Bones and Ligaments

According to Rouvièr, the innominate bone, the hemipelvis (▶ Fig. 1.1) consists of two columns. Understanding this column principle is the basis for acetabular fracture classification according to Letournel.^2,​3 Both columns are orientated in an inverted “Y”-shape, with integration of the acetabulum at its connection point (▶ Fig. 1.1).

The posterior column consists of the ischium and parts of the ilium (▶ Fig. 1.2). It is biomechanically more important and transfers the body weight from the sacroiliac joint and from the posterior and posterosuperior joint parts to the proximal femur. Thus, it consists of a thick and strong bone quality. Radiographically, a “sourcil” is part of this column, which can be relevant for certain diagnostic evaluations.⁴ The posterior border of the posterior column is formed by the greater sciatic notch, the ischial spine, the lesser sciatic notch, and the ischial tuberosity. The medial part of this column is comprised of parts of the body of the ischium and the posterior parts of the quadrilateral surface.

The anterior column consists of the pubis and parts of the ilium (▶ Fig. 1.3). It starts at a variable location of the iliac crest, runs across acetabular joint, and typically transects the obturator foramen at two locations leaving the foramen at the inferior pubic ramus. The inner side of the anterior column represents the anterior parts of the quadrilateral surface, and forms the osseous border of the obturator canal. The iliac fossa serves as the origin of the iliacus muscle, which, together with the psoas major muscle, forms a cranioventral “channel” to the lesser trochanter of the femur. The iliopectineal eminence forms the outer cortex of the anterior wall of the acetabulum (▶ Fig. 1.4). Its medial border approximately corresponds with the distal end of the anterior horn of the lunate surface, and therefore represents an important surgical reference point. The anterior column integrates the anterior and anterosuperior areas of the acetabulum (▶ Fig. 1.3).

The nearly hemispherical acetabulum is integrated between the anterior and posterior column structure described by Letournel. Thus, a confluence of the three pelvic bones forms the acetabulum: superiorly, the iliac bone, posteriorly the ischial bone, and anteriorly the pubic bone. After fusion of these three bones during adolescence, the hemipelvis (i.e., the innominate bone) is created.⁵ The iliac bone contributes to approximately 40%, the ischial to further 40%, and the pubic bone to 20% of the bony acetabulum.⁶

The entry plane of the acetabulum has an anterolateral and inferior inclination, forming an angle to the horizontal plane of around 50–60 degrees, and to the sagittal plane of 25–30 degrees.⁷ An 18.9-degree anteversion is observed. The anteversion is reduced in males as compared with females.⁷ The diameter of the acetabulum varies dependent upon body size. The mean diameter is approximately 50 mm.^7,​8,​9

The true articular surface, the lunate surface, is formed by a narrow anterior horn and a broad posterior horn together with its broad superior articular part, the acetabular dome, which transmits the body weight to the femur (▶ Fig. 1.5). Correspondingly, the C-shaped lunate surface has a cartilage thickness of > 2.5 mm at its superior and posterior segments.^10,​11 Deep cartilaginous defects can be present in up to 10% of cadaveric dissections starting from the internal rim, which may also transect the articular surface. These defects are most frequently observed at the acetabular roof—in rare cases separating the anterior and posterior horns.¹⁰ The size of the lunate surface was analyzed to be 2294 mm².¹²

Hatem et al measured the anterior and posterior horns as 10 mm proximal to their most distal parts. The anterior horn had an average width of 14.8 mm, whereas the posterior horn was larger with an average width of 19.7 mm.⁷

The anterior horn comprises 31% of the acetabular diameter and the posterior horn 41%, indicating that the acetabular fossa contributes with 28% to the acetabular diameter.⁷

Between both horns, the rough acetabular fossa (cotyloid fossa) forms the central acetabular floor which is not covered by cartilage. This medial acetabular wall is extremely thin, and forms a large part of the quadrilateral surface when visualized in medial plane. The acetabular fossa has an irregularly formed rim.¹⁰ The acetabular fossa contains the pulvinar, a synovial covered fat pad, and ligamentum teres, which is intraarticular but extrasynovial.

Between the anterior and posterior acetabular horns, part of the articular surface, the acetabular notch (a deficient acetabular rim area), is spanned by the transverse ligament, which is a noncartilaginous extension of the labrum, connecting the posterior and anterior horns. It has a large and wide origin from the posterior horn, and inserts at the anterolateral edge of the anterior horn. The acetabular fossa is medialized by 3–5 mm in relation to the lunate surface, and has a height of 4–5 cm and a width of 2–3 cm. It is filled by fatty tissue, the acetabular pulvinar, which is loosely attached to the periosteum and is enveloped by the base of the internal synovial sheet. The internal ligament of the joint can also be found here: the ligament of the head of the femur. This ligament extends from the base of the acetabular fossa to the fovea of the femoral head (fovea capitis femoris) and has a mean length of approximately 3.5 cm and a variable width (of up to 1 cm). It usually has three origins: a strong, uniform posterior origin at the medial part of the posterior horn; a weaker anterior origin at the medial part of the anterior horn; and a weaker central origin from the transverse acetabular ligament.¹³ Its external surface covers the femoral head, and its internal surface covers the pulvinar. The ligament is enveloped by an internal synovial sheet, and therefore is not actually intraarticular. Variations in size and strength can be present; in exceptional cases it can only consist of loose connective tissue. However, it is the guiding structure for the artery of the ligament of the head of the femur which runs centrally in the ligament.

The external border of the acetabulum consists of the bony acetabular rim, also termed limbus acetabuli, which forms the acetabular entry plane. It has a variable anterior shape: a curved anterior rim can be expected in 47.4%, a straight rim in 21.8%, an irregular rim in 14.3%, and an angular rim in 16.4%.^{9,​14,​15,​16}

The lunate surface is additionally enlarged by a fibrous–cartilaginous joint lip, the acetabular labrum, which is attached to the bony acetabular rim. It has a width of approximately 1 cm on both its superior and posterior sides, and a width of 0.5 cm on its anterior and inferior sides. The labrum has a triangular cross-sectional shape and extends into the joint space, forming a perilimbicus recessus between the capsule and labrum, which is normally absent in the area of the transverse acetabular ligament. It is attached to the acetabular rim, but separated from the capsule—the latter inserts more laterally.¹⁷ Especially, at the posterior rim, it significantly adds to the femoral head coverage.^18,​19 The labrum increases the acetabular depth by approximately 30%²⁰ and optimizes the distribution of forces around the joint.^21,​22 It is connected anteriorly and posteriorly to the transverse acetabular ligament.

1.2 Capsular Anatomy

The capsule is an important stabilizer of the hip joint, surrounding the joint as a cylindrical sleeve, from the acetabular rim to the base of the femoral neck, where it inserts posteriorly, more proximal than anterior.²³

Three supporting intrinsic capsular ligaments can be distinguished, consisting of the iliofemoral, pubofemoral, and ischiofemoral ligaments and the zona orbicularis, respectively:

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  Iliofemoral ligament: The largest and thickest ligament and consists of a medial and lateral part; both parts form an inverted “Y.”

  
  
  
  
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    Medial, inferior part originates between the anterior inferior iliac spine (AIIS) and the iliac portion of the acetabular rim,^{23,​24,​25} with vertically orientated fibers running to its insertion at the distal intertrochanteric line; it is tightened in external rotation and extension.²⁵

    
    
  • 
    

    The lateral, superior part starts proximal to the AIIS, running more horizontal to the anterior crest of the greater trochanter^{23,​24,​25} and is tightened in external rotation and flexion or in internal and external rotation during hip extension.^25,​26

  
  
• 
  

  Pubofemoral ligament: Originates from the superior pubic ramus and inserts on the distal region of the intertrochanteric line of the femur^{23,​24,​25}; it tightens in external rotation and hip extension²³ and in abduction.²⁵

  
  
• 
  

  Ischiofemoral ligament: Upper and lower bands originate from the ischial part of the acetabular rim, inserting medial at the anterosuperior and posteromedial site of the base of the greater trochanter, respectively^{23,​24,​25}; it tightens during internal rotation.²⁶

  
  
• 
  

  The zona orbicularis is a thick fiber bundle surrounding the femoral neck, which supports the hip stability by maintaining the femoral head within the acetabulum.^25,​27

Overall, the acetabular capsular origin is located approximately 13.0 mm distal to the AIIS, approximately 11.1 mm lateral to the iliopectineal eminence, and 5.1 mm proximal to the bony acetabular rim.²⁸ The anterior capsule has an average thickness of 1.3 mm, whereas the superior capsule is strongest with a thickness of approximately 3.7–4.0 mm.²⁸ The posterior capsule is thinner and more unstable than the anterior and superior capsule.²⁵ A potentially weak area of the anterior capsule is supposed to be between the medial band of the iliofemoral ligament and the pubofemoral ligament, suggesting the risk of developing communication between the hip joint and the iliopsoas bursa.

In contrast, at the femoral insertion, the capsule was thicker in the anterior part compared to the posterior part.^29,​30

The optimal relaxed position of the hip joint capsule was stated to be at 45-degree flexion, as this was associated with the lowest intracapsular pressure increase.³¹

Several muscles insert at different capsular parts, acting as dynamic capsular stabilizers^28,​32:

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  Iliocapsularis muscle: Contributes to a large area of the anteromedial capsule

  
  
• 
  

  Indirect (reflected) head of the rectus femoris: Contributes to the anterosuperior acetabular rim

  
  
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  Gluteus minimus tendon: Large and broad lateral capsular insertion

  
  
• 
  

  Piriformis tendon: No capsular attachments

  
  
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  Triceps coxae: Small, consistent capsular adhesions posterosuperior

  
  
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  Obturator externus tendons: Small, consistent capsular posteroinferior

1.3 Ligamentum Teres (Ligamentum Capitis Femoris)

The ligamentum teres is an intraarticular ligament and connects the femoral head with the acetabulum. It has a distal trapezoidal shape and originates from the bony acetabular notch and the transverse ligament to the fovea capitis, where it inserts at a nonarticular area in a round shape. The ligament is attached to the periosteum by two fascicles, originating at the ischial and pubic margins of the acetabular notch.³³ Intraligamentously, a pyramidal, fascicular appearance is observed.²³ It is potentially unstable in flexion and internal rotation,^23,​29 whereas it is tightened during external rotation.³³ It acts as a strong intrinsic stabilizer that resists joint subluxation forces.^33,​34

1.4 Bursae around the Hip

Several periarticular bursae are of surgical relevance. The anatomy of these different bursae can be classified according to their localization.

• 
  

  Anterior: Iliopectineal bursa is the largest bursa, present in 98% of cases; it is usually found anterior to the hip joint at the junction between the pubofemoral and iliofemoral ligaments and communicates with the joint in 15% of cases; it can have surgical relevance during dissection of the ilioinguinal approach.³⁵

  
  
• 
  

  Lateral: In the lateral hip joint area, several bursae can be found; these are often referred to the greater trochanter bursae, but can be distinguished to a trochanteric/subgluteus maximus bursa, a subgluteus medius/anterior subgluteus medius bursa, a subgluteus minimus bursa, a piriformis/posterior subgluteus medius bursa, and a gluteofemoral bursa.^35,​36

  
  
• 
  

  Posterior: Three main bursae can be present in the posterior part of the hip joint area, surgically relevant during the Kocher-Langenbeck approach; the obturator externus bursa communicates from the posteroinferior hip joint to the obturator externus tendon^35,​37; the obturator internus bursa is often observed where the obturator internus tendon runs in a “boomerang”-shaped path around the posterior ischium near the sciatic spine; the ischial or ischiogluteal bursa is located between the ischial tuberosity and the gluteus maximus muscle.³⁵

1.5 Relevant Muscles around the Hip

As single approaches for the treatment of acetabular fractures are preferred, the surgical anatomy of the periarticular muscles can be divided into the posterior muscle group and the anterior muscle group.

The relevant posterior muscles during the Kocher-Langenbeck dissection consist of the quadratus femoris muscle, the external obturator muscle, the triceps coxae (consisting of the inferior gemellus, the obturator internus, and the superior gemellus muscle), the piriformis muscle, as well as the gluteus medius et minimus muscles. Although the gluteus maximus muscle is dissected, it is usually not necessary to dissect its tendinous insertion. In addition, the two origins of the rectus femoris muscle must be considered during the surgical hip dislocation approach according to Ganz.

Relevant anterior muscles in surgical approaches to the acetabulum are dependent on the chosen approach. Using the ilioinguinal approach, knowledge of the anatomy of the abdominal wall muscles with the obliquus external and internus muscles—as well as the transversus abdominis muscle, the inguinal ligament, and the iliopsoas—is relevant. Using the intrapelvic approach, the obturator internus muscle and the iliopsoas muscle are relevant together with special ligamentous and fascial anatomic characteristics of this region.

1.5.1 Posterior Muscle Group

The posterior muscle group is described from inferior to proximal, starting with the quadratus femoris muscle up to the gluteal muscles (▶ Fig. 1.6, ▶ Fig. 1.7).

Gluteus Maximus Muscle

The gluteus maximus muscle is the most relevant extensor of the joint. It originates from the lateral aspect of the posterior sacral surface, the posterior outer ilium, and from the thoracolumbar fascia. Beside its insertion into the iliotibial tract, it broadly inserts, approximately 7.5 cm, at the linea aspera.³⁸

Quadratus Femoris Muscle

The quadratus femoris muscle, with its quadrangular or rectangular appearance, has its origin at the inferolateral edge of the posterior inferior pubis ramus along the anterior part of the ischial tuberosity, just above the hamstring origins. It has a 40-mm broad insertion at the posteromedial proximal femur along the posterior intertrochanteric crest between the greater and minor trochanter, approximately 2 cm posteromedial to the superior tip of the linea aspera.³⁸

Anteriorly, parts of the obturator externus tendon are in close relation to the superior muscle belly, and posterior to the muscle belly, the sciatic nerve is embedded in fatty tissues.

At the superior margin of the muscle belly, a triangular fat tissue area becomes visible which ends superior at the lower border of the inferior gemellus muscle. Within this fat tissue, close to the femur, the tendon of the externus muscle becomes visible.

From the surgical point of view, almost no dissection is required distal to the quadratus femoris muscle. Here, the gluteus maximus inserts with its broad tendon. Rarely, the tendon attachment has to be partially incised for better mobilization.

Functionally, the quadratus femoris acts as adductor and external rotator in the hip joint.

Obturator Externus Muscle

The obturator externus muscle acts, as the triceps coxae, as an additional external rotator of the hip joint. This muscle has its origin anterior to the external bony margin of the obturator foramen. Its cylindrical tendon passes around the inferior femoral neck, with connections to the capsule, inserting at the piriformis fossa at the greater trochanter. The exact oval-shaped footprint is located at the inferomedial greater trochanter two-thirds posterior of the distance of the anterior tip of its superomedial border.³⁸ Thus, the muscle dynamically stabilizes the femoral head within the acetabulum and allows external rotation of the hip in a neutral position and in 90-degree flexion. Secondary, it acts as an adductor during hip flexion.³⁹ The muscle has an overall length of 11 cm, integrating a tendon length of 5 cm.⁴⁰

The deep branch of the MCFA is responsible for relevant vascular supply to the femoral head. Regularly, a constant trochanteric branch can be identified, which guides to the deep branch.

Triceps Coxae Muscles

The triceps coxae muscles are the primary external rotators of the hip. This muscle group includes the inferior and superior gemellus and the obturator internus muscle and tendons. These three muscles have different nerve supplies but a conjoint nerve root. Therefore, these three muscles are considered as three different heads of a single muscle.⁴¹

The exact footprint is located on the medial surface of the greater trochanter, approximately 40% posterior to the anterior tip of the whole distance of the superomedial border.³⁸

The obturator internus originates from the inner pelvis part of the obturator foramen and from the quadrilateral surface (▶ Fig. 1.6). The muscle belly leaves the true pelvis through the greater sciatic notch. The muscle has an overall length of 16 cm, integrating a tendon length of 10 cm.⁴⁰

The inferior gemellus muscle often originates from the lateral surface of the ischial tuberosity and also from the its intrapelvic surface.⁴²

Piriformis Muscle

The piriformis muscle originates from the anterolateral surface of the S2–4 vertebra. It leaves the pelvis through the greater sciatic notch, creating a suprapiriform and infrapiriform foramen. The piriformis tendon inserts at the anterolateral facet of the greater trochanter and often has a connection with the obturator internus tendon (conjoint tendon) and other external rotator tendons. The exact footprint is located directly inferomedial at the center of the superomedial border of the greater trochanter.³⁸

These tendons have several connections with the hip joint capsule and especially the gluteus medius muscle.⁴⁰ The muscle has an overall length of 14 cm, integrating a tendon length of 10 cm.⁴⁰

The insertion of the tendons of piriformis and obturatorius internus muscles at the greater trochanter is variable.⁴³ Both tendons can insert as conjoint tendons^40,​44 or the obturator internus tendon crosses the piriformis tendon. In addition, these tendons can have a parallel course and insertion.⁴⁴

Several variations are observed in the literature (overview in^{45,​46,​47}). The most common variation is a division of the piriformis muscle into two heads, with the common peroneal nerve running between them.^45,​47

Gluteus Medius Muscle

Until today, no clear anatomic description can be made, especially regarding origin, muscle course, and insertion of the gluteus medius muscle.⁴⁸ Overall, several textbooks agree that the gluteus medius muscle has its origin somewhere at the outer iliac bone. More scientific analyses stated that the origin can be from the gluteal aponeurosis and from different areas of the iliac crest (overview in⁴⁸).

The fan-shaped muscle belly, composed of three parts, has no relevant connecting fibers to the outer iliac bone. The posterior muscle belly runs parallel to the femoral neck, while the anterior part has a nearly vertical orientation.⁴⁹ The superior gluteal nerve is innervating all three muscle parts by different branches. The exact footprint of the tendinous insertion at the greater trochanter is not fully clear. Most commonly it is described to be located on the lateral aspect of the greater trochanter.^38,​48

Gluteus Minimus Muscle

Until today, no clear anatomic description can be made especially regarding origin, muscle course, and insertion of the gluteus minimus muscle.⁴⁸ Overall, several textbooks agree that the gluteus minimus muscle has its origin somewhere at the outer iliac bone, most often between the anterior and inferior gluteal lines. Beck et al described the origin on the outer iliac surface starting 3–5 mm below the anterior superior iliac spine (ASIS) and between ASIS and AIIS, running parallel to the iliac crest up to the iliac tubercle, following the anterior gluteal line to the greater sciatic notch.⁵⁰ Muscle parts attach largely to the joint capsule. Overall, a fan-shaped appearance to the musculature can be present.

The gluteus minimus inserts irregularly with a long, thin tendon in most cases at the anterior greater trochanter.^48,​50 The exact footprint is located on the anterior aspect of the greater trochanter with its center approximately 2 cm inferolateral to the anterior tip.³⁸

1.5.2 Relevant Anatomy of the Anterior Wall

Knowledge of the anatomy of the outer and inner side of the anterior wall is essential when performing the ilioinguinal and intrapelvic approach.

Extrapelvic Abdominal Wall

Performing the ilioinguinal approach requires knowledge of the basic anterior wall anatomy, the course of the inguinal ligament, and the anatomy of the lacuna musculorum et vasorum.

During ilioinguinal surgery, the main step during dissection is the identification of the inguinal ligament. After dissection, the external oblique abdominal muscle, whose aponeurosis inserts at the anterior inguinal ligament (Poupart’s ligament), the internal oblique and transversus abdominal muscle fibers are released from the inguinal ligament. The tendinous insertion of these muscles consists of a thickened strip of the iliopsoas fascia that forms the superolateral part of the ilio-pectineal arch.⁵¹ No tendinous attachment to the inguinal ligament is usually present.

The inguinal ligament originates at the ASIS and inserts at the pubic tubercle medially (see ▶ Fig. 1.9). Fibers of the inguinal ligament reflect onto the superior pubic ramus to form the lacunar ligament, which is part of the inguinal canal.^52,​53

The transversus abdominal muscle is part of the superior and lateral inguinal canal. Its lower aponeurotic fibers broadly insert together with parts of the oblique internal muscle near the pubic tubercle, becoming part of Cooper’s ligament, the medially thickened periosteum of the superior pubic ramus (see later).

In summary, the inguinal canal consists of the aponeurosis of the external oblique muscle, which forms its anterior wall, the inguinal ligament forms the inferior border, and the transversus abdominis forms parts of the superior and lateral walls.

The rectus abdominis muscle inserts into the anterosuperior pubic ramus parasymphyseal.

Intrapelvic Abdominal Wall

During ilioinguinal and intrapelvic dissection, relevant structures have to be identified.

After opening the retropubic area, the superior pubic ramus is identified.

Macroscopically, the direct border at the superior pubic ramus to the true pelvis is formed by the pectineal ligament (Cooper’s ligament), which covers the posterior part of the pecten ossis pubis. Cooper’s ligament was also found as a lateral aponeurotic extension of the lacunar ligament (ligament of Gimbernat) onto the superior ramus.⁵⁴ It has a crescent-shaped course, with a lateral thin insertion without connection to the insertion of the iliopectineal ligament (iliopectineal arch). The latter only ends at the iliopectineal eminence.^52,​55 The iliopectineal arch represents fibers of the iliopectineal fascia, and is located lateral to the Cooper’s ligament and has a perpendicular orientation to the Cooper’s ligament.⁵⁴ The average length of the pectineal ligament is approximately 53 mm.⁵⁵ Overall, the pectineal or Cooper’s ligament represents a thickening of the pectineal fascia rather than a thickening from the periosteum.⁵⁵

The iliopectineal arch divides the lacuna musculorum from the lacuna vasorum (▶ Fig. 1.8, ▶ Fig. 1.9, ▶ Fig. 1.10). During ilioinguinal dissection a relevant surgical step is the identification of the iliopectineal arch, which has to be dissected to get access to the superior ramus and the anterior wall as part of the iliopectineal eminence.

During intrapelvic dissection, pericostal incision and pericostal mobilization of the pectineal ligament are essential for identifying the whole superior ramus extending up to the inferior iliac fossa without incising the iliopectineal arch.

1.6 Vascular Anatomy

This section provides a description of the surgically relevant periacetabular vasculature.

1.6.1 Hemipelvic Vascularity

Henle already reported a detailed description on the vascular supply of the acetabulum,⁵⁶ which was further enlarged by the works of Bergoin and Louis,⁵⁷ Letournel,³ Beck et al,⁵⁸ and Kathagen et al.⁵⁹

A vascular circle is surrounding the acetabulum and consists of the superior gluteal artery, the inferior gluteal artery, the internal pudendal artery, and the obturator artery—the latter additionally supplying the quadrilateral surface.^{58,​59,​60,​61,​62,​63}

The posterior ilium was found to be significantly more vascularized than the anterior part, corresponding to its biomechanical significance.⁶³ Medially, the superior ramus and the pelvic brim are surrounded by a rectangle configuration of vessels, anterior the corona mortis, superior the common iliac vessels, posterior the iliac internal vessels, and inferior the obturator vessels.^58,​63

The acetabulum is mainly vascularized by the artery of the roof of the acetabulum arising from the inferior gluteal artery, the artery of the ischium from the internal pudendal artery, and the acetabular branch of the obturator artery.⁶³ In contrast, Beck et al stated that the arteries of the roof of the acetabulum were mainly arising from the superior gluteal artery, whereas the main vascular effect of branches of the inferior gluteal artery was the connection between the superior gluteal artery and the obturator artery.⁵⁸ Even after periacetabular osteotomy, no relevant change in vascular supply was noted, as the created acetabular fragment showed sufficient vascular supply by the supra-acetabular and acetabular branches of the superior gluteal artery and branches from the obturator and inferior gluteal artery.⁵⁸

The external iliac fossa is primarily supplied by the superior gluteal artery (▶ Fig. 1.11). On the medial side, blood supply is received by branches of the fourth lumbar artery, the iliolumbar artery, and by the deep circumflex iliac artery. The fourth lumbar artery runs between the psoas major and iliacus muscles. It divides into two branches: the first branch anastomoses with the deep circumflex iliac artery at the medial iliac crest; the second branch anastomoses with the iliolumbar artery at the posterior region of the iliac wing.

The iliolumbar artery divides into three branches: a lumbar branch, an iliac branch, and a spinal branch. The lumbar and iliac branches cross the linea terminalis directly or up to 21 mm anterior to the sacroiliac (SI) joint.⁶⁴ The iliac branch supplies the iliac fossa and the linea terminalis supported by anastomoses with the deep and superficial circumflex iliac arteries and near the ASIS with anastomoses of the superior gluteal artery. In the region of the AIIS, anastomoses exist with branches of the medial and lateral circumflex femoral arteries.⁵⁸

Superior Gluteal Artery

The superior gluteal artery (SGA) supplies the supraacetabular roof region (▶ Fig. 1.11), forming multiple anastomoses with the ascending branch of the lateral circumflex femoral artery (LCFA).

It exits the inner pelvis through the greater sciatic notch proximal to the piriformis muscle and divides into two major branches: the superficial and deep branch. The superficial branch supplies the gluteus medius and maximus muscle running between these muscles. The deep branch supplies the gluteus medius and minimus muscle running between these two muscles.^{58,​59,​65,​66} The deep branch finally divides into superior and inferior branches, with a further subdivision of the inferior branch into a supraacetabular and an acetabular branch.⁶⁷

The superior branch runs along the margin of the gluteus minimus muscle in the direction of the ASIS, forming anastomoses with the superficial and deep circumflex iliac arteries, and with branches of the iliolumbar artery.

The inferior branch runs along the lateral side of the gluteus minimus muscle along with the superior gluteal nerve in the direction of the tensor fasciae latae muscle, forming anastomoses with branches of the ascending branch of the LCFA. This ascending branch also serves as the main vessel supplying the tensor fasciae latae muscle. The superior and inferior branches have a mean diameter of approximately 1.5–2 mm.

The supraacetabular branch finally enters the gluteus minimus muscle running intramuscular to the superior acetabular margin, to anastomose with the acetabular branch, running from the dorsal to the caudal edge of the gluteus minimus muscle.

Inferior Gluteal Artery

The inferior gluteal artery (IGA) exits the pelvis through the infrapiriform foramen, supplying the gluteus maximus and piriformis muscles, and the sciatic nerve. It supplies the posterior wall of the acetabulum by two to three smaller branches⁵⁸ (▶ Fig. 1.12).

It also supplies the posterior column and the ischial tuberosity by anastomoses to the posterior branch of the obturator artery, and parts of the posterosuperior acetabulum by anastomoses with the SGA.^{58,​59,​62}

As a variation, a common vascular trunk of the SGA and IGA can exist, leaving the pelvis through the suprapiriform foramen. This trunk then immediately divides into the SGA and IGA at the superior border of the piriformis muscle.^{58,​59,​62}

Internal Pudendal Artery

The internal pudendal artery (IPA) also leaves the pelvis more distal through the infrapiriform foramen, running medially to the ischial spine. On the outer side of the hemipelvis, it can support the vascular supply of the posterior wall and of posteroinferior parts of the posterior column.⁵⁹

Obturator Artery

The obturator artery (OA) arises from the main anterior branch of the internal iliac artery, but variably it can arise from the external iliac artery or even the inferior epigastric artery.⁵⁹ It supplies the quadrilateral surface, leaving the true pelvis through the obturator canal (▶ Fig. 1.13) supplying muscles of the medial compartment of the thigh. Here, first the OA divides into an acetabular branch, which runs into the acetabular fossa through the acetabular notch supplying the acetabular fossa, and a branch, which runs into the ligament of the head of the femur. Farther along its course, at the upper margin of the adductor brevis muscle, it divides into anterior and posterior branches. The anterior branch may anastomose with branches of the medial circumflex femoral artery. The posterior branch supplies the deep adductor muscles, and has a role in the supply of the inferior acetabulum. It anastomoses with the inferior gluteal artery.⁵⁹

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