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Saturday, March 13, 2004

Dog model indicates tendons can be directly attached to metal prosthesis

By Mary Ann Porucznik

Investigators for Scientific Exhibit SE051 report that tendon repair with a porous metal prosthesis shows clinical, biomechanical and histological evidence of biologic fixation in a canine model.

Direct tendon attachment to metallic prostheses has applications throughout orthopaedics. A soft-tissue attachment device was created to exploit the theoretical advantages offered by the new family of 100 percent porous metals: immediate postoperative full weight-bearing and long-term biologic in growth strength.

Researchers reattached 40 skeletally-mature canine supraspinatus tendons between two washers of porous tantalum. They evaluated fixation strength, clinical function and morphological changes at four time points: at surgery, at 3 weeks, at 6 weeks and at 12 weeks.

Tendon-implant strength as percent of normal rose significantly (p < 0.0014) over the course of time-from 39 percent at surgery, to 67 percent at 3 weeks, 99 percent at 6 weeks and 140 percent at 12 weeks (standard deviations 13, 19, 18 and 35). Stiffness of construct approached that of a normal tendon (p < 0.0299), increasing from 47 percent at surgery to 62 percent at 3 weeks, 94 percent at 6 weeks, and 132 percent at 12 weeks (standard deviations 27, 19, 18, and 38).

Gait analysis demonstrated resumption of preoperative function. The percent of total body weight at midstance did not differ at 3, 6 or 12 weeks (p = 0.062). The supraspinatus muscle atrophied significantly (p < 0.015) from 97 percent of normal at surgery to 77 percent of normal at 3 weeks. By 6 weeks, however, the muscle had recovered to 81 percent of normal volume (p < 0.02), and the muscle volume at 12 weeks hypertrophied to 92 percent of normal (p < 0.02). Histomorphometry showed collagen fibers attaching to the metal surface and increased cellular density within the metal trabeculae.

Researchers concluded that robust tendon attachment to a metallic prosthesis was achieved. Tendon strength and stiffness as well as gait parameters returned to normal. Sharpey's fiber surface attachment and cellular ingrowth were observed

The research team was led by John S. Reach, Jr, MD, and included Ian D. Dickey, MD; Robert Talac, MD, PhD; Mark E. Zobitz, MS; Julie E. Adams, MD; Hiroshi Minagawa, MD; Sean P. Scully, MD, PhD, and David G. Lewallen, MD, MS, all of Rochester, Minn. Funding was supplied by Implex and Zimmer.

Original title of exhibit:
Tendon Reattachment With a Porous Metal Prosthesis: an In-Vivo Canine Study

  Implant and tendon at surgery.
  Six-week histology, van Gieson staining x80.

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