Total Knee Arthroplasty

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. Question/purposes 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. Conclusion 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.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Is Femoral Component Rotation in a TKA Reliably Guided by the Functional Flexion Axis?

Oussedik

Scholes

Ferguson

et al. 2012

“…Infection after TKA is a devastating complication that threatens both life and function [8]. With modern prophylactic measures, a low incidence of 1% to 2% is to be expected [19].…”

Section: Introductionmentioning

confidence: 99%

High Infection Control Rate and Function After Routine One-stage Exchange for Chronically Infected TKA

Jenny

Bruno

Gaudias

et al. 2013

“…[They] believe that the long-term clinical results, wear resistance, and resistance to prosthetic failure depend on correct positioning of the devices.'' Despite studies [15,20] published since that of Lotke and Ecker, what constitutes ''correct component positioning'' remains elusive, but subsequent work [19] does show the small tolerance, biomechanically and clinically, for off-axis alignment in TKA.…”

Section: Discussionmentioning

confidence: 99%

“…Although it is difficult to say what is clinically significant based on a biomechanical study, in a concurrent clinical radiographic review published in the same paper, Hsu, et al [19] found a disturbing clinical correlation between increased implant malalignment and increasing lucent lines around the tibial components of otherwise successful implants at average 6 years followup. Other studies [15,20] Although previous work suggests the cylindrical axis (CA) is a better surrogate for the FEA [2,3,[8][9][10][11][12], there is no documentation in the literature regarding the relationship of either the TEA or CA to the femoral mechanical axis or the tibial mechanical axis. Because the goal of a contemporary TKA is to position the tibial component at a right angle to the tibial axis and the femoral component at a right angle to the femoral mechanical axis [15,19,20], it may be useful to know whether either axis being used as a surrogate is perpendicular to these longitudinal axes.…”

Section: Introductionmentioning

confidence: 99%

Cylindrical Axis, Not Epicondyles, Approximates Perpendicular to Knee Axes

Hancock

Winston

Bach

et al. 2013

Background The transepicondylar axis (TEA) is often used as a surrogate for the flexion-extension axis, ie, the axis around which the tibia moves in space, because of a belief that both axes lie perpendicular to the mechanical axis. However, studies suggest the cylindrical axis (CA), defined as a line equidistant from contact points on the medial and lateral condylar surfaces from 10 o to 120 o flexion, more closely approximates the axis around which the tibia moves in space.Questions/purposes We examined the TEA and CA angles relative to mechanical axes to determine whether one more consistently and closely approximates the surgical goal of orthogonality to the mechanical axis. Methods Three-dimensional (3-D) models were reconstructed from CT scans of five cadaver limbs. Three observers repeated three measurement sets to locate the TEA, CA, and femoral mechanical and tibial mechanical axes. Angles of the TEA and CA relative to the mechanical axes were calculated in two-dimensions (2-D) and as 3-D projections and compared for differences in magnitude and variance. Results Angles between CA and the mechanical axes were closer to 90°than the TEA in 2-D (92°versus 94°for the femur, 93°versus 94°for the tibia) and 3-D (88°versus 87°for the femur, 88°versus 86°for the tibia). Variance of the TEA was higher than the CA in 2-D. Conclusions The CA forms angles more orthogonal to the mechanical axes of the thigh and leg than the TEA. Clinical Relevance Although we found a consistently greater deviation of the TEA from the mechanical axis than the CA with small differences, future studies will need to determine whether these differences are biomechanically or clinically important.