Bones and Bony Landmarks

Introduction

The human skeletal system is composed of bones connected by various types of joints, which allow for movement and provide structural support. Bony landmarks are specific features on bones that serve as points of attachment for muscles, ligaments, and tendons.

Types of Joints

Fibrous Joints

Fibrous joints are immovable or only slightly movable joints where bones are joined by dense connective tissue. They provide stability and are found mainly in the skull and between certain long bones.

• Sutures: Immovable joints found between the bones of the skull. Examples include:

  • Coronal suture

  • Lambdoid suture

  • Sagittal suture

  • Squamous suture

• Interosseous Membrane: A sheet of connective tissue found between long bones such as the fibula and tibia, and the radius and ulna. It provides additional stability and surface area for muscle attachment.

Cartilaginous Joints

Cartilaginous joints are slightly movable joints where bones are connected by cartilage. They allow for limited movement and absorb shock.

• Intervertebral Joint: Found between the vertebrae of the spine, providing flexibility and cushioning.

• Pubic Symphysis: The joint between the two pubic bones in the pelvis, allowing for slight movement during childbirth.

Synovial Joints

Synovial joints are freely movable joints characterized by the presence of a synovial cavity filled with synovial fluid, which lubricates the joint and reduces friction.

• Key Features: Synovial fluid, articular cartilage, joint capsule, and ligaments.

• Examples of Synovial Joints:

  • Atlantoaxial joint

  • Carpometacarpal joint

  • Elbow

  • Hip

  • Intercarpal joint

  • Interphalangeal joint

  • Intertarsal joint

  • Knee

  • Metacarpophalangeal joint

  • Metatarsophalangeal joint

  • Proximal radioulnar joint

  • Shoulder

Types of Synovial Joints

Synovial joints are classified based on the shapes of their articulating surfaces and the types of movement they allow.

Movement Terms

Introduction

Movements at synovial joints are described using specific anatomical terms. These terms help in accurately describing the direction and type of movement occurring at a joint.

Abduction / Adduction

• Abduction: Movement away from the midline of the body. (e.g., raising the arm sideways)

• Adduction: Movement towards the midline of the body. (e.g., lowering the arm to the side)

• Common in ball-and-socket and saddle joints.

Flexion / Extension

• Flexion: Decreasing the angle between two bones (e.g., bending the elbow).

• Extension: Increasing the angle between two bones (e.g., straightening the knee).

• Occurs in hinge, ball-and-socket, and saddle joints.

Internal Rotation / External Rotation

• Internal (Medial) Rotation: Rotating a limb towards the midline.

• External (Lateral) Rotation: Rotating a limb away from the midline.

• Occurs in ball-and-socket joints (e.g., shoulder, hip).

• Movement involves pivoting around an axis.

Dorsiflexion / Plantarflexion

• Dorsiflexion: Movement at the ankle where the toes point upwards towards the sky.

• Plantarflexion: Movement at the ankle where the toes point downwards towards the floor.

Pronation / Supination

• Pronation: Rotating the forearm so the palm faces downwards or posteriorly.

• Supination: Rotating the forearm so the palm faces upwards or anteriorly.

• Occurs at the proximal radioulnar joint and involves a pivot joint.

• Example: Turning the palm face up is supination; turning it face down is pronation.

Opposition / Reposition

• Opposition: Movement of the thumb across the palm to touch the tips of the other fingers (thumb to pinky).

• Reposition: Returning the thumb to its anatomical position (thumb at rest).

Depression / Elevation

• Depression: Downward movement of a body part (e.g., lowering the shoulders).

• Elevation: Upward movement of a body part (e.g., shrugging the shoulders).

Inversion / Eversion

• Inversion: Turning the sole of the foot inward, towards the midline.

• Eversion: Turning the sole of the foot outward, away from the midline.

Additional info:

• These movement terms are essential for describing joint actions in clinical and anatomical contexts.

• Understanding joint types and movement terms is fundamental for fields such as physical therapy, sports medicine, and orthopedics.