THA through a direct anterior approach spares muscle, expedites recovery

During the past decade, the move toward less-invasive surgical techniques for total hip arthroplasty has been evident. The mini-incision approaches, however, have not always translated into faster surgical recoveries — mainly because there had not been a significant change to what was being performed underneath the skin incision.

The direct anterior approach has increased in popularity, most likely because it is a true muscle-sparing approach that does not detach or split any muscle or tendon to perform the procedure. The approach has pitfalls concerning the preparation of the femur for standard femoral stems, which often necessitates the use of a fracture-type table to extend the hip for better exposure.

Recently, shorter metaphyseal stems have been introduced by many manufacturers which allow for easier broaching during mini-incision surgery while sparing bone for future surgery if necessary. I use the Metha stem (Aesculap, Inc.), which lends itself to the direct anterior approach without the need for a fracture-type table. I utilize the stem as a bone-sparing option for patients with no radiographic signs of osteopenia and who are physiologically younger than 65 years.

Patient selection

In preoperative planning, I first assure the patient’s body habitus is conducive to the approach. If a patient has a large abdomen that would overlap and rest on the anterior incision, I do not use the direct anterior approach and use a standard posterolateral approach instead. I also do not consider the use of a short stem in patients with a body mass index (BMI) greater than 35 to 40.

Figure 1. AP (left) and frog leg lateral (right) radiographs of the hip are templated with a femoral neck cut that is at least 5 mm above the shoulder point of the base of the lateral femoral neck (red dot on AP radiograph). This assures the stem will lock into the femoral neck and is a deterrent to subsidence after surgery. The lateral side of the proximal femur is templated to make sure the anatomy of the femoral neck anteversion is conducive to the fit of the stem. Images: Mihalko WM

Additionally, the radiographs are templated to assure the patient’s proximal femoral anatomy will accommodate the femoral neck retaining stem (Figure 1).

In the operating room the patient is placed on a fluoroscopic table in the supine position with a sacral bump to allow for an extended hip position. The patient is prepped and draped, allowing access from the anterosuperior iliac spine (ASIS) to the mid-aspect of the thigh.

Making the incision

The medial edge of the tensor is usually palpable and is utilized as the line of the incision that extends from 2 cm below and lateral to the ASIS along this muscle edge (Figure 2). The skin incision is made but the subcutaneous tissues are dissected using Metzenbaum-type scissors to avoid trauma to the lateral femoral cutaneous nerve. The fascia of the tensor fascia latae is then incised and the interval between the tensor and sartorius is bluntly dissected.

Figure 2. The skin incision is made 2 cm distal and lateral to the anterosuperior iliac spine in the interval of the tensor and the sartorius along the medial edge of the tensor fascia latae muscle. The fascia is incised to bluntly dissect into the muscle interval.

Figure 3. Two Homan-type retractors are placed behind the posterior wall with the femoral neck behind it and in front of the anterior wall of the acetabulum. A Rich-type of retractor is used to retract the reflected head of the rectus for added visibility of the acetabulum.

The rectus and minimus interval is then determined and developed. In this interval the lateral femoral circumflex artery is ligated or coagulated, and the capsule is then bluntly uncovered with a Cobb elevator. The anterior capsule is then incised longitudinally and then released off of the base of the anterior femoral neck, exposing the hip joint. Two blunt retractors are placed around the femoral neck while making sure the lateral shoulder of the neck is retained to assure stability of the stem.

A second femoral neck cut is then made and this wafer of bone removed. This allows for easier removal of the femoral head from the acetabulum with a T-handle cork screw.

Releasing the hip capsule

The hip capsule often needs to be released off of the calcar and posterior aspect of the proximal femur, but care should be taken not to violate the external rotator attachment to the proximal femur. The neck of the femur is placed behind the posterior Homan-type retractor, and another retractor is placed over the anterior wall allowing excellent visibility of the acetabulum (Figure 3).

The reflected head of the rectus femoris can be left attached in most cases. The labrum is then excised. Reaming of the acetabulum is then carried out in the usual fashion and the acetabular shell is impacted in place.

Figure 4a. Figure-of-four positioning of the leg allows access to the proximal femur and the femoral neck for broaching and preparation.

Figure 4b. The broach handle and clearance to the proximal aspect of the incision are shown.

The leg is then placed in a figure-of-four fashion (Figure 4A). This allows the femoral neck to be broached in line with the incision (Figure 4B. The stem is designed such that the tip sits against the posterolateral aspect of the proximal diaphyseal cortex. A trial reduction of the hip is then performed, and leg length can be directly assessed by feeling the medial malleoli with the patient supine.

At this point the modularity aspect of the implant, which allows for neck angles of 130°, 135° and 140° as well a retroversion or anteversion angle of 7.5°, can be utilized to optimize joint stability. I assure proper placement of the femoral stem using fluoroscopic images (Figure 5).

Figure 5. AP (left) and lateral (right) fluoroscopic images of a THA with the femoral neck retaining stem show the proper lateral locking points along the femoral neck and proximal femoral cortex.

Potential pitfall

One pitfall of the use of this stem is the possibility of perforating the proximal lateral femoral cortex at the base of the greater trochanter. If this happens, the broach is redirected; if the stem is adequately seated into the proximal femur within the diaphyseal cortical bone, the metaphyseal type of stem can still be used with no difference in the postoperative course of care.

Once satisfied, the trial components are removed and the final implant, neck and acetabular insert, and head are implanted. A drain is placed exiting inferior to the incision and into the capsular space. The sartorius tensor interval is then closed with absorbable suture and the subcutaneous tissue and skin closed.

Figure 6. Postoperative radiographs show a THA performed through a direct anterior approach using a metaphyseal bone-sparing stem.

During the postoperative course, no abductor pillow is used; patients are more comfortable with the head of the bed elevated and the hip flexed. I do not encourage any hip precautions other than no hip extension for 6 weeks in physical therapy. The majority of patients are seen at 2 weeks for an incision check and then again at 6 weeks. Most patients at 6 weeks are not using any ambulatory aids. This surgical approach and use of the femoral neck retaining femoral stem has found a niche in my practice that has served patients well with overall subjectively good-to-excellent results (Figure 6).

• William M. Mihalko, MD, PhD, can be reached at University of Tennessee, Campbell Clinic Orthopaedics, 1458 West Poplar Ave, Suite 100, Memphis, TN 38017; 901-759-5512; e-mail: wmihalko@campbellclinic.com.
• Disclosure: Mihalko is a consultant for Aesculap, Inc., and receives royalties and research support for an unrelated topic/product to this article.