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Background: The pathogenesis of patellar tendon fibrosis caused by overuse remains unclear. In an effort to further investigate effective treatments for patellar tendon fibrosis attributed to overuse, it is necessary to construct a reliable animal model. Purpose: A rabbit patellar tendon fibrosis model was developed with the use of electrical stimulation to induce jumping. The pathogenesis and development of patellar tendon fibrosis were subsequently investigated with this model. Study Design: Controlled laboratory study. Methods: A total of 32 New Zealand White rabbits were randomly divided into a jumping group and a control group. Rabbits in the control group did not receive any treatment, while those in the jumping group jumped 150 times daily, 5 days per week. At 2, 4, 6, and 8 weeks after the initiation of treatment, the patellar tendons of 4 rabbits from each group were harvested and subjected to hematoxylin and eosin staining, immunohistochemical staining, and real-time polymerase chain reaction. The influence of jumping training on the expressions of histology- and fibrosis-related factors in the patellar tendon was assessed. Results: The histological changes of patellar tendon fibrosis in the jumping group were most pronounced at 4 weeks. When compared with the control group at corresponding time points, the mRNA and protein expressions of TGF-β1, CTGF, COL-I, and COL-III were upregulated significantly in the patellar tendon after jumping training for 4 weeks (P <.05). Intragroup comparison at different time points indicated that the mRNA and protein expressions of TGF-β1, COL-I, and COL-III were the highest at 4 weeks in the jumping group (P <.01). Conclusion: It was found that patellar tendon fibrosis occurred because of overuse and the peak changes occurred at 4 weeks. Jumping load increased the secretions of TGF-β1 and Smad3 in the patellar tendon, with CTGF upregulation and higher synthesis of COL-I and COL-III, which were considered the pathogenesis of fibrosis. Clinical Relevance: This study simulated the effects of jumping load on tendon fibrosis at different time points. Moreover, the time course relationship between jumping training and patellar tendon fibrosis in the rabbit model was determined, which provided a new animal model for the study of patellar tendon fibrosis. [ABSTRACT FROM AUTHOR]

Background: A patellar tendon injury is a common injury in sports. The optimal time to start training after an acute, proximal patellar enthesis injury is still unclear. Hypothesis: The time to start training after an acute, proximal patellar enthesis injury significantly affects healing of the patellar tendon 4 weeks after the injury. Study Design: Controlled laboratory study. Methods: The left hindlimbs of 35 mature female rabbits were randomly assigned to 5 injury groups including a 4-week natural healing group (NH4W) and 4 training groups that started low-intensity training at 24 hours (POST24), 48 hours (POST48), 72 hours (POST72), and 96 hours (POST96) after an acute patellar tendon injury, with 7 limbs in each group. The right hindlimbs of the NH4W group were used as a control group (CON). An acute, proximal patellar enthesis injury was created in all injury groups. The training groups underwent low-intensity quadriceps training for 2 hours per day and 3 days per week for 4 weeks. Histological and radiographic data were collected and analyzed. Results: The cell densities of the training groups were significantly lower than those of the NH4W and CON groups (P = .01). The fibrocartilage zone was significantly thicker in the POST24, POST48, and POST72 groups compared with the CON and NH4W groups and was the thickest in the POST24 group (P = .01). The bone surface to bone volume ratio was significantly higher in all the injury groups compared with the CON group and in the POST24 group compared with the other groups (P = .01). Trabecular thickness was significantly lower in all the injury groups compared with the CON group and in the POST24 group compared with the other groups (P = .01). Conclusion: Resting without training in the first 96 hours after an acute patellar tendon enthesis injury resulted in the best recovery of cell density in the tendon enthesis 4 weeks after the injury. Starting training 96 hours after the injury resulted in the best recovery of fibrocartilage zone thickness. Starting training 48 to 96 hours after the injury resulted in the best healing of the bone component of the attachment site 4 weeks after the injury. The optimal time to start training may be longer than 96 hours after an acute patellar tendon enthesis injury for the best overall healing of the tendon enthesis 4 weeks after the injury. Clinical Relevance: A rest of a minimal 72 hours may be needed for the best healing of a patellar tendon enthesis after an acute injury. Future studies are needed to determine the optimal time to start training after an acute patellar tendon injury. [ABSTRACT FROM AUTHOR]