Objective  To investigate A1 pulley thickness of flexor tendon in healthy volunteers and to analyze its influence factors.

  Methods  The study included 90 healthy volunteers and the A1 pulley thickness at bilateral fingers was measured using high frequency ultrasound. The following parameters were recorded for each participant: age, gender, weight, height, body mass index (BMI).

  Results  High-frequency ultrasound can clearly show A1 pulley. There was no significant difference in A1 pulley thickness between the bilateral fingers (P>0.05). A1 pulley thickness was significantly different in different fingers (P<0.05). Further comparison showed that A1 pulley thickness could be divided into two subsets: thumb and little finger ((0.196±0.051) mm), index, middle and ring fingers ((0.230±0.055) mm). A1 pulley thickness was positively correlated with age (r=0.468, P<0.001). The normal reference ranges for thumb and little finger were 0.09-0.23 mm, 0.12-0.30 mm and 0.12-0.32 mm, respectively. The normal reference ranges for index, middle and ring fingers were 0.11-0.27 mm, 0.15-0.35 mm and 0.17-0.35 mm in volunteers aged 3-19 yr., 20-49 yr., and ≥50 yr., respectively. Gender and BMI had negligible impact on A1 pulley thickness (P>0.05).

  Conclusion  High-frequency ultrasound can clearly show and measure A1 pulley. Site and age should be taken into account when determining the reference range of normal A1 pulley thickness. High-frequency ultrasound can be a quantitative evaluation method for A1 pulley lesions.