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Research Papers

BTX-A Administration to the Target Muscle Affects Forces of All Muscles Within an Intact Compartment and Epimuscular Myofascial Force Transmission

[+] Author and Article Information
Can A. Yucesoy1

 Biomedical Engineering Institute, Boğaziçi University, Istanbul, 34684 Turkeycan.yucesoy@boun.edu.tr

Önder Emre Arıkan, Filiz Ateş

 Biomedical Engineering Institute, Boğaziçi University, Istanbul, 34684 Turkey

1

Corresponding author.

J Biomech Eng 134(11), 111002 (Oct 26, 2012) (9 pages) doi:10.1115/1.4007823 History: Received January 11, 2012; Revised September 13, 2012; Posted October 10, 2012; Published October 26, 2012; Online October 26, 2012

Measurement of forces of mono- and bi-articular muscles of an entire intact muscle compartment can allow for a comprehensive assessment of the effects of Botulinum toxin type A (BTX-A) both at and beyond the injection site, and in conditions close to those in vivo. The goal was to test the hypotheses that BTX-A affects (1) the forces of not only the injected but also the noninjected muscles of the compartment, and (2) epimuscular myofascial force transmission (EMFT). Two groups of Wistar rats were tested: Control (no BTX-A injected) and BTX (0.1 units of BTX-A were injected exclusively to the mid-belly of TA). Isometric forces were measured simultaneously at the distal tendons of the tibialis anterior (TA) at different lengths, the restrained extensor digitorum longus (EDL) and the extensor hallucis longus (EHL) muscles and at the proximal tendon of EDL. Five days post-injection, BTX-A did affect the total forces of all muscles significantly: (1) The TA force decreased differentially (by 46.6%–55.9%) for most lengths such that a significant negative correlation was found between force reductions and increased muscle length. The maximum TA force decreased by 47.3%. However, the muscle’s length range of force production did not change significantly. (2) Distal and proximal EDL forces decreased (on average by 67.8% and 62.9%, respectively). (3) The EHL force also decreased (on average by 9.2%). The passive forces of only the TA showed a significant increase at higher lengths. EMFT effects were shown for the control group: (1) at the shortest TA lengths, the EDL proximo-distal force differences were in favor of the distal force, which was reversed at higher lengths. (2) the EHL force measured at the shortest TA length decreased (by 34%) as a function of TA lengthening. After BTX-A exposure, such EMFT effects disappeared for the EDL, whereas they remained as profound for the EHL. Exposure to BTX-A does affect forces of all muscles operating in an intact compartment. For the BTX-A injected muscle, the reduction in muscle force becomes less pronounced at higher muscle lengths. BTX-A also has effects on EMFT, however, these effects are not uniform within the anterior crural compartment. Decreased forces of the noninjected synergistic muscles suggest the presence of unintended additional effects of BTX-A both for the targeted distal joint and for the nontargeted proximal joint.

FIGURES IN THIS ARTICLE
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Copyright © 2012 by American Society of Mechanical Engineers
Topics: Force , Muscle
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Figures

Grahic Jump Location
Figure 1

The experimental setup. (a) Distal tendons of the tibialis anterior muscle (TA) and the extensor hallucis longus muscle (EHL) as well as the proximal and the tied distal tendons of the EDL muscle (EDL proximal and EDL distal, respectively) were each connected to a separate force transducer (FT). Throughout the experiment, the EDL and EHL muscles were kept at constant muscle-tendon complex lengths (Δlmt  = 0). Exclusively, the TA muscle was lengthened (Δlmt TA ) to progressively increasing lengths, at which isometric contractions were performed. Lengthening (indicated by double arrow) started from muscle active slack length at 1 mm increments by changing the position of the TA force transducer. (b) Experimental condition for joint angles: knee angle = 120 deg and the ankle is at maximal plantar flexion. The femur and the foot were fixed by metal clamps and the distal end of the sciatic nerve was placed on a bipolar silver electrode.

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Figure 2

Typical examples of force time traces measured at tendons of muscles of the anterior crural compartment. Superimposed traces recorded at 5 of the 13 total TA muscle lengths studied (a) the TA force, (b) the distal EDL force, (c) the proximal EDL force, and (d) the EHL force.

Grahic Jump Location
Figure 3

The effects BTX injection to TA muscle on its isometric muscle force-length characteristics. Absolute total and passive isometric forces are shown as mean values ± SD for the control group and the BTX injected group of animals. The TA muscle-tendon complex length is expressed as a deviation (Δlmt TA ) from the active slack length of BTX injected group. Significant differences between the TA force of the BTX injected group and the control group (Bonferoni post hoc test) are indicated by * (total force) and by † (passive force).

Grahic Jump Location
Figure 4

The effects of BTX injection to TA muscle on the EDL forces as a function of increasing TA muscle length. (a) Absolute total and passive forces exerted at the distal EDL tendon. (b) Absolute total and passive forces exerted at the proximal EDL tendon. (c) Normalized proximo-distal EDL total force differences. The EDL forces measured from the control group and the BTX injected group of animals, plotted as a function of TA length, are shown as mean values ± SD. The TA muscle-tendon complex length is expressed as a deviation (Δlmt TA ) from the active slack length of the BTX injected group. Forces in (c) are normalized with respect to the EDL peak total distal force of the corresponding animal group (i.e., 1.27 ± 0.22 N and 0.44 ± 0.48 N, respectively for the control and the BTX injected group). Note that a positive force difference indicates that a net epimuscular myofascial load is exerted on the EDL in the proximal direction and a negative force difference indicates a distally directed net epimuscular myofascial load.

Grahic Jump Location
Figure 5

The effects of BTX injection to TA muscle on the EHL forces as a function of increasing TA muscle length. Absolute total as well as passive forces exerted at the distal tendon of the EHL muscle measured from the control group and the BTX injected group of animals are shown as mean values ± SD. The TA muscle-tendon complex length is expressed as a deviation (Δlmt TA ) from the active slack length of BTX injected group.

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