Objective To summarize the occurrence mechanism of backside wear, the method of evaluating backside surface damage, the relationship between backside wear and osteolysis in acetabulum, and the approach to reduce backside wear in total hip arthroplasty with modular acetabulum prosthesis. Methods The recent articles about the backside wear in acetabular liners were extensively reviewed. Results Backside wear in acetabular liners is connected with micromotion between the liner and the shell, rough interface, thickness of the liner, and impingement. The methods to evaluate backside wear damage are only proceeded in revised acetabular liners. Backside wear can generate polyethylene particles that is likely related to the process of osteolysis in acetabulum through the screw holes of metallic shell. To reduce backside wear between the liner and the shell, measures such as improved locking mechanisms, smooth inner metallic shell, maximized shell liner conformity, improving the quality of polyethylene, and reducing impingement can be taken. Conclusion There is no method of evaluating the backside wear in vivo. The relationship between backside wear and osteolysis in acetabulum as well as aseptic loosening of acetabulum prosthesis is controversial.
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.