Anatomical landmarks and intraoperative "safe zone" for precise acetabular prosthesis placement in total hip arthroplasty for developmental dysplasia of the hip.

backgroundThe precise positioning of the acetabular prosthesis in total hip arthroplasty is critical, as it directly influences articulation with the femoral head prosthesis, hip biomechanics, and functional recovery. However, the absence of reliable anatomical landmarks for intraoperative guidance remains a significant challenge in achieving optimal implant orientation. This study aims to provide a theoretical and experimental basis for improving the accuracy of prosthesis implantation and supporting anatomical acetabular reconstruction in clinical practice.

methodsFrom September 2018 to December 2020, the pelvic three-dimensional CT data of 22 patients (36 hips) with DDH were collected in the orthopedics department of the First Affiliated Hospital of Bengbu Medical University. The CT data were imported into Mimics software for 3D reconstruction, and 1:1 scale pelvic models were fabricated using 3D printing technology. After restoring the morphology of the acetabular notch and fossa on the models, the acetabulum was reamed according to standard THA techniques. The inferior edge of the acetabular prosthesis was positioned 1-5 mm proximal and distal to the proximal line connecting the anterior and posterior acetabular notches (PLAPAN) to determine prosthesis inclination. The inferior edge of the acetabular prosthesis was rotated 1-5 mm pronating and supinating around the proximal point of the posterior acetabular notch (PPAPN) to determine prosthesis anteversion. The pelvis plain radiographs were taken, and the inclination and anteversion of the acetabular prosthesis were calculated at 22 positions. Statistical analysis was performed on the collected data.

resultsIn DDH, the intraoperative "safe zone" of acetabular prosthesis inclination in THA was (- 2 to   + 1 mm), that is, the lower edge of the acetabular prosthesis was 2 mm proximal ~ 1 mm distal to the proximal line of the anterior and posterior acetabular notches (the average inclination of the acetabular prosthesis was (35.06 ± 3.35)°-(41.64 ± 3.51)°). The optimal inclination of the acetabular prosthesis could be obtained when the lower edge of the acetabular prosthesis was parallel to the proximal line of the anterior and posterior acetabular notches (the average inclination of the acetabular prosthesis was (41.64 ± 3.51)°). The intraoperative "safe zone" of acetabular prosthesis anteversion in THA is (- 2 to  0 mm), that is, the lower edge of the acetabular prosthesis was 2 mm supinating ~ 1 mm pronating at the proximal point of the acetabular posterior notch (the average anteversion of the acetabular prosthesis was (10.67 ± 4.55)°-(20.86 ± 4.44)°). The optimal anteversion of the acetabular prosthesis could be obtained when the lower edge of the acetabular prosthesis was 1 mm of supination at the proximal point of the acetabular posterior notch (the average anteversion of the acetabular prosthesis was (14.58 ± 3.83)°).

conclusionIn THA for DDH, the acetabular notch and fossa provide reliable anatomical landmarks for precise prosthesis placement. This study further establishes a defined intraoperative "safe zone" for the prosthesis inclination and anteversion, providing surgeons with a clear theoretical target to enhance procedural safety and reduce the risk of dislocation.