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]

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 (
), 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

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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Altered Lower Extremity Biomechanics Following an ACL Injury and Surgery May Increase the Risk of Reinjury

Lepley, A., Gribble, P., Thomas, A., Tevald, M., Sohn, D., & Pietrosimone, B. (2015). Quadriceps neural alterations in anterior cruciate ligament reconstructed patients: A 6-month longitudinal investigation Scandinavian Journal of Medicine & Science in Sports DOI: 10.1111/sms.12435