H-Reflex Plasticity Following Cast Immobilization of Distal Radius Fractures
PURPOSE: The primary purpose of the study was to track changes in the Hoffman (H-) reflex after a period of cast immobilization following a distal radius fracture (DRF) up to 12-weeks post-fracture. Secondary to tracking the H-reflex, functional measures such as muscle thickness, grip strength, wrist flexion strength, range of motion, pain and function were assessed over the same time frame. METHODS: The study consisted of a fracture group (n = 5) and an age-matched uninjured control (CON) group (n = 5). Both groups were tracked over a 12-week period, with the fracture group undergoing four testing sessions (baseline, week 6, week 9 and week 12) and the CON undergoing three testing sessions at least three weeks apart; baseline testing for the fracture group was collected within two weeks of initial fracture date. Testing was completed on both limbs for the CON group, whereas for the fracture group measures were taken at each time point for the non-fractured (NFX) limb, and within the limits of tolerable pain for the fractured (FX) limb. This meant the fracture group’s FX limb H-reflex measures were completed only at week 9 and 12. Peak-to-peak amplitudes (and stimulus intensities) of H-reflex, Hmax, and maximal M-wave, Mmax, were the key parameters collected. Hmax was normalized and expressed as a ratio of Mmax (Hmax:Mmax). Additionally, the fracture group completed questionnaires to measure FX limb pain and disability (via patient-rated wrist evaluation [PRWE]) at each time point. RESULTS: The fracture group presented a significant effect of time for Hmax:Mmax stimulus intensity (p < 0.05), where the relative current intensity needed to evoke Hmax increased before decreasing as recovery progressed. The CON group demonstrated no significant effects over time or between limbs for all H-reflex parameters (p = 0.859). Functionally, the fracture group demonstrated significant changes over time for all secondary measures (p<0.05), aside from visual analog scale pain scores. With functional measures increasing over time to indicate recovery (i.e. increases in grip strength). CONCLUSIONS: The amplitude of H-reflex did not demonstrate significant changes over time as predicted. The fracture group’s decrease over time for Hmax:Mmax stimulus intensity reflects an unanticipated finding of increased excitability of Hmax. For the control group, this study verifies the stability of Hmax and Mmax over time and between limbs in this population. The fracture group’s functional measures show significant improvements over the 12-week span that were coupled with an initial increase and then decrease in the relative stimulus intensity needed to evoke H reflex, in the absence of detectable changes in H-reflex amplitude. The changes in the nervous system can have a profound impact on function after wrist fracture and cast immobilization. The novel findings in this study can have implications regarding the direction of future studies. As the H-reflex has been shown to have a degree of plasticity, with further study the reflex may be tracked in different interventions such as unilateral training in order to evaluate efficacy or investigate mechanisms of change/recovery.
Kinesiology, neuromuscular physiology
Master of Science (M.Sc.)