Abstract
PurposeCement augmentation of pedicle screws is able to improve screw anchorage in osteoporotic vertebrae but is associated with a high complication rate. The goal of this study was to evaluate the impact of different cement volumes on pedicle screw fatigue strength.MethodsTwenty-five human vertebral bodies (T12–L4) were collected from donors between 73 and 97 years of age. Bone density (BMD) was determined by quantitative computed tomography. Vertebral bodies were instrumented by conventional pedicle screws, and unilateral cement augmentation was performed. Thirteen vertebrae were augmented with a volume of 1 ml and twelve with a volume of 3 ml bone cement. A fatigue test was performed using a cranial–caudal sinusoidal, cyclic load (0.5 Hz) with increasing compression force (100 N + 0.1 N/cycles).ResultsThe load to failure was 183.8 N for the non-augmented screws and was increased significantly to 268.1 N (p < 0.001) by cement augmentation. Augmentation with 1 ml bone cement increased the fatigue load by 41% while augmentation with 3 ml increased the failure load by 51% compared to the non-augmented screws, but there was no significant difference in fatigue loads between the specimens with screws augmented with 1 ml and screws augmented with 3 ml of bone cement (p = 0.504).ConclusionCement augmentation significantly increases pedicle screw stability. The benefit of augmentation on screw anchorage was not significantly affected by reducing the applied volume of cement from 3 ml to 1 ml. Considering the high risk of cement leakage during augmentation, we recommend the usage of a reduced volume of 1 ml bone cement for each pedicle screw.Graphic These slides can be retrieved under Electronic Supplementary Material .
Highlights
Osteoporosis commonly causes vertebral fractures, and posterior spinal stabilization using pedicle screw fixation may be required [1,2,3,4]
Considering the high risk of cement leakage during augmentation we recommend the usage of a reduced volume of 1 ml bone cement for each pedicle screw
Various biomechanical studies have shown that pedicle screw fatigue load as well as pull-out force are significantly decreased in bone with reduced density and loosening of pedicle screws and progressive kyphotic deformity due to poor bone mineral density are frequently encountered in osteoporotic patients [5,6,7,8,9,10,11]
Summary
Osteoporosis commonly causes vertebral fractures, and posterior spinal stabilization using pedicle screw fixation may be required [1,2,3,4]. Cement augmentation of pedicle screws is increasingly used in order to improve fixation strength in osteoporotic patients [12,13,14,15]. Biomechanical studies have shown an approximately twofold increase in pull-out force and an increase in load to failure in cyclic testing by 52% for augmented pedicle screws [16,17,18,19]. Cement augmentation of pedicle screws is associated with relevant complications such as leakage and embolism [20, 21]. Symptomatic complications are reported in 5.5%, asymptomatic cement leakage in 66.7% and anaphylactic reactions in 1.2% of patients treated with augmented pedicle screws [21]. There is still controversy regarding the sufficient cement volume for screw augmentation
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