Abstract: Objective　To provide anatomical basis for the treatment of proximal interphalangeal (PIP) joint by the injury experiment of proximal phalanx trochlea.　Methods　Both of the upper hand specimens from 6 adults were dissected, and 36 fingers including index finger, middle finger and ring finger were selected for the study. The radial angle of PIP joints was measured when the  trochlea of proximal phalanx was intacted 10%, 20%, 30%, 40% and 50% of injuries at 0 °  PIP joint flexion. 　Results　The mean length of the two sides of the proximal phalanx was (10.25±1.12) mm, and the radial angle of PIP joints was (0.14±0.10) °. When 10% of injuries, it was (5.06±0.53) °, when 20% of injuries, it was (8.47±0.42) °, when 30% of injuries, it was (12.28±0.71) °, when 40% of injuries, it was (16.33±0.76) °, and when 50% of injuries, it was (20.03±0.75) °. The more severe the injury of the proximal phalanx trochlea, the larger the radial angle of PIP joints, meaning the more unstable the PIP joints (P<0.0001, Wilcoxon test).　Conclusions　The defect of the proximal phalangeal trochlea has a significant effect on the lateral stability of PIP joints. Lateral instability can occur when the injury reaches 10%.

Key words: Proximal phalangeal trochlea, 　Proximal interphalangeal joint, 　Stability, 　Applied anatomy