Sacrum fracture
Posterior view of the sacrum anatomy relative to the pelvic ring

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.

Illustration of the sacral plexus where several nerves including the sciatic nerve depart from

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.

Sacral fractures are categorised in relation to the anatomical area where they occur

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.

Left: Distal radius intraarticular, displaced fracture; Middle: Older distal radius fracture with callus formation; Right: Distal radius and ulna fracture, extraarticular and displaced

No 2.

Intra-articular fracture extends to the wrist joint (or articulation)

Extra-articular fracture is located outside of the wrist joint

Open fracture when bone fragments perforate the skin

Comminuted fracture when the bone breaks into multiple fragments

Non-displaced when the anatomical alignment of the bone is maintained or displaced when the bone fragments move apart.

Melone’s classification describes the characteristics of intra-articular fractures of the radius:

i    Stable fracture

ii    Unstable "die-punch"

iii   "Spike" fracture

iv Split fracture

v   Explosion injuries

Acetabular fracture of the pelvis

Acetabular fractures

These fractures are divided into:

Anterior pillar (not weight bearing part of joint)

Posterior pillar (often associated with dislocation of the hip including the weight bearing part of joint)

Transverse

Comminuted involving both column type 

Sacral / coccygeal fractures

The sacrum is a triangular-shaped bone formed by 5 fused vertebrae, which provide a posterior wall to the pelvic ring. At each side of the sacrum, the ala structures articulate with the ilium bones forming the sacro-iliac joints. Sacral fractures are usually parallel to the spine and can involve the ala. Less frequently sacral fractures may display an “H” shape, including a transversal fracture uniting both sides of the sacrum. Three zones are described where sacral fractures can occur that are along vertical lines relative to the alignment of the foramina. Sacral fractures may result in sacral instability and require treatment via sacroplasty (injection of bone glue into the fracture). Surgery is necessary in case of associated neurological symptoms.

Fractures of the coccyx involve the tailbone, the terminal portion of the spine situated below the sacrum formed by 3 to 5 fused vertebrae. Coccyx fractures occur when falling on a seated position. They are more common in elderly women and seldom require surgical treatment.

Falls from hight are a potential cause of sacral fractures

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

Strenuous sport activity is a risk factor for sacral fractures

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

Congenial spine malformation, Spina bifida

Pain to the lower back is a typical symptom a sacral fracture

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

3-D CT scan reconstruction of a sacral fracture in Zone III longitudinal

Diagnosis

During medical examination the physician will perform a simple test to detect a possible displacement of the sacral fracture along the vertical plane by applying one hand onto the pelvic iliac crest and the other hand pulling the leg. If displaced this will cause a displacement in vertical plane.

The diagnosis is confirmed with X-rays with inlet view (sacral canal and S1) outlet view (antero-posterior of sacrum) and cross-table lateral. Only 30% of fractures are visible through X-rays.

Superior images are obtained via CT scan with coronal and sagittal views or an MRI in case of neurologic involvement, to better characterise the fracture type and the involvement of other injuries to the pelvis and hip. The orthopaedic surgeon will opt for the best treatment suitable to the type of fracture and the general condition of the patient.

Treatment

Orthotic support of the lower back is helpful in conservative treatment of sacral fractures

Nonoperative treatment

A 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.

Sacral fracture before and after lumbo-sacral fusion under frontal and side views

Surgical treatment

If a sacral fracture presents a displacement above 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 and 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 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-likematerials (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.

Using crutches in deambulation supports patients in  the recovery from a sacral fracture

Rehabilitation

A sacral fracture requires an initial period of bed rest during which the patient may commence gentle exercise guided by a physiotherapist. The patient will undergo a transition from non-weight bearing to partial weight bearing until it is advised to stand on full weight. This phase may require full time assistance for daily living activities. A wheelchair, crutches or a walker may be used to support the patient during the first weeks up to 12 months after a sacral fracture.

Physiotherapy during the first 6-12 weeks post surgery include:

Ice/heat treatment

Anti-inflammatory therapy (NSAIDs)

Calcium and vitamin D administration

Exercise to strengthen quadriceps, hamstrings and gluteal muscles

Hydrotherapy

Massage

Guided return to activity

Use of walking devices

The use of a walker or a stick is useful to prevent falls and fractures in the elderly population

Prevention

The main prevention is avoidance of falls with the use of supporting devices and reduction of falling hazards at home and work place. Prevention of osteoporosis includes the administration of the bisphosphonate group of drugs with additional supplements of calcium and vitamin D.

Other preventive measures include:

Exercise and maintenance of muscular strength in the elderly (walking, swimming)

Use of supporting walking devices in the elderly