T Portal Anatomy 7

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7

Portal Anatomy

J.W. Thomas Byrd

There has been much variation, as well as pre- cision, in the description in the literature of portal placements for hip arthroscopy. The at- tention given to these detailed descriptions is important for two reasons: (1) accessibility of the joint and (2) avoidance of the major surrounding neurovascular structures.

The tip of the greater trochanter is the common landmark used in describing a variety of lateral portals.^1–3Equal variation can be found in the description of an anterior portal (Figure 7.1). Eriksson et al.,⁴Frich et al.,⁵and Gross⁶base the portal lateral to the femoral pulse. Ide et al.⁷describe an anterior portal 1 cm lateral and distal to the midpoint of a line between the anterior superior iliac spine and the symphysis pubis.

Johnson⁸also describes the symphysis pubis as a landmark, positioning a portal at the site of intersection of a sagittal line drawn distally from the anterior superior iliac spine and a transverse line drawn laterally from the pubic symphysis. Dorfmann et al.,⁹ follow- ing a cadaveric study, were most comfortable with a portal inserted midway along a line between the anterior superior iliac spine and the superior tip of the greater trochanter. Conversely, Glick et al.¹⁰describe an anterior portal at the site of intersection of a sagittal line drawn distally from the anterior superior iliac spine and a transverse line across the tip of the greater trochanter. Similarly, Watanabe¹¹ describes the same approach in his text on arthroscopy of small joints. A medial approach was also described by Gross,⁶ appli- cable in the pediatric population with hip dysplasia.

I use three standard arthroscopy portals (Figure 7.2).¹²Two of these are placed laterally (anterolateral and posterolateral) over the superior margin of the greater trochanter and can effectively enter the hip under direct fluoroscopic control. Positioning of the anterior portal requires more triangulation technique.

Herein are described the three standard portals that I use for hip arthroscopy (see Chapter 11) and the spe- cific anatomic relationship of the major structures to these portals (Table 7.1).¹³

All three portals are routinely established for each arthroscopic procedure and usually found to provide adequate accessibility of the joint. If, however, an al- ternative portal is necessary, knowing the anatomic relationship of the extraarticular structures to these

index portals should be helpful in safely establishing supplemental entry sites.

ANTERIOR PORTAL

The anterior portal is established by drawing a sagittal line distally from the anterior superior iliac spine and a tranverse line from the superior margin of the greater trochanter (see Figure 7.2). The intersection of these two lines marks the site of the anterior portal.

The portal must be directed approximately 45 degrees cephalad and 30 degrees toward the midline. In the clinical setting, this is performed under fluoroscopic control as well as direct visualization through the arthroscope from the anterolateral portal, which is established first for introduction of the arthroscope.

The anterior portal lies an average of 6.3 cm distal to the anterior superior iliac spine. It penetrates the muscle belly of the sartorius and the rectus femoris before entering through the anterior capsule (Figure 7.3).

Typically, the lateral femoral cutaneous nerve is divided into three or more branches at the level of the anterior portal. The portal passes within several millimeters of one of these branches, usually the most medial branch (Figure 7.4). Consequently, moving the portal more laterally, a maneuver that has occasionally been described for avoidance of the lateral femoral cutaneous nerve, is ineffective. It simply places the portal more within the remaining branches of the nerve. In fact, moving the portal more medially would more effectively avoid the lateral femoral cutaneous nerve, but this maneuver would be ill advised because of the increasingly closer proximity of the femoral nerve.

Because of the multiple branches, the lateral femoral cutaneous nerve is not easily avoided by al- tering the portal position, but it is protected by using meticulous technique in portal placement. Specifi- cally, it is most vulnerable to a skin incision placed too deeply, lacerating one of the branches.

Passing from the skin to the capsule, the anterior portal runs almost tangential to the axis of the femoral nerve and lies only slightly closer at the level of the capsule with an average minimum distance of 3.2 cm (Figure 7.5).

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Although variable in its relationship, the ascending branch of the lateral circumflex femoral artery is usually approximately 3.7 cm inferior to the anterior portal (Figure 7.6). In some cadaver specimens, a small terminal branch of this vessel has been identified ly- ing within millimeters of the portal at the level of the capsule. The clinical significance of this is uncertain, and there have been no reported cases of excessive bleeding from the anterior position.

ANTEROLATERAL PORTAL

The anterolateral portal lies most centrally in the safe zonefor arthroscopy and thus is the portal established first for introduction of the arthroscope. It is positioned directly over the superior margin of the greater trochanter at its anterior border (see Figure 7.2). Ac- counting for the slightly anterior position of the femoral head resulting from femoral neck anteversion, this allows a relatively straight shot into the hip joint under fluoroscopic guidance in the anteroposterior (AP) plane. Care should be taken during portal placement to assure neutral rotation of the hip because excessive internal or external rotation alters the relationship of the greater trochanter with the femoral head.

The anterolateral portal penetrates the gluteus medius before entering the lateral aspect of the cap-

Anterior superior iliac spine Femoral pulse

Pubic symphysis Greater trochanter A

B

D E

C

Anterior Portal Anterolateral Portal Posterolateral Portal FIGURE 7.1. Various descriptions of an anterior portal have been

proposed: (A) based lateral to the femoral pulse; (B) 1 cm lateral and distal to the midpoint of a line between the anterior superior iliac spine (ASIS) and symphysis pubis; (C) site of intersection of a sagittal line from the ASIS and a transverse line from the symphysis pubis; (D) midpoint of a line between the ASIS and superior tip of the greater trochanter; (E) intersection of a sagittal line from the ASIS and a transverse line from the tip of the greater trochanter. Note: I strongly discourage consideration of the portal described in B; this does not appear to represent a safe approach to the joint. Also, note that palpation of the femoral pulse as a landmark can be difficult once the surgical field has been sterilely prepared.

FIGURE 7.2. The site of the anterior portal coincides with the intersection of a sagittal line drawn distally from the anterior superior iliac spine and a transverse line across the superior margin of the greater trochanter.

The direction of this portal courses approximately 45 degrees cephalad and 30 degrees toward the midline. The anterolateral and posterolateral portals are positioned directly over the superior aspect of the trochanter at its anterior and posterior borders. (Courtesy of Smith &

Nephew Endoscopy, Andover, MA.)

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TABLE 7.1. Distance from Portal to Anatomic Structures Based on an Anatomic Dissection of Portal Placements in Eight Fresh Cadaver Specimens).

Portal Anatomic structure Average (cm) Range (cm)

Anterior superior iliac spine 6.3 6.0–7.0

Lateral femoral cutaneous nerve^a 0.3 0.2–1.0

Anterior Femoral nerve (level of sartorius)^b 4.3 3.8–5.0

Femoral nerve (level of rectus femoris) 3.8 2.7–5.0

Femoral nerve (level of capsule) 3.7 2.9–5.0

Ascending branch of lateral circumflex femoral artery 3.7 1.0–6.0

cTerminal branch 0.3 0.2–0.4

Anterolateral Superior gluteal nerve 4.4 3.2–5.5

Posterolateral Sciatic nerve 2.9 2.0–4.3

aNerve had divided into three or more branches and measurement was made to the closest branch.

bMeasurement made at superficial branch of sartorius, rectus femoris, and capsule.

cSmall terminal branch of ascending branch of lateral circumflex femoral artery identified in three specimens.

Source:From Byrd et al.,¹³with permission of Arthroscopy.

FIGURE 7.4. The relationship of the anterior portal to the multiple branches of the lateral femoral cutaneous nerve is shown. Multiple branches at the level of the portal are character- istic, and the branches always extend lateral to the portal. (Reprinted with permission from Byrd et al.¹³)

FIGURE 7.3. Anterior portal pathway/relationship to lateral femoral cutaneous nerve, femoral nerve, and lateral circumflex femoral artery. (Courtesy of Smith &

Nephew Endoscopy, Andover, MA.)

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sule at its anterior margin (Figure 7.7). The structure of most significance relative to this portal is the superior gluteal nerve (Figure 7.8). After exiting the sciatic notch, the superior gluteal nerve courses transversely posterior to anterior across the deep surface of the gluteus medius. Its relationship is the same with both the lateral portals, with an average distance of 4.4 cm.

POSTEROLATERAL PORTAL

The posterolateral portal is positioned similar to the anterolateral portal except at the posterior margin of the greater trochanter (see Figure 7.2). Again, it is a relatively straight shot under fluoroscopic control, but

it is facilitated by direct visualization through the arthroscope from the anterolateral portal. Maintain- ing direct visualization is of greater importance because the posterolateral portal gets closer to major structures, specifically the sciatic nerve.

The posterolateral portal penetrates both the gluteus medius and minimus before entering the lateral capsule at its posterior margin (Figure 7.9). Its course is superior and anterior to the piriformis tendon (Fig- ure 7.10). It lies closest to the sciatic nerve at the level of the capsule. The distance to the lateral edge of the nerve averages 2.9 cm.

Several technical errors or alterations in technique during arthroscopy can place the sciatic nerve at greater risk. First, although hip flexion may relax the capsule, easing distraction, it may potentially draw the

FIGURE 7.6. The ascending branch of the lateral circumflex femoral artery (arrow) has an oblique course distal to the anterior portal seen here at the level of the capsule. This specimen demonstrates a terminal branch (double arrow) coursing vertically adjacent to the portal.

(Reprinted with permission from Byrd et al.¹³) FIGURE 7.5. The femoral nerve (n) lies lateral to the femoral artery (a) and vein (v). The relationship of the anterior portal as it pierces the sartorius is shown. (Reprinted with permission from Byrd et al.¹³)

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sciatic nerve closer to the joint, making it more vulnerable to injury. Second, it is important to maintain neutral rotation during portal placement. If the hip is inadvertently externally rotated, this moves the greater trochanter more posterior relative to the femoral head and the hip joint (Figure 7.11). This type of starting position, again, can place the sciatic nerve more at risk for injury. Thus, although slight flexion may relax the capsule, excessive flexion should be avoided. Also, care should be taken to ensure that the hip is in neutral rotation during portal placement. In- traoperative rotation of the hip may facilitate visualiza-

tion of portions of the femoral head but should not be performed until after all portals have been established.

NOMENCLATURE

Special mention should be made of the nomenclature used in describing arthroscopy portals. The anterior portal is not a true anterior approach to the hip. How- ever, it is as far anterior as can safely and reliably be positioned. Thus, for distinction from the various lateral portals, it is referred to as the anterior portal.

FIGURE 7.7. Anterolateral portal pathway/relationship to superior gluteal nerve. (Courtesy of Smith & Nephew Endoscopy, Andover, MA.)

FIGURE 7.8. The superior gluteal nerve (arrow) is shown coursing transversely on the deep surface of the gluteus medius. It passes above the anterolateral portal (double arrows), which is seen between the deep surface of the gluteus medius and the capsule. (Reprinted with permission from Byrd et al.¹³)

FIGURE 7.9. Posterolateral portal pathway/relationship to sciatic nerve and superior gluteal nerve. (Courtesy of Smith & Nephew En- doscopy, Andover, MA.)

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Glick et al.¹⁰ refer to the portals placed over the anterior and posterior margins of the superior aspect of the greater trochanter as anterior paratrochanteric and posterior paratrochanteric portals. This nomenclature has also been adopted by McCarthy et al.¹⁴in their review of hip arthroscopy.

I have used the terms anterolateral and postero- lateralfor simplicity and consistency with the termi- nology commonly used for other joints. Standard portals are usually described in an abbreviated fashion, defining only their relationship to the joint. Portal descriptions in relationship to a topographic landmark are usually reserved for specialty portals or portals that are only occasionally used.

I recommend that, until the nomenclature be- comes truly standardized, when referencing literature on hip arthroscopy, it is always important to review

the details regarding the description of portal placement. One must not rely solely on the portal name to automatically create an image of which portal is be- ing discussed.

References

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FIGURE 7.10. The relationship of the postero- lateral portal is shown with the piriformis tendon (p) and the sciatic nerve (s). Note the anomaly where the sciatic nerve is formed from three divisions distal to the sciatic notch and the lateralmost division passes through a split muscle belly of the piriformis. (Reprinted with permission from Byrd et al.¹³)

FIGURE 7.11. Neutral rotation of the operative hip is essential for protection of the sciatic nerve during placement of the posterolateral portal. (Courtesy of Smith & Nephew Endoscopy, Andover, MA.)

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6. Gross RH: Arthroscopy in hip disorders in children. Orthop Rev 1977;6:43–49.

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