title: Joint gap assessment with a tensor is useful for the selection of insert thickness in unicompartmental knee arthroplasty.
abstract: BACKGROUND
  The success of unicompartmental knee arthroplasty relies on a lot of factors such as correct osteotomy and proper soft-tissue tensioning. A selection of insert thickness depends solely on the surgeon's subjective feeling. Recently, a tensor that is designed to assess soft tissue balance during unicompartmental knee arthroplasty has been developed. The purpose of this study was to compare the component gap throughout the range of motion among different distraction forces and examine the correlation between the component gap and the insert thickness.
  
  
  METHODS
  30 cases of 29 patients were included. All the patients received a conventional medial Zimmer Unicompartmental High Flex Knee System. Using a tensor under 10, 20, 30, and 40 lb distraction forces, after femoral component placement, the component gaps were assessed throughout the range of motion. The correlations between the component gap and the insert thickness selected were examined.
  
  
  RESULTS
  The component gap showed the same kinematic pattern among the different distraction forces and the value increased in proportion to the increase of the distraction force in unicompartmental knee arthroplasty. The insert thickness in unicompartmental knee arthroplasty was found to have a strong positive correlation with the component gap from 10 to 45° of knee flexion with a distraction force of more than 20 lb
  
  
  CONCLUSIONS
  With the use of the tensor, surgeons can quantify the component gap and objectify their insert thickness decision compared with the use of tension gauge.
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Takayama
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan. Electronic address: matsun@m4.dion.ne.jp.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Matsumoto
authors.affiliation: Department of Orthopaedic Surgery, Steel Memorial Hirohata Hospital, Himeji, Hyogo, Japan.
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Muratsu
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Atsuo
authors.initials: A
authors.lastname: Uefuji
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Nakano
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Kanto
authors.initials: K
authors.lastname: Nagai
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Tokio
authors.initials: T
authors.lastname: Matsuzaki
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Oka
authors.affiliation: Department of Orthopaedic Surgery, Kobe Kaisei Hospital, Kobe, Hyogo, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Ishida
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Takehiko
authors.initials: T
authors.lastname: Matsushita
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Kuroda
authors.affiliation: Department of Orthopaedic Surgery, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kurosaka
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology / Q000601:surgery*; D008297:Male; D020370:Osteoarthritis, Knee / Q000601:surgery; D010020:Osteonecrosis / Q000601:surgery; D010027:Osteotomy / Q000295:instrumentation; D016059:Range of Motion, Articular; D013314:Stress, Mechanical
keywords: Component gap; Insert selection; Kinematics; Tensor; Unicompartmental knee arthroplasty