Types of Freely Movable Joints

This lesson covers the two types of freely movable (synovial) joints required by the OCR GCSE PE specification (J587): hinge joints and ball-and-socket joints. You need to know the structure of each type, where they are found in the body, the movements they allow, and how they are used in sport.

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Overview

The OCR specification requires you to know two types of synovial joint:

Joint Type	Examples	Movements Allowed
Hinge	Knee, elbow	Flexion and extension
Ball and socket	Shoulder, hip	Flexion, extension, abduction, adduction, rotation, circumduction

graph TD
    A["Types of Freely Movable Joints"] --> B["Hinge Joint"]
    A --> C["Ball and Socket Joint"]
    B --> D["Knee"]
    B --> E["Elbow"]
    C --> F["Shoulder"]
    C --> G["Hip"]

    style A fill:#4a90d9,color:#fff
    style B fill:#e67e22,color:#fff
    style C fill:#27ae60,color:#fff

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Hinge Joints

A hinge joint works like the hinge on a door — it allows movement in one plane only (the sagittal plane), producing flexion (bending) and extension (straightening).

Structure

• One bone has a convex (rounded) surface that fits into a concave (hollowed) surface on the other bone.
• Strong ligaments on either side of the joint prevent sideways movement.
• The joint can only move forwards and backwards — it cannot rotate or move sideways.

The Knee Joint

The knee is the largest hinge joint in the body. It is formed where the femur (thigh bone) meets the tibia (shinbone). The patella (kneecap) sits at the front to protect the joint.

Feature	Detail
Bones involved	Femur, tibia (patella at the front)
Movements	Flexion and extension
Key muscles	Quadriceps (extension), hamstrings (flexion)
Sporting examples	Kicking a football (extension), bending the knee during a squat (flexion)

The knee also contains two important structures not found in all hinge joints:

• Meniscus (plural: menisci) — two C-shaped pieces of cartilage that act as additional shock absorbers between the femur and tibia. Meniscus tears are common in sports involving twisting (football, basketball, skiing).
• Cruciate ligaments (ACL and PCL) — cross-shaped ligaments inside the knee that provide stability and prevent the tibia from sliding forwards or backwards relative to the femur.

The Elbow Joint

The elbow is a hinge joint formed where the humerus (upper arm) meets the ulna and radius (forearm bones).

Feature	Detail
Bones involved	Humerus, ulna, radius
Movements	Flexion and extension
Key muscles	Biceps (flexion), triceps (extension)
Sporting examples	A press-up (extension), a bicep curl (flexion), shooting in basketball (extension)

Exam Tip: Hinge joints only allow flexion and extension. If an exam question asks about movements at the knee or elbow, do not include rotation, abduction, or adduction — these movements are not possible at a hinge joint.

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Ball-and-Socket Joints

A ball-and-socket joint allows the greatest range of movement of any joint type. The rounded head (ball) of one bone fits into the cup-shaped socket of another bone, allowing movement in all directions.

Structure

• The "ball" is the smooth, rounded end of one bone.
• The "socket" is the cup-shaped depression in the other bone.
• The ball can rotate within the socket, slide across it, and move in every direction.
• Strong ligaments and surrounding muscles provide stability to compensate for the wide range of movement.

The Shoulder Joint

The shoulder is the most mobile joint in the body. It is formed where the humerus (upper arm) meets the scapula (shoulder blade). The head of the humerus sits in the glenoid cavity (a shallow socket on the scapula).