General Information
A retrospective case analysis was conducted, involving 70 patients with DDH who were admitted to the Department of Orthopedics at Shenyang Medical College Affiliated Central Hospital from March 2017 to June 2020. All patients were clinically diagnosed with and confirmed to have Type III DDH. Ultimately, 52 patients meeting the inclusion criteria were included in the study.
The group treated with individualized spacer prostheses and acetabular prostheses using 3D printing is referred to as the "3D group" (26 cases), while the group treated with autologous femoral head structural bone grafting and traditional acetabular prostheses is referred to as the "Non-3D group" (26 cases). Please refer to Figure 1 for the study flowchart. All patients exhibited positive signs of the "4" sign and Trendelenburg sign, accompanied by significant limping gait and notable hip joint pain on the affected side, with incomplete dislocation of the femoral head.
The study obtained approval from the relevant medical ethics department at Shenyang Medical College Affiliated Central Hospital. All patients were informed about the study and provided voluntary consent to participate by signing an informed consent form.
Inclusion Criteria
(1) Patients with Crowe Type III DDH presenting with hip joint pain accompanied by limping gait and poor response to various conservative treatments; (2) Patients undergoing primary unilateral hip joint replacement; (3) Absence of coagulation dysfunction and other high-risk bleeding factors before surgery; (4) Presence of acetabular bone defects, managed intraoperatively with customized spacer prostheses or conventional autologous femoral head structural bone grafting.
Exclusion Criteria
(1) Patients with severe liver or kidney dysfunction, cerebrovascular accidents, or other contraindications for THA; (2) Patients with bilateral DDH.
Preoperative Patient Preparation and Management
Comprehensive preoperative examinations were conducted for all patients. Bilateral hip joint anteroposterior X-ray, bilateral full-length lower limb anteroposterior and lateral X-ray images were obtained (using the digital radiography (DR) system from Philips in the Netherlands). Additionally, bilateral hip joint CT scans with 3D reconstruction were performed (using the 256-slice spiral CT scanner from Philips in the Netherlands, with a scanning layer thickness of 0.6mm). Measurements included assessment of lower limb length discrepancy, distance from the femoral head rotation center to the teardrop horizontal and vertical distances (following the method described by Russotti et al. 11), evaluation of acetabular wall thickness, acetabular bone mass, and proximal femoral canal narrowing.
For the 3D group, CT data were used for virtual simulation, calculation, design, 3D model printing, and customization of individualized spacer prostheses.
Customization of Individualized Spacer Prostheses
The CT imaging data of bilateral hip joints of the patient (Figure 2A) were imported into Mimics 20.0 software (Materialise, Belgium) workstation in DICOM format for three-dimensional modeling (Figure 2B). Through a collaborative effort between engineers and surgical physicians, the true acetabular position and acetabular cup model for the prosthesis were calculated (Figure 3A). Parameters such as bone defect shape, size, etc., were measured, and the model of the spacer prosthesis was designed, followed by determining the placement position of the spacer prosthesis (Figures 3B and 3C) and selecting the femoral prosthesis model (Figure 3D).
Subsequently, the data from three-dimensional modeling and virtual design were exported in STL format and imported into FlashPrint 5 software (FlashForge Technology, China). The 3D models of the original hip joint, the hip joint after virtual design, and the spacer prosthesis were printed using PLA (polylactic acid) as the printing material (Figure 4) to conduct preoperative simulation and demonstrate the surgery.
Engineers utilize the EBM Q10 plus software (Acram AB, Sweden) to print personalized trabecular bone spacers designed with Ti-6Al-4V as the raw material (Figures 5A and 5B). The acetabular prosthesis (Figure 5C and 5D) used in surgery is also a 3D-printed trabecular bone structure. Detailed inspection and sterilization are required.
The personalized spacer prostheses printed need to be sent to a specialized quality inspection department for assessment, including strength, compression resistance, tensile strength, and fatigue resistance, among other aspects. Only spacer prostheses that pass the quality inspection can be put into use.
Surgical Procedure and Brief Process for the 3D Group
After the anesthesia takes effect, the patient is positioned on the lateral side (Figure 6A). A posterior lateral approach is utilized, and layer-by-layer dissection is performed. The external rotator muscle group is severed at the greater trochanter, and the joint capsule is detached. The hip joint is dislocated, and the femoral neck is cut approximately 1.5 cm above the lesser trochanter to remove the femoral head. Utilizing three-dimensional modeling and 3D models, the original acetabulum is identified along the inferior and inner aspect of the dislocated femoral head, and progressive clearing, excision of the acetabular labrum, and removal of proliferative tissue are performed. The acetabulum is reamed at the predetermined position and direction, and a new acetabulum is created at the true acetabular position (Figure 6B). After achieving the design effect, a trial reduction of the acetabular prosthesis is performed. Following this, the original acetabulum is reamed at the site of bone defect above the true acetabulum according to the designed position, direction, and acetabular reaming size (Figure 6B). Then, the spacer prosthesis trial is inserted. Subsequently, the individualized spacer prosthesis is installed and secured with screws. Bone cement is applied appropriately at the interface between the spacer prosthesis and the acetabular prosthesis before inserting the acetabular prosthesis and securing it with screws (Figure 6C). After placing the femoral side prosthesis, the hip joint is reduced. During reduction, stability, range of motion, tension of the sciatic nerve, and blood vessel tension are checked. If tension is significant, the soft tissues around the hip joint are moderately released. The incision is closed layer by layer.
Postoperative Management
Routine measures are taken to prevent infection and anticoagulation is administered postoperatively. The affected limb is maintained in neutral abduction and extension position after surgery. On the first postoperative day, follow-up X-rays of both hips in the anteroposterior and lateral views, along with full-length anteroposterior and lateral views of both lower limbs are obtained (Figure 6D). Passive and active exercises are initiated for the affected limb to improve quadriceps muscle strength and prevent joint dislocation. For the 3D group, standing and walking with assistance may be initiated on the first postoperative day after the follow-up examination. For the Non-3D group, crutch-assisted ambulation is recommended for the first week postoperatively, followed by full weight-bearing at 4-8 weeks after the follow-up examination.
Main Observational Indicators
(1) Radiological Evaluation: Preoperative and postoperative X-rays were taken on the first day, recording the pre- and postoperative differences in leg length between the two groups of patients; comparing the pre- and postoperative distances from the femoral head center to the teardrop level and vertically 11; comparing the acetabular cup anteversion angles between the two groups of patients; comparing the acetabular cup coverage rates between the two groups of patients on the first day postoperatively and at 3 months postoperatively 12.
(2) Surgical Evaluation: Comparing the surgical times between the two groups of patients: from the start of skin incision to closure of the surgical incision; intraoperative blood loss: the sum of blood collected by suction and absorbed by gauze; time to ambulation after surgery: the time from completion of surgery to the first standing from bed by the patient; time to discharge after surgery: the time from surgery completion to the patient leaving the hospital.
(3) Functional and Complication Evaluation: Recording the Harris hip function scores before treatment, at 3 months, 6 months, and 12 months postoperatively; recording complications at 3 months postoperatively. Subsequent annual follow-ups included bilateral hip X-rays to observe for dislocation, infection, nerve damage, bone resorption, and implant loosening.
Statistical Analysis
Statistical analysis was conducted using SPSS version 27.0 software. Descriptive statistics were employed to calculate the means and standard deviations for continuous variables, and frequencies for categorical variables. The Shapiro-Wilk test was used to assess normality for continuous variables, while the chi-square test was utilized for categorical variables. Quantitative data were analyzed using both independent samples t-tests and Mann-Whitney U tests. The level of statistical significance was set at p < 0.05.