Background: Severe traumatic knee injury, including injury to the anterior cruciate ligament (ACL), leads to impaired sensorimotor function. Although improvements are achieved by training, impairment often persists. Because good sensorimotor function is associated with better patient-reported function and a potential lower risk of future joint problems, more effective treatment is warranted. Temporary cutaneous anesthesia of adjacent body parts was successfully used on the hand and foot to improve sensorimotor function. The aim of this study was to test whether this principle of brain plasticity could be used on the knee. The hypothesis was that temporary anesthesia of the skin area above and below the knee would improve sensorimotor function of the ipsilateral knee and leg in subjects with ACL injury.
Methods: In this double-blind exploratory study, 39 subjects with ACL injury (mean age 24 years, SD 5.2, 49% women, mean 52 weeks after injury or reconstruction) and self-reported functional limitations and lack of trust in the knee were randomized to temporary local cutaneous application of anesthetic (EMLA®) (n = 20) or placebo cream (n = 19). Fifty grams of EMLA®, or placebo, was applied on the leg 10 cm above and 10 cm below the center of patella, leaving the area around the knee without cream. Measures of sensory function (perception of touch, vibration sense, knee kinesthesia) and motor function (knee muscle strength, hop test) were assessed before and after 90 minutes of treatment with EMLA® or placebo. The paired t-test was used for comparisons within groups and analysis of variance between groups, except for ordinal data where the Wilcoxon signed rank test, or Mann-Whitney test, was used. The number of subjects needed was determined by an a priori sample size calculation.
Results: No statistically significant or clinically relevant differences were seen over time (before vs. after) in the measures of sensory or motor functions in the EMLA® group or in the placebo group. There were no differences between the groups due to treatment effect (EMLA® vs. placebo).
Conclusions: Temporary cutaneous anesthesia of adjacent body parts had no effect in improving sensorimotor function of the knee and leg in subjects with severe traumatic knee ligament injury.