Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee

S. M. Ling, R. A. Conwit, Laura Talbot, M. Shermack, J. E. Wood, E. M. Dredge, M. J. Weeks, D. R. Abernethy, E. Metter

Research output: Contribution to journalArticle

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Abstract

Objective: To assess characteristics of active motor units (MUs) during volitional vastus medialis (VM) activation in adults with symptomatic knee osteoarthritis (OA) across the spectrum of radiographic severity and age-comparable healthy control volunteers. Methods: We evaluated 39 participants (age 65 ± 3 years) in whom weight-bearing knee X-rays were assigned a Kellgren & Lawrence (KL) grade (18 with KL grade = 0; four each with KL grades = 1, 2 and 4; nine with grade 3). Electromyography (EMG) signals were simultaneously acquired using surface [surface EMG (S-EMG)] and intramuscular needle electrodes, and analyzed by decomposition-enhanced spike-triggered averaging to obtain estimates of size [surface-represented MU action potentials (S-MUAP) area], number [MU recruitment index (MURI)] and firing rates [MU firing rates (mFR)] of active MUs at 10%, 20%, 30% and 50% effort relative to maximum voluntary force [maximal voluntary isometric contraction (MVIC)] during isometric knee extension. Results: Knee extensor MVIC was lower in OA participants, especially at higher KL grades (P = 0.05). Taking the observed force differences into account, OA was also associated with activation of larger MUs (S-MUAP area/MVIC × %effort; P < 0.0001). In contrast, the estimated number of active units (MURI/MVIC × %effort) changed differently as effort increased from 10% to 50% and was higher with advanced OA (KL = 3, 4) than controls (P = 0.0002). Conclusion: VM activation changes at the level of the MU with symptomatic knee OA, and this change is influenced by radiographic severity. Poor muscle quality may explain the pattern observed with higher KL grades, but alternative factors (e.g., nerve or joint injury, physical inactivity or muscle composition changes) should be examined in early OA.

Original languageEnglish (US)
Pages (from-to)1134-1140
Number of pages7
JournalOsteoarthritis and Cartilage
Volume15
Issue number10
DOIs
StatePublished - Oct 1 2007
Externally publishedYes

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Isometric Contraction
Knee Osteoarthritis
Physiology
Osteoarthritis
Knee
Quadriceps Muscle
Electromyography
Action Potentials
Neurophysiological Recruitment
Chemical activation
Muscles
Weight-Bearing
Muscle
Bearings (structural)
Needles
Healthy Volunteers
Electrodes
Joints
X-Rays
Wounds and Injuries

All Science Journal Classification (ASJC) codes

  • Rheumatology
  • Orthopedics and Sports Medicine
  • Biomedical Engineering

Cite this

Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee. / Ling, S. M.; Conwit, R. A.; Talbot, Laura; Shermack, M.; Wood, J. E.; Dredge, E. M.; Weeks, M. J.; Abernethy, D. R.; Metter, E.

In: Osteoarthritis and Cartilage, Vol. 15, No. 10, 01.10.2007, p. 1134-1140.

Research output: Contribution to journalArticle

Ling, S. M. ; Conwit, R. A. ; Talbot, Laura ; Shermack, M. ; Wood, J. E. ; Dredge, E. M. ; Weeks, M. J. ; Abernethy, D. R. ; Metter, E. / Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee. In: Osteoarthritis and Cartilage. 2007 ; Vol. 15, No. 10. pp. 1134-1140.
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abstract = "Objective: To assess characteristics of active motor units (MUs) during volitional vastus medialis (VM) activation in adults with symptomatic knee osteoarthritis (OA) across the spectrum of radiographic severity and age-comparable healthy control volunteers. Methods: We evaluated 39 participants (age 65 ± 3 years) in whom weight-bearing knee X-rays were assigned a Kellgren & Lawrence (KL) grade (18 with KL grade = 0; four each with KL grades = 1, 2 and 4; nine with grade 3). Electromyography (EMG) signals were simultaneously acquired using surface [surface EMG (S-EMG)] and intramuscular needle electrodes, and analyzed by decomposition-enhanced spike-triggered averaging to obtain estimates of size [surface-represented MU action potentials (S-MUAP) area], number [MU recruitment index (MURI)] and firing rates [MU firing rates (mFR)] of active MUs at 10{\%}, 20{\%}, 30{\%} and 50{\%} effort relative to maximum voluntary force [maximal voluntary isometric contraction (MVIC)] during isometric knee extension. Results: Knee extensor MVIC was lower in OA participants, especially at higher KL grades (P = 0.05). Taking the observed force differences into account, OA was also associated with activation of larger MUs (S-MUAP area/MVIC × {\%}effort; P < 0.0001). In contrast, the estimated number of active units (MURI/MVIC × {\%}effort) changed differently as effort increased from 10{\%} to 50{\%} and was higher with advanced OA (KL = 3, 4) than controls (P = 0.0002). Conclusion: VM activation changes at the level of the MU with symptomatic knee OA, and this change is influenced by radiographic severity. Poor muscle quality may explain the pattern observed with higher KL grades, but alternative factors (e.g., nerve or joint injury, physical inactivity or muscle composition changes) should be examined in early OA.",
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T1 - Electromyographic patterns suggest changes in motor unit physiology associated with early osteoarthritis of the knee

AU - Ling, S. M.

AU - Conwit, R. A.

AU - Talbot, Laura

AU - Shermack, M.

AU - Wood, J. E.

AU - Dredge, E. M.

AU - Weeks, M. J.

AU - Abernethy, D. R.

AU - Metter, E.

PY - 2007/10/1

Y1 - 2007/10/1

N2 - Objective: To assess characteristics of active motor units (MUs) during volitional vastus medialis (VM) activation in adults with symptomatic knee osteoarthritis (OA) across the spectrum of radiographic severity and age-comparable healthy control volunteers. Methods: We evaluated 39 participants (age 65 ± 3 years) in whom weight-bearing knee X-rays were assigned a Kellgren & Lawrence (KL) grade (18 with KL grade = 0; four each with KL grades = 1, 2 and 4; nine with grade 3). Electromyography (EMG) signals were simultaneously acquired using surface [surface EMG (S-EMG)] and intramuscular needle electrodes, and analyzed by decomposition-enhanced spike-triggered averaging to obtain estimates of size [surface-represented MU action potentials (S-MUAP) area], number [MU recruitment index (MURI)] and firing rates [MU firing rates (mFR)] of active MUs at 10%, 20%, 30% and 50% effort relative to maximum voluntary force [maximal voluntary isometric contraction (MVIC)] during isometric knee extension. Results: Knee extensor MVIC was lower in OA participants, especially at higher KL grades (P = 0.05). Taking the observed force differences into account, OA was also associated with activation of larger MUs (S-MUAP area/MVIC × %effort; P < 0.0001). In contrast, the estimated number of active units (MURI/MVIC × %effort) changed differently as effort increased from 10% to 50% and was higher with advanced OA (KL = 3, 4) than controls (P = 0.0002). Conclusion: VM activation changes at the level of the MU with symptomatic knee OA, and this change is influenced by radiographic severity. Poor muscle quality may explain the pattern observed with higher KL grades, but alternative factors (e.g., nerve or joint injury, physical inactivity or muscle composition changes) should be examined in early OA.

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