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
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.