Unstable pelvic fractures typically occur as a result of high-energy injuries. Associated organ system injuries are observed commonly with pelvic fractures because of the energy imparted to the patient. Head, chest, and abdominal injuries frequently occur in association with pelvic fractures. Fractures of the extremities and spinal column also can occur in patients with pelvic fractures.
Hemorrhage may accompany pelvic fractures. Most hemorrhage associated with pelvic fractures occurs as a result of bleeding from exposed fractures, soft-tissue injury, and local venous bleeding.  Arterial injuries also may contribute to hemorrhage with pelvic fractures, albeit less commonly than venous bleeding. 
Unstable and displaced pelvic ring disruptions cause significant deformity, pain, and disability. Deformities resulting from pelvic ring injuries include any combination of rotational and translational deformities. Significant permanent (sustained) pelvic deformities have been identified in poorer patient outcomes and decreased activity levels. [3, 4, 5]
Pelvic fractures historically have been treated nonoperatively. The earliest management of pelvic fractures consisted of prolonged recumbency followed by mobilization as fracture healing occurred and symptoms abated. Other methods also used to treat pelvic fractures included closed reduction under general anesthesia, traction, spica casts, pelvic slings, and turnbuckles. [6, 7, 8, 9]
Operative management of unstable pelvic injuries has increased because of several factors, including the following:
Improved and coordinated treatment of polytraumatized patients
Improved anesthetic techniques, including blood salvage systems
Advances in intraoperative fluoroscopic imaging techniques
Standardized pelvic implant systems
Better understanding of injury and deformity patterns
Operative management of unstable pelvic ring injuries allows earlier patient mobilization, thereby decreasing complications associated with recumbency. Operative management also allows correction and prevention of significant pelvic deformities, improving clinical outcomes. 
The pelvic ring consists of two innominate bones connected anteriorly at the symphysis pubis and posteriorly to the sacrum at the sacroiliac (SI) joints. Anatomically, the pelvis is divided into the false pelvis and the true pelvis. The false pelvis is defined as that portion of the pelvis from the iliac crests superiorly to the pelvic brim inferiorly. The true pelvis is defined from the pelvic brim inferiorly to the pelvic floor.
The bones of the pelvis are held together by strong ligaments that can be divided into the following four groups  :
Those connecting the sacrum and ilium
Those connecting the sacrum and ischium
Those connecting the two pubic bones at the symphysis pubis
Those uniting the sacrum and coccyx
The anterior and posterior SI ligaments link the iliac bones to the sacrum. Two distinct bands demarcate the posterior SI ligaments. The short posterior interosseus ligaments consist of fibers running from the ridge of the sacrum to the posterior superior and posterior inferior iliac spines. The long posterior SI ligament consists of fibers originating from the posterior superior iliac spine, which then intermingle with originating fibers of the sacrotuberous ligament, covering the short posterior SI ligament and attaching to the lateral sacrum. The anterior SI ligaments consist of fibrous bands that join the anterior surface of the sacrum to the adjacent anterior ilium. 
The sacrospinous and sacrotuberous ligaments connect the sacrum to the ischium. The sacrospinous ligament, originating from the lateral margin of the inferior sacrum and attaching at the ischial spine, assists in resisting external rotation forces of the pelvis.  The sacrotuberous ligament has a broad origin from the posterior superior and posterior inferior iliac spines and the entire lateral margin of the posterior sacrum. The sacrotuberous ligament courses posteriorly to the sacrospinous ligament, inserting on the ischial tuberosity. The sacrotuberous ligament resists sagittal plane rotational deformities and vertical shearing of the pelvis. 
The symphysis pubis is a movable, articular joint without a synovial membrane. An interpubic disk, the superior pubic ligaments, and the arcuate ligaments inferiorly connect the pubic bones. The remainder of the ligaments that surround the pelvis are ligaments that do not have significant stabilizing roles for the pelvis, including ligaments connecting the sacrum and coccyx, the lateral lumbosacral ligaments originating at the L5 transverse processes and attaching to the sacral ala, and the iliolumbar ligaments, running from the L5 transverse processes to the iliac crests. 
Pelvis as conduit for neurovascular structures
The pelvis acts to connect the axial skeleton with the appendicular skeleton of the lower extremities and, in this role, serves as a conduit for neurovascular structures.
The common iliac blood vessels enter into the false pelvis, in which the division into the external and internal iliac vessels occurs. The external iliac vessels continue through the false pelvis atop the pubic rami medial to the iliopectineal eminence. The internal iliac vessels dive into the pelvis, in which they divide into somatic branches, visceral branches, and limb and perineal branches. Other vessels of the pelvis include the terminal branch of the aorta, the median sacral artery, and the superior rectal artery, a continuation of the inferior mesenteric artery. 
Somatic segmental branches are as follows  :
Visceral branches are as follows:
Limb and perineal branches are as follows:
The neurologic contents of the pelvis collectively have been referred to as the lumbosacral plexus. This consists of what are individually known as the lumbar plexus and the sacral plexus. Anatomically, the lumbar plexus is an abdominal structure whose branches enter the pelvis. Conversely, the sacral plexus is entirely pelvic in origin. The lumbar plexus consists of nerve roots from L1 through L4. The sacral plexus consists of those more caudal nerve roots. Each plexus can be divided into ventral and dorsal branches. The larger nerves of the pelvis originate from the sacral plexus.
The most cephalic of the nerves of the pelvis are the ilioinguinal and iliohypogastric nerves. These originate from the L1 nerve root. Both enter the pelvis on the surface of the psoas muscle, which they cross obliquely as they travel distally. They penetrate the abdominal wall muscles to serve as cutaneous innervation of the areas surrounding the pelvis. The iliohypogastric nerve supplies the skin of the posterolateral buttock, while the ilioinguinal nerve supplies the root of the penis and scrotum. 
The lumber plexus can be divided into nerves consisting of dorsal or ventral branches. The psoas muscle anatomically separates these nerves. The femoral and lateral femoral cutaneous nerves are the primary dorsal branches of the lumbar plexus. The femoral nerve (L2-4) lies lateral to the psoas between the psoas and the iliacus as it enters the pelvis over the iliac wing.  It innervates the iliacus, then exits the pelvis beneath the inguinal ligament to supply both motor and sensory fibers to the anterior compartment of the thigh.  The lateral femoral cutaneous nerve also emerges lateral to the psoas. It travels over the iliacus and becomes superficial to supply sensation to the lateral thigh. 
The ventral branches of the lumbar plexus are represented in the obturator nerve (L2-4). The obturator nerve appears medial to the psoas just above the pelvis, it then enters the pelvis, with the vertebral column on its medial side and the psoas lateral to it. The obturator nerve travels with the internal iliac vessels and the ureter on the lateral pelvic wall. Coursing along the surface of the obturator internus, the obturator nerve then leaves the pelvis through the obturator canal.  Its main function is to provide motor innervation to the adductors of the thigh. 
The branches of the sacral plexus originate in the pelvis, in which the sacral plexus lies anterior to the piriformis muscle. The nerves of the plexus can be divided into ventral and dorsal branches, all of which exit the pelvis through the greater sciatic foramen notch. All branches pass below the piriformis muscle, except the superior gluteal nerve (L4-S1), which exits above the piriformis.  The dorsal branches of the plexus include the superior (L4-S1) and inferior (L5-S2) gluteal nerves and the common peroneal portion of the sciatic nerve (L4-S2). The anterior or ventral divisions supply the calf, plantar foot, and thigh through the tibial nerve (L4-S3). 
Muscle groups around pelvis
Several important muscle groups are around the pelvis. The muscles of the pelvic floor, the levator ani, and the coccygeus are voluntary muscles that support the pelvic viscera and control the voluntary sphincters of the rectum and urethra.  Additionally, the muscles of the pelvic floor have been noted to impart stability to the pelvic ring.  Another muscle around the pelvis is the piriformis muscle, which is an important anatomic landmark demarcating the division of the superior and inferior gluteal vessels and assisting with identification of the sciatic nerve.
Many other muscles originate and insert on the bones of the pelvis, a discussion of which is beyond the scope of this article and can be referenced from anatomy textbooks.
Pelvic fractures occur after both low-energy and high-energy events. Low-energy pelvic fractures occur commonly in two distinct age groups: adolescents and the elderly. Adolescents typically present with avulsion fractures of the superior or inferior iliac spines or with apophyseal avulsion fractures of the iliac wing or ischial tuberosity resulting from an athletic injury. Low-energy pelvic fractures in the elderly frequently result from falls while ambulating, which are highlighted by stable fractures of the pelvic ring. Elderly patients also may present with insufficiency fractures, typically of the sacrum and anterior pelvic ring. 
High-energy pelvic fractures most commonly occur after motor vehicle crashes. Other mechanisms of high-energy pelvic fractures include motorcycle crashes, motor vehicles striking pedestrians, and falls.
The incidence of pelvic fractures in the United States has been estimated to be 37 cases per 100,000 person-years. The incidence of pelvic fractures is highest in people aged 15-28 years. In persons younger than 35 years, males sustain more pelvic fractures than females; in persons older than 35 years, women sustain more pelvic fractures than men.  Most pelvic fractures that occur in younger patients result from high-energy mechanisms, whereas pelvic fractures sustained in the elderly population occur from minimal trauma, such as a low fall. 
Early stabilization of pelvic ring injuries has demonstrated improved outcomes in patients with pelvic fractures. Stabilization of pelvic fractures immobilizes bleeding cancellous surfaces, thereby decreasing overall blood loss.  Goldstein et al noted decreased operative time, blood transfusions, and hospital stays for patients who were treated within 24 hours of hospital admission.  Similarly, Latenser et al noted decreased complications, blood loss, hospital stays, long-term disability, and better survival for patients treated within 8 hours of hospital admission. 
Injury pattern and reduction of fracture-related displacements have been correlated with outcome results. Injuries involving the SI joint are associated with poorer results when compared with patients with either sacral fractures or iliac wing fractures. [7, 2, 16] Posterior pelvic displacement of 5 mm has been identified as leading to poorer patient outcomes.  Another study noted that patients with pelvic displacements greater than 1 cm in any plane had increased levels of pain when compared with patients with displacements less than 1 cm. Limb length discrepancy greater than 2.5 cm also has been implicated in poor results. 
Permanent neurologic injury contributes to poorer patient outcomes after pelvic ring injury, and is present in approximately 20% of patients with unstable pelvic ring injuries. [12, 21] Tile noted that permanent nerve damage led to unsatisfactory results in 12 of 248 patients.  Templeman et al also noted that neurologic injury was associated with compromised outcome in patients with sacral fractures.  Most neurologic injuries after pelvic ring injuries involve the L5 and S1 nerve roots, though injury may occur along any portion of the lumbosacral trunk. Management of neurologic injuries is expectant, as neurologic recovery has been documented as long as 4 years after injury. 
A study by Sharma et al focused on risk assessment for mortality in 566 patients with pelvic fracture.  High risk was defined (on the basis of blood pressure, examination, radiographs, and computed tomography [CT]) as open fractures, open-book injuries, abbreviated injury score of 4 or higher, and hypotension (systolic blood pressure ≤89 mm Hg). Mortality was 24% for high-risk pelvic fracture and 3% for low-risk pelvic fracture. The investigators concluded that assessment of mortality risk in patients with pelvic fracture can be aided by trauma mechanism, initial blood pressure measurement, radiography, and CT. 
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