"Taking action" to reduce pain-Has interpretation of the motor adaptation to pain been too simplistic?

Movement-evoked pain is not associated with pain at rest or physical function in knee osteoarthritis

INTRODUCTION

Knee Osteoarthritis (KOA) is mainly characterized by pain. The assessment of KOA-related pain frequently focuses on different constructs subject to sources of bias or drawbacks, as the classical Pain at Rest (PAR). Movement-evoked pain (MEP), recently defined as 'pain during walking', emerges as a differential concept, since PAR and MEP are driven by different underlying mechanisms. Given the novelty of the MEP approach, its association with PAR or with different performance-based tests has not been studied in KOA yet.

MATERIALS AND METHODS

A cross sectional study was conducted. PAR was measured, alongside the performance of four mobility tests and their corresponding MEP: Timed Up and Go Test, 10-metre Walk Test, 2-Minute Walk Test, and 6-Minute Walk Test. Association and agreement were explored for MEP versus PAR, while the correlation of the tests versus each corresponding MEP-measure was assessed.

RESULTS

Neither association nor agreement were found in the duality MEP versus PAR. Also, the lack of association between the performance of a mobility test and the perceived level of pain during the development of the test was stated.

CONCLUSION

Movement-evoked pain is neither related to pain at rest nor to functional performance in subjects affected by knee osteoarthritis. The results from our study suggest that MEP and pain at rest measure and refer to different constructs in knee osteoarthritis. The implementation of MEP as an outcome in exercise-therapy could enhance the tracking of results, as well as the development of tailored interventions under different conditions.

SIGNIFICANCE

This research elucidates the relevance of MEP, recently defined as 'pain during walking', through the analysis of its association with PAR and with functional performance (measured through four mobility tests) in knee osteoarthritis. The results from our study highlight the absence of either association or agreement between MEP and PAR, fact that supports and endorses the idea that both concepts measure and refer to different constructs in knee osteoarthritis.

Moving in pain - A preliminary study evaluating the immediate effects of experimental knee pain on locomotor biomechanics

Pain changes how we move, but it is often confounded by other factors due to disease or injury. Experimental pain offers an opportunity to isolate the independent effect of pain on movement. We used cutaneous electrical stimulation to induce experimental knee pain during locomotion to study the short-term motor adaptions to pain. While other models of experimental pain have been used in locomotion, they lack the ability to modulate pain in real-time. Twelve healthy adults completed the single data collection session where they experienced six pain intensity conditions (0.5, 1, 2, 3, 4, 5 out of 10) and two pain delivery modes (tonic and phasic). Electrodes were placed over the lateral infrapatellar fat pad and medial tibial condyle to deliver the 10 Hz pure sinusoid via a constant current electrical stimulator. Pain intensity was calibrated prior to each walking bout based on the target intensity and was recorded using an 11-point numerical rating scale. Knee joint angles and moments were recorded over the walking bouts and summarized in waveform and discrete outcomes to be compared with baseline walking. Knee joint angles changed during the swing phase of gait, with higher pain intensities resulting in greater knee flexion angles. Minimal changes in joint moments were observed but there was a consistent pattern of decreasing joint stiffness with increasing pain intensity. Habituation was limited across the 30-90 second walking bouts and the electrical current needed to deliver the target pain intensities showed a positive linear relationship. Experimental knee pain shows subtle biomechanical changes and favourable habituation patterns over short walking bouts. Further exploration of this model is needed in real-world walking conditions and over longer timeframes to quantify motor adaptations.

Evaluating peripheral neuromuscular function with brief movement-evoked pain

Movement-evoked pain is an understudied manifestation of musculoskeletal conditions that contributes to disability, yet little is known about how the neuromuscular system responds to movement-evoked pain. The present study examined whether movement-evoked pain impacts force production, electromyographic (EMG) muscle activity, and the rate of force development (RFD) during submaximal muscle contractions. Fifteen healthy adults (9 males; age = 30.3 ± 10.2 yr, range = 22-59 yr) performed submaximal isometric first finger abduction contractions without pain (baseline) and with movement-evoked pain induced by laser stimulation to the dorsum of the hand. Normalized force (% maximal voluntary contraction) and RFD decreased by 11% (P < 0.001) and 15% (P = 0.003), respectively, with movement-evoked pain, without any change in normalized peak EMG (P = 0.77). Early contractile RFD, force impulse, and corresponding EMG amplitude computed within time segments of 50, 100, 150, and 200 ms relative to the onset of movement were also unaffected by movement-evoked pain (P > 0.05). Our results demonstrate that movement-evoked pain impairs peak characteristics and not early measures of submaximal force production and RFD, without affecting EMG activity (peak and early). Possible explanations for the stability in EMG with reduced force include antagonist coactivation and a reorganization of motoneuronal activation strategy, which is discussed here.NEW & NOTEWORTHY We provide neurophysiological evidence to indicate that peak force and rate of force development are reduced by movement-evoked pain despite a lack of change in EMG and early rapid force development in the first dorsal interosseous muscle. Additional evidence suggests that these findings may coexist with a reorganization in motoneuronal activation strategy.

Effect of movement-evoked and tonic experimental pain on muscle force production

INTRODUCTION

When performing an exercise or a functional test, pain that is evoked by movement or muscle contraction could be a stronger stimulus for changing how individuals move compared to tonic pain. We investigated whether the decrease in muscle force production is larger when experimentally-induced knee pain is directly associated to the torque produced (movement-evoked) compared to a constant painful stimulation (tonic).

METHODS

Twenty-one participants performed three isometric knee extension maximal voluntary contractions without pain (baseline), during pain, and after pain. Knee pain was induced using sinusoidal electrical stimuli at 10 Hz over the infrapatellar fat pad, applied continuously or modulated proportionally to the knee extension torque. Peak torque and contraction duration were averaged across repetitions and normalized to baseline.

RESULTS

During tonic pain, participants reported lower pain intensity during the contraction than at rest (p < 0.001), whereas pain intensity increased with contraction during movement-evoked pain (p < 0.001). Knee extension torque decreased during both pain conditions (p < 0.001), but a larger reduction was observed during movement-evoked compared to tonic pain (p < 0.001). Participants produced torque for longer during tonic compared to movement-evoked pain (p = 0.005).

CONCLUSION

Our results indicate that movement-evoked pain was a more potent stimulus to reduce knee extension torque than tonic pain. The longer contraction time observed during tonic pain may be a result of a lower perceived pain intensity during muscle contraction. Overall, our results suggest different motor adaptation to tonic and movement-evoked pain and support the notion that motor adaptation to pain is a purposeful strategy to limit pain. This mechanistic evidence suggests that individuals experiencing prevalently tonic or movement-evoked pain may exhibit different motor adaptations, which may be important for exercise prescription.

What You Need to Know About Sacroiliac Dysfunction

Low back pain is the leading cause of disability worldwide, and sacroiliac dysfunction is estimated to occur in 15%-30% of those with nonspecific low back pain. Nurses are in the unique position to support and provide education to patients who may be experiencing sacroiliac dysfunction or possibly apply this knowledge to themselves, as low back pain is a significant problem experienced by nurses. A patient's clinical presentation, including pain patterns and characteristics, functional limitations, common etiologies and musculoskeletal system involvement, current diagnostic tools, and realm of treatments, are discussed along with their respective efficacy. Distinction is made between specific diagnosis and treatment of joint involvement and that of sacroiliac regional pain, as well as other factors that play a role in diagnosis and treatment for the reader's consideration.

Motor Unit Recruitment is Altered When Acute Experimental Pain is Induced at a Site Distant to the Contracting Muscle

Acute pain alters motor unit discharge properties in muscles that are painful or influence loading of painful structures. Less is known about the changes in discharge when pain is induced in distant tissues that are unable or have limited capacity to modify the load of the contracting muscle. We aimed to determine whether acute experimental pain alters quadriceps motor unit discharge when pain is induced in; (i) a muscle that is unlikely to be mechanically influenced by modified quadriceps activity (tibialis anterior: TA), or (ii) the antagonist muscle (biceps femoris: BF). Using a within-subject design, 16 adults performed force-matched isometric knee extension during pain-free control conditions, and trials after painful hypertonic saline injections into TA or BF. Surface and intramuscular electromyography recordings were made. Despite maintained force, discharge rate of quadriceps motor units was lower during Pain than Control conditions for TA and BF trials (both P < 0.001). Redistribution of motor unit activity was observed; some units were recruited in control or pain but not both. As modified quadriceps motor unit discharge has limited/no potential to modify load in the painful tissue to protect the painful part, the findings might support an alternative hypothesis that activity is redistributed to larger motor units.