Okay, so I’m going to start very ambitious but reading a pelvic X-ray is going to need to be a very basic skill when on call or when evaluating someone in the clinic. This review is going to be geared mainly towards the trauma setting.
I have not been able to find a resource online that will go step by step through a pelvic x-ray and prevent a systematic approach, but I am all about systematic. So lets do this.
Ok, the parts of the pelvic X-ray we are going to address are: (1)Skeletal Maturity (2)Dislocation (3)The 6 lines (4)Different Pelvic X-ray views
First, when reading any film, whether in the presence of one other person or a group of colleagues, begin with an introduction statement to what you’re reading. In this case, I might start with “This film is an AP(judet, obturator oblique, iliac oblique) of the pelvis.” You are off to a great start.
Next step, if appropriate you can comment on the skeletal maturity of the pelvis. This can also be inserted in the introduction above( “of a skeletally mature pelvis”). I’m going to address 2 components of the not-yet-skeletally mature pelvis that are important to understand: the risser sign and triradiate cartilage. Skeletal maturity can be assessed by looking at the Risser sign, which is the state of ossifications of the iliac crest epiphysis seen below. Obviously a Risser 0 would be the most immature while a 5 would represent skeletal maturity.
The second important aspect of an immature pelvis to understand at this stage is the triradiate cartilage. The triradiate cartilage is the structure that will ossify into the adult acetabulum (typically 13-16 years of age). The three distinct phases of each bone making up the triradiate cartilage allow hemispheric growth of both the acetabulum and pelvis. This is important to mention because the x-ray of a child can straight up confuse a person and its important not report that you see a massive acetabular fracture when the kid is just ten years old.
Ok, now you’re ready to start diagnosing some pelvic trauma. The next part which I think makes sense to address in this systematic approach, is the location of the femoral heads (and the bony integrity of the femurs, which is a separate discussion). First, 9 out of 10 hip dislocations are going to be posterior(flexed, adducted, internally rotated). In a posterior dislocation, you will frequently find the femoral head in the AP view to be superior and lateral to the acetabulum(occasionally can appear smaller than the contralateral head).
On the contrary, an anterior hip dislocation will have, generally, an inferiorly displaced and larger than the contralteral side.
Along with hip dislocations, one should always assess for a possible acetabular fracture as well, which is a great transition to the discussion of the six lines.
The 6 lines to assess in a pelvic x-ray are: (1) the iliopectineal line (2) the ilioishchial line (3) the dome of the acetabulum (4) the “tear drop” (5) the anterior rim of the acetabulum (6) the posterior rim of the acetabulum.
(1)The iliopectineal line is the radiographic landmark for the anterior column. It begins at the sciatic notch and travels along the superior pubic ramus to the pubis symphysis.
(2)The ilioischial line is the radiographic landmark for the posterior column. It begins at the sciatic notch and courses inferiorly to the medial border of the ischium. It should pass through the acetabular teardrop.
(3)The dome of the acetabulum
(4)The “tear drop” to evaluate the anteroinferior portion of the acetabular fossa
(5)The anterior rim of the acetabulum
(6)The posterior rim of the acetabulum
At this point, you have nearly completed reading the pelvic film. Lastly, look for an pubic symphysis diastasis or SI joint widening and evaluate any bony structure you have not yet (iliac wings, proximal femurs, pubic rami).
Lastly, one part of any film you should be able to evaluate is the quality of the film and its positioning and I will try to end every radiographic post on what to look for to assess if this film is one which you can feel comfortable with you evaluation. First, there should be minimal rotation. One way to assess this is to line up the tip of the coccyx vertically with the pubic symphysis. The line between the two should be vertical and 180 degrees. Rotation can also be assessed by looking at the symmetry of the obturator foramen. Secondly, the tilt of the pelvic x-ray should be neutral and neither an inlet or outlet view. Lastly, evaluate the femoral necks for any foreshortening, indicative of a leg that has not been internally rotated the 15 degrees to give a good view of the femoral neck (obviously could be due to other factors like trauma too).
Hopefully with this systematic method you will be able to assess the pelvis well and at least diagnose a broken pelvis vs. a normal pelvis and know what types of injuries you are going to see on CT. We’ll talk about specific types of pelvic fractures at a later time, but for now, go out and practice reading some pelvic films!