title: Distances between bony landmarks and adjacent nerves: anatomical factors that may influence retractor placement in total hip replacement surgery.
abstract: BACKGROUND
  Retractor placement is a leading cause of intraoperative nerve injury during total hip replacement (THR) surgery. The sciatic nerve, femoral nerve, and superior gluteal nerve are most commonly affected. This study aimed to identify the distances from bony landmarks in the hip to the adjacent nerves on magnetic resonance imaging (MRI) and the associations between anatomical factors and these distances that would guide the placement of retractors during THR surgery, in order to minimize the risk of nerve injury.
  
  
  METHODS
  We reviewed hip MRIs of 263 adults and recorded the distances from (1) the anterior acetabular rim to the femoral nerve; (2) the superior acetabular rim to the superior gluteal nerve; (3) the posterior acetabular rim to the sciatic nerve; and (4) the greater trochanter to the sciatic nerve. The effects of anatomical factors (i.e., gender, age, body height, body mass index (BMI), pelvic width, and acetabular version and morphology) on these distances were analyzed.
  
  
  RESULTS
  Distances from bony landmarks to adjacent nerves (in cm) were 2.06 ± 0.44, 2.23 ± 0.28, 1.94 ± 0.81, and 4.83 ± 0.26 for the anterior acetabular rim, superior acetabular rim, posterior acetabular rim, and greater trochanter, respectively, and were shorter in women than in men (P < 0.001). Multivariate analysis identified body height as the most influential factor (P < 0.001). Linear regression demonstrated a strong positive linear correlation between body height and these distances (Pearson's r = 0.808, 0.823, 0.818, and 0.792, respectively (P < 0.001)).
  
  
  CONCLUSIONS
  The distances from bony landmarks to adjacent nerves provide useful information for placing retractors without causing nerve injury during THR surgery. Shorter patients will have shorter distances from bony landmarks to adjacent nerves, prompting more careful placement of retractors.
authors.affiliation: Department of Orthopedics, China Medical University Hospital, China Medical University, Taichung, 40447, Taiwan.
authors.forename: Ta-I
authors.initials: TI
authors.lastname: Wang
authors.affiliation: Department of Radiology, China Medical University Hospital, China Medical University, Taichung, 40447, Taiwan.
authors.forename: Hui-Yi
authors.initials: HY
authors.lastname: Chen
authors.affiliation: Department of Orthopedics, China Medical University Hospital, China Medical University, Taichung, 40447, Taiwan.|Graduate Institute of Clinical Medicine, School of Medicine, China Medical University, Taichung, 40447, Taiwan.
authors.forename: Chun-Hao
authors.initials: CH
authors.lastname: Tsai
authors.affiliation: Department of Orthopedics, China Medical University Hospital, China Medical University, Taichung, 40447, Taiwan.|Graduate Institute of Clinical Medicine, School of Medicine, China Medical University, Taichung, 40447, Taiwan.
authors.forename: Horng-Chaung
authors.initials: HC
authors.lastname: Hsu
authors.affiliation: Department of Orthopedics, China Medical University Hospital, China Medical University, Taichung, 40447, Taiwan. alilin422@yahoo.com.tw.
authors.forename: Tsung-Li
authors.initials: TL
authors.lastname: Lin
mesh_terms: D000077:Acetabulum / Q000473:pathology*; D000328:Adult; D000368:Aged; D059925:Anatomic Landmarks / Q000473:pathology*; D000886:Anthropometry / Q000379:methods; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation / Q000379:methods*; D002081:Buttocks / Q000294:innervation; D005260:Female; D005267:Femoral Nerve / Q000473:pathology*; D005269:Femur / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D059348:Peripheral Nerve Injuries / Q000209:etiology / Q000473:pathology / Q000517:prevention & control*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012584:Sciatic Nerve / Q000473:pathology*; D055815:Young Adult
keywords: Adjacent nerves; Body height; Bony landmarks; Distances; Magnetic resonance imaging; Total hip replacement