Bikini Incision Modification of the Direct Anterior Approach.

Background: Although the direct anterior approach (DAA) represents an intermuscular and internervous approach to total hip arthroplasty (THA), it did not reach global acceptance until its adoption by large teaching centers. Today, >50% of primary THA procedures in Switzerland are performed via the DAA. Besides being truly minimally invasive, a key advantage of the DAA is the inherent stability that it provides. A shortcoming has been that the traditional longitudinal skin incision does not follow the skin tension lines¹ and therefore can result in wound-healing problems, poor scar cosmesis, and damage to the lateral femoral cutaneous nerve (LFCN). In 2011, we introduced the bikini-type skin-crease incision, and we have utilized it in most of our patients since, with excellent outcomes that are equivalent to those of the traditional incision and superior scar cosmesis². The bikini incision pertains only to the incisions made at the skin and subcutaneous tissues, which are oblique, whereas the deeper dissection beginning with the fascial sheath of the tensor fasciae latae (TFL) is still performed in the longitudinal direction. In most patients, the incision falls into the flexion crease or slightly distal to it, and today, in order to minimize direct damage to the LFCN³, the incision we perform is always lateral to the anterior superior iliac spine (ASIS)⁴. From January 2014 until August 2023, a total of 10,009 THA procedures were performed in our unit, with 8,769 being performed via the DAA and 4,969 of those being performed with use of the bikini incision type. The incision type was generally selected according to the experience of the surgeon, with the less-experienced surgeons utilizing classic incision techniques and the high-volume surgeons (i.e., >200 THAs per year) utilizing the bikini incision technique. The bikini incision was utilized in most straightforward cases, but it was not performed if a longitudinal incision had been utilized on the contralateral side or in technically challenging cases. The use of this incision has been adopted by others, with similarly excellent outcomes; however, there is potential for damage to the LFCN⁵. Several studies utilizing a bikini incision have described the incision as being made quite medial to the ASIS, potentially even crossing the medial branches of the LFCN. In contrast, over years of utilizing the bikini incision technique, our approach has evolved such that the incision is not made medial to the ASIS.

Description: The bikini-type (skin-crease) incision only differs from the classic longitudinal approach used for DAA THA with respect to the skin and subcutaneous tissue. To avoid damage to the LFCN, our bikini-type incision has evolved over the last decade to being located entirely lateral to the ASIS (Video 1)³.

Alternatives: The main alternative is the classic longitudinal incision used for DAA THA.

Rationale: The bikini incision is a valuable alternative that improves wound healing and scar cosmesis in DAA THA in technically straightforward hips, which account for >90% of our cases. The procedure can be divided into 10 steps, as described in the videos. Today, indications include primary or secondary osteoarthritis, femoral neck fracture, and revision THA involving head and/or liner exchange, and simple socket loosening without the need for proximal extension of the approach. Particularly in patients prone to hypertrophic scar formation (i.e., patients who are younger, have a darker skin type, are obese, etc.), this incision is a helpful alternative to the classic longitudinal incision. The classic longitudinal incision is still preferred for complex primary or revision THA cases in which extensile distal and/or acetabular exposure might be required, revision cases with a preexisting longitudinal DAA incision, cases of inguinal skin infection, or cases in which the contralateral side has been treated utilizing a longitudinal incision.

Expected outcomes: A recent review assessed 8 double-armed studies that included a total of 952 bikini incision procedures and 1,361 longitudinal incision procedures. In 3 of the 4 studies reporting postoperative scar appearance and patient satisfaction, those outcomes were more favorable following the bikini incision compared with the longitudinal incision, with the fourth study showing comparable results. Postoperative hip function was similar between the incision types in 3 of 4 studies assessing that outcome⁵. LFCN injury was the most frequently reported complication, but rates were low overall, and most injuries resolved. Only 2 of the included studies reported slightly higher risks of LFCN injury following use of the bikini incision technique, but their procedures involved large incisions made medial to the ASIS. On the basis of our own prior study as well as other recently reported data^2,4, we advocate that the incision be made lateral to the ASIS.

Important tips: Begin with the bikini incision in technically easier hips.Adjust the bikini incision according to radiographic hip morphology.Do not perform the skin incision too small, too distal, too proximal, or most importantly too medial.Secure the medial edge from tearing.Limit subcutaneous dissection.Change the dissection deep to the fascial sheath of the tensor from the oblique to the longitudinal direction.Appreciate that a bikini incision is less extensile.

Acronyms and abbreviations: ASIS = anterior superior iliac spineBMI = body mass indexCCD = caput column diaphysisDAA = direct anterior approachGT = greater trochanterLFCA = lateral femoral circumflex arteryLFCN = lateral femoral cutaneous nerveTFL = tensor fasciae lataeTHA = total hip arthroplastyOA = osteoarthritisROM = range of motion.