Fracture general principles

General

  • Terms

  • Fracture Types

  • Checklist

  • Description of Fractures

  • Fracture Mimics

Terms:

Fracture: interruption of the continuity of part of the skeletal system (=broken bone) 
Luxation: dislocation, interruption of the normal interrelation between the components of a joint.

When asked to confirm a fracture, the area in question is always imaged in (at least) 2 different directions.  A fracture is generally visible in one direction only. Therefore, never settle for an image in only one direction. 

If bone fragments are displaced as a result of a fracture, the X-ray beam will not be absorbed by the bone at the fracture site (= the gap) (fig. 1a). This is visible as a lucent line (= black line). Bone fragments may also be compressed (= impacted fracture), causing overlap of bone structures (fig. 1b). In this case there will be increased X-ray absorption at the fracture site, resulting in increased density (= whiter).  

Figure 1. Fracture gap in a proximal humerus fracture (a) and impacted distal radius fracture (b).

Fracture Types:

Terms:

  • Uncomplicated fracture: fracture where the adjacent skin is intact.
  • Complicated/open fracture: fracture with skin penetration of a fracture fragment.
  • Comminuted fracture: fracture with > 2 bone fragments.
  • Intra-articular fracture: fracture line continues up to the joint surface (fig. 2).

Figure 2. Left elbow. Open intra-articular comminuted fracture of the proximal radius and ulna, with air in the soft tissues.

  • Stress fracture: fracture resulting from excessive stress on the bone. Can be seen e.g. in the metatarsal bones of fanatical sportsmen (fig. 3a).
  • Pathological fracture: fracture line at the level of abnormal bone, as in a bone metastasis or bone cyst (fig. 3b).

Figure 3. A (cloudy) periostal reaction around the mid shaft of metatarsal III, image of a stress fracture (a). Pathological humeral shaft fracture in a child with a bone cyst (b) Normal epiphyseal plates (= growth plates).

  • Insufficiency fracture: fracture secondary to reduced bone strength, e.g. osteoporotic vertebral collapse.
  • Avulsion fracture: fracture at the site of a tendon insertion.  The bone is ripped loose from the insertion site by the tendon/muscle (excessive traction on the bone). 

Pediatric:

  • Greenstick fracture: incomplete fracture where the bone is bent (one-sided cortical interruption). These fractures are seen in the distal radius and ulna in particular (fig. 4).
  • Torus fracture (= buckle fracture): incomplete fracture creating a 'buckle’ of the cortex. The picture resembles the bottom of a Greek pillar. Torus fractures heal quicker than greenstick fractures.

Figure 4. Lateral image (a) and anteroposterior image (b) of a radial greenstick fracture and ulnar torus fracture.

  •  Epiphysiolysis: fractures of the epiphyseal plate (=growth plate) 
    Classification according to Salter & Harris (fig. 5)
    Type I: fracture through the epiphyseal plate.
    Type II: fracture through the epiphyseal plate and the metaphysis (most common)
    Type III: fracture through the epiphyseal plate and the epiphysis.
    Type IV: fracture through the epiphyseal plate, metaphysis and epiphysis.
    Type V: crush injury of the epiphysis.

    Memory aid based on the epiphyseal plate:  SALTeR Same level (I),Above (II), Lower (III), Through (IV), Ruined (V).

Figure 5. Epiphysiolysis as per Salter & Harris classification.

Checklist:

  1. Is everything imaged correctly and suitable for evaluation? (image in multiple directions!). 
  2. Is there soft tissue swelling?
  3. General impression of the bone (including osteoporosis, intra-ossal lesions).
  4. Check each cortex. Are there sharp or rounded cortex interruptions?
  5. Secondary signs of a fracture? (asymmetry, abnormal position, periostal response, changes versus old images).

Description of Fractures:  

Descriptions based on typical fracture types (fig. 6/7).

Figure 6. Various fracture types.

Figure 7. Spiral fracture of distal fibula (a) Avulsion fracture of the quadriceps tendon with retraction of the muscle (b).

Note: the above fracture types are less applicable in non-tubular bones (e.g. fractures of the calcaneus and carpal bones). In this case the terms ‘horizontal, vertical, coronal, sagittal or axial’ fracture lines are more appropriate.

Essential information

  • Location: proximal, middle, distal
  • Type of fracture line (see fig. 6)
  • Position:
    •    extent of dislocation (= displacement); medial, lateral, anterior, posterior, volar/dorsal, radial/ulnar.
    •    angulation
    •    rotation
    •    shortening (particularly in oblique fractures)

Practical information to add to a fracture description:

  • To avoid confusion, the following terms are used for the hands: volar (= palmar side) & dorsal (= back of hand). Use radial and ulnar for lateral and medial respectively.
  • Dislocation and angulation are usually described from the perspective of the distal fracture fragment.  See figure 8 as an example.

Figure 8. AP image (a) and lateral image (b) of the right lower leg/ankle. Extra-articular transversal fracture of distal tibia with dorsolateral dislocation over a half shaft width.

Fracture Mimics:

  • Unfused epiphyseal plate (= growth plate), e.g. in the elbow and shoulder (see fig. 3b, section General).
  • Unfused apophysis (= ossification center where tendon inserts). The apophysis at the base of metatarsal V is a notorious fracture mimic.
  • Accessory ossification centers, particularly in the feet (fig. 9).

In all the above-described mimics, it is crucial to evaluate older images. 
Additionally, when in doubt, it is useful to consult a book of reference describing the normal variations of the skeletal system (e.g. Keats, T.E.; Atlas of Normal Roentgen Variants That May Simulate Disease). Each Emergency Assistance department should have such a (thick!) reference book.

Figure 9. Lateral ankle image with an accessory ossification center dorsal from the talus; the os trigonum.

Sources:

  • Radiologic reporting of skeletal trauma.M J MJ Pitt and D P DP Speer Radiol Clin North Am 28(2):247-56 (1990)
  • B.J. Manaster et al. The Requisites – Musculoskeletal Imaging. 2007
  • N. Raby et al. Accident & Emergency Radiology – A Survival Guide. 2005.

Author

  • Annelies van der Plas, MSK radiologist Maastricht UMC+

24/01/2014 (translated 23/08/2016)

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