title: Accuracy of templating the acetabular cup size in Total Hip Replacement using conventional acetate templates on digital radiographs.
abstract: OBJECTIVE
  Templating of the acetabular cup size in Total Hip Replacement (THR) is normally done using conventional radiographs. As these are being replaced by digital radiographs, it has become essential to create a technique of templating using digital films. We describe a technique that involves templating the digital films using the universally available acetate templates for THR without the use of special software.
  
  
  METHODS
  Preoperative digital radiographs of the pelvis were taken with a 30 mm diameter spherical metal ball strapped over the greater trochanter. Using standard acetate templates provided by the implant company on magnified digital radiographs, the size of the metal ball (X mm) and acetabular cup (Y mm) were determined. The size of the acetabular cup to be implanted was estimated using the formula 30*Y/X. The estimated size was compared with the actual size of the cup used at surgery.
  
  
  RESULTS
  Using this technique, it was possible to accurately predict the acetabular cup size in 28/40 (70%) of the hips. When the accuracy to within one size was considered, templating was correct in 90% (36/40). When assessed by two independent observers, there was good intra-observer and inter-observer reliability with intra-class correlation coefficient values greater than 0.8.
  
  
  CONCLUSIONS
  It was possible to accurately and reliably predict the size of the acetabular cup, using acetate templates on digital films, without any digital templates.
authors.affiliation: Associate Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India.
authors.forename: Vignesh P
authors.initials: VP
authors.lastname: Krishnamoorthy
authors.affiliation: Registrar, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India.
authors.forename: Rajamani
authors.initials: R
authors.lastname: Perumal
authors.affiliation: Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India.
authors.forename: Alfred J
authors.initials: AJ
authors.lastname: Daniel
authors.affiliation: Professor, Department of Orthopaedics, Christian Medical College, Vellore 632004, Tamil Nadu, India.
authors.forename: Pradeep M
authors.initials: PM
authors.lastname: Poonnoose
keywords: Acetabular cup; Acetate templates; Radiographs; Templating; Total Hip Replacement