Flexor
tendinitis is a common and debilitating injury of elite and recreational athletes. Healing may be improved through intratendinous injection of
insulin-like growth factor-I (
IGF-I), which has been shown in vitro to stimulate mitogenesis and enhance tendon matrix production. This study investigated the effects of intratendinous injection of
IGF-I on tendon healing in an equine model of flexor
tendinitis.
Collagenase-induced lesions were created in the tensile region of theflexor digitorum superficialis tendon of both forelimbs of eight horses. Treated tendons were injected with 2 microg rhlGF-I intralesionally every other day for 10
injections, while controls received
0.9% NaCl. Tendon fiber deposition and organization were evaluated serially using ultrasonography throughout the 8 week trial period. Following
euthanasia, the tendons were harvested and
DNA,
hydroxyproline, and
glycosaminoglycan content determined, mechanical strength and stiffness evaluated, gene expression and spatial arrangement of
collagen types I and III assessed by northern blot and in situ hybridization, and tendon fiber architecture assessed by polarized light microscopy. Local soft tissue swelling was reduced in the
IGF-I treated limbs. Similarly, lesion size in
IGF-I treated tendons was smaller 3 and 4 weeks after initiation of treatment. Cell proliferation and
collagen content of the
IGF-I treated tendons were increased compared to controls. Mechanically,
IGF-I treated tendons showed a trend toward increased stiffness compared to saline treated controls. Considered together with the decreased soft tissue swelling and improved sonographic healing, these data support the potential use of intralesional
IGF-I for treatment of debilitating
tendon injuries.