Passive Knee Kinematics Before and After Total Knee Arthroplasty Are We Correcting Pathologic Motion? William M. Mihalko, MD PhD,* Mounawar Ali, MD,y Matthew J. Phillips, MD,y Mary Bayers-Thering, MS,y and Kenneth A. Krackow, MDy Abstract: The change in coronal plane deformity throughout a range of flexion before and after total knee arthroplasty (TKA) has not been reported. Unlike most alignment assessments traditionally reporting coronal plane alignment in a standing position under static conditions, this study reports deformity throughout the flexion arc before and after deformity correction. One hundred fifty-two TKA patients using the anteroposterior axis for femoral component rotation and computer navigation techniques were included in the study. Deformity before TKA ranged from 17.58 varus (deformity apex away from the midline) to 20.58 valgus (deformity apex toward the midline) in full extension. Before TKA, deformity was not constant through an arc of motion and significantly decreased with flexion of 608 and more ( P b .01). The deformity after performing a TKA was not different ( P = .478) throughout the flexion arc. The data determined that deformity is not constant throughout flexion in osteoarthritic knees preoperatively and that deformity throughout flexion can be corrected with the use of conventional alignment techniques during TKA. Key words: knee, arthroplasty, kinematics, alignment, computer navigation. n 2008 Elsevier Inc. All rights reserved. Improper restoration of the lower extremity me- chanical axis is one of the most important causes of failure and patient dissatisfaction after total knee arthroplasty. With the introduction of computer- assisted navigation systems for use during total knee arthroplasty, this problem can be diminished to a large extent. Many studies in the literature have reported on the postoperative coronal plane alignment and the decrease in the number of outliers resulting with computer navigation systems [1-5]. Although postoperative outcome measures of total knees are extensively reported, there have not been any reports concerning deformity correc- tion intraoperatively throughout a range of flexion. Traditionally, coronal plane deformity before and after surgery has been reported in full extension as measured on long-standing radiographs or comput- ed tomographic scans in full extension [1-5]. If the deformity present at the knee can be recorded throughout a range of flexion, then this intraopera- tive data before and after total knee arthroplasty can provide valuable insight into the pathomechanics of the arthritic knee and the amount of correction The Journal of Arthroplasty Vol. 23 No. 1 2008 57 From the *Department of Orthopedic Surgery, University of Virginia, Charlottesville, Virginia; and yDepartment of Orthopedic Surgery, State University of New York at Buffalo, Kaleida Health, Buffalo, New York. Submitted May 16, 2006; accepted December 10, 2006. No benefits or funds were received in support of the study. Reprint requests: William M. Mihalko, MD, PhD, Department of Orthopaedic Surgery, PO Box 800159, Charlottesville, VA 22908-0159. n 2008 Elsevier Inc. All rights reserved. 0883-5403/08/2301-0009$34.00/0 doi:10.1016/j.arth.2006.12.048