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

Freely moveable joints
Synarthroses
Diarthroses
Amphiarthroses
Syndesmoses
Anatomical characteristics shared by all synovial joints include:
Articular cartilage
A joint cavity
An articular capsule
Presence of fibrocartilage

Review Questions

Ankylosis means:
- Immobility of a joint due to fusion of its articular surface
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.