Te M.1, Baptista A.F.2, Chipchase L.S.1, Schabrun S.M.1
1Western Sydney University, School of Science and Health, Sydney, Australia, 2Federal University of Bahia, Biomorphology Department, Health Sciences Institute, Salvador, Brazil
Background: Patellofemoral pain (PFP) is a common musculoskeletal condition. Up to 50% of individuals diagnosed with PFP experience persistent symptoms at long-term follow up. Poor long-term outcomes may reflect a limited understanding of the pathophysiological factors that contribute to the persistence of PFP. Recent research in persistent musculoskeletal pain conditions, such as low back pain and lateral epicondylalgia, has demonstrated altered organisation of the primary motor cortex (M1), and suggests these changes contribute to persistent pain or altered motor control. As persistent pain and altered motor control is a common feature of PFP, it is possible that M1 organisation may be altered in PFP. However, this has not yet been investigated.
Purpose: This study compared the organisation of the M1 representation of three of the four quadriceps muscles in people with persistent PFP to those of healthy participants.
Methods: The M1 representations of rectus femoris, vastus lateralis and vastus medialis were mapped using single pulse transcranial magnetic stimulation in 11 individuals with persistent PFP and 11 healthy participants. Outcome measures included map volume, distance between maps, number of discrete peaks and pain intensity with a visual analogue scale.
Results: Individuals with PFP had reduced map volumes (F1, 60=22.97; p 0.001) and anterior shift in the primary motor cortex representation (F1, 60=4.73; p = 0.030) of all three quadriceps muscles compared with healthy participants. Greater overlap of the primary motor cortex representation (F1, 60=5.60; p = 0.020), and a reduction in the number of discrete cortical peaks (F1, 60=7.35; p = 0.009) of all three quadriceps muscles was also observed in PFP compared to controls. However, there was no relationship between altered primary motor cortex organisation and pain intensity in individuals with PFP.
Conclusion(s): These findings provide initial evidence of reduced corticomotor excitability (reduced map volumes) and altered M1 organisation (characterised by increased overlap in M1 representations and reduced number of discrete peaks), in individuals with PFP compared to healthy participants. These cortical changes could contribute to altered motor control of the quadriceps muscles and lead to persistent symptoms in individuals with PFP. The lack of association between cortical changes and pain intensity may be because pain is a complex phenomenon influenced by an array of biological, psychological and sociocultural factors.
Implications: These data have relevance for our understanding of the pathophysiology of PFP and also for the design of future treatments that aim to target M1 in this condition.
Funding acknowledgements: AF Baptista received a post-doc scholarship from CNPq (Brazilian Government Research Agency) to develop this study.
Topic: Musculoskeletal: lower limb
Ethics approval: This study was approved by the Western Sydney University Human Research Ethics Committee.
All authors, affiliations and abstracts have been published as submitted.
