Abstract
Background:
Accurate measurement of limb strength asymmetry differences between sexes may be important to consider when determining readiness to return to sport among adolescents following ACL reconstruction.
Hypothesis/Purpose:
The purpose was to compare isokinetic performance between females and males after ACL reconstruction but before return to sport clearance on isokinetic measures of limb strength asymmetry and flexor/extensor strength ratio. We hypothesized there would be no difference in limb strength asymmetry or flexor/extensor strength ratio between sexes measured by isokinetic testing.
Methods:
We retrospectively collected demographic, surgical, and injury information on patients aged 10 – 18 years at time of surgery. Patients completed isokinetic testing within 5-10 months after primary quadriceps tendon ACL reconstruction, and before return to sport clearance. Isokinetic testing assessed maximum torque at three speeds, 60, 180, and 300 degrees per second, through a limited range of knee extension and flexion. Maximum torque percent deficit of the involved leg compared to the uninvolved leg and flexor/extensor strength ratios were calculated. We compared peak torque extensor deficits and flexor deficits (the % difference between operative and non-operative sides) and flexor/extensor ratios at the three isokinetic test speeds within sexes and between sexes.
Results:
80 subjects were tested during the study period, of which 44 subjects met inclusion criteria (female: n=29, 66%). Injury characteristics and time since surgery were similar between sexes (Table 1). Greater extensor deficits among males and females were observed at 60 degrees/s compared to 180 degree/s (p=0.003) and 300 degree/s (p<0.001), and at 180 degrees/s compared to 300 degrees/s (p=0.001) (Figure 1). Females demonstrated significantly greater peak torque flexor deficits at 300 degrees/s, compared to males (p=0.04, Figure 2). Within males, greater flexor deficits were observed at 60 degrees/s compared to 180 degrees/s (p<0.001) and 300 degrees/s (p=0.001) (Figure 2). Within females, greater flexor deficits were observed at 60 degrees/s compared to 180 degrees/s (p=0.02, Figure 2). There were no significant interactions or main effects of sex or speed for either the operative or the non-operative limb peak torque flexor/extensor ratio.
Conclusion:
The results demonstrate greater peak torque flexor deficits among females compared to males at the fastest testing speed in our protocol. Currently, our results indicate variability both within and between sex isokinetic performance at different speeds and suggest that isokinetic testing at slower speeds may be most effective in determining strength deficits between limbs.
Tables and Figures:
Participant characteristics, compared between sexes. Continuous variables are presented as means ± sd, categorical variables are presented as n (%) included in the group.
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|---|---|---|---|
| Age (years) | 15.7 (1.5) | 16.3 (1.4) | 0.20 |
| Height (cm) | 162.4 (9.3) | 172.1 (8.1) | 0.002 |
| Mass (kg) | 61.0 (2.1) | 75.3 (22.1) | 0.007 |
| BMI (kg/m2) | 23.1 (4.0) | 25.1 (5.8) | 0.19 |
| Right side injury | 16 (55%) | 8 (53%) | 1.00 |
| Concomitant meniscus injury | 15 (52%) | 10 (67%) | 0.52 |
| Skeletally mature (pre-op X-ray) | 19 (66%) | 10 (67%) | 1.00 |
| Right leg dominant | 28 (97%) | 14 (93%) | 1.00 |
| Time since surgery (months) | 7.3 (1.7) | 7.0 (1.2) | 0.51 |
Sex by speed comparisons for peak torque extensor deficits. Error bars represent 95% confidence intervals. A main effect of speed indicated that among both groups, greater extensor deficits existed at 60 degrees/s compared to 180 degrees/s (p=0.003) and 300 degrees/s (p< 0.001), and at 180 degrees/s compared to 300 degree/s (p=0.001).
Sex by speed comparisons for peak torque flexor deficits. Error bars represent 95% confidence intervals.