Article

Variability in the Relationship Between the Distal Femoral Mechanical and Anatomical Axes in Patients Undergoing Primary Total Knee Arthroplasty

Department of Orthopaedic Surgery, Adult Reconstruction and Joint Replacement Service, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, New York.
The Journal of arthroplasty (Impact Factor: 2.67). 02/2013; 28(5). DOI: 10.1016/j.arth.2012.09.016
Source: PubMed

ABSTRACT

Currently, an intramedullary (IM) guide is often used for performing the distal femoral resection in total knee arthroplasty (TKA). However, this method assumes that in most patients, the distal femoral mechanical-anatomical angle (FMAA) is 5°. Preoperative, standing, AP hip-to-ankle radiographs were reviewed in 493 patients undergoing primary TKA, and the FMAA was digitally measured. Correlation coefficients relative to several radiographic measurements, along with demographic variables, were performed. A significant number of patients (28.6%) had an FMAA outside the range of 5°±2° (range 2.0°-9.6°). The only measurement demonstrating a fair/moderate correlation with the FMAA was the neck-shaft angle (r=-0.55). Using an IM resection guide, without obtaining AP hip-to-ankle radiographs to determine each patient's true FMAA, may lead to malalignment of the femoral component.

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    ABSTRACT: Preoperative planning in total knee arthroplasty with intramedullary guiding systems requires the measurement of the femoral mechanical-anatomical angle (FMAA) for optimal alignment correction. The main goal of this study was to assess the agreement between two digital FMAA measurements and the analog FMAA measurement. Overall 41 anteroposterior weight-bearing hip-to-ankle radiographs of patients undergoing total knee arthroplasty were used for the measurements of the FMAA. The analog method (gold standard, GS) was compared with two new digital methods (DIG1 and DIG2) using intraclass correlation (ICC) and Bland-Altman plots, measured by three blinded raters. The ICC for measurements of the FMAA comparing the GS and DIG1 was 0.48 (95% confidence interval [CI] 0.20-0.68), and 0.53 (95% CI 0.26-0.73) for comparing GS and DIG2. The ICC between raters for DIG1 was 0.79 (95% CI 0.68-0.88) and 0.88 (95% CI 0.80-0.93) for DIG2. Bland-Altman plots showed a mean difference between the GS and DIG1 of -0.44 degrees, with 95% limits of agreement from 1.21 to -2.09 degrees. The mean difference between the GS and DIG2 was -0.68 degrees with 95% limits of agreement from 0.99 to -2.35 degrees. It was concluded that the digital FMAA measurement is less reliable than analog measurement in total knee arthroplasty.
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