Fractures | Shape

n general, a fracture at the microstructural level results in a break in the columns of the osteons and or the cross bars of spongy bone. The splintering of bone at a microsrtructural level can be appreciated in the image below. Depending on the forces imposed, and the makeup of the bone, there will be variation of the shape of the actual fracture line. The resulting position of the fracture fragments may affect the shape the fracture as well.

Shape of the Fracture Line – Macroscopic Insight into Microscopic Changes

These images afford us the opportunity to get a sense of the irregular jagged edge of trabecular bone (a) because the resolution of the fracture is so clear in the X-ray image. The X-ray is of the ankle in a 15 year old male in the anteroposterior projection (A-P) and shows an avulsion fracture of the anterior portion of the distal tibia. Note the spikes of broken trabecular bone. The jagged edge is drawn across the fractured vessels in b. The shape of the fracture line is reminiscent of the spikes of splintered tree from the weather induced fracture of the tree stump (c).

Variations of the Shape of the Fracture Line

The basic shapes of the fracture line include transverse, oblique, and spiral. The following examples represent the shape of the fracture line.

Three Basic Shapes of Fractures

This A-P examination of the proximal right tibia shows an overlay reflecting the most common shapes of long bone fractures including a transverse fracture (a), oblique fracture (b) and a spiral fracture (c).

Examples of the shapes described above are shown below.

Transverse Fracture through the Base of the 5th Metatarsal

This X-ray shows a simple transverse fracture of the base of the shaft of the right fifth metatarsal with the position of the fracture fragments being anatomically aligned resulting in an overall normal shape to the bone. Image b shows the fracture overlaid in black. .

Spiral Fracture – 3 Fragments

The X-ray of the right humerus in A-P projection is from a 76 year old male and shows comminuted spiral fracture consisting of three fragments with a middle triangular or butterfly fragment. (dark green). There is reasonable anatomic alignment with excellent bone on bone contact. The fracture was treated with a sling and follow up 4 months later showed excellent healing .

Spiral Fracture with a Butterfly Fragment

The X-ray of the right ankle in the lateral projection shows a comminuted oblique fracture of the fibula with with a butterfly fragment (overlaid in turquoise in b) A fracture of the distal tibia is subtly visible on this projection on the anterior aspect of the tibia, but was better appreciated on the A-P projection The close relationship of the two bones in the ankle region and the presence of an interosseus membrane that binds the two bones into a single unit makes combination fractures common. .

Describing the Shape of a Fracture when the Fragments are Angulated

When fracture fragments are angulated there are a variety of ways of describing the fracture line. The easiest method is to define the direction of the apex of the angle created when the vectors of both fragments are drawn.

Shape of the Fracture Line and Shape Described by the Fragments

The A-P projection of the left humerus (a), is from a 76year old female who fell. Initial assessment of her X-Ray (b) defines a simple (size = 2 fragments) oblique (shape = green line, 3) fracture through mid shaft of the left humerus (position). This fracture is more complex because of the angulation created by the distal fragment (3) in relation to the proximal fragment (2. Management of the fracture will be decided based on the position of the fragments relative to each other. In this case (c) by drawing the vector of fragment 1 and 2 it is noted that there is angulation pointing laterally (yellow lines in c), and hence the fracture is described as being laterally angulated. In addition the fragments are distracted and bone on bone contact is limited. The need to intervene to improve bone on bone contact and improve alignment is necessary in this case. External manipulation was utilized with success.

Describing Angulated Fractures

The language utilized in describing the angulation of fractures can be quite confusing. The easiest method is to describe the direction of the apex of the angle when two lines are drawn along the axis of the vectors of the main fragments.

Language of Angulated Fractures

The diagram defines the language used in angulated fractures. The green lines represent the vectors of the fragments and the angle they form at the apex of the intersection. Image (a) shows a fracture that is laterally angulated so described because the apex of the angle points laterally. Similarly image (b) represents a medial angulation, image (c) a posterior angulation, and (d) an anterior angulated fracture.

The language is further confounded by the use of some traditional descriptors such as varus and valgus which are alternate descriptors for lateral and medial angulation

Examples and Alternate Language

The diagram labeled (a), shows representation of a fracture that has the apex angulated laterally. Image (b) shows a intertrochanteric fracture of the proximal left femur, with similar lateral angulation. This type of angulation is also known as varus angulation. Varus is a Latin word which means bow legged. A bowlegged stance is shown in image c. The diagram labeled (d), represents a fracture that is angulated toward the medial aspect. Image (e) shows a distal fibula fracture, with similar medial angulation. This type of angulation is also known as valgus angulation. Valgus is a Latin word which means “bandy legged or knock kneed. A knock kneed stance is shown in image (f).

Valgus and varus are common terms used in orthopedic medicine and the similarity of the words makes it difficult to recall the definition of each. Mnemonics have been used over the years to help remember the terms and a favorite is described below.

Varus the Pig?

The descriptions of a “valgus” and “varus” deformity are orthopedic terms referring angulated shapes not only in fractures but also in joint or bony deformities. Varus deformity is the term used for the inward deformity of the distal fragment and valgus the outward deformity. Varus means “bow legged”, and valgus “knock-kneed” and they are not only used to describe knee deformity but also deformity in other areas in orthopedics. That the words sound so much alike , there is often confusion in the terminology. Thus one of the mnemonics is to describe an old Russian woman walking down the street who is surprised by a pig that runs through her legs. She looks down between her legs and exclaims “Varus is the pig?” Because this is so ridiculous it is memorable. Another way of remembering the varus deformity is to recall the “air” of “v-air- us” describing the large amount of “air” between the legs or the “r” of varus refers to round so there is an inner roundness between the bow legged knees. The two fragments of valgus form an “L” is another method to help memorize the position of the fragments. The simplest is the description of the direction of the apex of the angle.

Language of Angulation of Hand and Foot Fractures

The language of angulated fractures around the hand and wrist are sometimes confusing as well. Which is the anterior surface and which is the posterior surface of the hand for example? By convention the anatomical position of the hand is with the palms facing forward, and thumbs facing laterally (in supination). Therefore the palmar surface which is also called ventral surface is the anterior surface while the volar surface also called the dorsal surface is the posterior surface. Additionally some descriptors relate to the direction in relation to the ulnar or radius. Thus terms such as “ulnar deviation” are used. In this context it is best to remember that the thumb and radius go together so that any descriptor that defines radial direction infers positioning in relation to the thumb (and therefore lateral)and those that define ulnar direction are pointed to the pinky and therefore medial. When there is displacement of a fragment the convention is to describe the displacement of the distal fragment.

The most common fracture around the wrist is the Colle’s fracture which classically has the apex of the angulation pointing ventrally.

Apex of the Fracture Showing Ventral Angulation in a Colle’s Fracture

The image demonstrates the lateral projection of an X-ray from a 40 year old man who fell on an outstretched hand and sustained a fracture of the distal radius. This fracture is called a Colle’s fracture and is characterized by its location being about 1.5 inches from the distal end of the radius, at the weak portion of the distal radius where the diaphysis meets the metaphysis called the at the cortico-cancellous junction. Additionally it is characterized by dorsal displacement of the distal fracture fragment but with ventral angulation of the apex of the fracture.

The specific shape of the Colle’s fracture is very specific and has been called the fracture with the dinner fork or bayonet deformity. The following images describe that shape.

Dinner Fork or Bayonet Deformity

In the Colle’s fracture the shape of the combined appearance of the proximal fragment, distal fragment and the carpals and metacarpals on clinical and lateral radiological examination is reminiscent of a dinner fork (or bayonet) and hence the deformity is called dinner fork or bayonet deformity. The apex of the angulation of the fracture is ventral, the distal fragment (red), is dorsally positioned in relation to the proximal fragment (green) forming the shaft and first portion of the head of the fork. The carpal bones and the metacarpals (blue) complete the remaining convex shape of the fork

In the foot the convention is to have the bottom of the foot directed posteriorly imagining the foot of a ballet dancer in an “en pointe” position on her toes. In this position the plantar surface points posteriorly and so it is also called the dorsal surface or posterior surface, while the front ventral or anterior part of the foot points anteriorly

Shape of Fractures Unique to the Pediatric Population

These fractures have previously been described but since they present with unique shapes and it is felt that they are briefly revisited in the context of the “shapes” of fractures.

A Little Crack

This X-ray shows a simple greenstick fracture of the distal shaft the radius of a 9month old child. Image b shows the fracture overlaid in black to enable better appreciation of the fracture. The name “greenstick” is used since the shape changes are reminiscent of the shape changes and fracture lines that occur with a young pliable branch of a tree. When such a branch is subjected to a breaking force it results in one of three fractures. The first is a transverse break on one side and extending along the long axis of the bone and without traversing the full width of the bone. This is an example of that type of greenstick fracture.

A Little Ruffle

Buckle or Torus Fracture of the Distal Radius

This X-ray shows a simple buckle or torus fracture of the shaft of both the radius and ulna in a young child. Image b shows the deformity overlaid in green. Torus fractures, or buckle fractures, are common injuries seen in children. The softer bones of children allow the bone to yield to the force without fracturing the bone and the bone just buckles; this is also known as an incomplete fracture. The mechanism this injury by falling on an outstretched hand. “Torus” is derived from the Latin word ‘tori’ which means swelling or protuberance. This is the clinical appearance of the deformity of the forearm. Treatment of the injury is by casting for a short duration, usually about three weeks. These injuries tend to heal quickly.

Bowing Fracture of the Radius and Ulna

This X-ray shows a bowing deformity fracture of the shaft of both the radius and ulna in a young child. Image b shows the deformity overlaid in green. Bowing fractures usually occur in the forearm and is a bending deformity without a grossly visible fracture or macroscopic break of the cortex. Microfractures are visible on microscopic evaluation. Periosteal reaction may not occur on subsequent imaging

References

Goldfarb, C A, Yuming Yin, Y, Gilula, L A, Fisher, A J, and Boyer, M I Wrist Fractures: What the Clinician Wants to Know Radiology Vol 219 pages 11-28 2001

Rang, M, Pring, M.E., Wenger, D R. , Rang’s Children’s Fractures 3rd Edition 2005 Lippincott Williams and Wilkins Philadelphia

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