Troubleshooting the Direct Anterior Approach

Introduction

The only true intermuscular and internervous approach in total hip arthroplasty (THA), the direct anterior approach (DAA) continues to increase in popularity. Several proposed advantages have been attributed to DAA utilization, including lower dislocation rates, more accurate cup position, quicker patient mobilization, less early postoperative pain, and shorter length of stay. Over the past 2 decades, the DAA has been facilitated by the development and refinement of surgical implants, retractors, and approach-specific instrumentation.

Compared with other approaches for THA, the DAA spares major soft-tissue structures stabilizing the hip. The posterior capsule, short external rotators, and gluteus maximus are preserved, helping to protect against posterior instability. Further, the gluteus medius and minimus are preserved, mitigating the risk of abductor weakness, Trendelenburg gait, and instability. This combination of factors potentially reduces the risk of dislocation and reduces soft-tissue violation that may result in permanent dysfunction. However, the DAA can be a technically demanding surgery; understanding of potential challenges is critical in ensuring a successful patient outcome.

The goal of this chapter is to review the potential complications of the DAA, including preoperative and patient-specific factors, intraoperative technical considerations, complications, and their management.

Preoperative Factors

Patient Assessment

Preoperative planning and patient assessment are critical to ensuring satisfactory outcomes with the DAA. The DAA may be used as a primary approach for virtually any THA.

Body Habitus and Physical Exam

Obesity is a concern for every primary THA, and certain considerations should be taken for the DAA. In obese patients, the pannus may drape over the surgical site. During the preoperative examination, the skin should be closely examined for any areas of breakdown, chronic skin changes, excessive moisture, fungal infection, or ulceration. Although pannus can be directed superiorly and away from the surgical field in the supine position, there is a concern for postoperative wound healing due to incisional maceration and fold moisture. In the obese population, studies have demonstrated a higher rate of prosthetic joint infection, higher rates of wound complications, and higher rates of wound complications requiring reoperation. Obesity and diabetes mellitus have been found to be significantly associated with postoperative wound healing complications. Purcell et al. noted no difference in periprosthetic infections between obese patients undergoing the DAA versus posterolateral approach. However, the authors did report a higher rate of wound complication in the obese DAA group. Patients should be counseled and educated on pannus management in the perioperative period, with a focus on keeping the area dry and free of pressure. Some authors describe using an abdominal binder to prevent the pannus from overlying the incision following surgery. Incisional wound vacuum devices have also been shown to decrease wound complications in high-risk patient populations. ^,

Special attention should be paid to actual and perceived leg length discrepancies. For surgeons using a standard table, recording preoperative supine leg lengths is critical for intraoperative guidance. In our experience, standing assessment of leg lengths using measured blocks under the operative limb can guide intraoperative lengthening goals for surgeons utilizing fluoroscopy intraoperatively.

Large hip and knee flexion contractures on the operative limb can preclude proper limb mobilization intraoperatively. These findings are especially pertinent to note when utilizing a specialized table, as hip extension for femoral exposure may be limited. Contralateral hip and knee flexion contractures can also interfere with fluoroscopy and assessment of limb lengths. External rotation contractures should be noted, as they frequently require further superior capsule and short external release for femoral mobilization.

Imaging Assessment

Preoperative imaging should be closely examined to recognize potential intraoperative challenges. Correlating radiographic limb length discrepancy with clinical and/or perceived discrepancies is imperative. Careful attention should also be paid to offset, which will influence cup placement (e.g., depth of medialization) and stem choice (e.g., standard vs. high offset). Preoperative assessment should include consideration of implants. Although almost any system can be used for the DAA, longer stems with ream-and-broach-style preparation often require a more extensile exposure to gain co-linear femoral canal access.

A horizontal or wide iliac wing can limit access to the femoral canal. Protusio, minimal femoral offset, and high neck shaft angles place the femoral canal close to the pelvis, potentially requiring larger, more extensile releases due to limited femoral canal access during broaching. Short varus necks with large superior neck osteophytes may also present a challenge to identifying the appropriate level at which the neck cut should be made. In this scenario, the use of intraoperative fluoroscopy allows the surgeon to confirm landmarks and level of resection.

Patients who have previously placed hardware from a posterior or lateral approach may be difficult to access via the standard DAA. A separate incision can be made to address the hardware. If it is felt that one surgical approach to remove the hardware will best preserve soft tissues, then that approach may be more appropriate.

Severe femoral deformity makes accessing the canal more difficult when using the DAA. For example, the need for a femoral shortening osteotomy and diaphyseal engaging stem in the setting of Crowe Type IV dysplasia may prove challenging. Conversely, the ability to utilize intraoperative fluoroscopy enhances cup placement and allows the surgeon to confirm the osteotomy level. Posterior wall or posterior column defects requiring grafting or augments can be difficult with the DAA, as can removing posterior acetabular hardware.

Operative Table Selection

The direct anterior approach can be safely performed on both a specialized surgical table and a standard operating table. Use of a specialized table to access the hip via an anterior approach has been utilized for decades, originally described by Judet and Judet and then expanded on by Matta et al. Prior studies have demonstrated no difference in intraoperative femur fracture rates, perioperative complications, or outcomes between a specialized surgical table and a standard table. ^, Variations and modifications to the standard surgical table also exist, including table attachments to maneuver and hold the operative leg, self-retaining retractors, and a femoral hook attachment that is used to elevate the femur. What follows will describe relative pros and cons of the different table options.

Specialized Surgical Table

The specialized surgical table secures the patient via a center groin post with both feet fixed in surgical boots on independent leg spars attached to the table. Acetabular exposure is easily performed and is similar across all table setups. Femoral access is consistently the more difficult portion of the DAA. It is aided by the specialized table through hyperextension, adduction, and external rotation of the operative extremity. A femoral bone hook can then be used to support the femur during broaching. The hydraulic hook should never be used as a tool to forcefully expose the femur due to fracture risk. Rather, the hook serves as a static retractor, holding the femur in a stable position during femoral preparation.

An advantage of the specialized table is decreased need for surgical personnel due to the leg spar and femoral hook holding the extremity in a secure, constant position. In cases for which traction is required, the table also provides a consistent and predictable force. The ability to utilize intraoperative imaging for evaluation of implant position, leg lengths, and offset is another valuable benefit of the specialized surgical table.

There are several disadvantages. Upfront cost and continued maintenance may result in a significant investment. Next, both the surgeon and operating room staff must be trained on how and when to manipulate the leg, with specific attention paid to preventing iatrogenic injuries such as nerve palsies, femur fractures, and ankle fractures. Finally, a radiology technician needs to be present for the case and must be facile with the appropriate views to limit operative and fluoroscopic exposure time.

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