Frequently asked questions
Below are answers to some of the questions frequently asked about LARS ligaments. A particular focus is given to ACL reconstructions, one of the most common applications.
- How long have LARS ligaments been available?
- What data does LARS have regarding ACL reconstruction?
- Aren’t all synthetic ligaments the same? I have had previous failures with other PET, PP, PTFE or carbon fibre ligaments.
- Is the technique for reconstruction using a LARS ACL ligament the same as for an autograft?
- Do LARS ACL ligaments cause synovitis?
- Do LARS ACL ligaments increase the risk of early onset osteoarthritis?
- What is the failure rate for the LARS ACL ligament and how does this compare with hamstring and patella tendon failure rates?
- One study produced high failure rates – this seems to be at odds with the rest of the data, what happened?
- What other complications arise with LARS and how do these compare with autografts?
1. How long have LARS ligaments been available?
Commercially available since 1992, LARS ligaments have been in use in countries such as the UK, France, Germany, Canada and Australia. Regulatory approval has been granted for LARS use in all countries where it has been sought. In countries where LARS is not available (e.g. the USA), it is because Corin has not yet commenced the often complex and costly regulatory procedures to secure approval in that country.
2. What data does LARS have regarding ACL reconstruction?
There are currently 22 published papers regarding LARS use in knee ligament reconstruction, with the bulk of these being in ACL and PCL. The 22 peer-reviewed studies/case series include one randomised controlled trial (level I evidence), three retrospective comparative studies (level III evidence), eleven case series (level IV evidence) and seven expert reviews (level V evidence). Many more congress abstracts and non-peer reviewed online papers are available. Each of these studies, with the exception of the Gäbler study1, observed excellent functional outcomes, minimal complications and high levels of patient satisfaction after a follow-up period of up to five years.
In addition, nine-year unpublished data on LARS has been presented at various congresses. While there is a lack of published long-term data for LARS ligaments, research is continuing.
Please contact Corin’s LARS product management team for more information on LARS published and unpublished data.
3. Aren’t all synthetic ligaments the same? I have had previous failures with other polyethylene terephthalate (PET), polypropylene (PP), polytetrafluoroethene (PTFE) or carbon fibre ligaments.
All synthetic ligaments are not created equal. They are designed for different purposes, with different materials and different structures. A ligament for permanent replacement of the ACL will have no requirement for in-growth of ACL tissue and must take the full load of a normal ACL2,3,4,5,6. A scaffold ligament however, will require porous fibres for fibroblastic in-growth and its function will eventually be overtaken by the newly formed collagen2,3,4,5,6. With this in mind, a valid like-for-like comparison cannot be made between different types of synthetic ligaments.
The same can be said for comparing synthetic ligaments of different structures and materials. Due to the differing material properties, it cannot be said that a ligament made from PET, with the same structure as a ligament made from PTFE, will perform in a similar manner with regards to mechanical performance or biocompatibility3,5,6. LARS is made from PET and is the only synthetic ligament to have undergone a vigorous torsion/flexion-extension fatigue test7.
Even within a particular material, structural differences will have a huge impact on the wear resistance, porosity and fibroblastic in-growth potential of a synthetic ligament8,9. LARS incorporates a patented ‘pre-twisted parallel fibre’ design, unique to its philosophy and different from previous synthetic ligament designs. An independent in-house study, performed by the Institute National de Researche Appliquèe (INRA), in France, confirmed braided and woven ligaments are far more susceptible to wear from the natural torsion in the ACL during knee movement 8,9 when compared with a ‘pre-twisted parallel fibre’ design.
Indeed, even the treatment of synthetic fibres post-manufacture can affect fibroblastic in-growth. LARS is chemically treated to remove an emulsion of fat enzymes that are used as a process aid during the carding and spinning of the strands which constitute the synthetic fibre. This emulsion can provoke pathological reactions in-vivo, such as synovitis and immuno-responses. This unique and thorough treatment of PET fibres is pivotal in the success of healing ACL tissue. This process has been shown to have great effect on fibroblastic proliferation surrounding the synthetic filaments, increasing fibroblastic growth by greater than 20 fold8,9. In side-by-side comparison in the laboratory, LARS ligaments supported over three times the fibroblastic culture of other previously-used PET ligaments8,9.
4. Is the technique for reconstruction using a LARS ACL ligament the same as for an autograft?
The technique for successful LARS ligament implantation is dependent upon the following criteria:
i. The ligament should not be over-tensioned, should be positioned appropriately and range of motion should be checked before fixation.
Over-tensioning an implanted ligament, either synthetic or autogenous, can reduce range of motion in the knee10. Overtightening will not only increase the likelihood of premature failure, but can result in excessive compressive forces on the knee, accelerating often pre-existing arthritic changes. Over-tightening of the LARS ligament will also take mechanical load from the ACL, leading to stress shielding and a neoligament of poor tissue quality.
It is important to ensure that the ligament will have minimal demand for elasticity during movement; the aim being to minimise fatigue. The avoidance of intra-articular elongation, by considering the functional anatomy of the knee8, will lead to a longer lifespan.
Correct positioning of the free fibres within the joint will also decrease the risk of wear8. By ensuring that the free fibres are unhindered in the intra-articular space and by positioning the woven intra-osseous section 1-2mm into the intra-articular space, shearing forces on free fibres will be reduced.
ii. A viable ACL stump.
The ACL has the potential for cell proliferation and healing12,13,14,15,16,17,18. Studies have demonstrated that the placement of a substitute provisional scaffold in the wound site of the ACL injury initiates healing of the ruptured ligament after primary repair15. Retaining the native ACL has many other potential advantages, such as preserving the complex ACL attachments and innervation of these structures, thereby retaining the mechano-receptive and proprioceptive function of these tissues15,19,20,21, even up to 42 months after injury22. Yu et al23 reported good fibrotic tissue in-growth where the LARS ligament was covered by sufficient ACL stump in rabbits. Seitz et al24 showed fibroblastic in-vivo in-growth into PET ligaments after implantation in sheep. Gao et al25 also demonstrated native tissue encapsulation in three patients when LARS ligaments were revised.
Overlooking any of these key criteria can greatly reduce the probability for a successful LARS graft.
5. Do LARS ACL ligaments cause synovitis?
The ACL is subject not only to extension and contraction, but also to shearing and torsion. The presence of transverse fibres when ligaments are subjected to torsion may create free micro-particles, or wear particles. Most early synthetic ligaments were either braided or woven in the intra-articular region; by the nature of their construction these were not designed to cope with such forces and therefore produced wear particles. It has been hypothesised that this is the primary mechanism for synovitis in the knee with synthetic ligaments23,26,27. This is believed to be due to the formation of free micro-particles during the normal motion of the knee.
The LARS ligament is designed to have free longitudinal fibres in the intra-articular portion of the knee to minimise these shearing forces. In addition, LARS ligaments should be aligned so that 1-2mm of woven (intra-osseous) section should be visible from the end of the femoral tunnel. This placement protects the free fibres from shearing without compromising functionality in movement.
To date, only one patient in one study has shown an incidence of synovitis. Gao et al25 reported that one of three patients who had a reported rupture, in 159 cases, demonstrated development of synovitis at three to five years. This can be contrasted against many other synthetic ligaments and their documented increased rates of synovitis, previously reported to be as high as 48%28,29,30.
6. Do LARS ACL ligaments increase the risk of early onset osteoarthritis?
Early onset osteoarthritis has been associated with ACL reconstruction, regardless of the nature of the graft, for quite some time31,32.
Rates of radiographically observed osteoarthritis in ACL reconstructed knees with autografts vary widely and in some studies are reported to be in excess of 70%33,34. In fact it has been noted that the reconstruction of the ACL did not appear to provide protection from degenerative change in the knee and high levels of osteoarthritis occur regardless of whether surgical intervention is undertaken.
Some authors have tried to demonstrate a relationship between the body’s inflammatory response to synthetic ligament wear particles and osteoarthritis35. Olsen26 evaluated the effects of injecting wear particles from six different types of ligaments, diluted in saline, into rabbit knees and found the results to be dependent on dose and particle size. He also noted that surgical technique needed to be evaluated. Although two of the ligaments were PET-based, neither shared similar design characteristics (woven vs free fibres) with the LARS ligament.
Some older generation synthetic ligaments have shown increased rates of osteoarthritis. Ventura36 showed a rate of osteoarthritis of 100% when using the Trevira ligament. The Ventura study however, differed from LARS implantation in a number of ways:
- The Trevira ligament is a woven PET design
- The Trevira ligament does not undergo the same chemical treatment before implantation
- The Trevira ligament was used either as a permanent replacement for the ACL or as an augment to an autograft as opposed to a scaffold
- There was a likely absence of a sufficient ACL stump (all chronic cases) and subsequent in-growth
To date, no reports of increased rates of osteoarthritis have been described specifically after using a LARS ligament.
7. What is the failure rate for the LARS ACL ligament and how does this compare with hamstring and patella tendon failure rates?
Hamstring and patella autograft failure rates vary – recent meta-analyses demonstrate that ACL reconstructions can deliver good to excellent results in as low as 60% and in as high as 95% of patients37,38,39. Shen et al40 also stated “as many as 20% to 30% of athletes fail to achieve their previous level of performance, suggesting that there is room for improvement” with traditional hamstrings and patella tendon reconstructions.
A number of studies reported very low failure rates for the LARS ligament in ACL reconstruction. Gao et al25 reported 94% (146/156) of patients had good to excellent results at three to five years follow-up. Huang et al41 reported 95% (41/43) of patients had good to excellent results at 10-49 months follow-up. Liu et al42 reported 93% (26/28) of patients had good to excellent results at greater than four years follow-up. Cerulli et al43 reported positive results in greater than 95% (24/25) at five year follow-up by an independent examiner. Nau et al44 reported 4% (1/26) failure in the LARS arm of his comparative study.
This is in contrast with other synthetic ligament designs over a similar follow-up period. Richmond et al45 and Barrett et al46 reported failure rates of 37.1% and 47.5% respectively in studies of Dacron reconstructions with mean long-term follow-ups of 50 and 48 months. Likewise, Schroven et al47 reported failure rates of 47.1% at five years follow-up and Dandy et al48 reported 40% of patients had an unsatisfactory outcome six years after reconstruction with Leeds-Keio ligaments.
8. One study produced high failure rates – this seems to be at odds with the rest of the data, what happened?
Gäbler et al1 reported a revision rate of 42% and post-operative problems of 69% in his study of 26 patients. The author cited a number of issues in this study including use by nine different surgeons, with varying levels of ACL experience and expertise (from 1 to 40 ACL reconstructions per year).
Furthermore, technique issues were also highlighted in the study. Despite quoting that procedures were performed in accordance with LARS recommended methods which specify no ligament over-tensioning and fixation in full extension10,11; the tibial fixation was made under manual tension and in 20° flexion. There is a possibility that this fixation technique could have increased the tensile stress on the ligament and may have led to an over-constrained knee, thereby resulting in premature failure or poor subjective results.
9. What other complications arise with LARS and how do these compare with autografts?
As with autografts, allografts and other synthetic ligaments, some complications with LARS ligaments have been reported. The most common complications have been loosening of femoral or tibial screws and associated pain, limited flexion and/or extension, rupture and superficial infection10,25,41,42,44. With the exception of Gäbler’s study1, reports of these complications have been remarkably low.
High levels of ligament laxity (69% had >5mm Lachmann) has been reported in LARS patients in a study by Lavoie et al49. Patients in this study reported high levels of satisfaction and no obvious ruptures were noted by the observers. Other studies have reported that where marked laxity was observed, readjustment of femoral or tibial fixation resolved laxity issues25,41,44. The LARS group has also demonstrated significantly less anterior displacement than the four-strand hamstring graft in the study by Liu et al42.
In comparison, patella tendon autograft recipients have been reported to experience anterior knee pain, extensor mechanism deficits, loss of sensitivity and the loss of extension50. Hamstring graft recipients often experience loss of knee flexor strength, rotational strength, increased laxity, habitual muscle injuries and weak re-grown hamstring tendons51,52,53,54.
Regardless of graft type, a degree of morbidity can be seen following autograft harvest which can affect recovery after ACL reconstruction55,56,57. Over the longer term, Von Porat demonstrated that ACL rupture, whether treated surgically or not, is clearly associated with an increase in osteoarthritis34.
References:
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2. Freeman JW, Kwansa AL. Recent advancements in ligament tissue engineering: the use of various techniques and materials for ACL repair. Recent Patents on Biomedical Engineering, 2008;1(1).
3. Mascarenhas R, MacDonald PB. Anterior cruciate ligament reconstruction: a look at prosthetics – past, present and possible future. McGill Journal of Medicine, 2008;11(1):29-37.
4. Chen J, Xu J, Wang A, Zheng M. Scaffolds for tendon and ligament repair: review of the efficiency of commercial products. Expert Review Medical Devices, 2009;6(1):61-73.
5. Bernardino S. ACL prosthesis: any promise for the future? Knee Surgergery Sports Traumatology Arthroscopy, 2010;18:797-804
6. Legnani C, Ventura A, Terzaghi C, Borgo E, Albisetti W. Anterior cruciate ligament reconstruction with synthetic grafts. A review of literature. International Orthopaedics (SICOT), 2010;34:465-471.
7. Data on file, Corin Group PLC.
8. Institut National de Recherche Appliquée (INRA). Testing (LARS Brochure).
9. Laboureau JP. The concept of S.T.I.F. – soft tissue internal fixation. Presentation held Intercontinental Hotel, Sydney. March 2008. Video and presentation available.
10. Dericks G. Ligament advanced reinforcement system anterior cruciate ligament reconstruction. Operative Techniques in Sports Medicine, 1995;3(3):187-205.
11. Laboureau JP, Marnat-Perrichet F. Isometric reconstruction of the anterior cruciate ligament: femoral and tibial tunnel placement. Yahia LH, eds. Ligaments and ligamentoplasties. Berlin: Springer-Verlag; 1997: 209-225.
12. Woo SL, Vogrin TM, Abramowitch SD. Healing and repair of ligament injuries in the knee. Journal of the American Academy of Orthopaedic Surgeons, 2000;8:364-372.
13. Murray MM, Spector M. Fibroblast distribution in the anteromedial bundle of the human anterior cruciate ligament: the presence of alpha-smooth muscle actin-positive cells. Journal of Orthopaedic Research, 1999;17:18-27.
14. Murray MM, Martin SD, Spector M. Migration of cells from human anterior cruciate ligament explants into collagen-glycosaminoglycan regeneration templates in vitro. Biomaterials, 2000;22:2293-2402.
15. Murray MM, Current status and potential for primary ACL repair. Clinical Sports Medicine, 2009 Jan;28(1):51-61.
16. Murray MM, Spindler KP, Ballard P, Welch TP, Zurakowski D, Nanney LB. Enhanced histologic repair in a central wound in the anterior cruciate ligament with a collagen–platelet-rich plasma scaffold. Published online 5 April 2007 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jor.20367.
17. Steiner ME, Murray MM, Rodeo SA. Strategies to improve anterior cruciate ligament healing and graft placement. American Journal of Sports Medicine, 36(1):176-189.
18. Spindler KP, Murray MM, Devin C, Nanney LB, Davidson JM. The central ACL defect as a model for failure of intra-articular healing. Published online 6 January 2006 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jor.20074.
19. Denti M, Monteleone M, Berardi A, Panni AS. Anterior cruciate ligament mechanoreceptors. Clinical Orthopaedics and Related Research, 1994;308:29-32.
20. Georgoulis AD, Pappa L, Moebius U et al. The presence of proprioceptive mechanoreceptors in the remnants of ruptured ACL as possible source of reinnervation of the ACL autograft. The Knee, 2001;9(6):364-368.
21. Ochi M, Iwasa J, Uchio Y et al. The regeneration of sensory neurons in the reconstruction of the anterior cruciate ligament. Journal of Bone and Joint Surgery [Br]. 1999;81(5):902-906.
22. Dhillon MS, Bali K, Vasistha. Immunohistological evaluation of proprioceptive potential of the residual stump of injured anterior cruciate ligaments (ACL). International Orthopaedics (SICOT), 2010;34:737-741.
23. Yu SB, Dong QR, Wang YB, Zuo ZN, Li DG. Histological characteristics and ultrastructure of polyethylene terephthalate LARS ligament following the reconstruction of anterior cruciate ligament in rabbits. Zhongguo Zuzhi Gongcheng Yanjiu yu Linchuang Kangfu, 2008;12(36):7061-7066.
24. Seitz H, Menth-Chiari WA, Lang S, Nau T. Histological evaluation of the healing potential of the anterior cruciate ligament by means of augmented and non-augmented repair: an in vivo animal study. Knee Surgery, Sports Traumatology Arthroscopy, 2008;16:1087-1093.
25. Gao et al. Anterior cruciate ligament reconstruction with LARS artificial ligament: a multicentre study with 3 to 5 year follow up. Arthroscopy: The Journal of Arthroscopic and Related Surgery, 2010;26(4):515-523.
26. Olsen EJ, Kang JD, Fu FH, Georgescu HI, Mason GC, Evans CH. The biochemical and histological effects of artificial wear particles: in vitro and in vivo studies. American Journal of Sports Medicine, 1988;16(6):558-570.
27. Lopez-Vazquez E, Juan JA, Vila E, Debon J, Reconstruction of the anterior cruciate ligament with a Dacron prosthesis. Journal of Bone and Joint Surgery, 1991;73(9):1294-1300.
28. Barry M, Thomas SM, Rees A, Shafighian B, Mowbray MAS. Histological changes associated with an artificial anterior cruciate ligament. Journal of Clinical Pathology. 1995;48:556-559.
29. Macnicol M, Penny I, Sheppard L. Early results of the Leeds-Keio anterior cruciate ligament replacement. Journal of Joint and Bone Surgery, 1991;73(B):377-380.
30. Klein W, Jensen K-U. Synovitis and artificial ligaments. Arthroscopy: The Journal of Arthroscopic and Related Surgery, 1992;8(1):116-124.
31. Feller JA. Graft choices for anterior cruciate ligament reconstruction. Cited Sept 2010, on: www.isakos.com/assets/innovations/Feller.Graft%20selection%20for%20ACL%20Reconstruction.pdf.
32. Øiestad BE, Holm I, Engebretsen L, Risberg MA. The association between radiographic knee osteoarthritis and knee symptoms, function and quality of life 10-15 years after anterior cruciate ligament reconstruction. British Journal of Sports Medicine, 2010 Aug;16 (epub ahead of print).
33. Pinczewski LA, Lyman J, Salmon LJ, Russell VJ, Roe J, Linklater J. A 10 year comparison of anterior cruciate ligament reconstructions with hamstring tendon and patella tendon autograft: a controlled, prospective trial. American Journal of Sports Medicine, 2007 Apr;35(4):564-574.
34. Von Porat A, Roos EM, Roos H. High prevalence of osteoarthritis 14 years after an anterior cruciate ligament tear in male soccer players: a study of radiographic and patient relevant outcomes; Annals of Rheumatic Disease, 2004;63:269-273.
35. Maletius W, Gillquist J. Long term results of anterior cruciate ligament reconstruction with a Dacron prosthesis. The frequency of osteoarthritis after seven to eleven years. American Journal of Sports Medicine, 1997;25:288-293.
36. Ventura A, Terzaghi C, Legnani C, Borgo E, Albisetti W. Synthetic grafts for anterior cruciate ligament rupture: 19 year outcome study. The Knee, 2010;17-2:108-113.
37. Biau DJ, Tournoux C, Katsahian S, Schranz PJ, Nizard RS. Bone-patella tendon-bone autografts versus hamstring autografts for reconstruction of anterior cruciate ligament: meta-analysis. Boston Medical Journal 2006;332:995-1001.
38. Poolman RW, Farrokhyarb F, Bhandarib M. Hamstring tendon autograft better than bone patella tendon bone autograft in ACL reconstruction. A cumulative meta-analysis and clinically relevant sensitivity analysis applied to a previously published analysis. Acta Orthopaedica, 2007;78(3):350-354.
39. Carey JL, Dunn WR, Dahm DL, Zeger SL, Spindler KP. A systematic review of anterior cruciate ligament reconstruction with autograft compared with allograft. Journal of Bone and Joint Surgery [Am], 2009;91:2242.
40. Shen W, Forsythe B, McNeill Ingham S, Honkamp NJ, Fu FH. Application of the anatomic double-bundle reconstruction concept to revision and augmentation anterior cruciate ligament surgeries. Journal of Bone and Joint Surgery [Am], 2008;90:20-34.
41. Huang JM, Wang Q, Wang ZM, Kang YF. Cruciate ligament reconstruction using the LARS artificial for reconstruction using LARS artificial ligaments under arthroscopy: 81 cases report. Chinese Medical Journal, 2010;123(2):160-164.
42. Lui ZT, Zhang XL, Jiang Y. Four-strand hamstring tendon autograft versus LARS artificial ligament for anterior cruciate ligament reconstruction. International Orthopaedics, 2010;34(1):45-49.
43. Cerulli G, Caraffa A, Antenucci R, Antinolfi P. Il legamento artificiale. Giornale Italiano di Ortopedia e Traumatologia, 2007;33(1):238-242.
44. Nau T, Lavoie P, Duval N. A new generation of artificial ligaments in reconstruction of the anterior cruciate ligament. Journal of Joint and Bone Surgery, 2002;84(B):356-360.
45. Richmond JC, Manseau CJ, Patz R, McConville O, Anterior cruciate reconstruction using a Dacron ligament prosthesis. A long-term study. American Journal of Sports Medicine, 1992;20(1):24-28.
46. Barrat GR, Lawrence L Jr, Shelton WR, Manning JO, Phelps R. The Dacron ligament prosthesis in anterior cruciate ligament reconstruction. A four-year review. American Journal of Sports Medicine, 1993;21(3):367-373.
47. Schroven ITJ, St. Geens, Beckers L, Lagrange W, Fabry G. Experience with the Leeds-Keio artificial ligament for anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy, 1994;2:214-218.
48. Dandy DJ, Gray AJ. Anterior cruciate ligament reconstruction with the Leeds-Keio prosthesis plus extra-articular tenodesis. Results after six years. Journal of Bone and Joint Surgery – [Br], 1994:76B(2):193-197.
49. Lavoie P, Fletcher J, Duval N. Patient satisfaction as related to knee stability and objective findings after ACL reconstruction using the LARS artificial ligament. The Knee, 2000;7:157-163.
50. Busam ML, Provencher MT, Bach BR. Complications of anterior cruciate ligament reconstruction with bone-patellar tendon-bone constructs: Care and prevention. American Journal of Sports Medicine, 2008;36:379-394.
51. Armour T, Forwell L, Litchfield R, Kirkley A, Amendola N, Fowler PJ. Isokinetic evaluation of internal/external tibial rotation strength after the use of hamstring tendons for anterior cruciate ligament reconstruction. American Journal of Sports Medicine, 2004;32:1639-1643.
52. Elminger BS, Nyland JA, Tillett ED. Knee flexor function 2 years after anterior cruciate ligament reconstruction with semitendinosus - gracilis autografts. Arthroscopy, 2006;22:650-655.
53. Eriksson K, Hamberg, P, et al. Semitendinosus muscle in anterior cruciate ligament surgery: Morphology and function. Arthroscopy, 2001;17(8):808-817.
54. Papandrea P, Vulpiani, M, et al. Regeneration of the semitendinosis tendon harvested for anterior cruciate ligament reconstruction. Evaluation using ultrasonogrphy. American Journal of Sports Medicine, 2000,28:556-561.
55. Feller JA, Webster KE, Gavin B. Early post-operative morbidity following anterior cruciate ligament reconstruction: patellar tendon versus hamstring graft. Knee Surgery, Sports Traumatology, Arthroscopy, 2001;9:260–266.
56. Weiler A, Scheffler S, Hoher J. Transplant selection for primary replacement of the anterior cruciate ligament (in German). Orthopade, 2001;31(8):731–740.
57. Keays S, Bullock-Saxton J, Keays A, Newcombe P. Muscle strength and function before and after anterior cruciate ligament reconstruction using semitendinosus and gracilis. The Knee, 2001;8:229-234.
Important: LARS is not available or cleared for distribution in all international markets. For more details, please contact your local subsidiary or distributor by visiting the Corin worldwide section of the Corin Group corporate website.
