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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 lines 1 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 cosmesis 2 . 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 LFCN 3 , 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 LFCN 5 . 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 outcome 5 . 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., Competing Interests: Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJSEST/A472)., (Copyright © 2024 The Author(s). Published by The Journal of Bone and Joint Surgery, Incorporated.)

Case: Seven years after hip arthroscopy for cam impingement, a 47-year-old female patient suffered a valgus impacted femoral neck fracture of her left hip that was stabilized with cannulated screws. After fracture healing, she experienced persisting sharp groin pain that could be elicited in flexion/internal rotation and extension/adduction. We suspected a ligamentum teres impingement at the border of the acetabular fossa due to a post-traumatic fovea alta and performed an arthroscopic ligament resection. Symptoms completely resolved thereafter., Conclusion: Valgus impacted femoral neck fractures with post-traumatic fovea alta may cause painful ligamentum teres impingement that can be treated with arthroscopic resection.

Background: Medialization of the cup with a respective increase in femoral offset has been proposed in THA to increase abductor moment arms. Insofar as there are potential disadvantages to cup medialization, it is important to ascertain whether the purported biomechanical benefits of cup medialization are large enough to warrant the downsides; to date, studies regarding this question have disagreed., Questions/purposes: The purpose of this study was to quantify the effect of cup medialization with a compensatory increase in femoral offset compared with anatomic reconstruction for patients undergoing THA. We tested the hypothesis that there is a (linear) correlation between preoperative anatomic parameters and muscle moment arm increase caused by cup medialization., Methods: Fifteen patients undergoing THA were selected, covering a typical range of preoperative femoral offsets. For each patient, a finite element model was built based on a preoperative CT scan. The model included the pelvis, femur, gluteus minimus, medius, and maximus. Two reconstructions were compared: (1) anatomic position of the acetabular center of rotation, and (2) cup medialization compensated by an increase in the femoral offset. Passive abduction-adduction and flexion-extension were simulated in the range of normal gait. Muscle moment arms were evaluated and correlated to preoperative femoral offset, acetabular offset, height of the greater trochanter (relative to femoral center of rotation), and femoral antetorsion angle., Results: The increase of muscle moment arms caused by cup medialization varied among patients. Muscle moment arms increase by 10% to 85% of the amount of cup medialization for abduction-adduction and from -35% (decrease) to 50% for flexion-extension. The change in moment arm was inversely correlated (R(2) = 0.588, p = 0.001) to femoral antetorsion (anteversion), such that patients with less femoral antetorsion gained more in terms of hip muscle moments. No linear correlation was observed between changes in moment arm and other preoperative parameters in this series., Conclusions: The benefit of cup medialization is variable and depends on the individual anatomy., Clinical Relevance: Cup medialization with compensatory increase of the femoral offset may be particularly effective in patients with less femoral antetorsion. However, cup medialization must be balanced against its tradeoffs, including the additional loss of medial acetabular bone stock, and eventual proprioceptive implications of the nonanatomic center of rotation and perhaps joint reaction forces. Clinical studies should better determine the relevance of small changes of moment arms on function and joint reaction forces.