Pelvic Fractures - Causes

Authored by Dr Mary Lowth, 12 May 2017

Patient is a certified member of
The Information Standard

Reviewed by:
Dr John Cox, 12 May 2017

Major pelvic fractures are caused by major trauma such as road traffic accidents, crush injuries (for example, being run over by a car or rolled on by a horse) and falls from height. Pelvic fractures caused by high-force or high-speed injuries are often unstable and they need urgent hospital treatment.

Less severe fractures which involve undisplaced fractures can occur after falls or trips, particularly if the bones are 'thin' (osteoporosis). For this reason painful but stable fractures are more common in elderly people who tend to have 'thinner' bones, and who are sometimes prone to falls.

Because the pelvis is a ring of bones, when forceful injury causes a fracture in one part of the structure, there is often a matching fracture at the opposite point in the ring. There are several common patterns, which depend upon the direction and severity of the trauma.

Stable and unstable fractures

Perhaps the most important way of classifying pelvic fractures is into stable or unstable fractures. Most pelvic fractures are stable:

Stable fracture: the broken bones are still properly lined up, so that the ring has kept its shape. Usually only one bone is affected, with a single fracture.

Common fracture patterns include: breaks across the top of one ilium, cracks to the pubic ramus on one side, or cracks in the sacrum. In each of these cases the other bones are intact and will keep the bony ring of the pelvis together. Pelvic avulsion fractures (in which a fragment of bone is broken off by the pull of a muscle) and pelvic stress fractures (hairline cracks which do not extend all the way across the bone) are also types of stable pelvic fractures.

Unstable fracture: this usually occurs when there are two or more breaks in the pelvic ring and the ends of the broken bones move apart. This type of fracture is more likely to occur after high-impact injury and there may, therefore, be other associated injuries.

These injuries involve much more bleeding than stable fractures, as the separation of the broken bones allows them to bleed much more freely. They may also involve direct damage to the internal organs.

There are some typical patterns of unstable fractures. These include 'open book' fractures, when the pelvis is broken at the front and the back by severe force from the front, and lateral (or sideways) force fractures which often fracture the pubic rami and the sacroiliac joints, sometimes also involving the hip socket.

Open and closed fractures

Pelvic fractures, whether stable or unstable, can also be divided into 'open' fractures, in which injuries to the skin mean that the broken bones are visible, or 'closed' fractures, in which the skin is not broken. Open fractures are more serious because infection can easily reach the wound, which may already be contaminated from the injury.

A pelvic avulsion fracture occurs when the tendon of a muscle comes away from the bone, taking a small chip of bone with it. This most commonly occurs at bottom of the ischium where the big hamstring muscles are attached, or on the front of the ilium where one of the large quadriceps muscles attaches.

These types of fractures typically occur during sports that involve speed and sudden stops, particularly in young people who are still growing. Examples are hurdling, sprinting, long-jumping, and soccer (particularly miskicks that hit the ground). A pelvic avulsion fracture may also be caused by a car accident.

Pelvic stress fractures are caused by repeated stresses to the bone, usually due to sport. They usually affect the pubic bone and cause exercise-related pain which gets gradually worse, but they do not usually prevent exercise. Sports involving repeated impact, such as running or jumping, carry the highest risk. Stress fractures often occur in those who suddenly increase their training distance or activity level, including sedentary people who suddenly start to exercise. They are uncommon in the pelvis, although more common in women and those with 'thinning' of the bones (osteoporosis).

Significant pelvic fractures can occur in anyone who experiences a major trauma. Less severe, stable fractures are most commonly seen in elderly people, particularly those with 'thinner' bones (osteoporosis). Avulsion fractures are particularly common in sporty teenagers. Stress fractures are typically seen in runners, although they more commonly affect other sites than the pelvis.

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