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Mechanism of pelvic injury

Pelvic Injuries Anatomy Mechanism of pelvic injury

Mechanism of pelvic injury can be broadly divided into two types: Low-energy and High-energy.

1. Low-energy injury resulting in isolated fracture with an intact pelvic ring. Common examples are:

Avulsion fracture (Usually in young athletes with sudden muscular contraction. Common sites are ASIS/AIIS/Pubis)
Direct fracture (Usually from a low impact fall. Common sites are the iliac crest or ischium)
Stress fracture (Caused by osteoporosis or malignancy. Common sites are the pubic rami or the sacro-iliac joint)

*Fig.16 Pelvic x-ray with an avulsion fracture at the Left Anterior Inferior Iliac Spine*. Image via Radiopaedia.org. Case courtesy of Dr Mark Holland

These types of low-energy injury are considered stable and can usually be managed with analgesia and rest.

Learning bite

It is important to be cautious when assessing low-energy injuries in the elderly, especially in females >80 years old where low energy impact is a main cause of pelvic ring injury.

2. High-energy injury resulting in disrupted pelvic ring

As mentioned before, the pelvis can be considered as a ring structure, which means a break in one area of the ring is usually accompanied by a break in another area of the ring. This depends on the mechanism and direction of force:

A. Anteroposterior Compression (APC) (Grade 1-3)

Usually results from frontal or head-on collision road traffic accidents. Force is transmitted from the anterior pelvis through to the posterior. This type of injury causes a widening of the pelvic ring as the pubic symphysis separates. Widening of the sacroiliac joints at the back of the pelvis can also occur, causing internal bleeding. This type of fracture is also known as “open book” fracture.

Fig.18 Edited image via *Radiopaedia.org.* *Case courtesy of Dr Matt Skalski*

Question 1

B. Lateral Compression (LC) (Grade 1-3)

Side on impact causing lateral compression of the pelvic ring to buckle and break. This is the most common type of pelvic fracture from a motor vehicle collision.

Fig.19 Edited image via *Radiopaedia.org.* *Case courtesy of Dr Matt Skalski*

Question 2

There is a theoretical risk that a pelvic binder may worsen this type of fracture, however it is impossible to identify types of injury by clinical assessment alone. It is better to apply a pelvic binder to stabilise the fracture and control potential bleeding.

C. Vertical Shear (VS)

Fall from a height on one leg or axial load mechanism causing displaced fractures of the anterior rami and posterior column with SI joint dislocation. This type of injury is vertically unstable and always requires operative management. Traction may be required to stabilise the hemipelvis.

Fig.20 Edited image via *Radiopaedia.org.* *Case courtesy of Dr Matt Skalski*

D. Complex Pattern Injury

When pelvic injuries involve a combination of two or more of the fractures described above, these are classified as complex pattern injuries and are completely unstable.