Background & Aims

Patellofemoral pain (PFP) is a musculoskeletal condition often associated with altered movement patterns and considered a biomechanical pathology. However, recent evidence shows motor cortex reorganization in these patients resembling other chronic musculoskeletal pain conditions. Despite these findings, little is known about how PFP impacts cortical motor activity.

The motor-related cortical potential (MRCP) is a negative deflection measured via electroencephalography (EEG), reflecting activity in cortical regions associated with movement planning and execution for real and imagined movements.

We hypothesized that, consistent with prior literature, movement execution (ME) of a modified single leg squat will create a more negative deflection than movement imagination (MI) and MI on the painful side will show a smaller deflection than the non-painful side, representing greater overall activity in the motor cortex during ME and deficits reported in motor imagery related to pain.

Methods

Three participants with chronic unilateral PFP performed a modified single leg squat task while EEG was collected. The non-squatting foot was placed on an eight-inch block to offload weight while the participant squatted to approximately 55 degrees of knee flexion. Participants performed 10 repetitions of ME followed by 10 repetitions of MI of the same task in response to a visual cue. Up to 60 repetitions were performed on each side. During a control condition, participants were shown the same cues but were asked not to perform or imagine the squat.

Data from channel Cz (vertex) was filtered, decomposed with ICA to remove artifacts from eye movements, re-referenced to the common average, and separated into epochs for each trial. Epochs were aggregated into bins based on side and task type (ME versus MI). Average waveforms were calculated for each participant and each condition. The difference between each condition and the control condition was used for analysis.

Results

All participants generated a MRCP related to ME bilaterally. Two participants generated a MRCP related to MI on at least the painful side. Amplitude of the MRCP for each side and condition was quantified by averaging the amplitude between 650 and 750 ms after the visual cue, based on reaction times for a similar task in the same patient population.

The MRCP amplitude for ME was -5.76 mA and -7.20 mA for the uninvolved and involved sides, respectively. The MRCP amplitude for MI was -0.02 and -1.61 for the uninvolved and involved sides, respectively.

Paired T tests compared amplitude of the MRCP generated during ME versus MI within side. Effect sizes were calculated using Cohen’s D, showing a very large effect of task type on amplitude. (Involved: T = -3.22, d = 2.75; uninvolved = T = -2.56, d = 2.87) Amplitude differences between ME and MI of the painful and nonpainful sides showed a medium and large effect size, respectively. (ME: T = -1.13, d = 0.66; MI: T = -1.34, d =0.88).

Conclusions

Consistent with previous studies and supporting our first hypothesis, the amplitude of the MRCP generated by ME was greater than the signal generated by MI for both the painful and nonpainful side. This result allows us to be confident our paradigm measures the process we expect to observe.

Our second hypothesis, that MRCPs of the painful side during MI would display reduced amplitude relative to the nonpainful side, was not supported. In fact, we observed the opposite: the amplitude of the MRCP generated by MI was greater on the painful side than on the nonpainful side. This increase in motor cortex activity may represent an increase in the effort of MI on the painful side relative to the nonpainful side. However, side-based amplitude differences observed during ME were much smaller than would be expected if squat task difficulty varied by side.

Further data collection and analysis is under way to determine how MRCP onset is impacted by PFP and if effects vary between ME and MI

References

Breckenridge, J. D., Mcauley, J. H., & Ginn, K. A. (2020). Motor Imagery Performance and Tactile Spatial Acuity?: Are They Altered in People with Frozen Shoulder??

Ferrari, D., Valdir, R., Oliveira, D. De, & Ferraz, M. (2018). Gait & Posture Higher pain level and lower functional capacity are associated with the number of altered kinematics in women with patellofemoral pain. Gait & Posture, 60(January 2017), 268–272. https://doi.org/10.1016/j.gaitpost.2017.07.034

Hallett, M. (1994). Movement-related cortical potentials.

Hassan, G., Rahimi, A., & Kajbafvala, M. (2019). Journal of Bodywork & Movement Therapies Electromyographic activity of the hip and knee muscles during functional tasks in males with and without patellofemoral pain. Journal of Bodywork & Movement Therapies, 23(1), 54–58. https://doi.org/10.1016/j.jbmt.2018.11.001

Holden, S., Straszek, C. L., Rathleff, M. S., Petersen, K. K., Roos, E. M., & Graven-Nielsen, T. (2018). Young females with long-standing patellofemoral pain display impaired conditioned pain modulation, increased temporal summation of pain, and widespread hyperalgesia. Pain, 159(12), 2530–2537. https://doi.org/10.1097/j.pain.0000000000001356

Jahanshahi, M., Jenkins, I. H., Brown, R., Marsden, C. D., Passingham, R. E., & Brooks, D. J. (1995). Self-initiated versus externally triggered movements. Brain, 118, 913–933.

Jankelowitz, S. K., & Colebatch, J. G. (2002). Movement-related potentials associated with self-paced, cued and imagined arm movements. Experimental Brain Research, 147(1), 98–107. https://doi.org/10.1007/s00221-002-1220-8

Lankhorst, N. E., Middelkoop, M. Van, Crossley, K. M., Oei, E. H. G., Vicenzino, B., & Collins, N. J. (2016). Factors that predict a poor outcome 5 – 8 years after the diagnosis of patellofemoral pain?: a multicentre observational analysis. 881–886. https://doi.org/10.1136/bjsports-2015-094664

Smith, B. E., Selfe, J., Thacker, D., Hendrick, P., Bateman, M., Moffatt, F., Rathleff, M. S., Smith, T. O., & Logan, P. (2018). Incidence and prevalence of patellofemoral pain?: A systematic review and meta-analysis. 1–18.

Sullivan, G. M., & Feinn, R. (2012). Using Effect Size—or Why the P Value Is Not Enough . Journal of Graduate Medical Education, 4(3), 279–282. https://doi.org/10.4300/jgme-d-12-00156.1

Te, M., Baptista, A. F., Chipchase, L. S., & Schabrun, S. M. (2017). Primary Motor Cortex Organization Is Altered in Persistent Patellofemoral Pain. 2224–2234. https://doi.org/10.1093/pm/pnx036

Presenting Author

Sarah Margerison

Poster Authors

Sarah Margerison

MS, DPT

University of Maryland, Baltimore

Lead Author

E-mail

Topics

  • Pain Imaging