The Effect of Rate of Distraction Osteogenesis on Structure and Function of Anterior Digastric Muscle Fibers

Effects of hyperbaric oxygen therapy on biochemical and histological parameters of muscle groups in proximity to the distracted rat tibia

We investigated the effect of hyperbaric oxygen therapy (HBOT) on rat muscles during tibial distraction osteogenesis (DO) at normal and hyperdistraction rates. Animals in groups 1 and 2 were distracted by 0.5 mm/day and those in groups 3 and 4 by 1 mm/day. Groups 2 and 4 received HBOT during distraction. Group 5 served as control. Superoxide dismutase (SOD; U/g protein), malondialdehyde (nmol/g protein), glutathione (mmol/g protein), and protein levels (g/dl) were determined. SOD was significantly higher in group 2 (4.59 ± 0.97) than in controls (2.19 ± 0.7) (P = 0.0001), and lower in group 4 (3.74 ± 1.70) than in group 2 (P=0.011). Malondialdehyde was significantly higher in group 2 (0.72 ± 0.23) than in controls (0.38 ± 0.10) (P=0.005). Total protein levels were better preserved with HBOT in distracted muscles: group 2 (3.24 ± 0.37) vs. group 1 (1.88 ± 0.60), and group 4 (3.45 ± 0.70) vs. group 3 (2.03 ± 0.75) (both P=0.0001). Numbers of fibres were lower in group 1 (4.88 ± 0.59) than in group 2 (6.07 ± 0.86), and in group 3 (5.13 ± 0.36) than in group 4 (6.14 ± 0.74) (both P=0.001). Numbers of nuclei were higher in group 1 (11.29 ± 2.47) than in group 2 (9.03 ± 1.53) (P=0.04), and in group 3 (12.43 ± 3.32) than in group 4 (9.08 ± 1.58) (P=0.001). Fibres and nuclei with HBOT were similar to those of controls. HBOT decreased the inflammatory cell infiltrate for group 1 (19.8 ± 8.54) vs. group 2 (4.2 ± 2.53) and group 3 (36.54 ± 11.29) vs. group 4 (21.5 ± 9.23) (both P=0.001). HBOT improves the adaptation of distracted muscle by increasing fibres and antioxidants while decreasing inflammation.

Skeletal and soft tissue response to automated, continuous, curvilinear distraction osteogenesis

PURPOSE

To document the bone formation and soft tissue changes in response to automated, continuous, curvilinear distraction osteogenesis (DO) at rates greater than 1 mm/day in a minipig model.

MATERIALS AND METHODS

Two groups of Yucatan minipigs underwent automated, continuous, curvilinear DO of the right mandible: group A, 1.5 mm/day (n = 5); and group B, 3.0 mm/day (n = 5). Each minipig underwent 12 mm of distraction followed by 24 days of fixation. The distracted and contralateral mandibles were harvested at the end of fixation. The percentage of surface area (PSA) of the regenerate occupied by bone, fibrous tissue, cartilage, and hematoma was determined using computerized histomorphometric analysis. The control groups consisted of DO wounds distracted discontinuously at 1 mm/day and the nonoperated contralateral mandible. The ipsilateral and contralateral digastric muscles were harvested and stained for proliferating cell nuclear antigen (PCNA), myogenic differentiation-1 (MyoD), and paired Box 7 protein (PAX7).

RESULTS

All 10 minipigs completed the distraction and fixation period. The PSA occupied by bone was similar for groups A (PSA 64.36% ± 5.87%) and B (PSA 63.83% ± 3.37%) and the control group (1 mm/day; PSA 64.89% ± 0.56%) but was less than that on the nonoperated side (PSA 84.67% ± 0.86%). The PSA occupied by cartilage and hematoma in all groups was minimal (<1.1%). The digastric muscles had no abnormal tissue or inflammation, and PAX7, MyoD, and PCNA expression had returned to the baseline levels.

CONCLUSIONS

The results of the present study indicate that bone formation in response to automated, continuous, and curvilinear DO at a rate of 1.5 and 3.0 mm/day is nearly identical to that with discontinuous DO at 1 mm/day. In addition, no deleterious effects were found on the digastric muscles.

Serial histologic and immunohistochemical changes in anterior digastric myocytes in response to distraction osteogenesis

PURPOSE

To document histologic and immunohistochemical changes in the anterior digastric muscle during distraction osteogenesis (DO).

MATERIALS AND METHODS

Nineteen Yucatan minipigs with mixed dentition were used for these experiments. Group A (n = 16) underwent unilateral mandibular distraction at a rate of 1 mm/day (no latency) for 12 days. Animals were killed at mid-DO (n = 5), end-DO (n = 5), mid-fixation (n = 4), and end-fixation (n = 2). Group B (n = 2) underwent acute 12-mm advancement, and group C (n = 1) dissection and osteotomy. Animals from groups B and C were killed at the end-DO time point. Digastric muscles from treatment and contralateral sides of all animals were harvested and embedded in paraffin. Specimens were stained with hematoxylin/eosin or immunohistochemically for proliferating cell nuclear antigen (PCNA; total cell proliferation), paired Box-7 gene protein (Pax7; satellite cells), or myogenic differentiation 1 protein (MyoD; differentiating myoblasts). Descriptive and bivariate statistics were computed to compare groups (P ≤ .05 statistically significant).

RESULTS

All animals survived the operation and observation period; there were no device failures. Two animals (1 at mid-DO, 1 at mid-fixation) were eliminated from the study because of postoperative infection. There was minimal digastric inflammation, fibrosis, and muscle fiber size variability during active DO. Immunohistochemical analysis showed statistically significant increases in PCNA (cellular proliferation), Pax7 (satellite cells), and MyoD (differentiating myoblasts) positive nuclei in digastrics at mid-DO and end-DO.

CONCLUSIONS

Results of this study indicate that there are minimal pathologic changes but significant increases in PCNA, Pax7, and MyoD positive nuclei during active distraction. This supports the hypothesis that the digastric muscle response to DO consists of proliferation and hypertrophy.

The adaptive response of jaw muscles to varying functional demands

Jaw muscles are versatile entities that are able to adapt their anatomical characteristics, such as size, cross-sectional area, and fibre properties, to altered functional demands. The dynamic nature of muscle fibres allows them to change their phenotype to optimize the required contractile function while minimizing energy use. Changes in these anatomical parameters are associated with changes in neuromuscular activity as the pattern of muscle activation by the central nervous system plays an important role in the modulation of muscle properties. This review summarizes the adaptive response of jaw muscles to various stimuli or perturbations in the orofacial system and addresses general changes in muscles as they adapt, specific adaptive changes in jaw muscles under various physiologic and pathologic conditions, and their adaptive response to non-surgical and surgical therapeutic interventions. Although the jaw muscles are used concertedly in the masticatory system, their adaptive changes are not always uniform and vary with the nature, intensity, and duration of the stimulus. In general, stretch, increases neuromuscular activity, and resistance training result in hypertrophy, elicits increases in mitochondrial content and cross-sectional area of the fibres, and may change the fibre-type composition of the muscle towards a larger percentage of slow-type fibres. In contrast, changes in the opposite direction occur when neuromuscular activity is reduced, the muscle is immobilized in a shortened position, or paralysed. The broad range of stimuli that affect the properties of jaw muscles might help explain the large variability in the anatomical and physiological characteristics found among individuals, muscles, and muscle portions.

Recommendations for optimal distraction protocols for various animal models on the basis of a systematic review of the literature

The principles of orthopaedic distraction osteogenesis (DO) have been successfully applied to the craniofacial skeleton, but the latency time, rate and rhythm of distraction, and length of the consolidation period that are optimal for long-bone distraction may be suboptimal for craniofacial DO. The aim of this study was to provide recommendations for optimal distraction parameters in animal experimental research on craniofacial DO. The data used were from studies, added to the PubMed database between 1 January 1973 and 1 January 2007, on the outcome of DO resulting from variations in a single distraction parameter while standardizing the other distraction parameters. Although experimental animal group sizes were rather small, especially in those studies that used large animals, and both skeletally mature and immature animals were used, the (in most cases quantitative) data provided useful information on the optimal parameters in craniofacial DO. A latency period may not be necessary at all. Distraction should be performed at a rate of 1mm/day (this may be halved when small animals such as rats are used) preferably with a continuous rhythm, followed by a consolidation period of 6-8 weeks. These recommendations can be used as basic guidelines for further animal experimental studies on craniofacial DO.

Morphological and Immunohistochemical Changes in Muscle Tissue in Association With Mandibular Distraction Osteogenesis

PURPOSE

Studies of changes in the surrounding soft tissue in association with distraction osteogenesis in the maxillofacial region, where various different kinds of tissue are tightly packed, are rare. In this study, we performed morphological and immunohistochemical investigations of muscle tissue during mandibular distraction osteogenesis.

MATERIALS AND METHODS

Japanese white rabbits were divided into 2 groups. In 1 group, the mandibular bone was distracted at a rate of 1 mm/day (DO group), whereas in the other group it was advanced by 10 mm all at once (O group). The cross-section of the anterior belly of the digastric muscle was examined using hematoxylin and eosin, periodic acid-Schiff (PAS), and proliferating cell nuclear antigen (PCNA) staining methods, as well as scanning electronmicroscopy (SEM).

RESULTS

In the DO group, the cross-section of muscle bundle revealed no remarkable changes. In PAS staining, type II fibers gradually disappeared with distraction, but eventually reappeared after a period of consolidation. In the SEM photographs, striation-like laminated structures were evident in the control and the 3-mm distraction, ambiguous in the 6-mm distraction, and not evident in the 10-mm distraction. In contrast, the structure appeared to be restored in the consolidation for 1 week thereafter. In the PCNA immunostaining, the numbers of PCNA-positive nuclei increased during periods of distraction, but subsequently tended to decrease gradually.

CONCLUSIONS

Although minute injuries were induced in muscle fibers in association with distraction osteogenesis, it is suggested that muscle fibers regenerate starting in the distraction period and thus can adapt to the environment.

Neuromuscular recovery after distraction osteogenesis at different frequencies in a rabbit model

The muscle and nerve responses to stresses applied during distraction osteogenesis have not been clearly defined. This study hypothesized that distraction resulting in 30% lengthening decreases muscle force generation of the lengthened muscle and increasing the frequency of distraction attenuates the decrease of force generation accompanying lengthening. This study investigated the effects of different distraction frequencies on neuromuscular recovery in a rabbit model. Animals were assigned into group 1 (low-frequency distraction) and group 2 (high-frequency distraction). Distraction was continued until a 30% increase in the original tibial length was achieved. After consolidation of the osteotomy, knee and ankle range of motion, muscle force generation, and neuromuscular junction parameters were evaluated. Lengthening of 30% resulted in significantly decreased range of motion compared with the control leg (P < 0.05). Lengthening of 30% also substantially decreased force generation of the peroneus longus muscle. However, force generation of the peroneus longus muscle in the high-frequency group was 70.5% +/- 6.5% of the control side, significantly higher than that in the low-frequency distraction group (49.7% +/- 4.8% of the control side, P < 0.05). There was no statistical difference between the 2 groups in neuromuscular junction morphology, although an abnormal shape of the postsynaptic neuromuscular junction was observed after distraction. The use of a high-frequency distraction technique during limb lengthening may result in a reduction in impairment of knee and ankle range of motion and improved muscle function compared with that observed with the use of low-frequency distraction. Repeated microtrauma to the soft tissues associated with high-frequency distraction may facilitate the regenerative capacity of the soft tissues and result in an improved outcome of muscle and nerve function.