4: Surgical Anatomy of the Anterior Hip and Thigh

John V. Horberg

Benjamin R. Coobs

Introduction

The DAA was first described as a surgical interval by Carl Hueter ¹ ^, ² in 1883 and was initially popularized in North America by Marius Smith-Petersen in 1917. ^2-4 The approach has steadily gained in popularity over the course of the past few decades as it has been adapted for total hip arthroplasty (THA), among many other uses. Preservation of the posterior musculature makes postoperative restrictions unnecessary, and the use of a true internervous plane has been shown to speed early postoperative recovery and mobilization. In this chapter, the relevant surgical anatomy necessary to safely expose the hip using the anterior interval is discussed and illustrated.

Superficial Anatomy and Surgical Landmarks

Landmarks (Figure 4.1; Table 4.1)

Figure 4.1

Superficial landmarks for DAA surgery.

Table 4.1

Deep Surgical Anatomy Musculature

Relevant musculature
Muscle	Origin	Insertion	Action	Innervation	Blood supply
Hip flexors
Psoas major	T12-L5 vertebrae	Lesser trochanter	Hip flexion	Femoral	Lumbar arteries
Psoas minor	T12-L1 vertebrae	Iliopubic eminence	Hip flexion	L1 ventral ramus	Lumbar arteries
Iliacus	Iliac fossa and sacral ala	Lesser trochanter	Hip flexion	Femoral	Medial femoral circumflex and iliac branch of iliolumbar arteries
Hip abductors and extensors
Tensor fasciae latae	Iliac crest and ASIS	Iliotibial band and proximal tibia	Abduct, flex, and IR thigh	Superior gluteal	Superior and inferior gluteal arteries
Gluteus medius	Ilium between anterior and posterior gluteal lines	Greater trochanter (posterior)	Abduct and IR thigh	Superior gluteal	Superior gluteal artery
Gluteus minimus	Ilium between anterior and inferior gluteal lines	Greater trochanter (anterior)	Abduct and IR thigh	Superior gluteal	Superior gluteal artery
Gluteus maximus	Ilium and dorsal sacrum	ITB, gluteal tuberosity	Extend and ER thigh	Superior and inferior gluteal	Superior and inferior gluteal arteries
Short external rotators
Piriformis	Anterior sacrum	Greater trochanter (superior)	ER thigh	Nerve to piriformis	Superior and inferior gluteal arteries and internal pudendal artery
Superior gemellus	Ischial spine	Greater trochanter (medial)	ER thigh	Nerve to obturator internus	Inferior gluteal artery and pudendal artery
Obturator internus	Ischiopubic rami and obturator membrane	Greater trochanter (medial)	Abduct and ER thigh	Nerve to obturator internus	Inferior gluteal artery
Inferior gemellus	Ischial tuberosity	Greater trochanter (medial)	ER thigh	Nerve to quadratus femoris	Medial femoral circumflex artery
Obturator externus	Ischiopubic rami and obturator membrane	Trochanteric fossa	ER thigh	Obturator	Obturator artery, medial femoral circumflex artery
Quadratus femoris	Ischial tuberosity	Intertrochanteric crest	ER thigh	Nerve to quadratus femoris	Medial femoral circumflex artery
Anterior thigh
Sartorius	ASIS	Pes anserinus	Flexion, abduction, an external rotation of hip; flexion and internal rotation of knee	Femoral	Superficial femoral, lateral femoral circumflex, and geniculate arteries
Rectus femoris	ASIS and superior acetabular rim	Patella and tibial tubercle	Extend knee	Femoral	Lateral femoral circumflex artery
Vastus lateralis	Greater trochanter and linea aspera	Lateral patella and tibial tubercle	Extend knee	Femoral	Lateral femoral circumflex artery and deep femoral perforating arteries
Vastus intermedius	Proximal femoral shaft	Patella and tibial tubercle	Extend knee	Femoral	Lateral femoral circumflex artery and deep femoral perforating arteries
Vastus medialis	Intertrochanteric line and medial linea aspera	Medial patella and tibial tubercle	Extend knee	Femoral	Femoral artery and profunda femoris
ASIS, anterior superior iliac spine; ER, externally rotate; IR, internally rotate; ITB, iliotibial band.

Anterior superior iliac spine (ASIS): The ASIS is a bony prominence at the anteriormost aspect of the iliac crest, which is palpable in most patients regardless of habitus; it serves as the origin for the sartorius and the medial aspect of the tensor fasciae latae.
Iliac crest: The iliac crest is a bony expansion at the superior aspect of the iliac wing extending from the ASIS anteriorly to the posterior superior iliac spine posteriorly and serving as the origin for the internal/external oblique and transversus abdominis muscle groups.
Inguinal crease: Overlying the inguinal ligament, a visible crease is present in most patients. The position can be altered by the presence of a large overhanging pannus, which can also cause skin irritation and maceration of the surgical wound. Care should be taken when placing an incision to avoid crossing this area if possible.
Pubic symphysis: The pubic tubercle and symphysis pubis can be palpated at the midline medial to the inguinal crease. The symphysis with the bilateral ASIS forms the anterior pelvic plane, which is referenced in some navigated technologies.
Greater trochanter: The greater trochanter can be palpated laterally in most patients regardless of habitus and is a common reference for incision placement.
Tensor fascia lata: Originating from the ASIS and anterior aspect of the iliac crest, the muscle belly of the tensor fascia lata is typically palpable. Longitudinal incisions should be placed overlying this muscle.
Patella: The proximal pole of the patella can be used to estimate leg length, and the lateral border of the patella can also be referenced for incision placement.

Application: Incision Placement (Figure 4.2)

Figure 4.2

A comparison of longitudinal and bikini incisions.

A, The longitudinal incision is made overlying the tensor fascia lata posterior to the midline of the muscle belly. Care is taken to keep the incision distal to the inguinal crease. B, The bikini incision is made parallel to the inguinal crease. Although some authors advocate for making the incision within the crease, wound complications can be avoided by making the incision 2 to 3 cm distal to the crease.

A variety of incision modifications have been described to access the Hueter interval for THA. ¹ ^, ³ ^, ^5-7 Currently, most anterior hip surgeons use a limited longitudinal incision for primary THA, whereas the bikini incision described by Leunig et al ⁵ has been gaining popularity. Dual-incision techniques using the Hueter interval anteriorly have fallen out of favor in recent years. ²

Longitudinal incision: The ASIS, greater trochanter, and inguinal crease are identified. The incision begins 1 to 3 cm distal and posterolateral to the ASIS and extends distally, centered over the palpable bulk of the tensor fascia lata and terminating after 7 to 10 cm. Care should be taken to limit proximal extension into the inguinal crease to minimize the risk of wound complications. The incision should be directed toward or lateral to the lateral pole of the patella and remain 2 to 3 cm anterior to the greater trochanter. Superficial dissection is carried through the subcutaneous tissue to the level of the tensor fascia lata. ⁷
Bikini incision: The ASIS, greater trochanter, and inguinal crease are again identified. The incision should be made parallel to the inguinal crease for 5 to 7 cm such that one-third of the incision is medial to the ASIS and two-thirds is lateral. Although the incision was originally made in the inguinal crease, many authors advocate for an incision 2 to 3 cm distal and parallel to the crease to limit wound complications in patients with an overlying pannus. Once through the dermis, deep dissection is performed longitudinally to the tensor fascia in the lateral aspect of the incision. ⁵ ^, ⁸

Neural Anatomy

The anterior interval exploits both an intermuscular and an internervous plane. The superficial plane is between the sartorius (femoral nerve [FN]) and tensor fascia lata (superior gluteal nerve [SGN]), and the deep plane is between the rectus femoris (FN) and the gluteus medius (SGN). Although the exposure is extensile proximally and distally, as is described in other chapters, a fundamental understanding of the neural structures that bind the primary working window of the interval is necessary to avoid complications (Figures 4.3 and 4.4).

Figure 4.3

An illustration showing femoral neck exposure with the ascending branches of the lateral femoral circumflex artery crossing the surgical field.

Figure 4.4

Branching patterns of the lateral femoral cutaneous nerve and their locations relative to the surgical field and the incision in the anterior fascia of the tensor fascia lata (TFL).

A, The sartorius type (36%); a dominant branch extends down the thigh anterior to the TFL and arborizes anterior to the typical fascial incision. B, The posterior type (32%); a dominant posterior branch crosses the TFL after passing under the inguinal ligament, placing it at risk during fascial incision. Minor branches extend distally anterior to the TFL. C, The fan type (32%); no dominant branch exists. The nerve arborizes extensively after passing under the inguinal ligament, making it impossible to preserve all branches when incising the anterior TFL.

(Original artwork by Matt Stolze.)

Lateral femoral cutaneous nerve (LFCN): The LFCN provides afferent sensory fibers to the proximolateral thigh. Surgical injury to this nerve can cause anesthesia or neuritis in as many as 81% of patients, which is typically not functionally limiting and generally improves with time. ⁹ The anatomy and arborization of the LFCN is quite variable and has been described and classified into three subtypes by Rudin et al ¹⁰ The “sartorius type” (36%) has a dominant anterior branch that follows the lateral border of the sartorius, with no or only small branches traversing the site of incision into the tensor fascia lata. The “posterior type” (32%) has a dominant or codominant posterior branch that diverges immediately distal to the ASIS and travels posteriorly. This branch is at risk with proximal extension of the approach. The “fan type” (32%) divides into multiple branches that fan out over the tensor fascia lata. It is not possible to avoid injuring some branches in this variant. ¹⁰
FN: The FN runs between the psoas major and the iliacus muscles and exits the pelvis under the inguinal ligament. It provides sensation to the anteromedial thigh and motor input to the psoas, pectineus, sartorius, and quadriceps group. ¹¹ The motor branches course laterally between the rectus femoris and the vastus intermedius to supply the vastus lateralis. The first branch crosses the femur 1 to 2 cm distal to the calcar ¹² and can be injured with distal exposure. ¹³ These branches can be spared with distal extension by elevating the vastus lateralis from posterior to anterior ¹⁴ ^, ¹⁵ or through an interbundle technique. ¹² The FN can also be injured directly or indirectly during retractor placement. ^16-18 As the FN travels distally, it lies closer to the acetabular rim, placing it at greatest risk for injury with anterior retractor placement at the 90° position. ¹⁹

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