Abstract
BackgroundAnatomic limb alignment often differs from mechanical limb alignment after total knee arthroplasty (TKA). We sought to assess the accuracy, specificity, and sensitivity for each of three commonly used ranges for anatomic limb alignment (3-9°, 5-10° and 2-10°) in predicting an acceptable range (neutral ± 3°) for mechanical limb alignment after TKA. We also assessed whether the accuracy of anatomic limb alignment was affected by anatomic variation.MethodsThis retrospective study included 314 primary TKAs. The alignment of the limb was measured with both anatomic and mechanical methods of measurement. We also measured anatomic variation, including the femoral bowing angle, tibial bowing angle, and neck-shaft angle of the femur. All angles were measured on the same full-length standing anteroposterior radiographs. The accuracy, specificity, and sensitivity for each range of anatomic limb alignment were calculated and compared using mechanical limb alignment as the reference standard. The associations between the accuracy of anatomic limb alignment and anatomic variation were also determined.ResultsThe range of 2-10° for anatomic limb alignment showed the highest accuracy, but it was only 73 % (3-9°, 65 %; 5-10°, 67 %). The specificity of the 2-10° range was 81 %, which was higher than that of the other ranges (3-9°, 69 %; 5-10°, 67 %). However, the sensitivity of the 2-10° range to predict varus malalignment was only 16 % (3-9°, 35 %; 5-10°, 68 %). In addition, the sensitivity of the 2-10° range to predict valgus malalignment was only 43 % (3-9°, 71 %; 5-10°, 43 %). The accuracy of anatomical limb alignment was lower for knees with greater femoral (odds ratio = 1.2) and tibial (odds ratio = 1.2) bowing.ConclusionsAnatomic limb alignment did not accurately predict mechanical limb alignment after TKA, and its accuracy was affected by anatomic variation. Thus, alignment after TKA should be assessed by measuring mechanical alignment rather than anatomic alignment.
Highlights
Anatomic limb alignment often differs from mechanical limb alignment after total knee arthroplasty (TKA)
Coronal alignment of the lower limb is a major determinants of successful total knee arthroplasty (TKA) [1,2,3], and mechanical limb alignment is considered the gold standard in the assessment of coronal alignment after TKA [4,5,6,7]
Results the 2-10° range for anatomic limb alignment showed the highest accuracy, anatomic alignment was not accurate in most knees with any of the three methods (3–9°, 65 %; 5–10°, 67 %; 2–10°, 73 %) (Table 2)
Summary
Anatomic limb alignment often differs from mechanical limb alignment after total knee arthroplasty (TKA). We sought to assess the accuracy, specificity, and sensitivity for each of three commonly used ranges for anatomic limb alignment (3-9°, 5-10° and 2-10°) in predicting an acceptable range (neutral ± 3°) for mechanical limb alignment after TKA. Many recent studies have used mechanical limb alignment to assess radiographic outcomes after TKA. Previous studies have found that knees within an acceptable range for mechanical limb alignment (neutral ± 3°) show better clinical outcomes after TKA than knees for which the coronal alignment was out of this range [3]. Despite recent disagreement regarding the usefulness of this range [11, 12], mechanical limb alignment within ±3° of neutral is most frequently used as an acceptable range to assess the alignment of the lower limb after TKA. There is a lack of information regarding which range for anatomic limb alignment can best predict the acceptable range for neutral mechanical limb alignment (neutral ± 3°) with the highest accuracy, specificity, and sensitivity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
