Sagittal cutting error changes femoral anteroposterior sizing in total knee arthroplasty

Abstract

Background: Prosthetic alignment and size are important factors in achieving a long-term survival in TKA. Although two-dimensional and three-dimensional (3-D) planning for component sizing has been introduced, it sometimes is difficult to cut the bones accurately according to preoperative planning. It is unclear whether changing sagittal alignment of the distal femur affects the AP dimension and sizing of the prepared bone.

Questions/purposes: We therefore determined whether the AP dimension of the prepared distal femur increases if the distal femur is cut in extension and decreases if it is cut in flexion.

Methods: One hundred knees were evaluated using 3-D imaging software. The AP dimension of the cutting surface was measured when the femoral component was aligned perpendicular to the anatomic axis. The measurement was repeated when the distal bone cut was planned in flexed positions of 3° and 5° and extended positions of 3° and 5°.

Results: The AP dimension of the prepared femur was increased by 2 and 3 mm with 3° and 5° extension, respectively. The AP dimension of the prepared femur was decreased by 2 and 3 mm with 3° and 5° flexion, respectively.

Conclusions: Our data suggest upsizing or downsizing of the femoral component can occur if the femoral osteotomy is performed in at least 3° extension or flexion.

Level of evidence: Level II, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Figures

Fig. 1A–B

The femoral component was aligned (A) perpendicular to the mechanical axis in the coronal plane and (B) parallel to the surgical epicondylar axis in the axial plane.

Fig. 2

The anatomic axis was defined as a line connecting the middle point of the femoral axis 15 cm proximal from the femoral intercondylar fossa (A) and the middle point of the femoral axis 5 cm proximal from the femoral intercondylar fossa (B).

Fig. 3

Measurement of the AP dimension of the distal femur in standard planning is shown. The distance from the anterior cortex to the most posterior point of the lateral posterior condyle of the bone is measured.

Fig. 4A–B

(A) The increment of the AP dimension of the distal femur in 5° flexion is shown. The measurement is drawn parallel to the distal cutting surface. (B) The decrement of the AP dimension of the distal femur in 5° extension is shown.

Fig. 5A–B

The graphs show the number of knees with differences in AP dimension of the distal femur in (A) 3° or (B) 5° extension.

Fig. 6A–B

The graphs show the number of knees with differences in AP dimension of the distal femur in (A) 3° or (B) 5° flexion.