BS2014: Bones, Joints & Movement

How many bones in the adult (human) skeleton

206

How many axial bones in the human skeleton

80

How many appendicular bones in the human skeleton

126

Role of axial skeleton

protection of internal organs

Role of appendicular skeleton

movement

appendicular skeleton

• bones of upper and lower limbs

• girdles that attach limbs to axial skeleton

What are the different types of bones found in the human skeleton

• flat bones

• irregular bones

• sesamoid bones

• short bones

• long bones

Flat bones

parallel layers of compact bone and spongy centre (e.g. skull, sternum)

Irregular bones

thin layers of compact bone surrounding a spongy centre (e.g. vertebrae, pelvis)

Sesamoid bones

bones embedded in tendon or muscle (e.g. patella)

Short bones

cube-shaped bones, with a spongy centre surrounded by a thin outer layer of compact bone (e.g. wrist, ankle)

Long bones

long shaft, two articular surfaces, mostly compact bone (e.g. femur, tibia, fibula, humerus)

Proximal epiphysis

end of the long bone closer to the centre of the body

Distal epiphysis

end of the long bone further away from the centre of the body

Epiphysis

end of the bone

Metaphysis

connects the diaphysis to the epiphysis of the bone

• contains the growth plate in children

Diaphysis

the shaft of the long bone

Epiphysial line

the remnant of the epiphyseal growth plate that appears in long bone after growth has ceased

Endosteum

thin vascular membrane of connective tissue that lines the inner surface of bones, containing osteoprogenitor cells, osteoblasts, and osteoclasts

Periosteum

dense fibrous vascular membrane of connective tissue that lines the outer surface of bones, that supplies blood, nerves and stem cells for bone growth, healing and fracture repair

Medullary cavity

central hollow space in the diaphysis that stores yellow bone marrow

Osteogenic cell

bone cells in the inner periosteum, endosteum and bone canals which undergo cell division to differentiate into osteoblasts for bone growth, repair, and remodelling

Osteoblasts

cells responsible for synthesizing new bone to create, reshape and repair bones

Osteoblasts trapped in ECM

differentiate into osteocytes

Osteocytes

mature bone cells which make up 90-95% of bone cells in the adult skeleton and maintain metabolism by exchanging nutrients and waste with blood

Osteoclasts

specialised multinucleated cells which are responsible for resorption of bone tissue to facilitate bone remodelling, repair and calcium regulation

Osteoclast functions

dissolve and break down old bone to make space for osteoblasts to create new bone tissue for growth and repair

RANK ligand in regulation of osteoclast activity

• interacts with RANK (receptor) triggering the differentiation, activation and survival of osteoclasts

• trigger the fusion of precursor cells to form mature multi-nucleated osteoclasts

• in osteocytes, RANK ligand interaction with its receptor can trigger osteocyte activity increasing resorption of bone

What works to balance the effect of RANK, and how

osteoprotegerin (OPG), acts as a decoy in binding to RANK ligand preventing RANK ligand from interacting and activating its receptors on the surface of osteoclasts

Parathyroid modulation of RANK and OPG balance

stimulates the production of RANK ligand while simultaneously repressing OPG expression to increase osteoclast activity

Oestrogen modulation of RANK and OPG

increases OPG expression and inhibits RANK ligand signalling to reduce osteoclast activity

bone marrow

spongy tissue which produces blood cells and stores fats

red bone marrow

site of production of red blood cells, white blood cells, and platelets

yellow bone marrow

stores fat and acts as an energy reserve, replaces red bone marrow with age

haematopoiesis

the continuous highly regulated process of producing new blood cells from haematopoietic stem cells within the red bone marrow

Bone marrow over the human lifespan

• when born, bone marrow is essentially red

• rapid conversion of red bone marrow to yellow bone marrow FROM new-born stage to adult stage

• at 25 years old, 50-70% of bone marrow is yellow/BMAT

Patten for BMAT development

in a centripetal pattern: from extremities to axial skeleton

Movement relies on…

joints

Fibrous joints

fibrous connective tissue rich in collagen fibres which joins bones

Cartilaginous joints

articulations where bones are connected by cartilage (no synovial cavity)

Synovial joints

type of joint in the human body, characterized by a fluid-filled cavity, articular cartilage, and a fibrous capsule between articulating bones

Composition & function of synovial joints

• articular cartilage — spongy tissue that covers the ends of bones, reducing friction and absorbing shock

• joint cavity — contains synovial fluid

• fibrous capsule — encloses the joint space and connects bones

• synovial fluid — lubricant produced by synovial membrane to reduce friction

• ligaments — fibrous tissue that connects bone to bone to provide stability

• tendons — fibrous tissue that connects bone to muscle

Which joints are associated with little or no movement

fibrous and cartilaginous

Which joints allow movement

synovial joints

Cartilage composition

collagen & elastin fibres, proteoglycan (heavily glycosylated proteins) & water

Chondroblasts

cells that differentiate into chondrocytes to drive cartilage formation (chondrogenesis)

3 main types of cartilage

• elastic cartilage — not associated with bone

• fibrocartilage — strongest

• hyaline cartilage — most abundant

Examples of elastic cartilage

• eustachian tube (connect middle ear to throat)

• external ear (auricle)

• epiglottis

Examples of fibrocartilage

• intervertebral discs

• menisci of knee joint

• pubic symphysis

• tendon/cartilage interface

Examples of hyaline cartilage

• bronchi

• larynx

• noise

• tranchea

• embryonic skeleton

• articular cartilage in synovial joints

The cartilage at articulating surfaces is?

hyaline cartilage

Chondrocyte orientation in different levels of the articular cartilage

• superficial zone — well organised small flat chondrocytes parallel to the surface of the bone

• middle zone — chondrocytes change shape to become more round and active, fibres in the ECM become bigger in diameter and more disorganised

• deep zone — chondrocytes form fibres which are perpendicular to the surface

Tidemark in the articular cartilage

the boundary between non-calcified articular cartilage and calcified articular cartilage

Bones found in the knee

• tibia

• femur

• patella

Tendons

fibrous connective tissue joining muscle to bone

Ligaments

fibrous connective tissue joining bone to bone

Organisational & functional differences between tendons and ligaments

• tendons

  • parallel rows of fibroblasts (dense)

  • well-organised collagen (stiffer)

  • properties: non-elastic, tough

  • connection: muscle to bone

  • function: facilitates movement

• ligaments

  • dispersed rows of fibroblasts (less dense)

  • less well-organised (more flexible)

  • properties: elastic, strong

  • connection: bone to bone

  • function: stabilizes joints

Types of tendon failure

• microscopic failure — single or several fibres

• macroscopic failure — whole tendon

Types of microscopic tendon failure

• tendinitis

• tendinosis

• carpal tunnel syndrome (CTS)

Tendinitis

inflamed/irritated tendon due to microtears

Tendinosis

chronic tendon degeneration (breaking down of collagen fibres)

Carpal tunnel syndrome (CTS)

tendons in the carpal tunnel become inflamed, compressing the median nerve and reducing control/sensation in some fingers

Macroscopic tendon failure example

tendon tear/snap — rupture from the bone or within the tendon

Examples of non-surgical tendon failure repair (RICE)

• Rest

• Ice (avoid swelling)

• Compression (immobilisation in special boot causing plantar flexion)

• Elevation (avoid swelling)

What is required regardless of whether non-surgical or surgical tendon repair is administered

• physiotherapy

• pain relief medication

Cons of non-surgical tendon failure repair

• takes time

• possible re-rupture

Surgical tendon failure repair

stitching the ends together or with graft

Risks of surgical tendon failure repair

• infection

• nerve damage

ACL (anterior cruciate ligament)

dense connective tissue connecting the femur to the tibia which stabilises the knee avoiding lateral movement

Surgical repair of torn ACL

• autograft or allograft (often patellar or hamstring tendon) sometimes synthetic e.g. carbon fibre

• screwed or stapled into place

How long does torn ACL recovery last

5-6 months

Effect of exercise on tendons

• mechanical adaptation → remodelling in response to strength and endurance training

• increased turnover of collagen → anabolism predominates, increased crosslinks between collagen fibres

• tendon fibroblasts → respond to stretch, alter expression of extracellular matric (ECM)

Effect of exercise on ligaments

increased strength and flexibility

Effect of exercise on cartilage

increased thickness (hyaline cartilage) → protection (reduced risk of injury and osteoarthritis)

Effect of exercise on synovial fluid

increased production → greater lubrication/cushioning/shock absorption

Classification of synovial joints

• ball-and-socket

• pivot

• hinge

• planar

• condyloid

• saddle

Ball-and-socket joint

allows multidirectional movements

Ball-and-socket joint locations

• shoulder (between humerus & scapula)

• hip (between pelvis & femur)

Pivot joint

bone rotating around another bone

Pivot joint location

elbow (between ulna/radius) — ulna rotates around radius

Hinge joint

limited to unidirectional movement

Hinge joint examples

• knee articulation (femur & fibula/tibia)

• elbow articulation (ulna/radius & humerus)

Planar joint

when 2 flat bones meet and slide over each other allowing multi-directional movement in one plane

Planar joint examples

• carpal planar joint

• sliding vertebrae joint

Condyloid joint

allows movement in two planes but prevents rotation

Condyloid joint example

• radiocarpal joint of the wrist (between radius and carpals)

• metacarpophalangeal joint (between metacarpal and phalanx)

Saddle joints

both articular surfaces are concave in the direction of 1 axis and convex in the direction of the perpendicular axis

Saddle joint example

between trapezium (carpal from wrist) and metacarpal from the thumb

Types of movements at synovial joints

• Gliding

• Rotational

• Angular

• Special

Anatomical positions

• medial/lateral — towards/away from the midline

• proximal/distal — close to/farther from from the trunk

Anatomical planes

• sagittal plane — divides the body into right and left portions

• coronal (frontal) plane — divides the body into anterior (front) and posterior (back) portions

• transverse plane — divides the body horizontally into superior (top) and inferior (bottom) planes

Gliding movements

relatively flat bone surfaces slide past one another, offering limited motion

Rotational movements

a bone revolves around its own longitudinal axis

Types of angular movements

• flexion

• extension

• hyperextension

• abduction

• adduction

• circumduction

Flexion

decrease in angle between articulating bones

Extension

increase in angle between articulating bones (often to restore anatomical position)

Hyperextension

increase in angle between articulating bones beyond the anatomical position

Abduction

bone moves away from the midline of the body

Adduction

bone moves toward the midline of the body

Circumduction

circular movement that combines flexion, extension, abduction, and adduction (distal part of bone moves in a circle)