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Editorial Commentary: Managing Excessive Posterior Slope in Anterior Cruciate Ligament Reconstruction: Where Do We Draw the Line?

      Abstract

      When an anterior cruciate ligament (ACL) reconstruction fails, surgeons often rush to critique graft placement, graft choice, size, and fixation amongst other factors. One often-overlooked but important risk factor for noncontact failure of ACL reconstruction is tibial alignment. Although the deleterious effects of varus and valgus malalignment have been well established, recent research calls attention to excess posterior tibial slope as an underappreciated risk factor for failure of ACL reconstruction.
      The results of the article “Does Posterior Tibial Slope Affect Graft Rupture Following Anterior Cruciate Ligament Reconstruction?” by Lee, Youm, Cho, Jung, Bae, Park, and Kim
      • Lee C.C.
      • Youm Y.S.
      • Cho S.D.
      • et al.
      Does posterior tibial slope affect graft rupture following anterior cruciate ligament reconstruction?.
      suggest that when a patient's posterior tibial slope is in excess of 12°, surgeons should consider anterior closing wedge osteotomy to correct the slope before revision anterior cruciate ligament (ACL) reconstruction. Certainly, a technically challenging procedure that carries significant potential morbidity cannot be taken upon lightly leaving us to ask: where exactly does one draw the line when determining what degree of posterior tibial slope (PTS) is excessive? An equally important question is how to draw the line.
      A survey of available literature reveals that several different methods have been used to “draw the line” used to measure and report posterior tibial slope using radiograph versus computed tomography scan versus magnetic resonance imaging and using the medial versus the lateral tibial plateau.
      • Hashemi J.
      • Chandrashekar N.
      • Mansouri H.
      • et al.
      Shallow medial tibial plateau and steep medial and lateral tibial slopes: New risk factors for anterior cruciate ligament injuries.
      • Hudek R.
      • Fuchs B.
      • Regenfelder F.
      • Koch P.P.
      Is noncontact ACL injury associated with the posterior tibial and meniscal slope?.
      • Sonnery-Cottet B.
      • Archbold P.
      • Cucurulo T.
      • et al.
      It is not clear that there is a defined standard of measurement that makes comparing data difficult from study to study.
      • Wordeman S.C.
      • Quatman C.E.
      • Kaeding C.C.
      • Hewett T.E.
      In vivo evidence for tibial plateau slope as a risk factor for anterior cruciate ligament injury: A systematic review and meta-analysis.
      Furthermore, we are limited by the quality and reproducibility of the images even with more advanced technology such as magnetic resonance imaging.
      • Weingberg D.S.
      • Willamson D.F.
      • Gebhart J.J.
      • Knapik D.M.
      • Voos J.E.
      Differences in medial and lateral posterior tibial slope: An osteological review of 1090 tibiae comparing age, sex, and race.
      Despite these limitations, it would be foolhardy to overlook the trend of increased PTS placing increased strain on ACL grafts, as several biomechanical studies have shown.
      • Fening S.D.
      • Kovacic J.
      • Kambic H.
      • et al.
      The effects of modified posterior tibial slope on anterior cruciate ligament strain and knee kinematics: A human cadaveric study.
      • Shelburne K.B.
      • Kim H.J.
      • Sterett W.I.
      • Pandy M.G.
      Effect of posterior tibial slope on knee biomechanics during functional activity.
      • Giffin J.R.
      • Vogrin T.M.
      • Zantop T.
      • Woo S.L.
      • Harner C.D.
      Effects of increasing tibial slope on the biomechanics of the knee.
      • Marouane H.
      • Shirazi-Adl A.
      • Adouni M.
      • Hashemi J.
      Steeper posterior tibial slope markedly increases ACL force in both active gait and passive knee joint under compression.
      In concordance with the findings of Lee et al., there are both retrospective and prospective studies to support the “12 degree rule” as a significant risk factor negatively affecting survival of ACL reconstruction.
      • Ahmed I.
      • Salmon L.
      • Roe J.
      • Pinczewski L.
      The long-term clinical and radiological outcomes in patients who suffer recurrent injuries to the anterior cruciate ligament after reconstruction.
      • Webb J.M.
      • Salmon L.J.
      • Leclerc E.
      • Pinczewski L.A.
      • Roe J.P.
      Posterior tibial slope and further anterior cruciate ligament injuries in the anterior cruciate ligament-reconstructed patient.
      • Salmon L.J.
      • Heath E.
      • Akrawi H.
      • Roe J.P.
      • Linklater J.
      • Pinczewski L.A.
      20-year outcomes of anterior cruciate ligament reconstruction with hamstring tendon autograft: The catastrophic effect of age and posterior tibial slope.
      Furthermore, there are case series supporting the use of osteotomy in cases of failed ACL revision in patients with PTS over 12°.
      • Dejour D.
      • Saffarini M.
      • Demey G.
      • Baverel L.
      Tibial slope correction combined with second revision ACL produces good knee stability and reduces graft rupture.
      • Sonnery-Cottet B.
      • Mogos S.
      • Thaunat M.
      • et al.
      Proximal tibial anterior closing wedge osteotomy in repeat revision of anterior cruciate ligament reconstruction.
      Perhaps the most tried and true and clinical evidence comes from the experience of our beloved canine companions who have long been well treated for ACL tear not with anatomic ligament reconstruction, but with osteotomy to reduce PTS.
      Meta-analysis and systematic review data reinforce what the conscientious ACL surgeon already knows; that failure of ACL reconstruction is multifactorial.
      • Feucht M.J.
      • Mauro C.S.
      • Brucker P.U.
      • Imhoff A.B.
      • Hinterwimmer S.
      The role of the tibial slope in sustaining and treating anterior cruciate ligament injuries.
      • Di Benedetto P.
      • Di Benedetto E.
      • Fiocchi A.
      • Beltrame A.
      • Causero A.
      Causes of failure of anterior cruciate ligament reconstruction and revision surgical strategies.
      Many of the studies are hampered by techniques used in the initial ACL reconstruction that could be criticized as suboptimal such as nonanatomic reconstruction, use of allograft in younger/active population, and use of a graft less than 8 mm in diameter. So, given all available information, where will you draw the line? Does a PTS of 12° justify corrective osteotomy? What if moving the electronically generated line a pixel or two drops slope to 11°? Challenging questions indeed!
      Personally, the work of Lee et al. serves as a poignant reminder of the value of well-performed weight-bearing radiographs in the evaluation of the failed ACL reconstruction. At some point, a patient with a failed ACL reconstruction despite the use of an anatomic technique with appropriate graft choice and fixation will walk into your office. When this occurs, take a few extra minutes to critically evaluate the patient's PTS and perhaps compare it with those of your successful ACL reconstructions in search of outliers. We may not have all the answers to the difficult questions, but should nonetheless remain cognizant of PTS when treating patients with ACL injury. The evaluation of PTS in a failed ACL reconstruction is not just for the dogs.

      Supplementary Data

      References

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        Posterior tibial slope and further anterior cruciate ligament injuries in the anterior cruciate ligament-reconstructed patient.
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        • Roe J.P.
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        • Pinczewski L.A.
        20-year outcomes of anterior cruciate ligament reconstruction with hamstring tendon autograft: The catastrophic effect of age and posterior tibial slope.
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        Tibial slope correction combined with second revision ACL produces good knee stability and reduces graft rupture.
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        • Beltrame A.
        • Causero A.
        Causes of failure of anterior cruciate ligament reconstruction and revision surgical strategies.
        Knee Surg Relat Res. 2016; 4: 319-324

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