Hip–Knee–Ankle Radiographs Are More Appropriate for Assessment of Post-Operative Mechanical Alignment of Total Knee Arthroplasties than Standard AP Knee Radiographs
Section snippets
Materials and Methods
This was a retrospective study of data collected routinely as part of our patients’ care and therefore did not require ethical approval [14].
Fifty consecutive HKA radiographs of patients who had undergone TKA at our institution were selected. These radiographs were taken at routine follow-up six weeks post-operatively and stored digitally on Kodak Picture Archiving Communications System (PACS). The HKA radiographs were taken as an antero-posterior view of the knee joint including hip and ankle.
Data Analysis
Graphs were created from data entered into Excel 2003 (Microsoft Corp, Redmond, WA, USA) and statistical analysis carried out using SPSS (IBM 2010, Armonk, NY, USA).
The intraclass correlation coefficient (ICC) was calculated for both intra-observer and inter-observer error. In order to assess overall alignment rather than an inaccurate angle, knees were categorised using the measured mechanical femorotibial angle as varus (≥ 2° varus), neutral (< 2° varus to < 2° valgus) or valgus (≥ 2° valgus) [7]
Results
The assessment of the standardised AP knee radiographs showed that on average 13.5 cm (range 12–16 cm) of femur and 12 cm (range 9–15 cm) of tibia could be seen. All generated standardised AP knee radiographs were cropped to these sizes.
The intraclass correlation coefficient values for intra-observer agreement of measurement of HKA radiographs were higher than standardised AP knee radiographs for both the anatomical and mechanical alignment (Table 1) with all HKA radiographs being acceptable (>
Discussion
Our study has demonstrated the inaccuracy of standard AP knee radiographs for assessing coronal limb alignment following total knee arthroplasty. The standardised AP knee radiographs showed a much lower level of both intra-observer and inter-observer agreement for anatomical axes and alignment. In terms of mechanical alignment, the standardised AP knees tended to indicate that the TKA was in 2° to 4° varus, whatever the actual alignment. The limits of agreement for the measurement of mechanical
Conclusion
When compared to measurements taken on HKA radiographs, standardised AP knee radiographs are insufficient to accurately assess the mechanical alignment of a TKA and tend to exaggerate the varus appearance of the implant’s mechanical alignment. We therefore reject our hypothesis. We recommend weight-bearing HKA radiographs as the routine post-operative assessment of knee arthroplasty patients to ensure that a more accurate measurement of the true alignment of the TKA is made.
Conflict of Interest
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Non-weightbearing imaging and standard knee radiographs are inferior to formal alignment radiographs for calculating coronal alignment of the knee
2021, RadiographyCitation Excerpt :This is especially true in patella malalignment or condylar asymmetry for example.6,18 Furthermore, there is evidence that SL measurements differ even when the same LL image is cropped: demonstrating that not all of the disagreement can be explained by positioning.19 Our data demonstrates a significant (p = 0.001) difference of greater than 2° between modalities.
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2014.11.024.