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Abstract
Purpose
We wanted to identify the difference of the measured values between a navigation system and radiographs when performing open and closed wedge high tibial osteotomy (HTO) under the control of a navigation system.
Materials and Methods
Thirty-two open wedge HTOs and 51 closed wedge HTOs were performed using a navigation system. The postoperative mechanical axis percent, which was planned on the navigation system, was 62%. The mechanical axis (MA) was measured before osteotomy and after fixation on the navigation system, and these were compared with the measured values from the radiographs. The difference of the postoperative MA between the navigation system and the radiographs was compared according to the type of HTO. The alteration of the tibial posterior slope angle was also compared.
Results
For the open wedge HTO, the mean MA after fixation was valgus 2.7° on the navigation system and the postoperative MA was valgus 4.0° on the radiograph. For the closed wedge HTO, the mean MA after fixation was valgus 3.5° on the navigation system and the postoperative MA was valgus 1.6° on the radiograph (p=0.000). The mean tibial posterior slope angle was increased by 5.3° after the open wedge HTO and it was decreased by 1.8° after closed wedge HTO (p=0.000).
Conclusion
Performing HTO with a navigation system could increase the surgical accuracy because the navigation system checked the intraoperative correction angle in real time. Weight bearing makes a difference for the postoperative MA between the navigation system and radiographs. This should be taken into account, according to the type of HTO.
Figures and Tables
Fig. 1
(A) The mechanical axis % (MA%) shown on the preoperative ortho-roentgenogram is evaluated by percentile denotation [(b/a)×100]. "a" is the width of tibia plateau and "b" is the distance from the medial border of the medial tibial condyle to the point at which the mechanical axis intersects the knee joint line. It shows medial deviation of the mechanical axis. (B) The mechanical axis % (MA%) shown on the postoperative ortho-roentgenogram is evaluated by percentile denotation [(b'/a')×100]. "a'" is the width of tibia plateau and "b'" is the distance from the medial border of the medial tibial condyle to the point at which the mechanical axis intersects the knee joint line. It shows lateral deviation of the mechanical axis.
Fig. 2
Change of mechanical axis after the open wedge high tibial osteotomy using navigation system. (A) A 64-year-old woman have the open wedge high tibial osteotomy under navigation control. In the preoperative roentgenogram, the mechanical axis (MA) is varus 9.4° and the mechanical axis % (MA%) is 9.2%. The posterior slope angle of tibia is 8.0°. In the navigation system, the MA is varus 7.4° and the MA% is 22%. (B) In the navigation system, the post-osteotomy MA is valgus 3.5° and the MA% is 57.7%. In the postoperative 2 week roentgenogram, the MA is valgus 5.2° and the MA% is 72.9%. The posterior slope angle of tibia is 12.1°. The postoperative MA and MA% in roentgenogram is larger than the postosteotomy MA and MA% in navigation system. (C) In the postoperative 4 month roentgenogram, the MA is varus 1.2° and the MA% is 37.4%. There are two proximal screws breakage of Puddu plate and loss of correction angle.
Table 1
Radiological Measurements and Measurements using Navigation System
*MA, angle between the femoral and tibial mechanical axis; †MA%, percentile denotation ((b/a)×100) of the point at which the mechanical axis of the low extremity intersects the line extending from the medial border to the lateral border of the tibial plateau on orthoroentgenogram; ‡-, negative values mean varus angles.
Table 2
Difference between the Post-osteotomy Mechanical Axis in Navigation System and Postoperative Mechanical Axis in Radiograph (Number of Cases)
*Group I, Group of cases in which the postoperative mechanical axis on radiograph is 2° smaller than the post-osteotomy mechanical axis on navigation; †Group II, Group of cases in which the difference between the postoperative mechanical axis on radiograph and post-osteotomy mechanical axis on navigation is within 2°; ‡Group III, Group of cases in which the postoperative mechanical axis on radiograph is 2° more than the post-osteotomy mechanical axis on navigation.
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