Molecular signaling within growth plates of the radius and tibia after periosteal stripping: an experimental study in lambs

Periosteal transection and elevation is a standard treatment for angular limb deformities in foals. It is used to correct axis deviations in the limbs at an early age to assure that the foals grow up with straight limbs to improve their chances to reach their full potential as future athletes. Although clinically proven, its mechanisms of action were never elucidated on a more basic scientific level. In this experimental study the molecular response to periosteal stripping was investigated within the growth plate and adjacent perichondrium. The study was based on the hypothesis that a growth restraining feedback loop related to Indian hedgehog (Ihh), parathyroid hormone related protein (PTHrP) and parathyroid hormone receptors (PTHR) was responsible for the corrective effect of periosteal stripping. Twelve 3 months old lambs underwent periosteal stripping of the distal lateral radius and tibia on one side. The contralateral side served as non-operated controls. Two animals each group were sacrificed at 2, 6, 10, 14, 18 and 21 days after surgery and the growth plates with minimal adjacent bone tissue were harvested for histological investigations. After decalcification, paraffin-embedded sections with routine hematoxylin-eosin stains were prepared to assess morphology and length of growth plates, whereas immunohistochemistry of Ihh, PTHrP, PTHR and the two cytokines fibroblast(FGF) and transforming growth factor (TGF) was performed to study different protein expression between operated limbs and controls. The results indicate that periosteal stripping caused an up-regulation of Ihh in the early preand hypertrophic zone of the growth plate, followed by an increase of PTHrP mainly in the perichondrium, while an increase of PTHR was noticed in all zones, although highest in the perichondrium and hypertrophic zones. The growth factors FGF and TGF were upregulated in all zones, but FGF in response to periosteal stripping was more intensely expressed in the proliferative zone and the highest peak of TGF was found in the perichondrium. Length measurements of the various growth zones revealed significant negative correlations between the proliferative and pre-and hypertrophic zones, indicating that indeed a negative feed back loop after periosteal stripping exists coupled by the Ihh/PTHrP/PTHR cascade.The hypothesis that periosteal stripping had an effect on the Ihh/PTHrP/PTHR related feedback loop in epiphyseal growth was confirmed in this experimental study in lambs. Since these mechanisms are very basic and similar in most species, it can be safely assumed that the effects in foals are similar. In fact, the asymmetric mechanical load in animals suffering from axis deviation may even increase the enhancing effect of length correction.