Polymethylmethacrylate augmentation of the pedicle screw: the cement distribution in the vertebral body

Abstract

Many studies have proven that the polymethylmethacrylate (PMMA) augmentation of the pedicle screw can significantly increase stiffness and strength of spinal fixation. Some major complications have also been reported. However, there are no reports discussing cement distribution and its morphology in the osteoporotic vertebral body, which is critical in the analysis of the biomechanical strength of the pedicle screw and the risk of cement leakage after pedicle screw augmentation. In this study, we used computed tomography (CT) to evaluate the cement distribution in the osteoporotic vertebral body after PMMA augmentation of a pedicle screw and to analyze the factors leading to cement leakage. Two groups of patients were studied. Group A consisted 25 osteoporotic patients (mean age of 73 years) with spinal instrumentation who had a total of 145 pedicle screws and cement augmentation with biopsy needles. Group B consisted of 23 osteoporotic patients (mean age of 74.6 years) with spinal instrumentation who had a total of 125 cannulated pedicle screws with cement augmentation. All patients had CT evaluation of the cement distribution in the vertebral body after the surgery. The cement distribution in the vertebrae was divided into four zones in the axial CT view: anterior onethird, middle third, and posterior third of vertebral body, and the pedicle. The morphology of the cement distribution around the pedicle screw was defined as scattered type or concentrate type. The leakage pattern was divided to anterior-lateral, posterior-lateral, and canal leakage. The correlations among bone mineral density (BMD), the cement leakage rate, and cement distribution morphology were also analyzed. The results showed that most augmented pedicle screws had cement extension into three of the four zones of the vertebral body (66.3%), followed by two zones (20%), all four zones (11.5%), and only one zone (2.2%). Overall, 123 screws (84.8%) in Group A and 108 screws (86.4%) in Group B had cement concentrate type distribution. The cement leakage rate in Group A is 18.3% and 13.6% in Group B. Patients with a BMD \0.6 g/cm 2 had significantly higher rates of cement leakage and tended toward a scattered cement distribution. There was only one patient who had a symptomatic leakage (sciatica) in Group B. We concluded that the cement distribution after pedicle screw augmentation with biopsy needle or cannulated screw technique was mostly localized in three zones of the vertebral body, and patients with lower BMD had a higher risk of cement leakage and scattered cement distribution.

Cement leakage in pedicle screw augmentation: a prospective analysis of 98 patients and 474 augmented pedicle screws

“…26 However, in the present series there was none of the symptomatic cement leakage reported in other studies. 11,19,25,46 The rate of cement-associated lung embolism was 4% in the present study. However, as in most cases, it was clinically asymptomatic.…”

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

“…It has been demonstrated that cement reaching the pedicle area leads to a higher risk for canal leakage. 17 However, when augmented with 1.5 ml of PMMA bone cement, none of the cement reached the pedicle. In addition, there was no significant difference in pullout strength between FPS-B2.0 and FPS-A2.0.…”

“…1,7,14,17,21,24 The main difference among these FPSs is the number of side perforations. Regardless of the different number of perforations, the pullout strength of PMMA-augmented FPSs is greater than that of nonaugmented conventional screws 3,5,9,10,12,26 or cannulated screws 8,16,18 in the osteoporotic condition.…”

“…The cement leakage was directly related to the volume of PMMA. A literature review indicated that the volume of PMMA used to augment the FPS ranges from 1.5 to 3.0 ml in clinical practice, 1,7,14,17,21,24 and the reported leakage rate of these clinical trials ranged from 0% to 23.8%. In the present study, 1.0, 1.5, and 2.0 ml of PMMA were chosen to investigate the optimal volume of PMMA for augmentation.…”

The relevance of biomaterials to the prevention and treatment of osteoporosis

“…The cement injection through the screws (figures 4 and 5) gets an increase in the resistance of the fractured vertebral body and avoids the pull-out of screws in osteoporotic spine [70,71].…”