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Graft Size Affects Graft Tension

      To the Editor:
      The recent review by Kirwan et al.
      • Kirwan G.W.
      • Bourke M.G.
      • Chipchase L.
      • Dalton P.A.
      • Russell T.G.
      Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction.
      entitled “Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction” has drawn our attention. First, we would like to compliment the authors on systematically assessing the literature to determine whether a particular initial graft tension results in a superior functional outcome of the knee after anterior cruciate ligament reconstruction (ACLR). Although initial graft tension has been proved to significantly contribute to the optimal functional outcome, there is a great variability in the amount of tension applied by surgeons during ACLR.
      • Kirwan G.W.
      • Bourke M.G.
      • Chipchase L.
      • Dalton P.A.
      • Russell T.G.
      Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction.
      That is why we very much appreciate the investigation and interest of Kirwan et al. in assessing the optimal initial graft tension applied during ACLR.
      A high initial tension of the graft may result in limited knee motion, tissue damage, and graft failure, whereas a lack of tension may lead to instability.
      • Kirwan G.W.
      • Bourke M.G.
      • Chipchase L.
      • Dalton P.A.
      • Russell T.G.
      Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction.
      Other important factors influencing clinical outcome after ACLR described by Kirwan et al.
      • Kirwan G.W.
      • Bourke M.G.
      • Chipchase L.
      • Dalton P.A.
      • Russell T.G.
      Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction.
      are graft choice, fixation technique, tunnel motion and placement, graft biologics, and postoperative rehabilitation. Unfortunately, they did not search for the effect of graft size on the optimal initial graft tension.
      In ACLR, especially when using hamstring tendons, large variations in the diameters of harvested ACL grafts are measured. We are unaware of any human, animal, or cadaveric trials that have evaluated the influence of graft diameter on the optimal initial tension and physical outcome after ACLR. A computer-based experiment indicated that even small changes in graft size resulted in large variation in joint stability of the knee and soft-tissue stresses.
      • Westermann R.W.
      • Wolf B.R.
      • Elkins J.M.
      Effect of ACL reconstruction graft size on simulated Lachman testing: A finite element analysis.
      Whether this impact of graft size affects clinical outcome is unknown. Hooke's law (F = kx) calculates the force (F) needed to stretch a structure by some distance (x), which is affected by a structure-dependent constant factor (k). This constant factor is directly proportional to the cross-sectional area of a structure.
      • Giuliodori M.R.
      • Lujan H.L.
      • Briggs W.S.
      • Palani G.
      • DiCarlo S.E.
      Hooke's law: Applications of a recurring principle.
      According to this law, a 6-mm-thick graft requires a different amount of traction than a 10-mm graft to obtain similar tension of the reconstructed ACL. Therefore we believe that graft size is another factor that is of importance to the outcome of ACLR and that graft diameter should be accounted for when assessing the optimal initial tension applied during graft fixation.
      To our surprise, none of the studies included in the systematic review accounted for graft size. Furthermore, we could not find any trials that specifically assessed the impact of graft size on the optimal initial tension. In our opinion, the conclusion of the review by Kirwan et al.
      • Kirwan G.W.
      • Bourke M.G.
      • Chipchase L.
      • Dalton P.A.
      • Russell T.G.
      Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction.
      of a trend toward an optimal initial graft tension of 78.5 to 90 N could not be drawn without any knowledge of the potential impact of the size of the graft. Therefore more research is required assessing the relation between graft size and initial graft tension and their combined effect on the outcome after ACLR. This will lead to a more optimal tension, which is hypothesized to positively affect clinical outcome and to further reduce the significant number of ACLR failures.
      • Middleton K.K.
      • Hamilton T.
      • Irrgang J.J.
      • Karlsson J.
      • Harner C.D.
      • Fu F.H.
      Anatomic anterior cruciate ligament (ACL) reconstruction: A global perspective. Part 1.

      References

        • Kirwan G.W.
        • Bourke M.G.
        • Chipchase L.
        • Dalton P.A.
        • Russell T.G.
        Initial graft tension and the effect on postoperative patient functional outcomes in anterior cruciate ligament reconstruction.
        Arthroscopy. 2013; 29: 934-941
        • Westermann R.W.
        • Wolf B.R.
        • Elkins J.M.
        Effect of ACL reconstruction graft size on simulated Lachman testing: A finite element analysis.
        Iowa Orthop J. 2013; 33: 70-77
        • Giuliodori M.R.
        • Lujan H.L.
        • Briggs W.S.
        • Palani G.
        • DiCarlo S.E.
        Hooke's law: Applications of a recurring principle.
        Adv Physiol Educ. 2009; 33: 293-296
        • Middleton K.K.
        • Hamilton T.
        • Irrgang J.J.
        • Karlsson J.
        • Harner C.D.
        • Fu F.H.
        Anatomic anterior cruciate ligament (ACL) reconstruction: A global perspective. Part 1.
        Knee Surg Sports Traumatol Arthrosc. 2014; 22: 1467-1482

      Linked Article

      • Initial Graft Tension and the Effect on Postoperative Patient Functional Outcomes in Anterior Cruciate Ligament Reconstruction
        ArthroscopyVol. 29Issue 5
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          The aim of this review was to investigate the effect of initial graft tension on patient-specific functional outcomes after anterior cruciate ligament reconstruction and determine whether a particular tension is associated with superior functional outcome.
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      • Author's Reply
        ArthroscopyVol. 30Issue 9
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          We would like to acknowledge the important contribution from Sorel and colleagues on this topic and thank them for their interest in our review. As discussed by Sorel et al., the correlation among graft size, graft tension, and patient outcomes has yet to be established in the literature. Indeed, the effect of either graft size or graft tension has received little attention. Our review focused specifically on graft tension and highlighted the lack consensus regarding optimal tension. The little work that has examined the effect of graft size on patient outcomes has conflicting results.
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