Preoperative radiographic parameters in the case of using a narrow-version femoral implant in total knee arthroplasty.

BACKGROUND

Recently, total knee arthroplasty (TKA) designs that allow the use of narrow-version femoral implants have been introduced to avoid femoral overhang. The purpose of this study was to investigate the frequency of the use of narrow-version femoral implants and identify the difference in radiographic parameters between using a narrow-version femoral implant and a standard-version femoral implant in TKA.

METHODS

A retrospective study was conducted on 504 primary TKAs using a TKA system (Anthem or Persona) that allowed narrow-version femoral implants. Anteroposterior (AP) dimension, mediolateral (ML) dimension, and modified aspect percentage ratio (ML/AP dimension) of the distal femur in preoperative radiographs were compared between a standard-version group (n = 275) and a narrow-version group (n = 229). A cut-off value of a modified aspect percentage ratio indicating the need for a narrow-version femoral implant was determined using the receiver operating characteristic (ROC) curve.

RESULTS

Mean ML dimension was 80.9 ± 6.1 mm in the standard-version group and 77.3 ± 4.4 mm in the narrow-version group (p < 0.001). Mean modified aspect percentage ratio was 138.8 ± 8.1% in the standard-version group and 131.7 ± 6.3% in the narrow-version group (p < 0.001). The optimum cut-off point of the modified aspect percentage ratio for narrow-version femoral implants was 135.4% (sensitivity: 72.0%; specificity: 66.7%) for Anthem and 133.3% (sensitivity: 75.9%, specificity: 76.4%) for Persona.

CONCLUSION

In the narrow-version femoral implant group, the ML dimension and the mean modified aspect percentage ratio were smaller than in the standard-version femoral implant group. A smaller modified aspect percentage ratio of the distal femur in preoperative radiographs could predict the need for narrow-version femoral implants in TKA. It was suggested that the cut-off point could be suggested as 135.4% for Anthem TKA design and 133.3% for Persona TKA design. These radiographic parameters are cost-effective and easily applicable for planning a TKA.A smaller modified aspect percentage ratio of the distal femur in preoperative radiographs could predict the need for narrow-version femoral implants in TKA. The cut-off point was 135.4% for Anthem TKA design and 133.3% for Persona TKA design.