Background/Purpose:

Obese children have a higher prevalence of lower extremity (LE) pain, with associated diminished quality of life, greater knee malalignment, generate less knee extensor force, and are less physically active compared to healthy weight (HW) children, putting them at risk to be obese adults. In adults, obesity is one major risk factor in developing osteoarthritis (OA) that negatively affects quality of life.  Obese children may have “adult” risk factors, which may confer a risk of developing OA. We explored the relationships between knee alignment, LE strength and quality of life in obese adolescents. We compared 1) knee alignment and lower extremity strength in OB and HW adolescents and 2) evaluated the relationship of BMI and LE strength, and LE strength and QOL.

Methods:

Adolescents (ages 11-18) recruited from pediatric community and tertiary centers were enrolled into two age and sex matched groups based on obesity status. Body mass index (BMI= kg/m²) was calculated to determine BMI Z-scores from CDC US 2002 data.  QOL was assessed using the Pediatric Quality of Life^TM(PedsQL) physical function score.  Frontal plane knee alignment was measured using umbilicus, knee and ankle landmarks.  LE strength was measured bothisokinetically: quadricep peak torque (QPT) and hamstring peak torque (HSPT) and isometrically: hip abductor peak torque (AbdPT) and hip extensor peak torque (ExtPT).  Peak torque was normalized to body weight and right side data were analyzed as all subjects were right leg dominant.  Means and standard deviations described the data.  Paired t-tests and Pearson’s correlations coefficients evaluated group differences and associations among variables of interest.  

Results:

12 males and 10 females were enrolled.  They were divided into 2 groups: OB and HW based on mean BMI and BMI z-scores are reported in Table 1.   Mean PedsQL physical function scores differ by group. (Table 1)

Mean right knee alignment did not differ between the OB and HW adolescents. (Table 1) The OB group had significantly lower QPT, HSPT, AbdPT, and ExtPT. (Table 1)

BMI Z-scores were negatively correlated with LE strength (QPT r= -0.443, p<0.05, HSPT r= -0.527, p< 0.05, AbdPT r= -0.394, p> 0.05, ExtPT r= -0.513, p< 0.05). LE strength measures were positively correlated with physical function scores (QPT r= 0.551, p< 0.05, HSPT r= 0.692, p< 0.001, AbdPT r= 0.538, p< 0.05, ExtPT r= 0.555, p< 0.05).

Conclusion:

OB adolescents have diminished LE strength compared to HW counterparts. Higher BMI Z-scores correlated with lower LE strength while lower LE strength correlated with reduced physical function.  LE strength may limit appropriate physical activity participation in obese adolescents further contributing to obesity and other risk factors that may lead to the development of knee OA. Future research need to explore why the muscles in obese children are not responding as expected to excess load by increasing muscular strength. 

	Obese (n-11)	Non-obese (n=11)	p value
Age (years, sd)	13.9 ± 2.12	14.0 ± 2	p> 0.05
BMI, (mean, sd)	29.56 ± 2.24	20.36 ± 2.94	p< 0 .001
BMI Z-score	1.96	0.19	p< 0 .001
PedsQL(mean, sd)	82.67 ± 10.59	91.76 ± 10.01	p< 0.05
Right knee alignment (mean degrees, sd)	173.82 ± 6.23	170.82 ± 2.09	p> 0.05
QPT (Nm/kg, sd)	1.44 ± 0.29	1.97 ± 0.32	p< 0 .001
HSPT (Nm/kg, sd)	0.77 ± 0.24	1.15 ± 0.22	p< 0.001
AbdPT (Nm/kg, sd)	0.71 ± 0.38	1.08 ± 0.27	p< 0.05
ExtPT (Nm/kg, sd)	0.94 ± 0.43	1.58 ± 0.44	p< 0.05
Table 1.  p< 0.05 level of significance,  sd= standard deviation

---

« Back to 2013 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/lower-extremity-strength-is-related-to-diminished-quality-of-life-in-obese-children/