Clinical reliability of the "furcation arrow" as a diagnostic marker

The radiographic entity known as the "furcation arrow" has long been used in practice even though little is known about its usefulness as a clinical indicator. The definitive study of the furcation arrow suggests that its presence on a radiograph reliably predicts furcation invasion, but this has not been confirmed in an in vivo investigation. The purpose of this study was to evaluate the furcation arrow in a clinical setting, testing the assertion that the furcation arrow image is an accurate predictor of furcation invasion. Specifically, we sought to determine the following. First, what is the prevalence of furcation arrow images in the radiographs of maxillary molars with periodontitis? Second, what is the interexaminer agreement on what constitutes a furcation arrow? Third, how does the presence or absence of a furcation arrow correlate with the true clinical status of the furcation? Fourth, what is the sensitivity and specificity of the furcation arrow as a diagnostic indicator?

Eighty-nine patients requiring surgical treatment of periodontitis in the maxillary molar regions were included in this study. Before surgery, one of five calibrated examiners viewed periapical and bitewing radiographs of the surgical site and recorded the presence or absence of a furcation arrow at each proximal furcation. Before administering anesthesia, the same examiner recorded a Hamp index value of each proximal furcation, with a second Hamp index taken after flap reflection and debridement. After surgery, each of the four remaining examiners independently reviewed the radiographs for furcation arrows. Descriptive statistical analysis was performed to correlate the appearance of the furcation arrow image to the actual degree of furcation invasion as determined by the intrasurgical Hamp index.

A total of 164 maxillary molars were examined, providing 328 interproximal furcations; 111 (33.8%) furcations were determined at surgical debridement to have a furcation invasion of Hamp degree 1 or greater. Of the 111 furcation invasions, 43 (38.7%) were predicted by a furcation arrow image seen by at least three of the five examiners. When comparing the appearance of the radiographic image to the extent of furcation invasion, 20 of 64 (31.3%) Hamp 1 furcation invasions and 23 of 47 (48.9%) Hamp 2 and 3 furcation invasions were predicted by furcation arrows observed by at least three of five examiners. The multirater kappa statistic for interexaminer agreement on the presence or absence of the image was 0.489. The sensitivity of the furcation arrow image as a diagnostic marker was 38.7%, and the specificity was 92.2%; the positive predictive value of the image was 71.7%, and the negative predictive value was 74.6%. Of the 324 furcations used to compare clinical indices, the agreement of preanesthesia and postdebridement Hamp indices was 0% for degree 3, 83.7% for degree 2, and 98.4% for degree 1 furcation lesions.

These data suggest that the furcation arrow has limited usefulness as a diagnostic marker of furcation invasion. The image is difficult to interpret and highly subjective and can correctly predict furcation invasions only approximately 70% of the time when present on the radiograph. In addition, when furcation invasions are truly present, the furcation arrow is seen in <40% of sites.