Effect of Decreasing Tibial Posterior Slope on the Extension-Gap during PS-TKA

PURPOSE: To evaluate the effect of decreasing tibial slope on extension gap during posterior stabilized total knee arthroplasty. MATERIALS AND METHODS: One hundred and ten cases of total knee arthroplasty which were done with posterior stabilized implant were included and we divided those into Group I; having flexion contracture (n=35) and Group II; no flexion contracture (n=75), and from each group, we evaluated the relationship between degree of decreased angle of tibial slope and frequency of additional resection of distal femur which was done for compensating insufficient extension gap during total knee arthroplasty and compared frequencies of additional distal femoral resections between 2 parts having more and less degree of decreased angle of tibial slope. RESULTS: In Group I and II, tibial slope decrease were 8.7degrees, 7.4degrees (p=0.145) and frequencies of additional resection were 51.4%, 24% (p=0.005) in average. Comparing 2 parts having more and less degree of decreased angle of tibial slope in each Group, frequencies of additional resection were 44.4%, 58.8% (p=0.505) and 13.2%, 35.1% (p=0.032). CONCLUSION: During posterior stabilized total knee arthroplasty, especially having no preoperative flexion contracture, decreasing tibial slope can be considered as a factor influencing on extension gap by removing greater anterior bone and the estimation of predictable tibial slope decrease through preoperative radiologic findings can be helpful in creating equal flexion and extension gaps.

Effect of the Decrease in Tibial Posterior Slope on the Patellar Height after Total Knee Arthroplasty

PURPOSE: To evaluate the effect of the decrease in posterior slope of the tibia on the patellar height after TKA. MATERIALS AND METHODS: One hundred and fifty three cases of TKA (CR type: 43, PS type: 110) were evaluated to measure the posterior slope of the tibia and the patellarheight on lateral radiographs of the knee before and after surgery. Then, we analyzed a correlation between two measurements. RESULTS: The decrease in tibial posterior slope and patellar height was average 6.6 degrees and 1.4mm, there was a weak correlation (r= -0.293, p=0.000), as more decrease in tibial slope, less decrease in patellar height. Comparing CR group with PS group, the decrease of posterior slope of tibia and patella height was average 3.5 vs 7.8 degrees (p=0.000) and 2.2 and 1.2 mm (p=0.146) respectively. There were also correlations (r=-0.438, p=0.003 vs r=-0.228, p=0.017) between two decreases. CONCLUSION: It is considered that the decrease in tibial posterior slope is one of elements influencing in patellar height, and through preoperative radiological examination, estimation of expected decrease in tibial posterior slope is helpful in preserving patellar height in TKA.

Tibial Plateau Coverage in total knee Replacement arthroplasty

Maximizing tibial coverage is an important consideration in total knee replacement arthroplasty to provide stability and even load transfer and to improve long term survival rate of the implants. We evaluated the coverage, underhang and overhang ratio for the proximal tibial resection surface during total knee replacement arthroplasty in Koreans. After cutting the proximal tibia, the outline of tibial resection surface was traced manually. We compared 5 tibial tray designs, AGC(Biomet, Warsaw, U.S.A.), Advantim(Wright medical technology, Arlington, U.S.A.), AMK(DePuy, Warsaw, U.S.A), MG II(Zimmer, Indiana, U.S.A.), Series 7000(Osteonics, New Jersey, U.S.A.), which have been commercially used in Korea for total knee replacement arthroplasty. The average percentage of coverage area were 83.3% in AGC, 81.6% in AMK, 80.3% in MG II, 80.2% in Advantim and 76.9% in Series 7000. The average percentage of underhang were 16.7% in AGC, 18.4% in AMK, 19.6% in MG II, 19.8% in Advantim and 23,1% in Series 7000. The average percentage of overhang were measured 7.97% in AGC, 7.86% in AMK, 8.01% in MG II, 8.77% in Advantim and 10.14% in Series 7000. So average coverage percentage of tibial cutting surface was 80.5% in Koreans. The factors which affect the optimal coverage, were the shape, dimensional interval of tibial trays and the number of practically useful tibial trays for Koreans.