Acetabular reconstruction has always been one of the difficulties in THA for Crowe type II and III DDH patients, because there is often large bone defect in the superolateral acetabulum during acetabular reconstruction in Crowe type II and III DDH patients, which makes it impossible to stabilize the standard hemispheroid cup(19). Structural autograft with a bulk femoral head is a good choice for reconstructing the acetabulum in Crowe type II and III DDH. Metal screws are used to fix bone graft, which not only ensure the stability of the acetabular cup, but also increase the bone reserve, so that the acetabular cup prosthesis bone ingrowth can achieve biological fixation(20).
Titanium alloy screws are often used in the fixation of bone graft in the superolateral acetabulum, which has satisfactory mechanical strength and exact fixation effect. However, due to the large difference between its elastic modulus and bone tissue, stress shielding often exists, especially when the bone graft does not heal or the bone graft is absorbed, and the titanium alloy screws need to be removed by a second operation (21). Some researchers have developed internal fixation devices made of high-purity magnesium, which has an elastic modulus close to that of bone tissue. In clinical applications, these devices have demonstrated stable mechanical performance and excellent biocompatibility (22). Huang et al. (23) achieved favorable clinical outcomes by utilizing pure magnesium screws for fixing bone grafts in the reconstruction of DDH acetabulum. Moreover, pure magnesium screws promote bone growth after degradation, facilitating the healing between the transplanted bone and the acetabular bone without the need for a second surgery for removal(24). In this study, we also found that the application of degradable high purity magnesium screws to fix bone grafts can effectively repair bone defects in Crowe type II and III DDH acetabulum, and the early clinical outcomes are satisfactory. However, the structural bone grafting still faces challenges, such as the inability of bone graft in terms of shape and size to meet the requirements of the acetabular bone defect area.
In recent years, with the application of 3D printing technology in orthopedic surgery, personalized precision treatment has provided new ideas for the reconstruction of acetabular bone defects(25). To design an IAP based on the size and shape of the acetabular bone defect in Crowe type II and III DDH using 3D printing technology, which can not only restore the center of rotation of the acetabulum, ensure the integrity of the acetabulum, but also reduce micro-movement and friction between multi-component fixation, and improve the long-term stability of the acetabular prosthesis. Zhang et al. (26) reported a case of Crowe type III DDH patient undergoing acetabular reconstruction using a 3D-printed IAP, with favorable short-term follow-up results. However, the limited number of reported cases in this study restricts the assessment of the effectiveness of 3D printed IAP in DDH acetabular reconstruction.
This study retrospectively analyzed 45 patients in our hospital who underwent acetabular reconstruction using either IAP or BG for Crowe type II and III DDH. Objective to compare the clinical and radiological outcomes of the two techniques for repairing acetabular bone defects associated with Crowe type II and III DDH.
In terms of clinical outcomes, there was no significant difference in HHS between the two groups at the last follow-up (P > 0.05), indicating that the two groups achieved consistent long-term clinical results. However, group A exhibited shorter surgical times and lower intraoperative blood loss compared to group B (Fig. 5A, B). This is because the structural autograft with a bulk femoral head involves intraoperative adjustment of graft bone, which extends the surgical time. The prolonged surgical time results in increased bleeding from the bone wound, and the intraoperative adjustment of the need for bone graft resulits in increased bleeding and trauma in the bone harvesting area. These factors account for the higher intraoperative blood loss associated with structural bone grafting. In contrast, the IAP, due to its preoperative personalized design using 3D printing technology, can perfectly match the acetabular bone defects in DDH patients. It simplifies the surgical procedures, shortens the surgical time, reduces intraoperative blood loss, and enhances the safety of the procedure. Furthermore, research indicates that early weight-bearing, while ensuring initial stability of the prosthesis, contributes to the recovery of hip joint function and reduces the occurrence of postoperative complications (27). Structural bone grafting takes time for the transplanted bone to heal. Premature weight-bearing may increase the risk of graft collapse, delaying the healing process. Patients undergoing this technique may need to avoid full weight-bearing postoperatively, leading to a longer recovery period (28). On the other hand, the 3D printed IAP is designed to closely match the height and close contact with the acetabular bone surface. This method ensures a better anatomical fit with the patient's hip joint structure and allows for improved biomechanical compatibility with the human body. Therefore, early weight-bearing is more advisable with these prostheses, as it can help restore hip joint function (29). From our study, it is clear that the IAP had a shorter full weight-bearing time than the BG(Fig. 5C). Additionally, HHS at 1 and 3 months postoperatively was higher in IAP compared to BG (Fig. 5D). Therefore, compared to BG, the use of IAP for acetabular reconstruction accelerates the recovery of hip joint function after THA, thus enhancing the overall quality of life for patients.
In this study, all patients achieved satisfactory radiological outcomes. Firstly, the proper placement and adequate coverage of the acetabular prosthesis on the acetabular bone were crucial to achieving favorable postoperative results. This ensured the biomechanical stability of the acetabular prosthesis, reducing the risk of cup loosening. Secondly, The COR had a significant impact on the hip biomechanics, which was crucial for the long-term survival of the hip joint and the restoration of LLD in the hip joint (30). Therefore, restoring a relatively normal COR was also a primary goal in the reconstruction of the Crowe type II and III DDH acetabulum. The ideal COR, V-COR is about 14–20 mm, and H-COR is about 15–38 mm (31). From the radiographic results, in this study, there was no significant difference in V-COR and H-COR, and both were within the range of the ideal hip joint rotation center, essentially restoring the biomechanical characteristics of a normal hip joint. Furthermore, in patients with DDH undergoing THA, LLD is also another serious problem. Restoring equal limb lengths not only alleviates pelvic and spinal tilt, reduces symptoms such as lower back pain and limping, thereby improving patient satisfaction with the surgery, but also reduces the occurrence of aseptic loosening of the prosthesis, increasing the lifespan of the implant, which is highly beneficial for patients (32). According to the report by Nossa et al. (33), postoperative LLD in the range of 0–1 cm is acceptable and does not adversely affect the subjective perception and clinical functional recovery of patients. In our study, the LLD values at the last follow-up were 3.0 ± 2.1 mm and 3.1 ± 2.7 mm for both groups, both less than 1 cm. Patients in both groups had normal gait after surgery, and there were no complaints of perceived LLD. Based on these results, it was evident that the COR and LLD in both reconstruction groups were restored to the ideal state. However, this study has some limitations. Firstly, the number of cases in this study is small, and there is no long-term follow-up, so the long-term clinical effect needs to be further observed. Secondly, this study is a retrospective summary, which is subject to selection bias, and evidence from prospective, randomized, controlled studies is still needed.
In summary, the application of 3D printed IAP in the reconstruction of the acetabulum for Crowe type II and III DDH patients exhibits radiological outcomes and long-term clinical efficacy consistent with BG. Moreover, it offers higher surgical safety and faster functional recovery of the hip joint after surgery. This approach holds promising prospects for reliable clinical application in the reconstruction of Crowe type II and III DDH acetabulum.