Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/3991
Title: The effect of therapeutic ultrasound on tendon healing and sensory nerve regeneration after achilles tendon rupture
Authors: Yeung, Chi-keung
Subjects: Hong Kong Polytechnic University -- Dissertations
Achilles tendon -- Wounds and injuries -- Treatment
Ultrasonics in surgery
Sensory receptors -- Regeneration
Issue Date: 2007
Publisher: The Hong Kong Polytechnic University
Abstract: Objectives Though ultrasound therapy has been reported effective in promoting healing of Achilles tendon rupture in a number of animal studies, the underlying mechanisms of its effect are still not well understood. Recent immunochemical studies on the injured rat's Achilles tendon showed in-growth of different types of sensory nerve fibers at the early stage of healing, suggesting the importance of the role of intact sensory function in tendon repair. Ultrasound is a form of mechanical energy that is transmitted through and into biological tissues as an acoustic wave. Thus it is important to relate the mechanical basis of ultrasound to the sensitivity of the tendon to mechanical stimuli through its sensory nerve fibers. Up to now there have been no reports addressing this relationship. Therefore, the purpose of this study was to investigate the role of the sensory nerve in tendon healing and its response to ultrasound stimulation in enhancing tendon healing. Methods A series of animal studies were carried out on totally 128 rats. The outcomes of tendon healing were assessed biomechanically (80 rats) and histologically (24 rats). The in-growth of sensory fibers was evaluated by immunohistochemical analysis (24 rats). The tendon injury model was the right medial Achilles tendon hemi-tenotomy. Pulsed ultrasound (PUS) was used for ultrasonic therapy (1 MHz, 2.5W/cm², duty cycle 20%, 5 minutes, 3 times per week). Animals with tendon injury were then randomly assigned equally into 4 groups: two neural intact groups received treatment of either sham PUS (control group) or true PUS (PUS group) to the injured area; the rats in the other 2 groups received an additional ipsilateral sciatic neurectomy (SN) and then the injured tendons were treated either by sham PUS (SN-control group) or true PUS (SN-PUS group). The animals were sacrificed at 2 or 4 weeks postinjury and bilateral Achilles tendons were harvested for biomechanical and histological analysis or immunohistochemical analysis.
Results: Two-way Analysis of Variance (ANOVA) on the biomechanical testing data showed that the PUS group had significantly higher normalized UTS and stiffness than the control group (p<0.01) in animals with intact nerve supply. However, in animals with sciatic neurectomy, no significant difference was found in normalized UTS and stiffness between the SN-PUS and SN-control groups (p>0.05). It was also demonstrated that neurectomy retarded the recovery of stiffness of the injured tendon, since there was no significant difference in normalized stiffness value between 4 weeks and 2 weeks (p>0.05) in the animals with sciatic neurectomy. Besides, the UTS of the injured leg in SN-contol group was significantly lower than that of the control group at 4 weeks postinjury. Histological analysis showed that in animals with intact neural supply, the collagen matrix was denser and the alignment of collagen fiber bundles more regular in the PUS group. It was found that the scar in the PUS-treated group was more mature, as demonstrated by the lowered fusiform fibroblasts to tenocytes ratio and the significantly higher collagen matrix area when compared to the controls. However, in animals with sciatic neurectomy, the injured tendon was healed by scar tissue with inferior properties revealed by high cellularity, a lower portion of collagen matrix, and a higher fusiform fibroblast to mature tenocytes ratio throughout the 4 weeks. There was no significant difference in the morphological appearance of the healing area between the SN-PUS and SN-control groups. Immunohistochemical analysis on tendons with intact neural supply revealed a significantly higher invasion of CGRP positive nerve fibers in the PUS group at 2 weeks postinjury, while this difference was not found in the 2 groups with sciatic neurectomy. In the two groups with sham PUS treatment (control and SN-control), the amount of invasion of CGRP positive fibers in injured tendons was significantly lower in the SN-control group. These results suggest a possible interaction between CGRP positive sensory nerve fibers and PUS in promoting tendon healing. Conclusion: Knowledge of the effects of therapeutic ultrasound on innervated and dennervated tendon models could help us to understand the possible mechanism of ultrasound-enhanced tendon healing. Results of this study suggested that PUS can improve tendon healing only when there is an intact nerve supply. Denervation impacted the tendon healing. This study suggests the importance of the involvement of neurological components in ultrasound-enhanced tendon healing and the vital role of tendon innervation.
Description: xix, 215 leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577P RS 2007 Yeung
Rights: All rights reserved.
Type: Thesis
URI: http://hdl.handle.net/10397/3991
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