The Direct Anterior Approach

CHAPTER 11 The Direct Anterior Approach

CHAPTER OUTLINE

KEY POINTS

The intermuscular interval between the rectus and tensor fasciae latae is used.

Specialized instruments are required.

This approach can result in slightly shorter cut-suture times.

In all fields of surgery, the shift from larger to smaller surgical approaches also requires changing the surgical paradigm one follows. In open surgery, the size of the approach is dictated by the requirements of the surgery; in minimally invasive surgery, the size of the surgical approach is much more of a fixed parameter. Enlarging the surgical approach is acceptable in open surgery, then, but is rarely performed in minimally invasive surgery.

The direct anterior approach in total hip arthroplasty uses the interval between the tensor fasciae latae muscle and rectus femoris and sartorius muscles. Although the intermuscular interval is directly anterior, the 6 to 8 cm-long skin incision is placed more laterally to protect the lateral femoral cutaneous nerve. A set of special retractors is used to provide an optimal view of the hip joint and to reduce the soft tissue stress. With the hip joint in situ, a double osteotomy is performed and the femoral head removed. After the acetabulum is exposed, it is prepared using an offset reamer handle. A similar instrument is used for the placement of the cup.

Femoral exposure is achieved through a combination of distinct steps that include positioning the operated leg in hyperextension, adduction, and external rotation, releasing the dorsal capsule, and then using a femoral elevator placed under the greater trochanter to lever the proximal femur upward. Although all these steps usually cannot guarantee complete leverage of the femur to or even above skin level, a fundamental principle of the direct anterior approach remains the fact that it is necessary to angulate the instruments during their insertion into the femoral canal. This angulation can be achieved by using the right instruments. A broach handle with an anterior as well as lateral offset (double offset) is the most important instrument.

INDICATIONS AND CONTRAINDICATIONS

Later in this book I discuss the possibility of using the direct anterior approach for revision total hip arthroplasty. I have not encountered any “approach specific” contraindications for using the direct anterior approach in revision cases. As in any surgical approach, the local skin situation is a limiting factor. No surgery should be performed if any skin infection exists in the area to be operated. However, with the direct anterior approach the incidence of skin irritation in obese patients might be higher than in lateral or posterior approaches, which can be explained by the fact that the area of incision is still quite close to the intertriginous zone.

Obesity usually is not a contraindication for using the direct anterior approach. In fact, we frequently observe the opposite. Even in very obese patients the area of the skin incision has a minimal fat pad. Severely obese patients also tend to have weaker muscle, and it is muscle strength that usually makes the exposure in the direct anterior approach more difficult. Muscle strength, in fact adversely affects the procedure more than obesity does.

Among those who perform this approach regularly there is a universal agreement that the more demanding parts of the procedure are the exposure and preparation of the femur. I have gained experience both with hemispherical press-fit cups of different designs as well as cemented cups. It is also possible to use a variety of different augmentation rings and perform bone impaction grafting. If implant-specific instruments must be used, it is essential that these instruments have offsets to achieve the correct alignment. The concept of instruments having offsets is even more important on the femoral side. In its pure form the direct anterior approach requires some angulation of the instruments during insertion into the femoral canal. In our experience, cemented and uncemented implant systems can be used for the femur using the direct anterior approach. Anatomic implant designs and such designs with lower profiles are easier to use.

PREOPERATIVE PLANNING

Templating of implant types and sizes should be performed as usual. The only difference between the direct anterior approach and other approaches is that with the direct anterior approach the osteotomy is performed without dislocating the hip joint. This is why this approach requires a precise definition of the starting point of the osteotomy. This point is found on the anteroposterior radiograph in the saddle that connects the femoral neck with the greater trochanter area and can be easily identified in situ (Fig. 11-1).

FIGURE 11-1 Preoperative planning starting from the piriformis fossa area and assessing the angulation of the true osteotomy. The second osteotomy is placed 1 cm closer to the head.

To ameliorate the removal of the femoral head, I recommend performing a double osteotomy to create a 1-cm disk of the neck. After removal of this disk, the increased space makes it easier to remove the femoral head.

TECHNIQUE

Patient Positioning

The patient is placed in the supine position on the operating table. A table attachment opposite to the operated side (e.g., an armboard) will make hyperabduction of the opposite leg during femoral exposure easier. Both legs should be draped in a manner that allows flexibility in manipulation. This allows the surgeon to cross the operated leg under the opposite leg during the surgical exposure of the femur and facilitates the change to the opposite side if a bilateral total hip arthroplasty is performed (Fig. 11-2).

FIGURE 11-2 A standard operating table is used to place the patient in the supine position. An additional armboard has been attached to the opposite side for use as a leg rest during femoral exposure. Both legs are draped flexibly.

Portal

The anterior superior iliac spine and the greater trochanter are palpated (Figs. 11-3 and 11-4). The proximal starting point is found two fingerbreadths laterally and two fingerbreadths distally to the anterior superior iliac spine. The initial incision should be kept small (6-7 cm) and extended as needed.

FIGURE 11-3 Coordinate system for the skin incision using the anterior superior iliac spine (ASIS) and the greater trochanter (GT) as starting points. The lateral femoral cutaneous nerve is in the area of this approach; placing the incision as laterally as possible protects that nerve. In the area of the incision, vessels perforating the iliotibial band can be found and must be cauterized (see Fig. 11-4).

FIGURE 11-4 Anatomic situs after skin removal showing the lateral femoral cutaneous nerve, iliotibial tract, and its perforating vessels in the area of the skin incision.

The incision is lengthened distally to increase acetabular exposure and proximally to increase exposure of the femur. The incision is located much more laterally than is the incision in the original Smith-Petersen approach (see later).

Note: Another technique for finding the incision location is to draw a line between the anterior superior iliac spine and the greater tuberosity. The proximal extent of the incision starts on this line about halfway between the two landmarks. The incision should angulate gradually toward the greater tuberosity rather than going straight distally.

One must avoid cutting into the tensor fasciae latae before precisely locating the correct portal. The index finger can be used in proximal to distal movements to palpate the interval between the tensor fasciae latae and sartorius (Fig. 11-5). An alternative technique is to identify the fascia of the gluteus medius muscle; it has consistently a whiter, more fascial appearance. The muscle immediately medial to this is the tensor fascia.

FIGURE 11-5 Palpating the space between rectus femoris and tensor fasciae latae. The white area is the fascia over the gluteus medius (Watson-Jones interval).

Tags: Replacement, Surgical Treatment of Hip Arthritis Reconstruction

Mar 10, 2016 | Posted by admin in Reconstructive surgery | Comments Off

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