Bones and Joints

Question 1

The skeleton contains 206 bones: 26 vertebral, 64 upper IMDb, 62 lower limb. What are the functions? (5)

Answer 1

Support, protection, movement (acts as levers), mineral and growth factor storage (main calcium and phosphate reservoir) and haemopoiesis (children - long bones of femur and tibia, adults - pelvis, skull, vertebrae and sternum).

Question 2

Bones may be classified by shape, what are the categories? (6)

Answer 2

Flat bones - curved, protect organs,
Sutural - within cranial structure,
Short bones - equal in height and width,
Irregular bones - e.g. Vertebrae
Sesamoid - embedded within a tendon/muscle
Long bone - longer than wide, muscles act on them a rigid levers.

Question 3

What is the structure of long bones?

Answer 3

Primarily compact bone, with perhaps spongy bone at the extremities.

Question 4

When describing a long bone, what is the diaphysis, metaphysis and epiphysis? What are the other components?

Answer 4

The diaphysis is the main shaft, the metaphysis is the flare adjacent to the epiphyseal growth plate, with the epiphysis on the other side. Then there is the articular cartilage (hyaline on the ends). Periosteum lines the rest of the bone with endosteum lining the medullary cavity (red in a child and yellow in an adult).

Question 5

How is the medullary cavity/bone marrow supplied in a long bone?

Answer 5

A Nutrient artery enters near the middle of the diaphysis via the Nutrient foramen.

Question 6

What’s the structure of short, flat and sesamoid bones?

Answer 6

Short (carpal and tarsal) consist mainly of spongy bone with a thin layer of periosteum, covered by compact bone on the outside with not epiphysis/diaphysis, the bone marrow is in the trabeculae. The base of the carpal bone comes after the proximal articular cartilage, then the shaft, the neck and the head.

Question 7

Apart from the medullary cavity of long bones, how is it supplied?

Answer 7

Periosteal arteries supply the periosteum and the outer 1/3 of the cortex, with the metaphyseal entering the metaphysis at the site of attachment to the capsule.
There’s an anastomoses between the the metaphyseal and epiphyseal arteries after epiphyseal fusion.

Question 8

What is avascular necrosis and how is it caused?

Answer 8

Death of bone due to interruption of blood supply.
Varied causes include: fracture, dislocation, steroid use, radiation and decompression sickness. It leads to the collapse of the necrotic segment and secondary osteoarthritis.

Question 9

What are joints and what are the 2 ways of classifying them?

Answer 9

Articulations between 2 or more bones.
Structural classification is based on the tissue between the bones and functional classification is according to the degree of movement.

Question 10

The sutures of the skull, the radioulnar interosseous membrane and the posterior sacroiliac joint are all examples of which type of joint (structural classification)?

Answer 10

Fibrous joints.

Question 11

A joint may be structurally classified as a cartilaginous joint, which can be primary or secondary, what’s the difference? Give examples.

Answer 11

A primary cartilaginous joint is one where the bones are united by hyaline cartilage e.g. At epiphyseal growth plates and the 1st sternocostal joint.
A secondary cartilaginous joint is where articulating bones are covered in hyaline cartilage with a pad of fibrocartilage between them e.g. At the pubic symphysis, intervertebral discs and manubriosternal joint.

Question 12

What is the third structurally classification of a joint, after fibrous and cartilaginous?

Answer 12

Synovial joint - a joint capsule containing synovial fluid, freely movable.

Question 13

What are the characteristics of a synovial joint?

Answer 13

Articular (hyaline, with some exceptions) cartilage, fibrous capsule, synovial membrane, bursts, tendon sheath, synovial fluid, fat pads, interarticular menisci/discs.

Question 14

Which element of a synovial joint has the function of:

1. Sacs lined with synovial membrane filled with synovial fluid, communicating or noncommunicating with joint cavity (cushion between bone and tendon/muscles around joint) - what’s it called when elongated?
2. For smooth, low friction movement, that resists compression?

Answer 14

1. Bursae - tendon sheaths are elongated bursae.

2. The articular hyaline cartilage.

Question 15

Which element of a synovial joint has the function of:

1. Thin, high vascularised and lines the capsule, as well as covering exposed osseous surfaces, tendon sheaths and bursae and produces synovial fluid - what does it not cover?
2. Pieces of fibrocartilage not covered by synovium.

Answer 15

1. The synovial membrane, which does does cover the articular cartilage or intraarticular discs/menisci.
2. Intraarticular discs/menisci.

Question 16

What is this describing?
Collagen (interlacing and longitudinal bundles), which completely encloses the joint except where interrupted by synovial protrusions (e.g. Bursae), which stabilises the joint, permits movements and resists dislocation?

Answer 16

The fibrous capsule.

Question 17

Synovial fluid is clear/pale _______, viscous and slightly ________ (pH) at rest. The volume is < ___ml in a large knee joint. It is composed of ___________ acid, lubricin, proteinase and collagenase. Functions: reduce __________, ________ absorption, nutrient and waste ___________.

Answer 17

Yellow
Alkaline
0.5
Hyaluronic
Friction
Shock
Transport

Question 18

Describe the blood supply to synovial joints.

Answer 18

It is via a periarticular arterial plexus.
The articular cartilage is avascular, and the fibrous capsule and ligaments have a poor blood supply, whereas the synovial membrane has a rich supply.

Question 19

When thinking about the nerve supply of joints, it may be useful to apply Hilton’s law, what is it?

Answer 19

Nerve supplying the joint capsule also supply the muscles moving the joint and the skin overlying their insertions.

Question 20

Synovial joints may be classed based on their shape, what are the different types? (6)

Answer 20

Planar joint, hinge joint, pivot, condyloid/ellipsoidal, saddle and ball and socket.

Question 21

Which type of joint is monoaxial, pulley shaped - convex surface of one bone fits into the concave surface of another? Give some examples.

Answer 21

Hinge joint e.g. Ulnohumeral, ankle and knee.

Question 22

Which type of joint had a surface that is flat/slightly curved for gliding/sliding movements, which are non axial? Give some examples.

Answer 22

Palmar joints e.g. Sternoclavicular, acromioclavicular and inter carpal joints.

Question 23

Which type of joint is monoaxial, with a rounded/pointed surface of one bone articulating with a ring formed by the concavity of another and a fibrous ligament? Give examples.

Answer 23

Pivot joint e.g. Proximal radioulnar joint and the atlantoaxial joint.

Question 24

What is a condyloid/ellipsoidal joint, which movements does it perform and what are some examples?

Answer 24

A condylar joint is biaxial, with the oval shaped condyle of a bone resting in the elliptical cavity of another.
Movements: flexion, extension, abduction and addiction (circumduction) e.g. Metacarpal-pharyngeal joints, radiocarpal joints and the atlanto-occipital joint.

Question 25

Why is a saddle joint called a saddle joint? Give an example.

Answer 25

A saddle joint is biaxial with one bone as the saddle (concavoconvex) and the other representing the legs of the rider. There are the 4 movements: flex/ext, abd/add e.g. At the 1st carpometacarpal joint.

Question 26

What type of joints are the hip, the shoulder and the incudo stapedial joints (middle ear) examples of? Please describe it.

Answer 26

Ball and socket joint - multiaxial ball like and cup - surfaces articulate, with 4 movements (flex/ex and abd/add) as well as rotation.

Question 27

What are the factors affecting joint stability and range of motion at synovial joints?

Answer 27

Structure/shape of articulating bones, strength and tension of joint ligaments, arrangement and tone of muscles, apposition of neighbouring soft tissue, hormones (e.g. Pregnancy causes relaxation) and use/disuse.

Question 28

Why do joints crack?

Answer 28

When bones are pulled away from each other, the synovial cavity expands, but the synovial fluid content stays constant, so a partial vacuum is produced and gases dissolved in the fluid are pulled out of the solution, making a popping sound.

Question 29

What is the effect of ageing on joints?

Answer 29

Decreased production in synovial fluid, thinning of articular cartilage, shortening of ligaments, decreased flexibility and degenerative changes.

Question 30

What is arthritis and its symptoms and signs?

Answer 30

Inflammation and stiffness of a joint. There are over 100 forms.
Symptoms: pain, swelling, stiffness.
Signs: redness, swelling, deformity, tenderness, reduced ROM, abnormal gait.

Question 31

Osteoarthritis is the most common form of arthritis, what is its cause and how could it be spotted on an X-ray?

Answer 31

It is a result of ‘wear and tear’ at the joint.
X-ray features:
Osteophytes (new bone formation at margins of arthritic joint),
Joint space narrowing,
Bone cysts (fluid filled sacs in the bone),
Subarticular/subchondral sclerosis (thin layer of increased bone density).

Question 32

What happens in the process of Rheumatoid Arthritis?

Answer 32

It’s an autoimmune disease where antibodies attack the synovium, leading to synovial inflammation causing a pannus (vascular fibrotic tissue) to erode the joint surface.

Question 33

Where is Rheumatoid Arthritis likely to be seen?

Answer 33

Joint erosion and deformity may be seen at the Metacarpal-pharyngeal joints and the Proximal interpharyngeal joints of the hands, the cervical spine and the feet (it may also involve large joints). There may also be damage to other organs including: eyes, skin, lungs, heart and blood vessels, kidneys and blood.

Question 34

Who’s likely to get Rheumatoid Arthritis?

Answer 34

The peak age is 40-50 years, but it can be juvenile. It is in 1% of the population, with the ratio of women:men = 2-3:1.

Question 35

What are the X-ray features of Rheumatoid Arthritis?

Answer 35

Narrowing of the joint space, 
Periarticular osteopenia (loss of bone substance adjacent to the joint),
Juxta-articular bony erosions,
Subluxation and gross deformity.