Description and validation of a navigation system for intra-operative evaluation of knee laxity

Figures & data

Figure 1. Percutaneous acquisition of lateral epicondyles during the registration phase. Reference arrays are mounted on the femur and tibia through the skin incision made for ACL reconstruction.

Figure 2. Software interface during (a) the anatomical registration phase and (b) antero-posterior laxity tests.

Table I.  Average results of laxity test on patients.

Test	VV (°)		AP (mm)		IE (°)
Flexion	0°	30°	30°	90°	30°	90°
Pre-op	5.6 (1.4)	4.8 (1.7)	12.0 (3.6)	8.8 (2.9)	22.6 (5.5)	26.6 (5.7)
Post-op	2.7 (0.9)	2.8 (1.3)	5.3 (2.0)	4.4 (1.8)	16.9 (4.9)	18.9 (4.9)

Table II.  Intra-surgeon repeatability of laxity tests. Standard deviation (St dev) of the repeated tests by the same surgeon in ACL-deficient (pre) and reconstructed (post) knees. These values were computed with ANOVA and the significance (p) is reported.

Test	VV (°)		AP (mm)		IE (°)
Flexion	0°	30°	30°	90°	30°	90°
St dev pre	0.6	0.5	0.7	0.7	1.3	1.2
p	0.6	0.8	0.93	0.82	0.66	0.7
St dev post	0.6	0.6	1	0.4	1.6	1.6
p	0.12	0.38	0.42	0.9	0.5	0.47

Table III.  Inter-surgeon repeatability of laxity tests. Median results of laxity tests for two expert surgeons (1 and 2) and one non-expert surgeon (3) in ACL-deficient (Pre) and reconstructed (Post) knees. Differences between surgeons were evaluated with pairwise 1-way ANOVA; the significance (p) of each test is reported.

Test		VV (°)		AP (mm)		IE (°)
Flexion		0°	30°	30°	90°	30°	90°
Pre	Surgeon 1	5.45	3.60	10.02	10.96	24.27	28.66
	Surgeon 2	5.17	4.25	13.25	8.12	17.94	24.75
	Surgeon 3	5.07	3.50	9.5	8.5	22.98	30.42
	p	0.8203	0.6375	0.0916	0.0906	0.0675	0.0583
Post	Surgeon 1	2.08	2.38	4.61	4.94	16.14	23.21
	Surgeon 2	2.94	2.38	6	3.75	12.20	16.75
	Surgeon 3	4.00	2.50	5.54	5.62	17.43	19.65
	p	<0.0001	0.8329	0.2896	0.134	0.1334	0.2498

Table IV.  Results of error propagation in kinematic tests due to errors in reference point acquisition of 40 mm for the hip center and 10 mm for other anatomical landmarks.

Decomposition		M/L (mm)	A/P (mm)	P/D (mm)	F/E (°)	AB/AD (°)	I/E (°)
Euler	Random error	2.1	1.5	1.7	0.7	1.3	2.1
	Max. error	3.5	2.6	2.9	1.3	2.2	3.7
Grood & Suntay	Random error	2.2	1.8	1.4	0.7	1.3	1.9
	Max. error	3.4	3.2	2.5	1.3	2.2	3.6

M/L = medio-lateral translation; AP = antero-posterior translation; P/D = proximo-distal translation; F/E = flexion-extension; AB/AD = abduction-adduction; I/E = internal-external rotation.