To establish a mechanical friction model between human skin and surgical drapes, verify the mechanical feasibility of the perineal-post-free traction technique in the Trendelenburg position, clarify its adaptability to patients with different body weights and analyze the safe angles, so as to provide a mechanical basis for clinical application.

(1) In vitro experiment: fresh porcine skin was used to simulate human skin. A friction coefficient tester was employed to measure the friction coefficient between porcine skin and surgical drapes under pressures of 40 mmHg and 80 mmHg, with five porcine skin specimens per group and three repeated measurements for each specimen. (2) In vivo experiment: 30 patients scheduled for hip arthroscopy using the perineal-post-free traction technique who voluntarily signed informed consent forms and met the inclusion were enrolled. The patients with history of previous hip surgery were excluded. The actual traction force and Trendelenburg angle at 10 mm of hip joint distraction were measured, the friction coefficient between skin and surgical drapes was calculated, and the consistency between in vitro and in vivo data was compared. (3) Group analysis: Patients were divided into a low-weight group (<60 kg), a medium-weight group (60–79 kg), and a high-weight group (≥80 kg). The trends of friction coefficient and angle in each group were analyzed. Statistical analysis was performed using SPSS 26.0 software. One-way analysis of variance or independent-samples t test was used for intergroup comparisons, and P<0.05 was considered statistically significant.

(1) In vitro experiment: The mean friction coefficients between porcine skin and surgical drapes under 40 mmHg and 80 mmHg were 0.371 and 0.433, respectively. The friction coefficient was positively correlated with increasing pressure (t=-3.1165, P=0.0143). (2) In vivo experiment: Thirty patients were included, consisting of 23 males and seven females. Age were from 16 to 66 years, (35±13) years on average; body weight were from 48 to 100 kg, (72±13) kg on average . The traction force ranged from 44.30 to 87.70 kg, (59.4±11.3) kg on average, the Trendelenburg angle ranged from 5.3° to 14.3°, ( 9.9±2.8)°on average, and the friction coefficient ranged from 0.43 to 1.18, 0.70±0.22 on average. (3) The applicable Trendelenburg angles for patients with low, medium, and high body weights using the perineal-post-free traction technique are 10°, 13°, and 15°, respectively.

At a Trendelenburg angle of 10° to 15°, the frictional force between skin and surgical drapes can counteract the lower-extremity traction force and ensure safe distraction of the hip joint space. For patients of different body weights, the minimum safe angle should be used to reduce complications, and a smaller body weight requires a larger angle. The findings provide important references for positioning in related orthopedic surgeries.