The Relationship between Knee Related Function and Objectively Measured Physical Activity after ACL Reconstruction

Abstract

Persistent quadriceps weakness and knee dysfunction have been reported after ACL reconstruction (ACLR). It is unclear if these clinical findings are related to physical inactivity among those with a history of ACLR. PURPOSE: To investigate the relationship between patient reported knee function, knee extension strength, and objectively measured physical activity in individuals with and without a history of ACLR. METHODS: 17 ACLR participants (Sex = 10F/7M, Age = 20.5 ± 1.9 yrs, BMI = 23.4 ± 3.5kg/m2, Time since surgery = 39.3 ± 18.7mo) and 17 matched controls (Sex = 10F/7M, Age = 20.5 ± 2.5 years, BMI = 23.1 ± 3.5kg/m2) enrolled. Participants completed the International Knee Documentation Committee (IKDC) form to assess knee function. Involved limb knee extension maximal voluntary isometric contraction (MVIC) strength (Nm/kg) and isokinetic knee extension strength (Nm/kg) was assessed at 60 and 180 deg/s using a multi-mode dynamometer. Moderate-to-vigorous physical activity (MVPA, min/day) was assessed with an ActiGraph GT3X-BT accelerometer worn on an elastic belt at the hip over a period of 7 days with a minimum of 4 days of wear with ≥10 hours per day. Wear time (min/day) was validated using recommendations of Choi et al and Freedson Adult VM3 cut points were used to categorize physical activity. Relationships between MVPA, knee extension strength, and IKDC score were assessed for all participants as well as within the ACLR group using Pearson’s product moment correlations (r). RESULTS: Overall, IKDC score (mean = 93.42 ± 6.95) was positively correlated with isokinetic knee extension strength at 180 deg/s (mean = 1.30 ± 0.45Nm/kg, r = 0.41, p = 0.02). In the ACLR group, IKDC score (mean = 90.19 ± 7.21) was positively correlated with knee extension MVIC strength (mean = 2.28 ± 0.78, r = 0.48, p = 0.05) as well as isokinetic knee extension strength at 180 deg/s (mean = 1.21 ± 0.55, r = 0.57, p = 0.02). There were no significant correlations between IKDC score, knee extension MVIC strength, or isokinetic knee extension strength and MVPA. CONCLUSIONS: MVPA is an important clinical outcome that may not be related to traditional patient reported or functional outcome measures after ACLR. Understanding the factors contributing to physical inactivity after ACLR may guide clinical intervention strategies aimed at promoting MVPA.