Two-portal repair of canine flexor tendon insertion site injuries: histologic and immunohistochemical characterization of healing during the early postoperative period.

PURPOSE: In vivo animal studies have indicated that the complex structure of the tendon-bone interface may not be restored after repair even under optimal conditions. Controversy exists about the histologic findings in the early postoperative period after tendon reattachment to bone; this may have impact on biomechanical properties. The objective was to study the histologic structure and immunohistochemical staining of the tendon-bone interface in a large model of digital flexor tendon-bone repair. The hypothesis was that the tendon-bone interface matures and assumes a progressively more anatomic histologic and immunohistochemical appearance during the first 6 weeks after repair.
METHODS: Twenty-four canine flexor digitorum profundus tendons were released from their insertion by sharp dissection and repaired to bone. The forelimb was immobilized after surgery and 10 minutes of daily passive motion rehabilitation was performed. Dogs were killed at 10, 21, and 42 days after surgery. Hematoxylin-eosin and immunohistochemical staining for types I, II, and II collagen were performed.
RESULTS: Although at both 10 and 21 days after surgery substantial inflammation was seen at the tendon-bone repair site, this had decreased markedly by 42 days. Although direct apposition of tendon to bone was seen at 42 days, the mature tendon-bone insertion site was not recreated by this time. Staining for types I and III collagen was diffuse throughout the tendon-bone insertion throughout the interval examined.
CONCLUSION: These findings suggest that at 6 weeks after surgery the intact tendon-bone repair site shows minimal histologic and molecular similarity when compared with unoperated specimens.