Abstract
Purpose
In vivo comparative gap measurements were performed in 3 different patella positions (reduced, subluxated and everted) using offset-type-force-controlled-spreader-system.
Methods
Prospectively, 50 knees were operated by TKA using a navigation-assisted gap balancing technique. The offset-type-force-controlled-spreader-system was used for gap measurements. This commercially-available instrument allows controllable tension in patella reduced position. The mediolateral gaps of knee extension (0°) and flexion (90°) angle were recorded in 3 different patella positions; reduced, subluxated and everted. Any gap differences of more than 3 mm were considered as a meaningful difference. Correlation between the difference with the demographic data, preoperative radiologic alignment and intraoperative data was analyzed. For statistical analysis, ANOVA and Pearson correlation test were used.
Results
The gaps in patella eversion demonstrated smaller gaps both in knee extension and flexion position compared to the gaps of patella reduction position. The amount of decreased gaps was more definite in knee flexion position. Statistically significant difference were observed for the lateral gap of patella eversion compared to gap of patella reduction in knee flexion position (p<0.05). There were notable cases of variability in knee flexion position. Significant portion 12 (24%) knees of patella subluxation and 33 (66%) knees of patella evertion demonstrated either increased or decreased gaps in knee flexion position compared from the gaps of patella reduction position.
Conclusion
The gaps in patella eversion demonstrated smaller gaps both in knee extension and flexion position compared to the gaps of patella reduction position. The amount of decreased gaps was more definite in knee flexion position. Therefore, the intraoperative patellar positioning has influence on the measurement of the joint gap. Keeping the patella in reduced position is important during gap balancing.
