Radiographic evaluation of anterior tibial translation in the prone position after total knee arthroplasty: comparison of BCS-TKA and PS-TKA.

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The purpose of this study was to evaluate the anterior tibial translation (ATT) in the prone position after total knee arthroplasty (TKA). Fifty subjects (50 knees) undergoing bi-cruciate substituting (BCS)-TKA (Journey II: Smith and Nephew) and age-gender matching 50 subjects (50 knees) undergoing posterior stabilizing (PS)-TKA, were included in this study. Approximately, sixmonths after surgery, and when the subjects had recovered their range of knee motion, following the Mae's method, accurate lateral radiographic imaging of the knee was performed with full knee extension in both supine and prone positions. The maximal protrusion length of the femoral posterior component, posterior to the extension line parallel to the tibial shaft from the edge of the posterior tibial plateau, was measured on lateral radiographs. The difference in length between the prone and supine positions was regarded as the prone-ATT. The posterior protrusion length of the femoral component, and the prone-ATT were compared between BCS and PS-TKA. The posterior protrusion length of the femoral component in the supine position was BCS-TKA 4.3 ± 1.9mm, and PS-TKA 8.7 ± 2.3mm. The length in the prone position was BCS-TKA 4.8 ± 2.3mm, and PS-TKA 10.7 ± 2.2m. Posterior protrusion length of the femoral component was significantly larger in both positions in PS-TKA when compared with BCS-TKA. In PS-TKA, posterior protrusion length of the femoral condyle was significantly larger in the prone position when compared to the supine position. No significant difference was observed in BCS-TKA. Prone-ATT was significantly larger in PS-TKA (2 ± 1.9mm) when compared to BCS-TKA (0.7 ± 2mm). Even in a position corresponding to daily movement such as the prone position, ATT was significantly larger in PS-TKA, when compared to BCS-TKA.