Definition

A sacral fracture is a break in the low portion of the spine located in the posterior side of the pelvic ring between the two hipbones.

Pathology

A fracture to the sacrum mostly occurs via trauma or as a stress fracture. The latter is common with overuse in athletes and military due to repetitive, submaximal pressure to the bone, which ultimately gives way. It is also present in the elderly with osteoporotic bones. Due to the density of nerves passing through the sacrum, a fracture in this region can be associated with nerve injuries, leading to serious neurological consequences.

Classification

Based on the Denis Classification a sacral fracture is defined according to the area where the break occurs:

Zone I: Fracture across the sacral ala, lateral to the foramina, is possibly associated with impingement of L5 nerve root (in about 5% of patients it is linked to neurological injury). It is the most common type of sacral fracture.

Zone II: Fracture through the neural foramina is associated with neurologic bladder; requires surgery for removal (debridement) of bone fragments, followed by reduction and internal fixation (posterior approach).

Zone III: Fracture across the entire sacral body has a high risk of neurologic injury (bowel, bladder, sexual dysfunction) in over 60% of patients. These fractures can be transversal (severe nerve dysfunction) or U-type, also named spino-pelvic dissociation (caused by axial loading).

Sacral fractures can be stable or unstable as well as comminuted or non-comminuted. In unilateral shear fractures of the pelvis caused by high energy trauma, a fracture to the pubic rami and posterior sacroiliac complex, if complete, is highly unstable and possibly associated with nerve injury and damage to internal organs.

Causes

Sacral fractures are usually caused by a direct trauma to the lower spine, which may result from a high energy impact. They can also occur when falling on one leg from a significant height posing heavy load on one side of the sacrum. Stress fractures can result from overuse and persistent load on the bone either following extreme physical activity in trained athletes, strenuous sport activities in non trained individuals and in older people with fragile, osteoporotic bones. The main causes for a sacral fracture include:

Car accidents

Fall from a significant height in young people

Fall from low height in elderly people

Extreme sport

Intense military training

Risk factors

Leading risk factors for a fracture to the sacrum include:

Frequent automobile driving

Working at height (carpenters, electricians, builders, painters)

Intense sport activity in athletes

Lack of physical fitness

Elderly age

Female gender: lower bone density after menopause

Conditions affecting the bones (osteoporosis, Paget disease, bone cancer)

Chronic medical conditions (hyper-/hypotension, stroke, heart arrhythmia, thyroid dysfunction)

Sacral defect

Asymmetric leg length

Congenital spine malformation

Spina bifida

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Symptoms

A fracture to the sacrum usually triggers an immediate and severe pain in the lower back. The patient is likely unable to move, stand up and walk. Depending on the severity of the fracture, a sacral fracture may present with various degrees of neurologic dysfunction. The most common symptoms are:

Pain to lower back, buttocks and hip

Pain in the front of the thigh and groin

Bruising and swelling around the sacral area

Changes in bowel and bladder function

Sexual dysfunction

Weakness of the legs

Treatment

Nonoperative treatment

An isolated fracture to the sacrum with a displacement below 1 cm without neurologic complications is normally treated conservatively. This includes an initial bed rest with analgesia to treat pain, followed by gradual weight bearing, exercise to restore flexibility to the lower spine and wearing an orthotic support to the lower back. The nonoperative treatment of a sacral fracture increases the risk of bone displacement and requires frequent monitoring by X-ray. In more serious fractures, surgery is avoided if the patient presents medical conditions that pose a risk of complications.

Surgical treatment

If a sacral fracture presents a displacement over 1 cm and is associated damage to soft tissue, persistent pain or delayed displacement, surgery is necessary. Decompression of the fracture is performed in case of neurologic damage. Numerous methods are available for the fixation of the sacral fracture that are suited to the particular anatomy of this region of the spine.

Percutaneous screw fixation whereby screws are placed through the skin (percutaneous) into the sacroiliac, trans-sacral or trans-iliac trans-sacral region. This approach is recommended in sagittal plane fractures. Caution is necessary not to injure the L5 nerve root or cause overcompression of the fracture potentially resulting into iatrogenic nerve dysfunction. This technique is prone to complication and cannot be used in osteoporotic bones or for the removal of bone fragments.

Posterior tension band plating may be performed via two incisions from the posterior side in addition to ilio-sacral screws. The larger opening allows a direct access and visualisation of the fracture. Ilio-sacral and lumbo-pelvic fixation is an invasive posterior approach to the lumbar spine and sacrum using pedicle screw fixation. The iliac screws are inserted in parallel to the angle of the outer ilium. Alternatively longitudinal and transverse rods can be used.

Decompression of neural elements consists in the fracture reduction using axial traction or via a posterior surgical approach followed by laminectomy or foraminotomy (opening of the foramen).

Sacroplasty means the reconstruction of the fractured sacrum using injection of glue-like materials (polymethylmethacrylate, PMMA) directly into the fracture.

Complications

Local infection: requiring antibiotic treatment as a preventive measure

Iatrogenic nerve injury: caused during surgery due to metal misplacement or exaggerated compression of the fracture

Malreduction: particularly in vertical displaced fractures

Deep vein thrombosis (DVT) and pulmonary embolism: thrombosis mostly occurs in the deep veins of the lower limbs due to prolonged immobility. Patients are usually treated with prophylactic administration of anti-clotting medications (Heparin).

Pressure ulcers: due to prolonged immobilisation and the fragile skin in the elderly, the pressure of the weight on specific areas of the body can form skin ulcers. This can be prevented using specific bed characteristics, massage and frequent reposition of the patient. When pressure ulcers become infected they need immediate antibiotic treatment.