Purpose: Sixty-eight skeletally mature New Zealand white rabbits were used to study the effects of iontophoresis- and injection-delivered sodium phosphate dexamethasone (DX) on the morphologic, histologic, microscopic, and biomechanical properties of uninjured rabbit patellar tendons over an initial 14-d period.
Methods: Three control (untreated, placebo iontophoresis, and placebo injection) groups and two treatment (iontophoresis and injection) groups underwent serum, ELISA tendon, histology, electron microscopy, and biomechanical analysis.
Results: Serum DX levels were detectable and quantifiable in both treatment groups at 1 h but were significantly greater (P < 0.05) in the injected group (11.29 ng.mL-1) compared with the iontophoresis group (6.34 ng.mL-1). The most significant histologic finding was a lack of a cellular inflammatory response in the DX-treated groups at 24 h. Ultrastructural analysis produced no significant differences between size or size ratio of collagen fibrils among any groups. Morphologic examination revealed only injection puncture marks seen in appropriate tendons. Biomechanical testing produced disruption at the patellar insertion in 81% of the specimens. No injected tendon failed at the injection site. Normalized biomechanical properties included: 1) Stiffness increased in control and iontophoresis groups from 1 to 24 h, then gradually declined; the DX-injected specimens showed a similar but delayed effect. 2) Peak load at failure for iontophoresis and control groups was greatest at 24 h. The DX-injected group again showed a delayed response. 3) In general, total energy to failure revealed no significant differences between groups at any time period.
Conclusion: It appears that iontophoresis or injection-delivered DX may produce anti-inflammatory effects without significantly altering ultrastructural or biomechanical characteristics of the rabbit patellar tendon within an initial 14-d period.