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The knee joint is the most complicated joint in the body. It consists of three articulations– two tibiofemoral and one patellofemoral. As is characteristic of synovial joints, the knee joint has a thin articular capsule that partially surrounds this joint cavity. Additionally, several ligaments, muscles, and cartilaginous structures support the movement of the knee.
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Plasticity is the property where an object loses its elasticity and undergoes irreversible deformation, even after the deformation forces are eliminated. If a material deforms irreversibly without increasing stress or load, then this is called ideal plasticity. For example, when a force is applied to an aluminum rod, it changes its shape, but it does not return to its original shape once the force is removed. Plastic deformation or ductility is thus a permanent deformation or change in the...
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Water-reducers, or plasticizers, are chemical admixtures used in concrete to improve strength and workability. These additives reduce the water-cement ratio without compromising workability, lower the cement content while maintaining the same workability, or increase workability to assist concrete placement in inaccessible areas.
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It is essential to understand how structural members behave under plastic deformation when the bending stress exceeds the material's yield strength. This state of deformation permanently alters the shape of the member, in contrast to the linear elastic behavior observed before yielding. The strain at any point in the member is expressed in terms of maximum strain. Notably, the neutral axis, which coincides with the centroid during elastic bending, shifts away from the centroid under plastic...
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In vivo Measurement of Knee Extensor Muscle Function in Mice
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Knee Extensors Muscle Plasticity Over a 5-Years Rehabilitation Process After Open Knee Surgery.

Martin Flück1, Claudio Viecelli1, Andreas M Bapst1

  • 1Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.

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|October 20, 2018
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Summary

Anterior cruciate ligament (ACL) rupture causes lasting muscle loss, worsened by surgery. However, years of physical activity can reverse these metabolic and mechanical changes in knee extensor muscles.

Keywords:
fiber typefocal adhesion kinaseloadingmitochondriasurgery

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Area of Science:

  • Muscle physiology
  • Orthopedics
  • Sports medicine

Background:

  • Anterior cruciate ligament (ACL) rupture leads to chronic knee instability and functional deficits.
  • Muscle atrophy and altered metabolic function are consequences of ACL deficiency and reconstructive surgery.
  • Long-term effects of ACL injury and treatment on muscle quality are not fully understood.

Purpose of the Study:

  • To investigate molecular and cellular changes in knee extensor muscles following ACL reconstruction.
  • To assess the impact of surgery, physiotherapy, and rehabilitation on muscle metabolism and mechanics.
  • To determine if muscle composition and function can recover years after ACL injury.

Main Methods:

  • Biopsies of the vastus lateralis muscle were taken from 9 patients at multiple time points post-ACL reconstruction (weeks 0, 9, 26, 260).
  • Analyses included muscle fiber cross-sectional area (CSA), capillary-to-fiber ratio, fiber type distribution, and mitochondrial density.
  • Molecular markers of mitochondrial respiration and focal adhesion kinase (FAK) phosphorylation were assessed.

Main Results:

  • Operated leg showed reduced quadriceps CSA, muscle fiber CSA, and capillary-to-fiber ratio compared to the contralateral leg.
  • Slow-type muscle fibers and mitochondrial volume density were significantly reduced in the operated leg post-surgery and early rehabilitation.
  • Muscle composition largely recovered by week 260, indicating reversibility of fiber type transformation.
  • FAK phosphorylation, a marker of mechanoregulation, increased post-rehabilitation but overall FAK levels decreased, correlating with mitochondrial content.

Conclusions:

  • ACL rupture causes persistent metabolic and mechanical deficits in knee extensor muscles, potentially exacerbated by post-operative immobilization.
  • Rehabilitation and long-term voluntary physical activity can lead to substantial recovery of muscle structure and function.
  • Slow-to-fast muscle fiber transformation is reversible in humans following ACL injury and treatment.