Multicentre randomised controlled trial protocol in China comparing postless hip arthroscopy with conventional perineal post-assisted hip arthroscopy to reduce perineal complications in patients undergoing hip arthroscopy for femoroacetabular impingement: the POSTLESS-HIP trial

Abstract

Introduction

Perineal complications—including nerve injury (eg, pudendal neurapraxia), soft tissue injury and sexual or urinary dysfunction—are well-documented adverse effects of conventional hip arthroscopy using a perineal post. Postless hip arthroscopy avoids direct perineal pressure, but high-quality randomised evidence is lacking.

Methods and analysis

This multicentre, prospective, parallel-group, randomised controlled trial will enrol 270 patients aged 15–60 years with femoroacetabular impingement syndrome requiring hip arthroscopy. Participants will be randomised 1:1 via a centralised system using stratified block randomisation by centre to postless hip arthroscopy or conventional perineal post-assisted traction. Sample size is calculated based on an assumed incidence of the primary composite endpoint (comprising perineal numbness, perineal pain, perineal soft tissue injury, sexual dysfunction and urinary dysfunction) of 10% vs 0.5%, yielding 114 per group (90% power, α=0.05); 135 per group accounts for 15% dropout. Surgeons cannot be blinded, but participants and outcome assessors are blinded. The primary outcome is the incidence of perineal nerve injury (perineal numbness, pain, soft tissue injury and sexual/urinary dysfunction) on postoperative day 1. Secondary outcomes include the incidence of perineal nerve injury at postoperative day 7 (discharge), non-perineal complications on postoperative day 1, preoperative preparation time, intraoperative traction time, total operative time, length of hospital stay censored at 6 weeks, patient-reported joint function outcomes assessed at 3 months using the Visual Analogue Scale (VAS), modified Harris Hip Score (mHHS), Hip Outcome Score and the International Hip Outcome Tool 12-item questionnaire, as well as a short-term economic evaluation consisting of 14-day postoperative VAS pain intensity, 14-day mHHS hip function and total direct healthcare costs within 14 days after surgery. Analyses will follow intention-to-treat principles.

Ethics and dissemination

Approved by the Chinese People's Liberation Army (PLA) General Hospital Ethics Review Board (No. 2024KY0158-KS001). Written informed consent will be obtained. Results will be published in peer-reviewed journals.

Trial registration number

NCT07322705.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• This prospectively registered, multicentre randomised controlled trial adheres to the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2025 guidelines, enhancing methodological transparency and reproducibility.

• Standardised protocols, central randomisation and blinding of participants and outcome assessors (via standardised perioperative communication) help minimise selection and detection bias.

• Blinding of surgeons is not feasible due to the overt nature of the traction intervention, which may introduce performance bias.

• The primary outcome is assessed only on postoperative day 1, potentially missing perineal symptoms that develop or resolve beyond this early time point.

Introduction

Background and rationale

Hip arthroscopy has become a widely adopted minimally invasive procedure for treating femoroacetabular impingement (FAI), labral tears and other intra-articular hip pathologies, with global utilisation rising steadily over the past decade.^1–4 However, the conventional technique using a perineal post for joint distraction is associated with a significant risk of perineal complications, including nerve palsy and soft tissue injury.^{5 6}

Adequate joint distraction is essential to facilitate safe instrument passage and optimal visualisation of the articular space. Conventionally, this is achieved using axial traction applied via a traction table with a padded perineal post positioned ipsilateral to the operative hip, which serves as a fulcrum but concentrates mechanical pressure on the overlying soft tissues and the underlying pudendal neurovascular bundle.^{7 8}

This approach carries a well-documented risk of iatrogenic perineal complications. Pooled data from observational studies report an incidence of pudendal neurapraxia ranging from 7% to 25%,^{6 8} manifesting as genital numbness, paraesthesia, pain or sexual and urinary dysfunction. Although often transient, these symptoms may persist for weeks to months and are consistently associated with reduced patient satisfaction and delayed functional recovery.^{5 7} A prospective cohort study found that 74% of patients reported some form of traction-related problem after conventional hip arthroscopy, with 32% experiencing groin-area symptoms, including numbness, swelling and lacerations.⁹ These findings suggest that the true burden of traction-related morbidity is substantially higher than previously recognised in retrospective reports. Patient surveys consistently rank genital numbness and sexual dysfunction among the most distressing postoperative complications, even when transient, underscoring the need for preventive strategies that prioritise perineal integrity.¹⁰

Local anatomical studies indicate that after exiting the Alcock canal, the main branches of the pudendal nerve (deep perineal nerve and dorsal nerve of the penis/clitoris) course through the deep perineal space. These branches lie in extremely close proximity (separated by only millimetres to 1.5 cm) to the corpus spongiosum (bulb), perineal body and internal pudendal vascular plexus.^{11 12} The effective load-bearing diameter and vertical pressure area of the perineal post far exceed this fine anatomical spacing. Consequently, mechanical compression cannot be isolated to a single structure; it inevitably involves the nerves, vessels and soft tissues simultaneously, forming an anatomical ‘neurovascular-soft tissue composite compression injury’. This mechanism shares a highly similar pathophysiology with perineal compression syndrome observed in long-distance cycling,¹³ providing a robust anatomical and biomechanical rationale for evaluating these complications as a unified clinical entity.

In response to these concerns, ‘postless’ traction techniques—employing thoraco-abdominal support and contralateral groin counter-traction without a perineal post—have been developed to eliminate direct perineal compression.^{7 8} Preliminary case series suggest comparable surgical exposure and lower rates of neurological injury.^{7 14} Notably, a landmark prospective series by Mei-Dan et al demonstrated the fundamental safety of this technique, reporting zero groin-related complications in 1000 consecutive cases.⁷ Despite these promising findings, existing evidence remains limited to uncontrolled cohorts. Because these studies lack a control group, they cannot establish a causal advantage over the conventional perineal post technique or definitively quantify the true reduction in perineal nerve injury.

To bridge this critical evidence gap, direct comparative data from a prospective randomised controlled trial (RCT) are strictly required. Given the high volume of hip arthroscopy procedures and the patient-important nature of perineal morbidity, there is an urgent need for high-quality, comparative evidence to inform traction method selection and enhance procedural safety.^{5 6} Therefore, this study aims to provide the first prospective RCT directly comparing the incidence of perineal nerve injury between postless and conventional perineal post-assisted hip arthroscopy. Ultimately, establishing the safety profile of postless traction in hip arthroscopy may provide a reference for other lower-limb procedures requiring traction, potentially promoting its broader application in orthopaedics.

Objectives

Primary objective

To compare the incidence of perineal nerve injury (defined as a composite of new-onset numbness, pain or urogenital dysfunction assessed on postoperative day 1) between postless and conventional traction techniques in patients undergoing hip arthroscopy for FAI.

Secondary objectives

These include: (1) clinical safety: incidence of perineal nerve injury at discharge (day 7) and non-perineal complications (day 1); (2) operative efficiency: preparation time, traction time, total operative time and length of stay (censored at 6 weeks); (3) functional recovery: Visual Analogue Scale (VAS),¹⁵ modified Harris Hip Score (mHHS),¹⁶ Hip Outcome Score (HOS)¹⁷ and the International Hip Outcome Tool 12-item questionnaire (iHOT-12)^{18 19} at 3 months and (4) Health economics: total direct healthcare costs and pain/function scores (VAS, mHHS) within 14 days.^{5 20}

We hypothesise that postless hip arthroscopy will significantly reduce the risk of perineal nerve injury compared with the conventional perineal post-assisted hip arthroscopy.

Methods and analysis

Study design

This protocol has been written in accordance with the Standard Protocol Items: Recommendations for Interventional Trials (SPIRIT) 2025 statement,²¹ and the completed SPIRIT checklist is provided as online supplemental file 1. This study is a two-arm, parallel-group, double-blind (blinding of participants and outcome assessors), multicentre, prospective RCT. The overall study design and outcome assessment framework are summarised in figure 1. This trial was registered prospectively at ClinicalTrials.gov (NCT07322705) on 17 November 2025.

Figure 1. Study design and outcome assessment framework.

Study population and recruitment

Inclusion criteria

1. Aged 15–60 years;

2. Diagnosed with FAI syndrome and indicated for hip arthroscopy based on comprehensive clinical evaluation—including medical history, symptoms, physical signs, physical examination and diagnostic imaging (eg, anteroposterior pelvic radiograph, frog-leg lateral radiograph, CT with three-dimensional reconstruction and hip MRI)—as well as diagnostic intra-articular hip injection;

3. Able to read and sign the informed consent form.

Exclusion criteria

1. History of high-energy hip trauma, previous ipsilateral or contralateral hip surgery, avascular necrosis of the femoral head, slipped capital femoral epiphysis, Perthes disease, severe osteoporosis, tumours, acetabular stress fractures or proliferative or immune hip diseases;

2. Diseases causing groin numbness, foot numbness, sexual dysfunction, urinary dysfunction, skin injuries, perineal injuries, nerve injuries, radicular pain and inner or outer thigh numbness;

3. Abnormal heart, lung, liver, kidney function, severe coagulation disorders, poorly controlled diabetes, judged by the researcher to have an infection risk;

4. Consciousness disorders, psychiatric disorders or neuromuscular dysfunction affecting lower limb function;

5. Active infection foci (systemic or local infectious lesions);

6. Pregnancy, lactation or planned pregnancy during the clinical study period;

7. Participation in another clinical trial within the past 3 months;

8. Patients deemed unsuitable for the clinical trial by the researcher for other reasons.

Recruitment

Participants will be recruited from orthopaedic outpatient clinics at 10 tertiary hospitals (the final number is subject to actual participation). Recruitment strategies include direct identification by surgeons during clinical visits and referrals from primary care providers. No online or community-based advertising will be used. The anticipated recruitment period is from 30 March 2026 to 30 September 2026, with the primary outcome assessed at the first day after surgery and final study completion expected by 30 December 2026.

Centre and surgeon eligibility

Centre eligibility

To ensure a baseline level of surgical expertise, only high-volume centres performing more than 50 hip arthroscopies annually were invited to participate. Additionally, the affiliated department of each participating surgeon must perform a minimum of 200 hip arthroscopy cases annually.

Surgeon eligibility

All surgeons performing the procedures must meet the following criteria:

1. Hold a valid Chinese medical licence.

2. Be qualified orthopaedic surgeons with a title of associate chief physician or above.

3. Have a minimum of 5 years of experience in hip arthroscopy.

4. Have completed specialised training in hip arthroscopy.

5. Successfully complete the trial-specific mandatory training programme and pass a competency assessment.

Medical intervention

Intervention and standardisation of procedures

All participants will undergo hip arthroscopy under general anaesthesia in the supine position. The operative technique, portal establishment and intra-articular procedures (eg, labral repair and osteoplasty) are standardised across all participating centres and will be identical between study groups.

Prior to patient enrolment, all surgeons will complete mandatory training using a standardised institutional procedural manual (frozen version dated December 2025), which includes step-by-step illustrations and guidance on intraoperative fluoroscopic assessment of joint distraction. A detailed intervention manual outlining the surgical protocol is provided as online supplemental file 2.

Experimental group: postless hip arthroscopy

This approach eliminates the use of a perineal post by relying on gravity-assisted counter-traction. The patient is placed supine on a conventional, non-traction operating table covered with a surgical draw sheet, with the buttocks positioned approximately 10 cm proximal to the distal edge of the bed. Cotton pads are applied to both ankles and feet, which are then secured in traction boots. A cotton pad is placed over the perineal area—fully covering the region but confined within the sterile field—and sealed with a medical-grade waterproof drape to prevent chemical irritation from antiseptic solution.

Two thickened, cotton-padded restraining straps are used for torso stabilisation: (1) one is positioned across the contralateral groin and tied securely to both sides of the operating table; (2) a second strap is placed at the thoracoabdominal junction (midline) and similarly secured, with tension adjusted to avoid compression of the chest or abdomen.

Following skin preparation and draping, longitudinal traction is gradually applied to the operative limb. Traction is titrated intraoperatively until fluoroscopic imaging confirms adequate lateral joint distraction of 8–10 mm. If initial traction is insufficient, minor adjustments are permitted, including fine-tuning the degree of Trendelenburg tilt (typically maintained between 10° and 15°), re-securing the traction boot to prevent slippage or administering additional neuromuscular blocking agents to reduce muscle tone. No prespecified traction force (eg, in kilograms) is used; the sole criterion for adequate distraction is radiographic confirmation of the target joint space.

Active comparator group: conventional perineal post-assisted hip arthroscopy

This represents the current standard of care in participating centres. A dedicated traction table equipped with a cylindrical, foam-padded perineal post (diameter 10–12 cm, padding thickness ≥3 cm) is used. The post is positioned against the ipsilateral groin and covered with a medical waterproof drape. Bilateral ankles and feet are padded and secured in traction boots. The contralateral limb is fixed at 45° abduction, while the operative limb is aligned straight with 15° internal rotation and 15° adduction. Longitudinal traction is applied incrementally until fluoroscopic confirmation of an 8–10 mm joint space is achieved, using the same intraoperative endpoint as in the experimental group.

Permitted concomitant care: anaesthesia

A standardised general anaesthesia protocol will be used for all participants. Induction: (list specific drugs and doses from the manual, eg, propofol 1.5–2.5 mg/kg, sufentanil 0.3–0.5 μg/kg). Maintenance: (eg, sevoflurane 1.5%–2.5% in oxygen/air, intermittent boluses of sufentanil as needed). Postoperative analgesia: (eg, intravenous parecoxib 40 mg before incision, followed by patient-controlled analgesia with sufentanil).

Participant adherence to postoperative protocol

All participants will receive standardised written and verbal postoperative instructions on discharge. Adherence to these instructions, including activity restrictions and medication regimen, will be assessed and reinforced by the dedicated follow-up coordinator during scheduled study visits.

Criteria for discontinuation of intervention

If, during the traction test in the allocated group, adequate joint distraction cannot be achieved despite repeated attempts, the originally assigned surgical technique will be abandoned, and the participant will be withdrawn from the study.

Adherence to the allocated traction protocol will be monitored by the unblinded surgical team and verified through operative notes and intraoperative fluoroscopic images reviewed by the data management team.

Outcomes

Primary outcome

The incidence of perineal nerve injury within the first day after surgery.

Definition (aligned with trial registry entry): perineal nerve injury is defined as the occurrence of any of the following five components on the first postoperative day, as attributed to the surgical traction method used during hip arthroscopy:

• Perineal numbness

• Perineal pain

• Perineal soft tissue injury

• Sexual dysfunction

• Urinary dysfunction

Among these components, perineal numbness is explicitly designated as the core driver component of this composite endpoint due to its highest clinical significance, direct pathophysiological link to pudendal nerve compression and the high reliability of its objective assessment.

Measurement tools and methods

Perineal numbness (core driver component): to ensure high measurement reliability, numbness is rigorously evaluated using a standardised, multidimensional assessment protocol.

Time point

All assessments are performed once, on postoperative day 1 (within 24 hours after surgery), consistent with the time frame stated in the trial registry.

Criteria for determination

The outcome is considered present if at least one of the five listed components (numbness, pain, soft tissue injury, sexual dysfunction or urinary dysfunction) is:

• Newly reported or clinically observed on postoperative day 1 (ie, not present preoperatively), or

• Clearly worsened compared with baseline, and

• Judged by the investigator as related to the intraoperative perineal traction.

• If none of the five components occurs or worsen at this time point, the outcome is recorded as absent.

Secondary outcomes

In accordance with the trial registration, the following secondary outcomes are prespecified to comprehensively evaluate clinical safety, functional recovery, patient-reported experiences and economic impact across both study arms.

Clinical outcomes

• Incidence of non-perineal complications.

Defined as the occurrence of pain, numbness or soft tissue injury at sites other than the perineum, specifically:

• Lower limb ankle numbness and soft tissue injury.

• Contralateral groin pain, numbness and soft tissue injury.

• Chest/abdominal wall pain, numbness and soft tissue injury at the site of chest strap fixation.

Assessment and grading of non-perineal complications

Pain is quantified using the VAS (0–10). Severity is graded as: mild (VAS 1–3), moderate (VAS 4–6) or severe (VAS 7–10).

Numbness is assessed using the same standardised cotton swab light touch test and 4-point scale as for perineal numbness: −2 (complete loss of light touch/anaesthesia), −1 (decreased sensation/hypoesthesia), 0 (normal sensation) and +1 (increased sensitivity/hyperesthesia).

Soft tissue injury is clinically graded based on physical examination findings: mild (erythema only, no skin break), moderate (abrasion, contusion or blister without skin breakdown) or severe (skin necrosis, full-thickness skin loss or requiring surgical intervention).

Duration criteria

For all non-perineal complications, symptoms are categorised as transient (resolved within 48 hours), persistent (present for ≥48 hours but resolved by discharge at postoperative day 7) or prolonged (persisting beyond discharge at postoperative day 7). This classification aligns with the follow-up schedule and enables standardised reporting of complication duration.

Time frame: assessed on postoperative day 1.

Incidence of perineal nerve injury at discharge

Includes perineal numbness, pain, soft tissue injury and associated sexual or urinary dysfunction.

Time frame: assessed at postoperative day 7 (time of discharge).

Perioperative procedural metrics

• Intraoperative traction time

• Preoperative preparation time (immediately before surgery)

• Total operating time

Time frame: recorded intraoperatively or immediately preoperatively.

Postoperative hospital length of stay

Defined as the average number of days from surgery to discharge.

Time frame: up to 6 weeks postoperatively.

Patient-reported outcome measures

Postoperative joint function and pain assessments

Evaluated using the following validated questionnaires:

• VAS (range 0–10; higher scores indicate worse outcomes).

• mHHS (range 0–100; higher scores indicate better outcomes).

• HOS (range 0%–100%; higher scores indicate better outcomes).

• iHOT-12 (range 0–100; higher scores indicate better hip function).

Time frame: assessed at 3 months postoperatively.

Health economic outcomes

Economic evaluation metrics

A short-term economic evaluation will be conducted from both healthcare sector and societal perspectives. The evaluation incorporates:

• Pain intensity: assessed using the VAS (reported as scores on a 0–100 mm scale).

• Hip function: assessed using the mHHS (reported as scores on a 0–100 scale).

• Mean total healthcare cost per patient: the primary cost input measure, adopting a healthcare system perspective. All direct medical costs related to the surgery and subsequent care (including fees for surgery, anaesthesia, medical supplies, hospitalisation, medication, imaging, laboratory tests and complication management) will be collected via the hospital information system. Costs will be calculated in Chinese Yuan and compared between the conventional perineal-post traction group and the perineal-post-free traction group.

Time frame: assessed at 14 days postoperatively (data collection period: from randomisation until 14 days postoperatively).

Safety monitoring

Incidence of adverse events (AEs)

Overall safety will be assessed by tracking the incidence of all AEs to evaluate the safety profile of the interventions.

Time frame: monitored within 3 months postoperatively.

Randomisation and blinding

Allocation ratio and stratification

Participants will be randomised 1:1 via a centralised system using stratified block randomisation by centre to either postless hip arthroscopy (experimental group) or the conventional perineal post-assisted (active comparator group).

Blinding

This study employs a double-blind design, with blinding applied to both participants and outcome assessors, as registered (NCT07322705). While the operating surgical team remains unblinded due to the inherent nature of the interventions, they are excluded from all outcome assessment and data analysis activities. To prevent participants from inferring their group assignment and to mitigate bias from subjective patient-reported components, we have implemented strict operational protocols:

• Standardised positioning recovery: all patients undergo surgery on the same type of operating table. Any differences in positioning exist only during the intraoperative period. Crucially, before the patient emerges from anaesthesia, all position-fixing devices (eg, foot boots, perineal posts) are completely removed, and the patient is repositioned to the centre of the bed in a standard supine position. This ensures that patients experience no differential physical sensations on waking that could reveal their allocation.

• Standardised communication and care: postoperative rehabilitation guidance, communication scripts for medical staff and follow-up content are strictly standardised. All participating medical staff have undergone unified training to ensure consistent interaction with patients across all groups.

• Medical record desensitisation: to prevent patients or their families from deducing the allocation through medical records, operative notes are strictly blinded. Specific group assignments or detailed intraoperative positioning procedures are not documented in the medical charts accessible to patients or unblinded personnel.

In the event of a medical emergency where knowledge of the allocated intervention is essential for immediate patient care, an emergency unblinding procedure is in place: the treating physician may request unblinding, and the allocation code can be accessed 24/7 via a secure, password-protected online portal managed by the central randomisation system. Access is restricted to the principal investigator or their designated deputy at each site. Any unblinding event will be thoroughly documented in the participant’s case report form (CRF) and reported to the trial coordinating centre.

Endpoint adjudication

To ensure an objective evaluation of the primary endpoint, which includes subjective patient-reported components, an internal Blinded Endpoint Assessment Panel is established. This panel is formed to maintain the blinding of the primary investigators and to provide an independent assessment of endpoint events.

Panel members include attending physicians not involved in the research team, as well as associate chief physicians or higher from external institutions. All members hold senior professional titles and are completely independent of the surgical and clinical care teams. They remain strictly blinded to group allocation throughout the evaluation process and do not have access to operative notes or videos that could reveal treatment assignment. The determination of whether a symptom is related to intraoperative traction will be made by this blinded panel based on prespecified definitions, rather than by the unblinded investigators.

Although a fully independent, external adjudication committee was considered, it is deemed practically unnecessary for this low-risk intervention, given the highly explicit and clearly defined primary endpoint events. Nevertheless, this internally blinded panel provides a robust safeguard against assessment bias.

Sample size and statistical analyses

A detailed, prospectively written statistical analysis plan (SAP) has been finalised. All primary, secondary and safety analyses will be conducted in strict accordance with the SAP, which is included as online supplemental file 3.

Sample size justification

The primary endpoint of this study is the incidence of perineal nerve injury on postoperative day 1, defined by the presence of any of the following: perineal numbness, perineal pain, perineal soft tissue injury, sexual dysfunction or urinary dysfunction. Sample size calculation is therefore based on this primary endpoint. According to data from previous literature,^{5 6} the assumed incidence of postoperative perineal numbness is 10% in the conventional perineal post-assisted hip arthroscopy group and 0.5% in the postless hip arthroscopy group. A two-sample proportion difference test will be used, with a two-sided significance level of α=0.05, statistical power of 1 – β=0.90 and a 1:1 allocation ratio between the experimental group and the active comparator group. The sample size will be calculated using the following formula:

$${\displaystyle {\displaystyle n_t=n_c=\frac{(Z_{1-\alpha }+Z_{1-\beta }{)}^2[P_c(1-P_c)+P_t(1-P_t)]}{(P_t-P_c{)}^2}}}$$

Note:

n_t: sample size of the experimental group,

n_c: sample size of the active comparator group,

Z_1-α, Z_1-β: critical values from the standard normal distribution,

P_c: incidence rate of perineal nerve injury on postoperative day 1 in the active comparator group,

P_t: incidence rate of perineal nerve injury on postoperative day 1 in the experimental group.

Based on the calculation, a sample size of 114 participants is required per group. Accounting for an anticipated dropout rate of 15%, each group should enrol 135 participants, resulting in a total planned enrolment of 270 participants.

Population of analysis

The trial defines three main datasets for different analysis purposes:

• Full analysis set (FAS):

Definition: includes all randomised participants, regardless of whether they received the allocated traction method or not.

Usage: serves as the primary basis for efficacy analyses and includes demographic and baseline characteristics.

• Per protocol set (PPS):

Definition: consists of participants included in FAS with evaluable primary outcome data and without significant protocol violations.

Usage: used for sensitivity analyses to evaluate the robustness of the primary efficacy outcomes.

• Safety set (SS):

Definition: comprises all randomised participants who received the allocated intervention.

Usage: utilised for safety evaluations including AEs, laboratory tests, etc.

Summary: the primary efficacy analysis will be conducted using the FAS adhering to the intention-to-treat (ITT) principle, while PPS will be used for sensitivity analysis. Safety assessments are based on the SS.

Statistical analysis

1. Software: all statistical analyses will be performed using SAS software (V.9.4 or higher).

2. Descriptive statistics:

   • Continuous variables: reported as number of observations (n), mean, SD, median, IQR, minimum and maximum.

   • Categorical/ordinal variables: presented as frequencies and percentages.

3. Hypothesis testing:

   • Continuous outcomes: two-sample t-tests will be used if data approximate a normal distribution; otherwise, Wilcoxon rank-sum test will be applied.

   • Categorical outcomes: χ² tests will be employed when assumptions are met; otherwise, Fisher’s exact test will be used.

   • Significance level: all comparisons between groups are two-sided with α=0.05.

4. Primary efficacy outcome analysis:

   • Primary endpoint: incidence of perineal nerve injury on postoperative day 1.

   • Analysis approach: a mixed-effects logistic regression model adjusting for study centre and the following prespecified covariates—traction force, FAI classification, preoperative VAS score and mHHS—will be used for between-group comparison. Because each participating centre contributes only one designated core surgeon, the surgeon and centre effects are strictly collinear; therefore, centre is modelled as a random intercept, and no separate surgeon-level random effect is included.

   • Presentation of results: adjusted OR (aOR) with 95% CI and two-sided p-value will be reported, derived from the mixed-effects logistic regression model.

   • Handling missing data: missing primary efficacy data will be imputed using worst observation carried forward (WOCF), assuming the occurrence of perineal nerve injury.

   • Sensitivity analysis: to verify the robustness of the primary findings, three prespecified sensitivity analyses will be conducted: (1) repetition of the primary analysis within the PPS; (2) modified ITT (mITT) analysis, excluding participants who did not receive the allocated traction or withdrew prior to surgery; (3) complete-case analysis without WOCF imputation, including only participants with non-missing primary outcome data.

   • Component-level analyses: in addition to the primary composite endpoint, prespecified separate component-level analyses will be conducted to evaluate the independent incidence and contribution of each individual component (numbness, pain, soft tissue injury, sexual dysfunction and urinary dysfunction). These components will be analysed using the same mixed-effects logistic regression model (or Fisher’s exact test for rare events) as the primary endpoint. As these analyses are intended to provide transparent insights into the drivers of the composite outcome rather than to test independent primary hypotheses, no adjustment for multiplicity will be applied.

5. Secondary efficacy and safety outcomes analysis:

   • Secondary efficacy outcomes (eg, other complications, operation time, patient-reported outcomes, economic costs) and safety outcomes (AEs, laboratory tests, physical examinations) will be summarised using descriptive statistics and appropriate statistical tests.

   • AEs will be coded according to the Medical Dictionary for Regulatory Activities (MedDRA) dictionary and summarised by system organ class (SOC) and preferred term (PT).

Oversight, monitoring and safety reporting

Hypothesis testing.

Primary efficacy outcome analysis.

Secondary efficacy and safety outcomes analysis.

Data monitoring committee (DMC)

In accordance with the SPIRIT 2025 statement and the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Good Clinical Practice (GCP) E6(R2) guidelines, the necessity of establishing an independent data monitoring committee (DMC) was carefully evaluated by the trial steering committee. Given the following considerations, no independent DMC will be appointed for this trial:

1. Low-risk intervention

The postless hip arthroscopy technique represents a modification of the standard perineal post-assisted traction method rather than a novel or high-risk intervention. Preliminary observational studies have demonstrated a favourable safety profile, with no significant or unexpected serious adverse events (SAEs) reported to date.

2. Short study duration and early primary endpoint

The recruitment period is limited to 6 months, with a total follow-up duration of 3 months. The primary outcome is assessed on postoperative day 1. This timeline does not support the operational feasibility or added value of a formal, independent DMC.

3. Non-fatal, reversible primary outcome

The primary endpoint—perineal nerve injury—is non-life-threatening, typically transient and does not represent a condition that would warrant early trial termination based on interim safety signals.

4. Existing oversight mechanisms

Comprehensive safety and data quality monitoring will be ensured through the following established mechanisms, rendering a separate DMC redundant:

Principal investigators at each participating site are responsible for daily monitoring of AEs and protocol compliance;

Ethics committees receive and review all SAE reports within 24 hours of occurrence;

Data management team performs regular logical checks, range validation and source data verification (SDV);

Interim analysis will be conducted by an independent statistician when approximately 50% of participants have completed follow-up. The results will be reported to the trial steering committee for informational purposes only; no formal stopping rules are predefined, and the analysis is not intended to inform early termination decisions.

Should any unexpected safety concerns emerge during the trial, the principal investigator will immediately convene an ad hoc safety advisory panel, comprising external clinical experts and methodologists, and report without delay to the relevant ethics committees.

Therefore, the roles of a formal steering committee and endpoint adjudication committee are fulfilled by the collective responsibility of the principal investigators and the trial coordinating centre. Consequently, this trial does not establish a formal steering committee or an endpoint adjudication committee.

Trial monitoring

This trial will be monitored in accordance with the risk-proportionate principles of ICH GCP E6(R2). Given the low-risk nature of the surgical interventions, the early assessment of the non-fatal primary endpoint (incidence of perineal nerve injury at postoperative day 1) and a total follow-up period of 3 months, an independent DMC was not appointed.

Trial quality and participant safety are ensured through the following integrated mechanisms:

1. A designated clinical research associate from the coordinating centre performs centralised logic and range checks on all electronic CRFs (eCRFs), supplemented by SDV of 10% of randomly selected CRFs;

2. All AEs are recorded; SAEs are reported to the lead ethics committee and sponsor within 24 hours of awareness;

3. The institutional review board conducts annual continuing review of the trial;

4. Each participant is assigned a dedicated follow-up coordinator, supported by automated reminder systems and reasonable reimbursement to maximise retention;

5. All 10 participating sites undergo mandatory study initiation training, and on-site monitoring visits are triggered if prespecified risk indicators are met (eg, ≥1 unexpected SAE or protocol deviation rate >20% at a site).

Safety and AEs

Safety analyses will be performed on the SS. Only postoperative AEs will be included in the analysis; preoperative AEs will be listed descriptively. All AEs will be coded using the latest MedDRA version available before database lock and summarised by SOC and PT. Analyses will report the number and percentage of participants with AEs, along with AE severity and outcomes, with between-group differences assessed using appropriate statistical tests; AE frequencies by SOC and PT and AE frequencies stratified by SOC, PT and severity.

Laboratory safety assessments—including full blood count, blood biochemistry, hepatitis B serology (six-item panel), coagulation profile and two sexually transmitted infection tests—will be summarised at screening/baseline and 1 day postsurgery using descriptive statistics (n, mean, SD, median, quartiles, min, max) for quantitative measures and frequency (%) for qualitative results.

Physical examination findings will include descriptive statistics for the Beighton score, assessing generalised joint hypermobility.

AEs will be actively solicited at scheduled study visits (postoperative day 1, at discharge (approximately day 7) and month 3) and passively monitored through medical records throughout the 3-month follow-up period. Participants will be instructed to contact the research team immediately if they experience any concerning symptoms.

All AEs will be graded for severity as mild, moderate, severe or life-threatening based on clinical judgement. The Common Terminology Criteria for Adverse Events V.5.0²² will be referenced where applicable.

SAEs are defined in accordance with the Chinese GCP guidelines (2020)²³ as any untoward medical occurrence that results in:

• Death;

• Is life-threatening;

• Requires hospitalisation or prolongation of existing hospitalisation;

• Results in persistent or significant disability/incapacity or

• Is a congenital anomaly/birth defect.

Reporting procedure

Investigators will notify the sponsor and the local ethics committee of all SAEs within 24 hours of becoming aware of the event.

• For fatal or life-threatening SAEs, a preliminary report will be submitted within 24 hours, followed by a complete written report within seven calendar days.

• For non-fatal and non–life-threatening SAEs, a complete report will be submitted within 15 calendar days.

All SAEs will be summarised and reviewed regularly by the principal investigator and sponsor for potential safety signals.

Handling and storage of data

All clinical trial data are collected through standardised clinical observation forms, outpatient follow-up, telephone interviews and Questionnaire Star surveys, with questionnaire management centralised by designated data clerks via postal distribution and non-responders contacted by telephone, email or through next of kin according to the protocol-specified visit schedule. Standardised CRFs are available from the corresponding author on reasonable request. Central randomisation system is used for treatment allocation, where randomisation numbers are assigned sequentially without modification or reuse, and subjects who withdraw prior to surgery retain their numbers with no reassignment. All data are transmitted using Hypertext Transfer Protocol Secure (HTTPS) protocol to ensure encryption during transmission and protect data confidentiality and integrity, with access restricted to authorised research personnel only and subject confidentiality protected throughout the study in compliance with blind design requirements. The strategies for handling outliers and missing data are prespecified in the SAP. Specifically, for the primary efficacy endpoint, missing values for perineal nerve injury will be imputed as event occurrence using the WOCF method. Data retention period is determined based on the agreement with the sponsor, and in the absence of specific circumstances requiring deletion, the data will not be deleted. All data handling and storage procedures are conducted in accordance with GCP requirements.

Timeline/participant schedule

The detailed schedule for participant enrolment, allocated interventions and outcome assessments throughout the trial is outlined in table 1. This timeline ensures systematic data collection at critical junctures: the primary outcome of perineal nerve injury is assessed on postoperative day 1, while secondary outcomes—including patient-reported outcome measures such as the mHHS and VAS—are evaluated at 3 months to capture meaningful functional recovery. Safety monitoring for AEs is conducted at all scheduled visits, from the immediate postoperative period through the final 3-month follow-up, to provide a comprehensive safety profile.

Table 1. Schedule of enrolment, interventions and assessments.

	Trial period
	Enrolment		Postrandomisation				Close-out
TIME POINT**	-ti to 0	0	t1	t2	t3	t4	t5
			Day 1	Day 7	Day 14	Week 6	Month 3
ENROLMENT:
Eligibility screen & consent	X
Baseline data collection	X
Randomisation
INTERVENTIONS
Hip arthroscopy without a perineal post (postless)
Hip arthroscopy with a perineal post
ASSESSMENTS:
Primary outcome: Incidence of perineal nerve injury††			X
Secondary outcomes: Incidence of complications at other sites††			X
Intraoperative traction time				X
Preoperative preparation time		X
Total operating time		X
Length of hospital stay						X
PROMs (mHHS, HOS, iHOT-12, VAS)							X
Safety monitoring (adverse events)							X
Economic evaluation: Cost data collection					X
Cost-effectiveness analysis					X

^*Economic evaluation outcomes (costs, VAS and mHHS) were assessed at 14 days postoperatively. Long-term safety data were collected at 3 months.

^†As defined in the study protocol and registry (NCT07322705): ‘Perineal nerve injury’ includes perineal numbness, pain, soft tissue injury, sexual dysfunction and urinary dysfunction. ‘Complications at other sites’ include ankle, contralateral groin and chest/abdominal wall complications.

HOS, Hip Outcome Score; iHOT-12, International Hip Outcome Tool 12-item questionnaire; mHHS, modified Harris Hip Score; PROMs, patient-reported outcome measures; VAS, Visual Analogue Scale.

Patient and public involvement (PPI)

Patients and/or the public will not be involved in the design, conduct, reporting or dissemination plans of this research.

Ethics and dissemination

Ethical approval and protocol amendments

This multicentre study will be conducted in strict accordance with the Declaration of Helsinki and applicable regulatory requirements. Ethical approval has been obtained from the Ethics Committee of Chinese PLA General Hospital (approval no. 2024KY0158-KS001), serving as the leading ethics committee.

Approvals were also granted by the institutional review boards of all other participating centres; the full list of approving committees is provided in online supplemental file 4. Any significant protocol amendments affecting participant safety, rights or scientific value will be submitted to the leading ethics committee for review and subsequently updated on the clinical trial registry (ClinicalTrials.gov: NCT07322705).

Informed consent

Written informed consent will be obtained in person by investigators or research coordinators who have completed GCP training.²³ The template informed consent form is available as an online supplemental file 5. Consent will be sought after eligibility screening but before randomisation, following a ≥24-hour reflection period as required by local ethics guidelines and the Guidance on the Construction of Ethics Review Committees for Clinical Research Involving Humans (2023).²⁴ For participants aged 15–17 years (minors under Chinese law), written proxy consent from a parent or legal guardian and assent from the minor using an age-appropriate form will be required in accordance with the Ethical Review Measures for Life Sciences and Medical Research Involving Humans (2023)²⁵ and the Declaration of Helsinki.²⁶

The informed consent process explicitly covers the collection, storage and use of deidentified participant data for the purposes of this study, including analysis of primary and secondary outcomes, safety assessments and scientific reporting, in accordance with Chinese laws and regulations on data privacy. No biological specimens will be collected beyond routine clinical care; therefore, no additional consent provisions for biospecimen use are required.

Dissemination of results

The results of this trial will be disseminated through peer-reviewed publications in orthopaedic and sports medicine journals, as well as poster and oral presentations at national and international academic conferences. A summary of the findings will be provided to all participating centres. The trial protocol and SAP will be available to qualified researchers on reasonable request; individual participant data will not be shared with external independent researchers. Authorship will follow the recommendations of the International Committee of Journal Editors.

Discussion

This study—the postless hip arthroscopy (POSTLESS‑HIP) trial—is designed to address a critical gap in the current evidence base: the lack of high-quality, direct comparative data on perineal nerve injury risk between postless and traditional perineal post-assisted hip arthroscopy. Although existing observational studies suggest that postless techniques may reduce perineal complications, these findings are limited by small sample sizes, non-randomised designs and heterogeneous outcome definitions. The primary innovation of this protocol lies in its prospective, multicentre, 1:1 randomised controlled design, with a standardised primary endpoint—perineal nerve injury (including numbness, pain, soft tissue injury or urogenital/sexual dysfunction) assessed systematically at postoperative day 1.

While we acknowledge that these components differ in specific pathophysiological mechanisms, clinical severity and measurement reliability, they are unified as a composite safety signal stemming from a common initiating factor: mechanical compression by the perineal post within a highly constrained anatomical space. Analogous to major adverse cardiovascular events in cardiovascular trials,²⁷ this composite endpoint captures the overall clinical impact of a ‘neurovascular-soft tissue composite compression injury’. Anatomically, the main branches of the pudendal nerve course through the deep perineal space in close proximity (millimetres to 1.5 cm) to the corpus spongiosum, perineal body and internal pudendal vessels.^{11 12} Because the effective contact area of the perineal post far exceeds this fine anatomical spacing, mechanical compression inevitably involves nerves, vessels and soft tissues simultaneously.²³ Pathophysiologically, this direct compression triggers a cascade of soft tissue ischaemia and local oedema, leading to secondary nerve sheath compression;^{7 9} thus, these symptoms rarely present in isolation but rather as concurrent symptom clusters, a mechanism highly similar to perineal compression syndrome in long-distance cycling.¹³

Furthermore, to ensure methodological rigour and address potential heterogeneity among the composite components, we have explicitly defined perineal numbness as the core driver of this composite endpoint. Numbness was selected due to its direct pathophysiological link to pudendal nerve compression and the high reliability of its objective assessment (using standardised VAS,¹⁵ cotton swab light touch tests and anatomical zoning). Finally, prespecified, separate component-level analyses will be conducted to evaluate the independent incidence and contribution of each individual symptom, ensuring transparency and clinical interpretability.

Key design decisions were made to enhance internal validity: centralised randomisation ensures allocation concealment; blinding of participants and outcome assessors is achieved through standardised perioperative communication protocols; and surgical procedures are harmonised via a detailed manual (eg, targeting 8–10 mm of joint distraction), with video documentation and random audits to monitor adherence.

The main limitations of the protocol include the unavoidable lack of surgeon blinding, which could introduce performance bias in intraoperative or postoperative management, and the fact that the primary outcome is assessed only at 24 hours, potentially missing delayed-onset or resolving symptoms. Additionally, we recognise that certain components of the composite endpoint, particularly urinary dysfunction on postoperative day 1, may be confounded by perioperative factors such as anaesthesia, catheterisation, analgesia and perioperative stress. However, because urinary dysfunction remains an unavoidable potential consequence of severe perineal compression,^{7 28 29} it is retained for comprehensive safety monitoring. By designating numbness as the core driver and conducting prespecified component-level analyses, we mitigate the risk of these perioperative confounders disproportionately driving the primary composite outcome. To mitigate the timing and blinding issues, the study employs a strict surgical standardisation manual and independent video review and includes a secondary assessment at hospital discharge (approximately postoperative day 7).

Furthermore, formal patient and public involvement (PPI) was not incorporated into the design, conduct or reporting of this research. This study is designed as an RCT to evaluate the safety and efficacy of the surgical techniques, grounded in existing clinical evidence and expert consensus. Therefore, PPI was not included within the current study cycle. Future research will consider integrating patient perspectives during the interpretation of results and knowledge translation phases. Additionally, while stratified randomisation was not implemented, centre-level variability will be accounted for statistically by including site as a random effect in the primary analysis model. Overall, the protocol adheres to the SPIRIT 2025 guidelines and balances methodological rigour with clinical feasibility, aiming to generate robust evidence to guide safer traction strategies in hip arthroscopy.