Course in articulations and joints of the human body

Joints

1. JOINTS General Features Vertebral column Upper limb

2. General Features

3. False joints continuous bone connections in which the intervening tissue consists of fibrous connective tissue, cartilage, or bone) Low to moderate mobility Synarthroses • Syndesmoses (fibrous joints) • Syncondroses (cartilaginous joints) (If the intervening tissue is mostly fibrocartilage, the joint is called a symphysis, e.g., the pubic symphysis.) • Synostoses (sites of bony fusion) (because a synostosis is immobile, it is no longer classified as a synarthrosis in the strict sense.)

4. True joints (-discontinuous connections in which the bones are separated by a joint space): • Mobility is variable. Depending on the attached ligaments Diarthrosis Classified according to various criteria • Shape and arrangement of the articular surfaces • Number of joint axes • Number of degrees of freedom Amphiarthroses "Stiff joints” whose mobility is greatly limited by strong ligaments (e.g., the sacroiliac joint and proximal tibiofibular joint) Ankylosis - abnormal bony fixation of a true joint Arthrodesis - surgical fusion of a joint for therapeutic reasons Pseudarthrosis ( nonunion )- "false joint" due to abnormal fracture healing

5. True Joints have the following characteristics: • joint space • articular surfaces covered by hyaline cartilage • joint cavity • closed joint capsule • ligaments and muscles acting as primary joint stabilizers Some joints also contain intra-articular structures that help the joint to function: menisci (e.g., In the knee joint), articular disk (e.g., In the temporomandibular joint), articular labrum (e.g., In the shoulder joint), intra-articular ligaments (e.g., the cruciate ligaments of the knee).

6. The joint space is shown greatly widened in the diagram to exhibit its features more clearly. The synovial fluid, produced mainly by type B synovilocytes , is a very viscous Intra-articular fluid with a high content af hyaluronic acid. The synovial fluid performs three main functions: • It nourishes the articular cartilage through diffusion and convection. • It lubricates the articular surfaces to reduce friction. • It cushions shocks by evenly distributing compressive forces.

7. Vertebral column

8. The primary curvatures are located in the thoracic and sacral regions and develop during embryonic and fetal periods, whereas the secondary curvatures are located in the cervical and lumbar regions and develop after birth and during infancy.

9. 1. Atlanto -occipital joint • Is a condylar synovial joint that occurs between the superior articular facets of the atlas and the occipital condyles. • Is involved primarily in flexion, extension, and lateral flexion of the head. 2. Atlantoaxial joints • Are synovial joints, consisting of two lateral plane joints, which are between articular facets of the atlas and axis, and one median pivot joint between the dens of the axis and the anterior arch of the atlas. • Are involved in rotation of the atlas and head as a unit on the axis.

10. Components of the occipitoaxial ligament 1. Cruciform ligament a. Transverse ligament • Runs between the lateral masses of the atlas, arching over the dens of the axis. b. Longitudinal ligament • Extends from the dens of the axis to the anterior aspect of the foramen magnum and to the body of the axis. 2. Apical ligament • Extends from the apex of the dens to the anterior aspect of the foramen magnum (of the occipital bone). 3. Alar ligament • Extends from the apex of the dens to the tubercle on the medial side of the occipital condyle. 4. Tectorial membrane • Is an upward extension of the posterior longitudinal ligament from the body of the axis to the basilar part of the occipital bone anterior to the foramen magnum. • Covers the posterior surface of the dens and the apical, alar, and cruciform ligaments.

11. INTERVERTEBRAL DISK Consist of a central mucoid substance (nucleus pulposus) with a surrounding fibrocartilaginous lamina (anulus fibrosus). Comprise one fourth (25%) of the length of the vertebral column. Allow movements between the vertebrae and serve as a shock absorber. Are avascular except for their peripheries, which are supplied from adjacent blood vessels. Nucleus pulposus • Is a remnant of the embryonic notochord and is situated in the central portion of the intervertebral disk. • Consists of reticular and collagenous fibers embedded in mucoid material. • May herniate or protrude through the anulus fibrosus, thereby impinging on the roots of the spinal nerve. • Acts as a shock-absorbing mechanism by equalizing pressure. Anulus fibrosus • Consists of concentric layers of fibrous tissue and fibrocartilage. • Binds the vertebral column together, retains the nucleus pulposus, and permits a limited amount of movement. • Acts as a shock absorber.

12. Ligamentum flavum • Connects the laminae of two adjacent vertebrae and functions to maintain the upright posture. • Forms the posterior wall of the vertebral canal between the vertebrae and may be pierced during lumbar (spinal) puncture. Ligamentum nuchae (back of neck) • Is a triangular-shaped median fibrous septum between the muscles on the two sides of the posterior aspect of the neck. • Is formed by thickened supraspinous ligaments that extend from vertebra C7 to the external occipital protuberance and crest. • Is also attached to the posterior tubercle of the atlas and to the spinous processes of the other cervical vertebrae.

13. Anterior longitudinal ligament • Runs from the skull (occipital bone) to the sacrum on the anterior surface of the vertebral bodies and intervertebral disks. • Is narrowest at the upper end but widens as it descends, maintaining the stability of the joints. • Limits extension of the vertebral column, supports the anulus fibrosus anteriorly, and resists gravitational pull.

14. Posterior longitudinal ligament • Interconnects the vertebral bodies and intervertebral disks posteriorly and narrows as it descends. • Supports the posterior aspect of the vertebral bodies and the anulus fibrosus, but it runs anterior to the spinal cord within the vertebral canal. • Limits flexion of the vertebral column and resists gravitational pull.

15. Deep or intrinsic muscles 1. Muscles of the superficial layer: spinotransverse group • Consist of the splenius capitis and the splenius cervicis. • Originate from the spinous processes and insert into the transverse processes (splenius cervicis) and on the mastoid process and the superior nuchal line (splenius capitis). • Arc innervated by the dorsal primary rami of the middle and lower cervical spinal nerves. • Extend, rotate, and laterally flex the head and neck. 2. Muscles of the intermediate layer: sacrospinalis group • Consist of the erector spinae ( sacrospinalis ), which is divided into three columns: iliocostalis (lateral column), longissimus (intermediate column), and spinalis (medial column). • Originate from the sacrum, ilium, ribs, and spinous processes of lumbar and lower thoracic vertebrae. • Insert on the ribs (iliocostalis); on the ribs, transverse processes, and mastoid process (longissimus); and on the spinous processes (spinalis). • Are innervated by the dorsal primary rami of the spinal nerves. • Extend, rotate, and laterally flex the vertebral column and head.

16. 3. Muscles of the deep layer : transversospinalis group • Consist of the semispinalis (capitis, cervicis, and thoracis); the multifidus; and the rotators. • The semispinalis muscles originate from the transverse processes and insert into the skull (semispinalis capitis) and the spinous processes (semispinalis cervicis and thoracis). • The rotators run from the transverse processes to spinous processes two vertebrae above (longus) and one vertebra above (brevis). • The multifidus originates from the sacrum, ilium, and transverse processes and inserts on the spinous processes. It is best developed in the lumbar region. • Are innervated by the dorsal primary rami of the spinal nerves. • Extend and rotate the head, neck, and trunk. Segmental muscles • Are innervated by the dorsal primary rami of the spinal nerves. • Consist of the following: 1. Interspinales • Run between adjacent spinous processes and aid in extension of the vertebral column. 2. Intertransversarii • Run between adjacent transverse processes and aid in lateral flexion of the vertebral column. 3. Levatores costarum (longus and brevis) • Extend from the transverse processes to ribs and elevate ribs.

17. Upper limb

18. Acromioclavicular joint • Is a synovial plane joint that allows a gliding movement when the scapula rotates and is reinforced by the coracoclavicular ligament, which consists of the conoid and trapezoid ligaments. Sternoclavicular joint • Is a double synovial plane (gliding) joint and united by the fibrous capsule. • Is reinforced by the anterior and posterior sternoclavicular, interclavicular, and costoclavicular ligaments. • Allows elevation and depression, protraction and retraction, and circumduction of the shoulder.

19. Shoulder (glenohumeral) joint • Is a synovial hall-and - socket joint between the glenoid cavity of the scapula and the head of the humerus . Both articular surfaces are covered with hyaline cartilage. • Is surrounded by the fibrous capsule that is attached superiorly to the margin of the glenoid and inferiorly to the anatomic neck of the humerus . The capsule is reinforced by the rotator cuff, the glenohumeral ligaments, and the coracohumeral ligaments. • Has a cavity that is deepened by the fibrocartilaginous glenoid labrum ; communicates with the subscapular bursa; and allows abduction and adduction, flexion and extension, and circumduction and rotation. • Is innervated by the axillary, suprascapular, and lateral pectoral nerves. • Receives blood from branches of the suprascapular, anterior and posterior humeral circumflex, and scapular circumflex arteries. • May be subject to inferior or anterior dislocation, which stretches the fibrous capsule, avulses the glenoid labrum , and may injure the axillary nerve.

20. Rotator (musculotendinous) cuff • Is formed by the tendons of the subscapularis, supraspinatus, infraspinatus, and teres minor muscles; fuses with the joint capsule; and provides mobility. • Keeps the head of the humerus in the glenoid fossa during movements and thus stabilizes the shoulder joint. Ligaments of the shoulder joint a. Glenohumeral ligaments • Extend from the supraglenoid tubercle to the upper part of the lesser tubercle of the humerus (superior glenohumeral ligament), to the lower anatomic neck of the humerus (middle glenohumeral ligament), and to the lower part of the lesser tubercle of the humerus (inferior glenohumeral ligament). b. Transverse humeral ligament • Extends between the greater and lesser tubercles, and holds the tendon of the long head of the biceps in the intertubercular groove. c. Coracohumeral ligament • Extends from the coracoid process to the greater tubercle. d. Coracoacromial ligament • Extends from the coracoid process to the acromion.

21. Bursae around the shoulder • Form a lubricating mechanism between the rotator cuff and the coracoacromial arch during movement of the shoulder joint. a. Subacromial bursa • Lies between the coracoacromial arch and the supraspinatus muscle, and usually communicates with the subdeltoid bursa. • Protects the supraspinatus tendon against friction with the acromion. b. Subdeltoid bursa • Lies between the deltoid muscle and the shoulder joint capsule and usually communicates with the subacromial bursa. • Facilitates the movement of the deltoid muscle over the joint capsule and the supraspinatus tendon. c. Subscapular bursa • Lies between the subscapularis tendon and the neck of the scapula. • Communicates with the synovial cavity of the shoulder joint.

22. Elbow joint • Forms a synovial hinge joint, consisting of the humeroradial and humeroulnar joints, and allows flexion and extension. • Also includes the proximal radioulnar (pivot) joint, within a common articular capsule. • Is innervated by the musculocutaneous, median, radial, and ulnar nerves. • Receives blood from the anastomosis formed by branches of the brachial artery and recurrent branches of the radial and ulnar arteries. • Is reinforced by the following ligaments: 1. Annular ligament • Is a fibrous band that forms nearly four-fifths of a circle around the head of the radius; the radial notch forms the remainder. • Forms a collar around the head of the radius, fuses with the radial collateral ligament and the articular capsule, and prevents withdrawal of the head of the radius from its socket. 2. Radial collateral ligament • Extends from the lateral epicondyle to the anterior and posterior margins of the radial notch of the ulna and the annular ligament of the radius. 3. Ulnar collateral ligament • Is triangular and is composed of anterior, posterior, and oblique bands. • Extends from the medial epicondyle to the coronoid process and the olecranon of the ulna.

23. Proximal radioulnar joint • Forms a synovial pivot joint in which the head of the radius articulates with the radialnotch of the ulna and allows pronation and supination. Distal radioulnar joint • Forms a synovial pivot joint between the head of the ulna and the ulnar notch of the radius and allows pronation and supination. Wrist (radiocarpal) joint • Is a synovial condylar joint formed superiorly by the radius and the articular disk and inferiorly by the proximal row of carpal bones (scaphoid, lunate, and rarely triquetrum), exclusive of the pisiform. • Has a capsule that is strengthened by radial and ulnar collateral ligaments and dorsal and palmar radiocarpal ligaments. • Allows flexion and extension, abduction and adduction, and circumduction.

24. Midcarpal joint • Forms a synovial plane joint between the proximal and distal rows of carpal bones and allows gliding and sliding movements. • Is a compound articulation: laterally the scaphoid articulates with the trapezium and trapezoid, forming a plane joint; and medially the scaphoid, lunate, and triquetrum articulate with the capitate and hamate, forming a condylar (ellipsoidal type) joint. Carpometacarpal joints • Form synovial saddle ( sellar ) joints between the carpal bone (trapezium) and the first metacarpal bone, allowing flexion and extension, abduction and adduction, and circumduction. • Also form plane joints between the carpal bones and the medial four metacarpal bones, allowing a simple gliding movement. Metacarpophalangeal joints • Are condyloid joints, supported by a palmar ligament and two collateral ligaments, and allow flexion and extension and abduction and adduction. Interphalangeal joints • Are hinge joints, supported by a palmar ligament and two collateral ligaments, and allow flexion and extension.