Joints are classified by degree of movement: Synarthrosis (Immovable joints) = Skull sutures - bones held tightly together by fibrous connective tissue, NO movement possible. Amphiarthrosis (Slightly movable joints) = Pubic symphysis, intervertebral discs - slight movement allowed. Diarthrosis (Freely movable/Synovial joints) = Knee, hip, shoulder, elbow - maximum movement. Skull sutures (Coronal, Sagittal, Lambdoid, Squamous) are the most important examples of completely immovable joints.

The Femur is the anatomical term for the thigh bone - the single bone of the upper leg, between the hip and knee. Key features: Head of femur (fits into acetabulum - hip joint, ball and socket), Neck of femur (common site of fracture in elderly - hip fracture), Greater and lesser trochanters (major muscle attachment points), Lateral and medial condyles (articulate with tibia - knee joint), and Intercondylar notch (where cruciate ligaments attach). The femur is the longest, largest, and strongest bone in the body.

The Pubic Symphysis is a secondary cartilaginous joint (symphysis) located at the anterior midline of the pelvis, joining the two pubic bones. It consists of a fibrocartilaginous disc with hyaline cartilage on each side. Normally a slightly movable joint (amphiarthrosis). During pregnancy, the hormone Relaxin causes the pubic symphysis to soften and widen, allowing the pelvis to expand during childbirth. Diastasis symphysis pubis = excessive separation during or after pregnancy.

Craniosynostosis is a condition where one or more of the fibrous joints between skull bones (sutures) fuse prematurely before the brain has fully developed. This restricts brain growth and causes an abnormal skull shape. Types include: Scaphocephaly (premature fusion of sagittal suture - elongated skull) and Trigonocephaly (premature fusion of metopic suture - triangular forehead). Treatment: surgery (cranial vault remodelling) to allow brain to grow properly.

Short bones are roughly cube-shaped with approximately equal length, width, and height. They provide limited movement and stability. Examples: Carpals (wrist bones) = Scaphoid, Lunate, Triquetrum, Pisiform, Trapezium, Trapezoid, Capitate, Hamate. Tarsals (ankle bones) = Talus, Calcaneus, Navicular, Cuboid, three Cuneiforms. Short bones consist mainly of spongy bone covered by a thin layer of compact bone. They are found where strength and some movement are needed (wrist, ankle).

Phalanges are the bones of the fingers and toes: Each finger has 3 phalanges (Proximal, Middle, Distal) and each thumb/big toe has 2 phalanges (Proximal, Distal). One hand = 4 fingers x 3 + 1 thumb x 2 = 14 phalanges. Two hands = 14 x 2 = 28 phalanges. One foot = same = 14 phalanges. Two feet = 14 x 2 = 28 phalanges. Total = 28 (hands) + 28 (feet) = 56 phalanges in the entire body.

Fontanelles (soft spots) are membrane-covered spaces between the incompletely ossified skull bones of infants, allowing the skull to flex during birth and the brain to grow rapidly after birth. Main fontanelles: Anterior (frontal) fontanelle = diamond-shaped, at junction of frontal and parietal bones, closes at 18-24 months. Posterior (occipital) fontanelle = triangular, closes at 2-3 months. A bulging fontanelle may indicate increased intracranial pressure; a sunken fontanelle may indicate dehydration.

Periosteum = covers the outer surface of bones (except at articular surfaces). Endosteum = thin connective tissue membrane lining the inner medullary cavity (marrow cavity) of bone and the surfaces of trabeculae in spongy bone. Synovium (Synovial membrane) = lines the inside of synovial joint capsules and produces synovial fluid. Perichondrium = dense connective tissue covering cartilage. Both periosteum and endosteum contain osteoblasts and osteoclasts important for bone remodelling and repair.

The joint at the base of the thumb (between the trapezium carpal bone and the first metacarpal) is a Saddle joint (Sellar joint). It is called a saddle joint because each articular surface is shaped like a saddle (concave in one direction and convex in the other). It allows movement in two planes (biaxial): Flexion/Extension and Abduction/Adduction, and also allows opposition (touching thumb to other fingers). The thumb's saddle joint gives humans the ability to perform precision grip - a uniquely human feature essential for tool use.

With advancing age, the skeletal system undergoes several changes: Bone density decreases (osteoclast activity exceeds osteoblast activity), Bone mass peaks at around 30 years and then gradually declines, Collagen content decreases (bones become more brittle and less flexible), Cartilage degenerates (Osteoarthritis becomes common), and Osteoporosis is the most serious age-related bone condition (especially in post-menopausal women). Fracture risk increases dramatically - hip, vertebral, and wrist fractures are most common. Prevention: exercise, calcium, and Vitamin D supplementation.