Kiss goodbye to the ‘kissing knees’: no association between frontal plane inward knee motion and risk of future non-contact ACL injury in elite female athletes

Figures & data

Figure 1. Superimposed skeleton model during a single-leg squat to estimate joint centres, using the method of Krosshaug and Bahr (2005).

Figure 2. The single-leg squat (a) and the vertical drop jump (b) tests, visually presenting the calculation of the lateral pelvic tilt (LPT) and frontal plane projection angle (FPPA) in 2A, and the medial knee position (MKP) in 2B. The FPPA angle and Medial Knee Position seen in these athletes would have a negative sign due to the valgus joint position.

Table 1. Frontal plane kinematic descriptive and statistical tests for differences between injured and non-injured.

	Injured		Non-Injured
	N	Mean (SD)	N	Mean (SD)	T-test p value	Cohen’s d	Adjusted OR (95% CI)*	AUC (95% CI)
Single-Leg Squat
Frontal plane projection angle (°)	54	−6.20 (11.26)	722	−8.90 (9.67)	0.09	−0.24	0.98 (0.95, 1.01)	41.65 (33.20, 50.09)
Medial knee position (%)	53	−2.92 (5.33)	689	−3.86 (4.28)	0.21	−0.18	0.96 (0.90, 1.02)	42.12 (33.39, 50.85)
Pelvic tilt (°)	54	4.94 (5.30)	722	5.00 (5.36)	0.94	−0.01	1.00 (0.95, 1.06)	47.99 (40.04, 55.93)
Drop Vertical Jump
Medial knee position at initial contact (%)	55	1.87 (3.43)	713	1.09 (3.24)	0.11	0.23	1.05 (0.96, 1.14)	55.13 (47.11, 63.15)
Frontal plane projection angle at initial contact (°)	55	4.27 (7.78)	713	2.50 (7.38)	0.11	0.23	0.98 (0.94, 1.02)	44.85 (36.84, 52.87)
Medial knee position at max flexion (%)	55	0.30 (4.90)	713	−0.97 (4.16)	0.07	0.26	1.05 (0.99, 1.12)	58.44 (50.23, 66.65)
Frontal plane projection angle at max flexion (°)	56	0.98 (12.99)	715	−1.64 (14.26)	0.15	0.20	1.01 (0.99, 1.02)	57.80 (49.69, 65.91)
Medial knee displacement (max-IC) (%)	55	−1.59 (2.28)	713	−2.06 (2.24)	0.15	−0.21	0.91 (0.81, 1.03)	42.62 (34.34, 50.89)
Frontal plane projection angle displacement (max-IC) (°)	55	−3.14 (6.84)	713	−4.12 (10.62)	0.34	0.14	0.99 (0.97, 1.02)	41.82 (33.42, 50.22)

* Odds ratio adjusted for previous ACL injury and sport (Handball or Football). For the variables frontal plane projection angle, frontal plane projection angle displacement, medial knee position and medial knee displacement, positive values (˃0) refers to knee varus, and negative values (˂0) refers to knee valgus.

Table 2. Summary of the inter-rater reliability from two separate sessions.

	Inter-rater reliability, team 1		Inter-rater reliability, team 2
	ICC	SEM	ICC	SEM
Single-Leg Squat
FPPA (°)	0.88	6.6°	0.95	1.9°
MKP (%)	0.87	3.0%	0.93	3.2%
LPT (°)	0.77	1.7°	0.72	1.5°
Vertical Drop Jump, initial contact
FPPA (°) Right	0.85	3.6°	0.70	3.5°
FPPA (°) Left	0.89	5.5°	0.72	4.5°
MKP (%) Right	0.85	1.6%	0.83	1.1%
MKP (%) Left	0.89	2.4%	0.60	1.5%
Vertical Drop Jump, peak knee flexion
FPPA (°) Right	0.91	4.4°	0.94	3.5°
FPPA (°) Left	0.93	6.6°	0.93	4.3°
MKP (%) Right	0.92	2.1%	0.81	1.1%
MKP (%) Left	0.94	2.6%	0.82	1.4%

ICC: Intraclass correlation coefficient; SEM: Standard error of measurement; FPPA: Frontal plane projection angle; MKP: Medial knee position

Krosshaug, T., & Bahr, R. (2005). A model-based image-matching technique for three-dimensional reconstruction of human motion from uncalibrated video sequences. Journal of Biomechanics, 38(4), 919–929. https://doi.org/10.1016/j.jbiomech.2004.04.033

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