Quadriceps neural alterations in anterior cruciate ligament reconstructed patients: A 6-month longitudinal investigation.
Lepley AS, Gribble PA, Thomas AC, Tevald MA, Sohn DH, and Pietrosimone BG. Scand J Med Sci Sports. 2015; [Epub Ahead of Print]
Take Home Message: Patients who sustained an anterior cruciate ligament tear often suffer quadriceps weakness, altered spinal-reflexive excitability during the first few weeks after the injury, and altered corticospinal excitability a few months after the injury.
Quadriceps muscle strength deficits are common following an anterior cruciate ligament (ACL) injury and reconstruction. This deficit may be partly due to neural inhibition and has implications with regards to return to activity and long-term joint health. Treating neural inhibition is often overlooked in rehabilitation because we need a better understanding about if and when these issues arise after an ACL reconstruction. Therefore, Lepley and colleagues completed a longitudinal, case-control study to assess changes in quadriceps spinal-reflexive and corticospinal excitability, quadriceps strength, and voluntary activation following ACL injury and reconstruction. Twenty patients who sustained an ACL tear and were scheduled for surgery participated in this study along with 20 matched control participants (matched based on age, height, mass, and activity level). The authors evaluated both groups at three time points, which corresponded to before surgery, 2 weeks post-surgery, and 6 months post-surgery. Both limbs in the ACL group were compared with a matched limb from a control participant. The authors collected self-reported function (IKDC scores), maximal voluntary isometric contraction, voluntary activation (central activation ratio), spinal reflex excitability (normalized Hoffmann spinal reflexes), and corticospinal excitability (active motor threshold, and normalized motor-evoked potential amplitudes) of the vastus medialis muscle at every time points. Participants in the ACL group demonstrated lower self-reported function, more quadriceps weakness, and less voluntary activation than control participants. The injured leg had a lower spinal reflex excitability before surgery and 2 weeks after surgery compared with the healthy controls. The contralateral limb in the ACL group also had lower spinal reflex excitability 2 weeks after surgery but both limbs were similar to controls by 6 months. Furthermore, ACL participants had altered corticospinal excitability compared with control participants but this was only detected at 6-months post-surgery.
The data presented in this study may be beneficial in helping clinicians better address quadriceps weakness, prior to and following surgery. The authors observed deficits in spinal-reflexive excitability during the first few weeks after an injury and surgery, which then improved. In contrast, diminished corticospinal excitability was only observed six months after surgery. These neural alterations were present when the ACL group also had clinical impairments in quadriceps strength and activation. This may indicate that the acute injury, which is associated with pain and swelling, may affect the spinal reflex and may eventually affect the other limb. As the pain and swelling decreases the spinal reflex improves but new issues arise higher up in the central nervous system (specifically, in the brain). If clinicians could address these deficits then patients could regain normal quadriceps muscle function and thus more normative joint biomechanics. The authors note that future research should assess modalities believed to target these neural pathways. For example, transcutaneous electrical stimulation and cryotherapy may be helpful in the early phase of rehabilitation to increase spinal-reflex excitability. Furthermore, muscle activation biofeedback may be helpful in the later rehabilitation stages (1 to 6 months post surgery) when we are concerned about corticospinal excitability. While more research will be needed it would be low risk for clinicians to try using more cryotherapy and transcutaneous electrical stimulation in the first few weeks after an injury and more biofeedback in the later stages. Hopefully, these therapies along with emerging therapies will help us address these neural issues and help our patients return to full function.
Questions for discussion: How much focus do you have on spinal-reflexive excitability training in the early stages of your ACL rehabilitation? What techniques have you found to be particular effective in addressing this issue?
Written by: Kyle Harris
Reviewed by: Jeffrey Driban
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