Determining the normal range of the calcaneus-metatarsal angles in the second-trimester fetal ultrasound examination using the novel measurement technique "Melek's angles": A cross-sectional study.

Abstract

Objectives: The aim of this study is to establish the normal calcaneus-metatarsal angles in order to facilitate the recognition of fetal foot deformities. Therefore, a novel measurement technique was determined using ultrasound and applied to nonanomalous fetuses in the 18th to 23rd gestational weeks.

Materials and methods: This cross-sectional study included 100 low-risk, nonanomalous fetuses in the 18th to 23rd weeks of gestation. Measurements were obtained using the novel measurement technique in fetal ultrasound examination. Fetal biometry, foot sole length, first and fifth metatarsal diaphyseal length measurements were taken. The acute angle measurement of the line segment passing between the calcaneus outer lateral and proximal fifth metatarsal with the long axis of the first metatarsal diaphysis (CA-mtt₁) and long axis of the fifth metatarsal diaphysis (CA-mtt₅) was taken. Interobserver and intraobserver reliabilities were assessed by intraclass correlations (ICC).

Results: A strong positive correlation was detected between bi-parietal diameter (BPD) and foot sole length, first metatarsal diaphyseal length and fifth metatarsal diaphyseal length (p < 0.0001). No significant correlation of these CA-mtt₁ and CA-mtt₅ angles with BPD was detected (p = 0.35, p = 0.82, respectively). The data suggest that the CA-mtt₁ and CA-mtt₅ angles remained consistently within a narrow range and were determined to be 20.0° ± 8.7° and 7.8° ± 7.5°, respectively. Intraobserver and interobserver agreement for CA-mtt₁ angle was moderate (ICC, 0.655) and moderate (ICC, 0.615), for CA-mtt₅ angle was moderate (ICC, 0.631) and moderate (ICC, 0.605), respectively.

Conclusion: A normal reference range was established for fetal sole length, first metatarsal diaphysis length, fifth metatarsal diaphysis length, CA-mtt₁ angle, and CA-mtt₅ angle in the 18th to 23rd weeks of gestation. It was determined that the CA-mtt₁ and CA-mtt₅ angles remained relatively constant within a narrow range throughout the assessed gestational weeks.