“E-Spot” (Obturator ‘E’xternus Tendon Femoral Origin) as an Intraoperative Landmark for Femoral Preparation During “Off-Table” Anterior Approach

Background: This study introduces the obturator externus tendon femoral origin, termed "E-spot," as a landmark during "off-table" anterior approach total hip arthroplasty (THA). Aims were to determine whether the E-spot could (1) be identified reliably in all cases and (2) help as a reference during femoral preparation to determine the extent of capsular release and femoral implant position. Methods: A retrospective analysis of 306 consecutive patients who underwent primary THA by the senior author via an anterior approach between October 2022 and October 2024 was conducted. We attempted to visualize and preserve the obturator externus tendon in all cases and then use it as a reference to determine the extent/completion of capsular release and femoral implant position. Clinical outcomes and complications were assessed at a minimum of 6 months postoperatively to up to 2 years. Results: E-spot could (1) be reliably identified as well as (2) the stem to E-spot distance measured in every case (306 out of 306 or 100% reproducibility). There was 1 periprosthetic fracture (Vancouver B2) requiring revision surgery at 2 months postoperatively and 1 dislocation at 3 months postoperatively (0.65% overall early complication rate). No other surgical complications were observed. Conclusions: Identifying E-spot in a systematic way is a safe and reliable method of enabling femoral exposure and referencing femoral component position. Based on these results, we now routinely use E-spot to determine the completion of femoral capsular release, assess femoral component position, assure hip stability, and protect the trochanter from injury during off-table anterior THA.