Quadriceps Muscle Strength, Size, and Activation and Physical Function After Anterior Cruciate Ligament Reconstruction


Persistent neuromuscular deficits in the surgical limb after anterior cruciate ligament reconstruction (ACLR) have been repeatedly described in the literature, yet little is known regarding their association with physical performance and patient-reported function.


To describe (1) interlimb differences in neuromuscular and functional outcomes and (2) the associations of neuromuscular outcomes with measures of physical and knee-related patient-reported function.


Cross-sectional study.




Thirty individuals after primary, unilateral ACLR (19 males; age = 21.5 years [range, 14-41 years]; 8 months [range = 6-23 months] postsurgery).


Knee-extensor isometric and isokinetic peak torque was measured with an isokinetic dynamometer. Cross-sectional area (CSA) was measured bilaterally for each of the quadriceps muscles via magnetic resonance imaging. We measured quadriceps central activation bilaterally via the superimposed-burst technique. Physical performance (single-legged hop tests, step length via spatiotemporal gait analysis) and patient-reported outcomes (International Knee Documentation Committee questionnaire and Knee Injury and Osteoarthritis Outcome Score Sport and Recreation subscale) were also recorded. We conducted Wilcoxon signed-rank tests to identify interlimb differences. Spearman ρ correlation analyses revealed associations between limb symmetry and neuromuscular and functional outcomes, as well as with patient-reported function.


Deficits in the surgical limb as compared with the nonsurgical limb were present for all outcomes (P < .05). Greater single-legged hop-test symmetry (83%) was significantly correlated with greater symmetry in knee-extensor isometric (63%; rs = 0.567, P = .002) and isokinetic (68%; rs = 0.540, P = .003) strength, as well as greater cross-sectional area of the vastus medialis (78%; rs = 0.519, P = .006) and vastus lateralis (82%; rs = 0.752, P < .001). A higher International Knee Documentation Committee questionnaire score (82.2) was significantly correlated with greater symmetry in knee-extensor isokinetic strength (rs = 0.379, P = .039).


Although deficits were observed in the surgical limb for all neuromuscular measures, greater symmetry in the size and strength of the quadriceps, rather than activation, was more strongly associated with physical performance after ACLR. Greater symmetry in strength was also more strongly associated with patient-reported function.