Date of Award

December 2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Kinesiology

First Advisor

Jennifer E Earl-Boehm

Committee Members

Kyle T Ebersole, Wendy E Huddleston, Marie K Hoeger Bement

Keywords

anterior knee pain, Central sensitization, EMG, Patellofemoral pain, quadriceps, quantitative sensory testing

Abstract

Context: Females with patellofemoral pain (PFP) are at higher risk, have higher rates, and experience worse long-term outcomes than males. Structural and functional changes have been observed in pain networks and neuromuscular systems in individuals with PFP. Central sensitization describes dysfunctional pain modulation which could lead to altered neuromuscular control. Evidence examining relationships between central sensitization and muscle function in PFP is lacking.

Objective: The purpose of this study is to determine whether females with PFP exhibit signs of central sensitization compared to pain-free females. Then, after grouping each individual based on her quantitative sensory test results into a centrally sensitized (CS) and non-centrally sensitized (NS) groups, we will determine whether quadriceps muscle function is altered during a static task, and whether quadriceps muscle function and knee kinematics are altered during a functional task. Participants: Thirty-three total females participated. For the first aim, a PFP and pain-free healthy control (CON) group were compared. For the second and third studies, the PFP group was further divided based on their quantitative sensory test (QST) results into the CS and NS groups and the CON group was maintained. Main Outcome Measures: QST measures included local and remote pressure pain thresholds (PPTs), conditioned pain modulation (CPM), and temporal summation of pain (TSP). Surface electromyography (EMG) was used to collect the time of vastus medials (VM) and vastus lateralis (VL) onset activation in response to an auditory stimulus (SRT) and peak activation response to a stimulus (PRT) during a maximal voluntary isometric contraction and stair descent tasks. Inertial measurement unit motion analysis was also used to collect peak knee flexion and peak knee abduction angles during stair descent. Results: Females with PFP exhibited impaired CPM and facilitated TSP relative to the CON group. No differences in PPTs at local or remote sites were observed. Once grouped by central sensitization status, no differences in VM and VL SRT or PRT were observed between- or within- groups during the static task. During the functional task, PRT for both muscles was later in the CS group compared to the CON group (p<0.001), but no differences in SRT or knee kinematics were observed between groups. Conclusions: Females with PFP exhibit enhanced pain facilitation with impaired pain inhibition compared to pain-free females. Quadriceps muscle function was not altered during a static task. Peak VM and VL activation during stair descent occurred later in the CS group compared to the CON group. Peak activation occurred just prior to maximum knee flexion and later than maximum knee abduction in the CS group, indicating the potential for reduced control during stair descent. However, similar activation onset times, and knee flexion and abduction angles were observed regardless of group. Altered muscle function may occur in females with centrally-sensitized PFP during a functional, weight-bearing task without changes in peak knee angles. Muscle function is not altered between groups during static non-weight-bearing task when grouped by central sensitization. Pain facilitation and pain inhibition mechanisms can be restored, but current treatment models and practice guidelines do not account for central sensitization. Clinicians should consider assessing signs of central sensitization during clinical examination of females with PFP.

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