The Role of Prophylactic Vertebroplasty at UIV+1 and Cement-augmented Fenestrated Pedicle Screw for Prevention of PJK/PJF in Patients With Osteoporosis: A Propensity Score–matched Analysis

Objective: To elucidate the role of prophylactic vertebroplasty (PV) at UIV+1 and cement-augmented fenestrated pedicle screw (CAFPS) in prevention of PJK and PJF.Background: Cement augmentation at UIV and UIV+1 was found to prevent PJK and PJF. But most studies are retrospective and have a selection bias due to multifactorial etiology of PJF, making it difficult to identify the efficacy of prophylactic cement augmentation. Methods: We enrolled 208 surgically treated adult spinal deformity (ASD) patients who were followed for at least 2 years, to elucidate whether prophylactic cement augmentation was truly minimizing the risk of PJK and PJF in a uniform population from one center database. Patients were classified into two groups. Two comparable groups were propensity-matched with one to one nearest neighbor matching. The main outcome variables including PJK, PJF, pedicle screw loosening and cement leakage were compared.Results：After propensity score matching, there were 58 propensity-matched patients in group A and B (n=29 in each group) whose parameters including age, BMI, BMD, number of instrumented vertebrae, SVA, spinal-pelvic parameters and the frequency of UIV and LIV were similar. The incidence of PJK showed no significantly statistical difference between group A and B (10.3% vs 13.8%, p >0.99). Compared to group A, group B had a higher proportion of patients developing PJF (24.1% vs 0%, p=0.01). Pedicle screw loosening at UIV and (or) LIV showed no difference (24.1% vs 3.4%, p=0.052) between two groups. In group A, cement leakage was detected in 5 cases via fluoroscopy, but none of them had neurological deficit or pulmonary cement embolism.Conclusion: Combined application of CAFPS and PV could reduce the incidence of PJF, but it could not prevent the development of PJK in the surgical management of ASD with low BMD or osteoporosis.

Augmented PMMA distribution: improvement of mechanical property and reduction of leakage rate of a fenestrated pedicle screw with diameter-tapered perforations

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.