Lecture Notes in Human Anatomy - Hryhorieva O.A., Svitlytskyi A.O. 2020

Anatomy of the Musculoskeletal System
Anatomy of Bones and Their Joints
Osteology

Lecture Plan:

1. Morphofunctional characteristics of continuous bone connections.

2. Morphofunctional characteristics of semi-continuous bone connections.

3. Morphofunctional characteristics of interrupted bone connections.

4. Classification of Joints.

Bones in The Human Body are linked together into a single functional whole. The Nature of their connection is determined by functional demands: in some PARTS OF THE Skeleton, movements between bones are more pronounced, while in others they are restricted.

Based on their development, Structure, and function, bone connections are divided into continuous (synarthroses), semi-continuous (symphyses), and interrupted (joints, or diarthroses).

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Continuous connections are bone joints characterized by the absence of a cleft or cavity between the bones, which are united by an intervening layer of tissue. Depending on the type of tissue between the joined bones, these connections are classified into fibrous connections (syndesmoses), cartilaginous connections (synchondroses), and bony connections (synostoses).

Syndesmoses are subdivided into fibrous (when Collagen fibers predominate in the connecting tissue) and elastic (when elastic fibers predominate). Depending on the size and Nature of the intervening layer, fibrous bone connections may take the form of ligaments (connecting vertebral processes), interosseous membranes (between the BONES OF THE forearm or leg), or sutures (a narrow layer measuring 2-3 mm between Skull bones). Sutures are further categorized as serrate (between the parietal and occipital bones), squamous (between the temporal and parietal bones), and plane (between the bones of the facial skeleton). Elastic-type continuous connections include the ligamenta flava between the vertebral arches.

Synchondroses are continuous bone connections formed by cartilaginous tissue; the range and amplitude of movement in synchondroses are limited and depend on the thickness of the Cartilage layer—the thicker the layer, the greater the mobility. Depending on the histological STRUCTURE OF THE cartilage, synchondroses are divided into fibrocartilaginous connections (between vertebral bodies) and hyaline cartilage connections (between the first rib and the Sternum, or between the diaphysis and epiphysis of a bone). Synchondroses can be temporary (such as between the sacrum and the coccyx), becoming replaced by synostoses with age, or permanent (between the pyramid of the Temporal bone and the Occipital bone), which persist throughout life. Hyaline connections are more resilient, yet they are also more brittle.

Synostoses are continuous bone connections mediated by osseous tissue, developing As a result of the replacement of Connective Tissue with bone; Examples include the ossification of epiphyseal cartilages and cranial sutures.

Continuous bone connections (except for synostoses) possess some degree of mobility.

Semi-continuous bone connections, or symphyses, are characterized by the presence of a small, slit-like cavity within the connecting tissue between the bones (e.g., the Pubic Symphysis, the symphysis of the manubrium sterni, and intervertebral symphyses); this cavity contains fluid.

Interrupted bone connections, or joints (articulations), are the most common and movable type of bone joints. Joints help maintain posture and the relative position of body parts in space, facilitate the movement of body segments relative to one another, and participate in whole-body locomotion. Each joint consists of the articulating bone surfaces, the Joint Capsule, and the joint cavity. The articulating surfaces are covered with hyaline cartilage, or more rarely fibrocartilage, which provides a smooth surface to facilitate sliding, minimize friction between the surfaces, and protect them from wear and tear. The articulating surfaces are mutually correspondent (congruent)—if one surface is concave, the other is convex; if this correspondence is lacking, additional intra-articular structures are present to enhance congruence.

The joint capsule hermetically encloses the joint cavity, attaching to the bones along the margins of their articulating surfaces. It consists of an outer fibrous membrane and an inner synovial membrane. The synovial membrane faces the joint cavity and is lined with a layer of endothelial Cells that secrete synovial fluid into the cavity, which reduces surface friction and absorbs mechanical shocks.

The joint cavity is a hermetically sealed, slit-like space bounded by the articulating surfaces and the synovial membrane, filled with synovial fluid that also serves a trophic function by participating in the nourishment of the hyaline cartilage.

Some joints contain additional structures (discs, menisci, ligaments, etc.) that improve surface congruence, increase joint mobility, promote the even distribution of pressure from one bone to another, and reinforce the joint capsule. Discs are complete cartilaginous plates (as in the temporomandibular joint); menisci are incomplete, crescent-shaped cartilaginous structures (as in the knee joint); articular Lips are fibrocartilaginous rims surrounding a socket (such as the glenoid labrum of the scapula); and ligaments are bundles of connective tissue running from one bone to another, which may be intracapsular or extracapsular.

Joints are classified According to the number of articulating surfaces, their shape, and joint function.

Based on the number of articulating surfaces, joints are distinguished as simple, complex, compound (complex/combined), or combined. Simple joints consist of two articulating surfaces (e.g., interphalangeal joints). Complex joints feature more than two articulating surfaces or comprise multiple simple articulations where movements can occur independently (e.g., the elbow joint). Compound joints are those partitioned into chambers either completely by a cartilaginous disc (temporomandibular joint) or partially by a meniscus (knee joint). A separate group comprises combined joints, which consist of several spatially separate joints functioning together (e.g., the proximal and distal radioulnar joints, or both temporomandibular joints).

The classification based on the shape of the articulating surfaces and joint function relies on the principle that surface geometry determines the number of axes around which movements occur—in other words, the function of the joint. Accordingly, joints are classified into Uniaxial joints, where movement occurs around a single axis of rotation; Biaxial joints, with movement around two axes; and multiaxial joints, allowing movement around numerous axes corresponding to the radii of a sphere, though practically three mutually perpendicular axes are recognized. An axis of rotation is an imaginary line passing through the center of the joint around which the bones rotate relative to each other. Movements in joints occur perpendicularly to the axis of rotation and are described with reference to the anatomical position of the body. Around the frontal axis, flexion and extension occur in the limbs, and forward and backward bending in the HEAD and trunk. Around the sagittal axis, movements away from the midline of the body—abduction and adduction in the limbs, and lateral flexion (side-bending) in the head and trunk—take place. Around the vertical axis, rotation occurs, including outward rotation (supination) and inward rotation (pronation) in the limbs, as well as twisting rotations of the Head and Neck.

Uniaxial joints include:

- pivot joints are joints with a cylindrical articular surface and a vertical axis of rotation parallel to the vertical axis of the body; these joints allow rotation (supination and pronation), such as the proximal radioulnar joint;

- hinge joints are joints with a spool-shaped (trochlear) articular surface and a transverse axis of rotation, allowing flexion and extension, such as the interphalangeal joints;

Biaxial joints include:

- ellipsoid (condyloid) joints are joints with ellipsoid articular surfaces, where one is concave and the other convex, allowing movements around two horizontal axes: flexion and extension around the frontal axis, and abduction and adduction around the sagittal axis, such as the radiocarpal joint;

- condyloid joints are joints featuring a convex articular head shaped like a prominent rounded process called a condyle, which fits into a corresponding socket on the articular surface of the joining bone. Such a joint allows movement around two axes: the primary axis of rotation is frontal (flexion and extension, forward and backward tilting), while the second axis can be either sagittal (lateral tilting, as in the atlanto-occipital joint) or vertical (supination and pronation, as in the knee joint). Thus, the atlanto-occipital joint permits forward/backward and lateral tilting, whereas the knee joint allows flexion, extension, supination, and pronation. Condyloid joints can

be regarded as a subtype of ellipsoid joints, serving as a transitional form between hinge and ellipsoid joints;

- saddle joints are joints with saddle-shaped articular surfaces, allowing movements around two horizontal axes: flexion and extension around the frontal axis, and abduction and adduction around the sagittal axis, exemplified by the first carpometacarpal joint.

Triaxial joints include:

- ball-and-socket (spheroidal) joints are joints in which one articular head is convex and spherical, while the other is concave, forming a matching socket; movements are possible around multiple axes, the main ones being the frontal (flexion and extension), sagittal (abduction and adduction), and vertical (rotation, supination, and pronation) axes. Transitioning from one axis to another produces circumduction. Examples include the hip and shoulder joints;

- plane joints are joints with nearly flat articular surfaces, allowing movements around multiple axes—flexion and extension, abduction and adduction, supination, and pronation. Shifting from one axis to another results in circumduction, though the range of motion is limited; examples include the intervertebral joints.

Connections of the Bones of the Upper Limb

The sternoclavicular joint connects the clavicle to the sternum, formed by the sternal end of the clavicle and the clavicular notch of the sternum. It is a simple, saddle-shaped joint, yet it Functions as a ball-and-socket joint due to an intra-articular disc that divides the joint cavity into two compartments, thereby increasing the range of motion and absorbing shocks. Movements in this joint occur around the vertical axis (forward and backward movement of the clavicle, along with the scapula), the sagittal axis (upward and downward movement of the clavicle and scapula), and the transverse axis (forward and backward Rotation of the clavicle).

The acromioclavicular joint connects the clavicle to the scapula.

The shoulder (glenohumeral) joint connects the humerus to the scapula, formed by the glenoid cavity of the scapula and the articular surface of the humeral head. It is a simple, ball-and-socket joint that permits movement around three axes of rotation: around the transverse axis—flexion (forward movement of the arm) and extension (backward movement of the arm); around the sagittal axis—abduction of the arm laterally up to the horizontal level and adduction toward the torso; and around the vertical axis—pronational (medial rotation toward the trunk) and supinational (lateral rotation away from the trunk) movements. Circumduction is also possible in the shoulder joint.

The elbow joint connects the humerus to the bones of the forearm. It is a compound joint formed by the humerus, ulna, and radius. The articulation of these bones creates three distinct joints enclosed within a single articular capsule: the humeroulnar, humeroradial, and proximal radioulnar joints. Overall, the elbow joint provides the forearm with movements of flexion and extension around the transverse axis, as well as pronation and supination around the vertical axis.

The humeroulnar joint is formed by the humerus and the ulna, featuring a single transverse axis of rotation that allows flexion and extension of the ulna.

The humeroradial joint is formed by the head of the humerus and the head of the radius. It is a ball-and-socket joint, but movements around the sagittal axis are restricted due to strong ligaments and the interosseous membrane between the radius and ulna. Rotational movements are possible around the vertical axis (pronation and supination of the radius and the hand attached to it). Movements around the transverse axis are identical to those in the elbow joint (flexion and extension).

The proximal radioulnar joint is formed by the head of the radius and the radial notch of the ulna. It is a pivot joint with a single vertical axis of rotation governing the rotation of the radius around the ulna.

The radiocarpal joint connects the hand to the forearm; it is a compound, ellipsoid joint with two axes of rotation: around the frontal axis—flexion (toward the palmar surface) and extension (toward the dorsal surface) of the hand; and around the sagittal axis—adduction (movement toward the ulna) and abduction (movement toward the radius) of the hand.

Age-related Features of the upper limb skeleton. Ossification is completed by the age of 20–25 in the clavicle, scapula, humerus, radius, and ulna; by 10–13 in the Carpal Bones; at 12 in the metacarpals; and at 9–11 in the Phalanges of the fingers. The greatest longitudinal growth of the upper limbs and their segments (except the hand) is observed at ages 12 and 15 in boys, and 13 and 15 in girls.

In the Skeleton of the Lower Limb, one distinguishes the Bones and Articulations of the Pelvic Girdle and the free lower limb.

The connections of the bones of the lower limb are divided into JOINTS OF THE pelvic girdle and the free lower limb.

The sacroiliac joint is formed by the auricular surfaces of the ilium and the sacrum. It is a simple, plane, slightly mobile joint.

The pubic symphysis is located between the pubic bones; it is a cartilaginous amphiarthrosis (slightly movable cartilaginous joint).

The hip joint is formed by the head of the Femur and the acetabulum of the hip bone. The articular capsule envelops most of the femoral neck and attaches to the hip and thigh bones in such a way that a significant portion of the femoral neck lies within the joint cavity. Inside the joint, there is also the ligament of the head of the femur, which transmits Blood Vessels and nerves. The joint is simple, nut-socket (cotyloid)—a variant of the ball-and-socket joint—and is classified as a multiaxial joint. Movements are possible around three axes: around the transverse axis—flexion and extension (forward and backward movement of the thigh); around the sagittal axis—abduction of the thigh away from the trunk and adduction; and around the vertical axis—supination and pronation. Circumduction is also possible in this joint.

The knee joint is formed by the articular surfaces of the femoral and tibial condyles. Its anterior surface is adjacent to the Patella, the largest sesamoid bone located within the tendon of the quadriceps femoris Muscle. The patella facilitates the smooth gliding of this muscle's tendon and increases the range of motion in the joint. The joint is complex and incongruent, meaning its articular surfaces are supplemented by intra-articular cartilages: the medial and lateral menisci. The menisci deepen the articular surface of the Tibia, thereby promoting an even distribution of pressure across the bone, while also acting as Shock absorbers and increasing the range of motion. The joint is hinge-ball in type, with movements possible around two axes of rotation: flexion and extension (forward and backward movement of the leg) around the transverse axis, and supination and pronation around the vertical axis. In the proximal region, the Fibula and tibia are connected by a plane joint with limited mobility. The distal ends of the leg bones are connected by a plane joint or connective tissue (syndesmosis). The knee joint is reinforced by ligaments located both inside and outside the joint cavity; these ligaments are connected to the menisci, joint capsule, condyles, and epicondyles of the femur and tibia. The knee joint features several synovial bursae, where fluid accumulates and inflammatory processes develop upon injury or disease.

The ankle joint is formed by the distal epiphyses of the leg bones and the talus (a tarsal bone). Connected together, the distal ends of the fibula and tibia (the medial and lateral malleoli, respectively) tightly embrace the trochlea of the talus like a fork. This connection is secured by strong ligaments. The ankle joint is classified as a complex hinge joint, having only a transverse axis of rotation around which flexion and extension occur.

Age-related features of the lower extremity skeleton. Complete Ossification of the tibia and fibula occurs at 20-24 years of age; in the Metatarsal Bones, it occurs at 17-21 years in males and 14-19 years in females; and in the phalanges of the toes, at 15-21 years in males and 13-17 years in females. The highest growth intensity of the lower limb in boys is observed at 12 and 15 years, with femoral length peaking at the same ages, and tibial and FOOT lengths at 12 and 14 years. In girls, The most significant increase in leg length occurs at 13 and 14 years, femoral length at 13 and 16 years, and foot length at 14 years.

The connections of the skull bones are predominantly represented by syndesmoses (sutures), though diarthroses (synovial joints) are also present. The sutures include serrate sutures between the frontal, parietal, and occipital bones; squamous sutures between the temporal and parietal bones; and plane sutures between the facial bones, with the exception of the articulation between the temporal bone and the Mandible.

The temporomandibular joint—between the temporal bone and the mandible—is ellipsoidal, combined, simple, and incongruent; it is formed by the mandibular fossa of the temporal bone and the condylar process of the mandible. The mandible can move upward, downward, forward, backward, and laterally.

The atlanto-occipital joint is ellipsoidal, combined, and simple; it is formed by the occipital condyles and the articular surfaces of the first cervical vertebra, the atlas. Small-amplitude movements are possible forward and backward around the transverse (frontal) axis, as well as lateral head tilts around the sagittal axis.

The atlantoaxial joint is combined and consists of a median joint and two lateral joints. The median joint is formed by the dens of the second cervical (axis) vertebra and the articular surface of the anterior arch of the atlas; it is a simple, cylindrical joint with a single vertical axis of rotation, around which head rotation occurs. The right and left lateral joints are formed by the flat articular surfaces of the First and Second cervical vertebrae, with movements identical to those in the median joint.

Age, sex, and individual CHARACTERISTICS OF THE skull. With age, the proportion of skull size to body length changes: in a newborn, this ratio is 1/4, whereas in an adult it is 1/8. In the newborn skull, a layer of connective tissue lies between the bones, and ossification of the sutures occurs only after 30 years of age. Increased masticatory movements with age lead to The formation of angles between the body and rami of the mandible. In females, the cranial capacity is slightly smaller, and bony prominences and irregularities are smoothed and less pronounced. Individual variations are most frequently manifested in the shape of the skull; three skull shapes are distinguished: long and narrow (dolichocephalic), short and broad (brachycephalic), and intermediate in length and width (mesocephalic).