title: Immobilization modulates macrophage accumulation in tendon-bone healing.
abstract: Tendon-to-bone healing occurs by formation of a fibrous, scar tissue interface rather than regeneration of a normal insertion. Because inflammatory cells such as macrophages lead to formation of fibrous scar tissue, we hypothesized immobilization would allow resolution of acute inflammation and result in improved tendon-bone healing. We reconstructed the ACL of 60 Sprague-Dawley rats using a tendon autograft. An external fixation device was used to immobilize the surgically treated knee in 30 rats. We evaluated tendon-bone interface width, collagen fiber continuity, and new osteoid formation histologically. Immunohistochemistry was used to localize ED1+ and ED2+ macrophages at the tendon-bone interface at 2 and 4 weeks. Biomechanical testing was performed at 4 weeks. Interface width was smaller and collagen fiber continuity was greater in the immobilized group. Immobilized animals exhibited fewer ED1+ macrophages at the healing interface at 2 and 4 weeks. In contrast, there were more ED2+ macrophages at the interface in the immobilized group at 2 weeks. Failure load and stiffness were similar between groups at 4 weeks. The data suggest early immobilization diminishes macrophage accumulation and may allow improved tendon-bone integration.
authors.affiliation: Laboratory for Soft Tissue Research, Sports Medicine and Shoulder Service, Hospital for Special Surgery, New York, NY 10021, USA.
authors.forename: Elias
authors.initials: E
authors.lastname: Dagher
authors.forename: Peyton L
authors.initials: PL
authors.lastname: Hays
authors.forename: Sumito
authors.initials: S
authors.lastname: Kawamura
authors.forename: Jon
authors.initials: J
authors.lastname: Godin
authors.forename: Xiang-hua
authors.initials: XH
authors.lastname: Deng
authors.forename: Scott A
authors.initials: SA
authors.lastname: Rodeo
mesh_terms: D000818:Animals; D002921:Cicatrix / Q000473:pathology / Q000517:prevention & control; D016267:External Fixators; D005269:Femur / Q000473:pathology / Q000601:surgery*; D007103:Immobilization / Q000379:methods*; D007719:Knee Joint / Q000473:pathology / Q000601:surgery; D008264:Macrophages / Q000473:pathology*; D008297:Male; D011183:Postoperative Complications / Q000473:pathology / Q000517:prevention & control; D051381:Rats; D017207:Rats, Sprague-Dawley; D013710:Tendons / Q000473:pathology / Q000637:transplantation*; D013977:Tibia / Q000473:pathology / Q000601:surgery; D014945:Wound Healing