Home Books Simon’s Emergency Orthopedics, 7e

Chapter 1: General Principles

R. Darrell Nelson

Fracture Principles

Biomechanics

An orthopedic fracture occurs when the stress applied to a bone exceeds the plastic strain beyond its yield point. A number of factors influence fracture patterns. These include the magnitude of force, its duration and direction, and the rate at which it acts. When a bone is subjected to repeated stresses, the bone may ultimately fracture even though the magnitude of one individual stress is much lower than the ultimate tensile strength of the bone. The strength of a bone is related directly to its density, which is reduced by any condition, such as osteoporosis, where the osseous structure is changed, thus lowering its resistance to the stress.

Terminology

Fractures can be described in a number of ways. No one system of classification is all-encompassing, and physicians dealing with fractures on a day-to-day basis must be aware of the terminology to better understand and convey information to their colleagues. It should be noted that to adequately describe a fracture, at least two perpendicular radiographic views should be obtained.

Direction of Fracture Lines

Transverse: A transverse fracture runs perpendicular to the bone (Fig. 1–1A).
Oblique: An oblique fracture runs across the bone at an angle of 45 to 60 degrees (Fig. 1–1B). These fractures are due to compression and flexure at the fracture site.
Spiral: A spiral fracture may be misdiagnosed as an oblique fracture; however, on closer study, a “corkscrew” appearance of the fracture is noted (Fig. 1–1C). It is a highly unstable fracture that is prone to poor healing. Spiral fractures are due to a torsional force. In pediatrics, a spiral fracture of the femur in a nonambulatory child is suspicious for nonaccidental trauma. However, a spiral fracture of the distal tibia in an ambulatory child is common and referred to as a “toddlers fracture.”¹
Comminuted: A comminuted fracture is any fracture where there are more than two fragments (Fig. 1–1D). Other examples of comminuted fractures are the segmental and butterfly fractures (Fig. 1–1E and 1–1F).
Compression: A compression fracture is one where the fractured ends are compressed together. These fractures are usually very stable (Fig. 1–1G). Compression fractures, also referred to as impacted fractures, are common in the vertebral bodies and lower extremities (e.g., calcaneus, femoral neck, and tibial plateau). When compression is significant, the fracture may become “depressed”, or pushed in, and is referred to as a depression fracture (e.g., depressed calcaneus fracture).