, , and prolonged hand-intensive activities. In the lower appendicular skeleton, fractures represent a prevalent injury, particularly in the elderly, where weakens the bone, making it prone to breaks from minor falls. These intracapsular fractures disrupt blood supply to the , diagnosed via X-rays or MRI, and carry high risks of ; -related bone loss, advanced age, and gender are key risk factors. Tibial fractures, common among runners, develop from repetitive high-impact loading causing microdamage accumulation in the . Diagnosis relies on MRI to detect early bone , as plain films may appear normal initially, with risk factors including sudden increases in training volume, low bone mineral , and female athlete triad components like energy deficiency. Hallux valgus, or deformity, involves lateral deviation of the big toe due to first metatarsal misalignment and medial deviation of the metatarsophalangeal . This condition causes and formation, diagnosed clinically and via weight-bearing X-rays measuring hallux valgus angle, with risk factors such as tight or high-heeled footwear, , and hyperpronation of the foot. General disorders affecting the appendicular skeleton include , a degenerative condition prevalent in weight-bearing joints like the hips, knees, and ankles, where breakdown leads to pain, stiffness, and spurs from chronic mechanical stress and inflammation. Diagnosis uses X-rays showing joint space narrowing, with risk factors including age, , prior joint injury, and genetic factors. Congenital anomalies such as , characterized by extra phalanges or digits in the hands or feet, arise from genetic mutations disrupting limb bud development during embryogenesis. These are often preaxial (thumb side) or postaxial, diagnosed prenatally via or postnatally by physical exam and , and may require surgical correction if functional impairment occurs. Across these conditions, shared risk factors include advancing age, which diminishes and repair capacity; high-impact or repetitive , increasing overuse injury likelihood; and nutritional deficiencies, notably , which impairs calcium absorption and mineralization, elevating and risks in both children and adults.

References

  1. [1]
    Anatomy, Appendicular Skeleton - StatPearls - NCBI Bookshelf - NIH
    Apr 21, 2024 · The appendicular skeleton comprises the upper and lower extremities. The shoulder and hip are important limb segments connecting the appendicular and axial ...
  2. [2]
    Appendicular Skeleton (126 bones) - SEER Training Modules
    Appendicular Skeleton (126 bones) · Femur (2) · Tibia (2) · Fibula (2) · Patella (2) · Tarsals (14) · Metatarsals (10) · Phalanges (28).
  3. [3]
    Types of Skeletal Systems - OpenEd CUNY
    The appendicular skeleton is composed of the bones of the upper limbs (which function to grasp and manipulate objects) and the lower limbs (which permit ...
  4. [4]
    Lab 5
    The axial skeleton is comprised of the vertebral column and ribs, whereas the appendicular skeleton consists of the appendages used for locomotion.<|control11|><|separator|>
  5. [5]
    Appendicular - Etymology, Origin & Meaning
    1650s, from Latin appendicula "a little addition, small appendage," diminutive of appendix (see appendix) + -ar. In anatomy, opposed to axial.Missing: skeleton | Show results with:skeleton
  6. [6]
  7. [7]
    Ch. 8 Introduction - Anatomy and Physiology 2e | OpenStax
    ### Summary of Appendicular Skeleton Organization
  8. [8]
    The Skeletal System: Appendicular Skeleton - UH Pressbooks
    The appendicular skeleton includes the bones that make up your upper limbs (arms) and lower limbs (legs). The axial skeleton is attached to the upper limbs ( ...Missing: components | Show results with:components
  9. [9]
    8.1 The Pectoral Girdle - Anatomy and Physiology 2e | OpenStax
    ### Summary of Pectoral Girdle Attachment to Axial Skeleton and Sternoclavicular Joint
  10. [10]
    8.3 The Pelvic Girdle and Pelvis - Anatomy and Physiology 2e | OpenStax
    ### Summary of Pelvic Girdle Attachment to Axial Skeleton and Sacroiliac Joint
  11. [11]
    8.2 Bones of the Upper Limb - Anatomy and Physiology 2e | OpenStax
    ### Summary: How the Humerus Connects to the Scapula
  12. [12]
    8.4 Bones of the Lower Limb - Anatomy and Physiology 2e | OpenStax
    ### Summary: How the Femur Connects to the Pelvis
  13. [13]
    Anatomy, Shoulder and Upper Limb, Shoulder - StatPearls - NCBI
    The shoulder girdle is composed of the clavicle and the scapula, which articulates with the proximal humerus of the upper limb.
  14. [14]
    Anatomy, Shoulder and Upper Limb, Clavicle - StatPearls - NCBI - NIH
    It serves as a connection between the axial and appendicular skeleton in conjunction with the scapula, and each of these structures forms the pectoral girdle.Missing: mobility | Show results with:mobility
  15. [15]
    Anatomy, Back, Scapula - StatPearls - NCBI Bookshelf - NIH
    The scapula or shoulder blade is the bone that connects the clavicle to the humerus. The scapula forms the posterior of the shoulder girdle.
  16. [16]
    The Pectoral Girdle – Anatomy & Physiology - UH Pressbooks
    The pectoral girdle consists of the clavicle and the scapula, which serve to attach the upper limb to the sternum of the axial skeleton.
  17. [17]
    Bones of the Upper Limb – Anatomy & Physiology - UH Pressbooks
    The upper limb has 30 bones: the humerus, ulna, radius, 8 carpal, 5 metacarpal, and 14 phalanx bones.
  18. [18]
    Anatomy Tables - Bones of the Upper Limb
    metacarpal bones, the bones located between the carpal bones and the phalanges of the hand, there are a total of five metacarpal bones in the hand; the ...
  19. [19]
    The Pelvic Girdle and Pelvis – Anatomy & Physiology - UH Pressbooks
    Because of the obvious differences between female and male hip bones, this is the one bone of the body that allows for the most accurate sex determination.
  20. [20]
    Anatomy, Bony Pelvis and Lower Limb: Pelvic Joints - NCBI - NIH
    Mar 6, 2023 · The pelvis joints include the pubic symphysis and the lumbosacral, sacroiliac, and sacrococcygeal joints. The bony pelvis also articulates with the lower limb.
  21. [21]
    Bones of the Lower Limb – Anatomy & Physiology - UH Pressbooks
    There are 30 bones in each lower limb. These are the femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and 14 phalanges. The femur is ...
  22. [22]
    Bones of the Lower Limb | UAMS Department of Neuroscience
    metatarsals, the bones located between the tarsal bones and the phalanges, there are five metatarsal bones in the foot. base, the proximal end of the metatarsal ...
  23. [23]
    Anatomy, Bony Pelvis and Lower Limb: Foot Bones - StatPearls - NCBI
    The forefoot contains the phalanges and metatarsals. The midfoot consists of the five tarsal bones, three cuneiforms, the navicular, and the cuboid. The ...
  24. [24]
    Biomechanics of the Upper Limb - Northwestern Scholars
    Jan 1, 2018 · Upper limb function allows for complex task accomplishment in reaching, prehension, and manipulation. The upper limb can be examined as a ...
  25. [25]
    [PDF] BIOMECHANICS OF THE UPPER LIMB - Semantic Scholar
    Dec 26, 2016 · This chapter discusses upper limb biomechanics according to the main joint functions of motion, stability, and strength, and addresses ...
  26. [26]
    Biomechanics of Normal Gait | PM&R KnowledgeNow
    Mar 20, 2025 · In normal gait, the heel contacts the ground first. The hip is flexed, the knee is nearly fully extended, and ankle is at neutral. This phase is ...
  27. [27]
    Human Lower Limb Joint Biomechanics in Daily Life Activities
    Feb 10, 2020 · This work summarizes the sagittal hip, knee, and ankle joint biomechanics for a broad range of daily movements, based on previously published literature.
  28. [28]
  29. [29]
    2.1. The Skeleton – Biomechanics of Human Movement
    In contrast, the upper skeleton has greater mobility and ranges of motion ... The appendicular skeleton is made up of all bones of the upper and lower limbs.