Magnetic Resonance Imaging of Double-Bundle Anterior Cruciate Ligament Reconstruction

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TOMMI KIEKARA

Magnetic Resonance Imaging of Double-Bundle Anterior Cruciate

Ligament Reconstruction

ACADEMIC DISSERTATION To be presented, with the permission of

the Board of the School of Medicine of the University of Tampere, for public discussion in the Auditorium of Finn-Medi 5, Biokatu 12, Tampere, on September 19th, 2014, at 12 o’clock.

UNIVERSITY OF TAMPERE

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TOMMI KIEKARA

Magnetic Resonance Imaging of Double-Bundle Anterior Cruciate

Ligament Reconstruction

Acta Universitatis Tamperensis 1965 Tampere University Press

Tampere 2014

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ACADEMIC DISSERTATION

University of Tampere, School of Medicine

Tampere University Hospital, Medical Imaging Centre Finland

Reviewed by

Professor Ilkka Kiviranta University of Helsinki Finland

Docent Mika Koivikko University of Oulu Finland

Supervised by Docent Timo Järvelä University of Tampere Finland

Professor Antti Paakkala University of Tampere Finland

Cover design by Mikko Reinikka

Acta Universitatis Tamperensis 1965 Acta Electronica Universitatis Tamperensis 1450 ISBN 978-951-44-9545-8 (print) ISBN 978-951-44-9546-5 (pdf )

ISSN-L 1455-1616 ISSN 1456-954X

ISSN 1455-1616 http://tampub.uta.fi

Suomen Yliopistopaino Oy – Juvenes Print

Tampere 2014 Painotuote^{441 729}

Distributor:

kirjamyynti@juvenes.fi http://granum.uta.fi

The originality of this thesis has been checked using the Turnitin OriginalityCheck service in accordance with the quality management system of the University of Tampere.

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ABSTRACT

Rupture of the anterior cruciate ligament (ACL) is a common knee trauma and often related to sport activities. If the patient experiences symptoms of knee laxity in daily activities or wishes to return to pivoting sports such as football, surgical treatment with ACL reconstruction is indicated. New surgical techniques, anatomical double-bundle (DB) and anatomical single-bundle (SB) ACL reconstructions, have been recently developed in an attempt to obtain better rotational stability and better long-term outcome compared with conventional ACL reconstruction. In DB ACL reconstruction, both fiber bundles of the torn ACL are reconstructed with grafts to reproduce the native anatomy and knee function. The anteromedial (AM) and the posterolateral (PL) grafts are inserted in separate bone tunnels that are drilled at the native ACL insertions at the femur and at the tibia.

The best imaging method to evaluate the postoperative knee is magnetic resonance imaging (MRI).

The aim of the present study was to evaluate the MRI findings of DB ACL reconstruction. The prospective study comprised 66 patients who were operated on between 2004-2008 and were evaluated with follow-up 1.5T MRI and clinical evaluation 2 years postoperatively. Two radiologists evaluated the MRI data blinded to the patients’ clinical data and all measurements were done independently. The MRI findings of the grafts and bone tunnels were assessed and the locations of the tunnels were measured with the modified quadrant method that was applied for the first time to MRI. The associations of the MRI findings and between the MRI and the clinical findings were calculated.

The main findings of study I were that only 3% of the patients had both grafts disrupted and that other complications were infrequent. Increased graft signal intensity (SI) has been previously associated with partial graft tears, graft impingement, and knee laxity in clinical evaluation. Increased SI was seen in 14%

of the intact AM grafts, in 51% of the intact PL grafts, and in 60% and 93% of the partially torn AM and PL grafts, respectively. The substantial proportion of intact grafts with increased SI 2 years after DB ACL reconstruction is a new finding with no similar previous reports in the literature. The oblique course of the PL graft was

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identified as a possible cause of volume-averaging artifact that might cause increased SI.

Study II showed that the tunnel locations were close to anatomical. The 3D computed tomography (CT) quadrant method used to evaluate the tunnel locations was shown to be applicable to conventional 2D MRI. The inter-observer agreement between the two radiologists’ measurements was estimated. The mean enlargement of the 4 tunnels was 56% of the original size. Tunnel enlargement was associated with tunnel communication that was seen in 11% of patients in the femur and in 29% of patients in the tibia. The frequency of tunnel communication was high in our material compared to the previous reports. In study III, a more anterior location of both tibial tunnels was associated with more partially visible and invisible grafts in MRI. Tunnel location was not associated with the results of the clinical evaluation. In study IV, tibial tunnel communication was associated with increased knee flexion range and increased AM graft SI was associated with reduced knee flexion. However, tunnel communication or increased graft SI was not associated with knee laxity.

This thesis describes the MRI findings and the frequency of complications of the grafts and tunnels after anatomical DB ACL reconstruction. T2-weighted images were sufficient in graft SI evaluation. Increased graft SI was a common finding and not helpful in the diagnosis of graft rupture. Contrary to previous reports, the findings of increased graft SI and tunnel communication were not associated with knee laxity. Because non-anatomical tunnel locations are a major cause of graft failure, the postoperative evaluation of tunnel locations with MRI is important. Based on the findings of this study and previous literature, a simple method for assessing the graft locations by measuring the tibial tunnel locations and the AM graft angle with sagittal MR images is proposed for clinical use.

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TIIVISTELMÄ

Eturistisiteen repeämä on yleinen urheiluun liittyvä polvivamma. Leikkaushoidon aiheita ovat häiritsevä polven väljyys päivittäisissä toiminnoissa ja potilaan halu palata polvea kuormittaviin urheiluharrastuksiin. Viime vuosina on kehitetty tavanomaisen eturistisiteen leikkaustekniikan vaihtoehdoksi anatominen leikkaustekniikka yhtä tai kahta jännesiirrettä käyttäen. Niillä pyritään saavuttamaan parempi polven tukevuus kiertoliikkeessä ja paremmat hoidon pitkäaikaistulokset kuin tavanomaisella leikkausmenetelmällä. Kaksoissiirretekniikassa revenneen eturistisiteen molemmat säiekimput rakennetaan uudelleen jännesiirteistä.

Anteromediaalinen (AM) ja posterolateraalinen (PL) jännesiirre pyritään kiinnittämään alkuperäisen eturistisiteen säiekimppujen kiinnityskohtiin ja näin korjaamaan ennalleen eturistisiteen rakenne ja polven toiminta.

Polvivaivojen selvittelyssä magneettikuvaus on paras kuvantamistutkimus myös polvileikkauksen jälkeen. Tämän väitöskirjatutkimuksen tavoitteena oli tutkia kaksoissiirretekniikalla tehdyn eturistisiteen korjausleikkauksen magneettikuvauslöydöksiä. Prospektiivisessa tutkimusasetelmassa 66 potilaalle tehtiin eturistisiteen korjausleikkaus kaksoissiirretekniikalla vuosina 2004-2008.

Seurantatutkimuksessa 2 vuotta leikkauksen jälkeen potilaille tehtiin magneettikuvaus 1.5 Teslan laitteella ja polven kliininen tutkimus. Kaksi radiologia tulkitsi kuvauslöydökset sokkoutettuna kliinisen tutkimuksen tuloksille ja suoritti mittaukset kuvista itsenäisesti. He arvioivat jännesiirteiden ja niiden kiinnitykseen käytettävien luun porakanavien eli tunnelien magneettilöydökset. Porakanavien sijainnit reisiluussa ja sääriluussa mitattiin quadrant method –mittaustavalla, jota sovellettiin ensimmäistä kertaa magneettikuviin. Tilastollisesti merkitsevät yhteydet magneettikuvauslöydösten välillä ja magneettikuvauslöydösten ja kliinisen tutkimustulosten välillä selvitettiin.

Osatyössä I havaittiin, että molemmat jännesiirteet olivat poikki vain 3 prosentilla potilaista ja että muitakin komplikaatioita esiintyi vähän. Jännesiirteen signaalilisän on aiemmin todettu olevan yhteydessä siirteen osittaiseen repeämään, ahtaaseen kulkureittiin ja polven väljyyteen kliinisessä tutkimuksessa. Signaalilisää todettiin ehjistä AM-siirteistä 14 %:lla, ehjistä PL-siirteistä 51 %:lla, osittain revenneistä AM-siirteistä 60 %:lla ja osittain revenneistä PL-siirteistä 93 %:lla.

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Signaalilisän yleisyys ehjissä jännesiirteissä 2 vuotta leikkauksen jälkeen on uusi löydös aiempaan kirjallisuuteen verrattuna. Mahdollinen syy signaalilisän yleisyyteen PL-siirteissä on siirteen kuvaussuuntaan nähden vinon kulkureitin aiheuttama tilavuuskeskiarvoistusartefakta. Osatyössä II porakanavien paikat quadrant method -menetelmällä mitattuna olivat lähellä anatomisia eturistisiteen kiinnityskohtia.

Mittaajien välinen tulosten yhtäpitävyys arvioitiin hyväksi. Porakanavat olivat suurentuneet keskimäärin 56 prosenttia alkuperäisestä koostaan. Porakanavien suurentuminen oli yhteydessä kanavien yhtenemiseen, jota todettiin 11 %:lla potilaista reisiluussa ja 29 %:lla potilaista sääriluussa. Porakanavien yhteneminen oli aineistossamme yleisempää kuin aiemmin on kirjallisuudessa kuvattu. Osatyössä III havaittiin, että jännesiirteiden näkymättömyys tai näkyminen osittain oli yhteydessä porakanavien sijaintiin edempänä sääriluussa. Kanavien sijainnilla ei ollut tilastollisesti merkitsevää yhteyttä kliinisen tutkimuksen tuloksiin. Sen sijaan osatyössä IV kanavien yhteneminen sääriluussa oli yhteydessä polven suurempaan liikelaajuuteen koukistuksessa ja toisaalta AM-siirteen signaalilisä yhteydessä pienempään liikelaajuuteen polven koukistuksessa. Porakanavien yhtenemisellä tai jännesiirteen signaalilisällä ei kuitenkaan ollut yhteyttä polven väljyyteen kliinisessä tutkimuksessa.

Väitöskirjatyössä esitetään jännesiirteiden ja porakanavien normaalilöydökset ja komplikaatiot ja niiden yleisyys polven eturistisiteen magneettikuvauksessa. Koska jännesiirteiden kiinnittäminen epäanatomisiin kohtiin on yleinen siirteen pettämisen syy, kiinnityskohtien mittaaminen magneettikuvista on tärkeää aiemmin leikatun potilaan polvivaivojen selvittelyssä. Tämän tutkimuksen tulosten ja kirjallisuuden perusteella esitämme uuden kliiniseen työhön soveltuvan mittausmenetelmän, jolla eturistisiteen jännesiirteen anatominen sijainti voidaan määrittää polven magneettikuvauksessa. Tässä yksinkertaisessa menetelmässä jännesiirteiden kiinnityskohdat sääriluussa ja AM-siirteen kulma mitataan sivusuunnan kuvasarjasta. Toisin kuin aiemmissa tutkimuksissa, magneettikuvauksessa todettu jännesiirteiden signaalilisä tai porakanavien yhteneminen ei ollut aineistossamme yhteydessä polven väljyyteen. T2-painotteiset kuvasarjat olivat riittäviä jännesiirteiden signaalimuutosten arviointiin. Jännesiirteiden signaalilisä oli yleinen löydös eikä siitä ole apua siirteen repeämän toteamisessa.

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1 ORIGINAL COMMUNICATIONS

This thesis is based on the following original publications, which are referred to in the text by the Roman numerals I-IV:

I Kiekara T, Järvelä T, Huhtala H and Paakkala A (2012). MRI of double- bundle ACL reconstruction: evaluation of graft findings. Skeletal Radiol 41:

835-842

II Kiekara T, Järvelä T, Huhtala H and Paakkala A (2014). MRI evaluation of the four tunnels of double-bundle ACL reconstruction. Acta Radiol 55:579-588

III Suomalainen P, Kiekara T, Moisala AS, Paakkala A, Kannus P and Järvelä T (2014). Effect of tunnel placements on clinical and magnetic resonance imaging findings 2 years after anterior cruciate ligament reconstruction using the double-bundle technique. Open Access J Sports Med (accepted) IV Kiekara T, Järvelä T, Huhtala H, Moisala AS, Suomalainen P and Paakkala

A (2014). Tunnel communication and increased graft signal intensity on magnetic resonance imaging of double-bundle anterior cruciate ligament reconstruction. Arthroscopy (accepted)

The original publications are reproduced with the permission of Springer International Publishing AG (I), SAGE Publications (II), Dove Medical Press Ltd (III), and Elsevier B.V. (IV).

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2 ABBREVIATIONS

ACL Anterior cruciate ligament

AM Anteromedial

ANOVA Analysis of variance AP Anterior-to-posterior

AX Axial

B0 Static magnetic field BPTB Bone-patellar tendon-bone

COR Coronal

CT Computed tomography

DB Double-bundle

FS Fat-saturated

IKDC International Knee Documentation Committee

IM Intermediate

KOOS Knee injury and Osteoarthritis Outcome Score LCL Lateral collateral ligament

LM Lateral-to-medial

MA Magic angle

MCL Medial collateral ligament MPR Multiplanar reconstruction MRI Magnetic resonance imaging

PACS Picture archiving and communicating system PCL Posterior cruciate ligament

PD Proton density-weighted/Intermediate density-weighted

PL Posterolateral

SAG Sagittal

SB Single-bundle

SE Spin echo

SI Signal intensity

T Tesla

TB Triple-bundle

TE Time to echo/echo time

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T1 T1-weighted

T2 T2-weighted

2D Two-dimensional

3D Three-dimensional

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3 INTRODUCTION

Knee injuries are very common in sports, and rupture of the anterior cruciate ligament (ACL) is the most commonly diagnosed internal derangement of the knee in sports injuries (Majewski et al. 2006, Haikonen and Lounamaa 2010). The estimated annual incidence of ACL rupture in the general population is 0.8- 1.2/1000 (Frobell et al. 2007, Gianotti et al. 2009). The typical mechanism of ACL rupture is a sudden change in direction on the weight-bearing knee that results in twisting or a valgus strain of the knee (Perera et al. 2013). A disrupted ACL usually fails to heal and functional impairment including joint laxity develops in the ACL- deficient knee. As a result, activity is decreased and the risk of osteoarthritis increased (Allen et al. 1999, Murray et al. 2000, Spindler and Wright 2008). A minority of ACL injuries are partial tears that are treated conservatively if the knee is stable (DeFranco and Bach 2009).

An estimated 175000 ACL reconstructions are performed annually in the USA and approximately 3000 in Finland (Gottlob et al. 1999, Rautiainen and Rasilainen 2011). The aim of the treatment is to restore normal knee function and stability (Beynnon et al. 2005b, Frobell et al. 2010). Indications for ACL reconstruction are knee instability in normal daily activities, a return to sports involving cutting and pivoting, and heavy work (Spindler and Wright 2008, Kallio 2010, Brophy et al.

2012). Conservative treatment comprising a structured rehabilitation program is an option for a subset of patients and results in a mid-term outcome similar to that of surgical treatment (Frobell et al. 2013). However, long-term results show that 30%

of patients fail to return to the pre-injury level in sports and 20-28% of patients have severe radiographic osteoarthritis 10 years after conventional arthroscopic ACL reconstruction (Biau et al. 2007, Ardern et al. 2011, Claes et al. 2013, Ajuied et al. 2013). These findings have highlighted the need for better treatment options.

The term conventional ACL reconstruction technique refers to the common techniques used in ACL reconstruction surgery before the development of anatomical double-bundle (DB) ACL reconstruction. These approaches differ mainly in the drilling of the femoral tunnel and include the outside-in technique (Harner et al. 1994), the freehand technique (Deehan et al. 2000), and the transtibial technique (Chen et al. 2003).

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In order to improve the results of surgical treatment, both the anatomy and the biomechanics of the ACL have been studied recently. The ACL comprises 2 fiber bundles, the anteromedial (AM) bundle and the posterolateral (PL) bundle, that are named according to their tibial insertions. Both bundles function in a complementary manner to control knee joint stability (Wu et al. 2010, Amis 2012).

These findings led first to the development of anatomical double-bundle (DB) and later to anatomical single-bundle (SB) ACL reconstruction techniques, both of which result in better rotational stability than conventional SB ACL reconstruction (Hussein et al. 2012b). The main principle behind these anatomical techniques is to reproduce the insertions and orientation of the native ACL (van Eck et al. 2010a).

Magnetic resonance imaging (MRI) is the most effective imaging method to aid in the diagnosis of ACL disruption and to evaluate complications of ACL grafts (Farshad-Amacker and Potter 2013). The MRI indications after ACL reconstruction include pain, laxity, stiffness, a new injury, preoperative planning of revision, or infection of the knee (Recht and Kramer 2002, Papakonstantinou et al.

2003). In total, 10-30% of patients have knee pain or laxity following conventional SB reconstruction (Yunes et al. 2001). Knee pain is the most common but nonspecific symptom of complications of ACL reconstruction, thus making further diagnostic imaging necessary (Passler et al. 1999, Collins et al. 2008). The complications of ACL reconstruction that are diagnosed with MRI include complete and partial graft ruptures, graft impingement, arthrofibrosis, graft or tunnel cysts, hardware failure, and infection (Recht and Kramer 2002, Papakonstantinou et al. 2003, Bencardino et al. 2009). MRI is also uselful in differential diagnosis and in the evaluation of concurrent meniscal, ligamentous, tendinous, chondral, and bony causes of knee pain (Karrasch and Gallo 2014). It is important to correlate the MRI findings with clinical examination (Casagranda et al.

2009).

The purpose of the present study was to evaluate the MRI findings of a novel surgical technique, the anatomical DB ACL reconstruction, in a prospective cohort. The MRI findings of the AM and the PL grafts and the characteristics and the anatomical locations of the bone tunnels were assessed. A radiologic quadrant method previously described using radiographs or 3D computed tomography (CT) for measuring the tunnel locations was applied to clinical MR imaging. The associations of the new MRI findings with the patient-reported and clinical evaluation findings in 2-year follow-up were investigated.

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4 REVIEW OF THE LITERATURE

4.1 Anatomy of the ACL

The ACL is a band of dense connective tissue that courses from the femur to the tibia in the knee joint (Duthon et al. 2006) (Figures 1 and 2). The femoral attachment of the ACL is at the posterior aspect of the medial surface of the lateral femoral condyle. From there, the ACL runs anteriorly, medially, and distally to the tibia (Figure 3). The tibial attachment is located anterior and lateral to the medial tibial spine.

Figure 1. The ACL seen from anteromedial direction in a flexed right knee.

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Figure 2. The anteromedial (AM, white arrow) and posterolateral (PL, black arrow) bundles of the ACL seen in MPR 3T MRI (3D True FISP WE isovoxel 0.6mm).

Because the ACL is surrounded by a synovial fold that originates from the posterior capsule, it is defined as intra-articular bur extra-synovial (Ellison and Berg 1985). Although previous histologic studies found no evidence to separate the ACL into different bundles (Odensten and Gillquist 1985), a recent anatomic dissection study states that the ACL consists of many small bundles 1 mm in diameter (Hara et al. 2009). Functionally, it is widely accepted that the ACL comprises anteromedial (AM) and posterolateral (PL) fiber bundles (Weber and Weber 1836, Palmer 1938, Girgis et al. 1975, Harner et al. 1999, Wu et al. 2010).

The bundles are named according to their insertion at the tibia. In anatomic dissection, the AM and PL bundles that both comprise approximately 20 small 1- mm bundles were identified more clearly when the knee was flexed (Hara et al.

2009). Also, a third intermediate band has been identified (Amis and Dawkins 1991), but the two-bundle model is the more generally accepted (Chhabra et al.

2006, Duthon et al. 2006).

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The ligament insertion sites at the femur and at the tibia are larger than the central part of the ACL, and thus making the ligament fan-shaped at both ends.

The length of the ACL is approximately 32 mm and the width of the central part is 10 mm in the extended knee (Duthon et al. 2006). At full extension, the length of the AM bundle is approximately 36 mm and the length of the PL bundle approximately 21 mm (Hollis et al. 1991, Zantop et al. 2008b). At 90^o of flexion, the length of the AM bundle increases by 3-4 mm and the length of the PL bundle decreases by 2-7 mm (Hollis et al. 1991, Takai et al. 1993). The length of the PL bundle increases by 3 mm in internal rotation (Zaffagnini et al. 2004). The size of the ACL femoral attachment is approximately 14 mm in cranial-to-caudal direction and 8 mm in anterior-to-posterior (AP) direction (Colombet et al. 2006, Edwards et al. 2008) (Figure 4). The size of the ACL tibial attachment is approximately 11 mm in lateral-to-medial (LM) direction and 18 mm in AP direction (Colombet et al.

2006, Edwards et al. 2007) (Figures 3 and 5).

Figure 3. Measurement of the AP diameter of the ACL tibial attachment. MPR 3T MRI (3D True FISP WE isovoxel 0.6mm).

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In the extended knee, the AM bundle is attached more proximally and the PL bundle more distally in a vertical orientation at the lateral femoral condyle (Chhabra et al. 2006, Colombet et al. 2006, Edwards et al. 2008, Zantop et al.

2008b) (Figure 4). In the tibia, the AM bundle is attached anteromedially and the PL bundle posterolaterally at the fossa of ACL insertion (Chhabra et al. 2006, Colombet et al. 2006, Duthon et al. 2006) (Figure 5).

The locations of the femoral AM and PL bundle insertion sites are measured as coordinates in x-y orientation by the radiographic quadrant method (Bernard et al.

1997) that has been applied to three-dimensional (3D) computed tomography (CT) (Lorenz et al. 2009). The femoral coordinates are aligned parallel to (x) and perpendicular to (y) the Blumensaat’s line (the roof of the intercondylar fossa, Figure 4).

Figure 4. The anatomical femoral ACL insertion and the weighted mean centers of the anteromedial (AM) and posterolateral (PL) bundles expressed by the quadrant method (Lorenz et al. 2009).

Modified from original publication II with permission from SAGE Publications.

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The locations of the AM and PL bundle tibial insertion sites were first measured in AP orientation of the tibial plateau from the sagittal radiographs (Staubli and Rauschning 1994). Currently, a similar x-y orientation of the AM and PL bundle insertions at the tibial plateau that includes both LM measurements (x) and AP measurements (y) using 3D CT is used (Lorenz et al. 2009) (Figure 5).

In the literature, the insertion sites of the anatomical AM and PL bundles expressed by the quadrant method are variable. The weighted means (by the number of specimens in each study) of the published insertions are as follows: the femoral AM bundle insertion x = 23% and y = 22%, the femoral PL bundle insertion x = 31% and y = 49%, the tibial AM bundle insertion x = 53% and y = 36%, and the tibial PL bundle insertion x = 49% and y = 51% (Yamamoto et al.

2004, Colombet et al. 2006, Edwards et al. 2008, Tsukada et al. 2008, Zantop et al.

2008a, Lorenz et al. 2009, Forsythe et al. 2010) (Figures 4 and 5).

Figure 5. The anatomical tibial ACL insertion and the weighted mean centers of the anteromedial (AM) and posterolateral (PL) bundles expressed by the quadrant method (Lorenz et al. 2009).

Modified from original publication II with permission from SAGE Publications.

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Recently, a slightly different anatomic coordinate axes method has also been described for 3D CT (Forsythe et al. 2010). The rationale for calculating the insertion site coordinates instead of measurements from anatomic landmarks is to be able to locate the anatomic insertion sites independent of knee size in anatomic ACL reconstruction surgery (Lorenz et al. 2009).

4.2 Biomechanics of the ACL

The primary function of the ACL is to resist tibial anterior translation (Butler et al.

1980, Amis and Dawkins 1991, Yagi et al. 2002, Wu et al. 2010). It also has a secondary role in resisting tibial rotation (Yagi et al. 2002, Yamamoto et al. 2004, Wu et al. 2010, Amis 2012).

The relative positions of AM and PL bundles change when the knee is flexed because the femoral attachments of the bundles move from vertical to horizontal orientation in extension-flexion movement when the patient is supine (Chhabra et al. 2006, Colombet et al. 2006, Edwards et al. 2008, Zantop et al. 2008b) (Figure 3).

In extension, the bundles are parallel in the coronal plane, but when the knee is flexed, the ACL rotates approximately 90^o externally and the bundles are crossed (Chhabra et al. 2006, Petersen and Zantop 2007). The PL bundle is shorter, runs a more oblique course in the coronal plane, and is attached further from the axis of tibial rotation than the AM bundle (Amis 2012).

In the unloaded extended knee, the PL bundle is tight and the AM bundle relatively loose (Amis and Dawkins 1991). When the knee is flexed, the AM bundle tightens and the PL bundle loosens (Amis and Dawkins 1991). The PL bundle tightens in internal and external rotation of the knee (Chhabra et al. 2006). When the knee is loaded by quadriceps muscle contraction as under weightbearing, both bundles are tight at low flexion angles and loosen with increasing flexion (Kurosawa et al. 1991, Jordan et al. 2007). Accordingly, the AM and PL bundles behave reciprocally in the unloaded knee but nonreciprocally in the loaded knee (Yasuda et al. 2011). By selectively cutting and reconstructing the bundles in vitro, it has been shown that the PL bundle stabilizes the knee more in near extension and the AM bundle in flexion (Amis and Dawkins 1991, Yagi et al. 2002, Wu et al.

2010). In conclusion, both bundles function in a complementary manner controlling knee joint laxity (Wu et al. 2010, Amis 2012). The roles of the two functional bundles of the ACL have been studied in order to develop surgical techniques that result in better rotational stability and clinical outcome than that

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achieved by conventional arthroscopic ACL reconstruction (Yunes et al. 2001, Freedman et al. 2003, Ristanis et al. 2003, Tashman et al. 2004, Logan et al. 2004).

4.3 ACL rupture

In sports, the knee is the second most commonly (17%) injured body part after the ankle (26%) (Haikonen and Lounamaa 2010). An ACL rupture is the most commonly (20%) diagnosed internal derangement of the knee in sports injuries (Majewski et al. 2006). The estimated annual incidence of ACL rupture in the general population is approximately 0.8-1.2/1000 (Frobell et al. 2007, Gianotti et al. 2009), of which an estimated 40% are partial ruptures (Yao et al. 1995, Van Dyck et al. 2011). The typical mechanism of ACL rupture is a sudden change in direction on the weight-bearing knee that results in twisting or a valgus strain of the knee (Perera et al. 2013). The ACL ruptures at approximately 2000 N load and at 20% elongation (Woo et al. 1991, Woo et al. 1999).

Two clinical tests are typically used in the clinical evaluation of the stability of the injured knee: the Lachman test and pivot shift. In a meta-analysis, the Lachman test had a sensitivity of 85% and a specificity of 94% in comparison with the pivot shift with a sensitivity of 24% and a specificity of 98% for diagnosing ACL disruption (Benjaminse et al. 2006). However, at the clinical examination immediately after the trauma, the knee is often too swollen to examine properly (Perera et al. 2013). In a recent British study, the diagnosis of ACL disruption was made clinically in 61% of cases and based on MRI findings in 39% of cases (Perera et al. 2013). Intraoperative evaluation of the pivot shift test under anesthesia before the start of arthroscopy is more reliable than in the clinic (Benjaminse et al. 2006).

For over 20 years, MRI has been used for the evaluation of the ACL and other structures of the knee (Remer et al. 1992). Already in 2003, a meta-analysis showed 94% sensitivity and 94% specificity for MRI diagnosis of ACL disruption with surgical confirmation (Oei et al. 2003). For 3T MRI, the recent reported sensitivity is 83% and specificity 99% (Van Dyck et al. 2011).

The direct MRI findings of acute full-thickness ACL rupture are complete discontinuity of fibers or irregular contour with increased signal intensity (SI) on intermediate density (PD)-weighted or T2-weighted images with reported 83-93%

sensitivity and 93-98% specificity (Remer et al. 1992, Robertson et al. 1994, Brandser et al. 1996). In addition, many indirect MRI findings have also been described that have low sensitivity but high specificity. The most helpful indirect

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findings are lateral compartment bone contusion (sensitivity 48% and specificity 97%) and posterior displacement of the lateral meniscus (sensitivity 56% and specificity 99%) (McCauley et al. 1994, Bining et al. 2009). The other indirect findings reported in the literature are as follows: the posterior cruciate ligament (PCL) buckle (sensitivity 52% and specificity 94%), the posterior PCL line (sensitivity 52% and specificity 91%), anterior displacement of the tibia (sensitivity 41% and specificity 91%), deep lateral femoral notch (sensitivity 19% and specificity 100%), the entire lateral collateral ligament (LCL) seen on one coronal image, hemarthrosis, and associated avulsion fractures of the lateral tibial rim, tibial spine, or posteromedial tibial plateau (Noyes et al. 1980, McCauley et al. 1994, Gentili et al. 1994, Brandser et al. 1996).

ACL tears are often associated with other internal derangements of the knee such as medial collateral ligament (MCL) or meniscal tears or posterolateral corner injuries (LCL tear, Segond fracture, biceps femoris tendon tear, popliteus tendon tear, and capsular tears) that can be diagnosed using MRI (Recondo et al. 2000, Bining et al. 2009, Farshad-Amacker and Potter 2013).

The clinical diagnosis of a partial ACL tear is based on an asymmetric Lachman test, a negative pivot shift test, a low-grade (< 4 mm) KT-1000 arthrometer measurement, and ultimately arthroscopic evidence of ACL injury (DeFranco and Bach 2009). Partial tears of the ACL are difficult to distinguish from total ruptures using MRI (Umans et al. 1995, Yao et al. 1995). The MRI findings of partial ACL tear are preserved continuity of some fibers, increased intrasubstance T2-weighted SI, and bowing of the ACL (Umans et al. 1995). Based on these findings, a partial tear and a full rupture of the ACL are diagnosed with fairly low sensitivity of 20- 70%, while the specificity is 62-89% (Umans et al. 1995, Van Dyck et al. 2012). In a 3T MRI study, the sensitivity and specificity of partial ACL tear were higher, 77%

and 95%, respectively (Van Dyck et al. 2011). In a preliminary study, the use of diffusion-weighted MRI to evaluate partial tear of the ACL improved the sensitivity to 96% and the specificity to 94% (Delin et al. 2013).

A disrupted ACL usually fails to heal in contrast to many other human ligaments (Kohn 1986, Murray et al. 2000). ACL disruption is associated with functional impairment of the knee including joint laxity, reduced quadriceps strength, and changes in knee joint loading, all resulting in decreased activity and increased risk of osteoarthritis (Allen et al. 1999, Spindler et al. 2005, Spindler and Wright 2008). However, approximately one third of patients are able to continue previous levels of activity with an ACL-deficient knee (Noyes et al. 1983a). These patients have good dynamic stability of the knee (Kaplan 2011). The ruptured ACL

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remnant may attach by scarring to the medial wall of the lateral femoral condyle or to PCL and provide some residual knee stability (Crain et al. 2005). The natural course of disrupted ACL leads to radiographic findings of osteoarthritis in 50-90%

of patients in 9-16 years after the injury (Noyes et al. 1983b, Kannus and Järvinen 1987, Sommerlath et al. 1991). The return to high-level sports activities with an unstable knee resulted in meniscal damage and osteoarthritis in 95% of cases in 20- year follow-up (Nebelung and Wuschech 2005).

The development of the knee osteoarthritis after trauma was first described as ACL injury cascade, in which an isolated ACL injury causes instability and secondary meniscal damage leading to osteoarthritis (Daniel et al. 1994). However, in recent years, the associated meniscal and chondral injuries at the initial trauma have been recognized as primary risk factors for osteoarthritis after ACL injury (Lohmander et al. 2007, Shelbourne and Gray 2009, Oiestad et al. 2009, Li et al.

2011, Murray et al. 2012, Shelbourne et al. 2012, Potter et al. 2012). Associated meniscal injuries are found in 15-40% of cases of ACL disruption (Levy and Meier 2003, Majewski et al. 2006). In a recent MRI study, all patients with isolated ACL tear sustained initial chondral injuries that progressed in 11-year follow-up (Potter et al. 2012). The proposed new term “knee trauma cascade” highlights the significance of these combined injuries resulting in osteoarthritis (Petersen 2012).

4.4 Conservative treatment of ACL ruptures

The conservative treatment of ACL rupture aims to rebuild muscle strength, joint mobility, and neuromuscular control to enable pre-injury activity levels (Risberg et al. 2004). In recent studies, a structured 24-week rehabilitation program aimed to improve the strength of the quadriceps and other lower limb muscles, and balance and coordination has been used (Frobell et al. 2010, Frobell et al. 2013). The outcomes were as good for moderately active patients with acute ACL disruption treated either with a rehabilitation program or with rehabilitation and additional ACL reconstruction in 5-year follow-up (Frobell et al. 2013). It is widely accepted that patients with little exposure to high-level activities that involve cutting or pivoting movements or heavy work may satisfactorily be treated conservatively (Kannus and Järvinen 1990, Beynnon et al. 2005b, Spindler and Wright 2008, Kallio 2010).

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4.5 Alternative ACL repair techniques

Repairing the disrupted ACL by suturing does not lead to healing of the ligament (Engebretsen et al. 1990). In the healing response technique of proximal ACL disruption, holes were made to femoral ligament attachment site and to the native ligament with 4-year results no better than conservative treatment (Steadman et al.

2012, Wasmaier et al. 2013). A new technique of bioenhanced ACL repair has recently been tested with in vivo animal models showing promising results of reduced chondral damage compared with ACL reconstruction at 12 months follow-up (Murray and Fleming 2013b). In bioenhaced ACL repair, looped sutures are fixed to small femoral and tibial tunnels and to the remaining tibial stump of the ACL and covered with autologous blood to activate the scaffold (Murray and Fleming 2013a, Murray and Fleming 2013b).

4.6 ACL reconstruction

The aim of the surgical ACL reconstruction is to restore normal knee function and stability (Beynnon et al. 2005b). Indications for ACL reconstruction are knee instability in normal daily activities, return to sports involving cutting and pivoting such as soccer, and heavy work such as firefighting or law enforcement (Spindler and Wright 2008, Kallio 2010, Brophy et al. 2012). The other aim is to prevent future degenerative meniscal and chondral changes by restoring the normal kinematics of the knee (Daniel et al. 1994, Jomha et al. 1999). An estimated 175000 ACL reconstructions are performed annually in the USA and approximately 3000 in Finland (Gottlob et al. 1999, Rautiainen and Rasilainen 2011).

The concept of reconstructing the ACL with autograft was developed in the 1970s and 1980s, initially by arthrotomy (Odensten et al. 1985, Andersson et al.

1989). The technique evolved to arthroscopical ACL reconstruction in the 1990s (Arciero et al. 1996). The transtibial SB ACL reconstruction has been the gold standard of operative treatment for over 20 years (Freedman et al. 2003b, Fu et al.

2008, Spindler and Wright 2008).

The first reports on DB ACL reconstruction in the 1980s went largely unnoticed (Mott 1983, Zaricznyj 1987). The technique was re-introduced in Japan in 1999 as a more anatomic way to reproduce the ACL anatomy and the technique was quickly adopted in the USA (Muneta et al. 1999, Yasuda et al. 2004, Cha et al.

2005). Based on the principle of reproducing anatomy, the anatomic SB ACL

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reconstruction was described in 2010 as an alternative to anatomic DB reconstruction for knees with small anatomic ACL insertions (van Eck et al. 2010a, Rabuck et al. 2012).

Anatomical ACL reconstruction is defined as the functional restoration of the native ACL (van Eck et al. 2010a). It can be performed either as an SB or DB procedure following the 4 principles of restoring native insertion site anatomy, the 2 functional bundles if the size of native insertions sites is appropriate, and the tension behavior of the native ACL and of individualizing the procedure by each patients native anatomy such as the size of the native insertion sites (Yasuda et al.

2011).

The latest modification is the triple-bundle (TB) ACL reconstruction, which comprises a bifurcating anteromedial/intermediate graft and a PL graft with two femoral and three tibial graft tunnels (Shino et al. 2005). In addition, if the ligament tear is confined only to the AM or PL bundles, only the torn bundle can be reconstructed separately (Ochi et al. 2009, van Eck et al. 2010b).

4.6.1 Graft type and fixation

The most commonly used autografts in ACL reconstruction are the bone-patellar tendon-bone (BPTB) graft and the 4-strand hamstring tendon graft (Beynnon et al.

2005b). A quadriceps tendon graft with or without patellar bone block has also been used (Lund et al. 2014). The graft is fixed either within the bone tunnels or externally to the cortical bone to obtain incorporation of the graft to the bone (Beynnon et al. 2005b). The most common graft fixation types are interference fixation with either metal or biodegradable screws and extracortical fixation with devices combining sutures and a post (Brand et al. 2000).

4.6.2 Conventional ACL reconstruction techniques

In the transtibial ACL reconstruction technique described by Rosenberg, the tibial tunnel is created first with a tibial guide to the anatomical tibial insertion of the native ACL (Beck et al. 1992, Chen et al. 2003). Then the femoral tunnel is drilled through the tibial tunnel to achieve an isometric femoral graft tunnel position so that the distance of the graft origin and insertion remains constant during knee flexion and extension to prevent graft rupture (Zavras et al. 2001, Musahl et al.

2005). The graft is fixed with the knee at full extension (Hussein et al. 2012b).

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This technique has been criticized because it results in non-anatomic femoral tunnel position (Desai et al. 2013). Another possible result of transtibial drilling is a mismatched graft that is drilled to tibial PL bundle insertion and to femoral AM tunnel insertion in an attempt to avoid graft impingement to the roof of the intercondylar notch (Kopf et al. 2010, Karlsson et al. 2011). A mismatched graft is more vertically oriented than the native ACL and is ineffective in restoring the rotational stability of the knee (Woo et al. 2002, Brophy et al. 2006, Yasuda et al.

2011).

In the outside-in technique, both the femoral and the tibial tunnels are drilled with specific guides to the anatomical insertions of the native ACL (Harner et al.

1994). In the freehand technique described by Pinczewski, the femoral tunnel is first drilled using an anteromedial portal at a point of 5 mm anterior to the attachment of the posterior capsule, and the tibial tunnel after that as in other techniques (Deehan et al. 2000).

4.6.3 Anatomical DB, SB and TB ACL reconstruction techniques

In anatomical DB ACL reconstruction, the insertion sites of the ruptured AM and PL bundles are identified and marked. The femoral tunnels for the AM and PL grafts are first drilled to the anatomical native ligament insertions using AM portal.

Then the tibial tunnels are drilled similarly to the native AM and PL bundle insertions with a tibial guide. The PL graft is tensioned and fixed with the knee in extension and the AM graft with the knee in 45-60^o of flexion (Järvelä 2007, Fu et al. 2008, Karlsson et al. 2011).

According to the anatomical ACL reconstruction concept, the anatomical SB technique is indicated if the patient’s native ligament insertion sites are too small for the two tunnels of the DB technique. In the anatomical SB technique, the femoral tunnel is first drilled to the center of the anatomical attachment of the native ACL at the medial wall of the lateral femoral condyle using AM portal (Steiner et al. 2009, van Eck et al. 2010a, Hussein et al. 2012b). Then the tibial tunnel is drilled at the center of anatomic tibial native ACL insertion with a guide and the graft is fixed with the knee at 15-20^oof flexion (Rabuck et al. 2012).

In anatomical TB reconstruction, the two femoral tunnels are drilled as in the DB technique. The PL graft is essentially similar to DB reconstruction. The AM graft is dissected at the distal end to make a bifurcating anteromedial/intermediate (AM/IM) graft. Three tibial tunnels are then drilled at the native ACL insertion

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and the grafts fixed at 15-20^o of flexion to produce a fan-shaped graft simulating the native ACL (Tanaka et al. 2012).

4.7 Outcomes of ACL reconstruction

The studied clinical outcomes are the same as the aims of surgery: subjective and measured knee function and stability and prevention of osteoarthritis and meniscal degeneration. The commonly used objective measurements for knee kinematics and stability are instrumented AP laxity measurement difference between the injured and the non-injured knee and the pivot-shift test for rotational instability.

Degenerative changes are evaluated using radiographic grades such as Kellgren- Lawrence (Kellgren and Lawrence 1957) or with MRI, which directly shows chondral damage and also associated meniscal degeneration (Potter et al. 1998).

Patient-reported outcomes are commonly evaluated with the Lysholm score (Lysholm and Gillquist 1982), the IKDC functional score (Hefti et al. 1993), the Cincinnati knee score (Noyes et al. 1989), and the knee injury and osteoarthritis outcome score (KOOS) (Roos et al. 1998) or with patient’s return to sport. A need for more precise outcome measurements of knee function to compare the different treatments and to reduce the risk of long-term osteoarthritis has been recognized (Karlsson et al. 2011).

The reported graft failure rate of conventional ACL reconstruction is 3-5%

(Spindler et al. 2003, Ahlden et al. 2012). Technical errors such as graft misplacement are a major cause of graft failure (Giffin and Harner 2001, MARS Group et al. 2010). The autograft type (BPTB autograft or hamstring autograft) or the means of graft fixation have not affected the outcome of surgery (Spindler and Wright 2008, Biau et al. 2009, Holm et al. 2010).

Both conventional and anatomical ACL reconstructions are effective in restoring the AP stability (Biau et al. 2009, Holm et al. 2010, Murray et al. 2012, Hussein et al. 2012b, Desai et al. 2013). The anatomical SB reconstruction results in slightly better AP stability and significantly better rotational stability than conventional ACL reconstruction (Hussein et al. 2012b). The DB reconstruction results in better AP and rotational stability than both SB reconstructions (Hussein et al. 2012b, Suomalainen et al. 2012, Xu et al. 2013).

In two recent meta-analyses of conventional ACL reconstruction, the rate of moderate to severe radiographic osteoarthritis 10 years postoperatively was 20-28%

(Claes et al. 2013, Ajuied et al. 2013). The associated meniscal or chondral injuries

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at the initial trauma result in 50-80% prevalence of osteoarthritis 10-15 years after conventional ACL reconstruction (Oiestad et al. 2010, Claes et al. 2013). For DB ACL reconstruction, moderate to severe radiographic osteoarthritis was found in 10% of patients in the 5-year follow-up of 20 patients (Suomalainen et al. 2012).

MRI evaluation is much more sensitive to chondral degeneration than radiographic evaluation which only shows findings of advanced chondral degeneration in osteoarthritis (Potter et al. 2012). A recent MRI study showed that all patients with acute isolated ACL disruption also had findings of chondral injury at the initial MRI, most often in lateral femoral and tibial condyles, and that the degeneration accelerated in 5-7 year follow-up (Potter et al. 2012). The chondral injury at the primary trauma of the ACL injury results in chondrocyte apoptosis leading to chondral degeneration and osteoarthritis (Lotz et al. 1999). In a recent meta- analysis, the rate of osteoarthritis was similar after ACL reconstruction and conservative treatment, thus emphasizing the impact of primary chondral injury (Chalmers et al. 2014).

Meta-analysis of long-term results with a mean follow-up of 13.9 years (SD 3.1) resulted in no statistical difference in subjective functional outcome by the Lysholm or KOOS scores after conventional ACL reconstruction or conservative treatment (Chalmers et al. 2014). In studies comparing conventional and anatomical DB ACL reconstruction with 5-year follow-up, no statistical difference in Lysholm scores was found (Hussein et al. 2012b, Suomalainen et al. 2012). The functional outcome results after conventional ACL reconstruction by the Lysholm score (0-100) were 82-90 at 10-15 years follow-up (Meuffels et al. 2009, Oiestad et al. 2010, Struewer et al. 2012). In Swedish material of almost 18000 ACL reconstructions, the mean KOOS score (0-100) was 79 at 5-year follow-up and at 2-year follow-up 77 and 78, for SB and DB ACL reconstructions, respectively (Ahlden et al. 2012). Based on recent meta-analyses, 63-76% of operated patients had returned to their preinjury level of sports (Biau et al. 2007, Ardern et al. 2011).

4.8 Conservative versus operative treatment

Two recent systematic reviews of the best treatment of ACL rupture came to the same conclusion: the methodological quality of most studies is poor and currently there is no evidence-based treatment strategy (Delince and Ghafil 2012, Smith et al.

2013). In a randomized controlled trial of 121 active patients with 5-year follow-up, the patient-reported and radiographic outcomes of conventional ACL

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reconstruction and structured rehabilitation did not differ although the mechanical stability was better in the ACL reconstruction group (Frobell et al. 2013). Cost- effectiveness of ACL reconstruction has been found to be better than structured rehabilitation in three published analyses (Gottlob et al. 1999, Farshad et al. 2011, Mather et al. 2013). This result is based on increased knee laxity in the rehabilitation group, which is assumed to lead to more meniscal surgery and eventually to knee prosthesis due to osteoarthritis in a greater proportion of patients compared with the ACL reconstruction group (Farshad et al. 2011, Mather et al. 2013).

4.9 MRI evaluation of ACL reconstruction

As the number of ACL reconstructions increased in the 1990s and 2000s, the MRI imaging of the postoperative knee also became more common (Recht and Kramer 2002). The indications for postoperative evaluation of ACL reconstruction with MRI include laxity, stiffness, pain, a new injury, preoperative planning of revision, and infection of the knee (Recht and Kramer 2002, Papakonstantinou et al. 2003).

Graft failure is a clinical term defined as pathologic knee laxity after ACL reconstruction (Bencardino et al. 2009). The reported conventional ACL reconstruction graft failure rate is 3-5% (Spindler et al. 2003, Ahlden et al. 2012). In total, 10-30% of patients have knee pain or laxity following conventional ACL reconstruction (Yunes et al. 2001). Knee pain is the most common but nonspecific symptom of complications of ACL reconstruction, thus making further diagnostic imaging necessary (Passler et al. 1999, Collins et al. 2008).

MRI is the best imaging modality for postoperative ACL reconstruction evaluation due to its superior soft tissue contrast, multiplanar capability, and lack of ionizing radiation (Farshad-Amacker and Potter 2013). The complications of ACL reconstruction that are diagnosed using MRI include complete and partial graft ruptures, graft impingement, arthrofibrosis, graft or tunnel cysts, hardware failure, and infection (Recht and Kramer 2002, Papakonstantinou et al. 2003, Bencardino et al. 2009). Some authors also consider tunnel widening a complication (Giaconi et al. 2009, Farshad-Amacker and Potter 2013). Because the clinical significance of many MRI findings is unclear at the moment, it is important to correlate the MRI findings with clinical examination (Casagranda et al. 2009).

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4.9.1 MRI techniques

Most imaging protocol recommendations in the literature are for 1.5 tesla (T) scanners. However, the same diagnostic properties of the sequences are achieved with 3 T scanners that produce better images with shorter scanning times (Craig et al. 2005). Spin-echo (SE) sequences are recommended for ACL graft imaging because metallic debris and orthopedic hardware produce more artifacts in gradient-echo sequences (Papakonstantinou et al. 2003). The recommended slice thickness for 1.5 T is 3-4 mm for axial, sagittal, and coronal images, and 2.5 mm for oblique images (Casagranda et al. 2009, Araujo et al. 2013).

The integrity of the graft is assessed with sagittal PD-weighted and T2-weighted fat-saturated (FS) images and preferably with sagittal or coronal oblique PD- weighted or T2-weighted images along the course of the graft (Papakonstantinou et al. 2003, Casagranda et al. 2009, Bining et al. 2009). Some authors recommend prescribing the routine sagittal plane along the lateral femoral condyle to minimize individual variability (Casagranda et al. 2009). In studies of graft signal intensity (SI), T2-weighted and PD-weighted sequences in sagittal, coronal, and oblique sagittal planes have been used (Sonoda et al. 2007, Saupe et al. 2008).

Coronal T1-weighted images are used to evaluate bone structure and coronal and sagittal T2-weighted FS images to assess the graft, bone bruise, and articular cartilage (Casagranda et al. 2009, Araujo et al. 2013). Axial T2-weighted FS images are recommended for the evaluation of the femoral attachment of the graft and also for graft integrity (Casagranda et al. 2009, Araujo et al. 2013). In studies of tunnel enlargement and tunnel communication, T1-weighted images in axial, coronal, and sagittal planes have been used (Siebold 2007, Järvelä et al. 2008, Siebold and Cafaltzis 2010).

4.9.2 Graft ligamentization period

The SI changes of the conventional ACL reconstruction graft during the first 12- 24 months after operation are called the ligamentization period (Amiel et al. 1986b, White et al. 2005). Immediately after the operation, the graft has low SI in T1- and T2-weighted images. After 3-8 months, however, the graft SI increases to intermediate due to revascularization and re-synovialization of the graft (Howell et al. 1991b, Schatz et al. 1997, Rispoli et al. 2001, White et al. 2005). Then, the SI decreases to low SI resembling the native ACL 12-24 months after operation (Rispoli et al. 2001, Vogl et al. 2001, Hong et al. 2005, White et al. 2005). However,

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recent studies have shown that the graft SI can remain increased at long-term follow-up after conventional ACL reconstruction with no clinical findings of graft failure (Saupe et al. 2008). Other authors have even stated that results on graft SI are contradictory and that knowledge about graft SI changes is currently insufficient (Miyawaki et al. 2014). The anatomical ACL reconstruction results in a more oblique position of the graft in the coronal plane, which has been proposed as an explanation of the prolonged increased SI of the anatomical grafts (Farshad- Amacker and Potter 2013). According to DB ACL reconstruction MRI studies, some increased graft SI can be seen after 12-24 months and should not alone be considered a sign of graft failure (Sonoda et al. 2007, Poellinger et al. 2009, Casagranda et al. 2009). In 4-strand hamstring grafts, the finding of some linear areas of increased signal between the graft strands is considered normal and represents the multistrand structure of the graft (Bencardino et al. 2009). BPTB grafts and quadriceps grafts constitute a single piece of tendon and should have more homogenous SI on MRI (Bencardino et al. 2009).

4.9.3 The magic angle effect in graft evaluation

The SI of tendons and ligaments depends on their orientation to the static magnetic field (B0) in short and moderate echo time (TE<37 ms) pulse sequences (Fullerton et al. 1985, Erickson et al. 1991, Peh and Chan 1998). In clinical imaging, this phenomenon is known as the magic angle (MA) artifact. It involves tissues that have a highly ordered collagen fibre structure: tendons, ligaments, labrums, menisci, intervertebral discs, articular cartilage, fibrocartilage, and also peripheral nerves (Bydder et al. 2007).

The highly ordered collagen fibers contain water that is bound to collagen molecules (Fullerton and Rahal 2007). The protons of water are subject to dipolar interactions whose strength depends on the orientation of the collagen fibers to B0

(Bydder et al. 2007). Usually, these interactions result in rapid dephasing of the MR signal that corresponds to the small amount of or lack of signal seen in tendons and ligaments (Bydder et al. 2007). The interactions of water bound to collagen molecules are gradually weaker in angles of collagen fibers from 20^o to 55^o to the B0 causing gradually increased SI up to sixfold in short TE pulse sequences (Fullerton and Rahal 2007). The MA is only detected if TE is shorter than 37 ms as in T1-weighted and PD-weighted pulse sequences (Peh and Chan 1998). In order to rule out the MA and to be able to reliably detect increased SI consistent with

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tendon pathology, T2-weighted sequences with longer TE are recommended for MRI evaluation of tendons that course at an angle close to 55^o to B0, such as the supraspinatus and infraspinatus tendons, the patellar tendon and the peroneal tendon (Shalaby and Almekinders 1999, Wright et al. 2001, Wang et al. 2005). It is also possible to reduce the MA by patient and limb position with respect to B0

(Fullerton and Rahal 2007). In most clinical MR imagers, the B0 is oriented parallel to the table and the longitudinal axis of the patient (Fullerton and Rahal 2007). In theory, stretching a tendon while imaging may also cause SI alteration because stretching moves water out from tendon (Puxkandl et al. 2002, Fullerton and Rahal 2007).

In pathologic conditions, loss of organized collagen structure with increased free fluid, mucinous vacuoles, cellular debris, fibrin, and disorganization of collagen fiber orientation is seen in ligaments and tendons (Fullerton and Rahal 2007).

When the organized collagen structure is disturbed, the SI of tissue is increased on all MRI sequences in angles close to B0, and the MA effect of the normal collagen structure is not seen (Fullerton and Rahal 2007).

In ACL reconstruction, graft harvesting, preparation, and avascularization cause changes to the collagen structure (Amiel et al. 1986a, Goradia et al. 2000).

Specifically, the preparation of hamstring grafts by folding and suturing causes heterogenity of the collagen fibre orientation (Kondo et al. 2012). In animal models, the histologic structure of both patellar and hamstring grafts begins to resemble that of native ACL by 12 months postoperatively, but the highly organized collagen structure of the native ligament is not achieved (Amiel et al.

1986a, Goradia et al. 2000).

Because the ACL reconstruction graft angle to B0 is significantly less than 55^o in MRI, some authors state that the MA is an unlikely cause of increased graft SI in short TE sequences (Jansson et al. 2001). However, as the MA effect begins at fiber angles as low as 20^o to B0, some MA effect should be expected (Schick et al.

1995, Fullerton and Rahal 2007). In a well-designed clinical MRI study, both PD- weighted and T2-weighted sequences were used in graft evaluation and increased graft SI was seen in a similar proportion of cases in both sequences (Saupe et al.

2008). In conclusion, PD-weighted sequences are not significantly affected and T2- weighted sequences are not affected by the MA effect in graft MRI evaluation (Saupe et al. 2008).

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4.9.4 Graft disruption and partial rupture

A graft is considered disrupted when intact fibers are absent and fluid signal is replacing the graft (Recht and Kramer 2002, Papakonstantinou et al. 2003, Collins et al. 2008, Bencardino et al. 2009, Casagranda et al. 2009). A partial tear shows some preserved fibers and a focal thinning of the graft (Collins et al. 2008, Casagranda et al. 2009). As in MRI diagnosis of native ACL disruption, other previously described findings that suggest graft disruption such as graft laxity, increased graft SI, anterior tibial translation, uncovered horn of the lateral meniscus, and buckling of the PCL have low sensitivity but high specificity (Collins et al. 2008).

4.9.5 Graft elongation

An elongated graft has intact fibers but the knee is clinically unstable (Sanders 2002). The primary MRI finding is posterior bowing of the graft, and the secondary findings are anterior tibial translation and buckling of the PCL (Sanders 2002).

4.9.6 Graft impingement

Non-anatomical tunnel locations in ACL reconstruction may lead to graft impingement, in which the graft rubs against the roof of the femoral intercondylar notch resulting in extension loss (Recht and Kramer 2002, Karlsson et al. 2011).

The MRI findings of graft impingement are posterior bowing of the graft, contact of the graft with the notch roof, and increased SI in T2-weighted and PD-weighted images in the anterior part of the graft (Howell 1998, Recht and Kramer 2002, Papakonstantinou et al. 2003).

4.9.7 Arthrofibrosis and cyclops lesion

Another complication that causes limited range of motion is arthrofibrosis, an excessive production of fibrous tissue around the graft and capsular contraction (Papakonstantinou et al. 2003, Farshad-Amacker and Potter 2013). A cyclops lesion is localized arthrofibrosis forming a nodule anterior to the graft and results in extension loss of the knee (Recht and Kramer 2002, Papakonstantinou et al.

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2003). The fibrous tissue is of low to intermediate SI in T1- and T2-weighted images (Farshad-Amacker and Potter 2013).

4.9.8 Cystic degeneration of the graft and tunnel cysts

Cystic degeneration of the graft is seen in MRI as a cystic lesion with low SI in T1- weighted images and high SI in T2-weighted images between intact graft fibers (Papakonstantinou et al. 2003). If large, it may cause limitated range of motion, and if it is situated in the part of the graft inside the tunnel, cystic degeneration may be associated with tunnel enlargement (Schatz et al. 1997, Papakonstantinou et al.

2003).

Ganglion cysts may form inside the bone tunnels, mainly in the tibia (Bencardino et al. 2009, Farshad-Amacker and Potter 2013). A tunnel cyst is well defined and has high SI of fluid in T2-weighted images (Bining et al. 2009).

Usually, tunnel cysts are asymptomatic and confined inside the bone tunnel. On some rare occasions, a tibial tunnel cyst may extend distally out of the tunnel and bone and present as a palpable mass (Bencardino et al. 2009). Inside the tunnel, a tunnel cyst may cause tunnel enlargement (Frick et al. 2006, Farshad-Amacker and Potter 2013).

4.9.9 Tunnel enlargement

The enlargement of the bone tunnels occurs postoperatively after ACL reconstruction and may complicate revision surgery (Wilson et al. 2004, Samuelsson et al. 2009). The etiology of tunnel enlargement is unknown and probably multifactorial (Wilson et al. 2004, Giaconi et al. 2009). Some enlargement can be caused intraoperatively by drilling and graft fixation because interference screws extrude cancellous bone during screw insertion (Buelow et al. 2002, Jagodzinski et al. 2005, Foldager et al. 2010, Siebold and Cafaltzis 2010).

Postoperative tunnel enlargement occurs in the first 3 months after ACL reconstruction (Wilson et al. 2004). Tunnel enlargement occurs more commonly with hamstring grafts than with BPTB grafts (Samuelsson et al. 2009). More tunnel enlargement is associated with extracortical graft fixation than with aperture fixation (L'Insalata et al. 1997, Beynnon et al. 2005a). More tunnel enlargement is seen with bioabsorbable screws than with metal screws, but metal screws cause artifacts and make postoperative MRI evaluation more difficult (Brand et al. 2000,

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Moisala et al. 2008). Most bioabsorbable screws are polylactide compounds and their resorption properties in clinical use are not well documentated (Konan and Haddad 2009). In a recent study, the remains of two newer-generation screws were present three years postoperatively (Cox et al. 2014). The resorption of bioabsorbable screws is hypothesized to induce production of cytokines that stimulate osteoclastic activity and lead to tunnel enlargement (Wilson et al. 2004).

In most studies, tunnel enlargement has not been associated with knee laxity or functional impairment (Samuelsson et al. 2009). Tunnel diameters can be measured using T1-weighted or PD-weighted MRI in which the tunnel margins are clearly visible (Järvelä et al. 2008, Siebold and Cafaltzis 2010).

4.9.10 Tunnel communication

Tunnel communication is seen only in DB ACL reconstruction where two graft tunnels are drilled close to each other in both the femur and in the tibia. Tunnel communication is defined as the absence of the bony bridge between the tunnels at 1 cm from the articular surface (Siebold and Cafaltzis 2010). In a prospective study with MRI done at 2 days and at 7 months postoperatively, tunnel communication was caused intraoperatively by drilling in 24% of patients in the tibia and later by tunnel enlargement in 19% of patients in both the femur and the tibia (Siebold and Cafaltzis 2010). Controversily, in other studies no postoperative tunnel communication was found (Järvelä et al. 2008, Hantes et al. 2010). The best modality to evaluate the bone tunnels is CT, which enables very good spatial resolution of bone and multiplanar reconstructions in the direction of the tunnels (Purnell et al. 2008, Hantes et al. 2010). If MRI is used to evaluate the postoperative knee, the bone tunnels are visible and it is possible to assess tunnel communication in axial, sagittal, and coronal T1-weighted images without the effective dose of CT (Siebold and Cafaltzis 2010).

4.9.11 Evaluation of native ACL insertion sites and graft tunnel location With the concept of anatomical ACL reconstruction, it has become necessary to measure the size of the ACL insertion of the individual patient in order to reproduce the anatomy with surgery (van Eck et al. 2010a, Yasuda et al. 2011). The size of the tibial insertion can be measured intraoperatively or in preoperative planning with 2D MRI, and the size of the femoral insertion can be measured with

Magnetic Resonance Imaging of Double-Bundle Anterior Cruciate Ligament Reconstruction

TOMMI KIEKARA

Magnetic Resonance Imaging of Double-Bundle Anterior Cruciate

Ligament Reconstruction

TOMMI KIEKARA

Magnetic Resonance Imaging of Double-Bundle Anterior Cruciate

Ligament Reconstruction

ABSTRACT

TIIVISTELMÄ

TABLE OF CONTENTS

1 ORIGINAL COMMUNICATIONS

2 ABBREVIATIONS

3 INTRODUCTION

4 REVIEW OF THE LITERATURE

4.1 Anatomy of the ACL

4.2 Biomechanics of the ACL

4.3 ACL rupture

4.4 Conservative treatment of ACL ruptures

4.5 Alternative ACL repair techniques

4.6 ACL reconstruction

4.7 Outcomes of ACL reconstruction

4.8 Conservative versus operative treatment

4.9 MRI evaluation of ACL reconstruction