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The anterior cruciate ligament: Chronicles of a legend

Open AccessPublished:March 14, 2023DOI:https://doi.org/10.1016/j.jisako.2023.02.002
      The anterior cruciate ligament (ACL) has remained an enigma for the past 100 years. Despite much research and discussion, opinions about this tiny structure continue to be divided and generate controversy. This issue of JISAKOS was conceived by the ISAKOS Knee Sports and Preservation Committee as a glimpse into the current understanding of ACL surgery philosophy and is dedicated to Professor Freddie Fu, who devoted his life to studying the ligament.
      The concept of “anatomic” ACL reconstruction (ACLR) pioneered by professor Fu is now widely accepted. The idea behind anatomic reconstruction is that the graft must be placed at the native anatomic insertion sites, have adequate collagen content and orientation to replicate kinematics, and preserve long-term knee health [
      • Fu F.H.
      • van Eck C.F.
      • Tashman S.
      • Irrgang J.J.
      • Moreland M.S.
      Anatomic anterior cruciate ligament reconstruction: a changing paradigm.
      ]. This concept was later refined to introduce the “individualized” ACL philosophy, which involves customising each ACLR regarding graft selection and diameter based on the patient's ACL footprint size, activity level, and lifestyle [
      • Hofbauer M.
      • Muller B.
      • Murawski C.D.
      • van Eck C.F.
      • Fu F.H.
      The concept of individualised anatomic anterior cruciate ligament (ACL) reconstruction.
      ]. However, the branding of all single-bundle ACL reconstructions as “anatomic” in all cases has been criticised, as the graft can still be placed at multiple locations within the anatomic boundaries of the footprint on the femur and tibia [
      • Borque K.A.
      • Laughlin M.S.
      • Pinheiro V.H.
      • Jones M.
      • Williams A.
      Rebranding the 'anatomic' ACL reconstruction: current concepts [published online ahead of print, 2022 Nov 23].
      ]. As a result, a one-size-fits-all approach has not been effective in ACL surgery and is no longer the standard of care. However, the “individualized anatomic” approach has also not yielded remarkable results, as evidenced by high rates of graft re-tear and poor rates of return to previous levels of sports or activity [
      • Gokeler A.
      • Grassi A.
      • Hoogeslag R.
      • van Houten A.
      • Lehman T.
      • Bolling C.
      • et al.
      Return to sports after ACL injury five years from now: 10 things we must do [published correction appears in J Exp Orthop. 2022 Nov 17;9(1):111].
      ].
      Double-bundle ACLR was once thought to be a solution to the shortcomings of a single-bundle ACLR in terms of rotational stability and functional outcomes [
      • Cha P.S.
      • Brucker P.U.
      • West R.V.
      • Zelle B.A.
      • Yagi M.
      • Kurosaka M.
      • et al.
      Arthroscopic double-bundle anterior cruciate ligament reconstruction: an anatomic approach.
      ]. However, this technique was ultimately found suitable and applicable only to a select group of patients [
      • Muller B.
      • Hofbauer M.
      • Wongcharoenwatana J.
      • Fu F.H.
      Indications and contraindications for double-bundle ACL reconstruction.
      ]. Extra-articular anterolateral procedures, such as an iliotibial band tenodesis or anterolateral ligament reconstruction, are now the new trend for select acute and chronic instability cases. Anterolateral complex injuries have been reported to occur in almost two-thirds of apparently isolated ACL tears [
      • Balendra G.
      • Willinger L.
      • Pai V.
      • Mitchell A.
      • Lee J.
      • Jones M.
      • et al.
      Anterolateral complex injuries occur in the majority of 'isolated' anterior cruciate ligament ruptures.
      ]. The two-year results of the STABILITY trial, which studied the effect of lateral extra-articular tenodesis (LET) on single-bundle hamstrings ACLR, yielded encouraging results. Those who underwent a LET had significantly lower graft re-tear rates and persistent rotatory laxity [
      • Getgood A.M.J.
      • Bryant D.M.
      • Litchfield R.
      • Heard M.
      • McCormack R.G.
      • Rezansoff A.
      • et al.
      Lateral extra-articular tenodesis reduces failure of hamstring tendon autograft anterior cruciate ligament reconstruction: 2-year outcomes from the STABILITY study randomized clinical trial.
      ]. Therefore, it is important to pay closer attention to this philosophy and technique, as it might impact ACL practice and research shortly.
      Besides anatomy, the role of biology in ACL surgery has also been a focus in recent years. Preserving the remnant during an ACLR has resulted in improved stability, although patient-reported outcomes are not superior [
      • Won S.H.
      • Lee B.I.
      • Park S.Y.
      • Min K.D.
      • Kim J.B.
      • Kwon S.W.
      • et al.
      Outcome differences of remnant- preserving versus non-preserving methods in arthroscopic anterior cruciate ligament reconstruction: a meta-analysis with subgroup analysis.
      ]. Another “blast from the past” besides the LET is the renewed interest in repairing femoral ACL tears with a dynamic augmentation device or a suture tape [
      • Hoogeslag R.A.G.
      • Huis In 't Veld R.
      • Brouwer R.W.
      • de Graaff F.
      • Verdonschot N.
      Acute anterior cruciate ligament rupture: repair or reconstruction? Five-year results of a randomized controlled clinical trial.
      ]. A significant limitation of this approach is that the practice currently is limited to a small number of authors and institutions, primarily confined to developed countries [
      • Li J.
      • Rothrauff B.
      • Chen S.
      • Zhao S.
      • Wu Z.
      • Chen Q.
      • et al.
      Trends in anterior cruciate ligament repair: a bibliometric and visualized analysis.
      ]. The best of both worlds is where the ACL remnant can be repaired while providing a biological augmentation using a small diameter graft [
      • Pardiwala D.N.
      • Lee D.
      Arthroscopic biological internal bracing with remnant repair for subacute ACL femoral avulsions [published online ahead of print, 2022 Nov 7].
      ]. Such a technique would preserve the native biology without relying entirely on suture repair, optimise cost, employ a more proven method for treating an ACL injury, and apply to a larger variety of tears.
      The use of technology in ACL surgery includes computerised navigation assistance and 3D printed templates and has been used to help place tunnels in the femur and tibia [
      • Zhu W.
      • Lu W.
      • Han Y.
      • Hui S.
      • Ou Y.
      • Peng L.
      • et al.
      Application of a computerised navigation technique to assist arthroscopic anterior cruciate ligament reconstruction.
      ,
      • Liu D.
      • Li Y.
      • Li T.
      • Yu Y.
      • Cai G.
      • Yang G.
      • et al.
      The use of a 3D-printed individualised navigation template to assist in the anatomical reconstruction surgery of the anterior cruciate ligament.
      ]. The use of wearable technology and intelligent knee braces promises to improve knee rehabilitation by enhancing compliance and targeting therapy based on specific deficits [
      • Marques J.B.
      • Auliffe S.M.
      • Thomson A.
      • Sideris V.
      • Santiago P.
      • Read P.J.
      The use of wearable technology as an assessment tool to identify between-limb differences during functional tasks following ACL reconstruction. A scoping review.
      ,
      • Riffitts M.
      • Cook H.
      • McClincy M.
      • Bell K.
      Evaluation of a smart knee brace for range of motion and velocity monitoring during rehabilitation exercises and an exergame.
      ]. However, such technology is still nascent and requires validation with currently accepted clinical criteria. Artificial intelligence (AI) can potentially be used for ACL injury prediction, diagnosis, intra-operative application and rehabilitation [
      • Corban J.
      • Lorange J.P.
      • Laverdiere C.
      • Khoury J.
      • Rachevsky G.
      • Burman M.
      • et al.
      Artificial intelligence in the management of anterior cruciate ligament injuries.
      ]. This is an enormous opportunity, the scale of which has yet to be fully understood. The ACL is indeed a living legend, that has espoused tremendous interest and is likely to hog the limelight in the foreseeable future.

      Source(s) of support

      Nil.

      Conflict of interest

      The authors declare the following financial interests/personal relationships that may be considered as potential competing interests:
      Chair, Knee Sports & Preservation, ISAKOS Associate Editor, Journal of ISAKOS Member, Newsletter Committee, ISAKOS Member, Publication Committee, ISAKOS

      Acknowledgment

      Nil.

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