Abstract
Purpose
The literature indicates that the tibial component in total knee arthroplasty (TKA) should be placed in internal rotation not exceeding 18 to the line connecting the geometrical center of the proximal tibia and the middle of the tibial tuberosity. These landmarks may not be easily identifiable intraoperatively. Moreover, an angle of 18 is difficult to measure with the naked eye.
Method
The angle at the intersection of lines from the middle of the tibial tuberosity and from its medial border to the tibial geometric center was measured in 50 patients with normal tibia. The geometric center was determined on an axial CT slice at 10mm below the lateral tibial plateau and transposed to a slice at the level of the most prominent part of the tibial tuberosity.
Similar measurements were performed in 25 patients after TKA in order to simulate the intra operative appearance of the tibia after making its proximal resection.
Results
This angle was found similar (p=0.43) in normal and operated tibiae (mean 20.4, range 15–24 versus 20.7, range 16–25, respectively). In 89.3% of the patients the angle ranged from 17–24.
No statistical difference (p=0.55) was found between women and men in both normal (mean 20.7, range 16–25 versus 19.9, range 15–24) and operated tibiae (mean 21.4, range 19–24 versus 20, range 16–25).
Conclusion
In 90% of the patients the medial border of the tibial tuberosity is in internal rotation of 1724 to the line connecting its middle to the tibial geometric center. Since this anatomical landmark may be more easily identifiable intraoperatively than the commonly used medial 1/3, this data can and provide surgeons a quantitative reference point. Together with routine intra operative ancillary measurements the rotation of the tibial component can be more accurately determined.
