Undisplaced or Minimally Displaced Fractures of the Pelvic Ring.: The normal pelvis is not totally rigid because of the slight mobility at the SI joints and symphysis pubis and the inherent elasticity of bone. A single break in the ring is possible. Nevertheless, the pelvis is not totally forgiving, and identification of a single break in the ring should prompt a search for a second disruption.

An isolated fracture of the superior or inferior pubic ramus is the most common pelvic fracture. These fractures are stable. They are common fractures in elderly people after a fall and should be considered in the evaluation of an acutely painful hip. Fracture of the body of the ischium is a rare injury that may result from a fall in the sitting position. These fractures around the obturator foramen are treated conservatively with bed rest, analgesia, and early mobilization.

Fracture of the superior and inferior pubic rami on the same side is a commonly encountered injury after a fall or MVC. These are generally stable fractures and are treated conservatively. However, the presence of significant displacement at the fracture site indicates a second disruption elsewhere in the pelvic ring that should be diagnosed. Alternatively, fractures of both rami on the same side may be associated with an unrecognized impaction fracture of the posterior pelvis.

If the patient with a ramus fracture reports posterior pelvic pain and plain radiographs do not reveal posterior injury, further investigations may reveal occult posterior fractures. A study performed more than 35 years ago found that patients who sustained apparently isolated pubic ramus fractures showed increased uptake of radionuclides on bone scans in the acetabulum and SI joint, suggesting that occult bony or ligamentous injury accounted for the pain.²¹ More recently, a study that prospectively evaluated elderly patients who were diagnosed with isolated ramus fractures on plain films found that 95% had sacral fracture detected by magnetic resonance imaging (MRI).²² This study does not imply a need to perform MRI on all elderly patients with ramus fractures in the ED; rather, it enhances our understanding of the pathophysiology of ramus fractures and underscores the importance of adequate analgesia in these patients. The lateral compression type I fracture described by Young and Burgess (Fig. 55-5)—characterized by pubic ramus fracture with ipsilateral sacral compression—bears special consideration among the mechanically stable pelvic fractures, as it has been shown to be associated with a mortality rate of 8% with a high incidence of associated injuries.^20,23,24

Also termed a straddle fracture, four-pillar injuries involve fractures of both pubic rami on both sides of the symphysis pubis, causing the so-called “butterfly segment” (Fig. 55-6). The injury is produced by a direct blow with a straddle mechanism. Although these fractures may occur without posterior arch disruption, four-pillar injuries are also commonly associated with lateral compression or vertical shear forces that may cause concomitant injuries to the posterior pelvic arch. CT of the pelvis is required in cases of four-pillar injuries to detect and classify precisely the posterior arch injury and plan orthopedic treatment.¹⁵ The genitourinary tract frequently is injured concomitantly with this type of pelvic fracture and should be evaluated carefully (see Fig. 55-6).

Isolated fracture of the iliac wing was described by Duverney in 1751 and now bears his name. It is caused by direct trauma to the iliac crest, usually by lateral compression forces. Although displacement is usually minimal because of the arrangement of the muscle attachments of the abdominal wall, orthopedic consultation is recommended. The fracture may extend into the acetabulum, altering the treatment and prognosis. Severely displaced fractures of the iliac wing require open reduction and internal fixation.¹⁵ It is worth noting that a high incidence of major associated nonpelvic injuries among patients with isolated iliac wing fracture has been reported.²³

Transverse Fractures of the Sacrum.: Transverse fractures of the sacrum do not compromise the pelvic ring. Transverse fractures at or below S4 are unlikely to be accompanied by neurologic injury.²⁵ An upper sacral transverse fracture is the result of a flexion injury, such as being struck on the lower back by a heavy load while bending over, or by direct forces to the sacrum, as in a fall from a great height.²⁵ The patient reports pain in the buttocks, perirectal area, and posterior thighs. There may be local pain, swelling, and bruising overlying the sacrum, and on gentle bimanual rectal examination, severe pain, abnormal motion, and palpable hematoma may be elicited. Radiographically, the fracture may be difficult to visualize on anteroposterior (AP) and lateral projections, in which case a pelvic outlet view may be helpful. Simple transverse fractures at or below S4 are treated conservatively. Above S4, neurologic injuries are common, necessitating careful clinical evaluation and surgery when neurologic compromise is present.

Avulsion Fractures.: These usually occur during athletic activities and are the result of a sudden, forceful muscular contraction or excessive muscle stretch. They are seen more commonly in older children and teenagers before closure of the corresponding physis occurs; adults may have the same symptoms from ligamentous injury at these sites without radiographic abnormality.

The ischial tuberosity may be avulsed during strenuous contraction of the hamstrings. There is pain on palpation of the involved tuberosity, and this pain is increased by flexion of the hip with the knee in extension (hamstrings stretched), but not with the knee flexed (hamstrings relaxed). Ischial tuberosity avulsion also may cause chronic discomfort with no history of acute injury.

A portion of the iliac crest epiphysis may be avulsed by contraction of the abdominal muscles. Similarly, the anterior superior iliac spine may be avulsed by forcible contraction of the sartorius muscle. Forceful contraction of the rectus femoris (as in kicking a ball) can result in the less common injury of anterior inferior iliac spine avulsion; however, this radiographic finding should be distinguished from a normal variant, the os acetabuli, which is a secondary center of ossification at the superolateral margin of the acetabulum.²⁶ Clinical examination is similar in these injuries and reveals local pain, swelling, and limitation of motion.

Conservative treatment, including analgesia and bed rest in a position that avoids tension on the affected muscles, is generally all that is required for avulsion injuries; surgical treatment is rarely necessary. Orthopedic consultation is advised for follow-up care.

Stress Fractures.: Stress fractures occur with vigorous athletic or military training and in the last trimester of pregnancy.²⁷ The diagnosis of stress fractures is based on the clinical evaluation and can be confirmed, if required, by radionuclide bone scan, although MRI has been shown to be a superior method for detecting these injuries.²⁸

Pathologic and Insufficiency Fractures.: Pathologic fracture related to neoplasm, Paget’s disease, or dietary osteomalacia is included in the differential diagnosis. Radiation therapy has also been shown to increase the risk of pelvic fracture.

Anteroposterior Compression.: Severe AP compression forces result in disruption at or near the symphysis pubis. Symphysis widening of less than 2.5 cm is considered a stable injury (the symphysis should normally be ≤0.5 cm in an adult but can increase 2-3 mm during or after pregnancy); however, with continued force in the AP direction, the hemipelvis externally rotates, tearing the sacrospinous, sacrotuberous, and anterior SI ligaments. The SI joint opens and hinges on the intact posterior SI ligaments. The resulting injury is aptly described as an “open-book” fracture. The pelvis is rotationally unstable in the horizontal plane, but the intact posterior SI ligaments maintain vertical stability.15,16

When diastasis of the pubic symphysis is greater than 2.5 cm on the AP radiograph, the posterior injury is usually seen as widening of the SI joint and occasionally as a sacral or iliac fracture (see Fig. 55-5).¹⁵ If the injurious forces continue, they may separate the hemipelvis, and the SI joint is seen as widely separated on the plain AP radiograph (Fig. 55-7) and the CT scan.¹⁵ The AP radiograph may be misleading in suggesting a pure open-book fracture in cases with symphysis disruptions greater than 2.5 cm. These cases commonly are associated with vertical shear fractures, and careful clinical and computed tomography (CT) assessment for vertical instability is essential to classify the fracture properly and plan treatment.¹⁵

These same forces also may injure the neurologic and vascular structures at the posterior arch; the overall volume of the pelvis is increased in the open-book injury, facilitating the expansion of a retroperitoneal hematoma. Several studies have demonstrated that patients with severe grades of AP compression injuries have the highest crystalloid and blood requirements.16,19

Lateral Compression.: Lateral compression of the pelvic ring results in varying degrees of internal rotation of the affected hemipelvis. Initially, this causes buckling of the sacrum and horizontal pubic rami fractures. Rami fractures may occur on the ipsilateral or contralateral side, the latter being referred to as the “bucket-handle” fracture (Fig. 55-8).

As the magnitude of force increases, the symphysis may disrupt, causing overlapping of the pubic bones. Note that on plain radiographs, evidence of injury to the sacrum may be subtle; overlapping pubic bones with any significant displacement should prompt a search for a posterior injury.

Similar to the AP injury, with increasing disruption of the posterior ligaments comes increasing rotational instability. In the most severe lateral compression trauma, the ipsilateral pelvis internally rotates to such a degree that the contralateral pelvis may externally rotate. This is referred to as the “windswept” pelvis. Lateral compressive injuries result in varying degrees of horizontal rotational instability; however, the vertical stability of the pelvis is maintained (see Fig. 55-8).

As internal rotation causes the pelvic volume to decrease, lateral compressive injuries are generally associated with lesser degrees of blood loss than are AP injuries.

Vertical Shear.: Vertical shear injuries represent the most unstable injuries to the pelvic ring and are associated with violent axial loading of the hemipelvis (e.g., fall from height, “submarining” underneath a dashboard). Fractures occur in vertical planes. Anteriorly, the symphysis and rami may be disrupted. Posteriorly, gross displacement and instability in the rotational and vertical planes may be present through the sacrum, the SI joint, or the ilium such that the hemipelvis may displace posteriorly and cephalad15,16 (see Fig. 55-9).

Avulsion of the ischial spine, the lower lateral lip of the sacrum, and the transverse process of the fifth lumbar vertebra (sites of insertion of ligaments) (Fig. 55-9 and Box 55-3) are important clues to the presence of vertical shear fractures.¹⁵ The vertical shearing forces transmitted through the bony pelvis are also transmitted through the rich vascular network and nerve plexus that are directly adjacent to the bone. This activity accounts for the major hemorrhage and neurologic injuries associated with vertical shear fractures.

Vertical Sacral Fractures.: A crucial distinction in considering sacral fractures is that transverse fractures do not involve the pelvic ring, but vertical fractures do. Vertical sacral fractures are caused by high-energy injuries and were classified by Denis into three groups according to whether the fracture line extends (1) laterally to the sacral foramina, (2) through the foramina, or (3) medially to the foramina, involving the central spinal canal²⁹ (Fig. 55-10). The radiographic diagnosis of this fracture hinges on careful examination of the symmetrical cortical lines that are normally present at the superior margins of the sacral foramina on the AP view. Disruption, distortion, or asymmetry of these lines is an important marker of sacral fractures.²⁶

There is a high risk of neurologic complications associated with these injuries: 6% when lateral to the foramina, 28% when through the foramina, and 58% when medial to the foramina.²⁹ Neurologic dysfunction correlates to the nerve roots involved but may include any bowel, bladder, or sexual dysfunction. Surgery is commonly performed for fractures associated with neurologic dysfunction, with the goals of bony fixation of the sacrum and decompression of affected nerve roots.