Back to Basics: Pelvic XRays
/Overview
Plain radiographs are a widely available modality that confer benefits of cost effectiveness and promptness, proving them very useful as an initial diagnostic choice when approaching several musculoskeletal concerns, particularly pelvic and hip pathologies. Pelvic and hip X-rays are almost always obtained, and with good reason, in patients presenting after significant blunt trauma to rule out bony abnormalities and underlying structural injuries in patients that are unstable or altered, have an abnormal pelvic exam, or have significant distracting injuries. While it is vital to have a high suspicion for pelvic injuries in high mechanism traumas, continue to have high concern in low energy traumas as well, especially in patients prone to pelvic injury due to underlying pathophysiology, such as the elderly or bone composition deficiencies, as they can lead to high morbidity if not diagnosed early in the course of illness.
Pelvic and hip X-rays are most frequently obtained when there is concern for fracture, joint dislocation and effusion, and several pediatric pathologies involving the pelvic girdle which are outlined below.
Before delving into the radiographic approach to pelvic and hip X-rays, let us first review some anatomy. Please review Dr. Goel’s excellent post on Pelvic X-rays that provides an excellent review on anatomy and overview on basic radiographic approach.
Pelvic and hip anterior-posterior (AP) and lateral images are most commonly obtained when assessing for pelvic bony abnormalities as many physicians have greater familiarity with interpreting these particular views. However, there are other radiographic views that can provide a more holistic view of the patient’s anatomy, allowing physicians to better visualize occult fractures that are uniquely displaced and that may not appear on the AP or lateral views. Please note that the more views that are obtained of a bone or joint, the higher the sensivity and specificity of plain radiographic imaging becomes in detecting bony abnormalities.
Hip Views
Pelvis Views
+ A/P Hip
+ A/P Pelvis
+ Horizontal/Surgical Hip
+ Inlet
+ Frog Leg Hip
+ Outlet
+ Judet/Oblique
Interpreting the Radiographic Pelvis
There is no one correct way in approaching a plain radiographic imaging of the pelvis or hip; however, ensure that you find an approach that allows you to evaluate each and every image in a methodical manner so as not to miss any lesions! Since I am a foodie at heart, I have chosen the mnemonic PB & JS to highlight my love of all things peanut butter and jelly.
PB & JS
Penetration/Positioning/Patient
- Pubic symphysis and coccyx in straight line in middle of screen with 1-3cm between superior pubic symphysis and tip of coccyx
- Greater and lesser trochanters should be clearly distinguishable
- Obturator rings symmetric
Bones
1. CORTICAL OUTLINE and BONY TEXTURE: evaluate for the integrity of the cortex throughout, as well as bony landmarks
a. Pelvis
- Ilium: iliac crest, anterior superior iliac spine, anterior inferior iliac spine
- Ischium: ischial tuberosity, ischial spine
- Pubis: superior pubic ramus, inferior pubic ramus
b. Hip
- Acetabulum: acetabular floor, anterior rim, posterior rim
- Femur: femoral head, femoral neck, greater trochanter, lesser trochanter
2. RINGS:
- Pelvic ring
- Obturator ring, bilaterally
- Sacral foramina
3. LINES:
a. Pelvis
- Iliopectineal (Iliopubic) line
- Ilioischial line
b. Hip
- Line of Klein (line along superior femoral neck that will intersect epiphysis)
- If abnormal, may indicate slipped capital femoral epiphysis (SCFE) as under Pediatric Quick Hits
- Shenton’s arc/line (undersurface of superior pubic ramus to medial aspect of femoral neck)
- If disrupted, can indicate fracture of femoral neck
- May also indicate developmental dysplasia of hip as under Pediatric Quick Hits
- Hilgenreiner line (horizontal line connecting triradiate cartilages)
- If abnormal, may indicate developmental dysplasia of hip as under Pediatric Quick Hits
- Also used in calculating acetabular angle, as depicted in graphic below:
- Perkin’s line (vertical through lateral edge of acetabulum)
- If abnormal, may indicate developmental dysplasia of hip as under Pediatric Quick Hits
- Principal compressive trabeculae
- Principal tensile trabeculae
- If either category of trabeculae is disrupted, may indicate subcapital femoral fracture
- If either category of trabeculae is disrupted, may indicate subcapital femoral fracture
- Intertrochanteric crest: delineates between intracapsular region proximal to line or extracapsular region distal to line
- Why does it matter: Intracapsular fractures are at higher risk of avascular necrosis due to common disruption of blood supply to femoral neck with fractures in this region
- Teardrop sign (radiographic projection of bony ridge running along the floor of the acetabular fossa)
- Occult acetabular fracture
- Can help calculate Waldenstrom’s sign as below, which is a non-specific indicator for joint effusion
- Abnormal if >11mm or >2mm difference from contralateral hip
- Can help calculate acetabular angle as below
Acetabular Angle
- Angle measured from Hilgenreiner’s line/teardrop sign to line intersecting most superolateral aspect of acetabular rooft as depicted above
- Measurement taken from Hilgenreiner’s line (prior to ossification) in children vs. inferior margin of teardrop sign (after ossification) in adults.
- Children: angle <28º at birth, >22º after 1 year
- Decreased angle: Down syndrome, achondroplasia
- Increased angle: developmental dysplasia of hip
- Adults: normal range is 33º to 38º
- Increased angle: neuromuscular disorders
Joints
1. Sacroiliac: 2-4mm, equal bilaterally
2. Pubis symphysis < 5mm
3. Hip (femoral/acetabular): 3-5mm
- Suspicion for dislocation based on image results:
- If femoral head is superolateral to joint space and appears smaller than contralateral femoral head, it indicates a posterior dislocation; the majority of dislocations are posterior dislocations and they can lead to sciatic nerve damage.
- If femoral head is inferomedial to joint space and appears larger than contralateral femoral head, it indicates an anterior dislocation; anterior dislocations can damage the femoral nerve and artery.
Soft Tissues
- Periosteal swelling
- Fat pads
- Gluteus minimus fat stripe - superior aspect of femoral neck
- Bulging of this pad may indicate presence of effusion in hip joint
- Iliopsoas - inferior to iliopsoas tendon
- Bulging of this pad may indicate presence of effusion in hip joint
- Obturator fat strip - iliopectineal line
- Displacement or bulging may indicate pelvic sidewall hematoma secondary to a fracture
Common Fracture Patterns
Because the pelvis is a ring-like structure, be wary that a fracture in one part of the ring is often accompanied by damage to bone, ligament or tendon structures at some other point in the structure.
Usually low-energy fractures have only one break in the ring, and there is usually maintained alignment of the broken ends. In this case, there is low likelihood of the bones dislocating abruptly and causing damage to underlying structures, in which case these are considered stable pelvic fractures. These fractures can usually be managed non-operatively.
In the instance of high-speed motor vehicle collisions or other high-energy mechanisms, be concerned about pelvic injuries that involve two or more breaks in the pelvic ring. Often, if broken in multiple places in the structure, these fractures will be displaced and unstable, causing increased risk of damage to underlying structures. Patterns that have been identified to be unstable are noted in the classification system below
+ Bonus Tips - Avulsion Fractures
Fracture Classifications (Young Burgess System)
A/P Compression (Head on mechanism)
APC I
Symphysis widening <2.5cm
- No posterior instability
- Non-operative management
- Weight bearing as tolerated
APC II/III
- Symphysis widening >2.5cm
- +/- Posterior stability
- *posterior instability = open book fracture
- require pelvic binders to prevent hemorrhage into increased pelvic space
- operative management
Lateral Compression (Side on mechanism)
LC I
SI joint compression without ligament rupture
- Non-operative management
- Weight bearing as tolerated
LCII/III
- SI joint rupture +/- APC injury to contralateral hemipelvis
- Operative management
- Pelvic binders can theoretically worsen this injury, however it concern for unstable fracture and unable to confirm, better to stabilize with a binder and confirm with plain imaging when able
Vertical Shear Fractures (axial load mechanism)
VS
- Displaced fractures of the anterior rami and posterior columns, including SI dislocation
- Operative management
- Traction often required acutely to stabilize hemipelvis location
Pediatric Quick Hits
+ Developmental Dysplasia of the Hip
+ Legg-Calvé-Perthes
+ Slipped Capital Femoris Epiphysis
COntent and illustrations by Sim Mand, MD
Peer Editing and post by Ryan LaFollette, MD
References
- Bassett, A. “Slipped Capital Femoral Epiphysis.” Orthobullets. https://www.orthobullets.com/pediatrics/4040/slipped-capital-femoral-epiphysis?expandLeftMenu=true
- Campbell, SE. “Radiography of the hip: lines, signs and patterns of disease.” Seminars in Roentgenology. 2005 Jul; 40(3): 290–319.
- “Chapter 6: Basic Approach to Hip/Pelvis X-Ray.” Emergency Medicine Images for Practice: An Overview of X-Ray, Ultrasound, CT, and MRI Images, by Mari Baker.
- Chiamil, Sara Muñoz, and Claudia Astudillo Abarca. “Imaging of the Hip: A Systematic Approach to the Young Adult Hip.” Muscles, Ligaments and Tendons Journal 6.3 (2016): 265–280. PMC.
- Clohisy JC, Carlisle JC, Beaulé PE, et al. A Systematic Approach to the Plain Radiographic Evaluation of the Young Adult Hip. The Journal of Bone and Joint Surgery American volume. 2008;90(Suppl 4):47-66. doi:10.2106/JBJS.H.00756.
- Khurana B, Sheehan SE, Sodickson AD, Weaver MJ. “Pelvic Ring Fractures: What the Orthopedic Surgeon Wants to Know.” RSNARadiographics. 2014 Oct.
- Lim, Seung-Jae, and Yoon-Soo Park. “Plain Radiography of the Hip: A Review of Radiographic Techniques and Image Features.” Hip & Pelvis 27.3 (2015): 125–134. PMC.
- “Pelvic Fractures.” OrthoInfo: Diseases&Conditions; American Academy of Orthopedic Surgeons. https://orthoinfo.aaos.org/en/diseases--conditions/pelvic-fractures/
- “Radiology of the hip.” Wheeless Textbook of Orthopaedics Online, www.wheelessonline.com/ortho/radiology_of_the_hip
- Souder, C. “Developmental Dysplasia of the Hip.” Orthobullets. https://www.orthobullets.com/pediatrics/4118/developmental-dysplasia-of-the-hip?expandLeftMenu=true
- Souder, C. “Legg-Calve-Perthes Disease (Coxa plana).” Orthobullets. https://www.orthobullets.com/pediatrics/4119/legg-calve-perthes-disease-coxa-plana
- Weatherford, B. “Pelvic Ring Fractures.” Orthobullets. http://www.orthobullets.com/trauma/1030/pelvic-ring-fractures
