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 degrees, and the radiographs were taken as an anteroposterior view of the knee joint. Images then were cropped from the HKA radiographs to generate 50 anteroposterior (AP) radiographs in order to allow clinicians 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.
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 centimeters of femur and 12 centimeters 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 study data.
Only 30 percent 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 percent of knees were aligned 2 degrees to 4 degrees varus, whereas HKA radiographs only had 26 percent of knees with this alignment.
The study results showed the repeatability of alignment measurements significantly was better among HKA radiographs; however, poor agreement of the mechanical alignment was observed between the two views.