[Relationship between screw numbers and severity of tibial bone defect in primary total knee arthroplasty].

Objective: To summarize experience of using screws and cement to rebuild tibial bone defect in primary total knee arthroplasty (TKA) and to discuss the relationship between the number of required screws and the severity of tibial bone defects.

Methods: From July 2009 to May 2015, 34 patients (40 knees) with varus knees underwent TKA, and the screw and cement technique was used to rebuild medial tibia plateau during operation. There were 8 males (8 knees) and 26 females (32 knees), and the average age was (65.00 +/- 7.25) years old (ranged,55 to 82 years old). One to 6 screws were used in each case. Extension stems were used in 2 cases (4 and 5 screws was used respectively). The area percentages of the bone defects measured as defect area/tibia plateau area, depth of each defect, the number of screws needed in each case, were all used to determine the relationship between the number of screws and the area percentage in certain depth of bone defect by statistic methods, as well as the relationship between screw number and defect depth.

Results: All the patients were followed up and the average duration was 24 months (ranged, 1 to 72 months). The average preoperative HSS score was 43.33 +/- 6.11 (ranged, 32 to 51 scores). Whereas the average postoperative HSS score was 92.15 +/- 4.64 (ranged,83 to 96 scores). The preoperative individual scores including pain, function, activity, nuscle strength, flexion deformity and stability were all improved compared with preoperation,and the differences were statistically significant. All the patients received normal alignment postoperatively, femoraltibial angle was improved from (167.00 +/- 6.39) degrees preoperatively to (175.00 +/- 2.69) degrees postoperatively, the tibial angle was improved from (78.09 +/- 4.51) degrees preoperatively to (88.75 +/- 1.24) degrees postoperatively. Both area percentage and depth of bone defect in a fitting Ologistic model had a significant statistical relationship with the screw number, and a rectangular coordinate system could be formed according to the relationship.

Conclusion: Screws and cement technique is a simple, safe and convenient method to rebuild tibial bone defects in primary TKA and its short-term and midterm effect are both reliable. During opera- tion, according to the rectangular coordinate system, the screw number needed in the operation can be inferred form th area and depth of tibia defect, which could have a guiding function in surgery.