Adjustment of Acetabular Cup Inclination Assisted by Smartphone during Revision Total Hip Arthroplasty: Surgical Technique and Report of Four Cases

We herein present a smartphone-assisted technique for acetabular cup placement during revision total hip arthroplasty (rTHA). Four patients were operated on: three were submitted to second-stage rTHA after infection, and one underwent surgery due to aseptic loosening. The technique entails three main steps: evaluation of the amount of lateral pelvic tilt (either clinically or radiographically); setting a supracetabular rod using the smartphone app as a reference for inclination adjustment; and acetabulum preparation and final cup placement using the smartphone to guide the inclination angle after considering the amount of pelvic tilt. Cup anteversion was adjusted according to the transverse acetabulum ligament. All 4 cases underwent a follow-up that ranged from 17 to 24 months. None of the patients required further revision, and no complications (intraoperative, early, or late postoperative) were observed. All cups were within the Lewinnek safe zone for inclination (42 degrees, 43 degrees, 47 degrees, and 41 degrees). The functional outcome per the Harris Hip Score was excellent for all patients. Smartphones are cheap tools that can assist physicians in the adjustment of acetabular cup inclination during rTHA; however, assessing the possible lateral pelvic tilt and considering it while placing the cup are crucial.