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

• Published in: Scandinavian journal of medicine & science in sports Vol. 29; no. 5; pp. 716 - 724
• Main Authors: Bodkin, Stephan G., Norte, Grant E., Hart, Joseph M.
• Format: Journal Article
• Language: English
• Published: Denmark Blackwell Publishing Ltd 01.05.2019
• Subjects: Acupuncture; anterior cruciate ligament; arthrogenic muscle inhibition; Knee; muscle function; patient acceptable symptom state; return to play; arthrogenic muscle inhibition; anterior cruciate ligament; patient acceptable symptom state; muscle function; return to play
• ISSN: 0905-7188; 1600-0838
• DOI: 10.1111/sms.13394

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%.