Bone Fracture Mechanisms — Orthopedic Trauma

Overview

Bone fracture mechanisms include traumatic forces, stress-related injuries, and pathological conditions. Below we delve into each category and show the typical fracture patterns they produce.

1. Traumatic Forces

Fractures caused by traumatic forces result from sudden, high-impact incidents. Different types of traumatic forces lead to characteristic fracture patterns:

Rotational Force — can cause a spiral fracture or a long oblique fracture that runs along the bone's length.
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Rotational force leading to a long oblique fracture. (Image placeholder)
Compressing Force on Long Axis — may result in a short oblique fracture.
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Compressing force mechanism leading to a short oblique fracture. (Image placeholder)
Crushing Force on Long Axis — produces a comminuted fracture in which the bone breaks into multiple fragments.
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Crushing force mechanism leading to a comminuted fracture. (Image placeholder)
Bending Force (Horizontal Axis) — often causes a fracture with a butterfly fragment (a triangular fragment resembling a butterfly wing).
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Bending force mechanism leading to a butterfly fracture. (Image placeholder)
Tension Force — tension can produce a transverse fracture or cause an avulsion where a small fragment is pulled off at a tendon/ligament insertion.
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Tension force mechanism leading to a transverse or avulsion fracture. (Image placeholder)

2. Stress Fractures

A stress fracture is a small break in the bone that occurs from repetitive microtrauma or prolonged mechanical loading.

Typical sites: weight-bearing bones such as the tibia, fibula, and femur.
Mechanism: repetitive stress causes bone resorption by osteoclasts to outpace bone formation by osteoblasts, eventually producing a fracture line.
Risk groups: long-distance runners, dancers, gymnasts, and others with repetitive high-load activity.
Contributing factors: nutritional deficiencies (e.g., low calcium or vitamin D), relative energy deficiency, and age-related bone loss.

3. Pathological Fractures

Pathological fractures occur when underlying bone disease weakens the bone, making it susceptible to fracture from minimal or normal forces.

Common causes:
- Osteoporosis
- Osteogenesis Imperfecta
- Long-term bisphosphonate therapy (atypical fracture risk)
- Lytic bone lesions from metastasis or multiple myeloma