Focal Loading
Definition
Force concentrated on a small contact area of the skull surface (as from a hammerhead, poker, or stone edge); produces a discrete depressed fracture with clear radiating cracks from an identifiable epicentre.
- Mechanism
- Force concentrated on a small contact area of the skull
- Typical causes
- Hammerhead, poker, stone edge
- Fracture pattern
- Discrete depressed fracture with radiating cracks
- Diagnostic feature
- Identifiable epicentre
Common questions
How does focal loading differ from diffuse loading in the resulting skull fracture pattern?+
Focal loading concentrates force on a small area, producing a localised depressed fracture with cracks radiating outward from that point. Diffuse loading spreads force over a broad area, such as from a fall onto a flat surface, and tends to produce more widespread linear fracturing without one clear point of maximum deformation.
Can the identifiable epicentre from focal loading help identify the type of weapon used?+
The epicentre and the shape of the depressed segment can indicate the approximate size and geometry of the striking surface, for example a rounded versus a linear or angular impression, which narrows the class of implement but does not usually individualise it to one specific object without other evidence.
Why do radiating cracks form around a focal impact rather than the bone simply breaking at the point of contact?+
The skull bends outward around the depressed area as it absorbs the impact energy, and this bending generates tensile stress on the outer table beyond the immediate contact zone, which propagates as cracks radiating away from the epicentre once the bone's tensile strength is exceeded.
Related terms
- Bearing Surface
- The area of the striking implement that was in contact with the skull at the moment of force transfer; its geometry can...
- Concentric Fracture
- An arc-shaped fracture encircling the impact zone, produced by outer-table bending tension at a distance from the focal impact; always post-dates the...
- Depressed Fracture
- A fracture where the impacted skull segment is driven inward beyond the elastic limit; the geometry of the depression reflects the bearing...
- Diffuse Loading
- Force distributed over a broad contact area (as from a fall onto a flat surface or a broad-surface blow); produces a broader...
- Hering's Principle
- The 1853 observation that a radiating fracture from a subsequent impact is arrested when it reaches a fracture line produced by a...
- Perimortem Fracture
- A fracture produced at or near the time of death while the bone retains green (fleshed) properties; distinguished by sharp fracture margins...
- Radiating Fracture
- A linear fracture extending outward from the impact point, initiated by inner-table tension as the outer table is compressed; propagates until arrested...
- Wedge Fracture
- The three-dimensional fracture geometry described by Berryman and Symes (1998): a conical inner-table failure zone wider than the outer-table defect, produced by...
- Wolff's Law
- The principle that bone is deposited and resorbed in response to mechanical loading history. Cortical thickness and trabecular orientation follow principal stress...