Is Static Alignment a Good Predictor of Dynamic Alignment after Total Knee Arthroplasty?

Abstract

Background: Total knee arthroplasty (TKA) is the only effective treatment of end-stage knee osteoarthritis (OA). Lower limb neutral alignment has been a criterion to predict prosthesis life; however, there has been recent controversy over this. Some researchers believe that lower limb static alignment does not significantly affect prosthesis life and some researchers have found that dynamic mechanical alignment may affect prosthesis life, which needs to be further studied.

Methods: Eighty-seven patients with knee OA were evaluated by a three-dimensional (3D) gait analysis system before TKA and six months after TKA, dynamic mechanical alignment and basic gait parameters were then calculated. Based on the static alignment of the lower limb on the postoperative X-radiographs, they were divided into a neutral alignment group (58 cases), varus alignment group (20 cases), and valgus alignment group (9 cases). Simple linear regression was used to assess the correlation between static and dynamic alignment. One-way analysis of variance (ANOVA) was used to compare the differences in gait parameters between and within groups.

Results: Eighty-seven patients were followed up for an average of six months after the operation. There was no significant difference in all gait parameters among the three groups after TKA. There was no correlation found between static alignment and dynamic alignment/knee adduction moment (KAM) after TKA, although patients showed a significant linear correlation before operation. There was a significant linear correlation between dynamic alignment and KAM before and after the operation.

Conclusions: Static alignment has no significant effect on postoperative gait function. Static alignment is no longer an effective predictor of the dynamic alignment or KAM six months after TKA, although they are correlated before TKA. The dynamic alignment allows for better prediction of KAM, which may be a risk factor for the life of the prosthesis.

Keywords: alignment; arthroplasty; gait analysis; knee joint; osteoarthritis.

Figure 1

The static lower limb alignment was measured on the radiograph. (A) Before operation; (B) after operation.

Figure 2

The marker model is part of the 3D gait analysis procedure. (A) Front view; (B) lateral view; (C) opposite view.

Figure 3

Gait analysis with VICON system. (A) Static model; (B) patient gait acquisition; (C) and (D) 3D view after dynamic model.

Figure 4

Some gait parameters of the same patient before and after TKA. The six green lines represent the dynamic parameter change of each gait, and the red line represents the average readings of six gait measurements. (A) Knee flexion/extension angle; (B) Dynamic alignment angle; (C) Knee flexion/extension force and (D) Knee adduction moment (KAM).

Figure 5

Correlation between static alignment and dynamic alignment before operation (p < 0.001).

Figure 6

Correlation between static alignment and dynamic alignment six months after TKA. (A) Neutrally-aligned group; (B) varus-aligned group; (C) valgus-aligned group.

Figure 7

Correlation between static alignment and KAM six months after TKA. (A) Correlation between preoperative static alignment and mean KAM (p < 0.001). (B) Correlation between preoperative static alignment and peak of KAM (p < 0.001). (C) Correlation between postoperative static alignment and mean KAM. (D) Correlation between postoperative static alignment and peak of KAM.

Figure 8

Correlation between dynamic alignment and knee KAM. (A) Correlation between preoperative dynamic alignment and mean KAM (p < 0.001). (B) Correlation between preoperative dynamic alignment and peak of KAM (p < 0.001). (C) Correlation between postoperative dynamic alignment and mean KAM (p < 0.001). (D) Correlation between postoperative dynamic alignment and peak of KAM (p < 0.001).