AN2.1-6 | General features of bones & Joints — Summary & Reflection

REFLECT

Before reading the summary, take two minutes to answer these questions in your notebook:

1. A 10-year-old falls while playing cricket. The X-ray shows a fracture through the growth plate of the distal radius (Salter-Harris type II). Using what you know about epiphyseal plates, what is the risk of NOT treating this correctly?

1. Your Biochemistry professor mentions that collagen requires vitamin C for its synthesis. How does this connect to what you have learned about bone structure? What would happen to bone in a patient with severe vitamin C deficiency (scurvy)?

1. An elderly patient presents with knee pain after a fall. As her doctor at a PHC, what is one anatomical reason you should also examine and X-ray the hip joint?

These questions do not have single right answers — discuss them with your batch during the tutorial.

KEY TAKEAWAYS

In this module, you have covered the general features of bones and joints — the structural and movement framework of the human body:

Bone Structure (AN2.1)
• Bone has four layers: periosteum (densely innervated outer covering), compact bone (hard shell), spongy bone (honeycomb trabeculae + marrow), and endosteum (inner lining).
• Blood supply: nutrient artery + metaphyseal + epiphyseal + periosteal vessels. Before epiphyseal fusion, epiphyseal vessels are end-arteries → risk of avascular necrosis.

Bone Types Including Sesamoids (AN2.3)
• Six types: long, short, flat, irregular, pneumatic, sesamoid.
• Sesamoid bones develop within tendons (patella, pisiform, hallucal sesamoids) — increase mechanical advantage and protect tendons.

Ossification & Epiphyseal Plates (AN2.2)
• Intramembranous → flat skull bones directly from mesenchyme.
• Endochondral → long bones via cartilage model.
• Primary centre (diaphysis, fetal life) → secondary centres (epiphyses, postnatal) → growth plates close with sex hormones at puberty.
• Medial clavicle is last to fuse (~25 years) — forensic landmark.

Cartilage (AN2.4)
• Avascular, aneural — heals poorly. Nutrients by diffusion.
• Hyaline (glassy, articular/costal/respiratory), Fibrocartilage (strongest, IVDs/symphyses/menisci), Elastic (ear, epiglottis).

Joints (AN2.5)
• Structural: Fibrous (sutures, syndesmosis, gomphosis) → Cartilaginous (primary/synchondrosis, secondary/symphysis) → Synovial (joint cavity, freely mobile).
• Six synovial types: plane, hinge, pivot, condyloid, saddle, ball-and-socket.
• Examine: Look → Feel → Move (active, passive, special tests).

Hilton's Law (AN2.6)
• A nerve supplies a joint, the muscles moving it, and the skin over their insertions.
• Predicts referred pain: hip pathology → knee pain (obturator nerve).
• Clinical rule: X-ray the joint above AND below the pain.