Abstract
INTRODUCTION
It has been reported that the rate of complications around the patella after Total Knee Arthroplasty(TKA) is 1–12%, and the patella dislocation is the most common one.
PURPOSE
We will report a case that had the patella dislocation after TKA caused by malrotation of the components.
CASE
67 years old, Female. The chief complaint was an instability of the right patella. She had undergone TKA due to osteoarthritis at another hospital. After 2 months, she felt a subluxation of the patella. And after 4 months, she had a reoperation of medial reefing and revision of the patella at the same hospital, and the doctor allowed her to flex her right knee within 70 degrees. However, after 3 months, she started experiencing pain with a feeling of dislocation and got it corrected and immobilized with a knee brace. 2 weeks later, she visited our hospital for the first time.
STATUS
148cm, 65kg. She could gait with an extension knee brace. Tenderness was seen around the right patella. She could bend her right knee from 0 degrees to 60 degrees. Extension lag and instability of varus and valgus were not existent.
An X-ray showed the FTA was 172 degrees on the right side. The right knee had a TKA(Stryker Scorpion Energy®/fixed surface), and the measurements of component after TKA were almost good. However, the patella had lateral subluxation. A CT image showed the femoral component inserted in internal rotation of 8 degrees from CEA and tibia component inserted in internal rotation of 23 degrees from the left Akagi line. We diagnosed right knee dislocation because of rotation failure of the components.
COURSE OF TREATMENT
We replaced implants which were produced by the same company. We replaced the tibial component externally referring to the Akagi's line. On the femur side, we augumented the femur component at the posterolateral and replaced it referring to the CEA. We made a lateral release and used a CCK surface. We did not replace the patella because the surviving patella bone was thin and patella tracking was satisfactory.2 weeks after the operation, she could bend her knee from 0 degrees to 120 degrees and walk with a cane. An X-ray showed the patella was reduced and a CT scan showed the appropriate rotation angle.
DISCUSSION
Regarding the treatment of patella dislocation after TKA, when there is malrotation of components, revision is recommended. The definition and the degree of malrotation are still controversial. It was reported that when total internal rotation angle was more than 7 degrees, Revision is recommended. This patient obtained the stability of patella due to the proper rotation angle of components.
