Purpose: To assess the preoperative planning of visualized simulative surgery (VSS) and clinical outcomes based on computer-aided design (CAD) and 3D reconstruction for proximal femoral varus osteotomy of DDH. Methods: A total of 31 consecutive patients (23 females and 8 males) with DDH who underwent proximal femoral varus osteotomy were retrospectively reviewed between June 2014 and July 2018. Patients were divided into conventional group (n = 15) and VSS group (n = 16) according to different surgical methods. In VSS group, 16 consecutive patients who underwent proximal femoral varus osteotomy were evaluated preoperatively with the aid of VSS. The VSS steps included morphological evaluation of DDH, simulated reconstruction of proximal femoral varus osteotomy, and the implantation of locking compression pediatric hip plate (LCP-PHP). Meanwhile, the osteotomy degrees, surgery time, and radiation exposure were compared between the two groups. Results: The average follow-up time was 33.5 months (range, 24 to 46 months). The varus angle for proximal femoral varus osteotomy was 24.2 ± 1.1° in VSS group and 25.1 ± 1.0° in conventional group (P = 0.4974). The surgery time was 31.0 ± 4.5 mins in VSS group and 48.2 ± 7.3 mins in conventional group, while radiography was 5.0 ± 1.5 times in VSS group and 8.3 ± 2.4 times in conventional group. There was a statistical significance in surgery time and radiography (P < 0.0001) when compared with the conventional group. Conclusion: The VSS can greatly decrease surgery time and radiation exposure for proximal femoral varus osteotomy, which could also be a tool to train young doctors to improve surgical skills and academic communication.
Keywords: Developmental dysplasia of the hip; Visualized simulative surgery; Osteotomy; Computer-aided design; Three-dimensional reconstruction
Supplementary Information The online version contains supplementary material available at https://doi.org/10.1186/s12891-022-05219-7.
Proximal femoral varus osteotomy with locking compression pediatric hip plate (LCP-PHP; Synthes, Switzerland) is an effective surgical procedure for DDH, which could provide a stable and concentrical hip joint in children via decreasing excessive neck-shaft angle [[
Precise preoperative planning play a vital role in the field of orthopaedics, which can provide radiological evaluation and detailed information before surgery [[
Based on computer-aided design (CAD) and 3D reconstruction, the present study was aim to assess the clinical outcomes of VSS for preoperative planning for proximal femoral varus osteotomy of DDH.
A total of 31 consecutive patients (23 females and 8 males) with DDH who underwent proximal femoral varus osteotomy were retrospectively reviewed between June 2014 and July 2018. According to different surgical methods, 15 patients treated by proximal femoral varus osteotomy were divided into the conventional group in the initial period, then 16 patients treated by proximal femoral varus osteotomy with the aid of VSS technology were divided into VSS group. Meanwhile, hip subluxation or classified as Tönnis grade I was excluded in this study. We collected the CT and clinical data from medical image database in our hospital. Power calculation was used in all cases of two groups. The study protocol was approved by the Institutional Review Board of the authors' institution. Informed consent was obtained from all their parent before carrying out any research work. All methods were carried out in accordance with relevant guidelines and regulations for human.
The CT scanning data were input into Mimics 20.0 software (Materialise, Leuven, Belgium) for 3-D reconstruction, which could be useful to observe and analyze deformity of the proximal femur in all directions (Fig. 1). Next virtual surgical instrument bank was constructed using SolidWorks 2015 software (SolidWorks Corp) (Fig. 2). Using the VSS, proximal femoral varus osteotomy was performed for preoperative planning as follows (Fig. 3). The correction angles for varus and rotation were determined in the preoperative image evaluation according to the contralateral parameters (unilateral DDH) or normal parameters (bilateral DDH) in both the VSS and the conventional groups. After the digital model of the proximal femur was input onto a reverse engineering software Geomagic Studio by the format of STL, the desired neck-shaft angle was determined and varus rotation was designed via preoperative virtual surgical protocol formulation. Place one K-wire above the ventral surface of the femoral neck on the computer, which marks the anteversion of the femoral neck. Then apply the aiming block for screws with the help of the positioner for the aiming device. After that, the proximal femoral varus osteotomy with LCP-PHP was simulated as preoperative planning (Fig. 4). The whole procedure using the VSS was presented as animation (Video).
Graph: Fig. 1 The preoperative 3-D reconstruction for DDH. a The 3-D image of DDH was reconstructed via Mimics. b Observation and analysis of the abnormal femur in all directions
Graph: Fig. 2 Construct virtual surgical instrument bank. a Positioner for aiming device. b Aiming block. c Varus plate 3.5 mm 110°. d Kirschner wires and screws
Graph: Fig. 3 Flow diagram of visualized simulative surgery for proximal femoral varus osteotomy
Graph: Fig. 4 The VSS for preoperative planning of proximal femoral varus osteotomy. a Geomagic reverses reconstruction of DDH. b Place a 2.0 K-wire above the ventral surface of the femoral neck, which marks the anteversion of the femoral neck. c Apply the aiming block for 3.5 mm screws with help of the positioner for aiming device, in order to place the central guide wire approximately 10 mm distal to the physis of the greater trochanter. d Calculate the varus angle via Solidworks design software. e Simulate proximal femoral varus osteotomy. f The osteotomy was performed with LCP-PHP as preoperative planning
The proximal femoral varus osteotomy with LCP-PHP was performed by one senior orthopaedic surgeon in our department (Fig. 5). In VSS group, an experienced orthopaedic doctor performed simulated surgery on the computer preoperatively according to the DDH patients' condition. With the aid of VSS, the surgeon can calculate the varus angle and perform proximal femoral varus osteotomy precisely. For example, the desired rotation angle was 15° in femoral varus for concentric reduction between femoral head and acetabulum, which was designed by an experienced orthopaedic doctor via VSS. Meanwhile, the control group performed the proximal femoral varus osteotomy with freehand manner. The post-operative neck-shaft angle, surgery time, and radiation exposure were recorded. No significant difference in post-operative management procedures between the two groups. A hip spica cast was used for 8 weeks and a double lower limb brace with hip abduction for another 8 weeks. Moreover, radiographs were taken at 2, 4 and 6 months and then every year until skeletal maturity.
Graph: Fig. 5 Radiographs for proximal femoral varus osteotomy via VSS. a The preoperative anteroposterior radiograph indicated that bilateral DDH occurred in a 4-year-old girl. b The proximal femoral varus osteotomy with LCP-PHP was simulated via VSS preoperatively. c The 3-D image of pelvis and femur were reconstructed via Mimics on the first postoperative day. d The post-operative radiograph showed anatomical correction and good appearance at 13 months of follow-up
The data in this study were statistically analyzed via SPSS 25.0 software (SPSS, Inc., Chicago, USA) and manifested as count (percentage) or mean ± standard deviation (SD). Student's t-test, chi-squared test, and Fisher's exact test were also used. Different parameters measured between two groups were assessed with an independent t-test for continuous variables, and a chi-square test or Fisher's exact test for the categorical variables. P < 0.05 was considered to be statistically significant.
The average follow-up time was 33.5 months (range, 24 to 46 months). In VSS group, post-operative radiographs showed excellent results at the final follow-up. On the first postoperative day, the varus angle for proximal femoral varus osteotomy was 24.2 ± 1.1° in VSS group and 25.1 ± 1.0° in conventional group (P = 0.4974). The surgery time was 31.0 ± 4.5 mins in VSS group and 48.2 ± 7.3 mins in conventional group, while radiography was 5.0 ± 1.5 times in VSS group and 8.3 ± 2.4 times in conventional group. One case suffered with epiphyseal growth plate violation by the implant in conventional group. There was a statistical significance in surgery time and radiography (P < 0.0001) when compared with the conventional group (Table 1). It is proved that the sample size of the two groups was sufficient when the Power calculation greater than 0.9.
Table 1 Comparison of operation data and functional outcomes
Conventional group ( VSS group ( Power calculation Osteotomy degrees, ° 25.1 ± 1.0° 24.2 ± 1.1° 0.4974 0.63740 Surgery time, mins 48.2 ± 7.3 31.0 ± 4.5 < 0.0001 1.00000 Radiography, times 8.3 ± 2.4 5.0 ± 1.5 < 0.0001 0.99205 McKay standard, n (%) 0.1441 Excellent 8 14 Good 4 1 Fair 1 1 Poor 2 0
It is proved that the sample size of the two groups was sufficient when the Power calculation greater than 0.9
Based on the McKay criteria [[
The goal of ideal corrective surgery for DDH in children is to achieve concentric reduction of the hip and avoid avascular necrosis (AVN), which is a technical challenge for orthopaedic surgeons [[
With the development of orthopaedic instruments, LCP-PHP has become widely used to reach a more precise angular correction with locking screws [[
Various navigation templates using 3D printing technology have been applied for the treatment of DDH in children, however, more bone markers are needed to increase the degree of fitting and the stability of the plate [[
Nevertheless, there were some limitations in the present study. First, more cases are required to evaluate the accuracy and efficacy of VSS for DDH because no significant difference was demonstrated for clinical outcomes or correction angle between the VSS and conventional groups. Besides, simulated operation on the 3D printing model or patient-specific instrument should be performed in future studies, which could increase its clinical value in orthopaedics surgery. Second, discrepancy in the collection angles between the preoperative planning and postoperative CT measurement and comparison of the epiphyseal growth plate violation rate between the groups should be included in the comparative analysis. Third, the femoral anteversion angle was also crucial for proximal femoral varus osteotomy and it would be better to present the data of the femoral anteversion angle before and after surgery during the VSS surgery. Meanwhile, the VSS could not be only used for proximal femoral varus osteotomy, the pelvic osteotomy or other pediatric hip diseases will also be taken into account to assess the VSS's effect in our following study.
The VSS based on CAD and 3D reconstruction can greatly decrease surgery time and radiation exposure for proximal femoral varus osteotomy, which could also be a tool to train young doctors to improve surgical skills and academic communication.
The authors would like to thank all the participating patients.
RD and QS were responsible for the conception and design of the study. RD and HG analyzed the data. WZ wrote and revised the paper. All authors contributed to the interpretation of the results and critical revision of the manuscript for important intellectual content. All authors have read and approved the final manuscript.
This study was supported by the Fundamental Research Funds for the Central Universities of Central South University (grant numbers 2019zzts900).
The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.
The Ethics Committee of Xiangya Hospital, Central South University approved the research proposal (IRB: 2019030517). Informed consent was obtained from all their parent before carrying out any research work. All methods were carried out in accordance with relevant guidelines and regulations for humans.
Not applicable.
The authors declare that they have no competing interests.
Graph: Additional file 1.
• VSS
- Visualized simulative surgery
• CAD
- Computer-aided design
• AVN
- Avascular necrosis
• LCP-PHP
- Locking compression pediatric hip plate
• DDH
- Developmental dysplasia of the hip
• 3D
- Three-dimensional
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By Wen Zhou; Haoyu Guo; Rongjie Duan and Qiang Shi
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