Impact of antagonistic muscle co-contraction on in vivo knee contact forces.
Adam Trepczynski, Ines Kutzner, Verena Schwachmeyer and 3 others
PMID 30409163WHAT IT FOUND
In 9 knee replacement patients, model changes linked to antagonist co-contraction increased predicted peak knee force by up to 1.70 bodyweight during stairs.
Static alignment did not explain the wide variation, and muscle activation patterns changed the predicted force.
Key findings
01Peak tibio-femoral contact forces varied substantially across the nine patients, and linear regression did not imply strong relationships with tibial implant angles or the mechanical axis angle.
02When the constrained model was compared with the sum-of-squared-muscle-stresses model, predicted tibio-femoral force increased by up to 1.70 ± 0.14 bodyweight and decreased by up to 0.63 ± 0.10 bodyweight.
03Force increases were mainly due to greater quadriceps and gastrocnemii co-contraction by up to 1.45 ± 0.31 bodyweight, while force reductions were mainly achieved by less quadriceps and hamstring co-contraction by up to 0.59 ± 0.05 bodyweight.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only nine patients with instrumented total knee replacements were studied, and the paper says this small cohort cannot represent all habitual and cultural variations of human locomotion. The model was constrained to match measured knee force, but the paper says there is no guarantee that the identified muscle activation pattern is the pattern actually used by a patient. EMG validation was available for only six of the nine patients. The study measured and modelled knee contact force and muscle activation agreement; it did not test a treatment or report symptom outcomes. Static alignment showed weak relationships with peak force in this small sample, so it does not establish that alignment is irrelevant to joint disease.
Declared interests
The study was funded by Deutsche Forschungsgemeinschaft and Bundesministerium für Bildung und Forschung. The supplied text does not report a separate author conflict-of-interest statement beyond this funding list.
The easy way to misread this
Do not read the modelled increase in knee contact force as proof that reducing co-contraction will improve symptoms or prevent joint failure. This was a small model-based study of nine knee replacement patients, and it measured force patterns rather than patient outcomes or treatment response.