Influence of hydroxyapatite-coated and growth factor-releasing interference screws on tendon-bone healing in an ovine model.
OBJECTIVE
Our purpose was to determine whether a bioresorbable interference screw coated with a hydroxyapatite-based mineral layer designed to release an engineered peptide growth factor (linkBMP-2 [where "BMP-2" indicates bone morphogenetic protein 2]) improved tendon-bone healing compared with a screw without coating.


METHODS
Tagged linkBMP-2 peptides were used to quantify binding efficiency and release kinetics on 9 mineral-coated BIORCI screws (Smith & Nephew, Andover, MA). Fourteen mature female sheep were used in this study. In each of the 14 sheep, each stifle was randomized to either receive a linkBMP-2-coated or uncoated interference screw (n = 14 per treatment). The sheep were euthanized at 6 weeks after surgery. Eight sheep were subjected to biomechanical testing for peak load at failure and stiffness, and six sheep were used for histologic analysis according to a semiquantitative scoring scale.


RESULTS
The linkBMP-2 molecule bound efficiently to the surface of mineral-coated interference screws. Over 80% of the initially bound linkBMP-2 was released during a 6-week time frame in vitro. Peak load at failure in the linkBMP-2-coated interference screw group (mean +/- SD, 449.3 +/- 84.7 N) was not significantly different from that in the uncoated group (421.0 +/- 61.8 N) (P = .22). Stiffness in the linkBMP-2-coated interference screw group (157.3 +/- 39.6 N/mm) was not significantly different from that in the uncoated group (140.6 +/- 20.3 N/mm) (P = .12). Histologic analysis showed that the tendons in the linkBMP-2-coated interference screw group had higher scores (better) than the uncoated group. In the linkBMP-2-coated interference screw group, mesenchymal cells were present at the interface between screw and tendon, whereas these cells were not present in the uncoated group.


CONCLUSIONS
We found that linkBMP-2 can be bound onto a mineral-coated BIORCI interference screw surface and subsequently released from the screw surface in a sustained manner. The histologic result of this study showed that the linkBMP-2-coated interference screw significantly improved the histologic scores of early tendon-bone healing in this sheep model.


CONCLUSIONS
This linkBMP-2 coating material may improve early tendon/ligament fixation.
Lu
Yan
Y
University of Wisconsin-Madison, Madison, Wisconsin, USA. luy@svm.vetmed.wisc.edu
Markel
Mark D
MD
Nemke
Brett
B
Lee
J Sam
JS
Graf
Ben K
BK
Murphy
William L
WL
D020341:Absorbable Implants; D000818:Animals; D016118:Anterior Cruciate Ligament / Q000601:surgery*; D055396:Bone Morphogenetic Protein 2; D001863:Bone Screws; D020099:Coated Materials, Biocompatible; D004195:Disease Models, Animal; D017886:Durapatite; D005260:Female; D005269:Femur / Q000473:pathology / Q000601:surgery*; D007718:Knee Injuries / Q000473:pathology / Q000601:surgery; D017847:Patellar Ligament / Q000473:pathology / Q000601:surgery*; D011474:Prosthesis Design; D012756:Sheep; D014945:Wound Healing
D055396:Bone Morphogenetic Protein 2; D020099:Coated Materials, Biocompatible; D017886:Durapatite