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Safety Profile of Bioabsorbable Shoulder Anchors

      To the Editor:
      We read with interest the article in the March 2007 issue entitled “Biodegradable Shoulder Anchors Have Unique Modes of Failure”
      • Barber F.A.
      Biodegradable shoulder anchors have unique modes of failure.
      by F. Alan Barber. In Dr. Barber’s article, he describes two cases as “sentinel events” to alert the physician of loose and degraded bioabsorbable anchor products within the glenohumeral joint, both of which caused mechanical symptoms and pain. The article does acknowledge that the incidence of these problems is very low.
      We would like to emphasize the rare nature of these cases and emphasize that while no implant is “risk-free,” a suture-on-suture construct is likely to be the safest configuration available. This is especially true when considering the alternatives of metal anchors or bioabsorbable anchors with hard suture posts, which might fracture or be harmful to the joint if they are left proud. Rupp et al.
      • Rupp S.
      • Georg T.
      • Gauss C.
      • Kohn D.
      • Seil R.
      Fatigue testing of suture anchors.
      have shown that in addition to the concerns of metallic implants described by Barber,
      • Barber F.A.
      Biodegradable shoulder anchors have unique modes of failure.
      the metallic eyelet–suture interface is much more abrasive than a bioabsorbable suture anchor. Historically, the abrasive relationship of suture on metal was fraught with suture failure, leading to frequent suture loose body formation, none of which has been reported or observed to be associated with chondral damage. Contemporary anchors constructed of absorbable material can take upwards of several years to initiate appreciable degradation. Thus, early macro-failure is more likely a result of technical issues relevant at the time of anchor insertion (i.e., insufficient anchor depth and anchor fragmentation at the time of insertion).
      Extensive research has been conducted by independent laboratories on the degradation of bioabsorbable polymers as well as the eyelet-suture interface.
      • Dejong E.S.
      • DeBerardino T.M.
      • Brooks D.E.
      • Judson K.
      In vivo comparison of a metal versus a biodegradable suture anchor.
      • Hollinger J.O.
      • Battistone G.C.
      Biodegradable bone repair materials Synthetic polymers and ceramics.
      • Pirhonen E.
      • Kaikkonen A.
      • Helevirta P.
      • Pohjonen T.
      • Tamminmaki M.
      • Tormala P.
      Development of a bioabsorbable suture anchor.
      The BioSutureTak (Arthrex, Naples, FL), one of the two anchors discussed in Dr. Barber’s case report, has demonstrated similar strength and failure load
      • Dejong E.S.
      • DeBerardino T.M.
      • Brooks D.E.
      • Judson K.
      In vivo comparison of a metal versus a biodegradable suture anchor.
      at up to 12 weeks of soft tissue healing. Since 1999, more than 6 million Arthrex suture anchors constructed of suture-on-suture eyelet configurations have been implanted. To date, fewer than 10 events regarding the unique modes of failure have been documented for all manufacturers with the US Food and Drug Administration Medical Device Reporting Database. If Arthrex were the only manufacturer, 10 reports of 6 million would represent a 0.000167% rate of occurrence. Only two reports of any damage within the joint were filed, neither of which were Arthrex devices.
      The tolerance of articular cartilage to suture can be traced back to Carter Rowe in the late 1970s, when open transossous Bankart repair was routinely performed without incident. Contemporary suture tying techniques often utilize multiple stacked half-hitches at the level of the articular surface, which have also not been shown to result in articular cartilage damage. In comparison to a loose piece of suture eyelet, one would anticipate these fixation points to be far more imposing to articular surfaces, yet there are no case reports describing this phenomenon. A similar scenario of intra-articular suture knots is an all-inside meniscal repair. The self-locking knots used in this application are in direct contact with the femoral or tibial surfaces, yet no reports of articular cartilage damage have occurred. While the incidence of suture-eyelet failure is not known and likely to be very low, it has not been reported as being associated with early failure at the time of revision surgery. On the other hand, alternatives such as metal or absorbable anchors that are left proud at insertion or become proud postoperatively are associated with devastating chondral damage.
      Contemporary anchors constructed of absorbable materials can take upwards of several years to degrade, and early softening or fracture is unlikely to occur, especially before 8 to 12 weeks where secure soft tissue healing has already occurred. Thus, the “cases for concern” that Dr. Barber presents may serve to highlight the technical issues with anchor placement rather than the inherent biomechanical properties of the anchor. When inserting bioabsorbable anchors, one should keep in mind the composition of the anchor as well as the suture–anchor construct properties. The interface between the suture and anchor has been studied extensively, and has consistently been shown not to be the weakest link in the repair construct; rather, the tissue–device interface and suture pullout from the tissue remain the weakest points of fixation. Angle and depth of insertion, as well as suture–eyelet orientation on the glenoid (especially with metallic anchors) has been associated with suture abrasion and early failure. Finally, at the time of implantation, it is plausible that, should the surgeon inadvertently fail to neutralize forces as the loop limb is tightened over the post limb, the suture eyelet can fail at the time of implantation. Even if unrecognized, it is far more likely that the small limb of suture would lodge in the axillary pouch or become embedded within soft tissue rather than be associated with articular cartilage damage. Compared to a bioabsorbable suture post, which might fragment and come loose during differential absorption, one might prefer a joint-friendly suture over a bioabsorbable fragment.
      We feel that there are numerous advantages to bioabsorbable anchors in the glenoid over metallic anchors, and there are few data to suggest that this report is anything more than a phenomenon relegated to an isolated or exceptionally rare event.
      We look forward to seeing additional research in the area of bioabsorbable implants, but feel that the currently available bioabsorbable anchors have an exceptional clinical safety profile, with very few complications.

      References

        • Barber F.A.
        Biodegradable shoulder anchors have unique modes of failure.
        Arthroscopy. 2007; 23: 316-320
        • Rupp S.
        • Georg T.
        • Gauss C.
        • Kohn D.
        • Seil R.
        Fatigue testing of suture anchors.
        Am J Sports Med. 2002; 30: 239-247
        • Dejong E.S.
        • DeBerardino T.M.
        • Brooks D.E.
        • Judson K.
        In vivo comparison of a metal versus a biodegradable suture anchor.
        Arthroscopy. 2004; 20: 511-516
        • Hollinger J.O.
        • Battistone G.C.
        Biodegradable bone repair materials.
        Clin Orthop Relat Res. 1986; 207: 290-305
        • Pirhonen E.
        • Kaikkonen A.
        • Helevirta P.
        • Pohjonen T.
        • Tamminmaki M.
        • Tormala P.
        Development of a bioabsorbable suture anchor.
        J Biomed Mater Res. 1999; 48: 875-880

      Linked Article

      • Biodegradable Shoulder Anchors Have Unique Modes of Failure
        ArthroscopyVol. 23Issue 3
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          Biodegradable suture anchors have facilitated and revolutionized arthroscopic tissue-to-bone repair, especially in the shoulder. However, the anchor is but a part of the repair construct, which also includes a suture, tied in a knot, that attaches the tissue (tendon or labrum) to bone. Bioabsorbable anchors may result in loose bodies. Two cases are reported as sentinel events highlighting this potential risk. In the first case, combining a nonabsorbable suture (forming the anchor eyelet) with an anchor body made from rapidly degrading copolymer resulted in the suture becoming a loose body as the anchor body reabsorbed.
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      • Author’s Reply
        ArthroscopyVol. 23Issue 8
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          The letter from Drs. Cole and Provencher underscores many of the points made in the March 2007 article “Biodegradable Shoulder Anchors Have Unique Modes of Failure.”1 I agree that the incidence of problems caused by suture anchors is indeed very low. While no implant is “risk-free,” biodegradable anchors have few reported problems and are associated with excellent clinical outcomes.2,3 As both the letter and article point out, while repair construct failure can occur at the bone, anchor, suture, tendon, or any interface between these components, the suture–tissue interface is the weakest link in the repair construct.
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