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Choosing a Knee-Ligament Graft
Note: This section addresses primarily the issue of graft choice for ACL reconstruction. However, many of the points germane to ACL-graft choice also apply to graft choice for reconstruction of other knee ligaments (e.g. PCL, LCL).
Please see also Evaluation of the Reconstructed Knee, Consequences of Details in Surgical Techniques, as well as Knee Biomechanics, Functional Anatomy of ACL and Other Ligaments.
For a brief overview of knee anatomy, physiology, and biomechanics, please click here.
For articles specifically addressing the topic of revision ACL reconstructions, please see Revision Reconstructions: Factors behind ACL-Graft Failures, Outcomes. Articles specific to patellar-tendon (PT) reconstructions can be found here. Articles specific to hamstring-tendon (HT or DLSTG) reconstructions can be found here. Articles specific to allografts can be found here.
For articles dealing with PCL grafting choices and biomechanical issues, please see PCL Injuries and Reconstructive Surgeries.
A 10-year Comparison of Anterior Cruciate Ligament Reconstructions with Hamstring Tendon and Patellar Tendon Autograft, Leo Pinczewski et al.; The American Journal of Sports Medicine, Baltimore; Preview March 2007. Comments: The deeply and penetratingly insightful article shows that both hamstring and patellar-tendon ACL reconstructions are good choices. But regardless of the method used, the 10-year ACL-reinjury and injury rate (i.e. rate of injury in both the affected [reconstructed] knee and the opposite [presumed never-injured] knee, combined) is something to keep in mind. The fifth paragraph under the Discussion section makes this clear: "The 10-year ACL reinjury rate, including graft ruptures and contralateral ACL injuries, was 22% for HT-graft-reconstructed knees and 30% for PT-reconstructed knees." This type of finding points strongly to lingering systemic concerns, for example the proprioceptive damage wrought by ACL injuries (e.g. tearing an ACL in one knee affects proprioception of the entire body, since the natural ACL contains tension-sensitive nerve endings which continuously send information to the brain; this function is lost if the ACL is torn, and is at best incompletely regained if the ACL is reconstructed, and now appears to be not regained at all in most people). It is also possible that people who incur ACL injuries are more ACL-injury-prone to begin with, perhaps due to certain biomechanical attributes or pre-existing vestibular-firmware attributes. This would also explain why people who tear an ACL in one knee are seemingly more prone to tearing the other ACL in the future. (Note: This preview-type article is provided as an Adobe PDF file. Adobe Acrobat Reader can be freely downloaded for all operating systems, including Microsoft Windows, Apple Macintosh, and all flavours of Unix/Linux, here.)
For insight into the biomechanical importance of thoroughly understanding the double-bundle (anteromedial and posterolateral) structure of the ACL, please see the February 2007 article The Role of the Anteromedial and Posterolateral Bundles of the Anterior Cruciate Ligament in Anterior Tibial Translation and Internal Rotation, by Thore Zantop et al., in the Knee Biomechanics, Functional Anatomy of ACL and Other Ligaments Subsection.
Biomechanical Evaluation of Two Techniques for Double-Bundle Anterior Cruciate Ligament Reconstruction -- One Tibial Tunnel Versus Two Tibial Tunnels, Wolf Petersen et al.; The American Journal of Sports Medicine, Baltimore; February 2007, Vol 35, p. 228-234. Comments: This study makes it clear that a dual-bundle (using a single femoral tunnel and two tibial tunnels) ACL graft is biomechanically superior to the traditional single-bundle ACL graft. Such a construct nicely duplicates the knee motion, particularly at and near full extension. Two other intriguing studies in this same vein are Chouliaras-AJSM-Feb07.shtml and Zantop-AJSM-Feb07.shtml. A double-bundle ACL reconstruction should be considered to be a modified installation procedure (i.e. two tibial tunnels instead of one) of the standard single-bundle graft, but the fundamental aspects and considerations pertinent to graft-source choice (e.g. patellar-tendon autograft versus hamstring/DLSTG autograft versus allograft) remain essentially the same. But because of the inherently increased complexity of double-bundle ACL grafting, the demands on the surgeon's skill are commensurately increased. In the future, widespread use of double-bundle ACL grafting should become more feasible as advanced technological tools enter the operating room. Given that the major cause of ACL-graft failure continues to be improper tunnel location (i.e. surgeon error), an ideal solution might entail having an automated electronic instrument that could scan a knee, then compute and indicate where the bone tunnels must be drilled. But for the meantime, traditional single-bundle grafting may be a safer choice simply because it brings less likelihood of surgeon error.
For a good discussion on the biomechanical shortfalls of the traditional single-bundle ACL graft, please see the superb February 2007 article Effectiveness of Reconstruction of the Anterior Cruciate Ligament With Quadrupled Hamstrings and Bone-Patellar Tendon-Bone Autografts -- An In Vivo Study Comparing Tibial Internal-External Rotation, by Vasileios Chouliaras et al., in the Knee Biomechanics, Functional Anatomy of ACL and Other Ligaments Subsection.
Two-bundle, four-tunnel anterior cruciate ligament reconstruction, Philippe Colombet et al.; Knee Surgery, Sports Traumatology, Arthroscopy; July 2006, Vol 14, p. 629-636. Comments: These authors found that ACL reconstruction via double-bundle grafting (with four tunnels, i.e. two in each bone) brings promising results. They cautiously note that their results are at least as good as other techniques, and note a trend towards better control of forwards tibial sliding (anterior drawer). Please note that, currently, only the hamstring-type graft is amenable to double-bundle grafting methods. (This article is cross-listed under ACL Reconstruction by Soft Tissue Autografts Section.)
Clinical Evaluation of Anatomic Double-Bundle Anterior Cruciate Ligament Reconstruction Procedure Using Hamstring Tendon Grafts: Comparisons Among 3 Different Procedures, Kazunori Yasuda et al.; KArthroscopy: The Journal of Arthroscopic & Related Surgery; March 2006, Vol 22(3), p. 240-251. Comments: These authors found that double-bundle ACL reconstruction brings substantially better results than single-bundle grafting. Keep in mind that there are two general graft-placement schools of thought: isometric (i.e. the bone tunnels are drilled in locations so that the graft will remain the same length throughout the knee range of motion) and anatomic (i.e. the bone tunnels are centered on the location of the original ACL stumps. (This article is cross-listed under the ACL Reconstruction by Soft Tissue Autografts Section.)
A Comparison of Bone–Patellar Tendon–Bone and Bone–Hamstring Tendon–Bone Autografts for Anterior Cruciate Ligament Reconstruction, Akio Matsumoto et al.; The American Journal of Sports Medicine, Baltimore; February 2006, Vol 34, p. 213-219. Comments: These authors looked at 72 patients who had either hamstring (BHB) or patellar-tendon (BPTB or simply BTB) grafting for ACL reconstruction. All reconstructions used the same fixation devices, thus controlling for this potential source of variation. They found that using the hamstring tendon as ACL-graft source avoids the problem of pain while kneeling (which is sometimes a problem with the patellar-tendon graft). But they also note that the hamstring graft brings problems such as persistent hamstring-group weakness. The authors additionally note that some of the problems noted with hamstring grafting can be attributed to the previously common use of outside-the-tunnel fixation devices, which led to the "bungee-cord" effect (i.e. the graft would move slightly inside the tunnel as it stretched elastically with each loading, thus preventing proper healing of graft to tunnel). The use of interference screws, as done for all patients in this study, addresses this concern. The minimum 5-year follow-up is good.
For a comprehensive overview of ACL-grafting techniques and pursuant considerations (including rehabilitation, graft ligamentization, potential problems, and other issues), please see the November 2005 article Clinical Sports Medicine Update: Treatment of Anterior Cruciate Ligament Injuries, Part 2, by Bruce Beynnon et al., in the ACL Reconstructions via Patellar-Tendon Autografts Subsection.
For a comprehensive overview of all the major considerations pertaining to treatment of ACL injuries (including discussions of the impact of concomitant injuries, including damage to other ligaments as well as to articular cartilage and menisci), please see the October 2005 article Clinical Sports Medicine Update: Treatment of Anterior Cruciate Ligament Injuries, Part I, by Bruce D. Beynnon et al., in the ACL Reconstructions via Patellar-Tendon Autografts (includes also Quadriceps Tendon Autografts) Subsection.
ACL Graft Choices, Dr. F.L. Avery; Orthopedic Associates of Portland, Maine. Comments: A well-written, scientifically-sound yet easy-to-read overview of current trends in ACL-graft choices.
Clinical Comparison of the Tutoplast Allograft and Autologous Patellar Tendon (Bone–Patellar Tendon–Bone) for the Reconstruction of the Anterior Cruciate Ligament: 2- and 6-Year Results, Ottmar Gorschewsky et al.; American Journal of Sports Medicine, Baltimore; August 2005, Vol 33, pages 1202-1209. Comments: The authors conclude that allografts are not the best choice for ACL reconstructions, especially for active people, given the comparatively high proclivity of allografts towards gradual stretching-out and subsequent failure (in comparison to autografts). They do note, however, that allografts are still a viable option for people with multiple, complex knee-ligament injuries. So, the graft of choice is still the patellar-tendon autograft.
Changes in Cross-Sectional Area of Hamstring Anterior Cruciate Ligament Grafts as a Function of Time Following Transplantation , Masayuki Hamada et al.; Arthroscopy, the Journal of Arthroscopy and Related Surgery; August 2005, Vol 21, pages 917-922. Comments: The authors found that the hamstring autograft increases encouragingly in cross-sectional area during the year after surgery. This provides tangible evidence that the ACL graft continues to ligamentize long after the typical formal-rehabilitation period of approximately 6 months. This is something to keep in mind when considering returning to knee-demanding sports. It is prudent to wait a year or longer, and to diligently continue physiotherapy and return-to-sports training (including sports-specific exercises and proprioceptive training, including plyometrics) during the latter half of the first postoperative year. (This article is cross-listed under the ACL Reconstruction by Soft Tissue Autografts Section.)
Graft Selection in Anterior Cruciate Ligament Reconstruction, Robin West and Christopher Harner; Journal of the American Academy of Orthopedic Surgeons; May/June 2005, Vol 13/3, pages 197-207. Comments: This article provides a plethora of excellent comments on graft selection, albeit given its publication date of May 2005, it might seem surprising that it overlooks a number of the most recent research studies in this realm. (One plausible explanation for this is that this paper was in preparation for many months; this would have resulted in some studies being published during the period of time between when the authors did their gathering of background research and the actual release of this article.) The section entitled "The Biology of Healing" is a must-read for anyone who is undergoing any type of ACL reconstruction, because it describes in good detail the various phases that all ACL grafts go through. For example, it notes that a graft first dies off (via avascular necrosis), reaching a strength of only 11% of a normal ACL. The longer revascularization of soft-tissue (e.g. hamstring/DLSTG) grafts is noted (as compared to patellar-tendon autografting), as is the very protracted ligamentization of allografts (cadaver grafts). The authors also note that patellar-tendon autografting is still the best choice of athletes and highly active people; it is also a good choice even for people who are not tremendously active. Hamstring autografting is considered to be not quite as good a choice if the person is very athletic; hamstring autografting brings the pronounced drawback of permanently hampered terminal knee flexion and permanent weakening of the hamstring group (remember that the hamstring group itself is important in protecting the ACL; this illustrates the very serious irony of harvesting hamstring tendons for ACL reconstruction). Also a must-read is the "Anterior Knee Pain" section, especially if you are concerned about pain while kneeling with the patellar-tendon autograft. Patellar-tendon autografting is renowned for its advantages of rapid and secure healing, characteristics which result from its having bone plugs at both ends. Allografting, as noted by subsequent authors (see, for example, Gorschewsky-AJSM-Aug05.shtml and Beynnon-AJSM-Oct05.shtml, both here in the Knee Library) is generally not considered to be the best choice (particularly for active people), given the higher risk of complications and graft failures (for which one cause is damage done or chemical residues left by allograft-disinfection procedures such as irradiation, chemical treatment, or cryogenic treatment), and also given the very protracted ligamentization period.
Clinical Sports Medicine Update -- Anterior Cruciate Ligament Reconstruction Autograft Choice: Bone-Tendon-Bone Versus Hamstring -- Does It Really Matter? A Systematic Review, Kurt P. Spindler et al., The American Journal of Sports Medicine, Baltimore; December 2004, Vol 32, p. 1986-1995. Comments: This exhaustive review of published research concludes that graft choice is not the primary factor in determing ACL-reconstruction success. It adds more fuel to the age-old patellar-tendon-versus-hamstring autograft debate (despite the generally accepted figures of 95% success rate for patellar-tendon and 90% success rate for hamstring autograft; see, for example, Noyes-AJSM-Jul97.shtml). Looking at the nuts-and-bolts biomechanics of ACL grafting, the patellar-tendon autograft has the undeniable and unique advantage of secure bone-to-bone healing (as a consequence of having bone plugs at both ends). Meanwhile, the hamstring autograft has the advantage of no discomfort while kneeling, but the drawback of rather high rates of bone-tunnel widening and other worrisome concerns. Another drawback of the hamstring autograft is that it compromises the strength of the hamstring group...an especially serious concern for females, given that females tend to have proportionally weak hamstrings to begin with. (Articles on the female proclivity to ACL injuries can be found here.) However, it should be kept in mind that hamstring-graft-anchorage methods have improved, thus alleviating the "bungee-cord effect" which plagued earlier hamstring-graft-anchorage schemes (i.e. the graft was anchored only at the ends of the tunnels furthest from the joint, thus allowing it to stretch along its entire length and therefore move inside the tunnel; this prevented proper healing). In the end, the choice of graft is something which the patient should make after having an in-depth discussion with his/her orthopedic surgeon.
Anterior Cruciate Ligament Reconstruction: Bone-Patellar Tendon-Bone Compared with Double Semitendinosus and Gracilis Tendon Grafts -- A Prospective, Randomized Clinical Trial, Paolo Aglietti et al.; Journal of Bone and Joint Surgery (American Volume); October 2004, Vol 86, p. 2143-2155. Comments: This study, involving 120 patients, compares the patellar-tendon and hamstring autografting methods. The authors concluded that both methods are valid, and that both methods have their advantages.
Reconstruction of the anterior cruciate ligament: Single versus double-bundle multistranded hamstring tendons, N. Adachi et al.; Journal of Bone and Joint Surgery, British Edition; May 2004, Volume 86-B, pages 515-520. Comments: These authors found that, despite that theoretical advantages of double-bundle ACL grafting, no clinical (i.e. measured functionally in real, live people) advantages could be found. However, it should be kept in mind that the biomechanical nuances of the human knee are quite difficult to measure in practice. No surgeon can detect, using manual-manipulation testing (e.g. Lachmann drawer test or the mechanical equivalent, the KT-1000/2000 arthrometer), whether the actual knee motion is that of a single-bundle ACL graft or a double-bundle one. But over the lifetime of a person, the biomechanical differences between a knee with a natural ACL and a reconstructed one show themselves in terms of accelerated wear to articular cartilage and menisci in the rebuilt knee. Such cartilage wear means osteoarthritis. (Note: ACL-injury-history knees also harbour a certain amount of irreversible damage from the initial injury event. This includes the aftermath of bone bruising and meniscal tearing.) Keep in mind that double-bundle grafting brings technical problems: it makes far greater demands on the surgeon's skill...and regular single-bundle ACL grafting is already very difficult for a surgeon to master. Evidence of this can be found in the fact that misplaced bone tunnels (i.e. surgeon error) are still the major cause of ACL-grafting failure. A correctly installed single-bundle ACL graft is much better than a poorly done double-bundle graft! (This article is cross-listed under ACL Reconstruction by Soft Tissue Autografts Section.)
A Five-Year Comparison of Patellar Tendon Versus Four-Strand Hamstring Tendon Autograft for Arthroscopic Reconstruction of the Anterior Cruciate Ligament, Leo A. Pinczewski et al.; American Journal of Sports Medicine, Baltimore; July 2002, Vol 30, pages 523-536. Comments: A superb and highly insightful study, accompanied by a penetratingly insightful discussion. With regards to being thorough in terms of controlling for the various factors germane to ACL-reconstruction outcome, and also with regards to having a sufficiently protracted follow-up time in the study (5 years is a reasonable minimum), the authors make the penetrating comment: "Despite the plethora of literature on ACL reconstruction, there are [as of early 2002] only three other scientifically valid reports that compare autograft patellar tendon with hamstring tendon graft constructs (Aglietti 1994, Marder 1991, and O'Neill 1996)... It would be inappropriate to extrapolate the results of one report to those of another unless account is taken of patient activity level, sex, age, timing of surgery, surgical technique, the rehabilitation program followed, and specific outcome measures." Using a 5-year follow-up, the authors found that patellar-tendon autografting and hamstring autografting bring similar results (despite the fact that the patellar-tendon autograft's bone plugs at both ends mean faster ligamentization). Regrettably, it seems that patellar-tendon autograft, in addition to resulting in pain while kneeling and lingering donor-site tenderness, can bring signs of osteopathic degeneration (in the tibiofemoral compartment) sooner than the hamstring autograft. However, it is worth keeping in mind that both options, by restoring knee stability, stop the damage that would be caused by regular giving-way and abnormal amounts of forwards tibial sliding. Granted, because of the bone-bruising and other damage which almost always tends to accompany full ACL tearing, any ACL-full-tearing knee will forever be more likely to develop premature osteoarthritis. But prompt reconstruction at least prevents further instability-induced damage. The reader should also keep in mind that hamstring autografting permanently reduces hamstring-group strength; this is worrisome because the hamstrings play a major role in protecting the ACL. Furthermore, the harvesting of the hamstring tendons results in a loss of terminal (end-range) flexion. (If you were to stand on one leg and pull your heel up towards your buttock, with a hamstring-type ACL graft you would no longer be able to pull your heel up as far. Although this active-range-of-motion deficit would not be overly noticeable in most activities, you would notice it if you were jumping over an obstacle.) In the end, there is no such thing as the perfect ACL graft; there is always a compromise to be made. Knee injuries are lifelong injuries; any person who incurs any type of complete (or severe partial) ACL tearing can expect to revisit the topic (or its aftermath) repeatedly as he/she subsequently progresses through life—irrespective of the reconstructive-surgery details. The authors observe that "the principal surgical determinants for outcome of ACL reconstruction are tunnel placement, graft choice, fixation choice, and type of postoperative rehabilitation program". (More comments are provided in the article.)
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