The relationship between knee joint effusion and quadriceps strength and activation after anterior cruciate ligament (ACL) injury and reconstruction.

Context: Knee joint effusion and quadriceps strength and activation deficits are common consequences of anterior cruciate ligament (ACL) injury and reconstruction. The presence of an effusion may initiate or worsen the quadriceps dysfunction present after ACL trauma. In simulated effusion studies, evidence indicates an inverse relationship between effusion size and quadriceps dysfunction. While this relationship was not found in patients after ACL injury, prior research was limited by a subjective clinical assessment of effusion grade.

Objective: The purpose of this study was to determine if the size of the knee joint effusion, measured via ultrasound, after ACL injury and reconstruction influences quadriceps strength and activation.

Design: Descriptive Laboratory Study.

Setting: Research Laboratory.

Patients or other participants: 41 individuals (23 females, age=21.8±7.5years, height =171.7±7.9cm, 15 mass =72.3±14.2kg), with an ACL injury reported for 2 sessions [one before 16 reconstruction and one ∽16 weeks after ACL reconstruction].

Main outcome measure: Three ultrasound images of the suprapatellar pouch and three trials of quadriceps strength and activation using the interpolated twitch technique were gathered from the ACL knee. Effusion cross-sectional area was measured using ImageJ, averaged and inputted into linear regression models to predict muscle strength and interpolated twitch activation. Analyses were considered significant at p≤0.05.

Results: No relationship was found between effusion size and strength (R2 = 0.086) or activation (R2=0.056) after ACL injury (p>0.05). After reconstruction, however, there was a small negative relationship between effusion size 24 and activation (R2=0.122; Standardized β=-0.349; p=0.025), while no relationship was found for effusion size and strength (R2=0.000; p≤0.05).

Conclusions: The size of the effusion after ACL injury does not influence strength or activation. However, after ACL reconstruction, effusion size does have a small influence on quadriceps activation, with a larger effusion being related to lower activation. Prior research using simulated effusions appear to overestimate the effects of effusion on quadriceps function.