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

Tendon to bone healing and its implications for surgery

“…Subsequent introduction of gentle loading can be beneficial, while aggressive loading leads to impaired healing 95 . Rodent rotator cuff models show that the period of immobilisation leads to better organisation of collagen at the insertion site and improved viscoelastic properties 79,96 , while cruciate ligament models demonstrate similar results along with reduced infiltration of phagocytes 97 . The emerging field of mechanobiology explores how the load applied to an enthesis influences its substructure, a concept originally proposed in relation to bone healing by Wolff in the 19 th century 98 .…”

Aktuelle Entwicklungen und Einsatzgebiete von Schulterorthesen

“…Ab der 3. Woche beginnt die reparative Phase, die vor allem durch die Entstehung von Kollagen I aus Kollagen III und die Bildung eines fibrovaskulä-ren Narbengewebes mit unzulänglicher struktureller Integrität gekennzeichnet ist [5,6]. Dieser Prozess dauert ca.…”

The Role of Mechanobiology in the Attachment of Tendon to Bone

“…A possible mechanism for the poor healing observed with exercise has recently been suggested by studies using a rat model of ACL reconstruction [133][134][135]. Cytokines produced by macrophages have been implicated in tendon-to-bone healing and reducing the number of macrophages improves the biomechanical behavior of the interface.…”

“…Cytokines produced by macrophages have been implicated in tendon-to-bone healing and reducing the number of macrophages improves the biomechanical behavior of the interface. Furthermore, immobilization seems to also block macrophage recruitment, thus contributing to improved interface healing [133].…”