QUADRICEPS STRENGTH CHANGES ACROSS THE CONTINUUM OF CARE FOLLOWING ANTERIOR CRUCIATE LIGAMENT INJURY IN ADOLESCENT MALES AND FEMALES

Abstract

Background:

Deficits in quadriceps strength have consistently been observed following anterior cruciate ligament reconstruction (ACL-R) and this deficit is frequently accompanied by altered lower extremity biomechanics that could increase risk of a second ACL injury. Regaining strength is a major focus for rehabilitation; however, it is unclear how quadriceps strength of both the involved (INV) and uninvolved (UnINV) limbs change across the continuum of care. Therefore, the purpose of this study was to examine quadriceps strength from the pre-operative time point until time of return to sport (RTS) in adolescent males and females.

Methods:

Cohort study design was used. A total of 60 adolescents participated (Males: N = 26, Age = 15.96? 1.23 yr, Ht = 177.14? 8.13 cm, Mass = 76.23? 1.23Kg; Females: N = 34, Age = 15.32? 1.12 yr, Ht = 163.11? 6.30 cm, Mass = 61.39? 7.38Kg) in the study. Participants were included in the study if they: 1) had a primary ACL-R, 2) participated in organized high-risk sports with an intention to return to sports, 3) completed assessments at the pre-operative timepoint (Pre), 12-weeks after surgery (12wk), and at time of RTS, and 4) completed the post-operative rehabilitation program. Five isokinetic repetitions of quadriceps strength (QUADS) of the INV and UnINV limbs were assessed at Pre, 12wk, and RTS, using a Biodex dynamometer (60?/sec). Peak strength was normalized to body weight (BW-1) and averaged across 5 trials. Separate 2 (limb – INV, UnINV) X 3 (time – Pre, 12wk, RTS) repeated measures of ANOVA were performed. With significant interaction, paired t-tests were performed to compare strength between each time point in each limb and between INV and UnINV limbs at each time point.

Results:

There were significant side by time interactions in adolescent females (F = 6.49, p = 0.002) and males (F=16.57, p < 0.001). Post hoc tests revealed that adolescent females had greater INV RTS QUADS than INV PRE QUADS (p= 0.001) and INV 12wk QUADS (p < 0.001), but no significant differences were observed between any time points in the UnINV limb. Adolescent males demonstrated decreased INV 12wk QUADS compared with INV Pre QUADS (p = 0.032), greater INV RTS QUADS than INV 12wk QUADS (p < 0.001). UnINV 12wk QUADS was lower than UnINV Pre QUADS (p < 0.037) and UnINV RTS QUADS was greater than UnINV Pre QUADS (p < 0.002). In both female and male participants, INV QUADS was significantly less than UnINV QUADS at Pre, 12wk, and RTS time points (Females: p < 0.001, p=0.007, p < 0.001, respectively; Males: p < 0.001, p < 0.001, p < 0.001, respectively).

Conclusion/Significance:

Quadriceps strength changes differently in adolescent females and males in both the INV and UnINV limbs across the continuum of care following ACL injury. While no changes were observed in UnINV QUADS over time, adolescent females improved INV QUADS from 12wk to RTS without changes in QUADS from Pre to 12wk. Although INV RTS QUADS was greater than INV Pre QUADS, INV RTS QUADS was 27% lower than RTS UnINV QUADS. Since UnINV QUADS is expected to be decreased due to reduced activity compared to that of pre-injury, strengthening the UnINV limb in addition to the INV limb appears to be a priority during rehabilitation. For adolescent males, INV QUADS decreased from Pre to 12wk and returned near to baseline at time of RTS, but not enough to surpass the Pre QUADS. Perhaps, minimizing the reduction of QUADS between the Pre and 12wk time points through an increase of exercise load during the early stages of rehabilitation may help to improve these deficits. Unlike female adolescents, adolescent males improved UnINV strength over time. This improvement may be a compensation of the decreased QUADS of the INV limb as significant deficits of QUADS were present at each time point.

Table 1.

Adolescent females quadriceps strength*

	Pre	12wk	RTS
INV	1.06 (0.36)	0.95 (0.33)	1.25 (0.34)
UnINV	1.61 (0.43)	1.67 (0.40)	1.71 (0.34)

*Mean (SD) (BW^-1)

Table 2.

Adolescent males quadriceps strength*

	Pre	12wk	RTS
INV	1.50 (0.47)	1.29 (0.45)	1.66 (0.48)
UnINV	2.00 (0.49)	2.23 (0.56)	2.34 (0.49)

*Mean (SD) (BW^-1)