Variation in Optimal Sagittal Alignment of the Femoral Component in Total Knee Arthroplasty

Abstract

Accurate sagittal alignment of the femoral component in total knee arthroplasty is crucial for prosthesis longevity, improved function, and patient satisfaction. However, there is variation in the techniques used to attain optimal sagittal femoral component placement in total knee arthroplasty. Femoral component flexion in imageless navigation is based on the mechanical axis rather than the distal femoral anatomy, and there is significant variability in the anatomy of the distal femur. The purpose of this study was to accurately determine the mean distal femoral flexion angle of a representative population and whether variability of the distal femoral flexion angle correlates with race, femur length, or radius of curvature. The mean degree of distal femoral flexion was determined by assessing distal femoral anatomy on computed tomography scans of paired femurs of 1235 patients without evidence of previous fracture, deformity, or surgical implants. The mean±SD distal femoral flexion angle was 2.90°±1.52°, with 80.2% of knees within 3°±2°. Therefore, placing the component in 3° of flexion from the mechanical axis would attain a satisfactory position in most cases. However, further analysis of the patient data revealed 11.4% of Asians, 7.3% of African Americans, and 8.3% of whites had a distal femoral flexion angle greater than 5°. Additionally, the data revealed a moderately strong negative correlation between the distal femoral flexion and the overall radius of curvature of the femur. This preliminary study highlights the need for improved methods for selecting femoral component position in the sagittal plane when using navigation for total knee arthroplasty. [Orthopedics. 2017; 40(2):102-106.].

Current concepts in total knee arthroplasty

“…Since the introduction of TKA in the 1970s, neutral mechanical alignment (NMA) has remained the most commonly adopted alignment technique for TKA. 24 The principle of NMA in TKA is to distribute load evenly across the components in the stance phase to promote symmetrical component wear, and increase component durability in TKA. 9 Intraoperatively, this is achieved by undertaking bone resections and placing implants perpendicular to the femoral and tibial mechanical axes, while externally rotating the femoral component, which also secondarily facilitates correct patella tracking.…”

“…Native limb alignment within the general population follows a Gaussian (normal) distribution, with only 5% to 5.5% of patients having natural NMA. 24 Consequently, in most patients undergoing TKA with NMA, the knee is forced into an unnatural position, with changes to native knee orientation in all three dimensions. 7 , 8 , 15 , 16 This may lead to modifications in the natural femoral flexion axis, periarticular ligament tension, quadriceps function, patella tracking, and knee kinematics through the arc of motion.…”

Is the femoral component flexion affected by the sagittal femoral shaft bowing in conventional intramedullary guided TKA?

“…Moreover, improper positioning of components during surgery may lead to early loosening of the implant due to impingement between the cam and the post in posterior stabilized systems [ 24 ]. Extensive study has been performed on ideal coronal alignment of the femoral component in total knee prostheses [ 3 ]. In contrast, there are limited studies addressed sagittal alignment of femoral component.…”

“…Total knee arthroplasty (TKA) relieves pain, restores function, is one of the most successful treatment for advanced knee osteoarthritis [ 1 , 2 ]. To maximize the success and longevity of a TKA, the surgeon must implant the components in the optimal position to re-create the knee anatomic alignment [ 3 ]. The TKA often sacrifices the natural anatomy of the knee, and nearly 15% of patients are not satisfied after TKA [ 2 ].…”

Flexible versus standard intramedullary rod in posterior stabilized primary total knee arthroplasty: protocol for a randomized controlled trial

“…One aspect influencing natural knee kinematics is sagittal placement of the femoral component [18]. The instruments used for alignment of the femoral component are classically used intramedullary, and implanting the femoral component can be performed either according to the longitudinal axis of the femur in the sagittal plane or according to the anatomy of the distal femur, taking into account sagittal bowing of the femur.…”