Tissue Engineering: A Real Tendon Transfer
Abstract & Commentary
Synopsis: An animal model using a collagen scaffold derived from porcine small intestine was shown to successfully repair a defect in the infraspinatus tendon of the shoulder.
Source: Dejardin LM, et al. Tissue-engineered rotator cuff tendon using porcine small intestine submucosa. Histologic and mechanical evaluation in dogs. Am J Sports Med. 2001;29(2):175-184.
This award winning (2000 O’Donoghue Sports Injury Research Award) study by Dejardin and associates from Michigan State University evaluated the healing potential of a collage scaffold in the repair of an infraspinatus tendon defect. In this study, both a healing model in the adult dog and cadaveric evaluation of the adult dog infraspinatus tendon were used to evaluate the regenerate potential of porcine small intestine submucosa (SIS) as a collagen scaffold in the management of large rotator cuff defects. This collagen scaffold is now clinically available, as an orthobiologic implant, as RestoreÓ (Depuy, Warsaw, IN) for rotator cuff repair. Sixteen adult dogs underwent bilateral infraspinatus tendon elevation with the left tendon replaced with a 15 ´ 50 ´ 1 mm, 10-ply SIS implant (experimental side), while the right tendon was sutured back to its original insertion site (sham operation). Five cadaveric specimens were mechanically tested to evaluate immediate repair strength. Eight dogs were sacrificed at 3 and 6 months and were tested both histologically (3 dogs) or mechanically (5 dogs). An additional 4 pairs of canine shoulders were used to evaluate histologic appearance and the mechanical strength of the normal infraspinatus tendon.
The SIS graft is prepared from pathogen-free pigs whose small intestines are processed mechanically and chemically to remove the mucosal, serosal, and muscular layers as well as cellular materials. The implant is further processed to reduce the bioburden (number of organisms on the implant), as well as to eliminate potential immunogenic properties. Processed SIS is a 0.1 mm thick sheet composed of more than 90% protein (cross-linked collagen). To produce a graft of sufficient mechanical strength, each SIS implant is manufactured using 10 individual layered sheets of processed SIS.
SIS-regenerated tendons appeared grossly similar, but slightly thinner than the contralateral sham-operated tendons. The SIS regenerated tendon however spanned the entire defect and presented a palpable tissue throughout the regenerate site. Gross appearance and mechanical strength mimicked those of the sham-operated tendons and native infraspinatus. Tissue ingrowth occurred without histologic evidence of foreign body or immune-mediated reactions or soft tissue adhesions. Although the ultimate strength of the SIS-regenerated tendon was significantly less than that of native infraspinatus tendons, it was similar to that of the repair tendon at both 3 and 6 months healing. In conclusion, the SIS collagen scaffold appeared to create a reliable tissue-engineered replacement of the rotator cuff in an animal model. This study suggests that the SIS implant served as a temporary scaffold for host tissue ingrowth and eventual tissue (rotator cuff) regeneration.
Comment by Robert C. Schenck, Jr., MD
As discussed in last month’s issue of Sports Medicine Reports, tissue engineering in orthopaedic surgery is creating new avenues of treatment. This study explored the ability to regenerate the rotator cuff tendon, a clinical area of limited options, that is until now. Tissue engineering is focused on the ability to induce tissue regeneration, the creation of identical tissue to that lost or injured, and can be contrasted to repair which restores the damaged area with a functional but different tissue. It is in regeneration that tissue engineering is directed through the use of 3 components: cells, scaffolds, and growth factors. These mechanisms create new tissue and are described with the suffix "genesis."1 For tissue regeneration to occur successfully, it usually requires at least 2 of the 3 components. However, regenerate can occur with 1 of the 3, as seen in this study, if performed in a normal host bed.
The indications for the RestoreÓ SIS scaffold in the repair of rotator cuff defects are still being defined but require a basic understanding of tissue engineering principles for proper patient application. Having such a scaffold available is a remarkable advance in the treatment of musculoskeletal defects and injuries. I would predict that the indications for the use of this implant would expand with the creation of different sizes and thickness of the orthobiologic implant. The presence of a normal host bed, in my opinion, is key to the successful use of this graft. The clinician must evaluate patient applicability on both long-standing clinical concepts of shoulder surgery (preoperative stiffness vs full range of motion), and newer tissue engineering principles (which of the 3 components—cells, scaffold, or growth factors—are available). A chronic massive cuff tear, with tendon retraction and scarring, limited vascularity, and poor shoulder range of motion, is probably not the ideal patient for this implant. Nonetheless, there are many soft tissue defect problems in orthopaedic surgery, which will find a successful indication for such new tissue engineering implants as the SIS patch used in studies by Dejardin and associates.2 Finally, thinking of the legal difficulties involved in the past with pedicle screw fixation, the clinician must be careful with the use of the SIS implant to follow manufacturers’ recommendations and FDA indications in order to avoid issues of off-label use.
In summary, the successful implantation of a collagen scaffold in the dog model has led to a clinically applicable orthobiologic implant now available for rotator cuff repair. Tissue engineering is taking hold of orthopaedic surgery.
References
1. Schenck RC. Strategic strategies: Contemporary tissue engineering. Medscape, 2001.
2. Dejardin LM, et al. Use of small intestinal submucosal implants for regeneration of large fascial defects: An experimental study in dogs. J Biomed Mater Res. 1999; 46:203-211.
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