Tensile properties of tendon after repair using titanium implants with different porosities in a rat model

Extensor mechanism and abductor reconstructions in total joint arthroplasty are problematic. Growing tendon into a metallic implant would have great reconstructive advantages. With the introduction of porous metal implants, it was hoped that tendons could be directly attached to implants. However, the effects of the porous metal structure on tissue growth and pore penetration is unknown. In this rat model, we investigated the effect of pore size on tendon repair fixation using printed titanium implants with differing pore sizes. There were four groups of six Sprague Dawley rats (n = 28) plus control (n=4). Implants had pore sizes of 400µm (n=8), 700µm (n=8), and 1000µm (n=8). An Achilles tendon defect was created, and the implant positioned and sutured between the cut ends. Harvest occurred at 12-weeks. Half the specimens underwent tensile load to failure testing, the other half fixed and processed for hard tissue analysis. Average load to failure was 72.6N for controls (SD 10.04), 29.95N for 400µm (SD 17.95), 55.08N for 700µm (SD 13.47), and 63.08N for 1000µm (SD 1.87). The load to failure was generally better in the larger pore sizes. Histological evaluation showed that there was fibrous tendon tissue within and around the implant material, with collagen fibers organized in bundles. This increases as the pore diameter increases. Printing titanium implants allows for precise determination of pore size and structure. Our results showed that tendon repair utilizing implants with 700µm and 1000µm pores exhibited similar load to failure as controls. Using a defined pore structure at the attachment points of tendons to implants may allow predictable tendon to implant reconstruction at the time of revision arthroplasty.