How reliable are currently available methods of measuring the anorectal angle?

A prospective study was undertaken to compare two different methods of measuring the anorectal angle (ARA), balloon proctography (BP) and cinedefecography (CD), as well as to evaluate the reproducibility of this measurement using each technique. One hundred four consecutive patients (75 women and 29 men) with constipation (63 patients), fecal incontinence (25 patients), or rectal pain (16 patients) underwent both BP and CD. The ARA was measured by taking lateral radiographs of the pelvis during rest (R), squeeze (S), and push (P). The same interpretation process was performed 2 to 12 months later by the same observer, blinded as to diagnosis and initial measurements. There were highly significant differences in each measurement category, R (P less than 0.0001), S (P less than 0.0001), and P (P less than 0.0004) between BP and CD. However, the correlation between the first and second measurements was excellent (P less than 0.0001). BP was consistently more difficult to interpret because of balloon configuration. Although BP and CD have poor correlation with each other, each examination can be reliably interpreted. CD appears to be a superior examination because of the added ability to delineate rectoceles, intussusceptions, and other structural defects.