Conceptual evolution in arthroscopic capsulotomy techniques and capsular management strategies for the hip

Abstract

The narrative review is conducted based on the literature on the hip joint capsule anatomy, biomechanics and arthroscopy capsular management to summarize the evolution of capsulotomy concepts and practice. Traditional transverse capsulotomy and T-shaped capsulotomy provide a good surgical visualization but affect the stability of joint. This has led to the adoption of modified transverse capsulotomy techniques and capsular closure; longitudinal capsulotomy techniques preserve joint stability and ensure a clear visualization, and the publication of expert consensus guidance has contributed to their ongoing standardization and normalization, but there are still certain limitations. However, evidence for the outside-in longitudinal capsulotomy techniques remains limited and largely indirect, derived mainly from technique descriptions and early case series. Hip arthroscopy capsular management has improved over time. This shows how modern surgical philosophy is gradually developed from just repairing anatomy. And it now pays more attention to rebuilding and protecting the capsular function. Besides, evidence of the outside-in longitudinal capsulotomy is still limited and largely indirect, so further comparative studies are needed.

Key Words: Hip arthroscopy; Capsular repair; Inside-out technique; Outside-in technique; Surgical approach; Biomechanics; Capsular closure; Capsulotomy

Core Tip: This narrative review summarizes the development of hip arthroscopic capsulotomy from inside-out techniques to outside-in techniques. It describes the progression from maximizing exposure to preserving capsular function. And it also discusses the evidence on capsular closure, current challenges, and future directions.

INTRODUCTION

Hip surgery has evolved over years. One of its most advanced applications is hip arthroscopy. Burman reported the first cadaveric hip arthroscopy in 1931. The hip is a large joint. It sits deep in body with tough capsule and narrow joint space, so that the hip arthroscopy is more difficult than any other arthroscopic to learn and perform[1]. Over the past decades, hip arthroscopy has developed rapidly, enabling treatment for quite a few conditions, including femoroacetabular impingement (FAI) and other complex diseases[2]. Among these advancements, the evolution of joint capsule capsulotomy techniques is of paramount importance. Unlike earlier reviews that look at the clinical outcomes, this review aims to trace the evolution of hip arthroscopy techniques. It also focuses on analyzing the principles for managing the joint capsule through different access routes, and aiming to examine the implications for the development of surgical philosophy.

LITERATURE SEARCH STRATEGY

A search was conducted in the PubMed and Web of Science databases using the keyword combination “hip arthroscopy”, “hip capsule”, “capsular management”, “capsulotomy”, and “capsular closure”, with the time frame set from database inception to June 2026. Searches were conducted in the CNKI, Wanfang Database, and China Medical Journal Full-Text Database, using the subject terms “hip arthroscopy”, “joint capsule”, “capsulotomy”, “capsular closure”, and “capsular management”, with the same time frame.

The inclusion criteria were as follows: (1) Publications written in English or Chinese; (2) Studies related to the aforementioned keywords, covering hip joint capsule anatomy, biomechanics, imaging, surgical techniques, or clinical efficacy; and (3) Literature types, including original clinical studies, systematic reviews and meta-analyses, cadaveric and biomechanical studies, technical reports, expert consensus statements, editorials, and conference abstracts when relevant to the scope of the review.

The exclusion criteria were as follows: (1) Duplicate publications or studies cited multiple times; (2) Studies for which full text was unavailable or that lacked key data; (3) Studies with weak relevance to the topic; and (4) Literature not in Chinese or English.

The last search was conducted on June 30, 2026. A representative search string used in PubMed was: (“hip arthroscopy”[Title/Abstract] OR “hip capsule”[Title/Abstract]) AND (“capsulotomy”[Title/Abstract] OR “capsular management”[Title/Abstract] OR “capsular closure”[Title/Abstract]). The authors screened the records by title and abstract, and then reviewed the full texts of potentially relevant articles. The authors acknowledge that the selection process was not systematic, and selective searching may lead to selection bias. 74 articles were selected.

ANATOMICAL APPLICATIONS AND BIOMECHANICAL FOUNDATIONS OF THE HIP JOINT CAPSULE

Anatomical location and structure of the hip joint capsule

The hip joint capsule serves not only as a stabilizing structure but also as a functional organ with distinct biomechanical characteristics and corresponding neural innervation. As the structural foundation of the hip joint, its implications must be considered in light of changes and advancements in surgical concepts. The hip joint capsule consists of multiple layers of dense connective tissue, which, together with the surrounding ligaments, are referred to as the joint capsule complex[3]. Anatomical and biomechanical studies have improved understanding of the relationship between capsular structure and function. The hip joint capsule[4-7] consists of an outer layer of longitudinal fibers and an inner layer of circular fibers, known as the annulus fibrosus. This bilayer structure allows the capsule to withstand multidirectional loads. The annular band is not an independent ring-shaped structure, but instead results from a dynamic morphological change where the joint capsule becomes concave toward the femoral neck in specific positions. This concavity narrows the joint cavity and functions similarly to a sphincter to maintain the joint’s negative pressure stabilization mechanism. The anterior portion of the joint capsule is reinforced by the iliofemoral ligament, one of the strongest ligaments in the human body, while the posterior portion is reinforced by the ischiofemoral ligament. Quite a few studies have reported that the capsule remains stable and keeps its structure due to the support provided by ligaments from various directions[8]. Furthermore, the joint capsule has numerous nerve endings. Preserving the nerves may contribute to improved capsular function after repair[9]. The thickness of the joint capsule varies considerably across different regions; in a cadaveric study of posterior hip capsule in the setting of total hip arthroplasty, the upper portion of the posterior joint capsule is the thickest, measuring approximately 3.48 mm, while the thinnest part of the lower portion measures approximately 1.59 mm[10]. This anatomical feature provides guidance for surgical suturing techniques. A recent study has also suggested that age may affect capsule healing after hip arthroscopy in patients with FAI syndrome[11].

Biomechanical role of the hip joint capsule

In recent years, the biomechanical role of the hip joint capsule has been clarified through numerous anatomical, cadaveric studies, and clinical comparative research, with its remarkable elasticity identified as a key characteristic. The study also revealed a maximum tensile strain of 39.21% ± 5.23%, a maximum tensile load of 142.06 ± 34.15 N, and an elastic modulus of 14.23 ± 5.62 MPa. The authors characterized the deformability and mechanical response of the joint capsule under various conditions to provide a reference for the strength requirements of joint capsule suturing in surgery[10]. The joint capsule-ligament complex also possesses capacity to resist multidirectional stresses in three-dimensional space. The ischiofemoral ligament, located posteroinferior to the joint capsule, works with the circumferential ligaments around the femoral neck[12] to resist posterior dislocation during hip flexion and adduction, while the medial bundle of the iliofemoral ligament, located in the anterosuperior capsule, serves as the core structure that resists anterior dislocation during extension and external rotation[13]. These functions differ depending on hip position. This means the incision location and repair method both matter for stability. A study utilizing a three-dimensional model has reported that, with the hip flexed to 90°, the tensile strains in the upper, middle, and lower portions of the normal joint capsule were 17.0%, 24.1%, and 26.0%, respectively. After traditional capsular repair, the values increased to 37.0%, 53.3%, and 68.3%, respectively[10]. This indicates that traditional repair can restore capsular stability, but it fails to restore the mechanical function of these regions. A finite element analysis stated that stress is distributed more uniformly after anatomical repair, whereas traditional repair methods tend to cluster stress in certain spots[14]. A systematic review and meta-analysis of biomechanical studies also reported that capsular repair or reconstruction significantly improved resistance to distraction, supporting the biomechanical rationale for capsular restoration[15].

Studies have reported that the joint capsule has plenty of mechanoreceptors such as annular bodies and Ruffini corpuscles. These nerve endings detect changes in joint position and tension. They also help with sensory feedback and muscle control[16]. These findings suggest that the joint capsule is not merely a passive structure maintaining the joint stability, and it may also play an active role through the nerves. This might partly explain why the capsule repair is associated with improved outcomes[17]. In other words, repair should aim to both restore its anatomical structure and preserve its neural innervation as much as possible. This matches the concept of “preserved innervation” mentioned above. Overall, the hip joint capsule plays a complex biomechanical role. It involves multi-level, regional, and neurodynamically regulated mechanisms. Future capsular management should focus on rebuilding and protecting function, not just capsulotomy and suturing.

INSIDE-OUT TECHNIQUES: TRADITION, LIMITATIONS, AND IMPROVEMENT

Foundations of traditional inside-out techniques

The inside-out technique involves entering the joint capsule first and then proceeding from the inside out. Logically, this approach aligns well with general practice and remains a classic surgical choice today. As mentioned earlier, the earliest use of hip arthroscopy can be traced back to 1931, when Burman proposed a technique that involved entering the joint via an anterior trochanteric approach along the direction of the femoral neck, noting that the tight fit between the femoral head and the acetabulum was the primary obstacle to accessing the central compartment[18]. Furthermore, early hip arthroscopy was primarily used for diagnostic purposes, mainly to observe the internal condition of the hip joint. Therefore, the early looks at how to better access the “interior” rather than the “exterior” was an inevitable development.

Hip arthroscopy was primarily used for diagnostic purposes historically. Traction is a basic part of hip arthroscopy. It helps to establish the access route[19]. The “inside-out” technique begins with the traction after the patient is anesthetized. A traction table is used to create a gap of approximately 1 cm between the femoral head and the acetabulum, and the gap is checked with fluoroscopy. Once this gap is confirmed, the surgeon makes the portals. The classic combination of access ports typically includes the anterior portal for visualization and the midanterior portal for manipulation[20]. After the portals are established, the surgeon performs an interportal capsulotomy. The instruments will be inserted through the anterior portal to create a transverse capsulotomy between the two portals. This connects the portals and allows the standard surgical procedure to proceed[21]. If further exposure of the femoral head-neck junction is required, a longitudinal capsulotomy can be made distally from the midpoint of the transverse capsulotomy, and this creates the “T-capsulotomy”. In recent years, the interportal capsulotomy has become the most common traditional technique in hip arthroscopy. It serves as the foundation for subsequent surgical strategies.

Biomechanical costs of inside-out techniques

The inside-out approach was a significant advancement in arthroscopic surgery. This technique lets surgeons view the conditions in the acetabular labrum, hip ligaments, and surrounding cartilage and soft tissues without an extensive capsulotomy, therefore improving the surgical visualization and procedural convenience[22,23]. However, this technique also causes considerable damage to the joint capsule and related ligaments, and it is also invasive to a certain degree, which has been supported by some biomechanical and clinical studies (Table 1).

Table 1 Comparison of different hip arthroscopic capsulotomy techniques and their biomechanical impacts.

Technique	Approach	Incision direction and relationship to iliofemoral ligament	Impact on iliofemoral ligament	Evidence level	Ref.
Interportal transverse capsulotomy	Inside-out	Transverse, perpendicular to fibers	Reported to disrupt the iliofemoral ligament; increased external rotation laxity	Category 1 and 3	[22,24,25,27]
T-capsulotomy	Inside-out	Transverse + longitudinal	Divides the ligament into four portions; considered to cause substantial disruption of restraint	Categories 3 and 4	[21,27,28,69,70]
Limited puncture capsulotomy	Inside-out (modified)	Limited longitudinal through hollow exchange rod	Reduces area of capsular injury, with a limited longitudinal incision	Category 1	[31]
Skip capsulotomy	Inside-out (modified)	Multiple short, non-communicating incisions	Designed to avoid transverse transection of iliofemoral ligament; continuity of fibers is preserved	Categories 4 and 6	[32,33]
Outside-in longitudinal capsulotomy	Outside-in	Longitudinal, parallel to iliofemoral ligament fibers	Minimizes transverse ligament injury; designed to preserve the fiber continuity	Categories 1, 4, and 5	[44,45,48,53,64]

The first injury addressed is that of the iliofemoral ligament. As mentioned previously, the iliofemoral ligament is the strongest ligament within the hip joint capsule, with predominantly longitudinally running fibers; the direction of the transverse capsulotomy in this approach is essentially perpendicular to these fibers[24]. A complete transverse capsulotomy between the approaches can result in the severing of most of the iliofemoral ligament and might even lead to its direct transection[25]. In biomechanical studies conducted on cadavers, Lee et al[25] confirmed that external rotation laxity was significantly increased at all flexion angles following a transverse capsulotomy, demonstrating the detrimental impact of a transverse capsulotomy on joint stability. Another biomechanical study indicated that, following a transverse capsulotomy between the surgical approaches, the force required to achieve 5 mm of traction decreased by an average of 9% compared with the intact capsule[26]. The T-capsulotomy, which is based on an intersurgical capsulotomy, has an even more pronounced effect on biomechanics. By adding a longitudinal capsulotomy to the transverse capsulotomy, the iliofemoral ligament is directly divided into four separate portions, thus completely severing the maximum constraining force that was originally present. Although the T-capsulotomy provides an enhanced field of view for hip arthroscopy, the damage and impact on biomechanical function are correspondingly significant[27,28]. This finding is consistent with a cadaveric biomechanical study showing that capsular repair can restore the anatomical structure and biomechanical function of the hip to some extent, although not always completely[29]. However, in a study involving 3277 patients, Heifner et al[30] found that although the use of T-capsulotomy is increasing, reports on the characteristics of capsular closure remain insufficient.

Improvements and development of inside-out techniques

As understanding of the ligament damage and impaired joint capsule function caused by traditional inside-out techniques has increased, these techniques have continued to develop. In recent years, greater emphasis on precision, individualization, and minimally invasive techniques has shifted the philosophy about arthroscopic surgery from a mere pursuit of convenience and optimal visualization to a focus on minimizing damage while ensuring surgical efficacy. The most direct improvement is to reduce the extent of capsulotomy, such as by using the limited capsular capsulotomy technique[31]. This technique involves puncture with a hollow exchange rod, followed by a limited longitudinal capsulotomy from the inside out to replace the traditional large-scale capsulotomy, thereby reducing capsular damage. A retrospective study of 82 patients with FAI demonstrated that the modified technique significantly reduced both the total operative time (50.2 minutes vs 62.2 minutes) and joint capsule suturing time (9.0 minutes vs 17.0 minutes). The study also reported better hip function scores [e.g., Modified Harris Hip Score (mHHS)] at 6 months postoperatively. There were no noticeable differences in complication rate between the two groups. This suggests that a small capsulotomy is safe to perform, as it maintains capsule and ligament functions without increasing risk.

However, this method mainly leads to a smaller capsulotomy, but not enough protection for the capsule. Hence, avoiding the transection of the ligament has become another important innovation. The skip capsulotomy technique[32] is different from the traditional techniques since a separate capsulotomy is created that avoids the transverse part of the iliofemoral ligament. Thus, the structure and function of the ligament would be preserved. In a cohort study of 300 hips[33], the average capsulotomy length was (19.9 ± 4.8) mm. The surgeons can also vary the length of the incision based on their experience. This is not just a modification for a smaller capsulotomy. It also demonstrates the change in the goal from getting a better view after ligament transection to preserving the ligament. This reflects the current view of the joint capsule and its ligaments as functional structures that have to be protected. Therefore, it marks a return to preserving function within an inside-out surgical approach.

Conceptual advancements in capsular repair and closure

As the research on capsulotomy and its surgical approaches have continued, concerns about the effects on joint stability gradually grew. This led to more interest in capsular closure. In the early era of hip arthroscopy, the joint capsule was typically left unclosed. It was believed that the joint capsule, being connective tissue, could heal autonomously, and that the strong bony structures of the hip joint could keep the joint stable[34]. Furthermore, from a technical standpoint, capsular repair was considered highly challenging, with excessive suturing potentially leading to postoperative joint stiffness. Indeed, in patients with pre-existing chronic joint conditions such as underlying joint stiffness, even routine suturing could hinder postoperative recovery[35]. Consequently, joint capsule repair was not routinely performed. However, clinical studies have revealed that some patients experience persistent pain or discomfort postoperatively, or even require reoperation, which has drawn attention to the quality of joint capsule healing[36].

Over the past several decades, a series of clinical studies have systematically compared the therapeutic outcomes of capsular closure vs non-closure. A cohort study[37] published in 2020 demonstrated that, among 111 elite athletes (62 with capsular closure, 49 without), those in the complete capsular-closure group had a significantly higher return-to-sport rate than those in the non-closure group (90.3% vs 75.5%; P = 0.03), a significantly shorter time to return to sport (4.7 months vs 5.8 months; P < 0.001), and a higher proportion of athletes who achieved the minimal clinically significant difference on the mHHS and Hip Outcome Score - Activities of Daily Living (HOS-ADL) scales.

Furthermore, several meta-analyses have provided evidence supporting the concept of capsular closure. In their 2024 meta-analysis of 322 patients, Shen et al[38] compared the outcomes of capsular repair vs non-repair following hip arthroscopy. Although their analysis was confined to patients without dysplasia or generalized ligamentous laxity, the findings support the superiority of capsular repair in improving functional outcomes. Moreover, in a meta-analysis that included 11 comparative studies involving a total of 1897 patients, Dasari et al[39] reported that the group with complete capsular closure exhibited significantly greater improvements in the mHHS and HOS-ADL functional scores when compared to the non-closure group. The non-closure group had a higher rate of revision surgery than the complete closure group and also a higher risk of total hip arthroplasty (THA) conversion [revision relative risk = 1.67, 95% confidence interval (CI): 1.14-2.45, P = 0.008; THA conversion relative risk = 2.01, 95%CI: 1.06-3.79, P = 0.03]. Similarly, another meta-analysis[40] confirmed that the postoperative mHHS and HOS-ADL scores in the capsular closure group were significantly better than those in the non-closure group, while the incidence of postoperative complications (odds ratio = 0.21, 95%CI: 0.08-0.54, P = 0.001) and THA conversion rate (odds ratio = 0.42, 95%CI: 0.21-0.83, P = 0.01) were significantly lower. However, evidence relating to revision surgery remains inconsistent across studies.

The mentioned systematic reviews and meta-analyses have reported better functional outcomes after capsular closure. However, some randomized controlled trials have not clearly shown a clinical advantage of capsular closure over non-closure[41,42]. Therefore, the value of capsular closure may also depend on clinical needs. As with conventional open surgery, the damage incurred during hip arthroscopy naturally requires surgeons to make every effort to repair it. However, it is important to note that the learning curve and time investment required for joint capsule repair and closure are substantially greater, resulting in increased demands on surgeons.

More importantly, the need for repair and closure of the joint capsule has encouraged consideration of techniques that minimize capsular disruption while preserving hip function. The “outside-in” injury model concept proposed in 2019 describes the characteristics of cartilage damage in dysplastic hips and provides a novel perspective on capsular management strategies under various pathological conditions[43]. This concept has also conceptually contributed to the exploration of outside-in techniques.

“OUTSIDE-IN” TECHNIQUE: INNOVATION, EVOLUTION, AND BREAKTHROUGHS

Summary and basic steps of the outside-in technique

The outside-in technique is a relatively novel method of capsular capsulotomy that differs from traditional inside-out and inter-approach transverse capsulotomy techniques. The core principle of this technique is to start outside the joint capsule. Under hip arthroscopic visualization, the surgeon makes a longitudinal capsulotomy from the outside in to reach the joint cavity for subsequent procedures. During surgery, the clearest difference is the direction of the incision. The outside-in capsulotomy runs parallel to the longitudinal axis of the femoral neck and perpendicular to the acetabular labrum. The traditional approach runs parallel to the structures[44]. A comparative clinical study has reported that the outside-in approach may provide comparable clinical outcomes to the inside-out approach[45]. Its aim is to keep the capsule stable and intact. This differs from the traditional approaches that focus on exposure.

Current clinical research and technical descriptions outline the primary steps of the outside-in technique as follows[46-48]: (1) Establish the approach and positioning. Under controlled traction and with the assistance of intraoperative fluoroscopy, create a space sufficient for puncture and establish a standard surgical approach. In certain cases, this technique may even be executed without traction, allowing for direct puncture to the anterior aspect of the femoral neck, followed by subsequent procedures performed via arthroscopy; (2) After inserting the arthroscope and clearing the soft tissues outside the joint capsule, identify key anatomical landmarks to establish reference points for the longitudinal capsulotomy, such as the tendon of the retraction head of the rectus femoris muscle; (3) Make a longitudinal capsulotomy in the joint capsule and insert the arthroscope into the joint to perform the necessary procedures. Traction can subsequently be increased as needed to access the central compartment from the peripheral compartment for deeper interventions; and (4) Finally, suture the joint capsule to restore its integrity and stability. Suturing through the incision created by the longitudinal capsulotomy is relatively simple and straightforward.

Early exploration of the outside-in technique

The outside-in technique did not appear by chance. It came from traditional methods that changed over decades. During the period, surgeons have learned more about the anatomical structure and biomechanical function of the hip joint capsule. Horisberger et al[49] built on the early work and proposed a new method. It reached the joint layer-by-layer from the outside in, guided by arthroscopy. Unlike traditional capsulotomy, this approach used a longitudinal capsulotomy in the joint capsule. In their initial case series, the authors reported shorter traction time, better outcomes, and less injury, though these findings were based on their initial experience. Another study[50] described a similar longitudinal capsulotomy technique. It focused on making a longitudinal capsular capsulotomy between the gluteus minimus muscle and the iliocapsularis muscle. Its aim was to preserve the main function of the iliofemoral ligament.

Later, Forster et al[51] came up with an improved method where the reflected head of the rectus femoris tendon served as the anatomical landmark for the procedure. Using this landmark, it became possible to guide the longitudinal capsulotomy between the two bundles of the iliofemoral ligament. These early efforts laid a base for further improvements. However, they also led to some problems[52]. The soft tissues around the hip are complex and differ a lot between people. Thus, it is hard to differentiate between these ligaments and muscles in open surgery, and even harder in arthroscopy. As a result, early outside-in techniques were technically demanding, reflecting the general steep learning curve of hip arthroscopy.

Technical improvement of the outside-in approach

A key technical improvement was described in the paper “Rapid Outside-In Capsulotomy”[53]. The paper introduced two main innovations. First, it used a spinal needle and guidewire under fluoroscopy as a real-time anatomical reference. Second it simplified the intraoperative localization by eliminating the need to identify specific ligament branches. These changes may make the technique easier to learn for surgeons with less experience in hip arthroscopy.

The main steps are as follows: The patient is positioned supine, and mild traction is applied to widen the joint space by about 1 cm; under fluoroscopic guidance, a No. 17-gauge spinal needle is inserted into the central joint compartment through the anterolateral approach toward the femoral neck; once the needle is in the right position, a guidewire is placed; the needle is then withdrawn, leaving the guidewire in place; an incision is made along the wire and the subcutaneous tissue is dissected bluntly; a cannula is then inserted, and the arthroscope is introduced through it; using the guidewire as a reference, the surgeon can quickly identify the femoral head, femoral neck, joint cavity, and acetabular labrum; after the structures are recognized, the capsulotomy is performed parallel to the femoral neck axis around the wire. The length of the capsulotomy is adjusted based on the lesion; finally, the wire is removed, and the rest of the procedure follows standard hip arthroscopy steps. This guidewire-guided method aligns with the safe approach principles of Maldonado et al[54], which emphasize precise intra-articular positioning and minimal tissue trauma through clear anatomical landmarks and fluoroscopy.

Several studies have reported the use of this technique, including FAI, pincer morphology, and slipped capital femoral epiphysis[55-62]. They suggested that it may make the procedure easier and the learning curve shorter, particularly for surgeons with little experience of hip arthroscopy. The iliofemoral ligament may stay stable, since the incision runs along the direction of the fibers. This could limit the impact on joint stability. Some techniques have been proposed to reduce the need for traction as well, which may decrease traction-related problems. Fluoroscopy might be needed less often, so both physicians and patients receive less radiation. A longitudinal capsulotomy may also make capsular closure easier, since it allows for simple and reliable suturing. However, these advantages come mainly from technical descriptions and early case series, not from the comparative clinical studies. Therefore, the technique requires further validation.

This technique also has limits[53]. In severe pincer-type FAI, the space between the femoral head and the acetabulum is narrow. This makes it hard to place the puncture needle into the central compartment. In these cases, a traditional approach may still be needed. The incision runs parallel to the ligament fibers, but surgeons sometimes need to release part of the deep fibers of the iliofemoral ligament to treat deep lesions near the acetabular rim. The long-term effects of this procedure require further study[63].

Expert consensus and clinical implementation

The Spine and Hip Joint Working Group of the Sports Medicine Branch of the Chinese Medical Association, in collaboration with the Hip Joint Working Group of the Sports Medicine Physicians Branch of the Chinese Medical Doctors Association, developed the “Expert consensus on clinical practice of outside-in longitudinal capsulotomy in hip arthroscopy” using a modified Delphi method. This document represents the first Chinese expert consensus specifically addressing the “outside-in longitudinal capsulotomy in hip arthroscopy”, marking a step toward standardizing the technique[64]. Nevertheless, as a consensus-based document, its recommendations should be regarded as expert guidance rather than evidence-based mandates, and their routine application requires further validation through comparative clinical studies.

The consensus proposed 14 recommendations. They cover the technique’s nomenclature, indications, key operative steps, management of capsular closure, postoperative rehabilitation, and the advantages and disadvantages of the technique. For indications, a general review has suggested that the outside-in longitudinal capsulotomy technique is suitable for most patients with FAI, particularly cam-type FAI[65]. For patients with joint laxity[66], this technique may provide additional benefits by preserving ligament integrity. For capsular closure, routine edge-to-edge suturing is suggested at the end of the procedure to help healing and restore joint capsule tension.

The publication of this consensus provides surgeons with standardized operational guidelines, helping to reduce uncertainty from technical variability. Academically, it represents a great advancement for China’s sports medicine community in standardizing hip arthroscopy techniques, strengthening the role on the international academic stage.

Requirements for capsule closure in different arthroscopic capsulotomy techniques for the hip

In hip arthroscopy, managing the joint capsule depends on balancing surgical exposure with the preservation of structural integrity. Over decades of development, hip arthroscopic capsulotomy techniques and capsular management strategies have advanced. Current methods of hip arthroscopic capsulotomy cover a broad spectrum, from enhancing the surgical field of view to prioritizing structural integrity. Some representative techniques are outlined below.

Periportal capsulotomy is a technique that preserves the joint capsule. As a conservative approach, it only expands the access paths without connecting them, so the damage to the soft tissues is minimal. However, the visualization it provides is limited to the central compartment[67]. This technique needs little traction and has a low risk of iatrogenic injury[68] (Table 2). Therefore, the capsular closure is usually not needed. However, because of the limitations, this technique is mainly used for arthroscopic diagnosis or simple procedures such as the removing loose bodies. The most widely used capsulotomy techniques are the interportal transverse capsulotomy[69] and the T-shaped capsulotomy, which adds a longitudinal capsulotomy to the former. The interportal transverse capsulotomy connects the operative portals with a transverse cut and greatly severs the iliofemoral ligament. The T-shaped capsulotomy substantially disrupts the iliofemoral ligament, potentially reducing its constraint function. Both techniques provide the surgeon with an excellent visualization from the central to the peripheral compartments. This makes the procedure simpler and allows complex deformity surgeries that would be hard under standard visualization. However, as mentioned earlier, both approaches may lead to much damage to soft tissues. This reduces the biomechanical stability of the hip joint and the integrity of its anatomical structure. Therefore, it is suggested to perform complete capsular closure at the end of the procedure. For the T-shaped capsulotomy, both the transverse and longitudinal incisions should be closed[70]. It is notable that the limited puncture capsulotomy technique is a modified version of inside-out approach. It uses a hollow exchange rod to make a limited longitudinal capsulotomy instead of a large transverse one. Although this modification reduces the area of joint capsule disruption, postoperative closure remains necessary due to the persistent discontinuity in the joint capsule. However, compared to the traditional transverse capsulotomy between access points, both the difficulty of closure and suturing time are significantly reduced. Meanwhile, the skip capsulotomy, a major breakthrough in the inside-out technique in recent years, fundamentally avoids the transverse transection of the iliofemoral ligament associated with the traditional transverse capsulotomy between access points by creating two independent, short capsulotomies at the access sites without connecting them. Since the continuity of the main body of the ligament is preserved, the overall stabilizing function of the joint capsule is maintained to the greatest extent possible. Despite the localized interruptions in the continuity of the joint capsule, current research on the necessity of closure for this technique remains insufficient. Therefore, it is generally recommended that decisions be made on a case-by-case basis after evaluating the specific intraoperative situation. Given that the course of the ligament is preserved, even when suturing is required, the technical demands are relatively low. Compared to the previously mentioned inside-out technique, the outside-in technique represents a different capsulotomy strategy. The longitudinal capsulotomy runs roughly parallel to the iliofemoral ligament fibers, avoiding transverse transection, which has less effect on joint stability than the transverse capsulotomy. Based on the technical description and expert consensus, routine edge-to-edge suturing is suggested at the end of the procedure to facilitate healing and restore joint capsule tension, and suturing through a longitudinal capsulotomy may be technically less demanding than repairing a transverse capsulotomy, although direct comparative evidence remains limited. It should also be noted that the recommendations apply to the general population; for individualized decision-making, the choice to close or not to close the joint capsule in certain special patients still requires precise assessment and judgment by the surgeon. Furthermore, the need for capsular closure in special populations[71] remains an area requiring consideration in future research, as outcomes are influenced by various factors beyond capsular closure itself.

Table 2 Capsular closure necessity and suturing difficulty across different capsulotomy techniques.

Technique	Disruption of capsular continuity	Closure strategy	Suturing difficulty	Rationale	Evidence level	Ref.
Periportal capsulotomy	Minimal (portal expansion only, no interconnection)	Generally not required	Relatively low	Low traction demand; minimal iatrogenic injury; limited to diagnostic or simple loose body removal	Category 4	[67,68]
Interportal transverse capsulotomy	Substantial capsular disruption	Recommended	Relatively high	Ligament considered severely disrupted; closure generally recommended to restore biomechanical stability	Category 3	[24,25,27,29]
T-capsulotomy	More extensive capsular disruption involving transverse and longitudinal limbs	Recommended	Relatively high	Substantial ligament disruption; both limbs generally require closure	Categories 3 and 4	[21,24,27,28]
Limited puncture capsulotomy	Moderate (reduced incision area via hollow exchange rod)	Generally recommended	Relatively moderate	Reduced capsular disruption; closure still recommended	Category 1	[31]
Skip capsulotomy	Localized (multiple short, non-communicating incisions)	Case-by-case	Relatively low	Ligament continuity largely preserved; suturing technically undemanding when performed	Categories 4 and 6	[32,33]
Outside-in longitudinal capsulotomy	Linear longitudinal incision, parallel to iliofemoral ligament fibers	Suggested based on expert consensus	Relatively low	Designed to avoid transverse transection; facilitates edge-to-edge closure	Categories 1, 4, and 5	[44,45,48,53,64]

Current limitations and discussion of different techniques

Before discussing the various technical limitations, it is necessary to distinguish the categories of evidence in this review. We grouped the evidence into six categories: Category 1 included direct comparative clinical evidence, such as randomized controlled trials, comparative cohort studies, comparative clinical studies, and meta-analyses of comparative clinical studies. Category 2 included non-comparative clinical evidence, including prospective or retrospective cohort studies, case series, and case reports. Category 3 included cadaveric, biomechanical, and computational studies. Category 4 included technical evidence from technical notes and operative technique papers. Category 5 included consensus statements, expert guidance, and editorial commentaries. Category 6 included studies available only as conference abstracts. These categories were just applied to the main text and in the Tables. They describe the type of evidence rather than a formal hierarchy of methodological quality.

Although available meta-analyses suggest that capsular closure has functional benefits[37-40], there are still certain limitations. Most included studies are retrospective or non-randomized, which may introduce selection bias: Patients that get capsular closure may start off with better characteristics than those do not get. Difference in surgical methods, recovery protocols, and outcome measures across studies also make it challenging to generalize the findings. Also, it is difficult to draw a conclusion regarding the superiority of capsular closure without randomized studies. Besides, there is a lack of long-term data on capsular healing, and most available studies are limited by short follow-up durations and small sample sizes[72].

The risks of capsular closure also deserve attention. Too much tension during closure may limit the function, particularly in patients with stiffness or those undergoing concomitant procedures[35]. The capsular tensioning lacks a clear standard, so that the clinical decisions still rely on surgeon judgment. Besides, the closure strategies should be individualized for the patients with borderline dysplasia or generalized ligamentous laxity, as it is important to balance between stability and mobility[71].

It is essential to consider the types of evidence when assessing the benefits of outside-in techniques. While cadaveric biomechanical studies[24-28] have provided useful mechanistic data of this technique, they do not prove its clinical superiority directly. The benefits attributed to the outside-in technique include decreased traction time, reduced need for fluoroscopy, and an easier learning curve. Most of the benefits come from technical reports[53] and early case series rather than from comparative studies. Expert consensus[64] provides a basic model for clinical practice, but it is not an evidence-based requirement. While the outside-in technique preserves the capsule, the traditional inside-out technique remains relevant in some cases. For severe cases of pincer-type FAI, the space between the femur and acetabulum becomes too narrow to perform the surgery safely using the outside-in technique, so the inside-out technique may be required. Similarly, inside-out surgery is performed for complex revision surgery with atypical capsule anatomy. Overall, the choice of technique should be considered for each patient.

Several factors influence the clinical outcomes. Concomitant procedures, such as labral repair, femoral osteochondroplasty and acetabular rim trimming, are different across studies. Each of these could have a great influence on patients’ recovery independently. Patient groups in different studies also differ. While some include high level athletes, others involve individuals with borderline dysplasia. This implies that the importance of capsular closure could be different depending on the population[37]. Postoperative rehabilitation is another key factor. It is not possible to recommend the same program to all patients. Differences in early mobilization, weight-bearing, and return-to-sport schedules might lead to different outcomes regardless of the capsular closure technique used.

Nevertheless, additional research needs to be done in order to determine the applicability of the results to certain patient groups. Most studies were conducted on patients with FAI and an intact capsule. In the case of borderline hip dysplasia, a recent retrospective series reported good short-term outcomes of the outside-in technique. However, this study is limited by small sample size and short follow-up[73]. For patients suffering from generalized ligamentous laxity, there is some information about the possibility of achieving good outcomes by managing the capsule. However, many meta-analyses did not include this group in order to avoid heterogeneity between groups. Thus, the optimal treatment for this patient category is yet unknown[74]. Information about revision arthroscopy is even more limited. Most studies describe the technical part of the procedure rather than compare methods. Therefore, the question arises whether the outside-in longitudinal capsulotomy can produce comparable effects in these subgroups. More research is needed. This gap may help define the direction of future research. The outside-in technique may also be more challenging in certain settings, since it requires professional training, fluoroscopy, and other institutional resources.

FUTURE OUTLOOK

Looking ahead, this paper suggests that future developments in arthroscopic capsular techniques for the hip may continue to advance in several directions. First, there should be a focus on standardization, individualization, and precision in the mutual selection of indications and surgical techniques. Currently, both the inside-out and outside-in technical approaches are advancing in parallel, each giving rise to various modified techniques and forming multiple clinically validated technical lineages. However, due to factors such as research duration and sample size, the indications for these modifications primarily rely on the surgeon’s subjective judgment and lack higher-level evidence-based support. In the future, long-term, large-scale studies will be necessary to establish precise medical decision-making that matches specific conditions with appropriate surgical techniques.

Second, there is a need to establish a mature system for assessing the quality of the joint capsule. Currently, the quality of capsular healing is still judged based on the surgeon’s subjective assessment. A comprehensive and mature assessment system has not been developed. In future research, intraoperative fluoroscopy, postoperative ultrasound, standardized physical examinations, and biomechanical tests should be used to assess the capsular recovery and healing in real time. This would help establish clearer criteria for capsular closure and provide a unified standard for evaluating different capsulotomy techniques.

Third, there should be a shift towards less invasive techniques. Whether the approach is improved from the inside out or the outside in, the basic principles of capsulotomy and repair remain the same. Future technical innovations may build on arthroscopic minimally invasive surgery to achieve an even lower level of invasiveness. This may include access methods that completely avoid cutting the joint capsule and rely on dilation, or biological therapies that promote healing and reduce recovery time. Fourth, the use of the procedure should be encouraged and training programs also created. While the outside-in technique has made learning easier, the general entry barrier for hip arthroscopy remains high. In the future, a combination of different learning methods, such as simulation training and surgical navigation systems, would play an important role in reducing the learning curve for younger surgeons.

CONCLUSION

Capsular management in hip arthroscopy has changed a lot over the years. Surgeons now care not only about exposure but also about preserving the capsule. This field has moved from traditional transverse capsulotomy and T-capsulotomy to modified T-capsulotomy, limited puncture capsulotomy, and skip capsulotomy, and more recently to the outside-in technique. Each advance was associated with increasing knowledge of the capsule’s anatomical structure, innervation, and biomechanics. This has led to expert consensus that preserving capsular function is one of the core ideas in this field. However, it should be noted that the majority of evidence regarding the outside-in approach remains indirect. Also, the so-called benefits require confirmation by more prospective comparative studies. Besides, the outside-in technique should not be regarded as a “gold standard”, as traditional approaches retain their value in selected clinical scenarios.

At present, there are still limitations with both methods. The boundaries of indications for the outside-in technique remain unclear, long-term evidence about the joint capsule healing is still insufficient, and efforts are still needed to promote its adoption. Meanwhile, changes to the inside-out technique have been mostly corrective. This suggests a need for completely new approaches. Several core issues still need to be addressed. One is to build an evidence base, which would include high-quality, long-term studies with large samples. Another is to set clear criteria for assessing recovery by using innovative imaging and biomechanics techniques. The third is to create systematic training programs for the technique. The steps may help promote the surgical principles, introduce innovations, and customize treatment for each patient.