Abstract
The reasons leading to rotational tibial malalignment in total knee arthroplasties (TKAs) remain unclear. A previous cadaver study has shown an increase in internal rotation of the anatomical tibial axis (ATA) after the tibial cut. This study investigates the influence of tibial slope on the ATA and the size of the resected tibial surface. CT scans of 20 cadaver knees were orientated in a standardized coordinate system and used to determine the position of the centres of rotation of the medial and lateral tibial articular surfaces and, hence, of the ATA, after a virtual resection of 6mm with 0°, 3.5°, 7° and 10° slope, respectively. Furthermore, at each slope, the radii of the medial and lateral tibial articular surfaces after resection were calculated. Compared to resection of 6mm with 0° slope, a slope of 3.5° resulted in a mean external rotation of the ATA of 0.9° (SD, 1.5°; P = 0.025). A slope of 7° resulted in a mean external rotation of the ATA of 1.0° (SD 2.0°; P = 0.030) and a slope of 10° had no influence on the rotation of the ATA. The radii of the medial and lateral articular surfaces of the cut tibiae were larger than those of the uncut tibia (P < 0.001). Differences in the posterior tibial slope should not contribute to a rotational malalignment when using the ATA to align the prosthetic tibial plateau. Although statistically significant, the change in ATA with increasing slope was negligible.
Highlights
Internal rotation error of the tibial component in total knee arthroplasty (TKA) has been linked to polyethylene wear, prosthesis loosening, stiffness and pain, and negatively influences patellofemoral kinematics [8, 14, 25]
For a 6mm resection, a posterior tibial slope of 3.5° resulted in a mean external rotation of the anatomical tibial axis (ATA)
A slope of 7° resulted in a mean external rotation of the ATA of 1.0° (SD 2.0°; P=0.030) and a slope of 10° did not lead to a rotation of the ATA
Summary
Internal rotation error of the tibial component in total knee arthroplasty (TKA) has been linked to polyethylene wear, prosthesis loosening, stiffness and pain, and negatively influences patellofemoral kinematics [8, 14, 25]. According to the principle of best fit and coverage of the resected bone surface, the surgeon places the tibial component centered between the anterior and posterior condylar margins on the medial tibial plateau [11]. This could be misleading because the position of the centers of the medial and lateral articular surfaces do not remain stationary after the tibia resection is performed. A cadaver study has reported an anterior shift of the center of the lateral articular surface at the level of the resection relative to the original joint line [11] This is in agreement with a further cadaver study showing that maximizing tibial coverage could lead to an internal malrotation [21]. To date, the influence of tibial slope on the internal rotation error possibly introduced by this technique has not been investigated
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