Notes on General Osteology

This is the part of the deep-learning notes that I organized for everyone in my school study group and completed myself. The nineteen of us divided the work, each completing the chapter assigned to us. I guided them through the writing, ultimately aiming for a publishable level.

I am conducting this kind of study-and-writing training among a group of first-year freshmen. The initial results may not be ideal, but I believe that given time, these medical students will grow into quite outstanding physicians.

Notes on General Osteology

Keywords: bone, osseous tissue, bone cell, bone matrix, fracture

Abstract: A brief account of bone formation, the differentiation process of bone cells, the basic features of normal human bone, and the classification of common orthopedic diseases.

I. Composition of Bone

Bone is an organ composed mainly of osseous tissue, which includes bone cells, collagen fibers, and matrix. Human bone develops (ossifies) on the basis of connective tissue or cartilage.

Bone Cells

There are four types of bone cells: osteoprogenitor cells (also called osteogenic cells), osteocytes, osteoblasts, and osteoclasts. Among them, osteocytes are the most numerous and lie within the osseous tissue; the other three types are distributed at the margins of the bone matrix.

Osteoprogenitor cells, also called osteogenic cells, are the stem cells of osseous tissue, located within the periosteum. They have multipotent differentiation potential and can differentiate into osteocytes, osteoclasts, chondroblasts, or fibroblasts; the direction of differentiation depends on the location and the nature of the stimulus. Osteoprogenitor cells exist in the outer and inner periosteum close to the bone matrix; when osseous tissue grows or remodels, they can divide and differentiate into bone cells.

Osteoblasts, also called bone-forming cells, are cells that promote bone formation, mainly derived from osteoprogenitor cells. Osteoblasts not only secrete large amounts of bone collagen and other bone matrix but also secrete important cytokines and enzymes, such as matrix metalloproteinases, alkaline phosphatase, osteocalcin, and osteoprotegerin, thereby initiating the process of bone formation. At the same time, through these factors they couple with osteoclasts, controlling the growth, maturation, and activation of osteoclasts. Osteoblasts are commonly found in growing osseous tissue, mostly gathered on the surface of newly formed bone matrix. Where bone formation is very active, such as in fractures, callus, and new bone caused by tumors or infection, osteoblasts may form multiple layers piled on the surface of the osseous tissue.

Osteocytes are the main cells of osseous tissue, embedded within the bone matrix. The cavity in which the cell body lies is called a lacuna, and each lacuna contains only one osteocyte cell body. The structure and function of osteocytes depend on their degree of maturity. Newly transformed osteocytes lie within the osteoid, and their morphological structure closely resembles that of osteoblasts. Osteocytes may participate in the bone-resorption process and are regulated by parathyroid hormone, calcitonin, and vitamin D3, as well as affected by mechanical stress.

Osteoclasts are multinucleated giant cells up to 50 um or more in diameter, with considerable variation in the size and number of their nuclei. Functionally active osteoclasts show clear polarity. When resorbing bone matrix, osteoclasts have the special function of continuously transferring calcium ions from the matrix into the extracellular fluid. The initial stage of bone resorption is the dissolution of hydroxyapatite; osteoclasts move actively and secrete organic acids that dissolve the bone minerals and break down hydroxyapatite. After the bone minerals are dissolved and absorbed, the next step is the resorption and degradation of the organic matter of bone. Osteoclasts secrete various proteolytic enzymes; after these hydrolyze the organic matter of bone, Howship's lacunae form on the bone surface. Throughout the degradation of organic matter and inorganic minerals, osteoclasts remain tightly attached to the bone surface. In addition, osteoclasts can produce nitric oxide (NO), which inhibits bone resorption, while at the same time the osteoclasts themselves decrease in number.

Bone Matrix

The bone matrix, briefly called bone substance, is the extracellular matrix of calcified osseous tissue. The bone matrix contains little water; water accounts for only 8%-9% of bone weight. The bone matrix is divided into organic and inorganic components.

The inorganic component is the bone mineral, also called bone salt, accounting for 65%-75% of dry bone weight, of which 95% is solid calcium and phosphorus. Amorphous calcium-phosphate solid is more abundant in young, newly formed osseous tissue (40%-50%) and less in old, mature osseous tissue (25%-30%).

Most of the bone mineral is distributed in the organic matter in the form of amorphous calcium phosphate and crystalline hydroxyapatite; the amorphous calcium phosphate subsequently organizes into crystalline hydroxyapatite.

Hydroxyapatite is mainly formed by the combination of calcium, phosphate, and hydroxyl groups; the crystals also adsorb many other minerals, such as magnesium, sodium, potassium, and trace elements including zinc, copper, manganese, fluorine, lead, strontium, iron, aluminum, and radium. Thus bone is a reservoir for calcium, phosphorus, and other ions; these ions may lie on the surface of hydroxyapatite crystals, may replace the main ions within the crystal, or both.

The organic matter includes collagen fibers and amorphous matrix (proteoglycans, lipids, especially phospholipids).

Collagen fiber is a kind of crystallized fibrinogen embedded in a matrix containing calcium salts. Collagen fibers form a reticular fibrous scaffold that gives bone its resistance to torsion. The mineral salts in bone ensure hardness, while collagen fibers ensure strength; the combination of the two makes bone one of the hardest materials in the world. Experiments show that human bone is even harder than a steel plate.

The amorphous matrix accounts for only about 10% of the organic matter; it is a gelatinous substance without fixed form, its main components being proteoglycans and proteoglycan complexes, the latter composed of proteoglycans and glycoproteins. The amorphous matrix also contains many non-collagenous proteins, accounting for about 0.5% of the organic matter. In recent years, the main substances isolated from the amorphous matrix include osteocalcin, osteopontin, bone sialoprotein, bone acidic protein-75, osteonectin, calcium-binding protein, and fibronectin. Each of these proteins has its own function.

The ratio of organic to inorganic matter in bone differs at different ages, so the hardness and toughness of bone also differ by age, and the nature of fractures differs accordingly. The approximate ratios and characteristics are as follows:

Structure of Bone

Bone is a calcified tissue whose hardness belies its appearance; it is composed of bone substance, periosteum, and bone marrow.

Bone Substance

Bone substance is composed of osseous tissue and, by structure, is divided into compact bone and spongy bone. Compact bone is dense in structure, strong in compression and torsion resistance, and distributed on the bone surface. Its hardness exceeds that of a steel plate, making it one of the hardest materials. Spongy bone is spongy, arranged from interwoven trabeculae, and distributed within the interior of bone. The trabeculae of spongy bone form a honeycomb structure that is light yet strong. The trabeculae are arranged parallel to the directions of compression and tension borne by the bone, so bone can bear considerable weight.

In flat bones, compact bone is distributed on the surface layers, called the outer and inner tables. The outer table is thick, tough, and elastic; the inner table is thin and brittle, so calvarial fractures most often involve the inner table. Spongy bone lies in between, called the diploë, through which diploic veins pass. In short bones and the epiphyses of long bones, the periphery is a thin layer of compact bone and the interior is abundant spongy bone.

The periosteum is mainly composed of fibrous connective tissue and covers the bone surface except at articular surfaces; it is rich in nerves, blood vessels, and lymphatics and plays an important role in bone nutrition, regeneration, and sensation.

The periosteum has inner and outer layers; the outer layer is dense and the inner layer loose. The marrow cavity and the mesh spaces of spongy bone are lined with a thin connective-tissue membrane: the endosteum.

The inner layer of the periosteum and the endosteum have the ability to differentiate into osteoblasts and osteoclasts, producing new bone and resorbing existing bone to remodel the bone. In childhood the periosteum is active and promotes bone growth; in adulthood it is relatively quiescent, maintaining the physiological state of bone.

When bone is injured (such as in fracture), the periosteum or bone becomes active again to promote fracture repair and healing. If the periosteum is excessively stripped or damaged, fracture healing becomes difficult. Therefore, during surgery, orthopedic surgeons should avoid damaging the periosteum as much as possible.

TCM treatment of fractures often follows the approach of tonifying the kidney and strengthening bone together with activating blood and resolving stasis. This approach, first, promotes bone regeneration and, second, improves the bone's blood circulation, shortening fracture-healing time.

Bone marrow is soft tissue filling the marrow cavity and the spaces of spongy bone, divided into red and yellow bone marrow. Red bone marrow contains red blood cells at various developmental stages and other immature blood cells, appears red, and has hematopoietic and immune functions.

The bone marrow of fetuses and infants is all red marrow. After age five, the red marrow within the diaphyses of long bones is gradually replaced by adipose tissue, appearing yellow and called yellow marrow.

Yellow marrow no longer has hematopoietic capacity, but when there is excessive blood loss or moderate anemia, yellow marrow can transform back into red marrow and restore hematopoietic function.

Red marrow persists for life in the vertebrae, ilium, ribs, sternum, and the epiphyses of long bones such as the humerus and femur. Clinically, bone-marrow aspiration is often performed at the anterior or posterior superior iliac spine to examine the marrow picture.

Osseous tissue contains blood vessels, lymphatics, and nerves.

The arteries of long bones include the nutrient artery, metaphyseal arteries, epiphyseal arteries, and periosteal arteries. They can be divided into the diaphyseal nutrient system, the epiphyseal-metaphyseal system, and the periosteal-cortical system. The nutrient artery is the main artery of long bones, usually 1-2 in number, entering the marrow cavity through the nutrient foramen of the diaphysis and dividing into ascending and descending branches that reach the bone ends, distributing to the inner layer of diaphyseal compact bone, the marrow, and the metaphysis.

The periosteum has abundant lymphatics, but whether lymphatics exist within the marrow or the bone cortex remains debated.

Bone has abundant nerves that accompany the nutrient vessels into the bone, distributed in the perivascular spaces of the Haversian canals. They are mostly visceral efferent (unmyelinated) fibers distributed to the vessel walls; somatic afferent fibers are mostly distributed in the periosteum. The periosteum is relatively sensitive to tension or tearing, so bone abscesses and fractures often cause severe pain.

Bone has a definite shape; its surface is covered by a thick dense connective-tissue membrane, the periosteum. Bone marrow is distributed in the marrow cavity and trabecular spaces. The periosteum is rich in blood vessels, lymphatics, and nerves, and bone constantly carries out metabolism, growth and development, regeneration, and remodeling.

Regular exercise promotes healthy bone development, while prolonged disuse leads to osteoporosis. Bone is the hardest connective tissue in the body; 99% of the body's calcium is stored in bone as hydroxyapatite, making bone the body's largest calcium reservoir and closely related to calcium and phosphorus metabolism. Bone marrow has hematopoietic function.

• Functions of Bone

    The skeleton and cartilage in bone play important roles in the human body.

Functions of the Skeleton

The skeleton carries out important functions in the human body, mainly including protecting and supporting the body, enabling movement, hematopoiesis, and metabolism; the skeleton also stores various minerals essential to the body.

Protective function: The skeleton is like a sturdy frame that protects the body's vital organs, avoiding injury from the outside as much as possible and cushioning the impact on organs in accidents. For example, the skull protects our brain tissue; the ribs and spine protect vital organs such as the lungs, heart, and liver; the pelvis protects the bladder and other urogenital organs. Without the skeleton's protection, the body's internal organs would be easily injured.

Supportive function: Through ligaments, joints, and muscles, the skeleton links into a stable whole that supports our body. The reason we can stand, run, and walk, and our upper limbs can flexibly perform various labors, is that the skeleton supports our body.

Hematopoietic function: Many of the body's hematopoietic cells are stored in the marrow cavity. Bone marrow produces blood cells such as red and white blood cells; after entering the circulatory system, these become part of our blood and play important roles in our life.

Motor function: Together with joints, ligaments, muscles, tendons, and other tissues, the skeleton coordinates the body's movement. The skeletal system is the foundation of the human locomotor system: bone provides support, ligaments maintain stability, joints are the pivots of the locomotor system, and muscles and tendons are its energy stations.

Metabolic function: The skeleton stores many minerals the body needs. It stores not only major elements such as calcium, iron, and phosphorus, but also various other elements such as magnesium, sodium, potassium, zinc, copper, manganese, fluorine, lead, strontium, iron, aluminum, and radium; these elements play very important roles in the body's metabolism.

Functions of Cartilage

Cartilage refers to the cartilage tissue in the human body, which is also a kind of connective tissue. Cartilage is mainly composed of intercellular substance and chondrocytes. Cartilage in young children is difficult to regenerate once injured; but cartilage in adults can regenerate through the perichondrium after injury.

Cartilage tissue plays protective and supportive roles in the body, and the specific functions of cartilage in different locations are not entirely the same.

In the spine, there is corresponding cartilage tissue above and below each vertebral body, varying in thickness—thicker at the periphery and thinner in the center, the central region being translucent, within the epiphyseal ring. These cartilage plates protect the spine, because when the spine is subjected to compressive impact, the cartilage acts as a cushion. In addition, this cartilage also nourishes the intervertebral discs and the vertebrae.

In the thorax, costal cartilage, ribs, and sternum together form the thoracic cage, protecting the various organs within the thoracic cavity. This cartilage also maintains the stability of the thoracic cage while enhancing its overall elasticity, so that the body can inhale and exhale easily and freely.

Most joints have cartilage tissue, which increases the range of joint motion and reduces the pressure and friction at the joint; cartilage also stabilizes and connects the joint structures. In addition, cartilage can absorb to a large degree the external impact borne by the joint.

Part of the nasal cartilage forms the nasal septum, which separates the nasal cavity. Nasal cartilage also participates in regulating and controlling nasal airflow, supports the nasal cavity, and makes it more aesthetic.

The cartilage of the inner ear and the epiglottic cartilage play important roles in phonation and hearing.

III. Classification of Human Bones

Anatomical Classification of Bones

By shape, bones are classified as long bones, short bones, flat bones, and irregular bones.

Long bones are mainly distributed in the limbs, are long and tubular, and consist of a shaft and two ends. The shaft is also called the diaphysis and has a cavity called the medullary cavity, whose main function is to hold bone marrow. On the shaft surface there are foramina where blood vessels enter and leave, called nutrient foramina. The two enlarged ends are called epiphyses, with smooth articular surfaces that form joints with adjacent bones. The part of the shaft adjacent to the epiphysis is the metaphysis. In youth it retains hyaline cartilage called the epiphyseal cartilage; the chondrocytes of the epiphyseal cartilage continuously divide, proliferate, and ossify, making the bone lengthen. After adulthood the epiphyseal cartilage ossifies, and the shaft fuses with the epiphysis; the residual trace is called the epiphyseal line. Injury to the epiphyseal cartilage leads to bony union between the epiphysis and metaphysis in children, a connection also called a bone bridge; the bone bridge causes premature partial or complete closure of the epiphyseal plate, resulting in limb shortening or angular deformity.

Short bones are cube-shaped and mostly occur in groups at sites of firm union and relatively flexible movement, such as the carpal and tarsal bones. Short bones can bear relatively large forces.

Flat bones are plate-like and help form the walls of the cranial cavity, thoracic cavity, and pelvic cavity, protecting the viscera—examples are the calvarial bones and ribs.

Irregular bones have irregular shapes, such as the vertebrae and, among the cranial bones, the sphenoid and ethmoid. A special type of irregular bone is the pneumatic bone, which has cavities communicating with the outside; the maxilla, frontal bone, temporal bone, and ethmoid are all pneumatic bones. Their main function is to produce resonance and reduce the weight of the head. The cavities of pneumatic bones contain mucosa and may develop infection or adhesions.

Muscles often attach to the bone surface, blood vessels and nerves pass through it, or it contacts adjacent organs; these factors affect and give bone its specific shape.

Histological Types of Bone

By timing of formation, the characteristics of bone cells and intercellular substance, and their arrangement, osseous tissue is divided into immature and mature bone tissue. The former is non-lamellar bone; the bone tissue initially formed in the embryo and the callus formed during fracture repair both belong to non-lamellar bone. Except in a few sites, all non-lamellar bone sooner or later eventually transforms into lamellar bone.

Non-lamellar bone, also called primary bone tissue, is of two kinds: woven bone and bundle bone. Woven bone is relatively common; its collagen fiber bundles are arranged in a woven pattern, hence the name. The bone cells in woven bone are more metabolically active than those in lamellar bone, but the bone-resorption activity of the former is often regional.

Lamellar bone, also called secondary bone tissue, is characterized by highly regular layered arrangement of collagen fiber bundles. The collagen bundles are generally relatively fine, so it is also called fine-fiber bone. The fine fiber bundles are usually 2-4 um in diameter, arranged in layers and tightly combined with bone salt and organic matter to form the bone lamellae.

Surface Features of Bone

    Muscles attach to the bone surface, blood vessels and nerves pass through it, or it contacts adjacent organs; these factors affect and give bone its specific shape. Some common anatomical terms relate to this feature of bone.

    Eminences on the bone surface: Because of traction by tendons or ligaments, elevations of varying degrees form on the bone surface. Those clearly rising above the surface are called processes, such as articular processes; sharper projections are called spines; projections with broad bases are called elevations; rough-surfaced elevations are called tuberosities or tubercles; linear high elevations are crests; low, rough crests are lines.

Depressions on the bone surface: Formed by contact with neighboring organs or structures, or by muscle attachment. Large, shallow smooth depressions are called fossae; smaller depressions are pits or foveae; elongated depressions are grooves; shallow depressions are impressions.

Cavities in bone: Formed to hold air or because certain structures pass through. Larger cavities within bone are called cavities, sinuses, or antra; small cavities are cells; elongated channels are canals or meatuses; the openings of cavities or canals are apertures or foramina; incompletely bordered holes are fissures.

Enlargements at bone ends: Round enlargements at bone ends are called heads or capitula; the slightly narrowed part below a head is the neck; oval enlargements are condyles; the projection of a condyle is the epicondyle.

Other features: Smooth bone surfaces are called faces; the edges of bone are borders; notches or indentations in an edge are incisures, which are passages for blood vessels, nerves, or tendons.

IV. Bone Development, Growth, Maintenance, and Remodeling

  Bone originates from the mesoderm. Starting in the 8th week of the embryo, mesenchyme is distributed in a membranous fashion and gradually ossifies, called intramembranous ossification; or it first develops into cartilage, which continues to ossify, called endochondral ossification. Intramembranous and endochondral ossification are the two forms of human skeletal formation.

    1. Intramembranous ossification: Some cells within the mesenchymal membrane differentiate into osteoblasts, which produce bone collagen fibers and matrix; calcium is gradually deposited in the matrix to form bone substance. This process is called intramembranous ossification. It is the type of osseous tissue formed by direct ossification of mesenchyme after it forms a membranous structure in the 8th embryonic week; it belongs to intramembranous bone formation and is mainly distributed in flat bones such as the skull.

  Its formation begins when mesenchymal cells differentiate into osteoprogenitor cells and form a primitive connective-tissue membrane; osteoblasts secrete bone matrix and calcify it at ossification centers to form radial trabeculae, while osteoclasts continuously remodel the bone until the final shape is achieved.

The calvarial bones are typical intramembranous bone. The anterior and posterior fontanelles at the sagittal suture in newborns are membranous structures; intracranial pressure can be assessed by palpating the anterior fontanelle. By age four, the skull has differentiated into the inner and outer tables and the diploë layer containing diploic veins; bone wax is used intraoperatively to manage diploic bleeding. The adult calvaria averages 5 mm thick, thickest at the external occipital protuberance (11-12 mm) and thinnest in the temporal region (only 1-2 mm). During ossification, subperiosteal osteoblasts continuously generate new bone and remodel it, ultimately forming the diploë structure.

 2. Endochondral ossification is an important physiological process of human skeletal development and repair, referring to the gradual replacement of cartilage tissue by hard bone tissue. This process is common in long-bone growth (such as limb bones), fracture healing, and correction of skeletal deformities; abnormalities may affect skeletal shape or function.

In childhood and adolescence, endochondral ossification governs longitudinal bone growth. For example, the chondrocytes of the epiphyseal plate continuously proliferate and calcify, gradually forming hard bone until the epiphyses close in adulthood. In fracture repair, the broken ends first form a cartilage callus, which gradually transforms into osseous tissue to complete healing. Impaired endochondral ossification may lead to short, deformed bones (such as dwarfism); overactivity may trigger osteophytes or joint deformation.

Modern medical cosmetology exploits this feature of endochondral ossification, performing autologous cartilage transplantation to alter facial form, such as rhinoplasty or contouring. But in rhinoplasty or contouring, slight ossification may occur after autologous cartilage transplantation (probability about 3%-5%), usually requiring no special treatment.

After mild injury, the skeletal system can heal on its own. When injured bone needs repair, osteoblasts and osteoclasts act in coordination to regenerate and self-repair the bone. The interaction between osteoclasts (responsible for bone resorption) and osteoblasts (responsible for bone formation) is the core of skeletal dynamic balance (bone remodeling). Through intercellular signaling and local microenvironmental regulation, the two form synergistic and antagonistic relationships, jointly maintaining structural stability and metabolic health of the skeleton. When bone bears mechanical load, osteoblasts promote bone formation by sensing stress signals; osteoclasts become active at sites of bone injury or low stress, clearing damaged osseous tissue.

This function of osteoblasts and osteoclasts is now also applied in biomedicine. When bone suffers major damage or osteoporosis occurs, people can regulate bone regeneration and development by culturing bone tissue in vitro or developing targeted drugs that regulate the activity of osteoblasts or osteoclasts. For example, anti-RANKL antibodies (such as denosumab) treat osteoporosis by inhibiting osteoclast activity; anti-sclerostin antibodies (such as romosozumab) activate the Wnt pathway and promote osteoblast-mediated bone formation.

Bone regeneration is an important part of modern regenerative medicine. In the past, people thought the fibula was of limited importance in the body, so when bone damage was severe, the patient's own fibula was harvested for bone grafting. But modern medicine can now use stem cells to differentiate directly into osteoblasts to repair bone defects while regulating osteoclast activity to optimize graft outcomes, making the repair of bone damage much easier.

V. Number of Human Bones and Basic Functions of Each

Adults have 206 bones in total, of which 6 auditory ossicles belong to the sensory organs.

By location, bones are divided into skull bones, trunk bones, and appendicular bones; the skull bones and trunk bones together are called the axial skeleton.

There are 29 skull bones, divided into the cranium (8 bones) and the facial skeleton (15 bones), plus 6 auditory ossicles.

There are 51 trunk bones in total, divided into vertebrae, ribs, and sternum. There are 26 vertebrae in all: 7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, and 1 coccyx, which together form the vertebral column, through which nerves pass. There are 12 pairs of ribs, totaling 24: pairs 1-7 are true ribs, pairs 8-10 are false ribs, and pairs 11-12 are floating ribs. There is only one sternum, divided into the manubrium, body, and xiphoid process.

There are 126 appendicular bones in total, divided into upper-limb bones (64) and lower-limb bones (62). The upper-limb bones are divided into the shoulder girdle and the free upper limb; the lower-limb bones into the pelvic girdle and the free lower limb.

The free upper limb includes the humerus, radius, ulna, and hand bones. The hand bones include the carpals, metacarpals, and phalanges. The carpals are typical short bones, 8 in number: scaphoid, lunate, triquetral, and pisiform, trapezium, trapezoid, capitate, and hamate. There are 5 metacarpals, numbered 1-5 from the radial to the ulnar side. There are 14 phalanges.

The free lower limb includes the femur, tibia, fibula, and foot bones. The foot bones include the tarsals, metatarsals, and phalanges. There are 7 tarsals: talus, calcaneus, navicular, medial cuneiform, intermediate cuneiform, lateral cuneiform, and cuboid. The tarsals occupy almost half of the whole foot, suited to the weight-bearing and support function of the lower limbs. There are 5 metatarsals and 14 phalanges.

Among these human bones, the humerus, ulna, radius, femur, fibula, tibia, metacarpals (5), hand phalanges (14), metatarsals (5), and foot phalanges (14) of the appendicular skeleton are all typical long bones, with a shaft and two ends and a medullary cavity in between. Whether the clavicle among the appendicular bones is a long bone is somewhat debated: although it too has a shaft and two ends, it has no medullary cavity in the middle. The ribs, the parietal and frontal bones among the skull, and the scapula among the appendicular bones are flat bones; the carpals (8) of the hand and the tarsals (7) of the foot are short bones; the patella is a sesamoid bone; the rest are basically irregular bones.

• Overview of the Basic Functions of Human Bones

There are 29 skull bones, of which 6 are the 3 pairs of auditory ossicles in the middle ear. The auditory ossicles transmit and amplify sound and connect to the inner ear to maintain body balance; their health is crucial to hearing. Ear infection, trauma, noise exposure, ototoxic drugs, and aging all affect the auditory ossicles.

Of the remaining 23 skull bones, except for the mandible and hyoid, they are firmly connected to one another by sutures or cartilage to form the cranium, which protects and supports the brain and sensory organs and forms the beginning of the digestive and respiratory systems.

The shoulder girdle, also called the pectoral girdle, consists of the clavicle and scapula. Its connection to the axial skeleton is relatively loose; it is linked to the ribs mainly through muscles, with the clavicle providing the only stable connection—also an adaptation to the flexibility needs of the upper limb.

The pelvic girdle, to meet the weight-bearing needs of the lower limbs, connects to the axial skeleton through the sacroiliac joint, a relatively firm joint.

In the course of evolution, humans learned to walk upright; the main function of the upper limbs is labor, while that of the lower limbs is weight-bearing. The upper-limb bones as a whole are relatively flexible, whereas the lower-limb bones are relatively stable.

Adults have 26 vertebrae: 7 cervical (C1-C7), 12 thoracic (T1-T12), 5 lumbar (L1-L5), plus one sacrum and one coccyx. The adult sacrum is formed by the fusion of the 5 sacral vertebrae of childhood during development; the adult coccyx is formed by the fusion of the 3-4 coccygeal vertebrae of childhood.

These vertebrae together form our spinal column, which plays an important supportive role in the body. Because each segment of the spine bears different body weight, the vertebral bodies gradually increase in size from top to bottom; this structural feature is determined by their function.

A vertebra is divided into a vertebral body and a vertebral arch (the atlas of the cervical spine has no vertebral arch). The vertebral body is the main weight-bearing part, with a vertebral foramen in its center. The successive vertebral foramina form the vertebral canal, which contains the spinal cord, its meninges, cerebrospinal fluid, spinal nerve roots, blood vessels, and a small amount of connective tissue.

There is also fat in the vertebral canal; healthy standards call for "a small amount, evenly distributed, with no obvious compression or space-occupying effect." Moderate fat protects the tissues within the canal to some degree, but excessive deposition causes spinal stenosis or nerve compression, leading to a series of symptoms such as low-back and leg pain and foot numbness—this is also one of the common diseases of our time.

The interior of the vertebral body is filled with spongy bone; the compact bone on the surface is relatively thin, and the upper and lower surfaces are rough, connecting with adjacent vertebrae through intervertebral discs. The vertebral arch is an arched plate of bone; its narrowed part adjacent to the body is the pedicle of the vertebral arch, whose upper and lower margins are the superior and inferior vertebral notches. The superior and inferior notches of adjacent vertebrae together enclose the intervertebral foramina, through which spinal nerves and blood vessels pass.

The vertebral arch gives off 7 processes in all (not every vertebra has an arch): 1) one spinous process, projecting backward or postero-inferiorly from the midline of the posterior arch, its tip palpable on the body surface; 2) one pair of transverse processes (2 in total), symmetrically on both sides of the arch. The spinous and transverse processes are attachment sites for muscles and ligaments; 3) two pairs of articular processes (4 in total), projecting upward and downward at the junction of the pedicle and lamina; the upward ones are the superior articular processes and the downward ones the inferior articular processes, and adjacent articular processes form the facet joints.

The spinal column has four physiological curves: cervical, thoracic, lumbar, and sacral. The cervical and lumbar curves bulge forward, while the thoracic and sacral curves bulge backward. Poor sitting posture over long periods, ankylosing spondylitis, trauma, degenerative changes, and congenital abnormalities can straighten the physiological curves, bringing all kinds of inconvenience and pain to the patient.

The four physiological curves have different functions. The cervical curve is the uppermost, balancing the head and giving it a certain flexibility. The thoracic curve is in the middle, giving the thoracic cage enough space to hold vital organs such as the heart and lungs. The lumbar curve is in the lower half, helping support body weight and balance and absorb stress from the upper body. The sacral curve is the lowermost, allowing the sacrum to connect stably with the pelvis and supporting the ischium.

Variations of the vertebrae may occur during embryonic development. If the posterior ends of the two vertebral arches fail to fuse completely, spina bifida results, common in the lumbosacral region. A mild form is spina bifida occulta, in which patients often have low-back pain; in severe forms the meninges, and even the spinal cord and cauda equina, herniate through it. The number of vertebrae may also vary: if the first sacral vertebra does not fuse with the other sacral vertebrae but forms a 6th lumbar vertebra, it is called sacralization of the lumbar (lumbarization). Conversely, if a lumbar vertebra fuses with the sacrum, it is called lumbarization of the sacrum (sacralization).

VI. Common Orthopedic Diseases

  By pathological nature, orthopedic diseases are broadly divided into six categories: trauma, degenerative diseases, infectious diseases, non-infectious inflammatory diseases, deformities, and tumors.

  Trauma is further divided into fractures, joint dislocations, and peripheral nerve injuries.

Common orthopedic fractures include clavicle fracture, humerus fracture, forearm fracture, hand injury, finger amputation, limb amputation, hip fracture, femur fracture, knee-joint injury, fibula fracture, tibia fracture, ankle-joint injury, foot fracture, spinal fracture, spinal-cord injury, and pelvic fracture; common joint dislocations include acromioclavicular, shoulder, elbow, and hip dislocations; common nerve injuries include upper-limb and lower-limb nerve injuries.

Common orthopedic degenerative lesions are mainly related to age and chronic strain; by site and nature they are divided into spinal degenerative disease, degenerative arthritis, chronic locomotor-system injury, and osteonecrosis.

Spinal degenerative lesions include cervical spondylosis, spinal stenosis, cervical ossification of the posterior longitudinal ligament, thoracic spinal stenosis, lumbar spinal stenosis, lumbar disc herniation, and spondylolisthesis; common degenerative arthritis involves the knee, hip, and hand and foot joints; common chronic locomotor-system injuries include chronic soft-tissue injury, nerve-entrapment syndromes, chronic bone and cartilage injury, and hallux valgus; common osteonecrosis includes femoral head necrosis, hand and foot osteonecrosis, Legg-Calvé-Perthes disease, vertebral osteochondrosis, and Osgood-Schlatter disease.

Common orthopedic infectious diseases include pyogenic diseases such as pyogenic osteomyelitis, pyogenic arthritis, and spinal infection, as well as spinal tuberculosis, hip tuberculosis, and small-joint tuberculosis.

Common non-infectious inflammatory orthopedic diseases include autoimmune diseases such as ankylosing spondylitis and rheumatoid arthritis, as well as metabolic diseases such as osteoporosis with vertebral fracture, gouty arthritis, and Kashin-Beck disease.

Common orthopedic deformities include spinal deformities, limb deformities, hand and foot deformities, and sequelae of brain and spinal-cord diseases. Spinal deformities include adolescent idiopathic scoliosis, congenital spinal deformity, and other types; limb deformities include congenital muscular torticollis, congenital hip dislocation, and gluteal muscle contracture; hand and foot deformities include congenital hand deformity, congenital clubfoot, and flatfoot; sequelae of brain and spinal-cord diseases include cerebral palsy and postpoliomyelitis sequelae.

Common orthopedic tumors include benign tumors, borderline tumors, malignant tumors, secondary metastatic tumors, and other tumors and tumor-like lesions.

Benign orthopedic tumors mainly include osteoma, osteoid osteoma, osteoblastoma, enchondroma, osteochondroma, and chondroblastoma; borderline bone tumors include giant-cell tumor of bone; common malignant orthopedic tumors include osteosarcoma, chondrosarcoma, Ewing sarcoma, multiple myeloma, chordoma, and synovial sarcoma. Many other malignant tumors metastasize to bone in late stages, such as breast, lung, and ovarian cancer bone metastases; these are called metastatic bone tumors. Orthopedics also sees other tumors and tumor-like lesions, such as bone cyst, aneurysmal bone cyst, eosinophilic granuloma of bone, fibrous dysplasia of bone, synovial chondromatosis, and pigmented villonodular synovitis.

References

1. Systematic Anatomy (Cui Huixian et al., eds.; People's Medical Publishing House, 10th ed., July 2024, pp. 6-33)
2. Human Anatomy (Qiao Xing et al., eds.; China Science and Technology Press, 1st ed., August 2017, pp. 8-9)
3. Atlas of Human Anatomical Structure and Function (Ken Ashwell, Australia; Ma Chao, chief trans.; Jiangsu Phoenix Science and Technology Press, 1st ed., September 2022, pp. 12-17)
4. The Locomotor System and Diseases (He Xijing et al., eds.; People's Medical Publishing House, 2nd ed., May 2021)
5. Practical Orthopedic Integrated Chinese-Western Diagnosis and Treatment (Cao Fujiang et al., eds.; Ancient Chinese Medical Books Press, 1st ed., June 2023, pp. 1-20)
6. Practice of Integrated Chinese-Western Treatment of Orthopedic Diseases (Yu Chuandong, Jiang Songtao et al., eds.; Scientific and Technical Documentation Press, 1st ed., January 2024, pp. 1-13)
7. Atlas of the Knowledge System of Systematic Anatomy (Hu Guangqiang et al., eds.; Science Press, 1st ed., April 2016, pp. 1-5)
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11. Essentials of Modern Orthopedics (Fang Xichi et al., eds.; Jilin Science and Technology Press, 1st ed., July 2023)