Abstract
Background:
The subject of sex-based differences in postoperative recovery after anterior cruciate ligament reconstruction (ACLR) between males and females has been incompletely investigated, with no published comparative analyses specifically in adolescent sub-populations, which represent those most affected by ACL injury.
Purpose/Hypothesis:
To compare the 6-month postoperative functional recovery following ACLR between adolescent males and females. We hypothesized that significant differences in postoperative strength, dynamic balance, and functional hop test performance would be seen between the sexes.
Methods:
All adolescent athletes with closed or closing growth plates who underwent ACLR at a single institution between May 2014 and May 2018 and who underwent functional return-to-sport (RTS) testing between 5-8 months post-operatively were considered for inclusion in this IRB-approved study. To control for potential graft-based rehabilitation differences or donor site morbidity as confounders, only primary ACLRs performed with hamstring autograft were included. Exclusions were previous knee surgery (contralateral or ipsilateral knee), concomitant injury other than meniscus tear, allograft supplementation, and incomplete medical records. Limb Symmetry Indexes (LSI) for strength (quadriceps, hamstrings, hip abductors, hip extensors), dynamic Y-balance (anterior, posterolateral and posteromedial distance), and functional hopping (single hop, triple hop, and cross-over hop for distance, and 6-meter timed hop) were compared between groups. To account for differences in physical characteristics between the sexes, one-way between group multivariate analysis of covariance (MANCOVA) was used, with p = 0.05.
Results:
Amongst 543 subjects (211 male, 332 female), there was no significant difference in age, BMI, incidence of concomitant meniscal pathology, use of regional anesthesia blocks, or time to functional testing between cohorts. However, height and weight differences were incorporated in the MANCOVA model. Females demonstrated a statistically significant greater deficit in quadriceps strength LSI compared to males (Table 1). Both males and females demonstrated 33% hamstring strength deficits, with no statistically significant sex-based differences in dynamic balance or functional hop testing, though single leg hop deficits were less severe in males, which trended towards significance (-4% vs. -8%, p=0.062).
Conclusion:
Females demonstrated greater quadriceps strength deficits than males at 6 months post-ACLR with hamstring autograft, which may translate into greater functional hop testing deficits. Severe hamstring strength deficits persist in both males and females at this time point, underscoring the potential importance of mitigating risk of ACL re-tear by delaying return to play until a later time point with more normalized, symmetric, performance-based metrics.
Strength, balance, and functional hop testing deficits in quadriceps, hamstrings, hip abductors, and hip extensors
| Groups | Males |
Females |
P-values |
|---|---|---|---|
| Quadriceps Strength: | |||
| Uninvolved limb | 4.57±1.2 (4.40, 4.73) | 4.27±1.0 (4.16, 4.39) | |
| ACLR limb | 4.61±1.2 (4.44, 4.78) | 4.11±1.1 (4.00, 4.23) | |
| Deficits (LSI%) | +3.4 (+0.5, +6.3) | -2.3 (-5.0, +0.4) | 0.011 |
| Hamstrings Strength: | |||
| Uninvolved limb | 2.31±0.7 (2.21, 2.41) | 2.17±0.6 (2.10, 2.24) | |
| ACLR limb | 1.48±0.6 (1.40, 1.57) | 1.40±0.6 (1.33, 1.46) | |
| Deficits (LSI%) | -33.0 (-38.0,-28.0) | -33.2 (-37.9, -28.6) | 0.943 |
| Hip abductor Strength: | |||
| Uninvolved limb | 1.90±0.6 (1.81, 2.00) | 1.85±0.7 (1.76, 1.93) | |
| ACLR limb | 1.94±0.6 (1.86, 2.03) | 1.92±0.8 (1.83, 2.01) | |
| Deficits (LSI%) | +3.8 (-0.8, +8.4) | +6.2 (+1.9, +10.5) | 0.490 |
| Hip extensor Strength: | |||
| Uninvolved limb | 3.36±1.2 (3.19, 3.53) | 3.25±1.0 (3.14, 3.36) | |
| ACLR limb | 3.41±1.3 (3.23, 3.59) | 3.27±1.1 (3.15, 3.38) | |
| Deficits (LSI%) | +4.2 (-1.5, +9.9) | +2.2 (-3.1, +7.5) | 0.637 |
| Anterior Reach: | |||
| Uninvolved limb | 61.9±7.8 (60.8, 63.0) | 59.5±6.5 (58.8, 60.2) | |
| ACLR limb | 60.3±7.5 (59.3, 61.3) | 57.9±6.3 (57.2, 58.6) | |
| Deficits | -0.7 (-3.1, +1.6) | -0.9 (-3.1, +1.2) | 0.905 |
| Posteromedial Reach: | |||
| Uninvolved limb | 101.6±11.2 (100.1, 103.1) | 94.2±8.8 (93.2, 95.2) | |
| ACLR limb | 101.2±11.5 (99.6, 102.7) | 92.9±10.6 (91.8, 94.1) | |
| Deficits | +0.5 (-0.1, +0.2) | +0.1 (-1.3, +1.5) | 0.718 |
| Posterolateral Reach: | |||
| Uninvolved limb | 96.5±11.3 (95.0, 98.0) | 91.1±8.7 (90.1, 92.0) | |
| ACLR limb | 96.3±11.4 (94.7, 97.8) | 90.3±9.4 (89.3, 91.3) | |
| Deficits | +0.8 (-1.1, +2.7) | -0.5 (-2.3, +1.2) | 0.334 |
| Composite Score: | |||
| Uninvolved limb | 95.5±8.7 (94.2, 96.9) | 96.6±7.3 (95.6, 97.5) | |
| ACLR limb | 94.8±8.8 (93.4, 96.1) | 95.6±8.0 (94.5, 96.6) | |
| Deficits | +0.3 (-0.9, +1.4) | -0.6 (-1.7, +0.5) | 0.319 |
| Single Hop: | |||
| Uninvolved limb | 1.29±0.27 (1.25, 1.34) | 1.07±0.21 (1.04, 1.10) | |
| ACLR limb | 1.22±0.28 (1.18, 1.27) | 0.97±0.23 (0.94, 1.00) | |
| Deficits | -4.0 (-6.9, -1.0) | -8.1 (-10.9, -6.9) | 0.062 |
| Triple Hops: | |||
| Uninvolved limb | 4.40±0.77 (4.27, 4.53) | 3.55±0.58 (3.47, 3.63) | |
| ACLR limb | 3.13±1.21 (2.92, 3.33) | 2.84±0.68 (2.75, 2.94) | |
| Deficits | -27.0 (-32.9, -21.1) | -20.0 (-25.5, -14.5) | 0.117 |
| Cross-over Hops: | |||
| Uninvolved limb | 3.82±0.84 (3.68, 3.97) | 3.04±0.60 (2.95, 3.13) | |
| ACLR limb | 3.62±0.80 (3.48, 3.76) | 2.85±0.61 (2.75, 2.94) | |
| Deficits | -4.5 (-7.0, -2.0) | -5.8 (-8.1, -3.5) | 0.501 |
| 6 meter Timed Hop: | |||
| Uninvolved limb | 2.12±0.47 (2.04, 2.20) | 2.45±0.44 (2.39, 2.51) | |
| ACLR limb | 2.21±0.49 (2.12, 2.29) | 2.57±0.50 (2.50, 2.64) | |
| Deficits | -1.7 (-3.9, +0.4) | -3.6 (-5.7, -1.6) | 0.244 |
Values are mean ± standard deviation with 95% confidence interval.
* p < 0.05.
Strength was measured in newton/kg.
LSI = Limb Symmetry Index
Dynamic balance reach was measured in centimeters.
Single, triple, and crossover hop distance was measured in meters. 6 meter timed hop was measured in seconds.