Application of 3D-printed osteotomy guide plates in proximal femoral osteotomy for DDH in children: a retrospective study

Hip dysplasia, subluxation and complete dislocation are some of the hip deformities included in developmental dysplasia of the hip (DDH), a common developmental deformity of the hip in infants and children [1, 2]. Patients often have structural changes in the soft tissues, cartilage and bone of the hip joint [3]. Delayed diagnosis and treatment will eventually lead to adverse outcomes such as hip osteoarthritis and femoral head avascular necrosis. Children's hip joints still have some potential for development [4]. Open reduction, pelvic osteotomy combined with proximal femoral derotation, and varus/shortening osteotomy are often used as standard treatment for children with DDH who are ineffective in conservative treatment or late diagnosis [5].

The hip joint has a complicated anatomy, and the patient's hip joint has varying degrees of deformity. The only way to ensure a precise osteotomy during surgery to achieve good coverage after acetabular rotation and accurate correction of femoral derotation, varus and shortening osteotomies is to fully understand the degree of deformity before surgery and to formulate a precise surgical plan. Conventional surgery is planned preoperatively by assessing the severity of the deformity with preoperative pelvic and femoral radiographs or CT scans. During surgery, the osteotomy is performed under C-arm fluoroscopy using anatomical markers. The surgical outcome depends on the experience of the surgeon. Gallien et al. conducted a clinical and radiological study of the surgical outcome of 39 patients (43 hips) treated for congenital hip dislocation using open reduction combined with osteotomy and found that even experienced operator did not ensure the desired surgical outcome (18% failure rate) [6]. There is therefore an urgent need for more accurate and tailored treatment for children with DDH.

The use of 3D-printed technology in orthopedic clinics is becoming increasingly popular as a result of rapid advances in computer science and imaging technology. This has had a significant impact on how orthopedic diagnoses and treatments are now carried out. Research has shown that the use of 3D-printed surgical navigation template can help orthopedic patients to receive tailored and precise surgical care [7, 8]. Before surgery, three-dimensional software was used to create a precise surgical plan and intuitively understand the deformity. The design of the guide plates is carried out in the 3D editing software according to the proposed preoperative plan, and the 3D printer is used to obtain the entity of the guide plates to be used intraoperatively. The surgeon simply needs to locate the bone marker fixed navigation template according to the preoperative plan; using the template as a guide, the surgeon can then choose the direction, angle and depth of the osteotomy or screw placement. Using this simple procedure, surgery precision is greatly improved, and operation time is reduced. However, there are very few reports of this technique being used to surgically treat children with DDH. This study aims to compare the application benefits of proximal femoral osteotomy between 3D-printed guide-assisted and traditional surgical therapy in children with DDH, in conjunction with clinical practice, and to assess its clinical application value by collecting patient data.

All 36 patients underwent open reduction, Salter pelvic osteotomy combined with proximal femoral derotation, and varus/shortening osteotomy satisfactorily. The surgical incisions healed in the first stage. Both the femoral osteotomy and pelvic bone graft sites recovered. During the follow-up period, no problems such as femoral head avascular necrosis, joint stiffness, or redislocation were discovered.

Preoperative neck-shaft angle (P = 0.429), preoperative anteversion (P = 0.266), follow-up time (P = 0.152), gender (P = 0.613), side (P = 0.731), Tönnis classification (P = 0.650) and age (P = 0.538) were not significantly different between the two groups (Table 1).

The results of the comparison of intraoperative observation indexes between the two groups were as follows: the operation time (total) of the guide plate group was shorter than that of the conventional group, 2.12 ± 0.13 h in the guide plate group and 2.69 ± 0.10 h in the conventional group, with a statistically significant difference between the two groups (t =  − 14.605, P < 0.001). The operation time (femoral side) was shorter in the guide plate group than in the conventional group, 0.39 ± 0.08 h in the guide plate group and 0.70 ± 0.08 h in the conventional group, with a statistically significant difference between the two groups (t =  − 11.635, P < 0.001). The X-ray fluoroscopy times (total) in the guide plate group were less than those in the conventional group, 4.50 ± 1.03 times in the guide plate group and 8.70 ± 1.03 times in the conventional group, and the difference between the two groups was statistically significant (t =  − 12.136, P < 0.001). The X-ray fluoroscopy times (femoral side) in the guide plate group were less than those in the conventional group, 2.56 ± 0.96 times in the guide plate group and 6.40 ± 0.99 times in the conventional group. The difference between the two groups was statistically significant (t =  − 11.660, P < 0.001). The intraoperative blood loss of the guide plate group was smaller than that of the conventional group. The guide plate group was 301.75 ± 31.61 ml, and the conventional group was 370.95 ± 35.82 ml. The difference between the two groups was statistically significant (t =  − 6.063, P < 0.001).

There was no significant difference between the guide plate group and the conventional group in postoperative neck-shaft angle (guide plate group: 121.31 ± 2.27°, conventional group: 122.41 ± 1.94°, t =  − 1.558, P = 0.129), postoperative anteversion angle (guide plate group: 15.68 ± 0.97°, conventional group: 16.03 ± 0.73°, t =  − 1.233, P = 0.226), hospitalization time (guide plate group: 12.25 ± 1.69 days, conventional group: 12.00 ± 2.00 days, t = 0.398, P = 0.693), hospitalization expenses (guide plate group: 28,817.06 ± 1645.26 yuan, conventional group: 29,586.75 ± 2038.49 yuan, t =  − 1.224, P = 0.229). At the last follow-up, the results of the Mackay clinical evaluation showed that 9 patients in the guide plate group were excellent, 5 patients were good, and 2 patients were fair; 9 patients in the conventional group were excellent, 7 patients were good, and 4 patients were fair. There was no significant difference (P = 0.742) between the two groups (Table 2).

DDH is a common hip deformity. Open reduction and pelvic osteotomy are performed to treat this disease, but often lead to complications such as avascular necrosis of the femoral head, redislocation and joint contracture [12, 13]. Clinical studies of combined proximal femoral osteotomy have been conducted by several scholars and have shown that femoral osteotomy significantly reduces the incidence of these complications [14‐16].

However, proximal femoral deformities are usually complicated. Inadequate preoperative recognition of the deformity or inappropriate osteotomy can lead to complications such as non-union of the osteotomized segment, changes in the eccentric distance of the femur and postoperative redislocation [17]. Traditional surgical procedures are challenging, and the technical requirements are high, for the osteotomy of complicated bone abnormalities or complex bone anatomical features. According to experience, the surgeon can typically only make basic preoperative measurements and execute intraoperative osteotomies. Guaranteeing the osteotomy effect is not only arduous and time-consuming but also challenging [18, 19]. In a follow-up study of 55 children with DDH who presented with postoperative redislocation, Tang Chenglin et al. found that 13 cases were caused by the failure to correct the femoral deformity as expected [20]. A femoral varus osteotomy will reduce the femur's length. Both lower limbs may not be the same length in older patients because they have weaker adjustment abilities than younger patients. According to a study by Umer et al. [21], patients younger than 5 to 6 years old had better clinical results than older patients. This is also the most common complication of femoral shortening osteotomy. The long-term existence of unequal lower limbs will cause abnormal gait in patients, which will further lead to adverse consequences such as pelvic tilt, scoliosis and low back pain [22].

The outcome of an osteotomy is influenced by the patient's quality of life and even their prognosis. Because of the complexity of the lower limb structure, various planes and dimensions are frequently affected by the malformation. Surgery relies on the surgeon's subjective judgment, which can easily result in intraoperative osteotomy angle, placement and direction decision-making errors that compromise the precision and safety of the procedure. The maximum benefit can only be ensured by thoroughly understanding the deformity's features, conducting thorough preoperative planning, and carrying out the operation following the anticipated plan. Clinical orthopedics faces a significant issue in figuring out how to implement osteotomy with precision, individualization and standardization.

Computer-assisted design has become a significant component of digital medicine because of the advancement of computer technology. We can review CT data on a personal computer and reconstruct it in various windows and perspectives with the aid of computer-assisted design technologies. Realize the measurement of length and angle in three dimensions; plan and simulate surgery before the procedure; build an internal plant and an osteotomy guide plate, among other things. The advancement of this technology in orthopedics allows the surgeon to create individualized and accurate osteotomy plans and perform three-dimensional reconstruction, accurate measurement, and simulated surgery on the patient's skeletal lesion site [23]. With the aid of 3D printed technology, the CT scan data enable the actual model to be made and the physical model created is extremely accurate [24, 25]. 3D printing offers a novel technique and concept for individualized, accurate and standardized orthopedic therapy [26‐28].

The design and 3D printing of osteotomy guide plates are beneficial for carrying out the established procedure accurately, conveniently, and with the least amount of intrusion possible. The traditional orthopedic osteotomy procedure is challenging. It is frequently only finished by senior doctors, even in big tertiary hospitals. The learning curve for this kind of surgery is too high for junior doctors with limited training. In comparison with conventional surgery, the use of osteotomy guide plates improves surgical outcomes while also lowering the operating threshold, making orthopedic osteotomy easier for junior surgeons to learn and use. The steps of the procedure can be made simpler, and the procedure time reduced by using the 3D-printed osteotomy guide plates. Honigmann et al. performed guide plates and conventional osteotomy in patients with wedge osteotomy of distal radius. The average operation time was 60 min in the 3D printing group compared to 90 min in the conventional group [29]. Our study found that 3D-printed guides significantly reduced operative time, decreased bleeding and lowered radiation exposure, but there was no statistically significant difference between the two groups in terms of postoperative measurements and evaluation at follow-up. This result may be due to the small sample size of the study, and we will next observe this result in a large-scale randomized controlled trial.

3D printing technology has a lower barrier to application compared to other new orthopedic technologies. The CT image data required for the design of the guide plates are available at all levels of hospital. Even in remote areas and primary care institutions, the design and printing of surgical guides can be commissioned from third-party companies to assist in traditionally difficult orthopedic operations, which not only benefits patients, but also helps to equalize medical resources and conditions. A novel approach to performing osteotomies is offered by computer-aided design, and 3D-printed osteotomy guide plates have a lot of application prospects.

Although the advantages of the application of the guide plates have been recognized by clinical practice, the number of large hospitals where this technology is widely available is also in the minority. The reasons for this are the lack of awareness of the technology among doctors, the lack of policies and the increase in medical costs. Brief clinical surveys have shown that even though 3D printing technology has been proven, most surgeons do not have a proper understanding of it. Some senior surgeons believe that they are too skilled to use other tools to demonstrate their profound surgical skills; some young surgeons consider this technology so advanced that it cannot be applied casually; and only a few surgeons who truly understand 3D printing have made this technology their right-hand man and promoted the development of this technology. Therefore, there is a great need to strengthen the popularization of 3D printing technology and unravel its mystery with the help of successful clinical cases, so that it can actually provide convenience for clinical practice. China identified 3D printing technology as an emerging strategic industry in 2013 and introduced several supporting policies to provide policy assurance for the application of 3D printing technology in clinical practice. Unfortunately, the corresponding medical service charges and medical insurance payment standards are extremely irregular. Only some provinces in the country have announced the fees for 3D printing medical services, but the specific names of the fees set by these provinces and the scope of implementation vary greatly and are not complete; many provinces lack corresponding fees. We believe that with the support of national policies and through the preliminary exploration of some provinces, the formulation of relevant policies and fee standards will become more and more perfect and unified. In our study, the design and printing of the guides took approximately 10 h. Although our study did not provide a clear figure for the cost, we roughly arrived at a price of approximately RMB 2,500 (approximately US$360) for the guides needed in our study, based on our calculations of labor, time and printing. The difference of hospitalization expenses between the two groups in our study was not statistically significant, since the guide plates were not designed and used at the corresponding cost to the patients. However, there was a significant advantage in the guide plate group in terms of shorter operative time and reduced bleeding, patients had less to spend on anesthesia, blood transfusions, C-arm photography, etc. Patients in the guide plate group had slightly lower costs than those in the conventional group, and by reducing the number of C-arms taken the patients had less exposure to radiation of medical origin, which would also benefit the patients. As national policies improve and 3D printing technology and equipment become more widespread, we believe that the cost of the guides will certainly drop significantly soon. In the meantime, we are working on developing an intelligent design and printing software for the guides, which will facilitate the promotion of this technology and reduce the cost.

Orthopedic surgeons attach great significance to the restoration of the lower limb alignment in the management of knee deformities and total knee arthroplasty, as it is essential for improving patients' symptoms and achieving surgical outcome. However, few reports have been published on preoperative and postoperative lower limb alignment changes in children with DDH, particularly in children in subluxation and complete dislocation, where the lower limb alignment is significantly shifted. The lower limb alignment also changes with the position of the femoral head after proximal femoral varus, which theoretically shifts the alignment inward. The LCP-PHP is used to fix the distal and proximal femur after osteotomy. It allows for a certain distance of outward movement of the proximal femur for force line recovery, as shown in Fig. 3, with two parallel lines a and b parallel to the femoral shaft at points A and B. The distance between the parallel lines a and b is the maximum distance of outward movement of the proximal femur. However, the distance that the proximal femur needs to be moved is different for children of different heights and different angles of proximal varus. The LCP-PHP is manufactured by the instrumentation company and cannot be used for personalized fixation. Theoretically, the distance of outward movement of the plate may be too large or too small for some patients. At the same time, the proximal plate is parallel to the femoral shaft. When the proximal femur is inwardly turned the proximal femoral cortex forms an angle with the proximal LCP-PHP and does not adhere well to the plate (Fig. 4). Tightening the plate proximal locking screw can easily pull the proximal femoral cortex toward the plate, which results in the loss of the required angle of varus for correction. Therefore, the same size of LCP-PHP currently used still has some shortcomings for clinical application. We will be investigating this issue with the aim of designing a customized and individualized plate and further validating its clinical value.

However, there are several shortcomings and problems in our study that still need to be resolved. (1) The follow-up period is brief; as avascular necrosis of the femoral head following surgery may not emerge for several years, the experimental results cannot accurately reflect the problems and long-term operation effects of the guide plate group and the conventional group. (2) Only the femoral side of the guide plate application is used in children who have improved postoperative hip function; the pelvic osteotomy effect is also important to note. The surgeon in this therapy group has extensive clinical expertise and has executed almost 100 pelvic osteotomies. The findings of this study also imply that there is no appreciable distinction between the conventional group and the guide plate group in terms of how femoral osteotomy affects them. Even yet, it is possible to underestimate the guide plate's application effect, and the use of the osteotomy guide plate during femoral and pelvic osteotomies may have distinct clinical outcomes. (3) Since the study was retrospective in nature, the reliability of the data is not as strong as it would be in a randomized controlled trial. For further confirmation, a large sample or multicenter randomized controlled trial is required.

This study showed that 3D-printed osteotomy guide plates supporting proximal femoral osteotomy in children with DDH have the benefits of an uncomplicated operation, decreased operation time, reduced blood loss and intraoperative radiation exposure, and high clinical application value. The development of the 3D-printed guide plates and the advantages of its intraoperative use are comparable across all types and levels of difficulty, despite the reality that we only reviewed one orthopedic operation. Therefore, computer-aided design and 3D-printed technologies have broad therapeutic applications and can be used for other challenging surgeries.