Anterior Cruciate Ligament (ACL)
The treatment of ACL ruptures has improved significantly in the last two decades with improving understanding of its anatomy and kinematics, arthroscopic surgical techniques, tunnel placement, graft fixation, treatment of coexisting meniscal and articular cartilage problems and rehabilitation.
The prevalence of Anterior Cruciate Ligament (ACL)
The prevalence of Anterior Cruciate Ligament (ACL) rupture is in about 1 in 3000 Americans- about 95000 injuries per year.
It is common in pivoting sports like Football, Rugby and Basketball but is also common with skiing.
The management of these injuries has evolved from nonoperative treatment to extra-articular augmentation and primary ligament repair to reconstruction using autograft or allograft.
As far back as 1845, Amédée Bonnet from Lyon described three essential signs indicative of acute ACL rupture: “In patients who have not suffered a fracture, a snapping noise, haemarthrosis, and loss of function are characteristic of ligamentous injury in the knee.”
In 1879, a Paris surgeon, Paul F. Segond, (1851-1912) published a study entitled ‘Clinical and experimental research into bloody effusions of the knee joint in sprains’, which was published in Progrès Médical. He described an avulsion fracture of the anterolateral margin of the tibial plateau, which he had found to be routinely associated with ACL tears. This fracture is considered a pathognomonic feature of ACL tears.
In 1895, A.W. Mayo Robson (Leeds, UK) performed the first cruciate (or, as it was then still called, crucial) ligament repair.
In 1903, F. Lange(25) of Munich performed the first ACL replacement, using braided silk. Ernest W. Hey Groves of Bristol performed the first ACL reconstruction using an iliotibial band. In 1963, Kenneth G. Jones, of Arkansas, revived the idea of using a central one-third of patellar tendon graft.
In 1968, Donald B. Slocum and Robert L. Larso43 (Eugene, Oregon) introduced the concept of rotational instability of the knee.
In 1972, D. L. MacIntosh, of Toronto, described the pivot shift, a sign that was earlier noticed by Hey Groves.. To remedy the instability, he described a technique using a fascia lata graft pedicled on the tibia.
1975, Rubin, Marshall, and Wang -prosthetic ACL made of Dacron.
In 1976, the contribution of John Lachman (1956-1989), of Philadelphia, became known through one his students, Joseph S. Torg, who described the Lachman test However, the principle of the test had been described by Noulis in 1875.
1981, D. J. Dandy (Cambridge) carbon fibre-reinforced ligament substitute.
In 1988, M. J. Friedman pioneered the use of an arthroscopically assisted four-stranded hamstring autograft technique.
Shelbourne K.D (1990) Accelerated Rehabilitation. Since then advances have been around graft fixation and techniques and producing predictable outcomes.
The diagnosis of an ACL rupture is made by eliciting a careful history understanding the mechanism of the injury and by knee examination. MRI scans are mainly useful in diagnosing coexisting meniscal and chondral injuries and in certain doubtful situations of ACL rupture.
Contact injury – there is sudden deceleration with the body moving forwards with a rotational force. This could happen in a tackle playing football or whilst the ski blades catch a bump of snow. Road traffic accidents are more likely to produce multi-ligament injuries.
Non-contact injury – the ACL ruptures with a twisting injury to the knee whilst changing direction to the opposite side with the foot planted. Landing from a jump with hyperextension or hyperflexion injuries can also cause ACL rupture.
The player often hears a pop and usually is unable to continue with the game and haemarthrosis generally develops soon after the injury.
Standing leg alignment and varus thrust in gait
Assess hyperextension of opposite knee
Tip- feel the end point whilst performing the Lachman test.
Pivot Shift Test
Tip – Start the pivot shift test from full extension and apply slight axial force in addition to valgus and internal rotation.
Check Posterior sag tibia (PCL) as it can lead to a wrong diagnosis of ACL injury.
Check collateral stability- missed lateral ligament injury can be a reason of ACL reconstruction failure.
(MRI scans or Arthroscopy are not needed for routine diagnosis of ACL rupture).
Decision on Surgery
The fundamental reason for surgical treatment is to stop symptomatic instability which can produce recurrent injury- especially meniscal tears. Not all patients with ACL rupture have this instability pattern. Hence predicting instability and recommending early surgery is an important role for the surgeon based on history, clinical examination and patient activity levels. This is because poor results from ACL reconstruction can often be due to presence of significant meniscal and chondral injuries from chronic instability. Hence it is important to know that a trial of rehabilitation is not a routine for all ACL injuries.
Timing of surgery can affect postoperative recovery of range of movements due to arthrofibrosis. Too delayed a reconstruction (>12 months) can result in higher meniscal injuries and degenerative changes (Keating 2005).
Factors affecting timing of surgery are –
- Associated ligamentous and/or meniscal injuries
- Preoperative condition of the knee- minimal or no swelling, minimal warmth, good strength, leg control and range of movements and preferably symmetrical extension
- Mental preparation of the patient/school/ work/holidays.
The main choices for graft for current day ACL reconstruction are –
- Autologous- Hamstring, Patellar tendon, quadriceps tendon
- Allograft- Patellar tendon, Hamstring, Achilles tendon
|Ultimate tensile strength of Normal ACL and some commonly used Autografts|
|Intact ACL||2160+/- 157|
|Patellar tendon (10mm)||2376+/-151|
|Single strand Semitendinosis||1216+/- 50|
|4 Strand Hamstring||4108+/-200|
|Quadriceps tendon 10mm||2352+/-495|
The choice of graft must be individualised based on the surgeonâ€™s personal experience, patient (occupation, hyperlaxity, graft availability- revision/multiligament) and rehablitation facilities. With appropriate tunnel positioning, graft fixation and rehabilitation either of these grafts can give good longterm results (Aglietti, Roe, Sajovic, Spindler, Pinczewski). This PUBMED LINK shows studies comparing Patellar tendon and Hamstring grafts.
Graft rerupture rates are similar for patellar tendon and Hamstring grafts. There is a higher incidence of problems with kneeling and sensitivity and numbness around scar with Patellar tendon graft harvest. Pinczewski also showed higher extension deficit with patellar tendon ACL reconstructions. There is a higher risk of tunnel widening (Aglietti), graft laxity (Barrett) with hamstring grafts. Wagner showed less pivot shift and thigh atrophy in the hamstring group.
Roe, Pinczewski et al showed no significant differences in the rate of graft rupture or contralateral anterior cruciate ligament rupture at 7 years. Patients with patellar tendon grafts had a greater prevalence of osteoarthritis (Pinczewski, Sajovic).
In patients with excessive joint laxity patellar tendon grafts have been shown to have superior results (Kim, Barrett).
Allografts have similar results to autografts but it is important to exclude irradiated and chemically treated allografts to make this comparison. Allograft patients have better function and less pain in the early stages. A meta-analysis by Prodromos shows that Bone-patellar-tendon-bone (BPTB) autograft normal stability was 66% versus 57% for BPTB allografts (P < 0.01). Abnormal BPTB autograft stability was 6 versus 16% for BPTB allograft. Hamstring autograft normal or abnormal stability rates were 77% and 4% and were compared to soft tissue allografts as a group which were 64% and 12% (P < 0.01).
Tunnel Position and the Isometric Point
Success of ACL reconstructions depend primarily on achieving proper tunnel position and graft fixation followed by appropriate rehabilitation. Malposition of tunnels can produce restricted movements, increased laxity or graft failure secondary to impingement. There is no isometric point for the tibial tunnel. Both tunnels have to be made within the anatomical foot print of the ACL.
Landmarks for tibial tunnel
- Posterior aspect of the tibial ACL footprint
- About 7mm anterior to the PCL with the knee flexed 90 degrees
- Between the tibial eminences
- Just posterior to the posterior edge of the anterior horn attachment of the lateral meniscus
- About 43% posterior to the anterior edge of the tibia along the length on the sagital plane of the tibia
- The oblique orientation of the tibial tunnel in the coronal plane (about 60-70 degrees) is important for transtibial drilling of femoral tunnel. This means that the entry point on the tibia is close to or sometimes through superficial MCL.
Landmarks for Femoral Tunnel
- The ACL femoral insertion has a length of 18mm width of 10mm and is 4 mm from the posterior articular cartilage. The tunnel has to be within the lower part of this footprint
- With the knee flexed 90 degrees and imagining the femoral tunnel position as the face of a clock, the aperture should be at 10-11 oâ€™clock for the right knee and 1-2 oâ€™clock for the left knee.
- Femoral tunnels can be drilled transtibial or through the medial portal. For anteromedial portal technique the knee should be flexed about 120 degrees to avoid damage to the lateral structures. For transtibial technique, the tibial tunnel has to be perfect and the knee is flexed 90 degrees
- A 5 or 6mm offset femoral guide is placed in the over-the-top position and the jig rotated slightly to achieve more lateral femoral tunnel aperture.
- To achieve more flexibility in tunnel positioning, the antero-medial portal can be used or the femoral tunnel can be drilled free hand via the tibial tunnel through a tunnel plug.
There is controversy on the best method of drilling the femoral tunnel. Both transtibial and anteromedial portal techniques can achieve optimal results though the post-operative radiograph will show a higher obliquity of femoral tunnel in the later technique for the same aperture.
The options for fixation of any graft are –
- Interference screw fixation- RCI screw, Softsilk, Bioscrew, Milagro
- Cortical fixation- Endobutton, WasherLoc/EZloc, Sutures over button
- Suspensory fixation in the aperture- Crosspin, Rigidfix
In general cortical fixation gives the best strength. When screws are used they have to cortico-cancellous- not purely cancellous. Over sizing screw diameter by 1mm or longer screw increases fixation strength. Concentric screw placement gives superior fixation strength compared to eccentric screw placement (Starch, Gwynne-Jones).
Screws produce less tunnel widening than Endobutton.
- Bioabsorbable screws make postoperative MRI interpretation easier.
- Patellar tendon graft fixation is stronger than Hamstring.
- All bioabsorbable screws are replaced by bone over time.
Tensioning of graft and Knee flexion angle at fixation
There is no consensus on flexion angle of the knee at the time of graft fixation. When fixed with the knee flexed at 20 degrees, the positional relationship as well as the load between femur and tibia is closest to that in the normal knee, In double bundle ACL reconstruction, knee flexion angles between 15 degrees and 45 degrees for graft fixation were found to be safe for the anteromedial graft, while 15 degrees of knee flexion was safe for the posterolateral graft. With an increase in initial tension, the tibia moved posterolaterally with external and valgus rotation, and consequently the contact force in the femorotibial joint increased and may potentially bring deleterious effects to the articular surface, leading to cartilage degeneration.
Pretensioning increases initial stiffness of graft but twisting and braiding reduces stiffness and tensile strength. Equally tensioned four-strand hamstring-tendon grafts have initial tensile properties that are higher than those reported for ten-millimeter patellar-ligament grafts.
Hamner DL, Brown CH Jr, Steiner ME, Hecker AT, Hayes WC. Hamstring tendon grafts for reconstruction of the anterior cruciate ligament: biomechanical evaluation of the use of multiple strands and tensioning techniques. J Bone Joint Surg Am. 1999 Apr;81(4):549-57
Cuomo P, Rama KR, Bull AM, Amis AA. The effects of different tensioning strategies on knee laxity and graft tension after double-bundle anterior cruciate ligament reconstruction. Am J Sports Med. 2007 Dec;35(12):2083-90.
Kim DH, Wilson DR, Hecker AT, Jung TM, Brown CH Jr. Twisting and braiding reduces the tensile strength and stiffness of human hamstring tendon grafts used for anterior cruciate ligament reconstruction. Am J Sports Med. 2003 Nov-Dec;31(6):861-7.
The common controversies in ACL reconstruction are single vs double bundle, graft choice, tunnel position, trans-tibial or trans medial portal drilling of femoral tunnel, tensioning and cycling of graft and use of postoperative brace.
THIS LINK gives the literature on these issues.
The role of primary repair of an acute ACL rupture
Nonaugmented primary repair of an ACL rupture has a high failure rate. The best results are with reconstruction and this has been shown by Lars Engebretsen in a comparative study of three different techniques.
GrÃ¸ntvedt T, Engebretsen L et al. A prospective, randomized study of three operations for acute rupture of the anterior cruciate ligament. Five-year follow-up of one hundred and thirty-one patients. J Bone Joint Surg Am. 1996 Feb;78(2):159-68.
More recently Steadman has described the â€˜healing responseâ€™ treatment for proximal ACL injuries in the skeletally immature patient with good success in this select group.
Steadman JR, Cameron-Donaldson ML, Briggs KK, Rodkey WG. A minimally invasive technique (“healing response”) to treat proximal ACL injuries in skeletally immature athletes. J Knee Surg. 2006 Jan;19(1):8-13.
Single or Double-bundle ACL reconstruction
Traditional ACL reconstruction concentrates on reconstructing the Antero-medial bundle of the ACL. As early as 1938, Palmer recognised two bundles to the Anterior cruciate ligament. The anteromedial (AM) and posterolateral (PL) bundles (named according to the relative position of their tibial insertions) are intertwined and recently the presence of an intermediate bundle has been recognised. The kinematic function of the bundles depends on the angular position of the knee, the PL bundle being tighter closer to extension and the AM bundle more in flexion.
There has been some benefit shown on KT1000 measurements and pivot shift tests in patients with anatomical double bundle ACL reconstruction when compared to single bundle reconstruction. The sensitivity of these tests in showing a sufficient clinical improvement and therefore justify a more complex ACL reconstruction is questionable. Hence the gold standard is still a single bundle reconstruction. There is also a higher risk of tunnel malpositioning and impingement due to a wider tibial footprint. More sensitive kinematic analysis and assessment of progression of arthritis can be useful parameters to decide on the future of double-bundle ACL reconstruction.
PUBMED LINK gives the current literature on double-bundle ACL reconstruction.
Single bundle ACL reconstruction
There are 11 randomised controlled studies with minimum 24 months follow-up that compare Patellar Tendon and Hamstring single bundle ACL reconstructions. With ACL injury, there is a 10% incidence of concomitant chondral injury and a 53% incidence of meniscal tears. Both patellar tendon and hamstring tendon autografts result in a functionally stable knee in more than 95% of patients at a minimum of 24 months of follow-up. About 19% of patients still have a positive pivot shift phenomenon. 40% of patients still have a positive Lachman test though most of them have a firm end point. Almost 77% of patients have a side-to-side laxity of less than 3 mm. Loss of up to 5 degrees of extension is common. Only 54% of patients have symmetrical extension. Both patellar tendon and Hamstring autografts have comparable results in Lysholm score, Tegner activity level, KT-1000 arthrometer side-to-side laxity measurement, single-legged hop test, or IKDC results. Grade A or B IKDC scores are found in 75%, the median Lysholm score is greater than 85 in these studies. Functional testing with the single leg hop test also shows a median jumping distance of 90% or more compared to the normal leg. There is 80% return to sport at preinjury level and 93% were satisfied with their results.
There is suggestion that Hamstring grafts can show a trend towards greater laxity at follow up (Barrett) though other authors have suggested comparable clinical and KT arthrometer laxity measurements (Sajovic, Ejerhed). There is evidence of higher incidence of anterior knee pain in patellar tendon ACL reconstructions. Risk of graft failure is about 3%.
Freedman KB, D’Amato MJ, Nedeff DD, Kaz A, Bach BR Jr. Arthroscopic anterior cruciate ligament reconstruction: a metaanalysis comparing patellar tendon and hamstring tendon autografts. Am J Sports Med. 2003 Jan-Feb;31(1):2-11
Anderson AF, Snyder RB, Lipscomb AB Jr. Anterior cruciate ligament reconstruction: a prospective randomized study of 3 surgical methods. Am J Sports Med. 2001;29(3):272-279.
Aune AK, Holm I, Risberg MA, Jensen HK, Steen H. Four-strand hamstring tendon autograft compared with patellar tendon-bone autograft for anterior cruciate ligament reconstruction: a randomized study with 2-year follow-up. Am J Sports Med. 2001;29(6):722-728.
Beynnon BD, Johnson RJ, Fleming BC, et al. Anterior cruciate ligament replacement: comparison of bone-patellar tendon-bone grafts with 2-strand hamstring grafts: a prospective, randomized study. JBone Joint Surg Am. 2002;84(9):1503-1513.
Ejerhed L, Kartus J, Sernert N, Köhler K, Karlsson J. Patellar tendon or semitendinosus tendon autografts for anterior cruciate ligament reconstruction? A prospective randomized study with a two-year follow-up. Am J Sports Med. 2003 Jan-Feb;31(1):19-25.
Ibrahim SA, Al-Kussary IM, Al-Misfer AR, Al-Mutairi HQ, Ghafar SA, El Noor TA. Clinical evaluation of arthroscopically assisted anterior cruciate ligament reconstruction: patellar tendon versus gracilis and semitendinosus autograft. Arthroscopy. 2005;21(4):412-417.
Harilainen A, Linko E, Sandelin J. Randomized prospective study of ACL reconstruction with interference screw fixation in patellar tendon autografts versus femoral metal plate suspension and tibial postfixation in hamstring tendon autografts: 5-year clinical and radiological follow-up results. Knee Surg Sports Traumatol Arthrosc. 2006;14(6), 517-528.
Feller JA, Webster KE. A randomized comparison of patellar tendon and hamstring tendon anterior cruciate ligament reconstruction. Am J Sports Med. 2003;31(4):564-573.
Eriksson K, Anderberg P, Hamberg P, et al. A comparison of quadruple semitendinosus and patellar tendon grafts in reconstruction of the anterior cruciate ligament. J Bone Joint Surg Br. 2001;83(3):348-354.
Shaieb MD, Kan DM, Chang SK, Marumoto JM, Richardson AB. A prospective randomized comparison of patellar tendon versus semitendinosus and gracilis tendon autografts for anterior cruciate ligament reconstruction. Am J Sports Med. 2002;30(2):214-220.
Barrett GR, Noojin FK, Hartzog CW, Nash CR Reconstruction of the anterior cruciate ligament in females: A comparison of hamstring versus patellar tendon autograft. Arthroscopy. 2002 Jan;18(1):46-54.
Sajovic M, Vengust V, Komadina R, Tavcar R, Skaza K. A prospective, randomized comparison of semitendinosus and gracilis tendon versus patellar tendon autografts for anterior cruciate ligament reconstruction: five-year follow-up. Am J Sports Med. 2006 Dec;34(12):1933-40.
Wagner M, Kääb MJ, Schallock J, Haas NP, Weiler A Hamstring tendon versus patellar tendon anterior cruciate ligament reconstruction using biodegradable interference fit fixation: a prospective matched-group analysis. Am J Sports Med. 2005 Sep;33(9):1327-36.
Double bundle ACL reconstruction (2 femoral and one tibial tunnel or Anatomical)
There are numerous studies that have compared single and double bundle ACL reconstructions. There appears to be no subjective difference and no difference in clinical outcomes currently measured. Many authors have reported better laxity correction and rotational stability with double bundle ACL reconstructions (Jarvela, Yasuda, Muneta, Aglietti).
Jarvela found better rotational stability as demonstrated by the pivot shift test in double bundle ACL reconstruction. The isokinetic peak torque of knee extension and flexion strength was 90% and 89%, respectively, in the double-bundle group and 87% and 86%, respectively, in the single-bundle group. The Lysholm score averaged 96.8 +/- 5.1 in the double-bundle group and 92.8 +/- 6.9 in the single-bundle group postoperatively. There was no significant difference in knee laxity. Muneta showed that negative Lachman and pivot-shift test results were found in more patients in the DB group than in the SB group. KT measurements averaged 2.4 mm in the SB group and 1.4 mm in the DB group, which was statistically significantly different. Yasuda compared anatomical (AD) and nonanatomical (N-AD) double bundle ACL reconstructions with single bundle ACL reconstructions and showed better laxity measurements with both AD and N-AD compared to single bundle.
Asagumo in a retrospective study noticed negative Lachman test in 64 cases (90%) and negative pivot-shift test in 62 cases (87%) in the double-bundle group. The Lachman test was negative in 45 cases (86%) and the pivot-shift test was negative in 42 cases (81%) in the single-bundle group. There was higher loss of full extension in the double bundle group. Functional outcome showed no difference.
Adachi measured anterior laxity with the knee in different positions and reported no difference between single and double bundle ACL reconstruction.
Järvelä T, Moisala AS, Sihvonen R, Järvelä S, Kannus P, Järvinen M. Double-bundle anterior cruciate ligament reconstruction using hamstring autografts and bioabsorbable interference screw fixation: prospective, randomized, clinical study with 2-year results.
Asagumo H, Kimura M, Kobayashi Y, Taki M, Takagishi K. Anatomic reconstruction of the anterior cruciate ligament using double-bundle hamstring tendons: surgical techniques, clinical outcomes, and complications. Arthroscopy. 2007 Jun;23(6):602-9.
Adachi N, Ochi M, Uchio Y, Iwasa J, Kuriwaka M, Ito Y. Reconstruction of the anterior cruciate ligament. Single- versus double-bundle multistranded hamstring tendons. J Bone Joint Surg Br. 2004 May;86(4):515-20.
Järvelä T. Double-bundle versus single-bundle anterior cruciate ligament reconstruction: a prospective, randomize clinical study. Knee Surg Sports Traumatol Arthrosc. 2007 May;15(5):500-7.
Muneta T, Koga H, Mochizuki T, Ju YJ, Hara K, Nimura A, Yagishita K, Sekiya I. A prospective randomized study of 4-strand semitendinosus tendon anterior cruciate ligament reconstruction comparing single-bundle and double-bundle techniques. Arthroscopy. 2007 Jun;23(6):618-28.
Yasuda K, Kondo E, Ichiyama H, Tanabe Y, Tohyama H. Clinical evaluation of anatomic double-bundle anterior cruciate ligament reconstruction procedure using hamstring tendon grafts: comparisons among 3 different procedures. Arthroscopy. 2006 Mar;22(3):240-51
Aglietti P, Giron F, Cuomo P, Losco M, Mondanelli N. Single-and double-incision double-bundle ACL reconstruction. Clin Orthop Relat Res. 2007 Jan;454:108-13.
Risks from Surgery
- Infection- rare
- Failure to regain extension (arthrofibrosis, Cyclops lesion, graft impingement, degenerative changes)
- Failure to regain flexion (arthrofibrosis, PCL impingement, degenerative)
- Scar sensitivity/numbness
- Persistent Pain
- usually due to chondral injuries
- Pain in the hamstring harvest site can last for 3 months
- patellofemoral pain (for Patella tendon graft)
- Persistent Instability- About 5% more often in deeper flexion
- Rerupture- 2-5%
- Nerve injury or bleeding- extremely rare
- Patella fracture, patellar tendon rupture (Patellar tendon graft)
- Loss in quadriceps or Hamstring strength- 95 % Hamstring strength regained at 3 years but strength loss is more noticed in deeper flexion.
You should see your doctor urgently if you:
- Have pain, swelling or tenderness in the joint which is getting worse,
- Develop a high temperature,
- See fluid, pus or blood coming from the incisions, or
- Develop numbness or tingling near to the joint
Contact your hospital ward nurse or your physiotherapist who would liaise with your Surgeon. If it is at late hours in the night, you may have to attend the emergency department and see the on call Orthopaedic Doctor who would assess your knee and speak to your surgeon.
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Timing of surgery
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Bottoni CR, Liddell TR, Trainor TJ, Freccero DM, Lindell KK. Postoperative range of motion following anterior cruciate ligament reconstruction using autograft hamstrings: a prospective, randomized clinical trial of early versus delayed reconstructions. Am J Sports Med. 2008 Apr;36(4):656-62
Mayr HO, Weig TG, Plitz W. Arthrofibrosis following ACL reconstruction–reasons and outcome. Arch Orthop Trauma Surg. 2004 Oct;124(8):518-22.
Meighan AA, Keating JF, Will E. Outcome after reconstruction of the anterior cruciate ligament in athletic patients. A comparison of early versus delayed surgery. J Bone Joint Surg Br. 2003 May;85(4):521-4
Church S, Keating JF. Reconstruction of the anterior cruciate ligament: timing of surgery and the incidence of meniscal tears and degenerative change. J Bone Joint Surg Br. 2005 Dec;87(12):1639-42
Spindler KP, Kuhn JE, Freedman KB, Matthews CE, Dittus RS, Harrell FE Jr. Anterior cruciate ligament reconstruction autograft choice: bone-tendon-bone versus hamstring: does it really matter? A systematic review. Am J Sports Med. 2004 Dec;32(8):1986-95. Review
Sajovic M, Vengust V, Komadina R, Tavcar R, Skaza K. A prospective, randomized comparison of semitendinosus and gracilis tendon versus patellar tendon autografts for anterior cruciate ligament reconstruction: five-year follow-up. Am J Sports Med. 2006 Dec;34(12):1933-40.
Wagner M, KÃ¤Ã¤b MJ, Schallock J, Haas NP, Weiler A. Hamstring tendon versus patellar tendon anterior cruciate ligament reconstruction using biodegradable interference fit fixation: a prospective matched-group analysis. Am J Sports Med. 2005 Sep;33(9):1327-36.
Roe J, Pinczewski LA, Russell VJ, Salmon LJ, Kawamata T, Chew M. A 7-year follow-up of patellar tendon and hamstring tendon grafts for arthroscopic anterior cruciate ligament reconstruction: differences and similarities. Am J Sports Med. 2005 Sep;33(9):1337-45.
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Barrett GR, Noojin FK, Hartzog CW, Nash CR. Reconstruction of the anterior cruciate ligament in females: A comparison of hamstring versus patellar tendon autograft. Arthroscopy. 2002 Jan;18(1):46-54
Aglietti P, Giron F, Buzzi R, Biddau F, Sasso F. Anterior cruciate ligament reconstruction: bone-patellar tendon-bone compared with double semitendinosus and gracilis tendon grafts. A prospective, randomized clinical trial. J Bone Joint Surg Am. 2004 Oct;86-A(10):2143-55
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