Fracture: A fracture is defined as a break in the continuity of the cortex of the bone. This discontinuity can be ‘complete’ if it affects both cortices and ‘incomplete’ when only a single cortex is involved. Incomplete injuries are commonly seen in the long bones (radius and ulna) of the forearm in children. These incomplete fractures are described as ‘greenstick’ when failure of the bone is under tension (convex side); and ‘buckle’ or ‘torus’ when bone fails under compression (on the concave side).

Dislocation: A dislocation is defined as a complete loss of contact between joint surfaces. It is often associated with significant injuries to adjacent ligaments, joint capsule and muscles. The direction of displacement of the distal joint surface determines the type of displacement. For example, in an anterior shoulder dislocation, the humeral head lies anterior to the glenoid cavity. A dislocation is a surgical emergency and should be reduced as soon as possible.

Subluxation: In a subluxation, the joint surfaces lose partial contact with each other. This is also described as ‘incomplete’ or ‘partial’ dislocation.

Sprain: A sprain is a stretch and/or tear of a ligament. It may be partial or complete, depending upon the severity of the injury.

Strain: A strain is an injury to either a muscle or a tendon. It may be partial or complete, depending upon the severity of the injury.

Displacement: Fracture displacement is always described in terms of the position of the distal fragment relative to the proximal.