ABSTRACT
PURPOSE: Cortical porosis, secondary to either vascular injury or stress-shielding, is a comorbidity of fracture fixation using compression bone plating. Locking plate constructs have unique mechanics of load transmission and lack of reliance on contact pressures for fixation stability, so secondary cortical porosis adjacent to the plate has not been widely investigated. Therefore, this study aimed to assess the effects of long-term locking plate fixation on cortical dimensions and density in a caprine tibial segmental ostectomy model. METHODS: Data was acquired from a population of goats enrolled in ongoing orthopedic research which utilized locking plate fixation of 2 cm tibial diaphyseal segmental defects to evaluate bone healing over periods of 3, 6, 9, and 12 months. Quantitative data included tibial cortical width measurements and three-dimensionally reconstructed slab density measurements, both assessed using computed tomographic examinations performed at the time of plate removal. Additional surgical and demographic variables were analyzed for effect on cortical widths and density, and all cis-cortex measurements were compared to both the trans-cortex and to the contralateral limbs. RESULTS: The tibial cis-cortex was significantly wider and more irregular than the trans-cortex at the same level. This width asymmetry differed in both magnitude and direction from the contralateral limb. The bone underlying the plate was significantly less dense than the trans-cortex, and this cortical density difference was significantly greater than that of the contralateral limb. These cortical changes were independent of both duration of fixation and degree of ostectomy bone healing. CONCLUSIONS: This study provides evidence that cortical bone loss consistent with cortical porosity is a comorbidity of locking plate fixation in a caprine tibial ostectomy model. Further research is necessary to identify risk factors for locking-plate-associated bone loss and to inform clinical decisions in cases necessitating long-term locking plate fixation.
ABSTRACT
PURPOSE: Locking plate fixation of caprine tibial segmental defects is widely utilized for translational modeling of human osteopathology, and it is a useful research model in tissue engineering and orthopedic biomaterials research due to its inherent stability while maintaining unobstructed visualization of the gap defect and associated healing. However, research regarding surgical technique and long-term complications associated with this fixation method are lacking. The goal of this study was to assess the effects of surgeon-selected factors including locking plate length, plate positioning, and relative extent of tibial coverage on fixation failure, in the form of postoperative fracture. METHODS: In vitro, the effect of plate length was evaluated using single cycle compressive load to failure mechanical testing of locking plate fixations of caprine tibial gap defects. In vivo, effects of plate length, positioning, and relative tibial coverage were evaluated using data from a population of goats enrolled in ongoing orthopedic research which utilized locking plate fixation of 2 cm tibial diaphyseal segmental defects to evaluate bone healing over 3, 6, 9, and 12 months. RESULTS: In vitro, no significant differences in maximum compressive load or total strain were noted between fixations using 14 cm locking plates and 18 cm locking plates. In vivo, both plate length and tibial coverage ratio were significantly associated with postoperative fixation failure. The incidence of any cortical fracture in goats stabilized with a 14 cm plate was 57%, as compared with 3% in goats stabilized with an 18 cm plate. Craniocaudal and mediolateral angular positioning variables were not significantly associated with fixation failure. Decreasing distance between the gap defect and the proximal screw of the distal bone segment was associated with increased incidence of fracture, suggesting an effect on proximodistal positioning on overall fixation stability. CONCLUSIONS: This study emphasizes the differences between in vitro modeling and in vivo application of surgical fixation methods, and, based on the in vivo results, maximization of plate-to-tibia coverage is recommended when using locking plate fixation of the goat tibial segmental defect as a model in orthopedic research.