Improvement in muscle strength after an anterior cruciate ligament injury corresponds with a decrease in serum cytokines

• Muscular weakness challenges the recovery from an ACL injury and surgery.
• Muscle weakness decreases from the time of an ACL injury occurrence.
• Serum cytokines decrease in parallel to the decrease in muscle weakness.
• A decrease in serum cytokines could decrease muscular weakness after an ACL injury.

The purpose of this communication was to identify if a decrease in serum cytokine concentrations associates with an improvement in muscle strength after an anterior cruciate ligament (ACL) injury. To establish groups with contrasting serum cytokine concentrations, subjects scheduled for ACL reconstructive surgery were separated into one of two groups (gender matched) based on their time from injury occurrence: (1) Early (<21-d from injury occurrence; n = 22) or (2) Late (⩾21-d from injury occurrence; n = 22). Before surgery, each subject provided a fasting blood sample and performed single-leg peak isometric force testing on the injured (INJ) and non-injured (NI) limbs. Compared to the NI limb, peak isometric force in the INJ limb was decreased (p < 0.05) in both groups (Early, ∼35%; Late, ∼18%). The deficit in peak isometric force, however, was increased (p < 0.05) in the Early compared to Late group. Similarly, serum granulocyte macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-6, and IL-13 were increased (all p < 0.05) in the Early group. These unique findings show a concurrent increase in muscular weakness and serum cytokine concentrations shortly after (<21-d) an ACL injury. Importantly, muscular weakness persisted thereafter (⩾21-d) but at an attenuated level and parallel to a decrease in circulating cytokine concentrations. We conclude that a decrease in serum cytokines associates with a reduction in muscular weakness after an ACL injury.