Nasolacrimal duct injury is a rare complication of rhinoplasty. Detailed regional anatomy knowledge is mandatory to avoid this complication. To display a reference line to protect the nasolacrimal duct from injury during lateral osteotomy, dacryocystography images of 10 patients who underwent rhinoplasty surgery at the authors' clinic were obtained. Lateral osteotomy lines and a line from the medial canthus to the alar groove were marked with radio-opaque wires before procedures. Horizontal and sagittal distances from these lines to the nasolacrimal duct were measured at the beginning, midpoint, and end of the nasolacrimal duct. No sign of nasolacrimal duct injury was observed postoperatively. The mean horizontal distances from the osteotomy lines to the nasolacrimal duct entrance, midpoint, and exit were respectively 0.23 ± 0.12 cm, 0.25 ± 0.11 cm, and 0.24 ± 0.11 cm, and the mean sagittal distances were respectively 0.61 ± 0.21 cm, 1.96 ± 0.28 cm, and 2.38 ± 0.32 cm. The mean horizontal distances from the medial canthus-alar groove line to the nasolacrimal duct entrance, midpoint, and exit were respectively 0.57 ± 0.1 cm, 0.51 ± 0.1 cm, and 0.46 ± 0.13 cm, and the mean sagittal distances were 0.91 ± 0.27 cm, 1.34 ± 0.27 cm, and 1.79 ± 0.3 cm. The osteotomy lines and the nasolacrimal duct were closest in the medial canthal region. The imaginary line from the medial canthus to the junction of the alar wings and cheek was always lateral and anterior to the nasolacrimal duct. Considering the three-dimensional shape of the nose, especially its projection, placement of lateral osteotomies medial to the medial canthus-alar groove line would decrease the risk of nasolacrimal duct injury.
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