Abstract
INTRODUCTION:
It has been reported that rotational deformity is present in varus osteoarthritis (OA) of the knee and the tibia rotates externally as the varus deformity progresses. Although many studies addressed the rotational alignment of the femoral and tibial component in total knee arthroplasty (TKA), the pre-and postoperative changes of the rotational alignment in varus OA knee has not been evaluated. The purpose of this study was to quantitatively analyze the alteration of rotational deformity after TKA for the varus OA knee.
METHODS:
Between July 2011 and December 2012, 157 patients (159 knees) with primary varus OA knee undergoing TKA were included. A mobile-bearing, posterior stabilized knee prosthesis was implanted with cement in all patients. Rotational deformities were evaluated with computed tomography (CT) before and after the operation. On the selected CT slices, the relative rotational position of the femur and tibia was quantified as an angle between the line perpendicular to the surgical epicondylar axis of the femur and the line connecting the tibial tubercle tip and the geometric center of the tibia. The knees were divided into three groups according to the preoperative varus deformity (Group I; 0–8° varus, n = 78, Group II; 9–17 ° varus, n = 71 and Group III; 18 ° or greater varus, n = 10) and the difference among the groups were statistically analyzed.
RESULTS:
Preoperatively, the average rotational deformity was 6.4 ± 0.9 ° (mean ± SE) external rotation of the tibia relative to the femur. This was significantly corrected to 0.9 ± 0.6 ° external rotation of tibia postoperatively (p < 0.05). The amount of preoperative rotational deformities were not significantly different among the groups (Group I; 6.6 ± 0.9 ° e.r.(external rotation of tibia), Group II; 4.3 ± 1.8 ° e.r., Group III; 5.7 ± 4.1 ° e.r.). Although the rotational deformity wasã��corrected to almost neutral in Group I and II (1.1 ± 0.4 ° e.r. and 1.4 ± 0.9 ° e.r. respectively), there was a tendency with postoperative internal rotation of tibia in Group III (4.2 ± 2.4 ° internal rotation of tibia, p = 0.10).
DISCUSSION AND CONCLUSION:
This study has demonstrated that rotational deformity in varus OA knee is significantly corrected after TKA. The knees with less preoperative varus deformity are more likely to be corrected to neutral but substantial rotational mismatch (internal rotation of the tibia) remains in the knees with severe varus deformity. This might be related to the amount of the medial soft tissue release required to obtain correct limb alignment. The surgeons who perform TKA should be aware of the information and carefully check the relative position of the tibial and femoral components especially in the knees with severe varus deformity.
