Hip-preserving treatment of early ONFH via arthroscopy: preoperative finite element analysis planning with 3D printing assistance

Abstract

Osteonecrosis of the femoral head (ONFH) is caused by the disruption of blood flow in the femoral head, leading to irreversible necrosis. Early intervention in ONFH is crucial to prevent femoral head collapse, preserve joint function, and delay or avoid the need for hip replacement. Currently, hip-preservation strategies for early ONFH face two significant technical challenges: (a) achieving precision targeting with minimal iatrogenic injury. (b) Precisely identify and target biomechanically optimal 3D location. This study combined hip arthroscopy ‌with‌ preoperative finite element mechanical analysis, ‌supplemented by‌ 3D printing technology, ‌aiming to propose a new strategy to guide the precision treatment for early ONFH. Patients treated by this strategy showed a significant decrease in Visual Analogue Scale (VAS) scores from preoperative to 14 days postoperatively, while Harris Hip score (HHS) showed a significant improvement from preoperative to 3-month postoperative follow-up. Of note, imaging results showed that no patient had ONFH progression within 3 years after surgery. This strategy realizes finite element analysis to preoperative planning guidance, practices the biomechanical treatment for early ONFH, worthing further studying and popularizing.

Introduction

Osteonecrosis of the femoral head (ONFH) is caused by the disruption of blood flow in the femoral head, leading to subchondral bone hypoxia and irreversible necrosis of bone marrow cells and osteocytes. This process results in the deformation and collapse of the articular surface, eventually developed into a severe disabling disease of secondary osteoarthritis^1,2. Therefore, early intervention in ONFH is crucial to prevent femoral head collapse, preserve joint function, and delay or avoid the need for hip replacement. Since the introduction of the first staging criteria by Ficat and Arlet in 1980³, at least 16 staging and classification systems have been developed to guide treatment. In particular, the Association Research Circulation Osseous (ARCO) and China-Japan Friendship Hospital (CJFH) Staging System developed in recent years have exerted a profound impact on guiding the clinical management of ONFH^1,4. These strategies, each formulated within different historical and research contexts, possess distinct advantages and limitations. Recent research has identified the disruption of the mechanical structure of the femoral head and the failure of remodeling as primary factors contributing to the continued progression of necrosis following surgical intervention. However, most protocols and preoperative evaluations for ONFH therapy predominantly rely on imaging results, lacking comprehensive biomechanical data support. Currently, hip-preservation strategies for early ONFH face two significant technical challenges: (a) achieving precision targeting with minimal iatrogenic injury. This procedure necessitates meticulous navigation to fulfill dual objectives: ensuring the accurate placement of the guide needle within the necrotic zone while maintaining the structural integrity of the surrounding trabecular bone. This requires millimeter-level precision to prevent iatrogenic damage to the weight-bearing columns and vascular networks within the femoral head-neck complex⁵. (b) Biomechanical optimization during remodeling necessitates that clinicians identify and target specific three-dimensional locations that simultaneously satisfy two biomechanical criteria: providing immediate load-bearing support to prevent collapse and permitting optimal biological conditions for bone regeneration. This requires a preoperative assessment of mechanical stress distribution and biological remodeling potential⁶.

Previously, utilizing arthroscopy, we established a direct monitoring channel to mitigate iatrogenic injury and prevent needle penetration of the articular surface, thereby effectively reducing the risk of iatrogenic injury to the femoral head during implant placement. However, this method exhibits a fundamental limitation, as it does not ensure both the precision of core decompression and the biomechanical efficacy of graft placement⁷. Furthermore, there remains a significant gap in assessing the necessity for support and determining the optimal location for implant placement⁸. In contemporary clinical medicine, there has been a significant integration of three-dimensional (3D) imaging and additive manufacturing technologies, which hold transformative potential for revolutionizing therapeutic strategies for ONFH⁹. Specifically, computer simulation systems utilize 3D imaging technology to establish finite element (FE) models of the femoral head^10,11. Through computer simulation-assisted biomechanics, the biomechanical characteristics and necrotic areas of early ONFH are analyzed to determine the necessity of implanting support structures. This process also involves identifying the optimal spatial positioning for support placement based on mechanical effects¹². Additionally, 3D printing technology enables the production of joint surgical guide plates, which can be used preoperatively to estimate the necrosis area and the depth of core decompression. This technology also facilitates the simulation of support material placement, thereby enhancing surgical accuracy and reducing complications^9,13.

In this study, our treatment strategy involves implementing a preoperative protocol utilizing 3D imaging and computer simulation, complemented by the completion of implant navigation through 3D printing technology. This approach aims to optimize the precision and individualization of treatment for ONFH. Notably, 3D imaging and printing technologies facilitate accurate anatomical modeling, patient-specific surgical simulation, and customized implant placement, thereby enhancing the optimization of ONFH treatment strategies in both biomechanical assessment and individualized care. Arthroscopy is employed to assess the collapsed area of the femoral head and evaluate cartilage integrity, thereby identifying therapeutic indications. The integration of FE analysis with a personalized 3D guide plate during preoperative planning ensures a precise alignment between the support structure and the stress collapse area. This alignment guarantees that the support is accurately positioned in the desired location, thereby minimizing iatrogenic injury.

Methods

The study was pre-registered on https://www.medicalresearch.org.cn [MR-50-24-021542] and was approved by the Ethics Committee of Daping Hospital (No.202496). Written informed consent was obtained from each subject. The study was conducted in accordance with the Declaration of Helsinki (2024) to ensure all methods adhered to relevant guidelines and regulations.

Strategic route

The precision treatment strategy comprises three fundamental technical steps, as illustrated in Fig. 1. Initially, a FE model of the femoral head was established based on the preoperative CT data of the patient with early ONFH for biomechanical analysis. For the definition of early osteonecrosis of the femoral head, we referred to the clinical staging criteria of Osteonecrosis of the femoral head developed by the International Association Research Circulation Osseous, and classified cases with ARCO Stage I and II as early ONFH requiring surgical intervention, whereas ARCO Stage 0 cases were not included in the treatment scope of this strategy, as they do not require surgical treatment in accordance with guidelines¹. Subsequently, the area for core decompression was delineated based on the biomechanical simulation outcomes, and a 3D printing guide plate was designed to ensure the once accurate puncture of the decompression guide needle. Concurrently, arthroscopy serves to assess the integrity of the articular cartilage and the extent of the lesion. It also addresses inflammatory synovium and intra-articular lesions, thereby enhancing operational safety. This approach establishes a direct monitoring channel to prevent iatrogenic injury by the needle during ONFH treatment, which is crucial for avoiding penetration of the articular surface by the guide pin and preventing damage to the already compromised blood supply. For patients with density changes in the femoral head that are highly suggestive of mechanical structural changes, a computer-generated digital model was utilized to analyze the stress concentration areas of the femoral head and to determine the optimal positioning for support material. An optimal solution algorithm was employed to design the spatial positioning and insertion angle that would provide maximum mechanical support. This data was then used to produce a customized 3D-printed femoral guide plate with a borehole passage. Subsequently, the 3D-printed guide plate was precisely positioned on the bone surface to direct the support material into the designated area, thereby facilitating precision treatment.

Fig. 1.

Illustrates the precision treatment flowchart of ONFH.

Recruit subjects

Subjects were recruited from a cohort of patients with early-stage ONFH between March 2021 and July 2023, as detailed in Table 1. All patients underwent preoperative imaging examination, and early-stage ONFH was diagnosed based on radiological and clinical evidence. Informed written consent was obtained from all patients.

Table 1.

Patient characteristics (n = 6, means ± SD).

	Male	Female
Case(n)	4	2
Age(year)	49.25 ± 6.625	55.5 ± 9.5
BMI(kg/m²)	25.68 ± 4.32	26.74 ± 3.44
Course of disease(year)	2.14 ± 0.58	2.25 ± 1.5
Mechanical structure changed
Yes	1	1
No	3	1
Implant support	1	1

Finite element analysis of hip joint biomechanics

The 3D geometry of the patient’s hip joint was reconstructed from CT data utilizing Mimics 24. The reconstructed model was subsequently exported in STL format and imported into HyperMesh 8.0 for finite element modeling. Based on the gray-scale values of the CT data, the image is segmented to determine the 3D morphology of trabecular bone, cortical bone, sclerotic bone, and collapse cavities. The 3D model reconstructed by software is compared with the CT data to assess its realism. Meshing was conducted using HyperMesh. All tissue types were modeled as linearly elastic and isotropic, with Young’s moduli set at 12,000 MPa for cortical and sclerotic bone, and 300 MPa for spongy bone, alongside a Poisson’s ratio of 0.3. Bone structures were distinctly categorized into cortical and trabecular bone, with both types being meshed using tetrahedral elements. At the articular surfaces, pentahedral elements were employed to simulate articular cartilage, with shared nodes at the interface between the cartilage and cortical bone to accurately model their mechanical interaction.

Biomechanical analysis and pre-implant simulation

The biomechanical analysis utilizing the FE method was conducted using Abaqus 2020. The simulation outcomes were subsequently processed and visualized with HyperView 2022. The distal femur was all degrees of freedom, while a downward load was applied to the proximal pelvis to simulate the force distribution in the hip joint during single-leg stance. As depicted in Fig. 2A, the preoperative model revealed a concentration of stress around the necrotic lesion, with stress transmission predominantly aligning with the orientation of the compressive trabeculae in the superior region. In patients requiring implants for collapsed area support, we employ finite element analysis to determine tantalum rod placement based on biomechanical stress patterns, thereby maximizing decompression efficacy while minimizing iatrogenic vascular injury risk. In contrast, the postoperative model demonstrated a significant reduction in stress around the lesion, particularly in the inferior region, with stress redistribution occurring along the tantalum rod (Fig. 2B). These findings indicate that the implantation of the tantalum rod effectively mitigated stress concentration around the necrotic cavity by redirecting mechanical loads through the high-strength implant, thereby reducing stress exposure in the defective region.

Fig. 2.

Personalized preoperative planning. (A) The load distribution around the necrotic lesion; (B) The load distribution effect of the implant on the stress concentration area.

Personalize 3D guide plate printing

A 3D model of the femoral head was automatically generated from CT data, and the surface curvature was extracted using Hypermesh software. The oblique area beneath the lateral femoral muscle on the lateral side of the greater trochanter of the femur serves as the fitting surface for the first locating plane, while the triangular area on the lateral side of the gluteal muscle trochanter of the proximal femur serves as the fitting surface for the second locating plane. The joint surface with the femur was obtained through inverse modeling using these two fitting surfaces. Based on the aforementioned biomechanical analysis, a CAD model with fixed guide holes was developed, and a personalized rigid plastic guide plate was subsequently printed (Fig. 3).

Fig. 3.

3D printing generates the guide plate. (A) Curvature extraction; (B) Design and optimize; (C) Fit detection; (D) CAD modeling; (E) 3D printing personalized guide plate.

Surgical procedures

The surgical procedure was conducted using hip arthroscopic techniques, specifically the anterolateral portal and the modified mid-anterior portal, in conjunction with a minimally invasive lateral approach, all performed by the same surgeon (Fig. 4). The patient was positioned supine on a table designed to facilitate hip traction and dynamic limb positioning. Following the application of traction to the operative limb, a standard anterolateral portal (ALP) was established adjacent to the anterolateral border of the greater trochanter. Subsequently, a modified mid-anterior portal (MMAP) was created under arthroscopic visualization from the ALP portal. After conducting diagnostic arthroscopy, necessary arthroscopic interventions for intra-articular hip pathology were undertaken. Thereafter, a minimally invasive lateral approach to the femur was initiated. This involved incising the tensor fascia lata and separating part of the lateral femoral musculature below the greater trochanter, thereby exposing the lateral aspect of the proximal femur. Following the exposure of the structure, the personalized 3D-printed guide plate was securely affixed to the proximal end of the femur. This facilitated the insertion of a 2 mm Kirschner wire into the pinhole, thereby accurately positioning the guide plate. Subsequently, a guide needle was advanced into the predetermined location of the femoral head, approximately 5 mm beneath the articular cartilage surface, via the guiding hole of the 3D guide plate, under the guidance of C-arm fluoroscopy. If the preoperative plan necessitated only core decompression, the procedure was concluded at this stage. However, if mechanical support was indicated by the preoperative design, a specialized hollow reamer was employed to create a bone channel with a diameter of 10 millimeters, following the direction and depth specified by the guide needle, after which a tantalum rod was implanted. The entire procedure was conducted under C-arm fluoroscopic guidance.

Fig. 4.

Schematic diagram of operation procedure. (A) Operative position; (B) Core decompression under guide plate (green arrows indicate arthroscopic channel, red arrow indicate 3D printing guide, blue arrow indicate puncture needle); (C) Arthroscopy monitor the decompression process; (D–E) The fluoroscopic image shows that with the assistance of the guide plate, the guide pin and the hollow reamer were accurately inserted into the predetermined position according to the design; (F) The intraoperative fluoroscopic image shows the position of the tantalum rod.

Statistical analysis

Statistical analyses were conducted using GraphPad Prism 8.0 software. To compare two independent groups, an unpaired two-tailed Student’s t-test was utilized, as it is suitable for evaluating the significance of differences between two independent samples. Statistical significance was determined by the P -value, with P < 0.05 indicating statistical significance and P < 0.01 indicating high significance. Data are presented as means ± standard deviation (SD).

Result

Surgical results and complications

Six patients with early ONFH underwent the novel treatment strategy, demonstrating significant clinical improvement. All patients successfully completed the surgical procedure without postoperative complications such as infection, thrombosis, or prosthesis loosening during follow-up. Notably, Visual Analogue Scale (VAS) scores decreased markedly from preoperative baselines to 14 days post-surgery, while Harris Hip Scores (HHS) showed substantial improvement from preoperative to 3-month postoperative assessments (Figs. 5A and 6B).

Fig. 5.

Early Postoperative Outcomes. (A) Quantification of VAS scores from preoperative and postoperative, n = 6; (B) Quantification of HHS scores from preoperative and postoperative, n = 6;.

Fig. 6.

Postoperative evaluation. (A) Representative X-ray images of pre-operation (Pre-op) and post-operation. (B) Representative CT images of pre-operation and postoperative re-examination.

Postoperative evaluation and follow-up

The evaluation protocol incorporated standardized preoperative and postoperative hip radiographs. Figure 6A demonstrates the characteristic radiograph of the ONFH, which preserves the spherical nature of the femoral head without the typical crescentic markings, indicating an early collapse. Postoperative imaging confirmed decompression of the necrotic region and evident incorporation of the support graft. Follow-up CT scans at 3 years demonstrated significant anatomical structure preservation, including stable necrotic volume, absence of subchondral collapse, and reparative border mineralization density comparable to adjacent healthy bone (Fig. 6B). This radiographic stability correlated with Harris Hip Scores, indicating successful arrest of disease progression through surgical intervention.

Discussion

The clinical outcomes of early ONFH varied widely between different groups. Pakos et al. reported a 5-year femoral head survival rate of 93.1%, Varitimidis et al. found a 6-year femoral head survival rate of 70%, and even the Floerkemeier team reported a femoral head survival rate of only 44%^14–16. At present, there is no objective standard and basic research on the spatial position of the support in the necrotic area of the femoral head, so it is necessary to propose a standard treatment strategy for early ONFH. With the help of biomechanical simulation and FE analysis, we can objectively evaluate the structural changes of the femoral head, and further determine the surgery plan¹⁷. Meanwhile, the arthroscopic monitoring can effectively reduce the times of attempted puncture during surgery, avoiding the damage to the main stems of epiphyseal arteries and the lateral region of the epiphyseal arterial network¹⁸. A prospective, randomized trial demonstrated a correlation between the quantity of drilling and the incidence rate of secondary osteonecrosis^19–21. More importantly, we found that using the guide plate designed by 3D printing technology can reduce such iatrogenic injuries by placing the implant once. Likewise, the new strategy might be more effective in delaying ONFH, and it remains an interesting subject that should be further explored and studied.

At present, our team have the technical reserve of core decompression and support the implantation of femoral head under the supervision of hip arthroscopy. Our previous clinical studies also confirmed that establishing a direct monitoring channel could avoid iatrogenic injury and prevent the needle from penetrating the articular surface, effectively reducing the injury risk of blood supply to the femoral head during implant placement (Results were not published). Similarly, Mark R team also suggests that it is very important to ensure the safety and increase the success rate of core decompression by direct vision guide in the joint²². Hip arthroscopy can not only visually monitor the progress of surgery, but also examine the cartilage in the hip joint, help grade cartilage damage, and predict the possibility of secondary osteoarthritis after surgery²³. Even better, hip arthroscopy can be used to treat the inherent injuries of the hip, such as synovitis, labrum injury, bony impingement, etc²⁴. However, this technique has clear limitations: isolated arthroscopic intervention cannot restore the biomechanical integrity of collapsed bone structures, and its efficacy depends heavily on precise preoperative planning and accurate necrosis localization²⁵. Currently, hip arthroscopy for ONFH treatment remains investigational, often requiring a combination with core decompression and biomaterial implantation for comprehensive implementation²⁶. We can, therefore, conclude that the aid of arthroscopic vision during the core decompression of the femoral head has the advantage over the traditional technique in directly observing the cartilage and necrotic site, while also needs to be combined with other technologies in the precise and individualized treatment of ONFH to ensure the treatment effect.

As an important tool of computational biomechanics, finite element analysis shows a unique value in the diagnosis and treatment decision-making of ONFH^27,28. In particular, the finite element analysis established by the Sino-Japanese Friendship Hospital further reveals the mechanical significance of lateral column integrity in preventing femoral head collapse²⁹. In recent years, the development of this technique makes it possible to introduce biomechanical evaluation into the design of ONFH preoperative scheme, which can quantitatively analyze the abnormal stress distribution in the necrotic area by establishing a patient-specific 3D finite element model of the femoral head for evaluating the necessity of the support implantation, while simulate the improvement degree of trabecular stress shielding effect of different support positions to optimize the individualized surgical scheme design^13,30. Therefore, the application of 3D finite element analysis in preoperative planning would be of great significance for improving the biomechanical effectiveness of the support. Nonetheless, the inability to ensure consistency between computer simulations and intraoperative execution significantly in preoperative planning, most treatment strategies only apply this technology to the postoperative evaluation of ONFH, which is clearly a waste. In this study, we explore the design of the directional guide plate by combining the advantages of 3D printing, which ensures the accurate matching of the support and the preoperative planning position, and maximizes the advantages of mechanical evaluation of finite element analysis. As the technology matures, 3D printing has become easier to use, cheaper and more accessible, whose application research in orthopedics’ field accounting for more than half of the world³¹. It is worth noting that some research teams have applied 3D printing technology in femoral head decompression, which confirmed the feasibility of applying 3D printing technology to ONFH treatment⁹. In our work, by optimizing the digital processing of femoral head CT data and the guide plate sticking to the cortical curvature of bone, we can use 3D printing technology efficiently to realize the personalized and accurate positioning under the guide plate navigation, ensuring the accurate matching of the support and the preoperative planning position. This technology realizes FE analysis to preoperative planning guidance, practices the biomechanical treatment for early ONFH, ensuring the support efficiency of the implant and the improvement of the mechanical structure of the femoral head.

But that is only part of the research. The evaluation of the new strategy was limited by surgical cases and follow-up time, which can only reveal postoperative functional improvement and pain relief. Lacking comparative studies with traditional strategies, whether core decompression guided by the new strategy can significantly improve the outcome of ONFH is unclear. In future research, the sample size should be increased and relevant cohort studies should be promoted to further validate the value of the strategy.

Author contributions

Conceived and Designed the study, Y.W. and L.C.; Performed operation, L.C.; Software, Data Curation and Visualization, S.S. and Y.L.; Biomechanical finite element analysis and 3D printing, Z.W.; CT data standardization and analysis, H.W.; Analyzed the data, Y.W.; Provided advice and technical assistance, H.C., L.Z. and L.C.; Writing—Original Draft, Y.W.; Writing—Review & Editing, Y.W.; Supervision, L.C.; Project Administration, L.C.; Funding Acquisition, Y.W. and L.C.; All authors read and approved the final manuscript.

Funding

This work was funded by a grant from the Chongqing Medical Scientific Research Project (Joint project of Chongqing Health Commission and Science and Technology Bureau, 2024MSXM020), fundings for Postdoctoral Innovation Talents Support Program of Daping Hospital (ZXBSH016) and fundings for Scientific Research Project of Chongqing Sports Bureau (A202478).

Data availability

Data are available upon reasonable request to chenliang_dphospital@tmmu.edu.cn.

Declarations

Competing interests

The authors declare no competing interests.