Is femoral component rotation in a TKA reliably guided by the functional flexion axis?
BACKGROUND
The position of the femoral component in a TKA in the axial plane influences patellar tracking and flexion gap symmetry. Errors in femoral component rotation have been implicated in the need for early revision surgery. Methods of guiding femoral component rotation at the time of implantation typically are derived from the mean position of the flexion-extension axis across experimental subjects. The functional flexion axis (FFA) of the knee is kinematically derived and therefore a patient-specific reference axis that can be determined intraoperatively by a computer navigation system as an alternative method of guiding femoral component rotation. However, it is unclear whether the FFA is reliable and how it compares with traditional methods.


OBJECTIVE
We asked if the FFA could be measured reproducibly at different stages of the operative procedure; (2) where it lies in relation to a CT-derived gold standard; and (3) how it compares with more traditional methods of judging femoral component rotation.


METHODS
Thirty-seven patients undergoing elective TKAs were recruited to the study. Preoperative CT scans were obtained and the transepicondylar axis (TEA) was identified. The TKA then was performed using computer navigation. The FFA was derived before incision and again after the surgical approach and osseous registration. The navigation system was used to register the surgical TEA. The FFA and surgical TEA then were compared with the CT-derived TEA.


RESULTS
The mean preincision FFA was similar to the intraoperative FFA and therefore deemed reproducible. We observed no differences in variability between surgical TEA and preincision FFA. The FFA was different from the CT-TEA and judged similar in accuracy to the surgical TEA.


CONCLUSIONS
The reliability and accuracy of the FFA were similar to those of other intraoperative methods. Further evaluation is required to ascertain whether the FFA improves on currently available methods for determining the ideal rotation of the femoral component during TKA.
Sydney Orthopaedic Research Institute, Suite 12, Level 1, 445 Victoria Avenue, Chatswood, NSW 2067, Australia.
Sam
S
Oussedik
Corey
C
Scholes
Duncan
D
Ferguson
Justin
J
Roe
David
D
Parker
D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005269:Femur / Q000601:surgery*; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000601:surgery*; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012399:Rotation; D013238:Stereotaxic Techniques; D025321:Surgery, Computer-Assisted; D014057:Tomography, X-Ray Computed