Isometric hip strength impairments in patients with hip dysplasia are improved but not normalized 1 year after periacetabular osteotomy: a cohort study of 82 patients

Figures & data

Figure 1. Flow of patients and healthy volunteers.: PAO = periacetabular osteotomy.

Table 1. Baseline characteristics of patients with hip dysplasia and healthy volunteers. Values are count unless otherwise specified

Characteristics	Patients with hip dysplasia (n = 100)	Healthy volunteers (n = 50)
Mean age (SD)	30 (9)	31 (9)
Mean BMI (SD)	23 (3)	23 (3)
Men	17	8
Preferred sports, h/week (IQR)	0 (2)	4 (10)
Preferred sports
Fitness	28	17
Running	19	10
Team sports	13	12
Gymnastics	7	3
Horseback riding	6	0
Racket sports	2	2
Swimming	2	0
Dancing	2	0
Other ^a	18	6
No preferred sports	3	0
General physical activity h/week
< 2.5 h/week	13	3
2.5 to < 5 h/week	19	7
5 to < 10 h/week	42	30
≥ 10 h/week	26	10
Back pain intensity
No	31	41
Very mild	23	7
Moderate	26	2
Fairly severe	14	0
Very severe	5	0
Worst imaginable	1	0
Posterior to anterior spring testing (SP)
Hip pain	12	0
Back pain	35	6
No pain	53	44
Positive FADIR test	83	3
Positive FABER test	74	2
Positive internal snapping hip test	30	0
Bilateral affection	89	–
NRS pain (range)	3 (2–5)	–
Centre-edge angle (°; SD)	17 (5)	–
Tцnnis acetabular index angle (°; SD)	14 (5)	–
Osteoarthritis grade 0/1	97/3	–

a Covers different combat and self-defense sports, bicycling and hiking.

IQR = interquartile range,

SP = spinous processes,

FADIR = flexion/adduction/internal rotation,

FABER = flexion/abduction/external rotation,

NRS = numerical rating scale.

Figure 2. Median isometric hip muscle strength in patients with hip dysplasia and in healthy volunteers in Nm/kg; box represents 25th and 75th percentiles and error bars represent 10th and 90th percentiles. PAO = periacetabular osteotomy.

Table 2. Mean changes in isometric hip muscle strength in Nm/kg

Hip strength	Volunteers		Before PAO		1 year after PAO		HD change (95% CI)	HD change
	n	mean (SD)	n	mean (SD)	n	mean (SD)		(%)	p-value
Flexion	50	1.8 (0.34)	100	1.2 (0.40) ^a	80	1.3 (0.32) ^a	0.13 (0.06 to 0.20)	11	< 0.001
Extension	50	2.5 (0.63)	97	1.8 (0.68) ^a	80	1.9 (0.59) ^a	0.09 (–0.05 to 0.23)	5	0.2
Abduction	50	1.5 (0.37)	99	1.2 (0.43) ^a	81	1.3 (0.44) ^a	0.10 (0.02 to 0.18)	8	0.02
Adduction	50	1.5 (0.46)	98	1.1 (0.44) ^a	80	1.1 (0.37) ^a	–0.03 (–0.11 to 0.06)	–3	0.5

a Statistically significantly lower than the values of the healthy volunteers (p < 0.01).

PAO = periacetabular osteotomy.

Table 3. Mean differences in muscle strength in Nm/kg between 100 patients and 50 volunteers

Hip strength	Before PAO			1 year after PAO
	Mean diff. (95% CI)	% diff.	p-value	Mean diff. (95% CI)	% diff.	p-value
Flexion	0.60 (0.48–0.73)	34	< 0.001	0.47 (0.34–0.60)	27	< 0.001
Extension	0.66 (0.44–0.87)	27	< 0.001	0.56 (0.34–0.79)	23	< 0.001
Abduction	0.30 (0.16–0.44)	20	< 0.001	0.20 (0.05–0.35)	13	0.008
Adduction	0.41 (0.27–0.56)	27	< 0.001	0.44 (0.29–0.59)	29	< 0.001

PAO = periacetabular osteotomy.

Figure 3. Profile of Copenhagen Hip and Groin Outcome Score (HAGOS) in patients and healthy volunteers in HAGOS points (0–100); error bars represent 95% confidence intervals. PAO = periacetabular osteotomy, ADL = physical function in daily living, Sport/rec = physical function in sports and recreation, PA = participation in physical activity, QoL = quality of life.

Table 4. Associations of change in HAGOS to change in muscle strength in HAGOS points/Nm/kg. Values are crude β coefficients with 95% confidence interval (CI) for associations between HAGOS and hip muscle strength measured before and 1 year after periacetabular osteotomy

Outcomes	Hip flexion (n = 80)		Hip extension (n = 78)		Hip abduction (n = 81)		Hip adduction (n = 79)
	β (CI)	p-value	β (CI)	p-value	β (CI)	p-value	β (CI)	p-value
HAGOS pain	13.4 (0.5 to 26.3)	0.04	6.3 (–0.5 to 13.1)	0.07	14.0 (3.3 to 24.7)	0.01	7.6 (–3.3 to 18.5)	0.2
HAGOS sport	13.2 (-4.1 – 30.5)	0.1	9.3 (0.6 to 17.9)	0.04	11.6 (–2.9 to 26.1)	0.1	0.9 (–13.5 to 15.4)	0.9

HAGOS = Copenhagen Hip and Groin Outcome Score, sport = physical function in sport and recreation.