The pelvis is composed of four bones: the two hip bones laterally and in front, and the sacrum and coccyx behind (▶ Fig. 7.1). The hip bone is a large, flattened, irregularly shaped bone that forms the sides and anterior wall of the pelvic cavity together with its counterparts on the opposite side. It consists of three parts, the ilium, ischium, and pubis, which are fused into one bony structure in adults. The hip bone is narrow in the middle and expands above and below, with a large oval shaped hole, the obturator foramen, on its inferior aspect. The acetabulum, a large cup-shaped articular cavity, is situated near the middle of the bone’s outer surface. The external surface of the upper part of the hip bone is smooth and gives attachment to the gluteal muscles. The ilium is divided into two parts, the body and the ala. The ischium, the lower and back part of the hip bone, consists of three portions: a body and two rami. The pubis, which forms the anterior part of the hip bone, is divided into a body, and a superior and an inferior ramus. The pubic ramus is a very thin bone, making it an easy target for fractures. The sacrum is a triangular bone at the base of the spine and consists of five vertebrae which usually are completely fused into a single bone in adults. The sacral canal in the middle runs throughout the greater part of the bone; its walls are perforated by the anterior and posterior sacral foramina through which the sacral nerves passes. The coccyx, or tailbone, comprised of four fused vertebrae, articulates superiorly with the sacrum and extends downward as an individual piece (▶ Fig. 7.2; ▶ Fig. 7.3).
Based on fracture pattern, pelvic fractures can be divided into pelvic ring fractures and acetabular fractures. The pelvic ring is divided into an anterior and posterior ring by the acetabulum. The acetabulum is divided into the anterior column, the posterior column, anterior wall, posterior wall. In the erect posture, the pelvis is inclined forward so that the anterior superior iliac spines and the front of the top of the symphysis pubis are in the same coronal plane. When an individual is standing, his or her weight is transmitted from the upper body and trunk, through the spine, the sacrum, sacroiliac joint, and acetabulum, and continues down to the lower extremities. When an individual is in the sitting position, his or her weight is transmitted down the spine, the sacrum, and sacroiliac joint to the ischium (▶ Fig. 7.4).
According to the AO fracture classification principle, the pelvis is considered one unit, with the location code of “6.” The following sections will be divided into discussions of the pelvic ring and acetabulum. The numbers “61” and “62” are used to represent the pelvic ring and acetabulum respectively (▶ Fig. 7.5; ▶ Fig. 7.6).
A total of 53 patients with 53 pelvic ring and acetabular fractures were investigated in the China National Fracture Study (CNFS). The fractures accounted for 3.01% of all patients with fractures and 2.89% of all types of fractures. The population-weighted incidence rate of pelvic ring and acetabular fractures was 9 per 100,000 population. The epidemiologic features of pelvic ring and acetabular fractures in the CNFS are as follows:
• More females than males
• The highest risk age group is 15–64 years
• The pelvic ring fracture is the most common pelvic ring and acetabular fractures
• Injuries occurred most commonly via falls and traffic accidents
Pelvic Ring and Acetabular Fracture by Sex in CNFS
Number of patients
Fig. 7.7 Sex distribution of 53 patients with pelvic ring and acetabular fractures in the China National Fracture Study (CNFS).
Fig. 7.8 (a) Age distribution of 53 patients with pelvic ring and acetabular fractures in the China National Fracture Study (CNFS). (b) Age and sex distribution of 53 patients with pelvic ring and acetabular fractures in the CNFS.
Fig. 7.9 Segment distribution of 53 patients with pelvic ring and acetabular fractures in the China National Fracture Study (CNFS).
Fig. 7.10 Causal mechanisms distribution of 53 patients with pelvic ring and acetabular fractures in the China National Fracture Study (CNFS).
A total of 14,420 patients with 14,555 fractures of the pelvic ring and/or acetabulum were treated in 83 hospitals of China over a 2-year period from 2010 to 2011. All cases were reviewed and statistically studied, comprising 3.48% of all fractured patients and 3.37% of all types of fractures. Of a total 14,420 patients, there were 685 children with 687 fractures, accounting for 1.25% of pediatric patients with fractures, and 1.20% of all types of fractures in children. The rest of the 13,735 adult patients had 13,868 fractures, representing 3.81% of adult patients with fractures, and 3.70% of all types of fractures in adults.
Epidemiological features of fractures of the pelvic ring and acetabulum are the following:
• More males than females
• The high-risk age groups are 36–40 and 41–45 years; while the high-risk age group for males is 41–45 years, the groups 36–40 and 41–45 years are at risk for females.
• Pelvic ring fractures occur more frequently than acetabular fractures.
Number of patients
Fig. 7.12 (a) Age distribution of 14,420 patients with fractures of the pelvic ring and acetabulum. (b) Age and sex distribution of 14,420 patients with fractures of the pelvic ring and acetabulum.
Fractures of the Pelvic Ring and Acetabulum in Adults by Fracture Segment Based on the AO Classification
Number of fractures
Fractures of the Pelvic Ring and Acetabulum in Children by Fracture Location
Number of fractures
Fig. 7.14 Fracture location distribution of 687 fractures of pelvic ring and acetabulum in children.
Number of patients
Number of patients
The pelvic ring is made up of paired innominate, pubic, ischial, and sacral bones. It is joined posteriorly by the sacroiliac joints and ligaments, and anteriorly by the pubic symphysis. The ischial bones, pubic rami, and pubic symphysis comprise the anterior ring. The sacroiliac joint is formed between the two auricular, or ear-shaped, articular surfaces of the ilium and sacrum, and connect to the posterior pelvic ring. The upper part of the sacroiliac articulation is formed by ligaments connecting the sacrum and ilium, while the lower part is separated by a space containing synovial fluid, thus comprising a synovial joint. The sacroiliac joint, together with posterior sacroiliac, sacrotuberous, and sacrospinous ligaments, as well as muscles and fascia of the pelvic floor, form the sacroiliac complex, a very important structure that maintains the stability of the pelvis. The sacrotuberous and sacrospinous ligaments enclose the greater sciatic notch and lesser sciatic notch, which form the greater sciatic foramen and the lesser sciatic foramen respectively, through which muscles, vessels, and nerves pass (▶ Fig. 7.17).
Based on AO classification, the location code for the pelvic ring is number “61.” According to the mechanism of injury, fracture location, and the stability of the pelvis, segment 61 fractures can be further divided into: 61-A: Posterior arch intact, stable; 61-B: Incomplete posterior arch disruption, partially stable; and 61-C: Complete posterior arch disruption, unstable (▶ Fig. 7.18; ▶ Fig. 7.19).
A total of 10,672 adult patients with 10,694 pelvic ring fractures were treated in 83 hospitals of China over a 2-year period from 2010 to 2011. All cases were reviewed and statistically studied, comprising 2.96% of all adult patients with fractures and 2.86% of all types of fractures.
Epidemiological features of pelvic ring fractures are the following:
• Slightly more females than males.
• The high-risk age group is between ages 36–40 and 41–45 years; while the age group 41–45 years is the high-risk for males, age group 36–40 years is at risk for females.
• The most common fracture type of segment 61 fractures is type 61-A, the same fracture type for both males and females.
• The most common fracture group of segment 61 fractures is group 61-A2, the same group for males, and the most common fracture group for females is group 61-A3.
Number of fractures
Fig. 7.21 (a) Age distribution of 10,694 fractures of segment 61. (b) Age and sex distribution of 10,694 fractures of segment 61.
Fig. 7.22 (a) Fracture type distributions of 10,694 fractures of segment 61. (b) Sex and fracture type distribution of 10,694 fractures of segment 61.
Fig. 7.23 (a) Fracture group distribution of 10,694 fractures of segment 61. (b) Sex and fracture group distribution of 10,694 fractures of segment 61.
61-A1 Avulsion fracture
M: 342 (66.80%)
F: 170 (33.20%)
0.14% of total adult fractures
3.69% of adult pelvic ring and acetabulum
4.79% of segment 61
5.74% of type 61-A
61-A1.1 Fracture involving anterior superior iliac spine, anterior inferior iliac spine, or pubic spine
61-A1.2 Iliac crest
61-A1.3 Ischial tuberosity
M: 2,862 (57.34%)
F: 2,129 (42.66%)
1.33% of total adult fractures
35.99% of adult pelvic ring and acetabulum
46.67% of segment 61
55.95% of type 61-A
61-A2.1 Iliac wing fracture, with one or more fragments
61-A2.2 Unilateral pubic rami fracture
61-A2.3 Bilateral pubic rami fracture
M: 1,036 (30.32%)
F: 2,381 (69.68%)
0.91% of total adult fractures
24.64% of adult pelvic ring and acetabulum
31.95% of segment 61
38.31% of 61-A
61-A3.1 Sacrococcygeal dislocation
61-A3.2 Nondisplaced sacral fracture
61-A3.3 Displaced sacral fracture
61-B1 Unilateral “open-book” injury (external rotational instability)
M: 449 (58.09%)
F: 324 (41.91%)
0.21% of total adult fractures
5.57% of adult pelvic ring and acetabulum
7.23% of segment 61
60.82% of type 61-B
61-B1.1 Anterior sacroiliac joint disruption + A injury*
61-B1.2 Sacral fracture + A injury*
M: 276 (65.87%)
F: 143 (34.13%)
0.11% of total adult fractures
3.02% of adult pelvic ring and acetabulum
3.92% of segment 61
32.97% of type 61-B
61-B2.1 Ipsilateral, anterior sacral buckle fracture + A injury*
61-B2.2 Contralateral, partial sacroiliac joint fracture/subluxation (bucket-handle) + A injury*
61-B2.3 Incomplete posterior iliac fracture + A injury*
M: 43 (54.43%)
F: 36 (45.57%)
0.02% of total adult fractures
0.57% of adult pelvic ring and acetabulum
0.74% of segment 61
6.22% of type 61-B
61-B3.1 Bilateral type B1 injury
61-B3.2 One side type B1 injury, the other side type B2 injury
61-B3.3 Bilateral type 61-B2 injury
M: 238 (65.38%)
F: 126 (34.62%)
0.10% of total adult fractures
2.62% of adult pelvic ring and acetabulum
3.40% of segment 61
72.37% of type 61-C
61-C1.1 Fracture of ilium + A injury*
61-C1.2 Sacroiliac dislocation or fracture dislocation + A injury*
61-C1.3 Fracture of sacrum (lateral, medial, or through the sacral foramina) + A injury*
M: 66 (71.74%)
F: 26 (28.26%)
0.02% of total adult fractures
0.66% of adult pelvic ring and acetabulum
0.86% of segment 61
18.29% of type 61-C
61-C2.1 Ipsilateral C1 lesion through the ilium, contralateral B1 or B2 injury + A injury*
61-C2.2 Ipsilateral C1 lesion through the sacroiliac joint (transiliac fracture dislocation, pure dislocation, transsacral fracture dislocation), contralateral B1 or B2 injury + A injury*
61-C2.3 Ipsilateral C1 lesion through the sacrum (lateral, medial, or through the sacral foramina) contralateral B1 or B2 injury + A injury*
M: 31 (65.96%)
F: 16 (34.04%)
0.01% of total adult fractures
0.34% of adult pelvic ring and acetabulum
0.44% of segment 61
9.34% of type 61-C
61-C3.1 Extrasacral on both sides (ilium, transiliac sacroiliac (SI) joint fracture/dislocation, transsacral SI joint fracture/dislocation, SI joint dislocation)
61-C3.2 One side C1 lesion through the sacrum (lateral, medial, or through the sacral foramina), the other side extra sacral lesion + A injury*
61-C3.3 Sacral lesion on both sides (lateral, medial, or through the sacral foramina) + A injury*
Note: * “A injury” includes: ipsilateral pubic or pubic rami fracture; contralateral pubic or pubic rami fracture; bilateral pubic or pubic rami fracture; isolated symphysis pubis separation ≥ 2.5 cm; isolated symphysis pubis separation < 2.5 cm; isolated symphysis separation, or locked; symphysis separation + ipsilateral pubic or ramus fracture; symphysis separation + contralateral pubic or ramus fracture; symphysis separation + bilateral pubic or rami fracture; without anterior lesion.
Pelvic ring fractures involve direct or indirect mechanisms. The direct mechanism includes a direct blow, motor vehicle crash, crush injury, fall, etc. Based on the direction of the force, the injury mechanisms can be classified into the following types: anteroposterior (AP) compression, lateral compression, and vertical shear. Different forces can result in different types of pelvic ring fractures. Indirect forces usually result in avulsion fractures from the traction of muscles or tendons.
The force of AP compression usually produces an “open-book”-type injury, that is, a symphysis disruption, by acting on the posterior superior spine and symphysis pubis, or by forced external rotation through the hip joints unilateral or bilaterally. If more force is applied, the anterior ligaments of the sacroiliac joint and the sacrospinous ligament may also be injured, and the posterior dislocation of sacroiliac joint, which is the traditional dislocation of the sacroiliac joint, may occur. In rare conditions, enormous AP force can lead to “anterior” dislocation of sacroiliac joint, in which the ilium dislocates anterior to the sacrum and often combines with symphyseal diastasis and fractures of pubic rami and ilia. Different locations upon which the AP compression is applied may lead to different types of “open-book” injuries.
The force of lateral compression can be transmitted by a direct blow to the iliac crest, often causing an internal rotation of the hemipelvis, or the so-called bucket-handle fracture. Lateral compression may also cause an ipsilateral injury through the femoral head, occasionally causing contralateral injury. The injuries caused by internal rotation account for the majority of pelvic fractures.
Shearing forces in the vertical plane can cause marked displacement of bony structures of the pelvic ring, and gross disruption of soft-tissue structures.
Complex forces, resulting from a combination of these injury patterns, often cause associated acetabular fractures. The most common combined mechanism is lateral compression and vertical shearing. The combined injury of the acetabulum and posterior pelvic ring can be described by three patterns: (1) Acetabular fractures associated with ipsilateral posterior pelvic ring injuries. (2) Acetabular fractures associated with controlateral posterior pelvic ring injuries. (3) Acetabular fractures associated with bilateral posterior pelvic ring injuries.
Pelvic ring injuries are generally high-energy fractures and frequently associated with multiple injuries. Evaluation of the patient should begin with an initial assessment to form a general impression of the degree or severity of the injury, such as to assess hemodynamic status, and the presence of other severe associated injuries. Physical examination should note the morphology of the pelvis and hip joint, as well as the function of the lower extremities. A careful examination of the painful area should be performed. The pelvic compression and separation test, Gaenslen’s maneuver, and the Yeoman test can be used to assess an injury and point to appropriate imaging studies.
The radiographic evaluation includes the AP, inlet, outlet, and Judet views of the pelvis. An AP view of pelvis is usually sufficient to uncover most pelvic injuries. Abnormalities depicted on the AP view can direct the need for the next set of radiographs, which usually include inlet and outlet views of the pelvis in pelvic ring fractures, and Judet (oblique) radiographs of the pelvis in acetabular fractures. Inlet radiographs of the pelvis allow the evaluation of pelvic brim integrity, AP displacement of the hemipelvis, internal/external rotation of the hemipelvis, and sacral impaction. Outlet views of the pelvis allow for confirmation of vertical displacement of the hemipelvis. Judet views of the pelvis illustrate the anterior and posterior columns of the acetabulum, free of superimposition. Computed (CT) or magnetic resonance imaging (MRI) should be performed when plain diagnostic radiographs are inconclusive, with regard to pelvic fractures or the presence of concomitant visceral or neurovascular injuries are suspected.
Patients with hemodynamic instability require emergency rehydration, and temporary stabilization of pelvic fractures, such as by pelvic ring pocket and external fixation, to decrease hemorrhage. Interventional radiology therapy can be applied if necessary. For instance, patients who sustain type B or C injuries often have concomitant severe bony and soft tissue injuries; for example, massive internal bleeding is commonly associated with complete sacroiliac joint disruption. To prevent recurrence of hemorrhage in such patients, temporary fracture stabilization should be performed.
For hemodynamically stable patients, surgical intervention should be performed 5 to 7 days after the injury. Either an external fixation device or open reduction fixation is used for isolated anterior arch fractures. The preferred treatment of choice for unstable pelvic fractures is anatomic reduction and rigid internal fixation. In addition, minimally invasive methods, such as percutaneous iliosacral screw fixation for fracture dislocations of the sacroiliac joint, are increasingly applied in the clinical setting. The sacral pedicel axial view projection is an optimal radiographic technique for percutaneous placement of iliosacral screws in clinical practice. AO classification of pelvis fractures provides a guide in selecting appropriate surgical plans: type A2 and B1 injuries, in which symphysis separation is less than 2.5 cm, can be managed nonsurgically; if symphysis disruption is greater than 2.5 cm, either an external fixation device or plate fixation can be applied; type B2 injuries, being relatively mild, require only reduction and maintenance in proper position; type B3 injuries with shortening of the limb > 1.5 cm should be considered for internal fixation. Operative reduction and internal fixation should be performed if the fracture fragments protrude into the perineal region.
Type C fractures should be treated with an anterior external fixation device combined with skeletal traction (8 to 12 weeks), or operative reduction and internal fixation. In addition to iliosacral screw fixation, posterior pelvic disruptions can be treated with the use of posterior tension band plate and the minimally invasive adjustable plate (MIAP). The MIAP conforms to the irregular shape of posterior pelvic ring and can be used without prebending. This plate also has a role in reducing compressed or separated fractures/dislocations. Favorable clinical and radiological outcomes can be achieved in treating posterior pelvic disruptions with MIAP.
The acetabulum is a hemispherical horseshoe-shaped articular cavity, with a diameter of 3.5 cm, which articulates with the head of femur. It is formed at the confluence of the ilium, ischium, and pubis, and is situated near the middle of the outer surface of the hip bone, between the anterior superior iliac spine and ischial tuberosity (▶ Fig. 7.24).
The hip joint is enclosed in a strong fibrous capsule and surrounding musculature, which provide a good amount of stability. At the lower brim of the acetabulum is the acetabular notch. The external surface of the acetabulum is partly articular, partly nonarticular; the articular segment forms a curved, crescent-moon shaped surface, the lunate surface; the nonarticular portion contributes to a circular depression, the acetabular fossa, situated at the bottom of the acetabulum, inside which the Haversian gland is located and enhances the depth of the hip joint.
The acetabulum is divided into anterior and posterior columns, and dome (▶ Fig. 7.25). The anterior column (iliopectineal) begins at the iliac wing and extends down the anterior portion of the acetabulum, through the superior pubic ramus to the symphysis pubis. It is composed of the iliac crest, the iliac spines, the anterior wall, the anterior one-half of the acetabulum, and the superior pubic ramus, and can be divided into major three parts: the iliac, acetabular, and pubic portions. The posterior column (ilioischial line) begins at the sciatic notch and extends down the posterior acetabulum into the ischium. It is composed of dense bone superior to the sciatic notch, posterior wall, and posterior one-half of the acetabulum and the ischium. The dome, or roof of the acetabulum, formed by the iliac bone, is the weight-bearing surface, making up 40% of the acetabulum.