Abstract
Background
Perineal post countertraction during hip arthroscopy risks complications. Postless traction avoids the perineal post but requires understanding the factors influencing traction force to optimize safety. This study investigated how gender, body mass index (BMI), traction states, hip rotation, lateral center-edge angle (LCEA), alpha angle, and femoral anteversion affect traction force during postless hip arthroscopy.
Materials and methods
This retrospective study included patients undergoing postless hip arthroscopy for femoroacetabular impingement syndrome (FAIS) between October 2023 and March 2024. Inclusion criteria comprised confirmed FAIS diagnosis and comprehensive intraoperative traction force documentation across six traction states (initial traction to 40 min post-capsulotomy) and three rotational positions (neutral, internal/external rotation at 15°). Traction force was measured using a force sensor. Preoperative LCEA, alpha angle, and femoral anteversion were radiographically assessed. Mann-Whitney U tests and repeated-measures ANOVA were used to assess sex-, state-, and rotation-related effects on traction force; Pearson or Spearman correlation analyses were used to analyze associations between BMI, alpha angle, LCEA, femoral anteversion, and traction force.
Results
A total of 34 patients (10 males, 24 females) were included in this study. Traction forces increased from initial gross traction to needle puncture of the capsule (P < 0.001), then decreased post-puncture (P < 0.001). In the vast majority of traction states, external or internal rotation position required higher forces than the neutral position to achieve adequate joint distraction for surgical visualization (P < 0.001). Males exhibited greater forces than females (P < 0.001). Positive correlations included BMI, LCEA, and alpha angle (P < 0.05). Femoral anteversion angle negatively correlated with traction. It was also found that LCEA was positively correlated with the difference in traction force between different rotational positions, while femoral anteversion was negatively correlated (P < 0.05).
Conclusions
Traction force during postless hip arthroscopy increases with higher BMI, larger LCEA, and elevated alpha angle, while greater femoral anteversion reduces traction requirements. Male gender and internal or external hip rotation consistently demand higher forces compared to females and neutral rotation. Traction force decreases after joint puncture and capsulotomy and decrease over time during surgery.
Supplementary Information
The online version contains supplementary material available at 10.1186/s12891-026-09529-y.
Keywords: Hip arthroscopy, Postless traction, Traction force
Background
With the increasing recognition of hip-related pathologies and advancements in surgical techniques, hip arthroscopy has gained broader clinical application. To facilitate adequate joint space visualization for central compartment procedures, preoperative limb traction is routinely employed. At present, a perineal post is most commonly used for countertraction. However, due to the inherent technical complexity of hip arthroscopy, prolonged perineal compression associated with this method may lead to a spectrum of postoperative complications, including soft tissue injuries such as perineal abrasions, superficial fascial necrosis, vaginal lacerations, etc., and neurological injuries, such as perineal sensory disturbance, pain, and sexual dysfunction [1–5].While most complications are transient, resolving within days to months, permanent sequelae have been documented [6]. Reported incidence rates vary substantially across studies, ranging from 1.4% to 74% [6–8].
To address these complications, clinicians have gradually tried and advocated postless hip traction in recent years. This approach eliminates perineal post utilization by positioning patients in Trendelenburg tilt, utilizing gravitational forces along the traction table and frictional resistance between the patient’s back and surgical table to counteract traction forces. Early report indicated that this approach significantly reduced the incidence of aforementioned perineal compression-related complications [9].
Existing biomechanical analyses have predominantly focused on post-assisted traction systems, with substantial evidence indicating that reduced traction forces correlate with decreased incidence and severity of associated complications [4, 5]. Notably, postless traction systems precisely possess the advantage of reducing the required traction force [10]. However, there are still few relevant studies on the influencing factors of postless traction systems. Moreover, significant heterogeneity in surgical approaches, measurement protocols, and force definitions across studies precludes reliable quantitative comparison of hip arthroscopy distraction forces [10, 11]. Consequently, identifying factors influencing traction force in postless systems may enhance preoperative estimation of individualized traction requirements and enable patient-specific risk stratification for traction-related complications.
Previous studies have mentioned that factors affecting hip joint stability, such as sex, BMI, joint range of motion and various imaging angles, may have an impact on traction [11, 12]. At the same time, in daily clinical practice and similar previous analyses [13], it is also found that the rotational position of the hip joint may affect the traction force. Nevertheless, relevant studies remain limited, particularly in Asian populations, and the results of different studies are variable [11].
Thus, this study aimed to investigate the potential impact of gender, BMI, traction states, hip rotation position, lateral center-edge angle (LCEA), alpha angle and femoral anteversion angle on traction force during postless traction in hip arthroscopy. We hypothesized that the above variables might influence the traction force required during the procedure.
Methods
Patients
This study retrospectively evaluated patients who attended the sports medicine clinic of our department and underwent arthroscopic surgery for the diagnosis of femoroacetabular impingement syndrome (FAIS) between October 2023 and March 2024. As shown in Fig. 1, the inclusion criteria were: patients with (1) confirmed FAIS diagnosis requiring arthroscopic intervention, and (2) comprehensive documentation of intraoperative traction forces across all required rotational positions. The diagnosis of FAIS was established based on a combination of: (1) clinical symptoms, (2) positive physical examination findings (pain with the Flexion-Adduction-Internal Rotation (FADIR) test and/or the Flexion-Abduction-External Rotation (FABER) test), (3) radiographic parameters including a LCEA > 25° and an alpha angle > 50° on preoperative imaging, and (4) failure of a minimum 3-month period of non-operative management. The exclusion criteria were as follows: (1) previous hip surgery, (2) avascular necrosis of the femoral head, (3) Ehlers-Danlos syndrome, (4) Legg-Calve-Perthes disease, and (5) pigmented villonodular synovitis, osteoid osteoma, synovial chondromatosis, and rheumatologic disease. This study was approved by the Ethics Committee of our hospital(M2019193). All research was performed in accordance with relevant guidelines and regulations. All patients who participated in the study provided written informed consent. It should be noted that this study adhered to traditional biological definitions of sex classification in human subjects, based on chromosomal and phenotypic characteristics.
Fig. 1.
Flowchart illustrating the patient selection process. FAIS, femoroacetabular impingement syndrome
Surgical method
As shown in the Fig. 2, The patient was placed supine on the operating table, with the contralateral arm secured to an abduction frame and the ipsilateral arm suspended and fixed on an anterior chest brace. The patient’s trunk remained in full contact with the traction sheet covering the table, while the buttocks were positioned at the table’s edge. Bony protuberances of both feet and ankles were padded with cotton wraps and secured within traction boots, with the contralateral leg stabilized in 45° abduction and the affected lower limb maintained in full extension with 15° internal rotation. The patient’s inguinal region on the contralateral side was secured to the operating table with a thickened safety strap wrapped in cotton pads, which serves as a countertraction mechanism. An abdominal belt was used around the abdomen to keep the patient’s back close to the table, which increased resistance and protected the patient from falling off the operating table. Once preparations were finalized, the operating table was slowly adjusted to the Trendelenburg position so that the patient’s head was low and feet were high by approximately 10°, using the friction between the patient and the operating table and the component force of gravity along the operating table to resist the traction force. After that, as previously described [13], an initial coarse traction force was applied to the feet (State 1). This was followed by controlled boot traction to achieve adequate hip joint distraction, with a target joint space width of 12–20 mm (State 2). The position and width of the bony space of the hip joint were determined by fluoroscopic images. Measurements were made from the lateral point, the most lateral aspect of the acetabular source line, along the acetabular source line, and perpendicular to the surface of the femoral head [14]. The measurements of the width were made on a mobile radiography system (OEC One CFD; General Electric). Under fluoroscopy, No. 22 puncture guide needle (Smith + Nephew, 1.2 mm in diameter) was inserted (state 3), and an anterolateral approach was performed. Then, a mid-anterior portal was made and the external and anterior (12 o’clock − 3 o’clock) joint capsules were incised (state 4). Before introducing arthroscopy into the peripheral compartment to decompress the CAM deformity, the pathology of the central compartment was addressed. A satisfactory CAM resection was confirmed by intraoperative fluoroscopy and dynamic examination. The capsule was routinely repaired at the end of the procedure. All patients received regular postoperative follow-up and were examined for complications including surgical site infection, perineal hematoma or abrasion, as well as lower limb numbness or pain.
Fig. 2.
Postless traction during hip arthroscopy. (A) Side view. (B) Top view. The patient was positioned supine on the traction table. The contralateral arm was secured to an abduction frame, while the ipsilateral arm was suspended. Counter-traction was achieved via a padded strap securing the contralateral inguinal region and an abdominal belt. Both feet were secured in traction boots, with the contralateral leg abducted (45°) and the affected limb extended and internally rotated (15°). The table was tilted to ~ 10° Trendelenburg
Traction force and radiographic measurement
A force sensor (DYLY-108; YOUNG Ltd) with a measuring range of 0–1000 N and an accuracy of 0.1 N was connected to the boot of the hip positioning system. The sensor was calibrated prior to measurement. The sensor’s measurement direction was aligned with the traction direction to ensure that the traction force remained consistently applied to the affected limb during surgery, while allowing internal or external rotation of the hip to be performed [15]. The sensor was connected to an electronic display that automatically displays the magnitude of the traction force in real time. Traction forces were measured at six key time points mentioned above: initial gross traction (state 1), traction to maneuverable width (state 2), after arthrocentesis (state 3), after capsulotomy (state 4), 20 min after capsulotomy (state 5), and 40 min after capsulotomy (state 6)(Four patients did not enter this state due to the time of surgery). Under each state, the hip was rotated to the internal rotation position (15°), neutral position, and external rotation position (15°). As shown in Fig. 3, these angles were determined by measuring the corresponding foot rotation and were manually measured and recorded by a surgeon (the corresponding author, with over 10 years of clinical experience) using a standard goniometer. Traction force was measured twice at each rotational angle, and the final value was calculated as the average of the two measurements.
Fig. 3.
Intraoperative measurement of traction force and hip rotation angle. (A)-(C) Measurement of lower limb traction force under different intraoperative states. Traction force was measured twice at each rotational angle with a force sensor (DYLY-108; YOUNG Ltd), and the final value was calculated as the average of the two measurements. (B)-(C) Measurement of intraoperative hip rotation angle. These angles were determined by measuring the corresponding foot rotation and were manually measured and recorded using a standard goniometer
All radiographic measurements were performed preoperatively. The alpha angle and LCEA were measured on 45°Dunn view and supine anteroposterior hip radiographs, respectively [16, 17]. Femoral anteversion was measured through multiple computed tomography cross-sections by Murphy’s method [18, 19].
Statistical analysis
IBM SPSS software (version 27.0; IBM Corp., Armonk, NY, USA) was used for statistical analysis and plotting. All data were tested for normality using the Shapiro-Wilk test. Mann-Whitney U test or independent sample t-test was used to compare the difference of traction force between male and female patients in each state and hip rotational position. Friedman test and post hoc Wilcoxon signed-rank test (with Bonferroni correction) or repeated measurement ANOVA were used to compare the differences in traction force between different states and different rotational positions. The four missing data in State 6 were supplemented by multiple imputation. Then Spearman test or Pearson test was used to analyze the correlation between BMI, alpha angle, lateral center-edge angle, femoral anteversion and traction force and traction difference under different states and different hip rotational positions. A value of P < 0.05 was considered significant. G*Power 3.1 (Universität Düsseldorf) was used to calculate the statistical power of the present study.
Results
General information
The study ultimately included 34 patients who underwent perineal postless hip arthroscopy for FAIS. The complete patient selection process is illustrated in Fig. 1, and detailed patient basic information are provided in Table 1. Post-hoc analyses demonstrated adequate statistical power (Power > 0.80) for most analyses supporting the core conclusions of this study. Specific power values are presented in Supplementary Tables 1–4.
Table 1.
Descriptive characteristics
| Parameter | Value (N = 34) |
|---|---|
| Age, y, mean (range) | 39.41 ± 9.38(19–62) |
| Sex | |
| Male | 10(29.41%) |
| Female | 24(70.59%) |
| BMI, kg/m2, mean (range) | 22.81 ± 2.93(17.44–28.67) |
| Alpha angle, deg | 53.83 ± 9.21 |
| LCEA, deg | 33.32 ± 8.63 |
| Femoral anteversion, deg | 15.70 ± 9.90 |
Measurement data were presented as mean ± s.d. and numeration data were expressed as percentages. BMI, body mass index, LCEA, lateral center-edge angle
Impact of Sex, surgical Status, and hip rotation position on traction force
Across all hip rotation positions from state 2 to state 5, male patients exhibited significantly greater intraoperative traction forces compared to females (P < 0.05; specific values are shown in Table 2).
Table 2.
Traction force of the joint capsule in different States and rotational positions
| State | Rotational Position | Force (Male, Newtons) | Force (Female, Newtons) | Force (All patients, Newtons) |
P
(Male and Female) |
P
(Male and All) |
P (Female and All) | Rotational Position Difference | Force (All Patients, Newtons) |
P (Difference Between Positions) |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Internal |
241.30 ± 41.01 (180–308) |
230.17 ± 29.99 (177–282) |
233.47 ± 33.35 (177–308) |
0.385 | 0.539 | 0.704 | Internal- Neutral | -0.82 ± 7.35 | 0.518 |
| Neutral |
245.05 ± 40.05 (185–308) |
229.81 ± 29.81 (177.5-287.5) |
234.29 ± 33.26 (177.5–308) |
0.229 | 0.395 | 0.600 | Internal- External | -1.51 ± 12.16 | 0.473 | |
| External |
244.85 ± 45.04 (187.5-322.5) |
230.88 ± 35.56 (166-289.5) |
234.99 ± 38.42 (166-322.5) |
0.342 | 0.496 | 0.681 | Neutral- External | -0.69 ± 9.81 | 0.684 | |
| 2 | Internal |
493.40 ± 62.23 (373–592) |
409.06 ± 44.23 (311-504.5) |
433.87 ± 62.78 (311–592) |
< 0.001 | 0.012 | 0.102 | Internal- Neutral | 19.93 ± 16.95 | < 0.001 |
| Neutral |
474.7 ± 60.44 (368.5-589.5) |
388.63 ± 40.06 (304–464) |
413.94 ± 60.82 (304-589.5) |
< 0.001 | 0.008 | 0.080 | Internal- External | 10.77 ± 24.86 | 0.017 | |
| External |
481.85 ± 61.94 (399.5–600) |
398.60 ± 43.00 (306.5–477) |
423.09 ± 61.78 (306.5–600) |
< 0.001 | 0.012 | 0.100 | Neutral- External | -9.16 ± 14.38 | < 0.001 | |
| 3 | Internal |
415.85 ± 55.20 (306–501) |
344 ± 44.20 (267–429) |
365.13 ± 57.42 (267–501) |
< 0.001 | 0.017 | 0.136 | Internal- Neutral | 10.65 ± 13.99 | < 0.001 |
| Neutral |
404.65 ± 47.70 (320.5-478.5) |
333.58 ± 37.02 (271-398.5) |
354.49 ± 51.54 (271-478.5) |
< 0.001 | 0.009 | 0.095 | Internal- External | -9.54 ± 24.99 | 0.033 | |
| External |
426.85 ± 52.65 (350.5-509.5) |
352.94 ± 40.27 (286.5-425.5) |
374.68 ± 55.27 (286.5-509.5) |
< 0.001 | 0.011 | 0.106 | Neutral- External | -20.19 ± 15.77 | < 0.001 | |
| 4 | Internal |
367.75 ± 55.03 (250–451) |
301.02 ± 36.74 (233–371) |
320.65 ± 52.15 (233–451) |
< 0.001 | 0.017 | 0.119 | Internal- Neutral | 5.60 ± 15.00 | 0.037 |
| Neutral |
359.45 ± 49.55 (258–441) |
296.54 ± 31.34 (248–365) |
315.04 ± 46.91 (248–441) |
< 0.001 | 0.013 | 0.077 | Internal- External | -8.56 ± 21.23 | 0.025 | |
| External |
376.20 ± 52.14 (288-471.5) |
309.63 ± 35.72 (259–395) |
329.21 ± 50.78 (259-471.5) |
< 0.001 | 0.014 | 0.110 | Neutral- External | -14.16 ± 14.85 | < 0.001 | |
| 5 | Internal |
343.75 ± 53.29 (226.5–422) |
283.40 ± 36.17 (221–363) |
301.15 ± 49.65 (221–422) |
< 0.001 | 0.024 | 0.141 | Internal- Neutral | 7.21 ± 13.41 | 0.646 |
| Neutral |
337.35 ± 48.80 (241–420) |
275.85 ± 28.59 (230–340) |
293.94 ± 45.03 (230–420) |
< 0.001 | 0.012 | 0.067 | Internal- External | -1.57 ± 20.70 | 0.185 | |
| External |
342.7 ± 51.26 (260-444.5) |
286.06 ± 32.46 (231.5–358) |
302.72 ± 46.23 (231.5-444.5) |
< 0.001 | 0.029 | 0.218 | Neutral- External | -8.78 ± 13.84 | < 0.001 | |
| 6 | Internal |
321.1 ± 68.94 (195-397.5) |
277.67 ± 32.91 (220-333.5) |
290.70 ± 49.68 (195-397.5) |
0.025 | 0.150 | 0.299 | Internal- Neutral | 2.53 ± 29.89 | 0.002 |
| Neutral |
331.94 ± 48.33 (234–403) |
269.40 ± 30.77 (218-328.5) |
288.17 ± 46.33 (218–403) |
< 0.001 | 0.019 | 0.112 | Internal- External | -8.45 ± 34.12 | 0.397 | |
| External |
345.61 ± 49.75 (257-423.5) |
279.34 ± 34.23 (217.5-352.5) |
299.15 ± 49.47 (217.5-423.5) |
< 0.001 | 0.018 | 0.117 | Neutral- External | -10.98 ± 9.23 | < 0.001 |
Data are presented as mean ± SD or mean ± SD (range)
Traction forces under different traction states are presented in Tables 2 and 3; Figs. 4, 5 and 6. The results demonstrated significant differences in traction forces across all surgical statuses (P < 0.05; Table 3). Traction force increased from the initial gross traction (state 1) to achieving the operative width (state 2), followed by a significant decline after joint puncture. Subsequently, traction forces progressively decreased throughout the procedure.
Table 3.
The difference of the traction force in different rotational positions and States
| Rotational Position |
1–2 | 1–3 | 1–4 | 1–5 | 1–6 | 2–3 | 2–4 | 2–5 | 2–6 | 3–4 | 3–5 | 3–6 | 4–5 | 4–6 | 5–6 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Internal | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | 0.088 |
| Neutral | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 |
| External | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 | < 0.001 |
The P values obtained after comparing the data in different rotational positions and different states are shown in the table
Fig. 4.
The mean traction force of all patients in different states and rotational positions. In the box plots of Figs. 3, 4, 5 and 6, the boundary of the box closest to 0 indicates the 25th percentile, the black line within the box marks the median, and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers above and below the box indicate maximum and minimum values except outliers and extreme values. Circles represent outliers and pentagons represent extreme values
Fig. 5.
The mean traction force of female patients in different states and rotational positions. In the box plots, the boundary of the box closest to 0 indicates the 25th percentile, the black line within the box marks the median, and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers above and below the box indicate maximum and minimum values
Fig. 6.
The mean traction force of male patients in different states and rotational positions. In the box plots, the boundary of the box closest to 0 indicates the 25th percentile, the black line within the box marks the median, and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers above and below the box indicate maximum and minimum values except outliers and extreme values. Circles represent outliers and pentagons represent extreme values
Table 2; Fig. 7 illustrate differences in traction forces across hip rotation positions under various traction states. Results revealed that to achieve equivalent joint distraction for surgical visualization, traction forces in external rotation position were significantly greater than those in the neutral position for states 2, 3, 4, and 6. Significant differences between internal and external rotation positions were observed in states 2, 3, and 4. However, internal rotation exhibited higher traction forces than external rotation in state 2, whereas the opposite trend was observed in other states. Additionally, external rotation consistently demonstrated significantly greater traction forces than neutral position across states 2–6 (P < 0.05; Table 2).
Fig. 7.
The mean traction force changes at different traction states and rotational positions in all patients. In the box plots, the boundary of the box closest to 0 indicates the 25th percentile, the black line within the box marks the median, and the boundary of the box farthest from zero indicates the 75th percentile. Whiskers above and below the box indicate maximum and minimum values except outliers and extreme values. Circles represent outliers and pentagons represent extreme values
Influence of BMI, LCEA, and alpha angle on traction force
Table 4 summarizes correlation analyses between preoperative BMI, LCEA, and alpha angle with traction forces under specific traction states and hip rotation positions, as well as differences in traction forces between rotation positions. Moderate positive correlations were observed between BMI and traction forces in states 2 (all rotation positions), 3 (all rotation positions), 4 (all rotation positions), 5 (internal and neutral rotation positions), and 6 (neutral and external rotation positions) (P < 0.01). For LCEA, weak to moderate positive correlations were identified in states 2 (internal and neutral rotation positions) and 3 (internal rotation position) (P < 0.05). Similarly, the alpha angle showed weak to moderate positive correlations with traction forces in states 2 (all rotation positions), 3 (internal and neutral rotation positions), 4 (neutral rotation position), and 5 (internal rotation position) (P < 0.05). Femoral anteversion angle exhibited weak to moderate negative correlations with traction forces in states 3 (internal and neutral rotation positions), 4 (internal rotation position), and 5 (internal rotation position) (P < 0.05).
Table 4.
Factors influencing the traction force
| State | Rotational Position | BMI | LCEA | α | FA | Rotational Position Difference | BMI | LCEA | α | FA |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Internal | 0.078 | -0.183 | -0.175 | -0.156 | Internal- Neutral | -0.238 | 0.356 a | -0.173 | -0.174 |
| Neutral | 0.131 | -0.196 | -0.098 | -0.118 | Internal- External | -0.040 | 0.320 | 0.070 | -0.487 b | |
| External | 0.080 | -0.203 | -0.145 | -0.014 | Neutral- External | 0.129 | 0.112 | 0.233 | -0.454 b | |
| 2 | Internal | 0.548 b | 0.476 b | 0.387 a | -0.213 | Internal- Neutral | 0.099 | 0.427 a | 0.064 | -0.332 |
| Neutral | 0.538 b | 0.369 a | 0.414 a | -0.169 | Internal- External | 0.097 | 0.483 b | 0.158 | -0.445 a | |
| External | 0.517 b | 0.246 | 0.355 a | -0.071 | Neutral- External | 0.051 | 0.269 | 0.235 | -0.465 b | |
| 3 | Internal | 0.479 b | 0.380 a | 0.358 a | -0.427 a | Internal- Neutral | 0.134 | 0.390 a | 0.058 | -0.312 |
| Neutral | 0.497 b | 0.314 | 0.363 a | -0.383 a | Internal- External | 0.062 | 0.304 | 0.106 | -0.491 b | |
| External | 0.469 b | 0.222 | 0.298 | -0.257 | Neutral- External | -0.020 | 0.179 | 0.092 | -0.451 a | |
| 4 | Internal | 0.502 b | 0.308 | 0.333 | -0.403 a | Internal- Neutral | 0.083 | 0.287 | 0.072 | -0.494 b |
| Neutral | 0.491 b | 0.278 | 0.349 a | -0.323 | Internal- External | 0.145 | 0.301 | 0.123 | -0.589 b | |
| External | 0.454 b | 0.148 | 0.325 | -0.203 | Neutral- External | -0.004 | 0.274 | 0.163 | -0.467 b | |
| 5 | Internal | 0.474 b | 0.287 | 0.340 a | -0.412 a | Internal- Neutral | 0.067 | 0.268 | 0.180 | -0.534 b |
| Neutral | 0.510 b | 0.282 | 0.339 | -0.314 | Internal- External | 0.192 | 0.295 | 0.292 | -0.482 b | |
| External | 0.321 | 0.289 | 0.255 | -0.261 | Neutral- External | 0.140 | 0.236 | 0.261 | -0.231 | |
| 6 | Internal | 0.355 | 0.128 | 0.204 | -0.343 | Internal- Neutral | -0.204 | 0.379 a | 0.141 | -0.294 |
| Neutral | 0.563 b | 0.215 | 0.330 | -0.289 | Internal- External | -0.145 | 0.345 | 0.210 | -0.321 | |
| External | 0.552 b | 0.236 | 0.262 | -0.220 | Neutral- External | -0.135 | 0.142 | 0.203 | -0.293 |
Data are presented as n per the Pearson correlation coefficient
Correlation strength was interpreted as follows:
Strong: |r| ≥ 0.7; Moderate: 0.4 ≤ |r| < 0.7; Weak: |r| < 0.4
BMI body mass index, LCEA lateral center-edge angle, α Alpha angle, FA Femoral anteversion
aP < 0.05
bP < 0.01
Notably, BMI and alpha angle showed no significant correlations with differences in traction forces between rotation positions. However, higher LCEA was associated with greater differences in traction forces between internal and neutral rotation positions in states 1, 2, 3, and 6, as well as between internal and external rotation in state 2 (P < 0.05). Conversely, greater femoral anteversion angle correlated with smaller differences in traction forces between internal and external rotation positions (states 1–5) and between neutral and external rotation positions (states 1–4) (P < 0.05). It also demonstrated negative correlations with differences in traction forces between internal and neutral rotation positions in states 4–5 (P < 0.05).
Discussion
This study demonstrates that postless hip arthroscopy demands significantly higher traction forces in males, non-neutral hip rotational positions, and patients with elevated BMI, LCEA, alpha angle, whereas greater femoral anteversion reduces traction requirements. Crucially, a characteristic intraoperative force trajectory was identified: maximal resistance occurs during capsular puncture due to the hip’s suction seal effect, followed by progressive decline post-capsulotomy. Compared with previous studies using post-assisted traction, the traction forces reported in the present study were relatively lower: Dillon et al. reported mean holding traction force of 55.8 ± 15.3 kgf (≈ 547.2 ± 150.0 N) and mean maximum traction force of 69.9 ± 14.1 kgf (≈ 685.5 ± 138.3 N), while Nicholas et al. documented a mean initial traction force of approximately 109 lbs (≈ 484.9 N), which decreased to 94.3 lbs (≈ 419.4 N) post-capsulotomy [10, 11]. This force reduction pattern mirrors findings observed in prior analyses of perineal post-based traction procedures, which may be attributable to standardized surgical protocols and population-specific demographic characteristics [13]. Additionally, compared with this previous report, the current study consistently demonstrated lower traction forces across various traction states and rotational positions [13]. This observation partially demonstrates the advantage of postless traction in this specific aspect.
In lower limb traction, the primary forces that must be resisted are the tension from muscles and soft tissues surrounding the hip joint, such as the iliofemoral ligament, ischiofemoral ligament, and pubofemoral ligament. Consequently, the required traction force for male patients is significantly greater than for females, likely due to males generally having more developed musculature and greater ligament strength. Similarly, to achieve equivalent joint distraction, significantly greater traction force is required during hip internal or external rotation compared to the neutral position. This can be explained as follows: during hip internal rotation, the internal rotator muscles and associated accessory muscles (e.g., adductors and psoas major) contract, while during hip external rotation, the external rotator muscles and their synergists (e.g., piriformis) activate, and at the same time, hip rotation also causes the joint capsule to be tautened—all of which thereby enhancing the joint’s resistance to traction forces. This observation aligns with previous studies, which reported that muscle volume serves as an ideal indicator for estimating hip joint stiffness and intraoperative traction requirements—a factor that may also explain the deeper positive correlation between BMI and intraoperative traction force [15]. However, no correlation between BMI and traction force was observed in their study, which is inconsistent with the findings of the present study: The results of this study showed a positive correlation between preoperative BMI and intraoperative traction force (P < 0.05, Table 4), and this is similar to the study by Nicholas et al. and Mei-Dan et al. (which showed a positive correlation between body weight and traction force), so the final results may need to be further studied to clarify [9, 11]. Additionally, the negative pressure within the hip joint capsule stabilizes the joint and resists traction. After capsular puncture, the loss of its seal eliminates this negative pressure, leading to a significant reduction in required traction force (approximately 70 Newtons in this study). Consequently, it has been proposed that capsulotomy or capsular puncture prior to traction may reduce traction force [20]. Theoretically, this approach could markedly lower the incidence of complications arising from high traction forces, including perineal compression injuries and operative limb neuropraxia, in procedures involving a perineal post. However, its practical applicability remains to be validated, and its utility in traction without a perineal post requires further investigation. Furthermore, it was observed that the traction force at 40 min post-capsulotomy (state 6) was lower than that at 20 min (state 5). This gradual reduction may be attributed to the creep phenomenon of the periarticular soft tissues, wherein prolonged tensile stress induces progressive plastic deformation in viscoelastic materials. In summary, these findings demonstrate that greater joint stability correlates with higher intraoperative traction demands, consistent with prior research conclusions [10–12].
It was also observed that LCEA and alpha angle exhibited positive correlations with intraoperative traction forces, though conclusions varied across studies. Some earlier studies align with the findings of the present study: Spencer et al. reported that smaller alpha angles correlate with reduced maximum traction force, while Mei-Dan et al. demonstrated a positive association between LCEA and both initial traction force and traction force 30 min later [9, 12]. However, Nicholas et al. found no significant relationship between LCEA and traction force [11]. LCEA, measured on an anteroposterior pelvic radiograph as the angle between a vertical line through the femoral head center and a line connecting the femoral head center to the lateral acetabular rim, quantifies acetabular coverage of the femoral head. A larger LCEA indicates deeper femoral head containment within the acetabulum, which may increase resistance to traction forces. This deeper coverage could also reduce surgical visibility and working space, necessitating greater force to achieve adequate joint distraction. Alpha angle, measured on axial MRI or radiographs of the femoral neck, reflects the degree of bony prominence at the femoral head-neck junction. Patients with larger alpha angles are prone to FAIS during hip motion, where the bony protrusion collides with the acetabular rim, potentially causing cartilage or labral damage. Additionally, this bony prominence itself may act as a direct mechanical block during traction, increasing resistance to joint distraction. However, this hypothesis require further in-depth research to confirm their validity and accuracy.
Similarly, it was observed that femoral anteversion—the angle of anterior inclination of the femoral head-neck axis relative to the distal femoral condylar axis in the horizontal plane—exhibited a negative correlation with intraoperative traction force. This aligns with a previous analysis of traction forces in procedures involving a perineal post [13]. We hypothesize that this relationship can also be explained through the lens of hip joint stability: Increased femoral anteversion alters the relative positioning of the femoral head within the acetabulum, positioning the proximal femur more anteriorly in its natural state. This, in the patient’s daily life, may reduce the contact area between the acetabulum and femoral head, diminishing the stability provided by bony congruency. Long-term osseous structural abnormalities could lead to gradual laxity of the joint capsule and ligaments as compensatory mechanism, which may contribute to increased instability of the joint’s inherent anatomical structure, thereby explaining the negative correlation with traction force.
This study may help surgeons to predict the required traction force based on the demographic characteristics, hip imaging characteristics, operation state, and intraoperative hip rotation position before surgery.
Limitations
This study has several limitations. First, the relatively small sample size and the underrepresentation of male participants, combined with the single-center recruitment of all patients, may introduce sampling bias. Additionally, during intraoperative hip rotation maneuvers, hip rotation angles were determined by measuring the corresponding foot rotation. However, some degree of knee rotation was permitted, which may have compromised the accuracy of hip rotational alignment assessment. The use of goniometer measurements for rotational angles—rather than the gold-standard intraoperative fluoroscopy measurements—further limits precision. Finally, the retrospective design of this study carries inherent limitations, including potential selection bias and unmeasured confounding variables. Future research will prioritize multicenter collaboration, advanced imaging techniques, standardized intraoperative protocols with fluoroscopic validation, and prospective designs to mitigate these shortcomings.
Conclusion
This study demonstrates that traction force during postless hip arthroscopy increase with higher BMI, larger LCEA, and elevated alpha angle, while greater femoral anteversion reduce traction requirements. Male gender and internal or external hip rotation consistently demand higher forces compared to females and neutral rotation. Traction forces decrease after joint puncture and capsulotomy and decrease over time during surgery.
Supplementary Information
Acknowledgements
Not applicable.
Clinical trial number
Not applicable.
Abbreviations
- BMI
Body mass index
- LCEA
Lateral center-edge angle
- FAIS
Femoroacetabular impingement syndrome
Authors’ contributions
G.G.: study design, data acquisition, analyses and interpretation of data, draft of manuscripts, tables and figures. Y.H.: data acquisition, analyses and interpretation of data, draft of manuscripts, tables and figures. X.Z.: study design, data acquisition, analyses, and interpretation of data. J.W.: study design, data acquisition, analyses, and interpretation of data. Y.X.: study design, data acquisition, analyses, and interpretation of data, manuscript with tables and figures. All authors critically reviewed and approved the fnal revised manuscript.
Funding
The work was supported by grant from the Beijing Municipal Natural Science Foundation (7244429).
Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
The Ethics Committee of the Third Hospital of Peking University approved this study (M2019193). This study was conducted in accordance with the Declaration of Helsinki. All patients who participated in the study provided written informed consent.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Guanying Gao and Yize Han contributed equally to this work.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.