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Editorial Commentary: Fascia Lata Allograft for Shoulder Superior Capsular Reconstruction: In the Fight Over Optimal Graft Choice for Irreparable Rotator Cuff Tears, Superior Capsular Reconstruction Proponents May Be Changing Their Gloves

      Abstract

      Optimal treatment of irreparable rotator cuff tears is still debated. Proponents of the superior capsule reconstruction (SCR) have previously used fascia lata autograft and acellular dermal allograft. Interest is growing in using fascia lata allograft as a new graft material. Well-designed biomechanical studies are important to understand the mechanical properties of the superior capsular tissue and fascia lata allograft. Recent biomechanical research shows that fascia lata allograft has similar initial stiffness (over the first 2 mm) and ultimate load compared to the native superior capsule. That said, ultimate load is the load at which a construct fails, whereas the yield point is the load on the stress–strain curve at which a material transitions from elastic to plastic deformation. In the shoulder where the SCR, for example, is going to be repetitively loaded, it is potentially more meaningful to talk about the yield point in order to stay within the elastic range. Using this framework, the yield point for fascia lata allograft is approximately one third the yield point of native capsular tissue. Additionally, “initial” stiffness is not the entire story. At greater loads, fascia lata allograft has higher displacement compared to native tissue. Of importance, fascia lata allograft failed by sutures slowly cutting through the allograft tissue; this may represent a limitation of the construct that could be addressed using stitch configurations resistant to cut through. Fascia lata allograft is a promising solution for SCR. Biomechanical studies require nuanced interpretation, and most of all, do not evaluate clinical healing.
      In the heavy-hitting world of shoulder surgery, the title of World Champion of Irreparable Rotator Cuff Tear Treatment is still hotly disputed. It seems that more opponents show up every year, while the old dogs continue to scuff over the cuff. Will arthroplasty replace all doubts? Will the overseas contender, superior capsular reconstruction (SCR), knock them all out? Will tendon transfers reach around from the back and throw a hay maker? Or will the In-Space balloon spacer (Stryker, Kalamazoo, MI) float like a butterfly and sting like a bee? The verdict is still out.
      Team SCR was founded in Japan by Mihata et al.
      • Mihata T.
      • McGarry M.H.
      • Pirolo J.M.
      • Kinoshita M.
      • Lee T.Q.
      Superior capsule reconstruction to restore superior stability in irreparable rotator cuff tears: A biomechanical cadaveric study.
      using fascia lata autograft, which showed excellent clinical results. After the importation of the technique to the United States and the availability of different allograft options, human acellular dermal allograft was used with mixed results.
      • Mihata T.
      • Bui C.N.H.
      • Akeda M.
      • et al.
      A biomechanical cadaveric study comparing superior capsule reconstruction using fascia lata allograft with human dermal allograft for irreparable rotator cuff tear.
      • Burkhart S.S.
      Editorial Commentary: Superior capsule reconstruction with dermal allograft: achieving the goal of joint preservation.
      • Pennington W.T.
      • Bartz B.A.
      • Pauli J.M.
      • Walker C.E.
      • Schmidt W.
      Arthroscopic Superior capsular reconstruction with acellular dermal allograft for the treatment of massive irreparable rotator cuff tears: Short-term clinical outcomes and the radiographic parameter of superior capsular distance.
      Several authors have expressed concern regarding the mechanical strength of acellular dermal allograft and its suitability as a replacement for fascia lata autograft due to reportedly greater retear rates.
      • de Campos Azevedo C.I.
      • Andrade R.
      • Leiria Pires Gago Angelo A.C.
      • Espregueira-Mendes J.
      • Ferreira N.
      • Sevivas N.
      Fascia lata autograft versus human dermal allograft in arthroscopic superior capsular reconstruction for irreparable rotator cuff tears: A systematic review of clinical outcomes.
      Therefore, fascia lata allograft has been explored as a possible tissue; a new set of boxing gloves, if you will.
      With their manuscript entitled “Superior Capsule Reconstruction With Fascia Lata Allograft Has Initial Stiffness and Ultimate Load Comparable to the Native Shoulder Superior Capsule: A Cadaveric Biomechanical Study,”
      • DeBellis N.
      • Tibone J.E.
      • Manning J.
      • Hung V.
      • McGarry M.H.
      • Adamson G.J.
      • Lee T.Q.
      Superior capsule reconstruction with fascia lata allograft has initial stiffness and ultimate load comparable to the native shoulder superior capsule: A cadaveric biomechanical study.
      DeBellis, Tibone, Manning, Hung, McGarry, Adamson, and Lee jump into the rough-and-tumble world of debates surrounding irreparable rotator cuff tears, where more than one author has received a black eye. The authors conduct an excellent cadaveric biomechanical investigation to evaluate the strength of the native shoulder superior capsule compared with an SCR with fascia lata allograft. After isolating the superior capsule, the specimen was tested cyclically and to failure using a linear, distracting force at 20° of abduction. After native capsular tissue was tested, SCR with fascia lata allograft was performed and the testing was repeated. The stiffness over the initial 2 mm and ultimate load were similar, which were the major findings of this study.
      This study has several excellent characteristics. First, this study is an important step in one of the big questions surrounding SCR: what is the best graft choice? Selecting the optimal graft material is an important first step in building a strong SCR construct. As some continue to express doubt on the mechanical integrity of dermal allograft as a structural graft, excellent biomechanical studies, such as this manuscript, help us determine which grafts have the optimal mechanical properties. Second, the authors did a great job actually isolating the superior capsular tissue and demonstrating that the native tissue has robust biomechanical characteristics. With these properties so well illustrated, it is hard to doubt the superior capsule plays an important structural role in normal shoulder function. Finally, performing the test on the SCR construct, as opposed to just the tissue, is an excellent design feature because it helps us understand the graft and suture anchor construct as a functional unit. In fact, with their discussion about suture slippage, the authors mention valuable limitations of the graft–construct as a unit, exposing areas of future research and development.
      While this is an excellent, reproducible experimental model and the stated conclusion of “initial stiffness and ultimate loads are comparable” is completely valid, we urge the reader to closely examine Figure 4 and remember the biomechanical definitions we forgot shortly after passing orthopaedic boards: ultimate load is the load at which the construct failed whereas yield point is the load on the stress–strain curve at which a material transitions from elastic to plastic deformation.
      In the shoulder where the SCR, for example, is going to be repetitively loaded, it is potentially more meaningful to talk about the yield point to stay within the elastic range. If we are instead designing a system that is reliant on the plastic deformation zone, our material will elongate over time, thereby leading to significant inefficiencies or failures. As collagen fibrils elongate, the structure as a whole theoretically loses its crimped fibers and will therefore have compromised structural integrity.
      • Veres S.P.
      • Harrison J.M.
      • Lee J.M.
      Repeated subrupture overload causes progression of nanoscaled discrete plasticity damage in tendon collagen fibrils.
      What would be the consequence if a structural engineer designed a bridge based on the ultimate load and plastic deformation instead of respecting the yield point and staying within the elastic zone? Using this framework, native capsule and fascia lata allograft look completely different. The yield point for the fascia lata allograft (123.8 N ± 54.3 N) is approximately one-third the yield point of native capsular tissue (386.9 N ± 63.6 N), which is statistically significant (P = .030).
      Additionally, “initial” stiffness is not the entire story. While the slope of the 2 curves are almost identical over the first 2 millimeters, they diverge significantly over the remainder of the graft. It may help to compare the displacement for a given force within the elastic zone of both tissues. At 200 N, the fascia lata graft has almost twice the displacement compared with native tissue. At 250 N, it is almost 3 times the displacement. Since a modest change in the definition of “initial” from 2 to 4 mm, would alter the conclusion of the study, it may be worth pondering over the origin of the 2-mm definition and if this is reflective of displacement seen by the SCR in vivo.
      Importantly, the authors discuss the mode of failure. It seems the SCR allograft failed with the sutures slowly cutting through the allograft tissue, which may represent a limitation of the construct rather than the actual strength of the allograft tissue. If this is the case, perhaps a strategically placed stop stitch or modified Mason–Allen stitch could reinforce the allograft tissue and prevent suture cut through.
      • Castagna A.
      • Conti M.
      • Markopoulos N.
      • et al.
      Arthroscopic repair of rotator cuff tear with a modified Mason–Allen stitch: Mid-term clinical and ultrasound outcomes.
      Additionally, as a proof of concept, the 2 tissues could be directly tested (not part of a construct) to help us tease out the limitations of the construct versus the allograft tissue by itself. Alternatively, to control for the suture slippage phenomenon that may be contributing to the decreased construct stiffness, a similar study could replace the knotless anchors used in the current study with anchors that require knot tying.
      These points are not meant to criticize the authors or invalidate their stated conclusion; however, they seek to help the reader critically analyze the data, consider the definitions of various terms used to describe the properties of material, reflect on which parameters are potentially the most meaningful, and help plan for future studies to build upon our current knowledge.
      We congratulate Dr. Lee and his coauthors on another excellent manuscript as they continue to refine our knowledge on the biomechanical properties of SCR and graft selection. However, as with any good scientific study, it yields many more questions than answers for the orthopaedic community as we try to tackle the challenging clinical entity of irreparable rotator cuff tears. We just hope we don’t end up with a black eye now that we’re in the fight as well.

      Supplementary Data

      References

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        Superior capsule reconstruction to restore superior stability in irreparable rotator cuff tears: A biomechanical cadaveric study.
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        Fascia lata autograft versus human dermal allograft in arthroscopic superior capsular reconstruction for irreparable rotator cuff tears: A systematic review of clinical outcomes.
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