Proximal to distal phalangeal articular angle of the first proximal phalanx: Reliability and correlation with round sign

Background: To reduce the rate of correction loss in hallux valgus surgery, a proximal to distal phalangeal articular angle (PDPAA) of the proximal phalanx of the greater toe of > 8 degrees is considered an indication for a combined Akin and Chevron osteotomy. The PDPAA is measured between the articular surfaces of the proximal phalanx of the greater toe. Viewed from a sagittal perspective, the joint surfaces are not per-pendicular aligned to the phalanx axis. Therefore, the PDPAA might be confounded by pronation. This study aims to, first, evaluate the intra-and interobserver reliability of the PDPAA and, second, to analyze the correlation to first ray pronation.Methods: In a consecutive series of 59 feet who underwent hallux valgus (HV) surgery, PDPAA, round sign and other angles were measured on weight-bearing radiographs pre-and postoperatively. After power analysis, the intraclass correlation coefficient (ICC) was used to calculate the intra-and interobserver re-liability. The correlation of PDPAA with the round sign as well as angles defining the HV and the Hallux valgus interphalangeus (HVI) were evaluated.Results: The PDPAA showed an excellent intra-and interobserver reliability (ICC 0.92 and 0.89, p < 0.05). The round sign did not correlate significantly with the PDPAA (p = 0.51). However, the PDPAA showed a moderate correlation with the interphalangeal angle (r = 0.51, p < 0.05) and fair inversely with the in-termetatarsal angle (r = -0.45, p < 0.05).Conclusion: First, measurement of PDPAA is reliable. Second, PDPAA is not associated with first ray pro -nation, but a false low PDPAA is geometrically possible. A high PDPAA correlates with a relevant HVI and inversely correlates with the HV like the HVI. Hence, first ray pronation should be treated first and a re-maining PDPAA of > 8 degrees after intraoperatively reevaluation separately.(c) 2022 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.