Influence of cement-augmented pedicle screws with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae over the adjacent segments: a 3D finite element analysis.

BACKGROUND: Polymethylmethacrylate (PMMA) is commonly used for cement-augmented pedicle screw instrumentation (CAPSI) to improve the fixation stability and reduce the risk of screw loosening in the osteoporotic thoracolumbar spine. Biomechanical researches have shown that various dose of cement (1-3 ml) can be injected to enhance screw stability. To date, there have been no studies on the relationship between adjacent segment degeneration and the volume of PMMA. This study aimed to explore the influence of CAPSI with different volumes of PMMA in osteoporotic lumbar vertebrae over adjacent segments by using finite element analysis. METHODS: Seven different finite element models were reconstructed and simulated under different loading conditions, including (1) an intact model, (2) three single-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml), and (3) three double-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml). To improve the accuracy of the finite element analysis, the models of the injectable pedicle screw and bone cement were created by using a three-dimensional scanning machine and the CAPSI patient's CT data, respectively. The range of motion (ROM), the stress of intervertebral discs, and the stress of facet in the adjacent segment were comparatively analyzed among the different models. RESULTS: The ROMs of the different segments were compared with experimental data, with good agreement under the different load conditions (21.3°, 13.55°, 13.99°, and 6.11° in flexion, extension, bending, and rotation at L3-S1 level, respectively). Compared with the intact model, the ROM, disc stresses, and facet stress in adjacent segments were found to be higher in the six operative models. Otherwise, with a larger volume of PMMA injected, the ROM, disc stresses, and facet stress slightly increased at the adjacent segment. However, the differences were insignificant with the biggest difference less than 3.8%. CONCLUSIONS: CAPSI could increase the incidence of disk degeneration in the adjacent segment, while within a certain range, different volumes of PMMA provided an approximate impact over the adjacent segment degeneration.

Effect and potential risks of using multilevel cement-augmented pedicle screw fixation in osteoporotic spine with lumbar degenerative disease.

BACKGROUND: The increase of augmented level and bone cement dose are accompanied by the rising incidence of cement leakage (CL) of cement-augmented pedicle screw instrumentation (CAPSI). But the effect and potential risks of the application of CAPSI to osteoporotic lumbar degenerative disease (LDD) have not been studied in the case of multilevel fixation. This study aimed to investigate the effectiveness and potential complications of using multilevel CAPSI for patients with osteoporotic LDD. METHODS: A total of 93 patients with multilevel LDD were divided into the CAPSI group (46 subjects) and the conventional pedicle screw (CPS) group (47 subjects), including 75 cases for three levels and 18 cases for four levels. Relevant data were compared between two groups, including baseline data, clinical results, and complications. RESULTS: In the CAPSI group, a total of 336 augmented screws was placed bilaterally. The CL was observed in 116 screws (34.52%). Three cemented screws (0.89%) were found loosened during the follow-up and the overall fusion rate was 93.47%. For perioperative complications, two patients (4.35%) experienced pulmonary cement embolism (PCE), one patient augmented vertebral fracture, and three patients (6.52%) wound infection. And in the CPS group, thirty-three screws (8.46%) suffered loosening in cranial and caudal vertebra with a fusion rate of 91.49%. The operation time and hospital stay of CAPSI group were longer than the CPS group, but CAPSI group has a lower screw loosening percentage (P<0. 05). And in terms of blood loss, perioperative complications, fusion rate, and VAS and ODI scores at the follow-up times, there were no significant differences between the two groups. CONCLUSIONS: Patients with osteoporotic LDD underwent multilevel CPS fixation have a higher rate of screw loosening in the cranial and caudal vertebra. The application of cemented pedicle screws for multilevel LDD can achieve better stability and less screw loosening, but it also accompanied by longer operating time, higher incidence of CL, PCE and wound infections. Selective cement augmentation of cranial and caudal pedicle screws may be a worthy strategy to decrease the complications.

The cement leakage in cement-augmented pedicle screw instrumentation in degenerative lumbosacral diseases: a retrospective analysis of 202 cases and 950 augmented pedicle screws.

PURPOSE: To evaluate the incidence, type and risk factors of cement leakage (CL) with cement-augmented pedicle screw instrumentation (CAPSI) in degenerative lumbosacral disease. METHODS: Two hundred and two patients using a total of 950 cement-augmented screws were enrolled. CL was classified into three types: type S: leakage via segmental veins; type B: leakage via basivertebral veins; and type I: leakage via pedicle screw instrumentation to paravertebral soft tissue. The age, gender, operation stage (primary or later stage), body mass index, bone mineral density, the number and type of augmented screw, the position of the tip of screw (lateral or internal part of vertebral body), the position of screw (left or right side), the volume of bone cement, location of the augmented vertebra (lumbar or sacrum), the type of CL and complications were recorded. Binary logistic regression correlation was used to analyze risk factors of veins leakage (type S and type B). RESULTS: The CL was observed in 165 patients (81.68%) and 335 screws (35.26%), leakage types of S, B and I were seen in 255 (76.12%), 77 (22.99%), and 30 (8.96%) of screws, respectively. Besides, double or multiple routes of leakage were seen in 27 screws. Number of augmented screw was a risk factor for vein leakage (OR 0.58; 95% CI 0.44-0.77; P = 0.000). Furthermore, the doses of cement (OR 0.79; 95% CI 0.61-0.99; P = 0.038) and the position of screw (OR 0.39; 95% CI 0.29-0.53; P = 0.000) were identified as risk factors for type S, and the doses of bone cement (OR 0.37; 95% CI 0.25-0.54; P = 0.000) and the position of the tip of screw (OR 0.07; 95% CI 0.04-0.13; P = 0.000) were risk factors for type B. CONCLUSIONS: CAPSI bears a high risk of asymptomatic CL, with a higher rate of leakage into segmental veins and basivertebral veins. As is known, more augmented screws and larger doses of cement are risk factors for veins leakage (type S and type B), while the tip of screw approaching to the midline of the vertebral body is another risk factor to type B. Thus, the CL could be reduced by the amelioration of operative techniques and procedures. These slides can be retrieved under Electronic Supplementary Material.

Comparison of pedicle screw fixation with or without cement augmentation for treating single-segment isthmic spondylolisthesis in the osteoporotic spine.

The present study examined the necessity of cement-augmented pedicle screw fixation in osteoporotic patients with single-segment isthmic spondylolisthesis.Fifty-nine cases were reviewed retrospectively. Thirty-three cases were in the polymethylmethacrylate-augmented pedicle screw (PMMA-PS) group, and the other 26 cases were in the conventional pedicle screw (CPS) group. Evaluation data included operation time, intraoperative blood loss, hospitalization cost, hospitalization days, rates of fusion, screw loosening, bone cement leakage, visual analogue scale (VAS) scores, Oswestry disability index (ODI), lumbar lordosis (LL), pelvic tilt (PT) and sacral slope (SS).The operation time and blood loss in the CPS group decreased significantly compared to those in the PMMA-PS group. The average hospitalization cost of the PMMA-PS group was significantly higher than that of the CPS group. There was no significant difference in the average hospital stay between the 2 groups. The initial and last follow-up postoperative VAS and ODI scores improved significantly in the two groups. There were no significant differences in VAS and ODI between the 2 groups at each time point. The last postoperative spine-pelvic parameters were significantly improved compared with those preoperatively. In the PMMA-PS group, the fusion rate was 100%. The fusion rate was 96.15% in the CPS group. No significant difference was found between the two groups for the fusion rate. Nine patients in the PMMA-PS group had bone cement leakage. There was no screw loosening in the PMMA-PS group. There were 2 cases of screw loosening in the CPS group. There were no significant differences in screw loosening, postoperative adjacent segment fractures, postoperative infection or postoperative revision between the 2 groups. The use of PMMA-PS on a regular basis is not recommended in posterior lumbar interbody fusion for the treatment of single-segment isthmic spondylolisthesis with osteoporosis.

Long-Term Outcomes of Peripheral Pulmonary Cement Embolism in Patients with Polymethylmethacrylate Augmentation: A Case Series with a Minimum Follow-Up of Five Years.

BACKGROUND: Pulmonary cement embolism (PCE) is a rare but lethal complication. However, few long-term follow-up studies have investigated PCE after polymethylmethacrylate augmentation. This study aimed to investigate both the clinical and imaging outcomes of patients with PCE during a follow-up period of at least 5 years. METHODS: A total of 1460 patients were initially included in this retrospective study. After exclusion, the clinical and imaging data were analyzed for selected patients, including the augmented level, location and length of the PCE, symptoms, therapy, migration and disintegration of the embolism, foreign body reaction, and status at follow-up. RESULTS: Twelve female patients (age range, 56-88 years) with PCE and more than 5 years of follow-up (range, 5-13 years) were eventually included. All emboli were found in subsegment pulmonary arteries and were classified as peripheral PCE. Although 2 patients experienced transient symptoms after surgery, the majority of patients (84.6%) were asymptomatic during follow-up. No other reported emboli were observed during the follow-up period. The imaging data showed that the cement embolus could remain in the initial position throughout the long-term follow-up. In terms of the length of the PCE, there was no statistically significant difference between the values post-operation and at the last follow-up time (P > 0.05). CONCLUSIONS: Patients with peripheral PCE do not develop known late complications. Moreover, polymethylmethacrylate can remain stable and inert in the pulmonary vasculature over the long term. Routine prophylactic anticoagulation may not be necessary for patients with peripheral PCE during follow-up.