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TKA mechanical alignment more accurate on hip-knee-ankle radiograph vs. anteroposterior radiograph
Standardized anteroposterior radiographs were insufficient for the accurate assessment of the mechanical alignment of total knee arthroplasty compared with hip-knee-ankle radiographs. Additionally, anteroposterior radiographs exaggerated the varus appearance of mechanical alignment in implants, according to study results.
Researchers retrospectively collected 50 hip-knee-ankle (HKA) radiographs of patients who underwent total knee arthroplasty. Patients were positioned in a bipedal stance, with the knee rotated internally by 5°, and the radiographs were taken as an anteroposterior view of the knee joint. The researchers then cropped the images from the HKA radiographs to generate 50 anteroposterior (AP) radiographs in order to allow the researchers to compare mechanical and anatomical alignment measures between the two views. HKA and AP radiographs were independently measured by one observer at different times. HKA measurements were calculated with Bland Altman plots.
The researchers calculated intraclass correlation coefficient (ICC) values for both intra-observer error and inter-observer error. In addition, knees were grouped utilizing the measured mechanical femorotibial angle as varus, neutral or valgus.
In the standardized AP radiographs, results showed 13.5 cm of femur and 12 cm of tibia could be observed on average.
ICC values for intra-observer agreement of HKA radiographs were higher for both anatomical and mechanical alignment compared with AP radiographs. Mechanical alignment was lowest in AP radiographs, and most of these had only fair agreement, according to the researchers.
Only 30% of knees were grouped correctly with standardized AP measurements, assuming HKA radiographs were correct. Additionally, nine valgus knees were incorrectly categorized as varus.
According to the researchers, AP radiographs estimated 52% of knees were aligned 2° to 4° varus, whereas HKA radiographs only had 26% of knees with this alignment.
The researchers reported that the repeatability of alignment measurements was significantly better among HKA radiographs; however, poor agreement of the mechanical alignment was observed between the two views. ‒ by Monica Jaramillo
Disclosures: Abu-Rajab reports no relevant financial disclosures. Please see the full study for a list of all other authors’ relevant financial disclosures.
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