Structural changes in the lengthened rabbit muscle

Positive effect of IGF-1 injection on gastrocnemius of rat during distraction osteogenesis

Distraction osteogenesis (DO) is used to form new bone between bone segments to lengthen the callus. Skeletal muscles frequently fail to adapt to distraction, which causes complications. Insulin-like growth factor-1 (IGF-1) has been implicated as a central regulator of muscle repair. We hypothesized that IGF-1 injection could reduce muscle complications in DO. A total of 102 Sprague-Dawley rats received DO or did not were randomly assigned into saline, IGF-1 and normal groups. On the day before the distraction, the rats in the IGF-1 group were injected with IGF-1. The gastrocnemius muscles of the rats were harvested at the 0, 1st, 4th, 7th, and 10th days of distraction. The weight of the muscles, cross-sectional area (CSA) of the muscle fibers, collagen volume fraction (CVF), maximum limit load (MLL), maximum contraction forces, and gene expression of Akt, MyoD, myogenin, myostatin, and collagen I were analyzed. The results indicated that IGF-1 injection had increased the weights, CSA of the muscle fibers, MLL and force generation of the gastrocnemius. Also, Akt, MyoD, and myogenin were upregulated, and myostatin was downregulated in the IGF-1 group. Injection of IGF-1 could attenuate the gastrocnemius atrophy, prevent fibrosis, increase MLL, and regulate the related mRNA.

Muscle metabolism during tibial lengthening with regular and high distraction rates

INTRODUCTION

Muscle regeneration is promoted when the Ilizarov method is used for limb lengthening and deformity correction, but the regenerative ability of muscles decreases when achieving large amounts of elongation. Much research has been dedicated to studying the capabilities of muscles under lengthening, but no reports are available that investigate the muscle metabolism. We supposed that energy turnover would be activated in skeletal muscles under lengthening as a response to distraction, and the activity of the energy turnover would grow in proportion to the increase in the distraction rate or amount.

MATERIALS AND METHODS

We compared the metabolism of canine anterior tibial muscles (ATMs) by regular and 3-mm high-frequency bone distraction in 30 dogs to obtain 14.5 ± 0.8% lengthening from the initial tibial length. Group 1 (n = 12) had manual lengthening with a rate of 1 mm per day. Three millimeters per day was produced with 120 increments in automated mode in group 2 (n = 12). An intact group (n = 6) served as controls. ATMs were harvested at the end of distraction, after 30 days of fixation, and 30 days after frame removal. We assessed the activity of lactate dehydrogenase, creatine phosphokinase, glucoso-6-phosphate dehydrogenase, and catalase and calculated the concentration of malone dialdehyde, sarcoplasmic and contractile proteins in the ATM extract.

RESULTS

Energy turnover reactions were activated in the ATM as a response to distraction forces, but the activity of the energy turnover did not grow proportionally to the increased distraction rate. Levels of sarcoplasmic and contractile proteins in the ATM decreased insignificantly in both groups.

CONCLUSIONS

High-frequency 3-mm daily lengthening results in compensatory energy turnover changes in the muscle, sufficient for prevention of catabolic processes.