The Journal of Bone and Joint Surgery (American). 2007;89:1000-1009.
doi:10.2106/JBJS.E.00886
© 2007 The Journal of Bone and Joint Surgery, Inc.
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Direct Tendon Attachment and Healing to Porous Tantalum: An Experimental Animal Study

John S. Reach, Jr., MSc, MD1, Ian D. Dickey, MD2, Mark E. Zobitz, MS3, Julie E. Adams, MD2, Sean P. Scully, MD, PhD4 and David G. Lewallen, MD2

1 Yale University School of Medicine, Yale Physicians Building, 800 Howard Avenue, New Haven, CT 06520. E-mail address: john.reach{at}aya.yale.edu
2 Department of Orthopaedic Surgery, Mayo Clinic, E 14 Mayo Building, 200 First Street S.W., Rochester, MN 55905. E-mail address for D.G. Lewallen: lewallen.david{at}mayo.edu
3 Biomechanics Laboratory, Mayo Clinic, 128 Guggenheim Building, 200 First Street S.W., Rochester, MN 55905
4 Department of Orthopaedic Surgery, University of Miami, P.O. Box 016960, Miami, FL 33101. E-mail address: SScully{at}med.miami.edu

Investigation performed at Mayo Clinic, Rochester, Minnesota

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from Zimmer, Warsaw, Indiana. In addition, one or more of the authors or a member of his or her immediate family received, in any one year, payments or other benefits in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Zimmer, Warsaw, Indiana). Also, a commercial entity (Zimmer, Warsaw, Indiana) paid or directed in any one year, or agreed to pay or direct, benefits in excess of $10,000 to a research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which one or more of the authors, or a member of his or her immediate family, is affiliated or associated. Implants were fabricated and supplied by Zimmer, Warsaw, Indiana.

Background: The ability to directly attach soft-tissue to metal would have broad clinical application. Previous attempts to obtain normal tendon-to-bone attachment strength have been unsuccessful. In the present study, we hypothesized that when the initial interface mechanical environment is carefully controlled, a highly porous form of tantalum metal would allow the ingrowth of tendon tissue with clinically relevant tendon-to-implant fixation strength approaching that of an intact tendon-to-bone insertion.

Methods: Supraspinatus tendons from forty skeletally mature dogs were reattached to the greater tuberosity between two custom-designed porous tantalum washers. Clinical function as judged on the basis of gait analysis, reattachment fixation strength and stiffness, and tendon function as seen through muscle volume were evaluated preoperatively, immediately postoperatively, and at three, six, and twelve weeks after surgery. Qualitative and quantitative histomorphologic evaluation was performed at three, six, and twelve weeks after surgery.

Results: Gait analysis with use of force-plate measurements demonstrated return to a normal gait pattern by three weeks after surgery. Tendon-implant strength as a percentage of normal, contralateral controls increased significantly, from 39% at the time of surgery to 67% at three weeks, 99% at six weeks, and 140% at twelve weeks (p < 0.0014). The stiffness of the construct also increased and approached that of normal tendon, measuring 47% at the time of surgery, 62% at three weeks, 94% at six weeks, and 130% at twelve weeks (p < 0.0299). Supraspinatus muscle volume initially decreased by 33% but recovered to 92% of normal by twelve weeks (p < 0.01). Histomorphologic evaluation showed Sharpey-like fibers inserting onto the surface of the porous tantalum. Quantitative histomorphometric analysis revealed a time-dependent increase in the density of the collagen tissue filling the metal voids below the implant surface of first the bottom washer and then the top washer.

Conclusions: Robust biologic ingrowth of tendon into a porous tantalum implant surface can be achieved under conditions of secure initial mechanical fixation. The strength and stiffness of the tendon-implant construct reached normal levels by six to twelve weeks in this animal model.

Clinical Relevance: Our results demonstrate the potential utility of highly porous metals in general and this specific form of porous tantalum in particular as a biomaterial for soft-tissue reconstruction. The ability to achieve healing of tendon and possibly other soft tissues directly to metallic devices should offer opportunities for the development of novel and potentially more physiologic orthopaedic implants.


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