How does anterior cruciate ligament reconstruction affect the functioning of the brain and spinal cord?A systematic review with meta-analysis

Objective:To examine the effect of anterior cruciate ligament(ACL)reconstruction on spinal-reflex and corticospinal excitability of the quadriceps muscle.Methods:A comprehensive electronic database search was performed to identify studies that objectively measured Hoffmann reflex to muscle response ratio,motor threshold,and motor evoked potentials after ACL reconstruction.Pooled standardized mean differences(SMDs)were computed using a random effects meta-analysis model.Results:A total of 13 studies were eligible for analysis.The Hoffmann reflex to muscle response ratio was significantly higher on both the reconstructed and non-reconstructed legs when compared with the healthy control leg(SMD=0.28,95%confidence interval(95%CI):0.08-0.49,p=0.006 and SMD=0.22,95%CI:0.04-0.40,p=0.016,respectively)but did not differ between legs(SMD=0.10,95%CI:-0.01 to 0.21,p=0.078).The motor threshold was significantly higher on both the reconstructed(SMD=0.76,95%CI:0.40-1.12,p<0.001)and non-reconstructed legs(SMD=0.47,95%CI:0.00-0.95,p=0.049)when compared with the legs of healthy controls.The reconstructed leg also had a higher motor threshold when compared with the non-reconstructed leg(SMD=0.20,95%CI:0.06-0.34,p=0.005).These changes were paralleled by bilateral reductions in quadriceps strength(ACL reconstructed:SMD=-0.78,95%CI:-1.07 to-0.49,p<0.001;non-reconstructed:SMD=-0.32,95%CI:-0.63 to-0.01,p=0.042)and quadriceps voluntary activation(ACL reconstructed:SMD=-0.73,95%CI:-0.97 to-0.50,p<0.001;non-reconstructed:SMD=-0.55,95%CI:-0.82 to-0.27,p<0.001)when compared with healthy controls.Conclusion:There is increased excitability of the spinal-reflex pathways and reduced excitability of the corticospinal pathways following ACL reconstruction.These changes are paralleled by reductions in quadriceps strength and voluntary activation,suggesting that rehabilitation interventions should focus on normalizing the excitability of neural pathways to effectively address quadriceps dysfunction after ACL reconstruction.

Estimates of voluntary activation in individuals with anterior cruciate ligament reconstruction:Effects of type of stimulator,number of stimuli,and quantification technique

Background:Accurate quantification of voluntary activation is important for understanding the extent of quadriceps dysfunction in individuals with anterior cruciate ligament reconstruction(ACLR).Voluntary activation has been quantified using both percent activation derived from the interpolated twitch technique and central activation ratio(CAR)derived from the burst superimposition technique,as well as by using different types of electrical stimulators and pulse train conditions.However,it is unclear how these parameters affect voluntary activation estimates in individuals with ACLR.This study was performed to fill this important knowledge gap in the anterior cruciate ligament literature.Methods:Quadriceps strength and voluntary activation were examined in 18 ACLR participants(12 quadriceps/patellartendon graft,6 hamstring tendon graft;time since ACLR:1.06±0.82 years,mean±SD)at 90°of knee flexion using 2 stimulators(Digitimer and Grass)and pulse train conditions(3-pulse and 10-pulse).Voluntary activation was quantified by calculating both CAR and percent activation.Results:Results indicated that voluntary activation was significantly overestimated by CAR when compared with percent activation(p<0.001).Voluntary activation estimates were not affected by pulse train conditions when using percent activation;however,3-pulse stimuli resulted in greater overestimation than 10-pulse stimuli when using CAR(p=0.003).Voluntary activation did not differ between stimulators(p>0.05);however,the Digitimer evoked greater torque at rest than the Grass(p<0.001).Conclusion:These results indicate that percent activation derived from the interpolated twitch technique provides superior estimates of voluntary activation than CAR derived from burst superimposition and is less affected by pulse train conditions or stimulators in individuals with ACLR.