| Objective:The purpose of this study was to summarize our experience of using screws and cement to rebuild tibial bone defect in primary TKA, and to study the relationship between the number of screws needed and the severity of tibial bone defects.Materials and Methods:1、 Clinical study:From February 2009 to May 2015,34 patients (40 knees) with severe varus OA knee underwent TKA, in which screw and cement technique was used to rebuild medial tibia plateau bone defects. There were 8 males(8 knees) and 26 females (34 knees), the average age of patients was 65±7.25 years old(ranged,55～82 years).1～6 screws were used in each case. Extension stem were used in 2 cases(4 and 5 screws was used each). The area percentages of the bone defects(defect area/tibia plateau area), depth of each defect and the number of screws used in each case were measured, O-Logistic statistic methods were used to determine the relationship between the number of screws needed and the area percentage in certain depth of bone defect, and the relationship between screw number and defect depth. 2、Finite element study:Six tibial finite element models with defects filled with screws were built using Mimics 11 software, among which 3 models filled with 1 oblique scew,1 perpendicular screws and 2 perpendicular screw respectively had 12% defect area and 12mm depth of tibial platform, three models filled with 1,2 and 3 perpendicular screws respectively had 20% defect area and 20mm depth of tibial platform. As a control,1 models only filled with cement had 12% defect area of tibial platform was built. Three-dimensional finite element analysis was used to calculate contact stresses on the surface of cancellous bone subjected to a compressive load from the tibial prosthesis and cement. And compared the stress with cancellous bone collapse stress threshold, and with the critical stress which would cause stress shelter, and compared the stress in different models in the same position, then analysis the optimal number of screws and better screw insert angle of two different kind of defects.Results:1.Clinical study:1. All patients were followed up and the average duration was 24 months(ranged,l to 72 months). The average preoperative HSS score was43.33 ± 6.11(ranged,32 to 51 scores). Whereas the average postoperative HSS score was 92.15± 4.64(ranged,83 to 96 scores)(P<0.01).The preoperative individual score including pain, function, activity, muscle strength, flexion deformity and stability were significantly improved compared with pre-operation, the differences were statistically significant(P<0.01). All cases received normal alignment postoperatively, femoral angle improved from 84.45°±3.59° (77°～90°)preoperatively to 85.29±2.28° (81° ～89°) postoperatively, and tibial angle improved from78.09°±4.51° (68°～87°) preoperatively to 88.75°±1.24° (86°～90°) postoperatively. 2. Both bone defect area percentage and depth in a fitting O-logistic model have significant statistical relationship to screw number used, and defect depths (X) and area percentages (Y) have linear relationship:in a rectangular coordinate system, spots on line Y1= 0.0141X]+0.2299 using one or two screws are at the same tendency; spots on line Y2= 0.0141X2+0.374, using two or three screws are at the same tendency.2、Finite element study:Compared with single cement technique, cancellous bone and bone cement boundary stress significantly decreases by 10% using screw and cement technique. For bone defects with defect area percentage of 12%, depth of 12 mm, using 1 screw can acquire best stability without bone resorption caused by stress shelter; for defect area percentage of 15%, depth of 20 mm, using 2 screws can acquire best stability without bone resorption caused by stress shelter.Conclusion:1.Clinical study (1) Screws and cement technique is a easy, safe and convenient way to rebuild tibial bone defects in primary TKA, its reported long-term effect is reliable, in this study its shortterm and midterm effect is reliable so far.(2) During operation, based on a given tibial defect, we can infer a tendency of the screw number needed according to the rectangular coordinate system formed, this could have a guiding function in surgery.2、Finite element study:(1) Compared with single cement technique, using screw and cement technique to repair defect, no matter the screws direction is vertical or oblique, can obviously decreases the stress on the border of cancellous bone and cement, then reduce the possibility of collapse of the cancellous bone. In terms of mechanics property, screw and cement technique is better than single bone cement technique, and for tibial defect whose area percentage is large but depth is less than 5 mm, screw and cement technique is recommended.(2) Vertical screw can get better stability than oblique one.(3) To gain a better prosthetic stability without bone resorption caused by stress shelter, area percentage of 12%, depth of 12 mm bone defects using one screw can get best stability; defect area percentage of 20%, depth of 15 mm, using two screw can get best stability. Screws used in different defects should be moderate, not the more the better. |
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