title: Augmented PMMA distribution: improvement of mechanical property and reduction of leakage rate of a fenestrated pedicle screw with diameter-tapered perforations.
abstract: OBJECTIVE This study investigated the optimum injection volume of polymethylmethacrylate (PMMA) to augment a novel fenestrated pedicle screw (FPS) with diameter-tapered perforations in the osteoporotic vertebral body, and how the distribution characteristics of PMMA affect the biomechanical performance of this screw. METHODS Two types of FPSs were designed (FPS-A, composed of 6 perforations with an equal diameter of 1.2 mm; and FPS-B, composed of 6 perforations each with a tapered diameter of 1.5 mm, 1.2 mm, and 0.9 mm from tip to head. Each of 28 human cadaveric osteoporotic vertebrae were randomly assigned to 1 of 7 groups: FPS-A1.0: FPS-A+1.0 ml PMMA; FPS-A1.5: FPS-A+1.5 ml PMMA; FPS-A2.0: FPS-A+2.0 ml PMMA; FPS-B1.0: FPS-B+1.0 ml PMMA; FPS-B1.5: FPS-B+1.5 ml PMMA; FPS-B2.0: FPS-B+2.0 ml PMMA; and conventional pedicle screws (CPSs) without PMMA. After the augmentation, 3D CT was performed to assess the cement distribution characteristics and the cement leakage rate. Axial pullout tests were performed to compare the maximum pullout force thereafter. RESULTS The CT construction images showed that PMMA bone cement formed a conical mass around FPS-A and a cylindrical mass around FPS-B. When the injection volume was increased from 1.0 ml to 2.0 ml, the distribution region of the PMMA cement was enlarged, the PMMA was distributed more posteriorly, and the risk of leakage was increased. When the injection volume reached 2.0 ml, the risk of cement leakage was lower for screws having diameter-tapered perforations. The pullout strengths of the augmented FPS-A groups and FPS-B groups were higher than that of the CPS group (p < 0.0001). All FPS-B groups had a higher pullout strength than the FPS-A groups. CONCLUSIONS The diameter of the perforations affects the distribution of PMMA cement. The diameter-tapered design enabled PMMA to form larger bone-PMMA interfaces and achieve a relatively higher pullout strength, although statistical significance was not reached. Study results indicated 1.5-ml of PMMA was a conservative volume for PMMA augmentation; more cement injection would significantly increase the risk of cement leakage.
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.|Department of Orthopaedics, 454 Hospital of PLA, Nanjing, Jiangsu Province, People's Republic of China.
authors: Quan-Chang
authors: QC
authors: Tan
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Jian-Wei
authors: JW
authors: Wu
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Fei
authors: F
authors: Peng
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Yuan
authors: Y
authors: Zang
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Yang
authors: Y
authors: Li
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Xiong
authors: X
authors: Zhao
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Wei
authors: W
authors: Lei
authors: Department of Orthopaedics, Xijing Hospital, the Fourth Military Medical University, Xi'an Shaanxi Province; and.
authors: Zi-Xiang
authors: ZX
authors: Wu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001843:Bone Cements; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D008297:Male; D019637:Orthopedic Procedures / Q000379:methods; D065289:Pedicle Screws; D019904:Polymethyl Methacrylate; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011897:Random Allocation; D013904:Thoracic Vertebrae / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed
chemical_list: D001843:Bone Cements; D019904:Polymethyl Methacrylate
keywords: A-L = anterior and lateral; BMD = bone mineral density; CPS = conventional pedicle screw; FPS = fenestrated pedicle screw; Fmax = maximum load; PMMA; PMMA = polymethylmethacrylate; VB = vertebral body; cement augmentation; cement distribution; fenestrated pedicle screws; osteoporosis; polymethylmethacrylate; vertebral body