Abstract
Although dual-threaded pedicle screws have been developed, the advantages over single-threaded screws remain controversial. We aimed to investigate the biomechanical performance of two types of dual-threaded pedicle screw by comparing their pullout strength with that of a single-threaded screw in relation to bone quality. Four types of pedicle screw with different thread patterns were designed. Type I: single-threaded screw; Type II: double-threaded screw; Type III: dual-threaded screw; Type IV: a newly designed double dual-threaded screw. Five types of polyurethane foams simulating various degrees of bone quality were used. These were: Type A: cancellous bone; Type B: cancellous bone with cortical bone in the upper margin; Type C: osteoporotic cancellous bone; Type D: osteoporotic cancellous bone with cortical bone in the upper margin; and Type E: osteoporotic bone with cortical bone in the upper and lower margins. A comparison of the pullout strength of Type I, II, and III screws in Type A, B, C and D bone specimens was performed. Type C and E bone specimens were used for comparisons among Type I, II, and IV screws. Compared to the single-threaded screw, the dual-threaded pedicle screws exhibited higher pullout strength in normal-quality bone and significantly lower pullout strength in compromised osteoporotic bone. However, the double dual-threaded screw exhibited better pullout biomechanics in osteoporotic bone with bi-cortical bone.
Highlights
It is well known that a pedicle screw can provide robust initial stability to a spinal segment, supplying critical support during fusion surgeries for various spinal diseases [1,2,3,4]
Newtons), with the trend being statistically significant (p = 0.105) (Figure 6b). In this experimental testing study, we found that, compared to a conventional pedicle screw, dual-threaded pedicle screws exhibited higher pullout strength in normal-quality bone and significantly lower pullout strength in osteoporotic bone, after controlling for several factors such as screw length, diameter, and insertion technique
Polyurethane foam blocks with consistent properties are used to simulate a particular human bone density, and this commonly accepted testing material can limit the bias caused by the variation of human bone quality, pedicle structures, and screw–cortical interface [5]
Summary
It is well known that a pedicle screw can provide robust initial stability to a spinal segment, supplying critical support during fusion surgeries for various spinal diseases [1,2,3,4]. The pedicle screw has been widely used in fusion surgery for degenerative spinal diseases [4]. As the general population continues to grow older, spine surgeons frequently encounter challenging cases in which patients present with an osteoporotic spine and require pedicle screw fixation for successful surgical treatment. The materials of the pedicle screw, such as stainless steel, titanium alloy, and nickel–titanium (NiTi) alloy, may potentially cause corrosion and release some harmful metallic ions into the human body [7,8,9]. In order to improve corrosion resistance and fixation capability, a growing number of coating techniques are being used for biomedical
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