A novel calcium phosphate–based nanocomposite for the augmentation of cement-injectable cannulated pedicle screws fixation: A cadaver and biomechanical study

Abstract

Background/objectiveBoth polymethylmethacrylate (PMMA) and traditional calcium phosphate–based cements have some deficiencies as augmentation materials for pedicle screw fixation. Here, a novel calcium phosphate–based nanocomposite (CPN) for the augmentation of pedicle screw fixation was developed based on previous study, and the handling properties, biomechanical performance, and biodegradation behaviour of CPN were evaluated and compared with clinical PMMA by means of a cadaver study and animal tests.MethodsBone mineral density of the lumbar vertebrae was tested. Pedicle screws were placed into the lumbar vertebrae under the guidance of three dimensionally printed templates; each of which was designed based on computed tomography (CT) reconstruction of each vertebrae ​and augmented with either PMMA or CPN. X-ray and CT scan were used to evaluate the accuracy of screw placement and dispersion as well as interdigitation of bone cement. The axial pull-out strength and maximum torque were tested using a mechanical testing machine. Degradation behaviour of CPN was evaluated by in vitro immersion tests for 8 weeks and in vivo rabbit femur defect model for up to 6 months, respectively.ResultsStandard mechanical tests revealed that PMMA was much stronger than CPN after setting (compressive strength 95 vs. 49 ​MPa, respectively, p ​< ​0.001). Results of the projection area and volume distribution of cement along the distal end of the screws revealed that CPN exhibited unique dispersing and interdigitation abilities compared with PMMA. Specifically, CPN dispersed uniformly and symmetrically along the screw, while PMMA was limited to the proximal part of the screw. Axial pull-out test results showed that the axial pull-out strengths of CPN- and PMMA-augmented pedicle screws were similar (1199 ​± ​225 ​N vs 1337 ​± ​483 ​N, respectively) and not significantly different (p ​= ​0.47), although CPN was an intrinsically weaker material than PMMA. Similarly, CPN showed average torque values of 0.72 ​± ​0.31 ​N·m slightly lower than those of PMMA (0.96 ​± ​0.23 ​N·m), but statistically there was no significant difference between CPN and PMMA (p ​= ​0.21). In a rabbit model of femoral bone defect, the implanted CPN maintained its clear boundary and there is no disintegration in the cement clump after 20 days and 24 weeks, and there was moderate bioabsorption of CPN and clearly new bone ingrowth at the absorbed sites after 24 weeks.ConclusionA new nanocomposite cement CPN, designed for replacing the nondegradable PMMA cement and overcoming the mechanical inferiority of calcium phosphate cement, was evaluated for its biomechanical and biodegradation behaviours in cement-injectable cannulated pedicle screws (CICPS) application. Although CPN is a mechanically weaker material than PMMA, CPN demonstrates similar biomechanical properties to PMMA in the application of augmentation for CICPS fixation in cadaveric vertebrae. This improvement in biomechanical property is attributed to a better dispersion and interdigitation mode of CPN. In a...

The Biomechanical Properties of Cement-Augmented Pedicle Screws for Osteoporotic Spines

“…The goals for such materials are to play a similar or even greater biomechanical role compared with PMMA as well as to be safe and biocompatible. A novel calcium phosphate-based nanocomposite (CPN) introduced by Sun et al 20 - 22 showed satisfying biodegradability, osteoinductivity in vivo, and exhibited equal even marginally higher maximal pullout force than PMMA. The dispersion pattern of the cement within cancellous bone is crucial to the effect of augmentation.…”

“…Although the mechanical strength of CPN is weaker than that of PMMA, CPN has a more regular and symmetrical dispersion, which is conducive to achieving biomechanical stability similar to that of cannulated pedicle screws augmented by PMMA. 22 In addition, silicone was found to be osteoconductive and nonhazardous to surrounding tissue and shown to exhibit nonexothermic curing, which was in contrast to PMMA. 23 Schmoelz et al 24 inserted 3 mL of self-curing elastomer (silicone) into a balloon cavity prior to cannulated pedicle screw insertion, and the elastomer group underwent significantly more mean cycles until loosening under cyclic cranio-caudal loading than the PMMA during in situ augmentation (9824 ± 1982 N vs. 7401 ± 1644 N).…”

Materials based o tricalcium phosphate as bone defects substitute (literature review)

“…% сульфату барію. Як рідку фазу використовували гідрофосфат натрію 0,25 моль [44]. Останніми роками КФЦ із додаванням магнію та стронцію показали швидке схоплювання, покращену механічну міцність і гарну швидкість резорбції.…”

Calcium phosphate‐based composite cement: Impact of starch type and starch pregelatinization on its physicochemical properties and performance in the vertebral fracture surgical models in vitro

“…[9][10][11] Calcium phosphate cement (CPC) has been suggested to be a possible alternative of PMMA due to its osteoconductivity and biodegradability. 4,[12][13][14][15][16][17][18] However, its clinical application is limited by some critical issues including short setting time, poor injectability, collapse in body fluids, low mechanical strength, and high brittleness. 12,13,[19][20][21][22][23] It has been suggested that these properties could be improved by adding cohesion promoters such as poly(l-lactide-co-glycolide) acid (PLGA), 24 poly(ε-caprolactone) (PCL), poly(l-lactic acid) (PLLA), 25 chitosan, 26 and starch.…”