Goniometric versus computerized angle measurement in assessing hallux valgus

Background: Digital workstations with high-resolution monitors are replacing standard radiographs for image evaluation and interpretation. Radiographic angles in the foot have been evaluated for interobserver and intraobserver reliability with plain films, but use of digital workstations has not been validated. Because the 1-2 intermetatarsal (IM) and hallux valgus (HV) angles help determine the most appropriate bunion procedure, the reliability of these measurements is important. Methods: The HV and 1-2 IM angles were evaluated on preoperative radiographs of 25 patients who subsequently underwent bunion procedures. A standardized technique using a film marker and goniometer on plain film was compared with use of a mouse and computerized angle measurement software at a digital workstation. Three foot and ankle surgeons conducted these measurements at various intervals. Completion of three readings of each radiograph in each format by each observer totaled 1,800 measurements. Results: Computerized measurement gave better overall reliability. For the HV angle, interobserver agreement (measurements within 2 degrees) improved from 66% with plain films to 81% with the digital workstation (p < 0.001). Intraobserver agreement increased from 72% to 80%. The 1-2 IM angle was similarly reliable with both methods for inter- and intraobserver agreement. Conclusions: This study validates the use of computer-assisted angle measurement on digital radiographs for assessment of HV and 1-2 IM angles. Computerized measurement may result in more reliable readings because it eliminates the error inherent with use of a goniometer and facilitates adjustment of radiographic lines on the computer to ensure correct alignment.