Diabetes mellitus alters the mechanical properties of the native tendon in an experimental rat model

The purpose of this study was to determine the effect of the diabetic phenotype on the mechanical properties of the native patellar tendon and its enthesis. Diabetes was induced via intraperitoneal injection of streptozotocin in Lewis rats. Control (n= 18) and diabetic animals (n= 20) were killed at 12 and 19 days for analysis. Statistical comparisons were performed using Student's t-tests and a two-tailed Fisher test with significance set at p < 0.05. Pre- and post-injection intraperitoneal glucose tolerance tests demonstrated significant impairment of glycemic control in the diabetic compared to control animals (p = 0.001). Mean serum hemoglobin A1c levels at 19 days was 10.6 ± 2.7% and 6.0 ± 1.0% for the diabetic and control groups, respectively (p = 0.0001). Fifteen of sixteen diabetic animals demonstrated intrasubstance failure of the patellar tendon, while only 7 of 14 control specimens failed within the tendon substance. The Young's modulus of the diabetic tendon was significantly lower than control specimens by 19 days post-induction (161 ± 10 N m^-2 compared to 200 ± 46 N m^-2, respectively) (p = 0.02). The metabolic condition of poorly controlled diabetes negatively affects the mechanical properties of the native patellar tendon. These altered structural properties may predispose diabetic patients to a greater risk of tendinopathy and/or traumatic rupture.