Anterior-Based Muscle-Sparing (ABMS) Approach for Total Hip Arthroplasty.

The anterior-based muscle-sparing (ABMS) technique for total hip arthroplasty (THA) has gained popularity in recent years because of its proposed advantages in terms of postoperative pain and periprosthetic dislocation risk.

Description: The procedure is performed with the patient in the supine position. A minimally invasive Watson-Jones approach is utilized to access the hip. Fluoroscopy can be utilized intraoperatively to assess acetabular cup position, version, and inclination. Femoral canal fill and leg lengths can also be assessed with use of fluoroscopy.

Alternatives: Nonoperative alternatives for the treatment of hip osteoarthritis include nonsteroidal anti-inflammatory drugs, physical therapy, and corticosteroid injections into the hip joint. Surgical alternatives to this procedure include the posterior approach (Moore or Southern), the direct lateral approach (Hardinge), and the direct anterior approach (Smith-Petersen). The Watson-Jones approach can also be performed with the patient in the lateral decubitus position (unlike in our technique where the patient is supine).

Rationale: The anterolateral (Watson-Jones) approach to the hip has been shown to be superior to the historically more common posterior approach with regard to length of hospital stay and dislocation risk^1,2. Supine positioning for this approach offers multiple advantages compared with lateral decubitus positioning. Leg lengths can be assessed intraoperatively both fluoroscopically and with manual palpation of the medial malleoli. Cup position can be assessed radiographically as well³. Supine positioning also allows for easily reproducible patient positioning.

Expected outcomes: Compared with the historically common posterior approach to the hip for THA, the anterolateral approach to the hip leads to, on average, a lower risk of hip dislocation^1,2. In a 2002 study by Masonis and Bourne, the dislocation rate for the posterior approach was 3.23% (193 of 5,981), whereas the dislocation rate was 2.18% (18 of 826) for patients who underwent THA via the anterolateral approach¹. In a study by Ritter et al. in 2001, which followed patients for 1 year postoperatively, no patients in the anterolateral approach group experienced a dislocation compared with 4.21% of patients in the posterior approach group². With use of the present technique, patients will benefit from the advantages of the anterolateral approach to the hip; however, they will also benefit from easy intraoperative leg length assessment and from radiographic assistance with regard to determining the appropriate position of the femoral and acetabular components³. In a study of 199 patients (including 98 patients who had intraoperative fluoroscopy and 101 who did not), 80% of implants in the fluoroscopy group were within the combined safe zone compared with 63% in the non-fluoroscopy group. However, this approach is not without its limitations. As mentioned in the above studies, dislocation remains a possible complication of the procedure, and a minimally invasive anterior-based approach can lead to intraoperative femoral fractures when exposure and releases are inadequate⁴. Femoral nerve palsies are also possible with excessive medial retraction during acetabular exposure. Additionally, the benefit of a reduction in the incidence of hip dislocation compared with a posterior approach might be overstated given improvement in posterior-approach dislocation rates if posterior soft-tissue repair is used⁵. Both direct anterior and anterolateral approaches have the same risks of fracture with poor exposure and of neurapraxia with excessive retraction, and there does not appear to be any difference in dislocation risk between these 2 approaches⁶.

Important tips: Although a pannus is more detrimental to a direct anterior approach, it could overlie the desired incision in the ABMS approach as well. The pannus could be held out of the field by taping it to the contralateral shoulder before preparing and draping.The preparative process is more time-consuming because both legs must be sterile for this procedure.Acetabular exposure often requires an assistant standing on the contralateral side of the table.Although not often needed, the obturator internus and gemelli might need to be released in order to ensure adequate exposure of the femur.If femoral canal exposure is still insufficient, a femoral suspension hook system might be needed.

Acronyms & abbreviations: ASIS = anterior superior iliac spineTFL = tensor fasciae lataeITB = iliotibial bandPOD = postoperative dayIV = intravenousBID = twice daily.