Pullout of a lumbar plate with varying screw lengths

Abstract

Background: Screw length pertains to stability in various orthopedic fixation devices. There is little or no information on the relationship between plate pullout strength and screw length in anterior lumbar interbody fusion (ALIF) plate constructs in the literature. Such a description may prove useful, especially in the treatment of osteoporotic patients where maximizing construct stability is of utmost importance. Our purpose is to describe the influence of screw length on ALIF plate stability in severely and mildly osteoporotic bone foam models. Methods: Testing was performed on polyurethane foam blocks with densities of 0.08 g/cm 3 and 0.16 g/cm 3 . Four-screw, single-level ALIF plate constructs were secured to the polyurethane foam blocks by use of sets of self-tapping cancellous bone screws that were 20, 24, 28, 32, and 36 mm in length and 6.0 mm in diameter. Plates were pulled out at 1 mm/min to failure, as defined by consistently decreasing load despite increasing displacement. Results: Pullout loads in 0.08-g/cm 3 foam for 20-, 24-, 28-, 32-, and 36-mm screws averaged 303, 388, 479, 586, and 708 N, respectively, increasing at a mean of 25.2 N/mm. In 0.16-g/cm 3 foam, pullout loads for 20-, 24-, 28-, 32-, and 36-mm screws averaged 1004, 1335, 1569, 1907, and 2162 N, respectively, increasing at a mean of 72.2 N/mm. Conclusions: The use of longer screws in ALIF plate installation is expected to increase construct stability. Stabilization from screw length in osteoporotic patients, however, is limited.

Comparison study of the pullout strength of conventional spinal pedicle screws and a novel design in full and backed-out insertions using mechanical tests

“…The rate of 5 mm/min, however, is commonly used. 13,15,[22][23][24][25][26]28,29 Screw stability is highly dependent on (1) the bone quality of the vertebra and the shape of the pedicle, (2) the insertion technique and (3) the screw design and its parameters. The bone-holding strength of the patients with the osteoporosis can be improved using the PMMA.…”

“…Improving the pullout strength of the pedicle screw is complicated because the pullout strength is dependent on several factors, including the screw design, insertion technique, bone quality and shape of the pedicle. 1,8–13 To date, several researchers have tried to improve the bone-holding strength of pedicle screws by focusing on these points. To improve the bone quality, polymethyl methacrylate (PMMA) bone cement was developed for injection into the vertebra body, especially for patients with osteoporosis.…”

An Optimization Study of the Screw Orientation on the Interfacial Strength of the Anterior Lumbar Plate System Using Neurogenetic Algorithms and Experimental Validation

“…The pullout strength of a single spinal screw is related to many factors, including the bone mineral properties [27], screw design [28], screw insertion technique [25], and experimental methodol ogy [29]. However, the pullout strength of an ALP system that includes four individual screws was complicated.…”