Intratendinous injections of platelet-rich plasma: feasibility and effect on tendon morphology and mechanics

BACKGROUND: Intratendinous injections may have important effects on the properties of collagen microarchitecture, morphology, and subsequent mechanical properties of the injected tendon. The purpose of this study was to examine the effects of intratendinous PRP injections; the injectant retention within tendons, the distribution of intratendinous injectant, and whether intratendinous injection or needle fenestration alters tendon morphology or mechanics. METHODS: Design: Controlled Laboratory Study. Interventions: In the first part of the study, 18 lamb extensor tendons were selected to receive methylene blue-containing PRP injection (PRP/MB), methylene blue only injection (MB), or needle fenestration. The volume of retained injectant was measured and injectant distribution and tendon morphology were examined microscopically. In the second portion of the study, 18 porcine flexor tendons were divided into control, needle fenestration, or saline injection groups. Young’s Modulus was then determined for each tendon under 0-4% strain. Main outcome measures: 1) Injectant volume retained; 2) Injectant distribution; 3) Post-injection/fenestration alterations in morphology, biomechanics. RESULTS: Intratendinous injectant is retained within the tendon. The difference between PRP and PRP/MB groups was not significant (p = 0.78). Intratendinous spread of the injectant solution within the tendon occurs primarily in the proximodistal direction, with very little cross-sectional penetration. Intratendinous injections resulted in microscopic morphology disruption (e.g., separation and disorganization of both the collagen bundles and cellular distribution). There were significant differences in Young’s Modulus between control (E(ctrl) = 2415.48) and injected tendons (E(inj) = 1753.45) at 4% strain (p = 0.01). There were no differences in Young’s Modulus between fenestrated and control tendons. CONCLUSIONS: Intratendinous PRP injections are retained within the tendon, and primarily distributes longitudinally with minimal cross-sectional spread. Intratendinous injections may alter tendon morphology and mechanics.