Efficacy: The primary goals of revision hip surgery are to reconstruct bone defects, stabilize prosthesis implantation, and restore the hip joint's rotation center [7]. The repair of acetabular bone defects involves autogenous/allogenic bone grafts and metal reinforcement blocks. However, bone grafts face issues of resorption and limited availability, and they fail to provide an initial stable base for the hip prosthesis. The shape and specifications of commercial metal reinforcement blocks are restricted, making it challenging to repair irregular, severe acetabular bone defects individually. Moreover, the implantation of cushion screws can be problematic due to directional issues during surgery. The benefits of 3D printing include: (i) the ability to accurately determine the size and shape of the bone defect through preoperative planning. Kavalerskiy et al. [8] verified the accuracy and necessity of using a 3D printing model preoperatively. The concordance rate between the type and size of the pad planned before surgery and that used during surgery was 100%, while the concordance rate for the size and planning of the acetabular cup during surgery was 64.3%. The size discrepancy in acetabular cups for patients with mismatches was less than 2mm. (ii) 3D printing technology allows for the fabrication of personalized cushion blocks, and the direction for screw implantation can be individually designed. This facilitation of screw implantation increases initial stability and meets various functional demands of reconstruction, thereby simplifying the renovation process. Giachino et al [9] studied and compared 3D printing technology with traditional planning methods, confirming that 3D printing planning significantly shortens operation and hospitalization times, and reduces total hospitalization costs. (iii) The mechanical properties and biological activity of porous tantalum contribute to the long-term stability of prosthesis implantation. Cassar-Gheiti et al [10] monitored 59 cases using Flying Buttress tantalum augments over an average of 8 years; the 10-year prosthesis survival rate was 88.9%, with a survival rate of 94.3% when considering revision as the endpoint. Radiological assessments using the improved Moore grading [11] indicated that 83.1% of patients achieved osseointegration with a score of 5, and 10.2% achieved a score of 4. Only 1.7% of patients exhibited three signs of osseointegration, and another 1.7% displayed one sign, confirming the long-term biological benefits of tantalum metal. Fang et al [12] reported that in 35 cases of 3D printed personalized augments and prostheses, followed for an average of 41.5 months, the HHS score increased from 47.8 ± 8.2 points pre-operation to 86.4 ± 5.1 points at the last follow-up, with one case each of sciatic nerve injury and dislocation, but no instances of prosthesis loosening or screw breakage. Following an average of 27 months post-operation, patients showed good clinical outcomes, with the HHS score rising from 36.22 ± 5.69 pre-operation to 78.55 ± 6.49 post-operation, and the VAS score decreasing from 6.55 ± 1.34 pre-operation to 1.77 ± 0.91, with no reported complications.
For severe acetabular bone defects, particularly Paprosky ⅲ type defects, the usual lack of effective support at the acetabular top often results in the upward movement of the COR and the relative shortening of the affected limb. Fu et al [13] explored the reconstruction of 18 cases of Paprosky III bone defects using 3D printed porous tantalum pads. LLD decreased from 31.7±4.2 mm before surgery to 7.7±1.4 mm post-surgery, and COR reduced from 50.7±3.9 mm before surgery to 22.3±1.7 mm at the last follow-up. This study demonstrated that customized augments can reconstruct the rotation center, effectively restoring the COR to a more normal position, reducing LLD, and maximally restoring lower limb length.
Achieving good initial stability during revision with a mortar cup is crucial. The prerequisite for bone fusion and growth in biological prostheses is obtaining initial stability, and the major advantage of a 3D printed bone trabecular mortar cup and metal augment is their rough outer surface, which provides a high friction coefficient with the bone bed, facilitating initial stability post-implantation [14]. Finite element analysis by Fu et al [15] indicates that the 3D printed trabecular metal block maintains good stability even when the patient stands on one leg immediately after surgery; full weight-bearing is possible right after surgery, though running and jumping are not recommended. In this study, the augment at the printed part provides robust support for the acetabular cup: the double cortex at the iliac crest, which has abundant bone, is securely fixed, and the challenge of inserting the pad screw is resolved. Additionally, the step-like design of the augment ensures that it firmly sits on the upper edge of the defective acetabulum.
Conventional acetabular support reinforcement augment placement typically occurs from the posterolateral position above the acetabulum, along the posterior column in front of the great sciatic notch, and is placed on the ilium below the gluteus minimus. Clinically, superior gluteal nerve injury is generally considered less common than injuries to the sciatic, femoral, or obturator nerves in traditional total hip replacements, with the incidence of occult subclinical injury reported as high as 77%[16]. The functional change in the abductor muscle due to injury is as high as 23%[17], which may lead to complications such as dislocation, claudication, and Trendelenburg sign. Most studies indicate that the superior gluteal nerve is safe within 5 cm of the greater trochanter, with exposure beyond this distance posing a risk of damage [18]. Cole et al [16] noted that if the length of the cushion reaches 68 mm, there is a risk of damaging the superior gluteal nerve during placement, and surgeons should remain vigilant. In this study, the printed support augment is positioned relatively forward, and the double incision design with subperiosteal peeling connecting the two incisions reduces peeling above the acetabulum, thereby lowering the risk of injuring the superior gluteal nerve and blood vessels, with no nerve injuries reported.
The advantages of this reconstruction strategy include: (i) personalized reconstruction simplifies complex surgeries, shortens operation time, and restores the height of the rotation center and the length of the lower limbs. (ii) It addresses the challenge of difficult nailing of the cushion block. (iii) The robust fixation of the double cortex at the iliac crest, where bone is abundant, and the designed step-like structure provide effective upper support for the mortar cup. (iv) The risk of injuring the superior gluteal nerve and blood vessels is minimized.