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Quadriceps Muscle Size, Quality, and Strength and Self-Reported Function in Individuals With Anterior Cruciate Ligament Reconstruction.

CONTEXT
Ultrasound imaging provides a cost-effective method of measuring quadriceps morphology, which may be related to self-reported function after anterior cruciate ligament reconstruction (ACLR).


OBJECTIVE
To compare quadriceps morphology and strength between limbs in individuals with ACLR and matched control limbs and determine their associations with self-reported function.


DESIGN
Cross-sectional study.


SETTING
Research laboratory.


PATIENTS OR OTHER PARTICIPANTS
Forty-two individuals with ACLR (females = 66%; age = 21.8 ± 2.6 years; time since ACLR = 50.5 ± 29.4 months) and 37 controls (females = 73%; age = 21.7 ± 1.2 years).


MAIN OUTCOME MEASURE(S)
Quadriceps peak torque (PT) and rate of torque development were assessed bilaterally. Ultrasonography was used to measure the cross-sectional area (CSA) and echo intensity (EI) of the rectus femoris, vastus lateralis (VL), and vastus medialis. Self-reported function was assessed via the International Knee Documentation Committee (IKDC) score and Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales. Paired-samples t tests were calculated to compare involved and uninvolved limbs. Independent t tests were conducted to compare groups (α = .05). Linear regression was performed to analyze associations between quadriceps function and self-reported function after accounting for time since ACLR, activity level, and sex, and models for EI added subcutaneous fat as a covariate.


RESULTS
Isometric PT did not differ between limbs or groups. Involved limbs had a lower rate of torque development compared with the control (P = .01) but not the uninvolved limbs (P = .08). Vastus lateralis CSA was smaller in the involved than in the uninvolved (P < .01) but not the control limbs (P = .10). Larger VL CSA (ΔR2 = 0.103) and lower VL EI (ΔR2 = 0.076) were associated with a higher IKDC score (P < .05). Larger VL CSA was associated with greater KOOS symptom (ΔR2 = 0.09, P = .043) and sports/recreational (ΔR2 = 0.125, P = .014) scores. Lower VL EI was associated with higher KOOS symptom (ΔR2 = 0.104, P = .03) and quality-of-life (ΔR2 = 0.113, P = .01) scores. Quadriceps PT and rate of torque development were not associated with IKDC or KOOS subscale scores.


CONCLUSIONS
Quadriceps morphology was associated with self-reported function in individuals with ACLR and may provide unique assessments of quadriceps function.