The achievement of proper limb and prosthetic alignment and well-balanced gaps are the surgical principles that underlie the success of TKA . Coronal radiographic features of the femur may have considerable implications to the application of these surgical principles in individual patients. We have observed many patients present with severe lateral bowing of the femur, varus condylar orientation, and large varus inclination of the tibial plateau, which often require modification of surgical techniques. We therefore determined the prevalence of lateral femoral bowing, varus femoral condylar orientation, and severe tibia plateau inclination in female Koreans undergoing TKA and the effects of these anatomical features on alignment and the effects of postoperative alignments on function.
Several limitations should be noted before interpreting our findings. First, as a result of the extreme female sex predominance in Koreans undergoing TKA [6, 17], the number of male patients treated during the study period was insufficient to provide the statistical power required to detect sex effects on outcomes. Therefore, we decided to exclude male subjects. However, considering the universally observed female dominance in TKA series [8, 19], we believe our findings have surgical implications for patients in many other regions. Second, we used only one conventional instrumentation system (Genesis II) and only one navigation system (Orthopilot), and different systems of standard instrument or navigation may produce different findings. Third, we used standing whole-limb AP radiographs for radiographic measurements, and although this radiographic view is known to have satisfactory accuracy and reliability [5, 35] and have been frequently used in previous studies with similar purposes [11, 26, 29, 30, 36, 40], it may be affected by several factors such as degree of rotation. To maintain the quality of radiographic images, we used a specially designed template to control rotation. Furthermore, patients with less than good images were excluded. Finally, the clinical value of navigation technology for TKA and whether outliers in the coronal plane are in fact associated with compromised longevity are topics of debate [4, 9, 14, 21, 27, 32, 33], but we convey no information regarding the longevity of prostheses.
We found femoral lateral bowing, varus femoral condylar orientation, and large varus tibia plateau inclination are common in female Koreans undergoing TKA. However, it is not feasible to compare our findings directly with those of previous studies because of differences in age and sex compositions of populations studied, the types of parameters measured, and the types of variables reported [11, 16, 26, 29, 30, 36, 38, 40]. Nonetheless, it appears that like the Korean female patients in this study, Asian (Chinese, Indian, and Japanese) patients undergoing TKA for medial osteoarthritis commonly exhibit lateral femoral bowing and varus condylar orientation and a larger tibial plateau inclination than healthy Western subjects (Table 7) [11, 26, 29, 30, 36, 40]. A high prevalence of lateral femoral bowing has been reported in China , India , and Japan , and a varus femoral condylar orientation tendency has been reported in India . Furthermore, a large tibia plateau inclination of > 3° was reported in a study of Japanese patients with knee medial osteoarthritis  and in a study of young healthy Chinese subjects . A lack of relevant information regarding coronal alignments in Western or other Asian countries prevents us from concluding that these anatomical features are unique in Asia. Future studies in other countries and in other ethnic groups are warranted to clarify this issue, which potentially has important surgical implications.
The findings in partial correlation analyses and subgroup comparisons partly support our hypothesis that femoral lateral bowing, femoral condylar orientation, and tibia plateau inclination are associated with postoperative limb and prosthesis alignment and that the use of navigation reduces postoperative alignment outliers. Nevertheless, our findings are intuitively understandable. It is well known that the accuracy of femoral bone resection using an intramedullary guiding system can be compromised by femoral anatomical variations and that this could result in incomplete intramedullary rod insertion and subsequently erroneous distal femur resection [25, 31, 40]. Previous Western  and Asian [13, 27] authors have also reported that knees with a varus deformity are subject to postoperative varus malalignment. One technical tip that the senior author (TKK) has used is to assure that the cutting block for distal femur resection makes contact with bone as anticipated based on an assessment of femoral condylar orientation. For example, if the femur has a varus femoral condylar orientation, the distal cutting block has to make contact only with the lateral femoral condyle to achieve neutral bone resection. On the other hand, few knees had tibia alignment outliers even when standard instruments were used. This finding is also intuitive because surgeons would be able to place the cutting block independently of the anatomy whether a standard extramedullary guiding system or a navigation system is used.
Our subgroup comparisons of the functional outcomes of aligned knees and outliers may provide some clues to resolving recent debate as to whether the restoration of neutral limb alignment is associated with better functional outcome [4, 23, 32]. Several authors have recently challenged the importance of the restoration of neutral limb alignment [4, 23, 32]. A previous study that compared aligned and varus-malaligned knees found no differences between the two in terms of American Knee Society, WOMAC, or SF-36 scores . In contrast, in our study, the mechanical tibiofemoral angle outlier had a lower American Knee Society knee score and SF-36 physical component summary score, and coronal tibial prosthesis alignment outlier had a low SF-36 physical component summary score. However, we found no differences in other functional scales. These findings suggest postoperative coronal alignment influences patient function but only to a limited extent, particularly given some of the many comparisons might have been significant by chance. However, coronal femoral prosthesis alignment outliers were not different in any functional scale. This suggests surgeons can be flexible to some extent when determining coronal component orientation to achieve a rectangular extension gap without adversely affecting functional outcomes.
In summary, our data document femoral lateral bowing, varus condylar orientation of the femur, and severe varus inclination of the tibial plateau are prevalent in female Koreans undergoing TKA and that the presence of these anatomic features can adversely affect postoperative limb and prosthesis alignments. Thus, these features should be considered during TKA to reduce the risks of adversely affecting postoperative limb and prosthesis alignments.
We thank Moon Jong Chang, MD (Department of Orthopaedic Surgery, Seoul National University Bundang Hospital), for his scientific debate and manuscript review and Sung Ju Kim, MS, PhD candidate (Department of Orthopaedic Surgery, Korea University), for his help with statistical analyses.
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