Any complete or incomplete interruption of the physical integrity of the os sacrum may be described as a sacral fracture.
Clinical presentation varies largely. On the one hand, traumatic fractures may be diagnosed in patients reporting with a history of trauma. Falls and other accidents that provoke pain of lower back and pelvic region usually prompt a thorough workup to identify its source. However, SF may be overlooked even in these classic cases since patients usually have multiple fractures and symptoms are often ascribed to those that don't affect the sacral bone. Athletes are more susceptible to stress fractures, but intense training is not required to suffer such lesion. Anamnesis may even reveal less hints at SF in patients who present with pathological fractures of the os sacrum. Osteoporosis or other, previously diagnosed skeletal disorders may point at a pathological fracture but don't reveal its location.
Commonly observed symptoms are lower back or pelvic pain, possibly pain radiation to abdomen, groin, buttocks and legs and limited hip range of motion. The skin covering sacral and pelvic region is usually tender. Complaints often worsen under exercise while symptoms may completely subside at rest.
Because most SF affect zone I, neurological deficits are rarely presented. If experienced, they may comprise radiculopathy and myelopathy with paresthesia, numbness and blunted reflexes. Sphincter control may be impaired .
Patients who present with multiple fractures - pubic fractures are frequently associated with SF - may present additional symptoms that mask sacral lesions. Here, pain and tenderness are located at the site of other fractures.
After anamnesis and clinical examination, plain radiography is usually chosen as first-line diagnostic imaging tool. However, most SF are not readily recognizable on plain film . Fracture lines may only be visible in cases of chronic pain and thus in older fractures, or if accompanied by displacement. In patients suffering from multiple fractures, other fractures may be visible and this fact often leads to SF being overlooked.
More sophisticated diagnostic imaging, e.g., magnetic resonance imaging and computed tomography scans, are the method of choice to confirm the diagnosis of SF and to assess their extent. The former allows for an additional evaluation of soft tissue injury which may account for neurologic deficits.
If patients are diagnosed with stress or pathological SF, radiographic examination and bone density measurements should be carried out to assess the overall condition of the patient's bones. If osteoporosis can't be confirmed, additional diagnostic measures may be indicated to identify the source of fragile bones.
Most SF may be treated conservatively. Patients should rest and receive analgesics; return to everyday activities should take place gradually. During recovery, a corset, brace or cane may be required to reduce physical loads on the sacral bone. However, depending on the anticipated recovery time, immobilization of the pelvic region may be associated with significant risks of vein thrombosis and thromboembolism. For each individual patient, these risks should be balanced against possible benefits and risks of minimally invasive surgery. Sacroplasty is a safe procedure that can be realized in a percutaneous approach, may significantly reduce pain, improve mobility and life quality. Early mobilization considerably shortens recovery times.
Classic osteosynthesis is indicated in those patients presenting with unstable, traumatic SF. Combined approaches, i.e., sacroplasty and classic fixation may be required to repair SF affecting osseous tissue of reduced density .
If an underlying disease has been identified, it should be treated accordingly to prevent future bone fractures.
Most SF have a good prognosis if adequately treated. In detail, prognosis depends on extent and severity of neurologic damage. Contrary to osseous lesions, the latter may be irreversible and leg movement, micturition, defecation and sexual activity may remain permanently restricted.
Any SF results from mechanical loads that exceed the resistance of the sacral bone. This allows classification of SF in two categories, namely traumatic fractures and pathologic SF.
The former are mainly diagnosed in patients who fell or who were involved in motor vehicle accidents, sports accidents or similar traumas that lead to physical overload of the os sacrum. Additionally, stress fractures resulting from continuous overload of healthy bones, inducible, for instance, by overtraining, are considered traumatic fractures.
In contrast, pathologic SF - they are sometimes also referred to as insufficiency fractures - may occur spontaneously or after sustaining minor trauma. Here, alterations in bone structure cause an intrinsic weakness of the osseous tissue. A variety of primary diseases may account for this condition, with osteoporosis being the most frequent reason for reduced bone densities. Since osteoporosis typically affects elder women, most patients presenting with pathologic SF pertain to this patient group. However, SF are not frequent complications of osteoporosis . Also, this condition is not limited to the elderly and osteoporosis may develop during or after pregnancy and thus predispose these women for SF . Besides osteoporosis, other disorders associated with altered bone metabolism may also render affected individuals more susceptible to SF. In this line, osteopenia, hyperparathyroidism, Paget's disease, rheumatoid arthritis, hip arthroplasty, prolonged use of corticosteroids and irradiation of the pelvic area shall be mentioned as examples . This list is by no means complete.
Epidemiology of SF varies between traumatic fractures and pathologic fractures. The former may affect patients of any race, both genders and any age. Even young, healthy athletes are susceptible for this kind of fracture, particularly if stress fractures are considered. Here, women are affected more often than men because even healthy females have a lower bone density than males and thus, their bones are less resistant to mechanical loads . This situation becomes even more apparent in post-menopausal women when serum estrogen levels diminish and bone density decreases further.
Pathologic fractures are more frequently observed in the elderly, particularly in women suffering from osteoporosis. Due to the physiological processes described above occurring in women that are contributing to lower bone density, it is not always easy to distinguish between a traumatic fracture in a healthy patient and a pathologic fracture in an individual suffering from skeletal disorders.
While traumatic fractures are generally diagnosed soon after occurrence, this is not necessarily the case for pathologic fractures. Indeed, pathologic SF prevalence is assumed to be highly underestimated because non-specific symptoms are usually ascribed to other diseases .
Pathophysiological events associated with SF largely depend on their precise location. As has been indicated above, SF a roughly divided into three types that affect zones I, II, and III of the sacral bone, respectively. Most SF affect zone I and cause only minor neurological deficits. If fractures pass through anterior or posterior foramina, i.e., if they are located within zone II, unilateral neurological failures due to compression or transection of single spinal nerves are to be expected. SF affecting zone III are generally more severe than the aforementioned types of fractures and may even induce cauda equina syndrome.
Spinal nerves originating from the sacral bone form part of the lumbosacral plexus. Other nerves contributing to this nervous network leave the vertebral column at distinct levels of the lumbar spine. And although roots of the latter are not directly affected by SF, tension exerted by displacement of more caudal osseus structures may eventually damage these nerves. This applies particularly to traumatic fractures that occur due to high mechanical stress.
Besides the above mentioned classification system, others have tried to describe SF and to associate certain patterns with specific symptoms. In this context, transverse fractures may be distinguished from vertical ones. The former are less frequently observed and are often related to more severe symptoms, e.g., to cauda equina syndrome. According to the aforementioned classification system, they affect zone III, but in fact, they usually pass through all zones of the sacral bone. High and low transverse SF may be differentiated . Additional categorization has been proposed regarding the final position of bone fragments, displacement and angulation.
In order to prevent traumatic fractures, the appropriate safety measures should be taken while riding a car or doing sports. Exercise is the main cause of stress fractures and therefore, exercise intensity should be augmented gradually. Overtraining should be avoided. In general, sports strengthen musculature and skeleton and are highly recommendable. Further preventive measures aim at maintaining or increasing bone density and thus are those recommended to prevent osteoporosis.
The os sacrum is composed of five sacral vertebrae that have grown together. It constitutes one of the lower parts of the vertebral spine and corresponds to the posterior portion of the osseous pelvis ring. The base of this bone connects to the lumbar spine while its apex is associated with the os coccyx. Additionally, it disposes of bilateral, articular surfaces joined to the ilium. This joint is designated sacroiliac joint. Spinal nerves that originate from the os sacrum form part of the lumbosacral plexus and mainly supply the pelvic region and the lower limbs.
If the physical integrity of the os sacrum is interrupted because mechanical forces exceed the resistance of that bone, the affected individual will sustain a sacral fracture (SF). Both factors, i.e., intense mechanical loads as well as reduced resistance, may account for SF. The former may be observed in patients of any age and usually occurs in falls, motor vehicle accidents or sports accidents. The latter is mainly a problem of elder women who suffer from osteoporosis. Here, bone density is considerably decreased and mechanical loads easily tolerated by healthy individuals cause the sacral bone to break.
SF may occur as an isolated fracture, but those forces that provoked SF often compromised parts of the pelvic bones, too. It has been estimated that nearly half of all patients presenting with pelvic fracture suffer from isolated or combined SF . Most commonly, SF are associated with pubic fractures.
SF may affect any part of the bone and while there is no universally accepted classification of such fractures, according to a retrospective analysis conducted several years ago, SF may affect either one of three sacral regions and each region is related to more or less specific symptoms :
While stable SF may be treated conservatively, instable and displaced fractures require surgical intervention, reduction and fixation. The precise characteristics of SF highly depend on the integrity of the pelvis. As long as the latter compresses the sacral bone, SF are usually stable. This is the case for lateral compression pelvic fractures. As soon as vertical shear forces act on broken pelvic and sacral bones, SF becomes unstable.
There are two main causes of SF: On the one hand, a person may sustain a severe trauma, e.g., they may fall, be involved in a motor vehicle or car accident. This trauma may submit the sacral bone to physical stress it can't resist. On the other hand, minor or even barely noticeable traumas may cause SF if the bone density of the sacrum is significantly decreased. In most cases, such a reduction in bone density is caused by osteoporosis, but a variety of other conditions may have similar consequences. Osteopenia, hyperparathyroidism, Paget's disease, rheumatoid arthritis, hip arthroplasty, prolonged use of corticosteroids and irradiation of the pelvic area may serve as examples.
SF may be associated with pain in the lower back or pelvic area. This pain may radiate to abdomen, groin, buttocks and legs. The hip motion range may be diminished. Symptoms usually aggravate during exercise, while they may relieve considerably while at rest and lying down.
In rare cases, neurological failures may be experienced. These may comprise a tingling sensation or even numbness in legs and pelvic area as well as the inability to control the sphincters of urinary bladder and anus.
Only few SF are reliably diagnosed by means of plain radiography. In general, magnetic resonance imaging or computed tomography scans are recommended to evaluate the condition of the sacral bone. The former also allows for an assessment of soft tissue injury which is of utmost importance since severe cases of SF may be related to neurological deficits due to spinal nerve damage.
Conservative treatment, i.e., bed rest, analgesics and gradual return to day-to-day activities, is indicated in most cases. During recovery, a corset, brace or cane may be required to reduce physical loads on the sacral bone. If such treatment is considered insufficient, distinct surgical interventions may be carried out to reduce and fixate the fracture.