Bone Anatomy Notes

Bone Anatomy

Learning Objectives

• Discuss bones of the appendicular and axial skeletons.
• Discuss curvatures of the spinal column.
• Discuss major categories of joints.
• Discuss the movements of the skeleton (joints).
• Discuss age-related changes in the skeleton.

Pre-Lecture Questions

• Name and identify the skull bones.
• Define the bony boundaries of the paranasal sinuses and its function.
• Compare the 3 abnormal curvatures of the spine and treatment.

Divisions of the Skeleton

Axial Skeleton

• Skull
• Spine or vertebral column
• Thorax
• Middle ear bones

Appendicular Skeleton

• Upper extremity bones (including shoulder girdle)
• Lower extremity bones (including hip girdle)

Axial Skeleton: The Skull

• The skull is made up of 28 bones in two major divisions: The cranial bones and the facial bones
  • 8 bones – cranium
  • 14 bones – face
  • 6 bones – middle ear
• Held together by sutures
• The mandible is the only freely moveable joint in the skull

Axial Skeleton: The Skull (Cranial Bones)

• Frontal bone
• Occipital bone
• Sphenoid bone
• Ethmoid bone
• Parietal bones (2)
• Temporal bones (2)

Axial Skeleton: The Skull (Facial Bones)

• Nasal (2)
• Maxilla (2)
• Zygomatic (2)
• Lacrimal (2)
• Palatine (2)
• Inferior concha (2)
• Mandible (1)
• Vomer (1)

Axial Skeleton: Paranasal Sinuses

• Sinuses are hollow portions of bones surrounding the nasal cavity.
• Functions of the paranasal sinuses are to lighten the skull and to amplify the sounds we make when we speak.

Axial Skeleton: The Fetal Skull

• Characterized by unique anatomic features not seen in the adult skull.
• Fontanels, or “soft spots,” allow the skull to “mold” during birth and also allow rapid growth of the brain.
• Permits differential growth or appearance of skull components over time.
  • Face forms a relatively smaller proportion of the cranium at birth than in the adult.
  • Head at birth is ¼ the total body height; at maturity, it is about ⅛ total body height.
  • Paranasal sinuses change in size and placement with skeletal maturity.

Axial Skeleton: The Hyoid Bone

• The hyoid bone is a U-shaped bone located just above the larynx (voice box) and below the mandible.
• Anchored by the narrow stylohyoid ligaments to the styloid process of the temporal bone.
• Only bone in the body that articulates with no other bones.
• Acts as a movable base for the tongue and is a point of attachment for the neck muscles and lower larynx during swallowing and speech.

Axial Skeleton: Vertebral Column

• Forms the flexible longitudinal axis of the skeleton.
• Characteristics of the vertebrae:
  • All but the sacrum and coccyx have a vertebral foramen.
  • Second cervical vertebra has an upward projection, the dens, to allow rotation of the head.
  • Seventh cervical vertebra has a long, blunt, spinous process.
• Divisions:
  • Cervical (7 bones)
  • Thoracic (12 bones)
  • Lumbar (5 bones)
  • Sacrum (1 bone)
  • Coccyx (1 bone)

Vertebral Column: Natural Curvatures

• Curvatures increase the resilience and flexibility of the spine, allowing it to function like a spring.
• 4 curvatures of the spine:
  • Primary curvatures
    • Thoracic
    • Sacral
  • Secondary curvatures
    • Lumbar
    • Cervical

Vertebral Column: Abnormal Vertebral Curvatures

• Lordosis - swayback (due to poor posture or disease).
• Kyphosis - hunchback.
• Scoliosis - side to side curvature. Relatively common condition that appears before adolescence.
• Treatments include braces, muscle stimulation, surgery.

Axial Skeleton: Thorax

• Composed of:
  • 12 pairs of ribs
  • Sternum or breastbone
  • Thoracic vertebrae

Thorax: Ribs and Sternum

Ribs:

• True ribs - rib pairs 1 through 7.
• False ribs - rib pairs 8 through 10.
• Floating ribs - rib pairs 11 and 12.

Sternum:

• Dagger-shaped bone in the middle of the anterior chest wall made up of three parts:
  • Manubrium
  • Body
  • Xiphoid process

Appendicular Skeleton: Upper Extremity

• Shoulder or pectoral girdle formed by two bones:
  • Scapula or shoulder blade
  • Clavicle or collarbone
    • Clavicle forms the only bony joint with the trunk, the sternoclavicular joint.
    • At its distal end, the clavicle articulates with the acromion process of the scapula.

Appendicular Skeleton: Upper Extremity

• Thirty separate bones form the bony framework of each upper limb:
  • Arm - humerus
  • Forearm - radius and ulna
  • Wrist - 8 carpal bones
  • Hand - 5 metacarpal bones
  • Fingers - 14 phalanges or finger bones

Appendicular Skeleton: Pelvic Girdle

• Hip or pelvic girdle formed by the two coxal or pelvic bones (one on each side) with sacrum and coccyx behind.
• Acetabulum is cup-shaped socket - articulates with head of femur.
• Each coxal bone is made up of three bones that fuse together
  • Ilium – flaring part at sides
  • Ischium – “sit bone” lower part
  • Pubis - front

Appendicular Skeleton: Lower Extremity

• Femur – Longest and heaviest bone in the body.
• Patella – Largest sesamoid bone in the body. Located in the tendon of the quadriceps femoris muscle as a projection to the underlying knee joint.
• Tibia – Is the larger, stronger, and more medially and superficially located of the two leg bones.
  • Articulates proximally with the femur to form the knee joint
  • Articulates distally with the fibula and talus

Appendicular Skeleton: Fibula and Foot

Fibula

• The fibula is smaller and more laterally and deeply placed than the tibia.
• Articulates with the tibia.

Foot

• Structure is similar to that of the hand, with adaptations for supporting weight.
• Foot bones are held together to form spring arches.
• The medial longitudinal arch is made up of the calcaneus, talus, navicular, cuneiforms, and medial three metatarsal bones.
• The lateral longitudinal arch is made up of the calcaneus, cuboid, and fourth and fifth metatarsal bones.

Skeletal Differences Between Men and Women

• Male pelvis: Deep, funnel-shaped, with a narrow pubic arch.
• Female pelvis: Shallow, broad, and flaring, with a wider pubic arch.

Articulations (Joints)

• Joints have two main functions: providing skeletal mobility and stability.
• Weakest part of the skeleton.

Joint Classifications:

Structural classification

• Fibrous or cartilaginous joints
• Synovial joints

Functional classification

• Synarthroses
• Amphiarthroses
• Diarthroses

Fibrous Joints (Synarthroses)

• Joined by collagen fibers of connective tissues, no joint cavity present and allow little or no movement.

Three types:

• Syndesmoses: Joints in which ligaments connect two bones.
• Sutures: Found only in the skull; teeth like projections from adjacent bones interlock with each other.
• Gomphoses: Between the root of a tooth and the alveolar process of the mandible or maxilla.

Cartilaginous Joints (Amphiarthroses)

• The articulating bones are joined together by cartilage, lacks joint cavity and not highly moveable.

Two types:

• Synchondroses: Hyaline cartilage present between articulating bones.
• Symphyses: Joints in which a pad or disk of fibrocartilage connects two bones.

Synovial Joints (Diarthroses)

• Articulating bones are separated by fluid-containing joint cavity and are freely movable joints.

Seven types:

• The joint capsule
• The synovial membrane
• Articular cartilage
• The joint cavity
• Menisci (Articular Disk)
• Ligaments
• Bursae

Types of Synovial Joints

Uniaxial joints

• Hinge joints
• Pivot joints

Biaxial joints

• Saddle joints
• Condyloid (ellipsoidal) joints

Multiaxial joints

• Ball-and-socket (spheroid) joints
• Gliding joints

Synovial Joints: Humeroscapular

• The shoulder (Glenohumeral) joint
• The humeroscapular joint is the joint between the head of the humerus and the glenoid cavity of the scapula; it is usually referred to as the shoulder joint.
• The glenoid labrum is a narrow rim of fibrocartilage around the glenoid cavity.
• This is the most mobile joint because of the shallowness of the glenoid cavity.
• Structures that strengthen the shoulder joint are ligaments, muscles, tendons, and bursae.

Synovial Joints: Elbow

• Humeroradial joint and Humeroulnar joint
• Classic hinge joint
• The humeroradial joint is a lateral articulation of the capitulum of the humerus with the head of the radius.
• The humeroulnar joint is the medial articulation of the trochlea of the humerus with the trochlear notch of the ulna.
• The proximal radioulnar joint is the articulation between the proximal ends of the radius and ulna just below the joint capsule.

Synovial joints: Proximal and Distal Radioulnar

• The proximal radioulnar joint is located between the head of the radius and the medial notch of the ulna.
• The distal radioulnar joint is the point of articulation between the ulnar notch of the radius and the head of the ulna.
• The two joints permit rotation of the forearm.
• Dislocation of the radial head is called a “pulled elbow”.
• Distal radioulnar joint
  • Acts with the proximal radioulnar joint
  • Permits pronation and supination of the forearm

Synovial Joints: Radiocarpal

• The point of articulation between the head of the radius and the scaphoid and lunate carpal bones forms a typical synovial joint, which is the radiocarpal joint.
• Loss of blood supply to a fractured scaphoid may result in necrosis of the broken fragment, which requires surgical removal or other specialized treatment.
• Only the radius articulates directly with the carpal bones distally (scaphoid and lunate).
• Joints are synovial.

Synovial Joints: Carpometacarpal

• There are three total carpometacarpal joints—one for the thumb and two for the fingers.
• The joint for the thumb provides a wide range of movements.
• The two joints for the fingers provide mainly gliding movements.
• The movements available with the thumb joint include flexion, extension, adduction, abduction, circumduction, and opposition.
• Thumb carpometacarpal joint is unique and important functionally.
• Loose-fitting joint capsule
• Saddle-shaped articular surface
• Opposition: Movement of great functional significance

Metacarpophalangeal and Interphalangeal Joints

Metacarpophalangeal joints:

• Rounded heads of metacarpal bones articulate with concave bases of the proximal phalanges.
• Capsule surrounding joints is strengthened by collateral ligaments.
• Primary movements are flexion and extension.

Interphalangeal joints:

• Exist between heads of phalanges and bases of more distal phalanges.
• Typical diarthrotic, hinge-type synovial joints.
• Two categories:
  • Proximal interphalangeal (PIP) joints: are located between the proximal and middle phalanges.
  • Distal interphalangeal (DIP) joints: are located between the middle and distal phalanges.

Hip Joint

• A joint capsule and ligaments contribute to the joint’s stability.
• The stability of the hip joint derives largely from the shapes of the head of the femur and the acetabulum.

The Knee Joint

• Largest and one of the most complex and most frequently injured joints.
• Tibiofemoral joint is supported by a joint capsule, cartilage, and numerous ligaments and muscle tendons.
• The knee joint is also known as the tibiofemoral joint.
• The knee joint permits flexion and extension; with the knee flexed, it also allows some internal and external rotation.

Ankle Joint

• Synovial-type hinge joint
• Articulation between the lower ends of the tibia and fibula and the upper part of the talus
• Internal rotation injury results in the common “sprained ankle”: A sprained ankle is an injury to the anterior talofibular ligament.
  • Other ankle ligaments, such as the deltoid ligament, also may be involved in sprain injuries.
• The bony structure of the ankle and foot, as well as the joints that exist between them, enhances stability and weight bearing rather than flexibility and a wide range of movements.
• The lateral malleolus is lower than the medial malleolus.

Vertebral Joints

• Vertebrae are connected to one another by several joints, forming a strong, flexible column.
• Bodies of adjacent vertebrae are connected by intervertebral disks and ligaments.
• Intervertebral disks are made up of two parts
  • Annulus fibrosus: is the intervertebral disk’s outer rim; it is made up of fibrous tissue and fibrocartilage.
  • Nucleus pulposus: is the disk’s central core; it is composed of a pulpy, elastic substance.

Measuring Range of Motion (ROM) of Synovial Joints

• An ROM assessment is used to determine the extent of a joint injury.
• ROM can be measured actively or passively; the two methods are generally about equal
  • Active ROM – the individual moves the joint or body part through its range of motion
  • Passive ROM – the health care provider moves the part with the patients muscles in a relaxed state
• ROM is measured with an instrument called a goniometer
  • A goniometer consists of two rigid shafts that intersect at a hinge joint

Angular Movements of Synovial Joints

• Flexion
• Extension and hyperextension
• Plantar flexion and dorsiflexion
• Abduction and adduction

Circular and Gliding Movements of Synovial Joints

Circular movements

• Rotation and circumduction
• Supination and pronation

Gliding movements:

• Articular surface of one bone moves over the articular surface of another without any angular or circular movement

Special movements

• Inversion and eversion
• Protraction and retraction
• Elevation and depression

ROM of the Neck

• Flexion: $45°$
• Extension / Hyperextension: $55°$
• Right / Left lateral flexion: $40°$
• Right / Left rotation: $70°$

ROM of the Jaw

• Protraction
• Retraction
• Elevation
• Depression

ROM of the Thoracic and Lumbar Spine

• Flexion: $70°$
• Hyperextension: $30-35°$
• Right / Left lateral flexion: $35°$
• Right rotation

ROM of the Shoulder

• Forward flexion: $180°$
• Hyperextension: $50°$
• Abduction: $180°$
• Adduction: $50°$

ROM of the Elbow

• Flexion: $150°$
• Extension: $0°$
• Supination: $90°$
• Pronation: $90°$

ROM of the Hand and Wrist

• Flexion: $90°$
• Extension: $90°$
• Hyperextension: $30°$
• Radial flexion: $20°$
• Ulnar flexion: $55°$
• Abduction
• Adduction
• Hyperextension: $10°$

ROM of the Fingers and Thumb

• Flexion
• Extension
• Abduction
• Adduction
• Opposition

ROM of the Hip

• Hip flexion (knee extended): $90°$
• Hip flexion (knee flexed): $120°$
• Hip extension: $45°$
• External rotation: $45°$
• Internal rotation: $40°$
• Abduction: $45°$
• Adduction: $30°$

ROM of the Knee

• Extension: $0-15°$
• Flexion: $130°$

ROM of the Ankle and Foot

• Dorsiflexion: $20°$
• Plantar flexion: $45°$
• Inversion: $30°$
• Eversion: $20°$
• Abduction
• Adduction

Cycle of Life: Articulations

• Bone development and the sequence of ossification between birth and skeletal maturity affect joints.
• Older adults
  • ROM decreases
  • Changes in gait
• Skeletal diseases manifest as joint problems
  • Abnormal bone growth (“lipping”)
  • Disease conditions can be associated with a specific developmental period

Cycle of Life: Age Related Changes in the Skeleton

• Changes in the skeleton begin at fertilization and continue over a lifetime.
• Dense bone structure of young and middle-aged adults permits these individuals to bear heavy loads.
• In later adulthood, reduced bone density makes fractures more likely and causes changes in posture and overall height.

Skeletal System: The Big Picture

• The skeletal system is a good example of increasing structural hierarchy in the body.
  • Skeletal tissues are grouped into discrete organs—that is, bones.
  • Skeletal system is more than a collection of individual bones.
  • Integration of the skeletal system with other body organ systems permits homeostasis.
  • The skeletal system consists of bones, blood vessels, nerves, and other tissues grouped to form a complex operational unit.
  • The skeletal system is a complex, interdependent functional unit of the body.

Review Questions

1. Freely moveable joints
2. Synarthroses
3. Diarthroses
4. Amphiarthroses
5. Syndesmoses
6. Anatomical characteristics shared by all synovial joints include:
7. Articular cartilage
8. A joint cavity
9. An articular capsule
10. Presence of fibrocartilage

Review Questions

1. Ankylosis means:
   • Immobility of a joint due to fusion of its articular surface
2. Factors that influence the stability of the synovial joint include:
   • All of these. (Shape of the articular surface, Presence of strong reinforcing ligaments, Tone surrounding muscles)

References:

• Marieb, E.N., & Hoehn, K. (2016). Human anatomy & physiology (10th ed). San Francisco, CA: Pearson Education Inc.
• Patton, K. T. (2019). Anatomy and physiology (10th ed.). St. Louis, MO: Elsevier Mosby.
• Patton, K. T., & Thibodeau, G. A.(2018). The human body in health and disease (6th ed.). Maryland Heights, MO: Elsevier Mosby.