The anterior cruciate ligament (ACL) is one of the most commonly injured ligaments in the knee that frequently results in reconstruction surgery. Some degree of chronic proprioception and postural balance deficiency has been reported following ACL reconstruction (ACLR) surgery, which may be associated with a higher risk of ACL re-injury in these patients. Stochastic resonance (SR) has been shown to improve proprioception in various clinical populations with comparable postural and proprioceptive deficiencies as the ACLR population.

In this dissertation, the existence of such deficiencies has been investigated in female ACLR participants and healthy controls. The effect of SR on improving the postural balance and knee proprioception in ACLR and healthy populations has also been studied. The ACLR participants were tested at three months (n = 19) and six months post-surgery (n = 15), while healthy participants were tested once (n = 28).

The SR vibration was applied locally to the knee region. Proprioception was evaluated using movement threshold and movement repeatability tests. The effects of the following factors on proprioception were studied:​ SR (ON vs. OFF), movement direction (flexion vs. extension), and limb condition (ACLR vs. contralateral;​ ACLR vs. healthy dominant control). Postural balance during single leg standing (duration of 30 sec) was assessed with new measures including entropic half-life (EnHL) and surrogate entropy (ΔE_surr). These measures were developed in conjunction with this dissertation. The effects of the following factors on postural balance were studied:​ SR (ON vs. OFF), limb side (ACLR vs. contralateral;​ ACLR vs. healthy dominant control), and vision (eyes open vs. eyes closed).

SR vibration successfully improved proprioception in the ACLR and healthy controls. These study results suggest that SR could potentially aid in pre/post-surgery proprioception rehabilitation.

This study showed that a postural balance deficiency was present when the ACLR limb was compared to healthy dominant control limbs. When the ACLR limb was compared to the contralateral, the deficiency was only present when the eyes were closed. These findings may suggest that the postural balance deficiency is subtle. Therefore, more stringent or demanding experimental protocols may be necessary to test postural balance in functional groups with deficiencies such as the ACLR group.b