Corticospinal excitability can discriminate quadriceps strength indicative of knee function after ACL‐reconstruction

Abstract

Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements) that might pose a conflict of interest in connection with the submitted article.Purpose: To investigate relationships between quadriceps strength and neural activity, and to establish a clinical threshold of corticospinal excitability able to discriminate between patients with quadriceps strength indicative of satisfactory and unsatisfactory knee function after ACLR. Methods: A total of 29 patients following primary, unilateral ACL-reconstruction (11 female, 23.2 ± 8.1 years of age, 7.3 ± 2.5 months since surgery) participated.Subjective knee function was quantified using the International Knee Documentation Committee (IKDC) subjective evaluation. Peak isokinetic knee extensor torque was assessed at 90°/s. Quadriceps corticospinal excitability was quantified via active motor threshold (AMT, %2-Tesla) using transcranial magnetic stimulation during a 5% maximal voluntary isometric contraction of the quadriceps. Pearson's r correlations were used to assess the relationship between peak knee extensor torque and AMT. Receiver operating characteristic (ROC) curves were used to establish a threshold of (a) mass-normalized peak knee extensor torque to discriminate satisfactory knee function (IKDC ≥ 75.9%), and (b) AMT to discriminate quadriceps strength indicative of satisfactory knee function. Likelihood ratios (LR) and the magnitude of change in pre-post-test probability were calculated for each threshold. Results: Active motor threshold was negatively correlated with mass-normalized peak knee extensor torque (r = −0.503, P = 0.005). Knee extensor torque ≥1.23 Nm/ kg was an excellent discriminator of satisfactory knee function (AUC = 0.890, P = 0.002; (+)LR = 9.56). An AMT ≤50.5% was an excellent discriminator of quadriceps strength indicative of satisfactory knee function following ACLR (AUC = 0.839, P = 0.005; (+)LR = 23.75). Conclusion: Lower corticospinal excitability was associated with lower quadriceps strength. An AMT above 50.5% was found to decrease the probability of having satisfactory knee strength by over 62%. K E Y W O R D Santerior cruciate ligament, arthrogenic muscle inhibition, muscle function, patient acceptable symptom state, return to play | 717 BODKIN et al.

Athletes after anterior cruciate ligament reconstruction demonstrate asymmetric intracortical facilitation early after surgery

“…A number of studies now indicate that corticospinal excitability alterations exist in patients that have returned to sport post ACLR and these alterations are related to quadriceps strength. [9][10][11][12][13][14]17 Therefore in human and animal models. [31][32][33][34] In conclusion, athletes after ACLR demonstrated interlimb differences in ICF during the course of post-operative rehabilitation.…”

“…Additionally, no studies to date have examined the relationship between intracortical excitability and quadriceps strength. However, studies have found that less corticospinal excitability (ie, higher motor thresholds) is associated with poorer quadriceps strength in patients after ACLR 10,17 . Understanding how the balance between inhibitory and facilitatory networks change in response to rehabilitation, and the relationship between these networks and quadriceps strength is needed to improve post‐operative rehabilitation protocols and outcomes.…”

Neuromuscular Function of the Knee Joint Following Knee Injuries: Does It Ever Get Back to Normal? A Systematic Review with Meta-Analyses

“…Decreased cortical excitability means that knee-injured patients need more stimulation to yield sufficient excitation in the primary motor cortex to generate muscle activation [ 98 ]. While the clinical importance of these changes in corticospinal and spinal-reflexive pathways is not fully understood, recently it has been shown that corticospinal adaptations are correlated with muscle strength and patient-reported knee function satisfaction following ACLR [ 99 ]. It may be that the decrease in cortical excitability is a protective long-term motor cortex adaptation, while a compensatory reflex mechanism maintains required muscle function when needed i.e.…”

How Much Time Is Needed Between Serial “Return to Play” Assessments to Achieve Clinically Important Strength Gains in Patients Recovering From Anterior Cruciate Ligament Reconstruction?

“…Patients with lower quadriceps strength have been shown to demonstrate neural adaptations after ACLR. 5,28 It is unknown if these underlying neurophysiologic adaptations influence the ability to regain muscle strength during the time of return to sport after ACLR. A duration of 2 months between visits was able to acceptably discriminate patients who were able to increase their knee extensor LSI by !5.75%.…”