Practical Guide to Identifying Hip Dislocations on X-Rays

How to easily identify the type of dislocation on an X-ray? Dr. García shares his method.

Topic taken and expanded from the book:
García-García R. TRAUMATOLOGY AND ORTHOPEDICS. Basic Topics for the Medical Student. Prado Publishing 2019; Chapter 51, “Traumatic Hip Dislocation,” page 537.

Roberto García García – Orthopedic Trauma Surgeon
January 2022

Traumatic hip dislocations are a common type of injury in the field of traumatology, and recognizing them is crucial for timely and effective treatment.

The hip joint, or coxofemoral joint, is highly mobile and remarkably stable, due to its ball-and-socket structure and protection by surrounding muscles. For this reason, dislocation typically occurs when trauma happens in a vulnerable position with poor coverage.

A blow to the front of the knee while the hip is in an adduction-flexion position (such as when sitting cross-legged) causes a posterior dislocation, as the posterior part of the femoral head is left exposed beyond the posterior rim of the acetabulum.

When the hip is in an abduction-flexion position, the anterior portion of the femoral head is exposed. A blow to the bent knee (or to the sole if extended), directed toward the femur in this position, leads to an anterior dislocation.

Finally, if the hip is in a neutral or near-neutral position, a high-energy impact is required for dislocation, resulting in a central fracture-dislocation due to a fracture of the acetabular floor.

Classification of Hip Dislocations

• Posterior. When the femoral head is displaced behind the acetabulum. This is further divided into two subtypes depending on its position relative to the acetabulum: iliac (above) and ischial (below). Most cases present with the hip in adduction and internal rotation—the same position at the time of trauma.
• Anterior. The femoral head is displaced in front of the acetabulum. It is subdivided into four types depending on the position of the head: pubic, subspinous, obturator, and inguinal (perineal or crural). The type depends on the degree of hip flexion at the moment of trauma. The femur is externally rotated and flexed.
• Central fracture-dislocation. The femoral head breaks through the quadrilateral plate of the acetabular floor and enters the pelvic cavity. These are classified as acetabular fractures. Some fracture-dislocation variants involve a posterior acetabular wall fracture with upward and backward displacement of the femoral head, appearing as impaction into the pelvic cavity.

Figure 1. Right hip dislocation, posterior type. A) Typical position of a posterior dislocation with hip in flexion and internal rotation (commonly described as the “modest” or “surprised bather” position), showing apparent shortening of the affected limb. B) AP X-ray of the right hip; the image corresponds to the clinical position.

For medical students who are not yet familiar with musculoskeletal trauma, determining the type of hip dislocation from an X-ray can be challenging.

To make this process easier for students of traumatology, I’ve developed a line-drawing method that aids in identifying the dislocation type quickly and visually.

Based on the Putti quadrants—commonly used in diagnosing developmental dysplasia of the hip—this technique offers a reliable, although not infallible, approach:

1. For better accuracy, the X-ray should include both hips in an anteroposterior (AP) view. (See Figure 1)
2. Identify the center of both acetabular cavities (approximated visually) and mark them with a point.
3. Draw a horizontal line connecting both acetabular centers.
4. Draw a vertical line perpendicular to the first, passing through the center of the acetabulum on the dislocated side.
5. These two perpendicular lines form four quadrants: superomedial, superolateral, inferomedial, and inferolateral.
6. Carefully observe which quadrant the femoral head occupies. In a normal hip, the head spans all four quadrants but is predominantly in the lateral ones. (See Figure 2)
7. In a dislocated hip, the femoral head loses its relation with the acetabulum and shifts into one quadrant. While it may overlap more than one, it typically predominates in one (with exceptions):
   • If the head is in the lateral quadrants, the dislocation is posterior.
     • If in the inferolateral quadrant (IL), it is an ischial dislocation.
     • If in the superolateral quadrant (SL), it is an iliac dislocation.
   • If the head is in the superomedial quadrant (SM), it indicates a central fracture-dislocation (acetabular fracture).
   • If in the inferomedial quadrant (IM), the dislocation is anterior.

Figure 2. Right hip dislocation, anterior type. A) Typical posture of anterior dislocation with flexion and external rotation. B) Radiographic image of the same patient.

Figure 3. AP pelvis radiograph showing both normal hip joints. Two perpendicular lines cross at the center of the acetabular cavity.

Figure 4. Hip quadrants. The acetabular floor line is highlighted. Normally, the femoral head is centered and spans all four quadrants.

Figure 5. AP pelvis X-ray including both hips. A) Right acetabulum appears empty with the femoral head outside the socket. B) Fracture of the posterior acetabular rim.

Figure 6. Same radiograph as Figure 5. B) Drawn lines form quadrants; the femoral head is in the superolateral quadrant (SL), indicating a posterior iliac dislocation.

Figure 7. A) Posterior-ischial dislocation. B) Femoral head located in the inferolateral quadrant (IL).

Figure 8. A) Central fracture-dislocation. The femoral head breaks through the acetabular floor. B) The head is found in the superomedial quadrant.

Figure 9. Indeterminate cases. A) Left hip dislocation with lateral displacement of the femoral head. B) Oblique X-ray confirms posterior displacement.

Figure 10. Indeterminate cases. A) Right hip dislocation with lateral femoral head displacement. B) Oblique projection confirms posterior displacement.

Figure 11. Indeterminate case. Inferior dislocation of the femoral head with comminuted fracture of the femoral neck and greater trochanter.

We’d love to hear your thoughts! Have you encountered similar cases or do you have advice about managing hip dislocations?

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