title: Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty.
abstract: In this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM).
  
  
  
  After navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position.
  
  
  
  We found a lower flexion of 8.3° (8.8°, P < .001) and lower internal rotation of 9.2° (9.5°, P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8° (11.8°, P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group.
  
  
  
  For implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning.
authors.affiliation: Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany.
authors.forename: Markus
authors.initials: M
authors.lastname: Weber
authors.affiliation: Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Woerner
authors.affiliation: Department of Orthopedic and Trauma Surgery, Vilsbiburg Hospital, Vilsbiburg, Germany.
authors.forename: Ernst
authors.initials: E
authors.lastname: Sendtner
authors.affiliation: Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Völlner
authors.affiliation: Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Grifka
authors.affiliation: Department of Orthopedic Surgery, Regensburg University, Medical Center, Bad Abbach, Germany.
authors.forename: Tobias F
authors.initials: TF
authors.lastname: Renkawitz
mesh_terms: D000077:Acetabulum / Q000601:surgery; D000203:Activities of Daily Living; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D005260:Female; D057925:Femoracetabular Impingement / Q000209:etiology / Q000517:prevention & control*; D005269:Femur / Q000601:surgery; D006621:Hip Joint / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011183:Postoperative Complications / Q000209:etiology / Q000517:prevention & control*; D011184:Postoperative Period; D011446:Prospective Studies; D016059:Range of Motion, Articular; D012399:Rotation; D025321:Surgery, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed
keywords: combined anteversion; femur first; impingement; range of motion; total hip arthroplasty