Customised three-dimensional printed revision acetabular implant for large defect after failed triflange revision cup

[Advances in revision surgery after primary total hip arthroplasty for Crowe type developmental dysplasia of the hip]

Objective

To review research advances of revision surgery after primary total hip arthroplasty (THA) for patients with Crowe type Ⅳ developmental dysplasia of the hip (DDH).

Methods

The recent literature on revision surgery after primary THA in patients with Crowe type Ⅳ DDH was reviewed. The reasons for revision surgery were analyzed and the difficulties of revision surgery, the management methods, and the related prosthesis choices were summarized.

Results

Patients with Crowe type Ⅳ DDH have small anteroposterior diameter of the acetabulum, large variation in acetabular and femoral anteversion angles, severe soft tissue contractures, which make both THA and revision surgery more difficult. There are many reasons for patients undergoing revision surgery after primary THA, mainly due to aseptic loosening of the prosthesis. Therefore, it is necessary to restore anatomical structures in primary THA, as much as possible and reduce the generation of wear particles to avoid postoperative loosening of the prosthesis. Due to the anatomical characteristics of Crowe type Ⅳ DDH, the patients have acetabular and femoral bone defects, and the repair and reconstruction of bone defects become the key to revision surgery. The acetabular side is usually reconstructed with the appropriate acetabular cup or combined metal block, Cage, or custom component depending on the extent of the bone defect, while the femoral side is preferred to the S-ROM prosthesis. In addition, the prosthetic interface should be ceramic-ceramic or ceramic-highly cross-linked polyethylene wherever possible.

Conclusion

The reasons leading to revision surgery after primary THA in patients with Crowe type Ⅳ DDH and the surgical difficulties have been clarified, and a large number of clinical studies have proposed corresponding revision modalities based on which good early- and mid-term outcomes have been obtained, but further follow-up is needed to clarify the long-term outcomes. With technological advances and the development of new materials, personalized prostheses for these patients are expected to become a reality.

Shape suitability and mechanical safety of customised hip implants: Three-dimensional printed acetabular cup for hip arthroplasty

Background

Owing to an increase in the number of hip arthroplasty surgeries, the number of implant replacement surgeries is increasing rapidly as well. This necessitates the study of hip joint conditions. Therefore, Paprosky defined a classification system to indicate the degree of damage to the hip joint. In this study, a customised hip implant suitable for Paprosky classification Type ⅡC and over was designed. The shape, suitability, and mechanical safety of the worst-case model for the implant were evaluated.

Materials and methods

To identify the implant size depending on states over Type ⅡC acetabulum bone loss, a size range was selected and a customised implant was designed according to the computed tomography data within the size range. The implant was designed for the flange, hook, and flattened model types. The worst-case selection test was conducted using finite element analysis. The von Mises stresses of the flange, hook, and flattened models were found as 76.223, 136.99, and 80.791 MPa, respectively. Therefore, the hook-type model was selected as the worst case for the mechanical performance test.

Results

A bending test was conducted on the hook-type model without fracture and failure at 5344.56 N. The proposed customised implant was found suitable for Type ⅢA acetabulum bone loss, whereas the shape suitability and mechanical safety were verified for the worst case.

Conclusion

The shape of a customised implant suitable for Paprosky ⅢA type was designed. The shape suitability and mechanical safety were evaluated using finite element method analysis and bending tests. Clinical validation is required through subsequent clinical evaluation.

Design, fabrication, and structural safety validation of 3D-printable biporous bone augments

The use of commercial products such as a cup and liner for total hip arthroplasty for patients with severe bone defects has a high probability of failure. In these patients the cup alone cannot cover the bone defect, and thus, an additional augment or cage is required. In this study, we designed three-dimensional (3D) printable bone augments as an alternative to surgeries using reinforcement cages. Thirty-five sharp-edged bone augments of various sizes were 3D printed. A biporous structure was designed to reduce the weight of the augment and to facilitate bone ingrowth. Two types of frames were used to prevent damage to the augment’s porous structure and maintain its stability during printing. Furthermore, two types of holes were provided for easy augment fixation at various angles. Fatigue tests were performed on a combination of worst-case sizes derived using finite element analysis. The test results confirmed the structural stability of the specimens at a load of 5340 N. Although the porosity of the specimens was measured to be 63.70%, it cannot be said that the porous nature was uniformly distributed because porosity tests were performed locally and randomly. In summary, 3D-printable biporous bone augments capable of bonding from various angles and bidirectionally through angulation and bottom-plane screw holes are proposed. The mechanical results with bone augments indicate good structural safety in patients. However, further research is necessary to study the clinical applications of the proposed bone augment.

Graphic abstract

Total knee arthroplasty in a young patient with achondroplasia

Achondroplasia is a genetic skeletal dysplasia, characterised by dwarfism, with upper and lower limb deformities, that can lead to knee osteoarthritis; the surgical treatment is a challenge due to the particular joint anatomy variances. We present a 40-year-old woman, affected by achondroplasia with severe left knee osteoarthritis; the patient was treated conservatively with poor results. Between the ages of 12 and 17 years, she underwent multiple operative procedures for lower limb lengthening and a partial correction of the valgus deformity, by applying an external fixator. The patient was successfully treated with cemented posterior stabilised, fixed-bearing, total knee arthroplasty. The patient affected by achondroplasia, with severe knee osteoarthritis, should be considered for total joint replacement, which can be carried out with or without additional extra-articular osteotomy for alignment correction. Due to skeletal dysplasia in joint deformities, knee replacement requires careful preoperative planning and special technical considerations.