Assessment and validation of CT scanogram to compare per-operative and post-operative mechanical axis after navigated total knee replacement

Abstract

Our objective was to assess and validate low-dose computed tomography (CT) scanogram as a post-operative imaging modality to measure the mechanical axis after navigated total knee replacement. A prospective study was performed to compare intra-operative and post-operative mechanical axis after navigated total knee replacements. All consecutive patients who underwent navigated total knee replacement between May and December 2006 were included. The intra-operative final axis was recorded, and postoperatively a CT scanogram of lower limbs was performed. The mechanical axis was measured and compared against the intra-operative measurement. There were 15 patients ranging in age from 57 to 80 (average 70) years. The average final intra-operative axis was 0.56°varus (4°varus to 1.5°valgus) and post-operative CT scanogram axis was 0.52°varus (3.1°v arus to 1.8°valgus). The average deviation from final axes to CT scanogram axes was 0.12°valgus with a correlation coefficient of 0.9. Our study suggests that CT scanogram is an imaging modality with reasonable accuracy for measuring mechanical axis despite significantly low radiation. It also confirms a high level of correlation between intra-operative and post-operative mechanical axis after navigated total knee replacement.

Do Patient-specific Guides Improve Coronal Alignment in Total Knee Arthroplasty?

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The impact of limb loading and the measurement modality (2D versus 3D) on the measurement of the limb loading dependent lower extremity parameters

“…However, it could be shown that isolated rotation of the leg has no relevant influence on HKA measurements [14]. Furthermore, it could be demonstrated that the use of a CT scanogram for measuring HKA shows reasonable accuracy [22].…”

Measurement of rotational deformity: using a smartphone application is more accurate than conventional methods

“…). We considered this value (CTV) obtained from the CT scan as the ‘true’ value, as clinically a CT scan can provide a very objective, accurate, and reproducible measure of both rotation and mechanical alignment …”

“…We considered this value (CTV) obtained from the CT scan as the 'true' value, as clinically a CT scan can provide a very objective, accurate, and reproducible measure of both rotation 3 and mechanical alignment. 4 We then recruited 31 volunteer orthopaedic surgeons of various levels of experience, including 10 consultants and 21 trainees. The mean number of years of orthopaedic experience was 9.7 ± 7.4 (range 4-34 years).…”