Gamma loop dysfunction in quadriceps on the contralateral side in patients with ruptured ACL

Area of Science:

• Neurophysiology
• Musculoskeletal Research
• Biomechanics

Background:

• Unilateral anterior cruciate ligament (ACL) rupture can lead to compensatory changes in the uninjured limb.
• The gamma loop plays a crucial role in proprioception and muscle force regulation.

Purpose of the Study:

• To investigate neurophysiological abnormalities in the quadriceps femoris gamma loop on the uninjured side of patients with unilateral ACL rupture.
• To assess the impact of prolonged vibration stimulation on muscle function in the uninjured limb.

Main Methods:

• Measured maximal voluntary contraction (MVC) and integrated electromyography (I-EMG) of quadriceps femoris muscles in 13 ACL patients and 10 controls.
• Applied 20-minute vibration stimulation to the infrapatellar tendon of the uninjured limb.
• Compared pre- and post-stimulation MVC and I-EMG responses.

Main Results:

• ACL patients exhibited significantly different MVC and I-EMG percentage changes compared to controls.
• The uninjured quadriceps femoris in ACL patients showed less decrease in MVC and I-EMG after vibration stimulation than controls.
• This suggests an altered response to prolonged proprioceptive input.

Conclusions:

• Abnormal responses to prolonged vibration stimulation indicate a potential dysfunction in the gamma loop of the uninjured quadriceps femoris in ACL rupture patients.
• The gamma loop's normal function is essential for evoking typical MVC and I-EMG responses to vibration.
• These findings highlight the need to consider neurophysiological adaptations in the uninjured limb post-ACL injury.