Corticosteroids Reduce the Tensile Strength of Isolated Collagen Fascicles

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Abstract
Background: Overuse tendon injuries are frequent. Corticosteroid injections are commonly used as treatment, although their direct effects on the material properties of the tendon are poorly understood. Purpose: To examine the influence of corticosteroids on the tensile strength of isolated collagen fascicles. Study Design: Controlled laboratory study. Methods: Single strands (300-500 [.mu]m) of rat-tail collagen fascicles were incubated in either high (1 mL of 40 mgmL-1 mixed with 0.5 mL saline 9%) or low (1 mL of 40 mgmL-1 mixed with 2 mL saline 9%) concentration of methylprednisolone acetate (Depomedrol) for 3 or 7 days, while the control segment from the same fascicle was kept in saline (N = 64). After the incubation period, the fascicles underwent displacement to failure in a mechanical test rig at 0.13 mm/s, and thereafter hydroxylysyl pyridinoline and lysyl pyridinoline cross-link content was evaluated in a high-performance liquid chromatography system. Data for each group were analyzed with a 2-way analysis of variance (time × incubation) for ultimate stress (mean ± standard deviation). Results: In the high-concentration groups, strength was reduced after 3 (16.6 ± 4.6 MPa) and 7 (8.6 ± 1.7 MPa) days compared to the controls (30.2 ± 5.0 MPa and 25.6 ± 4.6 MPa, respectively; P <. 05). In the low-concentration groups, strength was reduced after 3 (12.0 ± 3.1 MPa) and 7 days (10.9 ± 2.5 MPa) compared to the controls (31.5 ± 5.0 MPa and 32.4 ± 5.6 MPa, respectively; P <. 05). The amount of cross-linking was unaffected by the intervention. Conclusion: Data show that the tensile strength of isolated fascicles is markedly reduced after 3-and 7-day incubation in both high and low concentration of corticosteroids, although the observed effect on whole tendon remains unknown. Clinical Relevance: Corticosteroids may weaken specific regions of the injected tendon and leave it more prone to rupture. This weakening effect is manifested in the individual collagen fascicles that constitute the tendon.

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