Influence of Hydroxyapatite-Coated and Growth Factor–Releasing Interference Screws on Tendon-Bone Healing in an Ovine Model
Received 13 November 2008; accepted 10 June 2009. published online 09 November 2009.
Purpose
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.
Clinical Relevance
This linkBMP-2 coating material may improve early tendon/ligament fixation.
aComparative Orthopaedic Research Laboratory, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.
bDepartment of Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.
cDepartment of Pharmacology, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.
dDepartment of Orthopedics and Rehabilitation, University of Wisconsin-Madison, Madison, Wisconsin, U.S.A.
Address correspondence and reprint requests to Yan Lu, M.D., Comparative Orthopaedic Research Laboratory, Department of Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Dr, Madison, WI 53706-1102, U.S.A.
Supported by the Wallace H. Coulter Foundation (Translational Research Partnership Grant) and the National Institutes of Health (R03AR052893). The authors report no conflict of interest.
Note: To access the supplementary tables accompanying this report, visit the December issue of Arthroscopy at www.arthroscopyjournal.org.
ABSTRACT