Radiographic Summary

Fractures may involve the columns, walls, or dome of the acetabulum. They are classified by Letournel and Judet as five elementary and five associated fractures. Elementary fractures are predominantly single-plane injuries. Associated fractures are combinations of the elementary types, and are multiplane and more complex. The AP pelvis radiograph is typically the first imaging study followed by CT scanning. Some patients may have additional 45° oblique pelvis radiographs, known as Judet views. CT is more sensitive than plain radiographs for detecting acetabular fractures.

Five fracture types in the Letournel–Judet classification account for 80-90% of cases. Posterior acetabular wall fractures are the most common. A portion of the posterior articular surface and rim is sheared from the pelvis by posterior dislocation of the hip. Transverse acetabular fractures divide the hemipelvis through the acetabulum into superior and inferior portions, and do not involve the obturator ring. Radiographically, part of the superior articular surface or dome remains attached to the intact ilium. The fracture plane actually is oblique from superomedial to inferolateral. A combination of posterior wall and transverse injuries characterizes the transverse and posterior wall fracture. The T-shaped fracture combines the transverse fracture with a vertical fracture most commonly passing through the acetabular fossa and notch and the inferior ischiopubic ramus. The both-column fracture is a complex injury with no part of the articular surface of the hip socket remaining attached to the axial skeleton. The “spur” sign, representing the edge of intact ilium adjacent to the fracture, is pathognomonic of the both-column fracture.

Clinical Implications

Acetabular fractures result from significant force driving the femoral head into the hip socket, either laterally through the hip (as from a direct blow against the greater trochanter from a fall) or through the femur (as in the “dashboard” mechanism). They are associated frequently with hip dislocation and injuries to the femur and knee as well as the sciatic nerve. All patients with acetabular fractures require appropriate analgesia, hospitalization, and orthopedic consultation.

Pearls

1. 
   

   Due to the overlapping nature of the anterior and posterior components of acetabular anatomy, oblique (Judet) views are often necessary for identification and characterization of acetabular fractures.

   
   
2. 
   

   Acetabular fractures may be associated with sciatic nerve injury, femoral head osteonecrosis, or post-traumatic osteoarthritis and may result in significant long-term disability.

   
   
3. 
   

   Failure to diagnose an associated hip dislocation with acetabular fracture is a medico-legal pitfall.

Radiographic Summary

Ramus fractures may involve one or both rami. AP pelvis radiographs are the initial study obtained. Superior ramus fractures may be oblique to horizontal and parasymphyseal, more vertical and in the midportion of the superior pubic ramus, or vertical and far laterally near the acetabulum (a “pubic root” fracture). Inferior ischiopubic ramus fractures are usually nearly vertical and may appear incomplete, or may be undisplaced and virtually invisible on conventional radiographs. An ipsilateral incomplete or “buckle” fracture of the anterior sacral wall may accompany pubic ramus fractures. These may be subtle, seen only as a slight irregularity of the contour of the superior edge of one or more sacral neural foramina. Additional inlet and outlet pelvis views can be used to supplement the AP radiograph. These are views of the entire pelvis with the x-ray beam angled caudally through the pelvis (the inlet view) or cephalad through the pelvis (the outlet view). These fractures may be part of more complex pelvic ring disruptions (see “Pelvic ring fractures” further on).

CT scan may demonstrate nondisplaced ramus fractures with increased accuracy as compared to radiographs. The extent of ramus fractures and the potential involvement of pubic root fractures at the anterior acetabular articular surface are better characterized on CT scan. CT scan also has utility in assessing intra- and extra-peritoneal injuries (such as bladder ruptures) that may accompany bony pelvic trauma.

Clinical Implications

Isolated pubic ramus fractures may be seen in the setting of falls or direct trauma among elderly patients. They can also occur as a stress fracture related to exercise among young patients or in pregnant women. Treatment typically consists of analgesics, crutches to assist with ambulation, and follow-up with orthopedics or primary care within 1-2 weeks.

Pearls

1. 
   

   Pubic ramus fractures may develop as insufficiency fractures in elderly patients who present with pain concerning for femoral neck fractures and no history of trauma.

   
   
2. 
   

   In osteopenic elderly patients, if plain films do not show a suspected fracture, MR is important to demonstrate the ramus fracture and to exclude hip fracture.

Radiographic Summary

Fractures of the right and left superior pubic and inferior ischiopubic rami are usually readily identifiable on a standard AP radiograph of the pelvis as well as on CT scan. The superior ramus components are usually fractured in a vertical plane when associated with vertical shear (VS) injuries. Other fracture patterns may occur. Orthopedic surgeons will usually obtain inlet and outlet views in addition to the AP radiograph to characterize displacement and plan management. These fractures may be part of a VS pelvic ring disruption (see “Pelvic ring fractures” further on).

Clinical Implications

Bilateral pubic rami fractures in isolation are a rare injury, and may be produced by a straddle-type injury or VS mechanisms. They are also seen as part of an injury complex associated with lateral compression (LC) injuries, especially LC type III fractures in the Young–Burgess classification (see “Pelvic ring fractures” further on). These fractures have a significant risk of major hemorrhage and concomitant bladder and urethral injury. Interventional radiology may be required to embolize vessels in patients with severe hemorrhage. Retrograde urethrography should be obtained prior to Foley catheter placement to rule out associated disruption of the urinary tract.

Pearls

1. 
   

   Consider associated genitourinary and retroperitoneal injuries in the setting of bilateral pubic ramus fractures.

   
   
2. 
   

   These fractures may also present as insufficiency fractures in older, osteopenic patients, and if plain films are not diagnostic their presence may be established by using MR if the clinical situation indicates.

Radiographic Summary

AP pelvis radiographs demonstrate avulsion fractures as separation of the apophysis of the iliac crest, the anterior superior iliac spine, the anterior inferior iliac spine, or the ischial tuberosity from the underlying normal pelvic bones. Other images are usually not needed, although inlet, outlet, or Judet views may be used to confirm the diagnosis if the AP image is equivocal. CT is not required. It should be noted that some asymmetry in the immature ossification foci (particularly those of the ischial tuberosities) is a common finding in children, and is not necessarily indicative of avulsive trauma.

In younger patients with less bony maturation, only a thin rim of avulsed subchondral bone is visualized at the site of injury on radiographs, with the majority of the avulsion affecting the nonossified cartilaginous apophysis.

Clinical Implications

Apophyseal avulsion fractures are uncommon sport-related injuries seen among 14- to 25-year-olds. Iliac crest avulsions result from the sudden contraction of the external obliques, internal obliques, and transversus abdominus muscles. Patients will often report feeling and hearing a “pop” and have immediate pain, limiting their ability to continue activity.

Avulsion fracture of the anterior superior iliac spine results from forceful contraction of the sartorius muscle, resulting in avulsion of its ASIS origin. This injury is most commonly seen in teenage sprinters and hurdlers due to the need for forceful and sudden hip flexion in these sports. Patients with this injury will have pain on hip flexion and abduction.

Avulsion fracture of the anterior inferior iliac spine results from forceful contraction of the rectus femoris muscle, resulting in avulsion of the AIIS origin of its direct head. This is typically an injury seen in teenage soccer players or other sports that involve kicking. Patients present with pain on hip flexion and tenderness along the AIIS following the injury.

Avulsion fracture of the ischial tuberosity results from forceful contraction of the hamstrings, resulting in avulsion of their origin. This is the most common of the pelvic avulsion fractures. This classically is an injury in a teenage sprinter or hurdler. Patients will complain of pain sitting and flexing the thigh. Management is conservative, with rest, NSAIDS, crutches to assist with ambulation, and primary care follow-up in 1-2 weeks.