Graft Selection in Anterior Cruciate Ligament ?· Graft Selection in Anterior Cruciate Ligament Reconstruction…

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  • Graft Selection in AnteriorCruciate Ligament Reconstruction

    Robin V. West, MD, and Christopher D. Harner, MD

    Abstract

    Advances in surgical technique andrehabilitation have resulted inmarked improvement in the outcomeof anterior cruciate ligament (ACL)reconstruction over the past 10 years.Most recent series approach a 90%success rate in terms of restoration ofknee stability, patient satisfaction, andreturn to full athletic activity.1 The op-timal graft material remains contro-versial, regardless of the graft tissueselected. The graft should have struc-tural properties similar to those of thenative ACL; these properties shouldbe present at the time of graft implan-tation and persist throughout the in-corporation period. The ideal mate-rial also should allow secure fixation,permit rapid biologic incorporation,and limit donor site morbidity.

    The graft options available in-clude autograft and allograft tissue

    as well as synthetic ligaments. Au-tograft options include the patellar,hamstring, and quadriceps tendons(Fig. 1, A). Allograft choices consistof the quadriceps, patellar, Achilles,hamstring, and anterior and poste-rior tibialis tendons, as well as thefascia lata (Fig. 1, B). Patellar tendonautografts have been the most pop-ular graft choice because of theirstrength characteristics, ease of har-vest, rigid fixation, bone-to-bonehealing, and favorable clinical out-comes. However, donor site morbid-ity of patellar tendon autografts hasled to the investigation and use of al-ternative graft sources.

    Synthetic ligaments are classifiedas scaffolds, stents, or prostheses.The prototype is the carbon fiberscaffold ligament. The scaffold stim-ulates fibrous tissue ingrowth and

    contributes to the ultimate strengthof the new ligament. A stent, such asthe Kennedy ligament augmenta-tion device, supports and protectsautograft tissues during the healingphase, when the autogenous tissueis weakest. Examples of prostheticligament substances include poly-ethylene and Gore-Tex (W. L. Gore,Flagstaff, AZ).2

    In selecting a graft for ACL recon-struction, results of the preoperativeexamination, as well as patient age,activity level, and comorbidities,must be considered. Graft sources canbe compared on the basis of many cri-teria, including biomechanical prop-erties, biology of healing, ease of graftharvest, fixation strength, graft sitemorbidity, and return-to-play guide-lines (Table 1).

    Dr. West is Assistant Professor, Center for SportsMedicine, University of Pittsburgh Medical Cen-ter, Pittsburgh, PA. Dr. Harner is Blue Cross ofWestern Pennsylvania Professor and Director,Center for Sports Medicine, University of Pitts-burgh Medical Center, Pittsburgh.

    None of the following authors or the departmentswith which they are affiliated has received anythingof value from or owns stock in a commercial com-pany or institution related directly or indirectlyto the subject of this article: Dr. West and Dr.Harner.

    Reprint requests: Dr. Harner, Center for SportsMedicine, 3200 South Water Street, Pittsburgh,PA 15203.

    Copyright 2005 by the American Academy ofOrthopaedic Surgeons.

    The ideal graft for use in anterior cruciate ligament reconstruction should have struc-tural and biomechanical properties similar to those of the native ligament, permitsecure fixation and rapid biologic incorporation, and limit donor site morbidity. Manyoptions have been clinically successful, but the ideal graft remains controversial.Graft choice depends on surgeon experience and preference, tissue availability, pa-tient activity level, comorbidities, prior surgery, and patient preference. Patellar ten-don autograft, the most widely used graft source, appears to be associated with anincreased incidence of anterior knee pain compared with hamstring autograft. Useof hamstring autograft is increasing. Quadriceps tendon autograft is less popularbut has shown excellent clinical results with low morbidity. Improved sterilizationtechniques have led to increased safety and availability of allograft, although allograftshave a slower rate of incorporation than do most types of autograft. No graft hasclearly been shown to provide a faster return to play. However, in general, patellartendon autografts are preferable for high-performance athletes, and hamstring au-tografts and allografts have some relative advantages for lower-demand individu-als. No current indications exist for synthetic ligaments.

    J Am Acad Orthop Surg 2005;13:197-207

    Vol 13, No 3, May/June 2005 197

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  • Anatomy andBiomechanics of theNormal ACL

    The normal ACL functions as the pri-mary restraint to anterior translationof the tibia and as a secondary restraintto tibial rotation and varus or valgusstress.9,10 The native ACL has an av-erage cross-sectional area of 44 mm2,an ultimate tensile load of up to 2,160N, a stiffness of 242 N/mm, and astrain rate of 20% before failure.3,4,11

    The forces in the intact ACL range

    from 100 N during passive knee ex-tension to approximately 400 N onwalking and up to 1,700 N with cut-ting and acceleration-deceleration ac-tivities.6,12 The ACL experiences loadsexceeding its failure capacity only withunusual loading patterns on the knee.

    Biomechanical Propertiesof ACL Grafts

    The biomechanical properties of thevarious graft materials have been stud-

    ied extensively. In one early study,Noyes et al3 subjected human ligamentgraft tissues of varying sizes to high-strain-rate failure tests. To assess therelative strength of these grafts, theresults of the failure tests were com-pared with the mechanical propertiesof normal ACLs in young adults. Themean ultimate tensile strength andmean stiffness of the normal ACLswere 1,725 N and 182 N/mm, respec-tively. The bonepatellar tendonbonegraft (14 mm) had 168% the tensilestrength and almost four times the

    Figure 1 A, Autografts. Hamstring (top) and patellar (bottom) tendons. B, Allografts. Patellar (top) and Achilles (bottom) tendons.

    Table 1Comparison of Anterior Cruciate Ligament Graft Types

    Biomechanical Property

    GraftTensile

    load (N)Stiffness(N/mm)

    BiologicIncorporation

    Method ofFixation

    Graft SiteMorbidity

    Outcomes/Return to

    Play (months)

    Patellar tendonautograft3,4

    2,977 620 Bone-to-bonehealing (6 wks)

    Interferencescrew

    Anterior kneepain; larger

    incision

    4-6

    Quadruplesemitendinosus/gracilis5

    4,090 776 Soft-tissue healing(8-12 wks)

    Variable Hamstringweakness

    Increasedlaxity/6

    Patellar tendonallograft6

    Similar topatellar tendon

    autograft

    Similar topatellar tendon

    autograft

    Bone-to-bonehealing, slowincorporation

    (>6 mos)

    Interferencescrew

    None >6

    Quadricepstendon7,8

    2,352 463 Bone-to-boneand soft-tissue

    (6-12 wks)

    Variable Similar topatellar tendon

    autograft

    Limited data

    Graft Selection in Anterior Cruciate Ligament Reconstruction

    198 Journal of the American Academy of Orthopaedic Surgeons

    Scott J Sevinsky

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  • stiffness of the normal ACL. The semi-tendinosus and gracilis tendons pro-vided 70% and 49% of the reportedstrength of the normal ACL, respec-tively. The patellar tendon graft wasthe only one of those tested (of thegracilis tendon, semitendinosus ten-don, quadriceps tendon, fascia lata,iliotibial band) that was stronger thanthe normal ACL. Because the mechan-ical properties of the grafts are alteredduring incorporation into the hostbone, these results represent thestrength only at the time of initial im-plantation. Currently, the results of thegrafts tested have little clinical signif-icancebecausesingle-bundlehamstringand 14-mm patellar tendon grafts arerarely used. Smaller patellar tendongrafts (3.0 Mrad, which are nec-essary to kill viruses, have detrimen-tal effects on graft strength. Therefore,aseptic harvest and a cleaning processconsisting of antibiotic soaks, multi-ple cultures, and low-dose radiation(

  • of the normal ACL and stiffness to aslow as 13%.17 The final phase consistsof graft healing, with remodeling ofthe collagen structure into a more or-ganized pattern. As the graft heals, itsmechanical properties improve, butit never reaches the stiffness andstrength of the graft material at thetime of implantation.17

    Healing of the graft attachment sitemay be responsible for most of thegraft strength after transplantation.From a biologic standpoint, patellartendon grafts have the advantage ofbone-to-bone healing compared withsoft-tissue grafts. Bone-to-bone heal-ing is similar to fracture healing, andit is stronger and faster than soft-tissue healing. With bone-to-bonehealing, the graft can be healed to thehost bone within 6 weeks. Soft-tissuegrafts usually incorporate into thehost bone within 8 to 12 weeks.18

    Autografts and allografts undergoa similar process of incorporation, in-cluding graft necrosis, cellular repopu-lation, revascularization, and collagenremodeling. However, allografts havea slower rate of biologic incorpora-tion. Jackson et al19 compared the his-tologic and microvascular status of pa-tellar tendon autografts and allograftsin a goat model. At 6 weeks, the al-lografts demonst