Author: Lam, Wai-ling
Title: Effect of acoustic pressure waves on callus innervation and fracture healing
Degree: M.Phil.
Year: 2006
Subject: Hong Kong Polytechnic University -- Dissertations
Fractures -- Treatment
Extracorporeal shock wave therapy
Department: Department of Rehabilitation Sciences
Pages: xxiv, 360 p. : ill. ; 30 cm
Language: English
Abstract: Fracture healing is a highly complex regenerative process which includes the action of many different cell types. Low Intensity Pulsed Ultrasound (LIPU) has been shown an effective modality for enhancing fracture healing but the mechanism of which is still not well understood. Innervation in bone has been found to play an important role in fracture healing. It has been demonstrated that sensory nerve fibers were found to be reduced or absent in nonunions. LIPU transfers mechanical energy into tissues. This study was to test the hypothesis that sensory nerves in bone may play a role in sensing and responding to the mechanical stimulation provided by LIPU, and in turn, promotes fracture healing. A diaphyseal transverse fracture was created on the right tibia in 120 matured female Sprague-Dawley rats (weight 261.44+-18.38g, at 12 weeks of age) in this study. They were assigned randomly into 4 groups: the sham LIPU neural intact group, the LIPU neural intact group, the sham LIPU neurectomy group and the LIPU neurectomy group. For animals in the LIPU treated groups, LIPU was given daily at the fracture site starting on the 2nd day after the fracture was created. Sham exposure was introduced to those animals in the sham LIPU treated groups. Resection of the sciatic nerve of the fractured limb was performed on the animals in the neurectomy groups. In order to facilitate similar immobilization as that caused by sciatic neurectomy, patella tenotomy was employed on animals in the neural intact groups. Rats were sacrificed for tissue morphometrical analyses and biomechanical testing on days 7, 14 and 21 post-fracture, according to the groups to which they belonged. Two-way ANOVA was used for statistical comparisons among the four groups (a=0.05). Results on the callus index evaluated from X-rays demonstrated that there was a significant main effect of innervation (p<0.01) on callus size where larger callus was found in the groups with neurectomy. Results on union rates obtained from X-rays and those obtained during pin removal before mechanical testing (palpation) showed a higher union rate in the two neural intact groups, with the highest union rate in the LIPU treated neural intact group (73% from X-ray and 89% from palpation before mechanical testing). Meanwhile, the union rate was comparable between the two groups with nerve resection. Results on total bone mineral density (BMD) indicated a significant interaction (p<0.05) between the two factors (innervation and LIPU). Results on the Bonferroni multiple comparison test suggested that the introduction of LIPU could significantly increase the total BMD in the fractured callus (p<0.05) in the neural intact limbs. However, such an increase in total BMD, caused by the introduction of LIPU, was not found in the limbs with sciatic neurectomy. Results on morphological studies indicated that groups with intact nerves healed better and faster than those without, and that a more matured callus was found in the LIPU-treated group when compared with the sham treated group in the groups with intact nerves. The rate of maturation was similar in the two groups with nerve resection. The results of the present study confirm the accelerating effect of LIPU on fracture healing. Denervation could delay the healing of a fracture by developing a larger yet immature callus (as observed from results on union rate and morphological studies). The results also demonstrated that with the resection of sciatic nerve, the promoting effect of LIPU on fracture healing could greatly be reduced. This implies the importance of the callus innervation in sensing and responding to the mechanical stimulus generated by LIPU on fracture healing.
Rights: All rights reserved
Access: open access

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