Structures of the pelvis

The human pelvis represents a complex anatomical region shared by organs of the gastrointestinal tract, genitourinary tracts and the reproductive system. An intricate neurovascular network accompanies all these structures that often requires collaboration of interdisciplinary teamwork in the presence of injury.

Blood vessels

1.Arteries: main arteries are highlighted in red.

The abdominal aorta descends towards the pelvis and divides at L4 (surface marking of the umbilicus) into left and right common iliac arteries which branch further into the external and internal iliac arteries. The external iliac arteries continue to supply the lower extremities as femoral arteries and other branches. The internal iliac arteries branch and remain within the pelvic region to supply blood to pelvic organs, gluteal muscles and the perineum.

2. Veins

The anatomical position of the pelvic veins follows the same path of the arteries and mostly take their names. The femoral vein reaches the pelvis through the inguinal ligament and becomes the external iliac vein. Important to note is the presence of pre-sacral venous plexus, which is vulnerable to profuse bleeding in pelvic injury.

Learning bite

 Pre-sacral venous plexus bleeding can be profuse and difficult to control in major pelvic injury. 

Nerves

The nerves exiting L4 and L5 form the lumbo-sacral trunk and merge with the sacral plexus, which consists of the sacral nerves from S1 to S4. The sacral plexus descends along the posterior pelvis.  The main nerves of the sacral plexus include:

• Sciatic nerve which is the largest human nerve formed by branches of L4-S3. The nerve innervates the muscles of the posterior thigh and the hamstring portion of the adductor magnus. It also innvervates the muscles of the leg and foot via its terminal branches.
• Pudental nerve which innervates the muscles and skin of perineum
• Superior and inferior gluteal nerves innervate the gluteal muscles

Learning bite

The sciatic nerve arises from the sacral plexus, which can be affected by a pelvic injury.

Lymphatic system

The pelvis has an extensive lymphatic system made of large number of lymph nodes and lymphatic ducts. Lymph nodes are mostly located along blood vessels. Their function is to combat potential infections.

Organs

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Pelvic fractures can be suspected by the identification of ecchymosis over the iliac wings, pubis, labia, or scrotum. Pain on palpation of the pelvic ring is an important finding in alert patients, important to note it is NOT recommended to “spring” the pelvis. In addition, assessment of peripheral pulses can identify vascular injuries. Inspect the flank, scrotum, urethral meatus, and perianal area for blood, swelling, and bruising. Laceration of the perineum, vagina, rectum, or buttocks may be associated with an open pelvic fracture in blunt trauma patients. Skin folds in obese patients can mask penetrating injuries and increase the difficulty of assessing the abdomen and pelvis.

Learning bite

Pelvic organ injury can be difficult to diagnose and requires complex multi-disciplinary management.

Interpretation of pelvic x-ray

You should start by tracing three rings on the AP pelvic x-ray: the main pelvic ring and two obturator foramen rings.

If any of the rings are disrupted, think fracture and look for a second one.

If either joint space is widened, think main pelvic ring fracture.

Learning bite

Trace 3 rings and measure 3 joint spaces on a pelvic X-ray to assess for ring fractures.

 

Here are two useful resources for further details on interpretation of pelvic x-ray:

1. How to Read Hip and Pelvis X-Rays. Taming the RSU. Emergency Medicine tamed. 2014.
2. Jones J, Yap J. Pelvic radiograph (an approach). Radiopaedia. 2014. Last revised 2022.