Pelvis — Surgical Anatomy and Approaches

Introduction

The pelvis presents the orthopedic surgeon with one of the most complex regional anatomical environments, combining the bony pelvic ring (the load-transmitting structure between the spine and the lower extremities) with the pelvic viscera, the iliac vessels and their branches, the lumbosacral plexus, and the abdominal wall musculature. The surgical approaches to the pelvis must navigate this complexity while providing access to specific bony regions for fracture fixation, tumor resection, joint replacement, or other procedures. The principal approaches — the ilioinguinal approach (Letournel), the anterior intrapelvic (modified Stoppa) approach, the Kocher-Langenbeck (posterior) approach, the extended iliofemoral approach, and the anterior (Pfannenstiel) approach to the symphysis — each provide access to specific regions of the pelvis with characteristic risks and benefits. This chapter, drawing on Orthopaedic Surgical Approaches, AO Principles of Fracture Management, and Netter’s Concise Orthopaedic Anatomy, addresses the surgical anatomy and principal approaches to the pelvis.

Bony Anatomy

The pelvic ring comprises two innominate bones (each formed by the fusion of the ilium, ischium, and pubis at the triradiate cartilage) and the sacrum, joined anteriorly at the pubic symphysis and posteriorly at the sacroiliac (SI) joints. The detailed anatomy was addressed in Topics Trauma-19 (pelvic ring) and Trauma-20 (acetabulum). The principal bony landmarks relevant to surgical approaches include: Iliac crest: The superior margin of the ilium, palpable from the ASIS anteriorly to the PSIS posteriorly. The crest provides the bony graft donor site classically used for bone harvesting. Anterior superior iliac spine (ASIS): The anterior projection at the anterior end of the iliac crest. The origin of the sartorius and the inguinal ligament. The lateral end of the inguinal ligament attaches here. Anterior inferior iliac spine (AIIS): Just below the ASIS. The origin of the direct head of the rectus femoris. Posterior superior iliac spine (PSIS): The posterior projection at the posterior end of the iliac crest. Often marked by a dimple in the overlying skin. Posterior inferior iliac spine (PIIS): Just below the PSIS. Greater sciatic notch: The large posterior notch between the PIIS and the ischial spine, transmitting the sciatic nerve and other structures. Lesser sciatic notch: Between the ischial spine and the ischial tuberosity, transmitting the obturator internus, pudendal nerve, and pudendal vessels.

Ischial spine: The bony projection at the junction of the body and ramus of the ischium. Ischial tuberosity: The “sit bone” — the inferior weight-bearing portion of the ischium. The origin of the hamstrings. Pubic tubercle: The bony projection on the superior pubic ramus, lateral to the symphysis. The medial end of the inguinal ligament attaches here. Iliopectineal eminence: The bony prominence at the junction of the ilium and the superior pubic ramus, marking the location of the iliopectineal line on the pelvic brim. Pelvic brim (linea terminalis): The continuous line from the sacral promontory across the iliopectineal line to the pubic tubercle, separating the true pelvis (below) from the false pelvis (above). Quadrilateral surface: The flat bone of the medial acetabular wall facing into the true pelvis. Visualized through the anterior intrapelvic approach.

Muscular Anatomy

The principal muscles relevant to pelvic approaches include: Abdominal wall muscles: External oblique, internal oblique, transversus abdominis, rectus abdominis. These are encountered in anterior pelvic approaches. Iliacus and psoas (iliopsoas): Originate from the iliac fossa and the lumbar vertebrae respectively, joining to insert on the lesser trochanter. Encountered in approaches that enter the iliac fossa from above. Gluteus maximus: The principal posterior pelvic muscle, providing hip extension. Encountered in the Kocher-Langenbeck and extended iliofemoral approaches. Gluteus medius and minimus: The principal hip abductors, originating from the outer iliac wing. Their preservation is critical to gait function after pelvic surgery. Piriformis: From the anterior sacrum through the greater sciatic notch to the greater trochanter. The principal landmark for identifying the sciatic nerve in posterior pelvic surgery. Obturator internus: From the inner pelvic surface around the lesser sciatic notch to the greater trochanter. Sartorius: From the ASIS to the medial tibia. Encountered in the ilioinguinal approach. Rectus femoris: From the AIIS and the supra-acetabular ilium to the patella via the quadriceps tendon. Encountered in anterior hip and pelvis approaches.

Neurovascular Anatomy

The pelvic surgery anatomy is dominated by the dense neurovascular structures:

Iliac Vessels The common iliac arteries branch from the abdominal aorta at approximately the level of L4 and divide into the internal iliac (hypogastric) and external iliac arteries at approximately the SI joint. The external iliac artery continues across the pelvic brim to become the femoral artery beneath the inguinal ligament; it gives off the inferior epigastric artery just above the inguinal ligament. The internal iliac artery has numerous branches supplying the pelvic viscera, the gluteal region (superior gluteal artery), the obturator region (obturator artery), and the perineum (pudendal artery). The iliac veins parallel the arteries. The common iliac veins join to form the inferior vena cava. The left common iliac vein is particularly vulnerable to injury in the anterior approaches because of its medial position relative to the artery. The corona mortis (“crown of death”) is a vascular anastomosis between the obturator artery (from the internal iliac) and the external iliac/inferior epigastric system, crossing the superior pubic ramus. The corona mortis is present in 30 to 80 percent of individuals and is at substantial risk during ilioinguinal and anterior intrapelvic approaches; injury produces significant bleeding that may be difficult to control because the vessel retracts into the obturator foramen. Lumbosacral Plexus The lumbosacral plexus is formed from the anterior rami of L4 through S4. The principal nerves include: Femoral nerve (L2-L4): Descends through the iliac fossa anterior to the iliacus muscle, then passes beneath the inguinal ligament lateral to the femoral artery. Innervates the iliopsoas, quadriceps, sartorius, and pectineus. Obturator nerve (L2-L4): Descends through the pelvis on the lateral wall, passing through the obturator foramen. Innervates the obturator externus and the adductor compartment of the thigh. Sciatic nerve (L4-S3): The largest nerve in the body. Exits the pelvis through the greater sciatic foramen, typically inferior to the piriformis muscle. Innervates the hamstrings and (via its peroneal and tibial divisions) all the muscles of the leg and foot. Superior gluteal nerve (L4-S1): Exits the pelvis through the greater sciatic foramen, superior to the piriformis (the only nerve to do so). Runs between the gluteus medius and minimus, supplying both muscles and the tensor fasciae latae. Iatrogenic injury during the lateral approach to the hip is a recognized cause of postoperative abductor weakness. Inferior gluteal nerve (L5-S2): Exits inferior to the piriformis. Supplies the gluteus maximus. Pudendal nerve (S2-S4): Exits the pelvis through the greater sciatic foramen below the piriformis, then re-enters through the lesser sciatic foramen. Supplies the perineum.

Lateral femoral cutaneous nerve (L2-L3): Crosses anterior to the iliacus muscle and passes beneath the inguinal ligament approximately 1 to 2 cm medial to the ASIS. Provides sensation to the lateral thigh. Frequently encountered (and at risk) in anterior pelvic approaches; injury produces meralgia paresthetica. Lumbar Plexus Within the Psoas The lumbar plexus lies within the substance of the psoas muscle and is at particular risk in lateral transpsoas approaches to the lumbar spine (XLIF/LLIF — see Topic Anatomy-1). The L4 nerve root is the most caudal and is at greatest risk at the L4-L5 level.

Ilioinguinal Approach (Letournel)

The ilioinguinal approach (Letournel, 1960s) is the classical anterior approach to the pelvis and acetabulum, providing access to the entire anterior column of the acetabulum, the iliac wing, the pelvic brim, the quadrilateral surface (from anterior), and the symphysis pubis. The approach is used for acetabular fracture fixation (anterior column, anterior wall, anterior column with posterior hemitransverse, both-column patterns), iliac wing fracture fixation, pelvic ring fracture fixation (combined with other approaches), tumor resection, and selected revision pelvic procedures. Patient Positioning The patient is supine on a radiolucent table. The bladder is catheterized. The legs are draped to permit hip flexion as needed during the procedure. Surface Landmarks and Incision The principal landmarks are the iliac crest, ASIS, inguinal ligament, and the midline of the pubic symphysis. The skin incision follows the iliac crest from approximately 2 cm posterior to the iliac crest highpoint, curves around the ASIS, and continues medially along the inguinal ligament to the midline at the symphysis. Approach — The Three Windows The classical Letournel approach uses three “windows” through the abdominal wall, with the inguinal canal traversed in the process: The lateral (first) window: Between the ASIS and the iliopsoas. The lateral femoral cutaneous nerve crosses this region and is identified and protected. The iliacus is reflected medially from the inner table of the ilium, providing access to the iliac wing, the iliac fossa, and the anterior column of the acetabulum. The middle (second) window: Between the iliopsoas medially (containing the femoral nerve and the lateral femoral cutaneous nerve) and the external iliac vessels (artery and vein) medially. The window provides access to the pelvic brim and the superior portion of the quadrilateral surface.

The medial (third) window: Between the external iliac vessels laterally and the spermatic cord (or round ligament in females) and the rectus abdominis medially. The window provides access to the superior pubic ramus and the symphysis. Critical Structures The structures crossing the operative field that must be identified and protected include: The lateral femoral cutaneous nerve beneath the inguinal ligament near the ASIS. The femoral nerve, artery, and vein in the femoral sheath beneath the inguinal ligament. The iliopsoas muscle containing the femoral nerve. The inguinal ligament itself, which is reconstructed at closure. The corona mortis vascular anastomosis crossing the superior pubic ramus. The inferior epigastric vessels ascending behind the rectus abdominis. The spermatic cord (or round ligament) traversing the inguinal canal.

Closure and Complications The closure includes meticulous repair of the inguinal canal floor and the inguinal ligament to prevent inguinal hernia (a recognized complication). Other complications include inguinal hernia (3 to 8 percent), lateral femoral cutaneous nerve injury with meralgia paresthetica (very common — 20 to 60 percent — but often transient), vascular injury (the principal feared complication, particularly to the corona mortis or the inferior epigastric vessels), deep vein thrombosis, and infection.

Anterior Intrapelvic (Modified Stoppa) Approach

The anterior intrapelvic (modified Stoppa) approach was developed by Hirvensalo and Cole (1993) as a modification of the original Stoppa hernia approach, providing access to the pelvic brim, the quadrilateral surface, and the posterior column of the acetabulum from anterior, without the morbidity of the three-window ilioinguinal approach. Patient Positioning The patient is supine on a radiolucent table, with the bladder catheterized. Surface Landmarks and Incision A Pfannenstiel-type transverse incision is made approximately 2 cm above the pubic symphysis, or a midline vertical incision can be used for extended exposure. Approach The skin and subcutaneous tissue are incised. The rectus abdominis is divided in the midline (with the linea alba being the avascular plane). The transversalis fascia and

peritoneum are encountered; the peritoneum is retracted cephalad to enter the preperitoneal space (the space of Retzius). The dissection then proceeds laterally along the pelvic brim. The corona mortis is identified and ligated when present. The iliac vessels are identified and retracted laterally. The iliopsoas muscle with the femoral nerve within it is retracted laterally. The obturator nerve and vessels are identified entering the obturator foramen. The pelvic brim, the quadrilateral surface, the medial wall of the acetabulum, and the posterior column from anterior can all be visualized through this approach. Reduction and plating of fractures in these regions can be performed. The modified Stoppa is increasingly preferred over the classical ilioinguinal for many acetabular fracture patterns because of better visualization of the quadrilateral surface and the medial wall, with reduced overall morbidity compared with the three-window approach. Complications The complications include vascular injury (corona mortis, iliac vessels), bladder injury (if the bladder is not adequately drained), obturator nerve injury, and inguinal/femoral hernia (less common than with the ilioinguinal approach).

Kocher-Langenbeck (Posterior) Approach

The Kocher-Langenbeck approach is the classical posterior approach to the pelvis and acetabulum, providing access to the posterior wall, posterior column, and the ischial region. The approach is used for posterior wall and posterior column acetabular fracture fixation, transverse and T-shaped fracture fixation (when the posterior column is dominant), open reduction of posterior hip dislocations, and tumor resection of the posterior pelvis. Patient Positioning The patient is prone or lateral decubitus with the affected side up. The lateral decubitus position is more commonly used because it allows easier sciatic nerve monitoring and easier conversion to anterior or extended approaches if needed. Surface Landmarks and Incision The greater trochanter, the PSIS, and the midline of the gluteus maximus mark the line of the incision. The skin incision begins at the PSIS, curves down and laterally over the greater trochanter, and extends distally for approximately 5 to 8 cm into the proximal thigh. Approach The skin and subcutaneous tissue are incised. The fascia lata and gluteal aponeurosis are opened in line with the skin incision. The gluteus maximus is split in line with its fibers;

the principal innervation (inferior gluteal nerve) enters from the medial side, so the splitting is typically biased laterally to preserve innervation. Beneath the gluteus maximus, the short external rotators are encountered (from superior to inferior: piriformis, gemellus superior, obturator internus, gemellus inferior, quadratus femoris). The piriformis is identified — this is the critical anatomical landmark for the sciatic nerve, which typically exits the pelvis just inferior to the piriformis. The sciatic nerve is identified and protected throughout the remainder of the procedure (with some surgeons placing a vessel loop around the nerve for retraction). The short external rotators are then incised at their trochanteric insertions and reflected medially. The posterior hip capsule is exposed. Trochanteric osteotomy or trochanteric flip osteotomy (Ganz) can be performed to extend the exposure proximally to the supra-acetabular region and to permit safe surgical hip dislocation. Complications The complications of the Kocher-Langenbeck approach include sciatic nerve injury (the principal concern — 10 to 30 percent of patients have some degree of postoperative sciatic nerve dysfunction, predominantly peroneal-division injury; many recover but residual deficits are common), heterotopic ossification (10 to 90 percent, substantially reduced by indomethacin or low-dose radiation prophylaxis), infection, wound complications, and abductor dysfunction (with extensive proximal extension or trochanteric osteotomy nonunion).

Extended Iliofemoral Approach

The extended iliofemoral approach (Letournel) provides the most comprehensive access to both columns of the acetabulum from a single approach. However, the substantial morbidity (heterotopic ossification rates of 50 to 90 percent, abductor dysfunction, infection) has caused this approach to be largely abandoned in favor of combined approaches (Kocher-Langenbeck plus ilioinguinal in stages) for the most complex acetabular fractures.

Approach The patient is in lateral decubitus. The skin incision combines a posterior portion (along the iliac crest from the PSIS) with an anterior portion (curving down to the greater trochanter). The gluteus maximus is reflected posteriorly, and the gluteus medius and minimus are reflected anteriorly (with trochanteric osteotomy to preserve their attachment to the bone fragment). The approach provides access to both columns of the acetabulum from outside the pelvis. The principal complications limit the use of this approach to selected severe injuries where other approaches are inadequate.

Pfannenstiel Approach to the Pubic Symphysis

The Pfannenstiel approach provides direct access to the pubic symphysis for symphyseal disruption fixation, anterior pelvic ring stabilization, and selected exposures of the inferior pubic region. Approach The skin incision is transverse approximately 2 cm above the pubic symphysis, similar to the obstetric Pfannenstiel incision but typically smaller. The rectus abdominis is split or divided in the midline (with care for the bladder). The anterior aspect of the symphysis is exposed and the symphyseal plate is applied. Complications The complications include bladder injury (with inadequate decompression or aggressive retraction), infection, and wound complications.

Summary and Take-Home Points

The pelvic surgical anatomy is dominated by the complex relationships among the bony pelvis, the iliac vessels and their branches (including the dangerous corona mortis anastomosis crossing the superior pubic ramus), the lumbosacral plexus (with the sciatic nerve exiting the greater sciatic notch typically inferior to the piriformis and the femoral nerve within the iliopsoas), the pelvic viscera (bladder, rectum), and the abdominal wall. The ilioinguinal approach (Letournel) uses three windows (lateral around the iliopsoas, middle between iliopsoas and iliac vessels, medial between iliac vessels and spermatic cord/rectus) to provide comprehensive anterior access to the iliac wing, pelvic brim, and anterior column of the acetabulum. The modified Stoppa (anterior intrapelvic) approach provides similar access through a transverse suprapubic incision and the preperitoneal space, with better visualization of the quadrilateral surface and reduced morbidity. The Kocher-Langenbeck (posterior) approach through gluteus maximus split provides access to the posterior wall, posterior column, and ischial region, with the sciatic nerve below the piriformis being the principal neurological concern. The extended iliofemoral approach provides the most comprehensive single-incision access but is largely abandoned because of high morbidity (especially heterotopic ossification). The Pfannenstiel approach provides direct access to the symphysis pubis for anterior pelvic ring stabilization. The principal neurovascular structures at risk in pelvic surgery include the iliac vessels (particularly the corona mortis and the left common iliac vein), the sciatic nerve (in posterior approaches), the femoral nerve (within the iliopsoas in anterior approaches), the lateral femoral cutaneous nerve (beneath the inguinal ligament, with meralgia paresthetica a common complication), the obturator nerve (in the obturator foramen), the superior gluteal nerve (between the gluteus medius and minimus), and the pudendal nerve (around the ischial spine). The bladder and rectum are the visceral structures requiring protection.

The chapter that follows turns to the hip, where the principles of pelvic anatomy continue and the head/acetabular blood supply considerations introduce additional surgical concerns.