TRANSCUTANEOUS ELECTRICAL NERVE STIMULATION’S EFFECT ON QUADRICEPS ARTHROGENIC MUSCLE INHIBITION: A SYSTEMATIC REVIEW
Background Arthrogenic muscle inhibition (AMI) is a multifactorial condition which results in the inability to fully voluntarily activate musculature surrounding an affected joint, in absence of a structural lesion to the muscle or innervating nerve. Despite the frequent presence of AMI following knee joint injury, the current evidence-base regarding treatments to directly address AMI is limited. Transcutaneous electrical nerve stimulation (TENS) is a promising disinhibitory intervention that warrants further investigation concerning its effectiveness in counteracting the detrimental influences of quadriceps AMI. Objectives The primary aim of this systematic review was to critically analyse and evaluate the current evidence-base relating to the effectiveness of TENS as a disinhibitory intervention to improve neuromuscular function of the quadriceps in pathological knee joints. Search strategy A comprehensive search of online databases including CINAHL, Medline, Embase, Scopus, Cochrane Library, and SPORTDiscus, was conducted using pre-determined keywords to identify relevant publications in April 2018. Eligibility criteria All relevant studies identified using the search strategy that investigated the use of TENS as a disinhibitory modality for quadriceps AMI and that satisfied the strict pre-determined inclusion and exclusion criteria were accepted. Data collection and analysis Risk of bias and methodological quality of included studies were assessed using the 11- point Physiotherapy Evidence Database Scale and were scored as excellent, good, fair, or poor quality. Main results Five studies, graded as either good or poor quality, satisfied the eligibility criteria for this systematic review. Three outcome measures were used to quantify changes in AMI following intervention. Three included studies evaluated the disinhibitory effects of TENS within a single treatment session with the patient at rest, while the other two included studies observed the effects of TENS in conjunction with exercise through multiple treatment sessions over a multi-week intervention period. All three studies examining the effects of TENS within a single treatment session observed significant improvements in voluntary quadriceps activation or excitability, but not for quadriceps strength. Significant improvements were observed in voluntary quadriceps activation and strength for participants with tibiofemoral osteoarthritis exercising with TENS. However, only large effect sizes were found for participants with acute anterior cruciate ligament injuries exercising with TENS and no significant improvements were observed between groups. Conclusions Based on the results from the systematic review, good quality evidence indicates TENS is effective as a disinhibitory intervention for quadriceps AMI immediately upon application, and when used as an adjunct therapy to therapeutic exercise for short-term benefits in voluntary quadriceps activation and strength. Greater clinical effects may be observed in participants with chronic knee pathologies who demonstrate persistent quadriceps weakness compared to severe acute knee injuries. Further research is required to determine the precise neural pathways by which the disinhibitory mechanisms of TENS operates, as well as optimal TENS dosage to produce the greatest clinical effects.