by Sara Nikolić and Gregor Prosen
Introduction
Pelvic fractures carry life‐threatening injury potential which should be identified or suspect during the primary assessment of patients with major trauma. The prevalence of pelvic fracture in studies of patients with blunt trauma is between 5% and 11.9%. The mortality from pelvic fractures in patients who reach hospital is reported to be between 7.6% and 19%. Usually, injuries are secondary to massive force, such as a road traffic accident or fall from a height. Fractures may be associated with vascular, soft tissue and visceral injuries. If the pelvic ring is broken in two places, the fracture is likely to be unstable. Isolated ring fractures, however, tend to be stable. Patients who survive a pelvic fracture are at risk for significant complications such as chronic pain, leg length discrepancy, sexual dysfunction, or nerve palsy.
Case Presentation
A 27-year-old woman was in a car accident. She is hemodynamically stable with vital signs as follows: temperature of 36.4°C, heart rate of 70 bpm, blood pressure 120/80 mmHg, respiratory rate 10/min, oxygen saturation 99% on room air. During the secondary survey, pelvic bones are not stable, and there is a pain on palpation. You placed a pelvic binder and ordered a pelvic X-ray.
Important Anatomical Considerations
The three bones compose the pelvis (the sacrum and the two innominate bones). Strong ligaments keep these three bones together. These are crucial for maintaining pelvic stability. A large array of ligaments traverses the interior and exterior surface of the posterior aspect of the pelvis.
Two ligaments originate from the side and back of the sacrum and insert into the ischial spine and ischial tuberosity.
The pubic symphysis, a fibrocartilagenous joint, is supported by ligaments. However, adds little to the overall stability of the pelvis. The urethra and bladder lie close to the pubic symphysis, and there is a 20% risk of injury if symphysis is disrupted.
Torn or rupture of the ligaments can cause separation of three bones. In this situation, the nerves and vessels running close to them, especially at the posterior, can also be injured. The bleeding is usually venous and extraperitoneal and can be life-threatening.
If bones fracture but the ligaments remain intact, a tamponade effect can be achieved, and the degree of hemorrhage limited.
Mechanism of Injury
The Young-Burgess system identifies four types of pelvic ring disruption, based on interpretation of radiographic images: anteroposterior compression, lateral compression, vertical shear and combined mechanical injury.
- Anteroposterior compression causes “open book” look at one or both sides of the pelvis. A diffuse force will disrupt the pubic symphysis, while a more direct force fractures the pubic rami in a vertical plane. For the pubic bones to separate by over 2,5 cm, one or both of the ligaments associated with sacroiliac joints have to be torn. An anteroposterior force can also push the flexed femur backward so that the femoral head impacts and fractures the posterior margin of the acetabular rim.
- Lateral compression produces a horizontal fracture through the ipsilateral pubic symphysis and momentary medial displacement of the hemipelvis. A lateral compression force can also impinge on the upper femur causing central dislocation of the hip.
- Vertical shear forces the hemi-pelvis upwards and towards the midline and can tear all the sacroiliac ligaments on the affected side as well as the pubic symphysis ligaments.
- Complex pattern happens in less than 25% of cases. The pelvis is exposed to two or more of the forces mentioned above. A combination of injuries results in a complex radiological picture.
X-Ray Views
The routine pelvic view is anteroposterior (AP) projection, and in 94% of cases, a correct diagnosis can be made from this view. When the fracture is noted in the AP view, special views (inlet and outlet view and oblique views) for further investigations are recommended.
Radiographic interpretation is systematized with ABCS approach:
- Alignment
- Bones
- Cartilage and joints
- Soft Tissues
Normal findings
AP View Interpretation Summary
- A
- Adequacy and quality
- Ensure that the whole of the pelvis is visible
- Alignment
- Assess the borders of the three circles namely, the pelvic brim and the two obturator foramina.
- Adequacy and quality
- B
- Bones
- Check each of the following systematically:
- Pubis Sacrum
- Acetabulum
- Femoral heads
- Iliac crest
- Lumbar vertebrae
- Pubis Sacrum
- Check each of the following systematically:
- Bones
- C
- Cartilage and joints
- Check the pubic symphysis
- Check the sacroiliac joints
- Check the acetabulum
- Check the pubic symphysis
- Cartilage and joints
- S
- Soft Tissues
- Check the disruption of fat planes inside the pelvis
- Check for soft tissue shadows outside the pelvis
- Check the disruption of fat planes inside the pelvis
- Soft Tissues
Details
A
In this step, focus the three circles enclosed by the pelvis. One is created by the pelvic brim (A) and the other two by the obturator foramina (B) (Figure 2).
Trace around the edge of the large circle. Normally this has a smooth edge which is not disrupted by the sacroiliac joint or pubic symphysis unless the patient is very old. The pelvic brim cannot be disrupted in only one place. As the pelvis is not completely rigid, this disruption may take the form of a minimal diastasis. The inner margins of both obturator foramina should then be inspected in the same way as the pelvic brim. Again these are rarely broken in only one place. Complete the examination of the foramina by tracing along its superior border to the inferior surface of the neck of the femur. This is known as Shenton’s line (Figure 3).
B
Examine the outer edges of the pelvis and its bony structure for evidence of fractures. These may present as areas of increased density, lucency, or alteration of the internal trabecular pattern. Fractures away from the three bony circles can occur in isolation. The start point of the examination is the pubic symphysis. Then, slowly progress to the right or left side. Focus on the posterior and anterior joint margin, the ilioischial line (posterior column), and the iliopectineal line (anterior column). To finish the exam, look for “teardrop sign” (acetabular floor) (Figure 4).
Next, focus on the anterior inferior iliac spine, anterior superior iliac spine and look for the iliac crest to the sacrum. The sacrum should also be examined for symmetry of its foramina (Figure 5).
C
Check for either widening or overlapping of bones at the level of the symphysis pubis (A). If you see one of those, disruption in the pelvic brim should be investigated. Sacroiliac joints (B) at the right and left sides must also be checked for widening, defects in the cortical surface, overlapping of bone, and lack of congruity of the joint margin (Figure 6).
S
Check for soft tissue shadowing both inside and outside the pelvis because hematoma and tissue edema can produce swellings which are visible on the anteroposterior radiograph. Normally the obturator internus muscle is seen on both sides of the pelvis as a dark grey line, which is due to the muscle or fat plane. Loss of this line indicates extra-peritoneal hemorrhage or soft tissue edema. Conversely, intra-peritoneal hemorrhage can displace the line.
Inlet and outlet views should ideally be requested if there is clinical or radiological evidence of a pelvic fracture. An inlet view looks down the lumen of the true pelvis. It is better than the anteroposterior view for showing the orientation of fractures of the pubic rami. Outlet views are used to detect the degree of vertical displacement of the fracture fragments.
Oblique (Judet) views are used to define acetabular fracture patterns. If a fracture or abnormality of the acetabulum is suspected computed tomography will usually be necessary once the patient has been adequately resuscitated and stabilized.
Abnormal Findings
Pubic rami fracture
Pubic rami and ischium fracture
Complex pelvic fracture – open book fracture. Pay ettention to symphisis pubis and sacroiliac joint seperations.
Femoral neck fracture – Right femoral neck fracture after fall. Check the Shenton’s line alignement.
Hip dislocation (antero-inferior)
Hip dislocation (posterior)
Acetabular fracture
Hints and Pitfalls
Ensure that the whole of the pelvis can be seen, including the iliac crests, both hips, and the femurs distal to the lesser trochanters. The adequacy of the penetration should also be assessed. Pelvic rotation is determined by lining up the symphysis pubis with the midline of the sacrum.
It is common for part of the iliac crest to be missing or poorly penetrated in the films so that fractures cannot be seen. A rotated film causes asymmetry of the bony circles and the sacroiliac joints. Failing to trace around the bony edges, especially the iliac crests and sacral foramina, will lead to fractures being missed.
Epiphyseal lines may be misinterpreted as fractures. Remember that the Y-shaped (triradiate) cartilage separating the pubis, ischium, and ilium in the acetabular floor does not fuse until puberty.
Accessory ossification centers (in particular the one in the posterior acetabulum) may also be mistaken for fractures. However, apophyses are usually bilateral, have a sclerotic margin, and are not associated with overlying soft tissue signs.
Being systematical is crucial to make possible for the non-specialist to interpret pelvic radiographs accurately. Table 1 shows the summary of how to read a pelvic x-ray.
References and Further Reading
- Lee C, Porter K. The prehospital management of pelvic fractures. Emergency medicine journal: EMJ. 2007 Feb;24(2):130-3. PubMed PMID: 17251627.
- Holmes E, Misra R. A-Z of emergency radiology. New York: Cambridge University Press; 2004. 152-6 p.
- Starr AJ, Malekzadeh AS. Fractures of the Pelvic Ring. In: Bucholz RW, Heckman JD, Court-Brown CM, editors. Rockwood & Green’s Fractures in Adults, 6th Edition. Philadelphia, PA: Lippincott Williams & Wilkins; 2006. p. 1585-666.
- Driscoll PA, Ross R, Nicholson DA. The Pelvis. ABC of Emergency Radiology. London: BMJ; 1993. p. 927-31.
- Jones J. Pelvic radiograph (an approach) 2014 [updated March 2016; cited 2016 May 23]. Available from: http://radiopaedia.org/articles/pelvic-radiograph-an-approach.