Does altered modulation of the H-reflex is a risk factor for patellofemoral pain?

Abstract

Patellofemoral pain (PFP) is characterized by anterior knee pain, which mainly affects women and its symptoms are exacerbated by activities that increase the compressive forces in the patellofemoral joint. Currently, it is speculated that the PFP is a precursor of knee osteoarthritis, one of the most common musculoskeletal disorders in the adulthood and whose total knee replacement is a treatment option, generating high costs for health systems. In this direction, it is necessary to develop effective treatment plans for PFP, also in order to prevent the progression to knee osteoarthritis. However, for treatment effectiveness, it is necessary to act on the precursors of the disorder, which is an arduous task in the context of PFP, since its etiology is not defined. The treatment of biomechanical changes, mentioned as possible precursors of PFP does not demonstrate good prognosis in the long term, suggesting that other factors, including neurophysiological, may be involved. Our research group has pioneered in revealing that women with PFP have decreased amplitude of the Hoffmann-reflex of the vastus (VM), indicating a change in the transmission of afferent sensory information and the motor neurons of the VM in women with PFP. Then, our group has also demonstrated that the Hoffmann-reflex amplitude is inversely related to the chronicity of this disorder. Thus, two hypotheses were raised: (1) the reduction in the excitability of the Hoffmann-reflex is a precursor of PFP? Or (2) the reduction in excitability is a by-product of long term pain? However, only transversal studies were performed until now, which does not establish any cause-effect. In this sense, this project aims, in an unprecedented manner, longitudinally monitor the excitability of Hoffmann-reflex and the appearance of the first symptoms of PFP in women previously asymptomatic, in order to investigate these hypotheses and this possible relationship. For this, we will recruit women aged between 18 and 22 years without any signs or symptoms of any musculoskeletal disorder in the lower limbs. As it is a study prospective observational cohort, we will make at least three evaluations for obtaining the electrophysiological signals (Hoffmann-reflex), one per year. Among these annual evaluations, the participants will be accompanied by interviews (every 3 months) to detect the possible emergence of symptoms of PFP. In case of any knee pain, volunteers must attend the laboratory to confirm the presence of PFP and this time a new evaluation will be conducted along the same lines of predetermined annual evaluations. We will also apply the Anterior Knee Pain Scale and some clinical tests as step down test and star balance test to evaluate the physical function of the sample. In order to achieve the main objective of the project, the amplitude of the Hoffmann-reflex obtained at the initial evaluation will be compared between the PFP and control groups (those who won't develop PFP). Then these baseline Hoffmann-reflex amplitude will be assessed in a logistic regression model in order to identify if this variable is a predictor of the occurrence of PFP.