Optimal definitions for computing HKA angle in caos: an in-vitro comparison study

Figures & data

Figure 1. Optical markers attached on the femur and the tibia.

Figure 2. Definitions of the knee center explained on a schematic.

Figure 3. Boxplot of precision for nine definitions of the Knee Centers. The middle line represents the median, the box extends from the lower to the upper quartile, and the vertical line extends from the first decile to the ninth decile. Values which are inferior or superior to respectively the first and the ninth deciles are represented by separated points. Solid triangles in each box represent the mean precision values.

Table 1. HKA precision (mean ± SD, (min–max)) in degrees according to the KC and the FP definitions.

	FPhelical	FPcircle	FPepi_before	FPdistal_condyles	FPpost_condyles	FPepi_after	FPtibial_spines
KChelical	−0.05 ± 0.65	−0.10 ± 1.18	−0.22 ± 1.94	0.11 ± 0.82	0.22 ± 0.96	−0.23 ± 1.00	−1.00 ± 3.53
	(−3.58–1.13)	(−3.23–5.04)	(−3.83–5.75)	(−1.59–4.45)	(−2.11–3.31)	(−2.53–2.05)	(−16.12–5.31)
KCcircle	−0.05 ± 0.51	0.03 ± 1.00	−0.22 ± 1.93	0.14 ± 0.93	0.10 ± 1.43	−0.21 ± 0.82	−0.60 ± 2.93
	(−2.96–0.89)	(−3.17–5.35)	(−3.68–5.88)	(−1.73–5.32)	(−2.42–3.58)	(−1.79–1.68)	(−13.69–4.75)
KCepi_before	−0.05 ± 0.58	0.22 ± 1.64	−0.24 ± 2.14	0.25 ± 1.52	0.31 ± 2.21	−0.24 ± 0.92	−0.10 ± 2.40
	(−3.33–0.96)	(−3.78–5.43)	(−4.15–6.24)	(−2.02–7.33)	(−4.74–3.29)	(−2.10–1.51)	(−13.83–5.24)
KCnotch	−0.06 ± 0.58	0.02 ± 1.04	−0.15 ± 2.33	0.18 ± 1.12	−0.08 ± 1.67	−0.02 ± 1.15	−0.43 ± 2.37
	(−3.66–1.14)	(−3.70–5.55)	(−4.28–6.34)	(−1.97–6.09)	(−2.63–3.70)	(−2.32–2.88)	(−10.71–3.80)
KCdistal_condyles	−0.00 ± 0.91	−0.44 ± 1.96	−0.12 ± 2.06	0.46 ± 2.01	0.16 ± 2.08	−0.22 ± 0.99	−0.68 ± 4.43
	(−3.55–3.91)	(−3.84–5.62)	(−4.01–6.16)	(−2.48–8.22)	(−4.75–3.18)	(−2.54–1.85)	(−18.31–8.00)
KCpost_condyles	−0.21 ± 1.05	0.06 ± 1.68	0.07 ± 1.98	0.29 ± 1.63	0.10 ± 2.34	0.29 ± 1.39	−0.96 ± 5.08
	(−3.70–2.44)	(−3.91–5.38)	(−3.27–4.91)	(−2.17–7.41)	(−4.29–4.33)	(−2.53–3.09)	(−18.06–12.50)
KCepi_after	−0.06 ± 0.52	−0.42 ± 1.99	−0.34 ± 2.17	0.43 ± 2.12	0.44 ± 2.18	−0.16 ± 0.87	−0.10 ± 2.20
	(−3.13–0.90)	(−6.54–4.56)	(−4.32–6.44)	(−2.46–8.88)	(−7.98–3.02)	(−1.86–1.42)	(−12.74–5.31)
KCtibial_spines	−0.10 ± 0.81	0.05 ± 1.63	0.04 ± 1.99	0.22 ± 1.26	−0.07 ± 1.88	0.35 ± 1.34	−0.28 ± 3.06
	(−5.04–1.39)	(−3.26–4.67)	(−3.64–5.44)	(−1.80–6.49)	(−2.75–4.03)	(−3.33 − 2.04	(−13.63–4.28)
KCeminence	−0.23 ± 1.30	0.13 ± 1.73	0.11 ± 2.06	0.25 ± 1.27	−0.02 ± 2.04	0.37 ± 1.62	−0.26 ± 3.03
	(−3.61–3.07)	(−3.85–5.01)	(−3.22–5.01)	(−2.84–6.66)	(−3.16–4.54)	(−3.78–3.48)	(−13.66–4.71)

FP and KC combinations having the sum (Mean + SD) inferior to 1° are highlighted in green. Noninvasive methods are in gray.

Table 2. HKA accuracy (mean ± SD, (min–max)) in degrees according to the KC and the FP definitions.

	FPhelical	FPcircle	FPepi_before	FPdistal_condyles	FPpost_condyles	FPepi_after	FPtibial_spines
KChelical	−0.36 ± 0.91	−0.46 ± 1.40	−0.20 ± 2.11	0.42 ± 1.20	−0.01 ± 1.65	0.09 ± 1.40	0.05 ± 3.33
	(−2.56–1.55)	(−3.49–2.32)	(−8.39–3.92)	(−1.81–4.50)	(−6.39–3.73)	(−3.46–3.68)	(−13.39–8.82)
KCcircle,	−0.52 ± 0.71	−0.36 ± 1.17	−0.20 ± 2.12	0.39 ± 1.23	0.02 ± 1.65	0.12 ± 1.34	−0.12 ± 3.04
	(−2.01–2.55)	(−3.47–2.19)	(−8.37–3.82)	(−1.82–4.40)	(−6.39–3.81)	(−3.06–3.64)	(−11.78–8.31)
KCepi_before	−0.32 ± 1.05	−0.11 ± 1.75	0.06 ± 2.28	0.29 ± 1.59	0.28 ± 2.00	0.55 ± 1.35	−0.18 ± 2.73
	(−3.05–2.15)	(−3.85–3.09)	(−8.57–4.60)	(−4.67–3.04)	(−7.34–5.65)	(−2.45–6.31)	(−12.16–7.62)
KCnotch	−0.16 ± 0.68	0.07 ± 1.08	−0.11 ± 2.27	0.25 ± 1.18	−0.06 ± 1.70	0.24 ± 1.24	−0.34 ± 2.77
	(−2.57–2.21)	(2.54–3.49)	(−8.43–6.44)	(−2.16–4.55)	(−6.43–4.73)	(−3.05–4.31)	(−9.71–7.64)
KCdistal_condyles	−0.09 ± 1.04	0.15 ± 1.64	0.42 ± 2.26	0.68 ± 1.96	0.38 ± 1.98	0.85 ± 1.39	−0.27 ± 4.00
	(2.82–2.51)	(−2.95–4.03)	(−7.97–4.49)	(−5.01–6.68)	(−7.34–5.65)	(−2.40–6.41)	(−15.37–10.58)
KCpost_condyles	0.32 ± 1.31	0.14 ± 1.77	0.26 ± 2.23	0.16 ± 1.57	−0.04 ± 2.15	0.57 ± 1.53	−1.16 ± 5.82
	(−3.11–3.64)	(−3.35–4.13)	(−7.68–6.92)	(−3.62–4.68)	(−7.34–5.99)	(−3.88–7.19)	(−18.44–10.61)
KCepi_after	−0.23 ± 1.22	0.03 ± 2.26	0.25 ± 2.35	0.36 ± 2.11	0.64 ± 1.90	0.66 ± 1.35	−0.14 ± 2.65
	(−3.63–1.55)	(−3.00–4.13)	(−9.58–5.10)	(−4.90–7.89)	(−8.48–5.97)	(−2.83–6.10)	(−11.33–6.26)
KCtibial_spines	−0.06 ± 0.84	−0.05 ± 1.64	−0.02 ± 2.06	0.11 ± 1.27	−0.15 ± 1.85	0.36 ± 1.35	−0.02 ± 2.99
	(−2.56–1.92)	(−3.65–2.42)	(−8.62–4.29)	(−2.70–4.95)	(−6.79–4.57)	(−3.85–5.23)	(−11.55–8.75)
KCeminence	0.02 ± 1.32	−0.36 ± 2.09	−0.13 ± 2.12	−0.10 ± 1.37	−0.33 ± 1.95	0.09 ± 1.54	−0.02 ± 2.98
	(−1.57–3.01)	(−4.03–2.73)	(−8.03–4.22)	(−4.28–2.47)	(−6.75–4.96)	(−4.03–4.93)	(−11.12–9.14)

FP and KC combinations having the sum (Mean + SD) inferior to 1° are highlighted in green. Noninvasive methods are in gray.

Table 3. p-Values between FP and KC combinations and either the FP_helical – KC_notch (top) and FP_helical – KC_{tibial_spines} (down) for the accuracy (NA: Not Applicable).

	FPhelical	FPcircle	FPepi_before	FPdistal_condyles	FPpost_condyles	FPepi_after	FPtibial_spines
KChelical	0.33	*	*	0.06	*	*	*
	0.79	0.09	*	0.23	*	0.09	*
KCcircle,	0.88	0.07	*	*	*	*	*
	0.57	0.26	*	0.20	*	0.12	*
KCepi_before	0.15	*	*	*	*	*	*
	0.45	*	*	*	*	0.11	*
KCnotch	NA	0.12	*	0.07	*	*	*
	0.47	0.40	*	0.25	*	0.19	*
KCdistal_condyles	0.16	*	*	*	*	*	*
	0.47	*	*	*	*	0.09	*
KCpost_condyles	*	*	*	*	*	*	*
	0.14	*	*	*	*	*	*
KCepi_after	*	*	*	*	*	*	*
	0.21	*	*	*	*	0.11	*
KCtibial_spines	0.47	*	*	*	*	*	*
	NA	*	*	0.17	*	0.11	*
KCeminence	*	*	*	*	*	*	*
	0.13	*	*	0.10	*	*	*

Only non-significant results are presented (p > 0.05), significant results are represented with the (*) symbol.