Abstract
Strong stiffness provided by locking-plate system has resulted in nonunion and delayed union for long bone fracture. Longer bone plate can lengthen the working length to reduce the structural stiffness of the fixation device but will enlarge skin incision. Using the semi-rigid locking screw may be helpful but the efficacy was unclear. In simulated fracture model, four rigid locking screws were continually inserted beneath the fracture gap. The other four rigid/semi-rigid locking screws were equally distributed or concentrated at screw holes superior to the fracture gap. Axial compressive load was exerted to compare the biomechanical performance under various screw configurations and plate working length. Results revealed that using the semi-rigid locking screws, the structural stiffness of the fixation structure were lowered by 29.5%–45.1% comparing to the model with the same screw configuration using rigid locking screws. Semi-rigid screw models with shorter working length represented comparable flexibility of the fixation structure to the rigid locking screw model with longer working length. Compared to rigid locking screw, semi-rigid locking screw may provide similar flexibility with shorter bone plate, which may be beneficial to reduce the required plate length so that the skin incision may be minimized for fracture reduction.
Highlights
The locking mechanism between bone screws and plate forms a strong structure without being tightly compressed to the fractured segments, which is beneficial to patients suffered from osteoporosis.[4,5]
It was noted that models with identical working length would result in similar axial stiffness using the same type of screw
Due to different considerations in bone-healing modes, the reduced fixation stiffness is preferable in locking-plate system because better flexibility of the fixation device may provide greater interfragmental movement, which can promote better mechanical stimulation at the fracture site to achieve an ideal secondary bone healing
Summary
With great capability in maintaining structural stability in treatment of bony fractures, the locking-plate system has been widely agreed in orthopedic trauma care in the recent decades.[1,2,3] the locking mechanism between bone screws and plate forms a strong structure without being tightly compressed to the fractured segments (required by conventional compression plate fixation), which is beneficial to patients suffered from osteoporosis.[4,5] The secondary bone healing, depending on callus formation,[3] requires a greater theoretical interfragmentary strain interval between 2%–10% compared. Advances in Mechanical Engineering to primary healing (less than 2%).[6] locking plate with excessive structure stiffness would be problematic to ideal bone healing due to weakened mechanical stimulation at fracture site. Clinical problem such as nonunion, delayed union, required secondary procedures, implant failures, and loss of alignments were reported.[7,8,9]
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