This document provides information on bones and joints:
- It describes the two types of bone (cortical and cancellous), their structures and properties. Long bones like the tibia have a shaft and ends made of these bones.
- Bone remodeling, growth, blood supply and common musculoskeletal problems are discussed. Peak bone mass is important for bone health.
- Different joint types (fibrous, cartilaginous, synovial) and their structures are outlined. Synovial joints like the knee allow more movement.
- Common bone and joint injuries in children and their causes are summarized. Stress fractures can result from overuse or low bone density.
3. CORTICAL BONE
• Dense, hard bone found in cortex
• Three quarters of skeletal tissue
• High mineral content
Carter & Hayes, 1976
4. • Stiffer than cancellous
• Withstands greater stress, less
strain
• Fractures when strain exceeds
2%
Carter & Hayes, 1976
Cortical Bone
5. • Low surface area
• Porosity 5-30%
• Slow metabolic rate
• Develops in line of stress
Einhorn,1996
Cortical Bone
6. TIBIA
• The shaft of the tibia is mainly compact
bone
• A central medullary cavity containing
mainly fat
• The ends are compact bone
• With an inner core of cancellous bone
• The periosteum is the vascular fibrous
connective tissue investing bone
7. TRABECULAR OR CANCELLOUS BONE
• Found inside cortical shell e.g.
Vertebrae
• Consists of horizontal and vertical
plates
• Spaces are filled with bone marrow
• Large surface area
• Porosity is between 30-90%
8. • Greater capacity to store energy
• In vitro fractures at strains >75%
• Metabolically more active
• More sensitive to changes in endocrine
hormones
Carter & Hayes,1976; Einhorn, 1996
Trabecular or Cancellous Bone
9. • Compressive strength is proportional to
the square of the apparent density
• Small changes in density
• Large change in strength
Dalen et al., 1976
Cancellous Bone
10. • Organic matrix
• Type I collagen forms 90% of skeletal
weight
• Mineral hydroxyapatite ratio
• Calcium 10
• Phosphate 6
• Carbonate 1
Bone
11. BONE REMODELLING
• Bone is a living tissue
• Osteoclastic activity i.e. bone
resorption takes only few days
• Osteoblastic or bone formation takes
several months
14. A HEALTHY SKELETON DEPENDS
ON A BALANCED RANK LIGAND:
OPG RATIO
Prevents
Bone Loss
RANK
Ligand
OPG
Increases
Bone Loss
RANK
Ligand
OPG
RANK
Ligand
OPG
15. A HEALTHY SKELETON REQUIRES A BALANCE
OF BONE RESORPTION AND FORMATION
Resting Reversal
Activation
Adapted from Baron, R. General Principles of Bone Biology. In: Primer on the Metabolic Bone Diseases and Disorders of Mineral
Metabolism. Favus MJ (Ed.) 5th Edition. American Society for Bone and Mineral Research, Washington DC, 2003: 1–8
When bone turnover is
increased, bone loss
dominates
Formation: 3 months
Resorption: 10 days
20. • Changes in bone function lead to
changes in bone
• Bone is laid down where needed
• Bone is resorbed where it is not
needed
Wolff, 1892
Wolff’s Law
21. • Osteogenesis is induced by
dynamic not static strains
• The optimal type of osteogenic
activity should provide relatively
high levels of strain
Rubin & Lanyon, 1984
Mechanical Strain
22. • Tensile forces result in osteoclastic
activity
• On the convex side of an angulated
bone
• Compressive force results in
osteoblastic activity on concave
side
Bone
23. Bones require
• Normal hormones
• Adequate calories
• Particularly protein
• Calcium
• Vitamin D
• Regular weight bearing exercise
Bone
24. Age (years)
Attainment of Peak
Bone Mass
Consolidation Age Related Bone Loss
Men
Women
Menopause
0 10 20 30 40 50 60
Fracture
threshold
1. Compston JE. Clinical Endocrinology 1990;33:653-682
D1202
Age Related Changes in Bone Mass1
25. PEAK BONE MASS
• Genetic
• Environmental factors
• Mechanical strain
• Hormones
26. PEAK BONE MASS
• Weight bearing activity during
adolescence and early adulthood was
a far more important predictor of peak
bone mass than calcium intake
Welten et al., 1994
27. LOW PEAK BONE MASS
• Growing bone has a greater capacity to
add new bone to skeleton than mature
bone
Forwood & Burr, 1993
28. OSTEOGENESIS
• Muscle action is main stimulus for
bone formation
• Mechanical force
• Weight bearing
Birge et al., 1968
31. FLAT BONES AND IRREGULAR BONES
Flat bones
• Usually consist of two layers
of compact bone
• Cancellous bone lies in
between
• Found in the skull and
sternum
Irregular bones
• Occur in the face and
vertebrae
32. SESAMOID BONES
Sesamoid bones
• Develop in tendons where
they cross bone
• Or articular surfaces,
patella
• Sesamoids in relation to
thumb and hallux
33. LONG BONES
Long bones
• Have a cartilaginous
ossification
• Are found mainly in the limbs
and consist of:
• Shaft (the diaphysis), which is ossified
from the primary center of ossification
during intrauterine life
• The cavity of the shaft, contains red
marrow in the fetus, yellow fat in the
adult
34. BONE GROWTH
• Diaphysis: shaft ossified from primary
center of ossification which appears 6-8th
week of intrauterine life
• Epiphysis: ossified from secondary center
• Growth plate is cartilage
• Injury of epiphysis affects growth
35. EPIPHYSIS
• Is ossified from a secondary center of
ossification
• These usually appear shortly after birth
• Except for the lower end of the femur,
which appears 9 months intrauterine life,
just before birth
• Epiphysis unite with the diaphysis (shaft)
from puberty to early twenties depending
on the bone involved
36. METAPHYSIS
• The portion of the diaphysis beside the
epiphysis is called the metaphysis
• This is the region where osteomyelitis tends
to occur in young people
• The metaphyseal arteries are end arteries
until ossification is completed i.e. the
epiphyseal plate is ossified
37. BONES
• Long bones grow in length from epiphyseal
plates
• Increase in width is from periosteum
• Damage to the epiphyseal growth plate can
lead to premature closing and retards normal
growth
• Anabolic steroids will also cause early closure
38. EPIPHYSES
• Traction epiphyses
• The tibial tuberosity
• Osgood-Schlatters
• Medial epicondyle of the humerus, in
‘little league elbow’
• Compression epiphysis
• The distal end of the humerus
39. MUSCULOSKELETAL PROBLEMS
• Younger athletes
• Suffer many of the same injuries and
illnesses as adults
• Differences is the structure of growing bone
Avulsed epiphysis
42. GROWTH PLATE FRACTURES
SALTER-HARRIS CLASSIFICATION
• Type 1 and type 2 heal well
• Type 3 and type 4 involve joint surface as
well as growth plate
• Type 5 compression of growth plate
• Difficult to detect
• Growth ceases
43. BLOOD SUPPLY OF BONE
• Periosteal arteries enter bone at several
points to supply the compact bone
• Nutrient arteries supply spongy bone and
bone marrow
44. BLOOD SUPPLY OF BONE
• Periosteal arteries enter the bone at several
points to supply the compact bone
• Nutrient arteries supply the spongy bone
and bone marrow
• Epiphyseal arteries supply the epiphysis
• Metaphyseal arteries supply the metaphysis
45. BLOOD SUPPLY OF BONE
• Periosteal arteries occur particularly at the sites of
attachments of muscles and tendons
• If a group of muscles inserted into a bone is
paralysed before puberty
• That bone will be shorter than the equivalent bone on
the other side
• Due to reduced blood supply from the muscles
involved
• The lack of stimulus to bone from lack of muscle
contractions
• After puberty only muscle bulk is reduced
46. • Epiphyseal arteries supply the epiphysis
• Metaphyseal arteries supply the metaphysis
• These are end arteries until epiphysis unites
with diaphysis
Blood Supply of Bone
47. AVASCULAR NECROSIS
• Bones that have a large surface area covered
with articular cartilage tend to have a poorer
blood supply
• Avascular necrosis occurs if blood supply is
cut off due to fracture
• e.g. head of femur, due to fracture of neck of
femur
• Proximal portion of the scaphoid
• Body of talus or dislocation e.g. lunate
48. APOPHYSIS
• Tendon attachment to growth plate
• Traction injuries may occur
• Medial epicondylitis
• Limit numbers of pitches in baseball
• Osgood-Schlatters lesion of tibial tuberosity
• 12-16 year olds
50. BONES IN CHILDREN
• More flexible
• More elastic
• Less brittle
• Growth plate is weakest link
• Periosteum thicker
51. • Articular cartilage thicker
• Junction between
• Metaphysis and epiphysis vulnerable
• Shearing forces
• Tendon attachment to apophysis weak
Bones in Children
52. EATING DISORDERS
May result in
• Delayed bone growth
• Delayed menarche
• Low peak bone mass
• Osteopenia or osteoporosis
• Increased musculo-skeletal problems
53. ARTICULAR CARTILAGE
• The thickness of the cartilage
depends on the stress to which it is
normally subjected
• Varies over the joint surface
• Patella has the thickest articular
cartilage
54. • Articular cartilage is avascular
• Nourished by synovial fluid, from capillaries
in the synovial membrane
• When the articular surfaces are in contact
Hollingshead, 1969
Articular Cartilage
57. STRESS FRACTURESSTRESS FRACTURES
• Biomechanical causes
• Training errors
• Athletic triad
• Amenorrhea
• Eating disorders
• Osteoporosisor osteopenia
• X-ray many times negative
• MRI is extremely sensitive
• Stress fracture of the femoral neck is potentially
serious and need often surgery
58. JOINT
• Junction between two bones
• Function and movement depends
• Size and shape of articular surfaces
• Soft tissues surrounding the joint
59. RANGE OF JOINT MOVEMENT
• Shape of articulating surfaces
• Restraint due to ligaments and muscles crossing joint
• Pain, weakness, spasm or contracture of muscles
• Bulk of adjacent soft tissue
• Impingement of bony surfaces
• Scarring of skin due to injury or burns
60. MUSCLES
• Muscle can only act on a joint, if it crosses
the joint
• Muscles that have a common action on the
joint tend to have same nerve supply
• Usually nerve of compartment gives an
articular branch to joint
• Exception, flexors of the elbow, where
median, ulnar and radial all give branches
62. FIBROUS JOINTS
• Fibrous union
• Slight movement
• Gomphosis i.e. tooth and its socket
• Sutures
• Syndesmosis
63. FIBROUS (SUTURE)
• Consists of dense fibrous connective
tissue between the bones
• Periosteum covering the opposing
surfaces of the bones
• Synostosis
• Fusion of the bones across the
sutural joints continues throughout
life
65. PRIMARY CARTILAGINOUS
• Cartilage continuous with bone
• No movement
• Rib and costal cartilage: costo-
chondral joints
• First costal cartilage and sternum
• Diaphysis and epiphysis
66. • Epiphysis and diaphysis
• Rib and costal cartilage
• 1st
costal cartilage and manubrium
sternum
• No movement
Primary Cartilaginous
68. SECONDARY CARTILAGINOUS
• Hyaline cartilage
• Disc of fibro-cartilage
• Mid line joints
• Very little movement
• Intervertebral discs
69. • Manubrium and body of sternum
• Pubic symphysis
Secondary Cartilaginous
70. SYNOVIAL
• Hyaline articular cartilage
• Capsule
• Synovial membrane lines capsule,
non articular structures inside joint
• Never lines articular cartilage
• Discs or menisci are fibro cartilage
71. TYPES OF SYNOVIAL JOINTS
• Shape of articular surface
• Plane
• Hinge
• Condylar
• Pivot
• Saddle
• Ellipsoid
• Ball and socket
72. TYPES OF SYNOVIAL JOINTS
SHAPE OF ARTICULAR SURFACE
• Plane: talo-calcaneal
• Hinge: elbow, interphalangeal joints
• Condylar: knee, metacarpophalangeal
• Pivot: superior radio-ulnar, atlanto-axial
• Saddle: trapezium-base first metacarpal
• Ellipsoid: wrist
• Ball and socket: hip, shoulder, talo-calcaneo-
navicular
73. DESCRIPTION OF A JOINT
Classify
• Shape of articular surfaces
• Cartilage covering surface
• Attachments of capsule
• Ligaments, disc
• Haversian pads of fats fill joint spaces
• Synovial membrane
• Movements
• Relations
• Blood and nerve supply
• Clinical significance
74. CAPSULE
• Collagen
• Expanded tendon
• Sesamoid bone
• Thickened to form ligaments
• Haversian pads of fats fill joint
spaces
75. PLANE JOINT
• Surface is flat
• Only allows gliding movement
• Non-axial e.g. facet joints of vertebrae
• Talo-calcaneal joint
Talo-calcaneal
76. HINGE JOINT
• Movement in one plane (uniaxial)
e.g. elbow
• Interphalangeal joints in hand and
foot
• Strong ligaments on sides, weaker
anterior and posterior
77. PIVOT JOINT
• Allows rotation around a single axis
• Uni axial
• Atlanto axial
• Superior and inferior radioulnar joints
78. SADDLE JOINT
• Saddle-shaped concavo-convex
surfaces
• Movement in two planes (biaxial) e.g.
carpo-metacarpal of the thumb
(trapezium and base of first metacarpal)
79. CONDYLARJOINT
• Two axes at right angles to each
other
• Movement in two planes (biaxial)
• Meta-carpophalangeal
• Sternoclavicular
• Atlanto-occipital joints
80. BALL AND SOCKET JOINT
• Allows movement in three axes
• Multiaxial
• Hip
• Shoulder
• Talocalcaneo-navicular joints
81. SYNOVIAL JOINTS
• Discs of fibro cartilage or menisci in some joints
• Blood supply at periphery
• Increase the depth and mobility of the joint
• Synovial folds in joints
• Synovial membrane
• Nerve endings also in fat
• Infrapatellar fat pad
• Facet joints of lumbar vertebrae
• Elbow
82. CAPSULE
• Consists of collagen (type I)
• Thickened to form ligaments
• Expanded quadriceps tendon
• Sesamoid bone in quadriceps tendon
• Synovial membrane lines the inner
surface of the capsule and non articular
structures inside capsule
84. HAVERSIAN PADS OF FAT
• Fat pads are semi-liquid at body
temperature
• They fill the changing spaces that
occur during movement
• These pads help to reduce friction
between moving tissues
85. SENSORY SUPPLY
• Sensory nerves in fibrous capsule and
ligaments and synovial membrane
• Information about pain
• The position of the joint (proprioception)
• Poor proprioception predisposes to injury
Isakov & Mizrahi, 1997
86. SYNOVIAL JOINT
• The epiphyses of many long bones are
intracapsular
• Injury to a joint, before the cessation of
growth, may damage the epiphyseal
cartilage
• The articular surfaces are covered by
hyaline or articular cartilage
87. HYALINE CARTILAGE
• Hyaline cartilage is avascular
• Nutrition is by diffusion from the synovial
fluid
• Must be in contact with the opposing
articular surface
88. OPEN AND CLOSED KINETIC CHAIN
• Open kinetic chain
• The distal segment is free in space
• Raising the hand in the air
• Closed kinetic chain
• The distal segment is fixed
89. THE DEGREES OF FREEDOM
• Joints can also be classified by degrees of
freedom
• Reflects the axis of movement
• If a joint has only one axis
• It has only one degree of freedom
90. • Nonaxial: no axis of rotation
• Uniaxial: move in one axis
• Have one degree of freedom
• Acromioclavicular 1
• Elbow 1, radioulnar 1
• Proximal and distal interphalangeal
1
• Biaxial: move in two axes
• Have two degrees of freedom
• Metacarpophalangeal 2 +
• Wrist 2 +
• Multiaxial: move in three axes
• Have three degrees of freedom
• Maximum any joint can possess
• Shoulder 3
• Sternoclavicular 3
• Hip 3
• Talocalcaneonavicular 3
The Degrees of Freedom
91. CLOSE-PACKED
• Stable position
• Surfaces fit together
• Ligaments taut
• Spiral twist
• Screw home articular surface
• Stable position
92. LEAST-PACKED
• Joint more likely to be injured in least-
packed position
• Capsule slackest
• Joint held in this
• Position when injured
• Fluid in knee held in 20° flexion
93. • Shape of articulating surfaces
• Restraint due to ligaments and muscles crossing joint
• Pain, weakness, spasm or contracture of muscles
• Bulk of adjacent soft tissue
• Impingement of bony surfaces
• Scarring of skin due to injury or burns
RANGE OF JOINT MOVEMENT
Editor's Notes
Alterations of the RANK Ligand/OPG ratio are critical in the pathogenesis of bone diseases that result in increased bone resorption:
Unopposed RANK Ligand (i.e. an elevated RANK Ligand/OPG ratio) within the skeleton promotes bone loss
Restoring a balanced RANK Ligand/OPG ratio or inhibiting RANK Ligand decreases osteoclast activation and bone resorption.1–3
In many diseases involving increased bone resorption, RANK Ligand expression is upregulated by osteoclastogenic factors (growth factors, hormones, cytokines), while OPG expression is simultaneously downregulated.3
Bone remodelling is the process by which old bone is replaced by new bone.
Bone remodelling consists of four phases: resting, resorption, reversal and formation.1
During the resorption phase, osteoclasts remove both mineral and organic components of bone matrix by generating an acidic microenvironment between the cell and bone.
Once the osteoclasts have resorbed most of the mineral and organic matrix, they undergo apoptosis during the reversal phase and osteoblasts are recruited to the bone surface.
In the formation phase, osteoblasts deposit new, healthy osteoid (unmineralised collagen matrix), which is subsequently mineralised, resulting in good-quality bone.
This figure by Compston (1990), illustrates the changes in bone mass throughout life and shows the rapid bone loss that occurs at the menopause. Bone mass in both men and women increases until a peak is attained at around age 30. In both sexes, a slow rate of bone loss starts at around age 40. However, in women, the accelerated postmenopausal phase of bone loss is superimposed on top of this slow loss phase. Rates of bone loss in postmenopausal women can be as great as 5-6% per year. In women, oestrogen deficiency is the major determinant of bone loss after the menopause due to the removal of the ‘brakes’ from Osteoclastic activity.
The accelerated bone loss is important to remember when looking at preventative therapies for osteoporosis. Unlike treatment for the established disease when relatively large increases in bone mass are observed in response to therapy, a preventative strategy may be said to have been effective if the bone mass is maintained.
National Osteoporosis Society, Menopause and osteoporosis therapy - GP manual 1993.
National Osteoporosis Society, Priorities for Prevention.
Hosking D J et al, J. Bone Miner. Res., 1996: 11 (1); S133, 153.