An algorithm for locating the center of the ankle joint in knee navigation surgery

Figures & data

Figure 1. In the sagittal plane, the center of the ankle is defined as the high point of the talar dome and the corresponding high point of the tibial articular surface.

Figure 2. Example of CT image with the center of the ankle and the medial/lateral malleolar axis inserted (diagrammatic). A = anatomically defined center of ankle joint; B = most medial point; C = most lateral point.

Table I.  Correlations for various measures in normal ankles.

		Medial center (mm)	Lateral center (mm)	Total (mm)
Medial center (mm)	Pearson correlation	1.000	0.132	0.630*
	Sig. (2-tailed)	–	0.455	0.000
	N	34	34	34
Lateral center (mm)	Pearson correlation	0.132	1.000	0.854*
	Sig. (2-tailed)	0.455	–	0.000
	N	34	34	34
Total (mm)	Pearson correlation	0.630*	0.854*	1.00
	Sig. (2-tailed)	0.000	0.000	–
	N	34	34	34

*Correlation is significant at the 0.001 level (2-tailed).

Table II.  Linear regression coefficients for predicting lateral from total with no constant.

	Unstandardized coefficients		Standardized coefficients
Model	B	Std error	Beta	t	Sig.
1 total (mm)	0.569	0.005	0.999	121.547	0.000

a. Dependent variable: lateral center (mm).

b. Linear regression through the origin.

Figure 3. Illustration showing how the mid-point of the ankle joint in the sagittal plane (A, illustrated on a coronal view) passes posterior to the axis joining the most prominent points on the medial (B) and lateral (C) malleoli.