title: A refined definition improves the measurement reliability of the tip-apex distance.
abstract: BACKGROUND
  Tip-apex distance (TAD) is reported as a good predictor for cut-outs of lag screws and spiral blades in the treatment of intertrochanteric fractures, and surgeons are advised to strive for TAD within 20 mm. However, the femoral neck axis and the position of the lower limb in the lateral radiograph are not clearly defined and can lead to measurement errors. We propose a refined TAD by defining these factors. The objective of this study was to analyze the reliability of this refined TAD.
  
  
  METHODS
  The radiographs of 130 prospective cases with unstable trochanteric fractures were used for the analysis of the refined TAD. The refined TAD was independently measured by 2 raters with clinical experience of more than 10 years (rater 1, 2) and 2 raters with much less clinical experience (rater 3, 4) after they received a training about the new measurement method. Intraclass correlation coefficient (ICC [2,4]) was calculated to assess the interrater reliability.
  
  
  RESULTS
  The mean refined TADs were 18.2:18.4:18.2:18.2 mm for rater 1:2:3:4. There was a strong correlation among all four raters (ICC 0.998, (95% CI: 0.998, 0.999).
  
  
  CONCLUSIONS
  Regardless of the clinical experience of raters, the refined TAD is a reliable tool and can be used to develop new TAD recommendations for predicting failure of fixation. Future studies with larger samples are needed to evaluate the predictive value of the refined TAD.
authors.affiliation: Department of Joint Reconstructive and Orthopaedic Surgery, Toyama Municipal Hospital, Toyama, Japan. Electronic address: sakagoshijp@yahoo.co.jp.
authors.forename: Daigo
authors.initials: D
authors.lastname: Sakagoshi
authors.affiliation: Department of Joint Reconstructive and Orthopaedic Surgery, Toyama Municipal Hospital, Toyama, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Sawaguchi
authors.affiliation: Department of Orthopaedic Surgery at Hokuriku Hospital, Kanazawa City, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Shima
authors.affiliation: Department of Joint Reconstructive and Orthopaedic Surgery, Toyama Municipal Hospital, Toyama, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Inoue
authors.affiliation: Department of Joint Reconstructive and Orthopaedic Surgery, Toyama Municipal Hospital, Toyama, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Oshima
authors.affiliation: AO Clinical Investigation and Documentation, Davos, Switzerland.
authors.forename: Sabine
authors.initials: S
authors.lastname: Goldhahn
mesh_terms: D000369:Aged, 80 and over; D001837:Body Weights and Measures; D001863:Bone Screws; D005260:Female; D005594:Fracture Fixation, Intramedullary; D006620:Hip Fractures / Q000000981:diagnostic imaging* / Q000601:surgery*; D006801:Humans; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results