Three joint types by movement allowed
Joints are classified by how much movement they allow. A fixed (fibrous) joint allows none -- bones held by fibrous tissue (skull sutures). A slightly movable (cartilaginous) joint allows a little, joined by cartilage (the vertebrae). A freely movable (synovial) joint holds synovial fluid and allows the greatest range (hip, knee, shoulder, elbow). Its two 0413 subtypes are the ball-and-socket (hip, shoulder) and the hinge (knee, elbow).
Synovial joint: five parts, five jobs
Five structures make a synovial joint, each with a function credited separately. Cartilage caps the bone ends, cushioning impact and reducing friction. The synovial membrane lines the capsule and secretes synovial fluid. Synovial fluid fills the cavity, lubricating the joint and nourishing the cartilage. The joint capsule is a tough sleeve enclosing the joint. Ligaments join bone to bone and stabilise the joint.
Seven movements; range vs stability
0413 needs seven movements. Flexion decreases the joint angle (bending); extension increases it (straightening). Abduction moves a limb away from the midline; adduction moves it back. Rotation turns a part around its long axis. Two are ankle-only: plantar flexion (toes down) and dorsiflexion (toes up). A ball-and-socket joint moves in every plane, the greatest range; a hinge joint moves in one plane only, a smaller range but more stable.
Drawn from real examiner reports.
Bigger range does not mean more stable
Students assume "more movement = a stronger joint", but the two trade off. A ball-and-socket joint (shoulder, hip) moves in every plane -- the greatest range -- but relies on ligaments and muscles, not bone shape, so it is less stable and dislocates easily. A hinge joint (knee, elbow) moves in one plane, so it has a smaller range but is more stable.
Ligament vs synovial membrane
These two are persistently confused. A ligament connects bone to bone and stabilises the joint. The synovial membrane lines the inside of the capsule and secretes synovial fluid -- it does not hold bones together. Fix it: ligament = bone-to-bone holding the joint together; membrane = lining that makes the fluid.
Digest 1.2: ligament and synovial-membrane functions are persistently confused (s22 P13 Q1c).
Knee is a hinge, not ball-and-socket
Because the knee bends through a large range, candidates classify it by feel and call it a ball-and-socket joint. It is a hinge joint -- it feels flexible only because that one plane (flexion/extension) has a big range. A true ball-and-socket joint (hip, shoulder) moves in multiple planes. Classify by how many planes a joint moves in, not how far it bends in one.
Digest 1.2: the knee (a hinge joint) is sometimes wrongly classified as ball-and-socket (s23 P13 Q9b(ii); s23 P12 Q2c(i)).
Ankle: plantar flexion, not flexion
The ankle has its own movement terms, but candidates use general flexion/extension for it. Pointing the toes down, away from the shin (tiptoe, striking a ball) is plantar flexion, not flexion. Pulling the toes up, towards the shin, is dorsiflexion, not extension. Mixing these with the terms used at the shoulder or elbow is a repeated slip.
Digest 1.2: ankle movements (plantar flexion/dorsiflexion) are mixed up with the flexion/extension terminology used at the shoulder (s22 P13 Q8a; w23 P13 Q1a).
Abduction vs adduction
These opposite movements are easy to swap. Abduction moves a limb away from the midline -- think "abduct = take away". Adduction moves a limb back towards the midline -- "add = back to the body". Raising the arm out sideways is abduction; lowering it to the side is adduction. Only ball-and-socket joints (hip, shoulder) allow this pair; a hinge joint cannot.
Flexion vs extension
Candidates confuse the direction of these two. Flexion decreases the joint angle (bending it), e.g. bending the elbow to lift a weight. Extension increases the angle (straightening it), e.g. straightening the knee. Quick check: if the parts either side of the joint move closer it is flexion; if they open apart it is extension.
Joint capsule vs ligament
Both help hold a joint together, so they get muddled. The joint (fibrous) capsule is a tough sleeve enclosing the whole joint and sealing in the synovial fluid. A ligament connects one bone directly to another to stabilise the joint. The capsule wraps the entire joint; ligaments tie particular bones together.
Name the exact phase, not the activity
A movement example only scores if it names the exact phase. A bicep curl has both flexion (lifting) and extension (lowering); "running" has a plantar-flexion push-off and a dorsiflexion swing. Name the joint, the movement, the activity and the exact moment.
Match the command word
Size your answer to the command word. "State/identify/name" wants the term only. "Describe" wants it in full: what it is and what it does. "Explain" wants a reason linked to the named activity. Over-writing a "state", or under-developing an "explain", wastes marks.
Comparison: answer both sides
For "compare" or "describe a difference", give a two-sided point, not a fact about one joint. "The shoulder moves in every plane" is only half -- add "whereas the knee moves in one plane". Cover both joints on both properties: range and stability.
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