Acetabular Exposure in the Efficient Direct Anterior THA
The authors describe a stepwise capsular exposure technique that provides good acetabular exposure and proper femoral elevation.
Kristoff Corten, MD, PhD, and Jens Vanbiervliet, MD
The efficient direct anterior (EDA) total hip arthroplasty (THA) is a systematic and reproducible hip replacement procedure that can be done on a regular operating room (OR) table. The EDA intra-capsular technique relies on a stepwise capsular exposure followed by 3 sequential capsulotomies, allowing for adequate acetabular exposure and proper femoral elevation.
In this article, we review the stepwise surgical technique. First, some background and the rationale for the soft tissue, which is the most challenging part during the learning curve.
Evidence-based Soft Tissue Releases
A stepwise and systematic procedure is often the key to reproducibility, especially for surgeons in the learning curve. For the anterior approach, the learning curve is estimated to be between 20 and 50 cases, [1-3] which is not insignificant for a surgeon who averages only a few THAs per month.
Therefore, every effort should be made to minimize this learning curve.  One strategy to do is to adopt an evidence-based capsular releasing sequence prior to acetabular exposure and femoral elevation. We believe any capsular release should strike a balance between sufficient femoral exposure and minimal violation of the soft tissues.
The key is to understand which structures should be released for proper mobilization of the femur. Recent anatomic studies have improved our insight into the surgical anatomy of the proximal femur (Figure 1). [4-6] We have merged these insights into a femoral releasing strategy restricted to capsular release.
Figure 1. Surgical view on the anatomy of the insertions of the soft tissues of the proximal part of the right femur. [4,6] The interconnections between the short external rotators and the abductors are also shown. 
In a cadaver study, Matsuura et al  found that release of the superior capsule allows for more elevation than release of the posterior capsule with the hip in 15° and 25° of extension. They defined the superior capsule as the attached area between the ilium and the trochanteric fossa.
The question remains whether it is possible to avoid releasing any of the external rotators when the superior capsule is released. Ito et al  showed that the anterior insertion site of the conjoint tendon of the obturator internus and the gemelli muscles varies significantly and is closely related to the insertion site of the superior capsule. Moreover, the insertion site of the conjoint tendon is also very closely related to the piriformis tendon.  Thus, it is likely that the insertion sites of the short external rotators are also damaged when the superior capsule is released.
It was shown by Solomon et al  that retraction after release of the obturator internus/conjoint tendon is unlikely to occur due to strong interconnections between the postero-superior capsule and the short external rotators (Figure 2). These findings also suggest that not only the medial surface, but also the superior margin of the greater trochanter should be released. The release of the superior capsule, therefore, should be sufficient to safely elevate the femur during femoral preparation.
Figure 2. The retractor can be safely placed at the interval between the gluteus minimus and the greater trochanter when the fat pad becomes visible. The appearance of this fat pad indicates free access to the bold spot at the lateral surface of the greater trochanter.  Often, the obturator internus will be cut due to its close insertion to the superior capsule.  The inner surface and the superior margin of the greater trochanter is free of tissue.
However, this can only be done in cases in which the anterior and superior margins of the greater trochanter are released together with the inner surface. It is likely that part of the short external rotators is damaged. It is unlikely that this would lead to retraction and subsequent instability because of the interconnections with the posterior capsule, the piriformis, and the obturator externus.
A crucial step for a reproducible procedure is identifying intraoperative landmarks for a sufficient release. Again, the literature suggests possible solutions.
Solomon et al  defined a distinct fat pad anterior to the interconnections between the conjoint tendon and the gluteus medius. They suggested that exposure of this fat pad would be an important landmark for sufficient release of the greater trochanter, with enhanced mobilization of the gluteus medius and proximal femur during THA.
Applying this finding to the EDA, the appearance of the fat pad during the release indicates accessibility of the space between the trochanteric insertion of the gluteus medius and the bold spot at the lateral surface of the greater trochanter. This allows enhanced mobilization of the proximal femur and free access to the lateral trochanter for safe retractor placement without violating any of the abductor muscles (Figure 2, above).
Ito et al  have shown that the anterior insertion site of the obturator internus is within the anterior half (ie, 43%) of the antero-posterior width of the inner surface of the greater trochanter. The superior capsule inserts anteriorly to the obturator internus. As a result, the posterior extension of the capsular release should not go beyond the most postero-superior edge of the femoral neck-trochanter junction to avoid jeopardizing the piriformis and the postero-superior capsule. The release should be limited to the anterior 10 mm to 15 mm and should not extend beyond this landmark.
The surgeon pulls the femur in the lateral and anterior direction during the release. When the femur is properly released, the tip of the greater trochanter can be elevated beyond the acetabular rim without hyperextension. This can easily be checked. The manual pull also allows the surgeon to perfectly feel when the femur is delivered. Unfortunately, this is only a qualitative measure and is prone to inter-subject variability, which makes it less reproducible as a surgical landmark. A distinct intraoperative finding is the capsular “flip sign”: The postero-superior capsule will flip over the tip of the greater trochanter when the femur is pulled in the lateral and anterior direction. This is an indicator of a sufficient superior capsular release.
Stepwise Surgical TechniqueOR Setup
The patient is positioned on a regular OR table. Long fixation posts are connected at the contralateral side, just opposite the shorter fixation posts on the ipsilateral bar. These posts allow for connection of the retractors with a self-retaining system that holds the retractors in a stable position (Gripper, MedEnvision; Aarschot, Belgium) (Figure 3). It also allows the surgery to be done with the help of only 1 scrub nurse. The scrub nurse works mainly from the contralateral side of the patient and can focus on the core tasks while the retractors are held in a stable position by the fixation posts.
Figure 3. Regular OR table setup with fixation posts attached to the table.
Both legs are draped free so that they are easily accessible during the procedure to test hip stability and assess leg length (Figure 4).
Figure 4. The EsySuit (MedEnvision; Aarschot, Belgium) is applied to both legs, which are prepared freely in the surgical field (a). The incision foil is prepared (b). The legs are covered with a stockinette and are easily accessible (c).
The bikini skin incision is located 3 fingerbreadths distal to the anterior superior iliac spine. The incision is two thirds lateral and one third medial to the spine. The lateral cutaneal nerve is not in jeopardy because the medial one third of the incision is not explored at the sub-dermal level.
The tensor fascia lata (TFL) muscle belly is identified and the fascia incised. The interval between the TFL and the rectus is opened and the vessels of the lateral circumflex artery are coagulated (Figure 5).
Figure 5. The bikini incision is 8 cm to 10 cm long and parallel to the groin crease (a), 3 fingerbreadths distal to the anterior superior iliac spine (b). The TFL muscle belly is identified and the fascia incised (c). The vessels of the lateral circumflex artery are identified and coagulated (d).
Four retractors are used to provide visualization of the anterior capsule (Figure 6). The anterior retractor is placed over the anterior capsule, distal to the anterior inferior iliac spine, and is directed toward the contralateral kidney. It is placed underneath the iliocapsular muscle over the anterior capsule and the anterior rim. The superior, inferior, and lateral retractor expose the anterior capsule.
Figure 6. The anterior capsule is exposed by retractors.
The capsular release is started with the anterior capsulotomy and head extraction, followed by the inferior and the superior capsulotomy (Figure 7).
Figure 7. The anterior flap is created (a) and the corkscrew (b) is inserted into the femoral head. The neck is osteotomized (c) and the head is extracted (d).
Capsular Releasing Sequence
For the inferior capsulotomy (or release of the pubo-femoral ligament), the ipsilateral leg is placed on top of the contralateral leg. This provides slight external rotation and delivers the lesser trochanter and pubo-femoral ligament into the surgical view.
For the superior capsulotomy, the leg is left in neutral position and a bone hook is placed at the calcar to pull the femur in the lateral and anterior direction (Figure 8). This allows the surgeon to clearly feel when the release is completed.
Figure 8. (a) The pubo–femoral ligament is released off the calcar (a). The bone hook is placed inside the femur at the level of the strong calcar bone and the femur is pulled in the lateral and anterior direction (b). A clear “pop” can be felt when the superior capsule is released.
Acetabular Exposure, Reaming, and Socket Insertion
Acetabular exposure is facilitated when the capsule has been released. This allows the surgeon to mobilize the femur in the posterior direction. Retractors are placed in a stepwise manner:
- Anterior retractor
- Posterior retractor
- Postero-inferior retractor
The posterior retractor is placed between the posterior rim and the posterior capsule, and it it is used to push the femur in the posterior direction. The postero-inferior retractor is placed at the ischial bone, just posterior to the transverse acetabular ligament (TAL), and it exposes the TAL. Reaming is initiated with regular or offset reamers (Figure 9).
Figure 9. The TAL is visible after proper retractor placement (a). Fluoroscopy is not required due to a good visualization of the acetabulum and the reaming. Reaming with a straight reamer is done (b) and the socket is inserted (c). Overview of the OR setup (d). The ceramic liner is inserted (e). The fixation posts hold the retractors (f).
Adequate acetabular exposure can be done through the EDA on a regular OR table in a systematic and reproducible manner. It relies on a stepwise capsular exposure followed by 3 sequential capsulotomies and reliable placement of the retractors, which are held in a stable position.
- A stepwise capsular release prior to acetabular exposure provides adequate mobilization of the femur.
- A reproducible retractor placement ensures adequate visibility of the acetabulum.
- The retractors are held in a stable position to minimize soft tissue damage and optimize the view on the acetabulum during reaming and component insertion.
- The transverse acetabular ligament is used as an important surgical landmark for socket positioning in the sagittal plane.
- The body axis is used as a landmark for socket positioning in the frontal plane (socket inclination).
Videos of the described surgical technique are accessible are available here.
Kristoff Corten, MD, PhD, is from the Hip Unit, Orthopaedic Department, at Ziekenhuis Oost-Limburg, Genk, Belgium. Jens Vanbiervliet, MD, is a resident in orthopaedic surgery at Ziekenhuis Oost-Limburg, Genk, Belgium.
Dr. Vanbiervliet has no disclosures relevant to this article. Dr. Corten has disclosed that he is a paid consultant and paid speaker for Biomet; that he receives royalties from, is a paid consultant and paid speaker for, and receives research support from DePuy Synthes; that he receives royalties and has stock or stock options in MedEnvision; that he is a paid speaker for Smith & Nephew; and that he is a paid speaker for and receives research support from Zimmer.
- Woolson ST, Puoliot MA, Huddleston JI. Primary total hip arthroplasty using an anterior approach and a fracture table. Short term results from a community hospital. J Arthroplasty 2009;24: 999-1004.
- D’Arrigo C, Speranza A, Monaco E, Carcangiu A, Ferretti A. Learning curve in tissue sparing total hip replacement: comparison between different approaches. J Orthop Traumatol. 2009;10:47-54.
- Spaans AJ, van den Hout JA, Bolder SB. High complication rate in the early experience of minimally invasive total hip arthroplasty by the direct anterior approach. Acta Orthop. 2012;83:342-6.
- Matsuura M, Ohashi H, Okamoto Y, Inori F, Okajima Y. Elevation of the femur in THA through a direct anterior approach: cadaver and clinical studies. Clin Orthop Relat Res. 2010;468:3201-6.
- Solomon LB, Lee YC, Callary SA, Beck M, Howie DW. Anatomy of piriformis, obturator internus and obturator externus: implications for the posterior surgical approach to the hip. J Bone Joint Surg Br. 2010;92:1317-24.
- Ito Y, Matsushita I, Watanabe H, Kimura T. Anatomic mapping of short external rotators shows the limit of their preservation during total hip arthroplasty. Clin Orthop Relat Res. 2012;470:1690-5.