title: A mathematical method for precisely calculating the radiographic angles of the cup after total hip arthroplasty.
abstract: We established a mathematical method to precisely calculate the radiographic anteversion (RA) and radiographic inclination (RI) angles of the acetabular cup based on anterior-posterior (AP) pelvic radiographs after total hip arthroplasty. Using Mathematica software, a mathematical model for an oblique cone was established to simulate how AP pelvic radiographs are obtained and to address the relationship between the two-dimensional and three-dimensional geometry of the opening circle of the cup. In this model, the vertex was the X-ray beam source, and the generatrix was the ellipse in radiographs projected from the opening circle of the acetabular cup. Using this model, we established a series of mathematical formulas to reveal the differences between the true RA and RI cup angles and the measurements results achieved using traditional methods and AP pelvic radiographs and to precisely calculate the RA and RI cup angles based on post-operative AP pelvic radiographs. Statistical analysis indicated that traditional methods should be used with caution if traditional measurements methods are used to calculate the RA and RI cup angles with AP pelvic radiograph. The entire calculation process could be performed by an orthopedic surgeon with mathematical knowledge of basic matrix and vector equations.
authors.affiliation: Department of Orthopaedics, Chinese PLA General Hospital, Beijing 100853, People's Republic of China. Electronic address: zhaojx84@126.com.
authors.forename: Jing-Xin
authors.initials: JX
authors.lastname: Zhao
authors.affiliation: Department of Orthopaedics, Affiliated Hospital of the Academy of Military Medical Sciences, No. 8 Dongdajie Road, Beijing 100071, People's Republic of China; Department of Orthopaedics, Chinese PLA General Hospital, Beijing 100853, People's Republic of China. Electronic address: xiuyunsu@gmail.com.
authors.forename: Xiu-Yun
authors.initials: XY
authors.lastname: Su
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing 100084, People's Republic of China. Electronic address: xiaoruoxiu@126.com.
authors.forename: Ruo-Xiu
authors.initials: RX
authors.lastname: Xiao
authors.affiliation: Department of Orthopaedics, Beijing Tsinghua Chang Gung Hospital, No. 1 Block Tiantongyuan North, Beijing 102218, People's Republic of China; Department of Orthopaedics, Chinese PLA General Hospital, Beijing 100853, People's Republic of China. Electronic address: zhaozhao_02@163.com.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Department of Orthopaedics, Chinese PLA General Hospital, Beijing 100853, People's Republic of China. Electronic address: zhanglihai301@gmail.com.
authors.forename: Li-Hai
authors.initials: LH
authors.lastname: Zhang
authors.affiliation: Department of Orthopaedics, Chinese PLA General Hospital, Beijing 100853, People's Republic of China. Electronic address: zhanglcheng218@126.com.
authors.forename: Li-Cheng
authors.initials: LC
authors.lastname: Zhang
authors.affiliation: Department of Orthopaedics, Chinese PLA General Hospital, Beijing 100853, People's Republic of China. Electronic address: pftang301@163.com.
authors.forename: Pei-Fu
authors.initials: PF
authors.lastname: Tang
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip; D006801:Humans; D011184:Postoperative Period; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Cup; Mathematics; Radiographic anteversion angle; Radiographic inclination angle; THA