Barton Harris, MD
The direct anterior approach for total hip arthroplasty has been gaining favor with surgeons and patients alike in the last several years. A true internervous approach, it offers the potential advantages of decreased muscle injury, accurate component positioning, low dislocation rate and faster early recovery. While long-term follow-up results appear to show the expected excellent outcomes similar to other traditional approaches, the direct anterior approach may facilitate shorter length of stay and return to work and activities for patients.
Most surgeons find that initial exposure of the hip joint is quite easy, regardless of whether the surgeon uses a special table or not. The acetabular exposure affords direct visualization and ready in-line access for reaming and broaching. Femoral exposure, however, can be challenging, particularly in learning curve. The majority of hip surgeons using the anterior approach use some form of specialized operating table or attachment to make this exposure more facile. This specialized equipment allows the leg to be maximally extended and adducted to gain access to the femoral canal.
Specialized table vs. regular operating room table
The specialized tables, while useful for many, can have some disadvantages. These tables are expensive, often costing in excess of $100,000. A smaller hospital may not have the resources to purchase a table, and larger facilities may be unwilling to buy more than one, making running more than one operating room at a time for hip replacement difficult. These tables also require a trained assistant to manipulate the leg rather than leaving the control of the limb in the hands of the surgeon. These devices can exert tremendous forces, and there have been rare reports of ankle fractures—and more common reports of trochanteric fractures— as a result. Traction nerve palsies have also been reported. The table itself is quite large and may be difficult to use in smaller operating rooms.
We prefer the use of a regular operating room table for the direct anterior approach. This requires no additional equipment and may be performed in any size operating room. It facilitates easy patient positioning and allows simultaneous bilateral procedures. Direct comparison of leg lengths and range of motion / stability assessment are easily performed, as the limb is draped free. The surgeon maintains control of the limb making iatrogenic fracture less likely. The table is positioned with the base of the table toward anesthesia and the head of the bed moved to the foot (Figure 1). This allows ample room for fluoroscopy and positions the patient so that the break in the table can facilitate extension of the hip. A gel pad can also be utilized to further assist. The patient is positioned so that the gluteal fold is at the break in the table, which is then used as a fulcrum to elevate the femur (Figure 2).
Figure 1. Table set up
Figure 2. Patient positioning
Incision and femoral exposure
The direct anterior approach has been described in detail in other publications. The approach is performed in the internervous Smith-Peterson interval. The incision usually begins three fingerbreadths distal and lateral to the ASIS to avoid the lateral femoral cutaneous nerve and is carried distally, centered over the greater trochanter (Figure 3). The superficial fascia of the TFL is incised and a finger bluntly swept over the muscle medially.
Figure 3. Where to begin the incision
Lateral mobilization of the Tensor is greatly facilitated by incising the deep fascia of this muscle longitudinally. Retractors are placed above and below the femoral neck outside the capsule. A retractor placed deep to the Tensor and lateral to the trochanter can be helpful. The vascular leash of the circumflex vessels is identified and cauterized or ligated. A retractor is placed anteriorly over the acetabulum and gentle release of the iliocapsularis and reflected head of the rectus is performed. Use caution that the anterior retractor is placed directly over the acetabulum and that the assistant does not rotate the retractor on its side, potentially tenting the femoral nerve over the edge of the retractor. Capsulotomy is performed and retractors placed inside. Femoral neck osteotomy may be performed in a single cut or a “napkin ring” fashion, using the saddle as a reference point based on preoperative x-rays. There can often be a sharp edge on the cut surface of the femoral head. Be sure that this does not damage the fibers of the Tensor during removal as this muscle injury can propagate over the course of the procedure. A small incision in the posterior capsule allows posterior retractor placement to depress the femur during acetabular preparation. An inferior retractor allows ready access for reaming and visualization of the transverse acetabular ligament for reference (Figure 4). Once the acetabular component has been placed, exposure of the proximal femur is performed (Figure 5).
Figure 4. Retractor placement
Figure 5. Femoral exposure
Release and stability
The table is placed in slight Trendelenburg position, and the leg of the bed flexed slightly. The leg is maximally externally rotated and adducted. A retractor is placed medially on the calcar, and a bone hook is inserted into the cut surface. This bone hook is used to pull the femur laterally before elevating the femur with a retractor placed behind the trochanter. This critical maneuver ensures that the trochanter is not behind the acetabulum during attempted elevation and avoids trochanteric fracture. Capsular release is performed in a stepwise fashion (Figure 6). The superior capsule may be safely elevated from the entire interior surface of the trochanter. It has been well demonstrated that the abductors insert laterally and are not in danger during this release. Occasionally the piriformis is released, but avoid any further distal release for improved stability.
Figure 6. Capsular release
Maintaining the posterior structures also makes it difficult to over-lengthen the leg. A large retractor placed behind the trochanter is used to gently elevate the proximal femur. A curved canal finder is recommended to sound the canal to ensure that the trajectory of the broach is appropriate and does not violate the lateral cortex. Routine broaching is performed. Single- or double-offset broaches can make this easier, but beware that an offset broach can introduce torque on the broach, and the surgeon should use caution to maintain the same degree of anteversion. It is often helpful to obtain a fluoroscopic image with one of the early broaches to get a sense of where work needs to be done with subsequent broaches. Reduction should be relatively easy with traction and internal rotation. Lengths may be checked both clinically and radiographically. Stability is checked anteriorly in maximal external rotation with the hip extended as well as posteriorly in hip flexion with internal rotation (Figure 7). Following final implantation of components, simple closure of the superficial fascia of the TFL followed by periarticular injection is performed. Routine skin closure and dressing of choice completes the operation. No postoperative abduction pillow or hip precautions are used.
Figure 7. Stability check
As with any technique new to a surgeon, it is highly recommended that as much education as possible be done before using the technique on patients. This can be done through surgery observation, cadaver courses, and review of literature and available video presentations. Easier cases are on slender patients with low muscle mass and high femoral offset. With experience, it is possible to perform this approach without difficulty on all patients. While the learning curve can be steep, for most surgeons the direct anterior approach becomes a preferred approach once familiar.
If you’re ready to observe surgery using this approach with Dr. Harris, schedule your visit today.