Rotational component alignment in patient-specific total knee arthroplasty compared with conventional cutting instrument.

BACKGROUND

Although many studies investigated the accuracy of customized cutting block (CCB), the data on rotational alignment are still lacking. The study aimed to assess whether CCB improved the component rotational position compared with conventional cutting instrument (CCI) using computed tomography scanning.

METHODS

Eighty-six of 102 total knee arthroplasties from the previous randomized study were analyzed. The outcomes were rotational position of the femoral and tibial components, frequency of outliers and intra-class correlation coefficient.

RESULTS

The mean femoral component rotation was not different between CCB versus CCI: 0.9° ± 0.8° versus 1.1° ± 1.1° (P = 0.29). Both groups had similar outlier frequencies: 2% (CCB) versus 2% (CCI) (P = 0.74). CCB had nearly 1° less mean tibial component deviation compared with CCI (P < 0.001): (1) dorsal tangent reference (DTR): 0.7° ± 0.8° versus 1.5° ± 1.0°, and (2) tibial trans-epicondylar reference (TTR): 0.5° ± 0.9° versus 1.4° ± 1.1°. Outlier frequencies were similar: (1) DTR: 0% CCB versus 5% CCI (P = 0.24), and (2) TTR: 5% in CCB versus 12% CCI (P = 0.20). Measurements based on tibial tubercle showed that CCB had ~ 1.4° less mean tibial component deviation compared with CCI: 0.3° ± 1.4° versus 1.7° ± 1.6° (P < 0.001) with a corresponding, less frequency of outliers: 0% versus 19% (P = 0.002). However, there was poor intra-observer reproducibility (0.61).

CONCLUSIONS

CCB did not improve femoral component rotational alignment compared with CCI nor affect outlier frequency, but it marginally improved the accuracy of tibial rotational alignment. The tibial tubercle reference point had poor intra-observer reproducibility.