title: Comparison of MRI- and CT-based patient-specific guides for total knee arthroplasty.
abstract: BACKGROUND
  The patient-specific guide for total knee arthroplasty (TKA) is created from the data provided by magnetic resonance imaging (MRI) or computed tomography (CT) scans. It remains unknown which imaging technology is suitable for the patient-specific guide. The purpose of this study was to compare the accuracy of implant positioning and operative times between the two types of patient-specific guides for TKA.
  
  
  METHODS
  Forty arthritic knees were divided into two treatment groups using MRI-based (PS-MRI group) or CT-based (PS-CT group) patient-specific guides in this prospective, comparative study. The guide in the PS-MRI group had a cutting slot, whereas that in the PS-CT group only had a pin locator. The operative times were compared between the two groups. The angular error and number of outliers (deviations >3°) of the implant position using pre- and postoperative CT were investigated in both groups.
  
  
  RESULTS
  The mean operative time was significantly shorter in the PS-MRI group (109.2 ± 16.5 min) than in the PS-CT group (129.5 ± 19.4 min) (p<0.001). There were no significant differences in the accuracy of the implant position regarding the coronal, sagittal, and axial planes between the groups (p>0.05).
  
  
  CONCLUSIONS
  To reduce the operative time, guides with additional functions, such as cutting and positioning, should be used. Both CT- and MRI-based-guides would result in the same accuracy in three planes but high inaccuracy in the sagittal plane. The use of patient-specific guide based on MRI might not be cost-effective.
  
  
  METHODS
  level 2.
authors.affiliation: Department of Orthopaedic Surgery, Kinki University Faculty of Medicine, Japan. Electronic address: asada@med.kindai.ac.jp.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Asada
authors.affiliation: Department of Orthopaedic Surgery, Kinki University Faculty of Medicine, Japan.
authors.forename: Shigeshi
authors.initials: S
authors.lastname: Mori
authors.affiliation: Department of Orthopaedic Surgery, Kinki University Faculty of Medicine, Japan.
authors.forename: Tetsunao
authors.initials: T
authors.lastname: Matsushita
authors.affiliation: Department of Orthopaedic Surgery, Kinki University Faculty of Medicine, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Nakagawa
authors.affiliation: Department of Orthopaedic Surgery, Kinki University Faculty of Medicine, Japan.
authors.forename: Ichiroh
authors.initials: I
authors.lastname: Tsukamoto
authors.affiliation: Department of Orthopaedic Surgery, Kinki University Faculty of Medicine, Japan.
authors.forename: Masao
authors.initials: M
authors.lastname: Akagi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D017076:Computer-Aided Design; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007720:Knee Prosthesis; D008279:Magnetic Resonance Imaging / Q000706:statistics & numerical data*; D008297:Male; D008875:Middle Aged; D061646:Operative Time; D066230:Patient-Specific Modeling; D057285:Precision Medicine / Q000379:methods; D011474:Prosthesis Design; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data*
keywords: Computed tomography; Magnetic resonance imaging; Patient-specific guide; Patient-specific instrumentation; Total knee arthroplasty