title: Cup implantation accuracy using the HipCOMPASS mechanical intraoperative support device.
abstract: BACKGROUND
  While navigation systems have been developed to increase implantation accuracy in total hip arthroplasty (THA), they are not yet sufficiently versatile or commonly used. Therefore, to elevate the appeal of such systems, we have developed HipCOMPASS, a simple and effective mechanical angle indicator for use in supine THA.
  
  
  OBJECTIVE
  How accurate is the mean cup orientation [in terms of errors in radiographic anteversion (RA) and inclination (RI)] in cases where HipCOMPASS is used for intraoperative support? Does HipCOMPASS increase this cup orientation accuracy compared to THA cases without it? Does HipCOMPASS increase mean operation time?
  
  
  METHODS
  We measured cup orientation in 97 THA cases with HipCOMPASS and in 80 cases without it. Then we compared the angles determined in preoperative planning with the angles revealed by postoperative computed tomography (CT) for both groups. The discrepancy between them was defined as an error. Errors greater than 10° were considered outliers. Additionally, mean operative time with and without the Hip COMPASS were compared.
  
  
  RESULTS
  With the use of HipCOMPASS, the mean absolute error values in radiographic anteversion and inclination were 2.9° ± 2.3° (range 0°-12.8°) and 2.9° ± 2.1° (0.1°-7.7°), respectively. In contrast, without the use of HipCOMPASS, radiographic anteversion and inclination error values were 8.8° ± 5.8° (0.1°-25.4°) and 6.1° ± 4.5° (0.2°-21.0°), respectively. Outlier occurrence rates were 1.0 % with HipCOMPASS and 48.8 % without it. Mean operative times with and without HipCOMPASS use were 109.2 ± 23.8 min (74-199 min) and 137.6 ± 40.6 min (71-298 min), respectively.
  
  
  CONCLUSIONS
  The study has found that HipCOMPASS dramatically increases implantation accuracy and it is also a simple and highly versatile tool that can be implemented quickly. Given its low cost in addition to its favourable accuracy, simple implementation, and short operative time, HipCOMPASS can be regarded as a very useful and effective THA support device.
  
  
  METHODS
  Retrospective comparative study, Level 3.
authors.affiliation: Department of Orthopedic Surgery, Niigata University, 757 1bancho, Chuoukuasahimatidori, Niigata City, Niigata 951-8510 Japan.
authors.forename: Ken
authors.identifier: 0000-0002-8199-5999
authors.initials: K
authors.lastname: Suda
authors.affiliation: Saiseikai Niigatadaini Hospital, 280-7, Nishikuteraji, Niigata City, Niigata 950-1104 Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Ito
authors.affiliation: Department of Orthopedic Surgery, Niigata University, 757 1bancho, Chuoukuasahimatidori, Niigata City, Niigata 951-8510 Japan.
authors.forename: Dai
authors.initials: D
authors.lastname: Miyasaka
authors.affiliation: Department of Orthopedic Surgery, Niigata University, 757 1bancho, Chuoukuasahimatidori, Niigata City, Niigata 951-8510 Japan.
authors.forename: Norio
authors.initials: N
authors.lastname: Imai
authors.affiliation: Niigata Rinko Hospital, 114-3 1chome, Higashikumomoyamacho, Niigata City, Niigata 950-8725 Japan.
authors.forename: Izumi
authors.initials: I
authors.lastname: Minato
authors.affiliation: Department of Orthopedic Surgery, Niigata University, 757 1bancho, Chuoukuasahimatidori, Niigata City, Niigata 951-8510 Japan.
authors.forename: Naoto
authors.initials: N
authors.lastname: Endo