Pedicle screw loosening remains a significant concern in clinical settings, particularly for patients with osteoporosis. The utilization of detachable duet screws has the potential to enhance the load capacity necessary for spinal orthopaedic surgery, while minimizing the risk of pedicle fracture or rupture. This study employed biomechanical testing to simulate the distraction process involved in spinal deformity correction. The analysis of the findings demonstrated a notable 1.67-fold increase in MFL during tensile tests when the connection of two detachable duet screws was applied.
In relation to the duet screw, there exist solely a few clinical reports[17, 18]. To be more specific, the implementation of the satellite rod technique, utilizing duet screws, has demonstrated potential for sequential correction, leading to enhanced orthopaedic outcomes and heightened stability in spinal deformity surgery. Diverging from the conventional duet screw, our approach incorporates a detachable design in order to enhance the screws' resistance to loosening during the distraction process in goat models, thereby facilitating the distribution of stress. To this day, there have been limited reports on the biomechanical investigation of duet screws. The findings of our study substantiate the initial hypothesis that the utilization of detachable duet screws yields superior performance compared to a single screw.
The present study also observed characteristic phenomena of toggling, which is the most commonly observed pattern of pedicle screw loosening. These findings align with previous reports[19, 20]. The presence of a crush region at the interface between the bone and screw reduces the screw's ability to securely hold in the cortical bone of the pedicle, making early postoperative screw loosening unavoidable. The utilization of detachable duet screws presents notable benefits due to their ability to connect multiple screws in an arbitrary manner and their detachability, which facilitates the completion of spinal orthopaedic surgery while minimizing the accumulation of metallic residue within the body. By employing detachable duet screws prior to reaching their maximum load capacity, a higher corrective force can be exerted, resulting in a greater degree of correction.
This study possesses certain limitations. Firstly, the utilization of goat specimens in our experiment deviates from the actual conditions of the human spine in terms of size, anatomy, and kinematics[16], which are inherent consequences of employing comparative animal data to establish clinical applicability. Nevertheless, previous studies have suggested that the width of partial vertebral bodies in goats is comparable to that of human vertebral bodies[14]. Additionally, the restricted accessibility of fresh human spines and the substantial variability in geometry and mechanical properties due to factors such as age, sex, and bone mineral density present further challenges.[21]. The specimens utilized in our investigation exhibited elevated and uniform bone density, in contrast to the comparatively lower and less uniform bone density observed in humans. Consequently, to mitigate the influence of confounding variables, the goat can be considered a relatively appropriate animal model for the specific objectives of our study. Furthermore, our experimentation involved the connection of solely two detachable duet screws, with subsequent tests conducted accordingly. The biomechanical implications of connecting three or more pedicle screws remain uncertain. Predicting the requisite number of screws for attaining adequate strength in spinal orthopaedic surgery poses a challenge. In the event of osteoporosis, additional screws may be affixed during the surgical procedure to accomplish spinal correction. Consequently, future investigations will be conducted to ascertain the optimal quantity of detachable duet screws that should be simultaneously secured, accounting for varying bone density conditions. Finally, the etiology of screw loosening appears to be influenced by multiple risk factors[22, 23]. Of these, osteoporosis is a crucial risk factor of screw loosening[24]. The density of bone at the interface between the bone and screw has been found to be closely linked to the occurrence of screw loosening[3, 25]. Notwithstanding, reducing the intraoperative fracture of pedicle as much as possible can also reduce the incidence of postoperative screw loosening to a certain extent.