Abstract
Introduction
Malrotation of a femoral component is a cause of patellofemoral maltracking after total knee arthroplasty (TKA). We have developed a balanced gap technique in posterior stabilized total knee arthroplasty (PS-TKA) using an original tensor instrument. One of characteristics of this instrument is the ability to measure gaps even if there is a bone defect, because it has two paddles, and we can attach block augmentations. In addition it can measure the gap after a reduction of the patella with an offset mechanism. In the balanced gap technique, the femoral component rotation is decided by a tibial cut surface and ligaments balance using the tensor device. This study investigated retrospectively whether rotational alignment of femoral component rotation influenced patellofemoral joint congruency in PS- TKA.
Material and Methods
We evaluated the radiographs of 52 knees of 42 patients, who underwent TKA (NexGen LPS-Flex, fixed surface, Zimmer) by one surgeon (S.A.) for osteoarthritis or rheumatoid arthritis. All procedures were performed through a medial parapatellar approach and a balanced gap technique using a developed versatile tensor device. We measured lateral patella tilt and lateral patella shift at post-op. 6 months. To assess the rotational alignment of femoral component rotation, condylar twist angle (CTA) was measured, and to assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was measured using the epicondylar view radiographs.
Results
We performed the lateral release on 4 knees (7.6%). The average lateral patella tilt and CTA, and LOA were 3.00 ± 3.2°, 0.95 ± 2.5°, 1.50 ± 1°, respectively. There were two cases which had more than 10°tilt. We did not find any case of lateral patella shift. There was no statistical correlation with lateral patella tilt and CTA (r=0.17, p=0.2) (figure 1). There was no statistical correlation with the patella tilt and LOA (r=-0.1, p=0.9) (figure2). The case with 13.4°patella tilt was post-traumatic osteoarthritis (ACL and MCL injury). There were two cases which were cut patella obliquely, and each patella tilt was 13.0°and 3.3°.
Discussion
Previously we reported that the rate of a lateral release decreased by a balanced gap technique compared with a conventional measured resection technique. Although the balanced gap technique resulted in a patient's specific wide variability for femoral component rotation, this variable rotation was not found to be associated with abnormal patella tilt and patella shift.
