The impact of quadriceps femoris strength asymmetry on functional performance at return to sport following anterior cruciate ligament reconstruction

Abstract

Study design: Cross-sectional study.

Objectives: To investigate the impact of quadriceps femoris (QF) muscle strength asymmetry at the time of return to sport on self-reported function and functional performance of individuals following anterior cruciate ligament reconstruction (ACLR).

Background: Evidence-based QF strength guidelines for return-to-sport decision making are lacking. Objective guidelines necessitate understanding the impact of QF strength deficits at the time of return to sport on function and performance.

Methods: Fifty-five individuals (mean age, 17.3 years) who were cleared for return to sport following primary ACLR (ACLR group) and 35 uninjured individuals (mean age, 17.0 years) in a control group participated in the study. QF strength (maximum voluntary isometric contraction) was assessed, and the quadriceps index (QI) was calculated [(involved strength/uninvolved strength) × 100%]. The ACLR group was further subdivided into 2 groups, based on the QI: high quadriceps (QI of 90% or greater) and low quadriceps (QI of less than 85%). The International Knee Documentation Committee Subjective Knee Evaluation Form score was used to assess self-reported function, and hop tests were used to assess functional performance. Multivariate analysis of variance and hierarchical regression analyses were performed.

Results: The individuals in the ACLR group were weaker, reported worse function, and performed worse on hop tests compared to those in the control group (P<.05). The low-quadriceps group demonstrated worse performance on the hop tests compared to the high-quadriceps group and the control group (P ≤.016). Hop test performance did not differ between the high-quadriceps and control groups (P ≥.14). QF strength predicted performance on the hop tests beyond graft type, presence of meniscus injury, knee pain, and knee symptoms.

Conclusion: At the time of return to sport, individuals post-ACLR who had weaker QF (QI of less than 85%) demonstrated decreased function, whereas those with minimal QF strength deficits (QI of 90% or greater) demonstrated functional performance similar to uninjured individuals. QF strength deficits predicted hop test performance beyond the influences of graft type, presence of meniscus injury, knee pain, and knee symptoms.

FIGURE 1

Performance of the single-leg hop tests (top), including the single hop for distance (cm), triple hop for distance (cm), crossover hop for distance (cm), and 6-meter timed hop (seconds). For the single-, triple-, and crossover-hop tests, the goal was to hop forward as far as possible, while maintaining a controlled landing on the ipsilateral limb. For the timed-hop test, the goal was to hop on the single limb, as quickly as possible, over a distance of 6 m. For this study, 2 measurement trials were obtained for each limb, tested in random order, and the average of the trials for each limb was used to calculate a limb symmetry index (LSI) for distance-hop tests (Equation 2) and the timed-hop test (Equation 3). The bottom panels show an example of a participant completing the single hop for distance. For the single hop for distance, the participant starts in a single-limb stance position on the test limb (A), moves into a semi-crouched position (B), utilizes upper extremity swing and test-limb extension to propel forward (C), and hops forward as far as possible (D), to land on the same limb (E) and maintain control of the landing without loss of balance or contralateral foot contact (F).

FIGURE 2

Scores on the International Knee Documentation Committee Subjective Knee Evaluation Form, where higher scores indicate better function. (A) *ACLR group significantly less than control group (P<.001). (B) *Control group significantly greater than both the HQ and LQ groups (P<.001). Abbreviations: ACLR, anterior cruciate ligament reconstruction; HQ, high quadriceps; LQ, low quadriceps.

FIGURE 3

Limb symmetry index scores on the single-leg hop tests, where scores below 100% indicate deficits in the involved limb. (A) *ACLR group significantly lower than control group for all 4 hop tests (P≤.03). (B) *LQ group significantly lower than HQ and control groups (P≤.016). ^†LQ group significantly lower than control group (P<.003). Abbreviations: ACLR, anterior cruciate ligament reconstruction; CH, crossover hop; HQ, high quadriceps; LQ, low quadriceps; SH, single hop; TiH, timed hop; TrH, triple hop.