| Objects: To investigate the positioning of Kirschner wires(K-wires)in the application of patellar modified tension-band wiring(MTBW),and to study the biomechanical effects of the positioning of K-wires and the configurations of fixation.Methods: A new method was used to build up the 2D coordinate system of the patella.Based on the coordinate system,the height,width,and thickness of the patella were measured on the postoperative X-ray images of patients who underwent MTBW surgery,and the position and direction of K-wires on both coronal and sagittal planes were measured as well.The placing level of K-wires was classified by identifying the anterior-posterior direction of the patella in a model derived from a health subject.Patella fracture-MTBW finite element(FE)models with K-wires placed at 5 levels and steel wires placed in 2 configurations were reconstructed.FE analysis was used to calculate the displacement and stress of these models in the testing condition of 45° knee extension,and inter-level and inter-configuration comparisons of the results were conducted.Results: The male patella is larger than the female in height and width(height,46.66 ± 4.22 mm vs 41.88 ± 3.29 mm,P = 0.005;width,53.85 ± 3.24 mm vs 48.84 ± 3.87 mm,P = 0.001),while similar in thickness(22.87 ± 1.96 mm vs 21.67 ± 1.38 mm,P = 0.10).On the coronal plane,K-wires are placed centrally and longitudinally as a whole;individually,the two are placed roughly on the trisector lines and in a non-parallel fashion with slightly wider space between the proximal ends(angle between two K-wires,2.68 ± 3.22°,P < 0.001).On the sagittal plane,K-wires are also centered as a whole,and point to distal and posterior slightly(angle between K-wires and longitudinal axis,2.09 ± 5.20°,P = 0.04).The positioning of Kwires shows no significant difference between surgeons.The FE modeling of different levels and configurations was proved to be feasible.With K-wires placed deeper,the pressure of the fracture surface increases(+0.20 ± 0.20 MPa,R = 0.99,P = 0.001),and the impact of the improper stress and the stress of K-wires decreased(improper stress area,27.47 ± 11.73%,R =-0.96,P = 0.01;stress of K-wires,101.56 ± 22.73 MPa,R =-0.93,P = 0.02).When the Kwires are placed around or deeper than the midline(Level 3-5),the fractures show more stability(displacement is 77% of Level 1-2),and the bone contact stress declines(66%-75% of Level 1-2).The figure-of-zero wiring demonstrates superior stability and compression effect than the figure-of-eight wiring(displacement,0.19 ± 0.05 mm vs 0.32 ± 0.05 mm,P < 0.001;pressure,+0.23 ± 0.21 MPa vs +0.17 ± 0.20 MPa,P = 0.002),and it also alleviate the stress of bone and implants(stress of the bone in contact with K-wires,9.21 ± 2.59 MPa vs 9.94 ± 2.22 MPa,P = 0.02;stress of K-wires,97.55 ± 27.15 MPa vs 105.58 ± 22.67 MPa,P = 0.02;stress of steel wires,80.51 ± 4.28 MPa vs 87.61 ± 7.26 MPa,P = 0.01).Conclusions: The height and width of patella deviates between genders.The position and direction of K-wires remain consistent among surgeons in the application of MTBW.FE analysis is feasible for the investigation of MTBW technique.Deep enough positioning of Kwires and the use of figure-of-zero wiring can improve the biomechanical properties of MTBW. |
PDF Full Text Request