Ultrastructural studies of collagen fibril populations in regenerating rat tendon
Collagen fibril diameter distributions were measured in the regenerating Extensor Digitorum Longus tendon of adult rats subsequent to surgically created lesions. Three lesions were performed: 1) Complete Tenotomy: This consisted of the transection of the tendon without surgical repair the proximal stump being left to retract. Regeneration periods of 10, 30, 60, 120, and 240 days were investigated. 2) Partial Tenotomy: A full thickness defect was removed from the central third of the tendon (lesion area) over a distance of approximately 4mm leaving two tendon strips (lateral strips) on either side of the lesion. Regeneration periods of 10, 30, 60, 120, and 240 days were investigated. 3) Sequential Tenotomy: A full thickness defect was removed from the middle half of the tendon (primary lesion area) over a distance of approximately 4mm. After 30 days the major portion of the lateral strips was removed to create the secondary lesion area. Regeneration periods of 40, 60, 120, and 240 days were studied. Collagen fibril populations within the lesion areas of each tenotomy were unimodal in diameter distribution throughout this investigation with fibril diameters 100nm. Mean and mass average diameters were found to significantly increase between 10 and 240 days postoperatively within lesion areas of complete and partial tenotomy, values from the partial tenotomy being significantly greater than those from complete. These differences were attributed to the higher levels of stress to which the tendon was exposed after partial tenotomy. Mean and mass average fibril diameters within the primary lesion area of the sequential tenotomy were found to decrease between 40 and 60 days postoperatively, these values increasing thereafter. These changes in diameter were not significant overall. The range of the distribution was found to exceed those from either complete and partial tenotomy at 240 days. Mean and mass average diameters were found to be significantly smaller than those from the partial tenotomy, no significant difference being found from the complete tenotomy. No significant difference was found between secondary lesion area and complete tenotomy in either mean or mass average diameters. The increase in frequency of small diameter fibrils observed in the primary lesion area of sequential tenotomy was thought to reflect the increased tensile stress to which this area was exposed 30 days postoperatively. Fibril mean and mass average diameters within the lateral strips of the partial tenotomy were found to decrease between 30 and 60 days after which time they increased. Lateral strips of sequential tenotomy showed a further increase in frequency of small diameter fibrils up to 60 days. The range of diameters in both areas was found to exceed that of controls in the later part of the study, however at 240 days postoperatively the range of diameters within the lateral strips of the sequential tenotomy exceeded that of the partial tenotomy. The observed increase in frequency of small diameter fibrils within the lateral strips was thought to represent the production of a new population of fibrils in response to increased tensile stress postoperatively. The further increase observed after sequential tenotomy was thought to be a separate response to the further increase in stress produced 30 days postoperatively Immunogold labelling for types 1 and III collagen was attempted using partially tenotomised specimens. Although type III collagen was identified as the predominant form 10 days postoperatively, type I collagen being the major type identified by 240 days, the results of this work were considered unreliable due to high levels of label which were present intracellulariy.