Bones and Joint Classification

Bones and Joints

An athlete's body is built on the skeleton: over 200 bones that do rather more than hold the shape. Five jobs, and the last two surprise people: - Protects vital organs. The cranium shields the brain, the ribs the heart and lungs. - Gives muscles something to pull against. No attachment, no movement. - Provides joints, which is where the movement actually happens. - Makes blood cells and platelets, in the bone marrow. - Stores minerals, calcium and phosphorus above all. Those five are worth learning as jobs rather than as a list, because exam questions ask what happens when one of them fails.

A broken femur

A cyclist badly fractures their femur. Select ALL THREE consequences that follow from what a femur actually does.

• The leg can no longer act as a lever, so powerful movement is lost
• Blood cell production in that bone's marrow is disrupted
• The large thigh muscles lose part of their attachment point
• Digestion of food is impaired
• Insulin production stops
• Lung capacity falls

Four shapes of bone

Bones are classified by shape, and the shape follows the job. If you can say what a bone has to do, you can usually classify it without having memorised it:

Classify each bone

Find the femur

The femur is the long bone of the thigh, and the longest bone in the body. Tap the FEMUR on the skeleton.

From the job

A bone is long and thin, and a muscle pulling on one end of it swings the far end through a wide, fast arc. Which classification is it, and why?

• Long, because that shape works as a lever and levers turn a small muscle movement into a large one
• Short, because it has to bear the weight of the limb
• Flat, because a muscle needs a wide surface to attach to
• Irregular, because the shape does not fit the other categories

Shape follows job

The femur is a _____ bone, because it acts as a lever to produce large, fast movements. The carpals in the wrist are _____ bones, clustered together for stability and weight bearing. The cranium is a _____ bone, broad and plate-like so that it can protect the brain underneath. The vertebrae are _____ bones, doing protection and muscle attachment at once.

Hinge against ball and socket

Where two bones meet you get a joint. Two types do most of the work in sport, and they are built on opposite compromises:

Range or stability?

A bowler can circle their arm right over at the shoulder, but nobody can circle their lower leg at the knee. Why has the body built them differently?

• Range and stability are a trade-off: the shoulder buys movement in all directions at the cost of stability, while the knee stays in one plane so it can carry load safely
• The shoulder has more muscles around it than the knee does
• The knee is a larger joint, and larger joints cannot rotate
• People could circle the knee with enough training

One passage of play

Follow a netball player through four movements and name the joint doing the work each time.

• She bends and then straightens her elbows to push out a chest pass. Which joint type, and which movements?
• To shoot she raises one arm above her head and swings it back and round. Which joint allows that range?
• Landing, she keeps her eyes on the ball by turning her head while her body turns the other way. Which joint type lets the head rotate?
• As she releases the ball she flexes her wrist forward and also tilts it sideways. Which joint type allows both?

The vertebral column

The spine is a stack of irregular bones, and it changes as it goes down because the job changes with it. At the top the cervical vertebrae in the neck are small and light, because they carry only the head and need to move a great deal. The thoracic vertebrae in the chest carry the ribs. Lower down the lumbar vertebrae are the thickest of all, because everything above them is resting on them, which is also why the lower back is where lifting injuries happen. Below those, the sacrum is fused into the pelvis, and the coccyx is the small tail of bone at the very bottom.

Down the spine

Put the regions of the vertebral column into order, from the top of the neck to the base of the spine.

• Cervical (neck)
• Thoracic (chest)
• Lumbar (lower back)
• Sacrum
• Coccyx (tailbone)

The other two

Two more joint types complete the set, and both are easiest to remember by the movement they allow. • A pivot joint lets one bone rotate about another. The one you need is in the neck, between the atlas and the axis, and it is what you use to shake your head. • A condyloid joint moves back and forth and side to side, but does not fully rotate. The wrist is the example. One discipline is worth more than the names here. When a question asks about a movement, name the movement as well as the joint: flexion, extension, abduction, adduction, rotation. An answer that says "the hinge joint at the knee" is worth less than one that says "flexion at the hinge joint of the knee", and it is the same amount of writing.

Shake your head

A defender shakes their head to signal "no" to a team-mate. Which joint type is producing that movement, and what is the movement called?

• A pivot joint, performing rotation
• A hinge joint, performing flexion and extension
• A condyloid joint, performing abduction
• A ball and socket joint, performing circumduction

Which are true?

Select ALL THREE statements that are TRUE.

• Shoulders dislocate more easily than knees because a ball and socket trades stability for range
• The ankle allows flexion and extension but not rotation
• An answer naming the movement as well as the joint scores more than one naming only the joint
• The knee is a pivot joint, which is why footballers can turn on it
• A hinge joint can move in all directions if the muscles around it are strong enough
• The wrist is a hinge joint, since it bends forward and back

Skeleton summary

The skeleton protects organs, gives muscles attachment, provides joints, makes blood cells and stores minerals. Bones are classified by shape: the femur is a _____ bone acting as a lever, while the cranium is a _____ bone protecting what is underneath. Joints are classified too: the elbow is a _____ joint moving in one plane, while the hip is a _____ joint moving in all directions, and the second buys that range at the cost of stability.