Objective To develop a new method to restore hip rotation center exactly and rapidly in total hip arthroplasty (THA) with the assistance of three dimensional (3D) printing technology and evaluate its clinical and radiological outcomes. Methods From March 2014 to July 2018, a total of 17 patients (five hips of four men and 16 hips of 13 women) with end‐stage osteoarthritis secondary to developmental dysplasia of the hip who underwent THA were analyzed and followed up retrospectively. The average age is 58.00 ± 8.12 years (range from 45 to 71 years). Simulated operations were performed on 3D printed hip models for preoperative planning. The morphology of Harris fossa and acetabular notches were recognized and restored to locate the acetabular center. The size of bone defect was measured by the bone wax method. The agreement on the size of acetabular cup and bone defect between simulated operations and actual operations were analyzed. Harris Hip Score (HHS) was used to evaluate the recovery of hip joint function. The vertical distance and horizontal distance of the rotation center on the pelvis plain radiograph were measured, which were used to assess the efficacy of restoring hip rotation center and acetabular cup migration. Results The mean sizes of bone defect in simulated operations and THA were 4.58 ± 2.47 cm2 and 4.55 ± 2.57 cm2 respectively. There was no significant difference statistically between the sizes of bone defect in simulated operations and the actual sizes of bone defect in THA (t = 0.03, P = 0.97). The sizes of the acetabular cup of simulated operations on 3D print models showed a high rate of coincidence with the actual sizes in the operations (ICC = 0.93). All 17 patients were available for clinical and radiological follow‐up. The average follow‐up time was 18.35 ± 6.86 months (range, 12–36 months. The average HHS of the patients was improved from (38.33 ± 6.07) preoperatively to the last follow‐up (88.61 ± 3.44) postoperatively. The mean vertical and horizontal distances of hip rotation center on the pelvic radiographs were restored to 15.12 ± 1.25 mm and 32.49 ± 2.83 mm respectively. No case presented dislocation or radiological signs of loosening until last follow‐up. Conclusions The application of 3D printing technology facilitates orthopedists to recognize the morphology of Harris fossa and acetabular notches, locate the acetabular center and restore the hip rotation center rapidly and accurately.

BackgroundThe acetabular pathomorphology in patients with Crowe type II and III developmental dysplasia of the hip(DDH)often present complicated changes, which bring challenges to the anatomical reconstruction of acetabulum in total hip arthroplasty (THA). The objective of this study was to develope a novel 3D printed integral customized acetabular prosthesis, which provides a promising way to reconstruct the acetabulum with higher accuracy and efficiency by digital softwares, compared with previous 3D printing model method.Methods15 patients (18 hips) with end-stage hip osteoarthritis due to Crowe type II/III DDH who underwent primary cementless THA from January 2015 to November 2021 were included. The 15 patients consisted of 3 men (3 hips) and 12 women (15 hips) with an average age of 53.89 ± 8.48 years (range from 32 to 69 years). The novel 3D printed integral customized acetabular prosthesis was designed by the model method and software method respectively. The indicators of the cup size, the volume and superficial area of bone defect, the inclination and anteversion of acetabular cup, the horizontal and vertical distance of hip center and working time were compared between two methods.ResultsThere were statistically significant difference between the software group and model group on the volume and superficial area of bone defect as well as working time (t = 2.397, 2.707,138.509, P < 0.05). The mean anteversion and inclination of acetabular cup in the software group and model group were(15.17±0.52)°,(40.24±0.58)°and (33.79 ±13.43)°, (30.50 ±11.03)°respectively, the difference was statistically significant (t = 5.859, 3.767, P < 0.05).There were no statistically significant difference between the software group and model group on cup size, the horizontal and vertical distance of hip center(t =1.458,0.114, 1.712, P > 0.05)ConclusionsThe application of digital softwares could design and develope the novel 3D printed integral customized anatomical acetabular prosthesis in THA for □Crowe type II and III DDH with high accuracy and efficiency.