Relationship Between Changes in Physical Activity and Knee Health 18 Months after ACL Reconstruction.

Purpose: This study aimed to determine the relationship between changes in daily physical activity (PA) and knee health 18 months after anterior cruciate ligament reconstruction (ACLR). Knee health was defined using structural (quantitative magnetic resonance imaging [MRI]) and functional (patient-reported and objectively-measured knee function) constructs.

Methods: Eighteen individuals (83.3% female, 19.7 ± 5.6 years old, BMI 23.9 ± 3.7 kg/m2) completed testing. Daily steps over one week and structural cartilage health, measured using a waist-worn accelerometer (Actigraph wGT3X-BT) and T2 relaxation time on MRI, respectively, were collected six and 18 months after ACLR. Eighteen months after ACLR patient-reported and objectively measured knee health were assessed using the International Knee Documentation Committee Subjective Knee Form (IKDC) and isometric quadriceps strength, respectively. A linear regression model was used to test the relationship between the change in PA from six to 18 months after ACLR and the percent change in T2 relaxation time of four cartilage regions (lateral and medial femoral and tibial cartilage) from six to 18 months after ACLR. A Fisher's Exact test assessed the relationship between change in PA (increase/decrease) between six and 18 months after ACLR and adequate/inadequate knee function using patient-reported (IKDC) and objectively measured (quadriceps strength) knee function 18 months after ACLR.

Results: Participants averaged 7547.3 ± 2439.7 daily steps six months after ACLR and 7504.9 ± 3736.3 daily steps 18 months after ACLR. There was no association between change in PA and structural knee health (p = 0.069) or knee function (p = 0.638).

Conclusions: Average daily steps did not change from six to 18 months after ACLR. PA from six to 18 months after ACLR was not associated with knee health outcomes at 18 months.