Bone-patellar tendon-bone graft preparation technique to increase cross-sectional area of the graft in anterior cruciate ligament reconstruction/ Tehnika obrade kost-ligament casice-kost kalema za povecanje povrsine poprecnog preseka kalema kod rekonstrukcije prednjeg ukrstenog ligamenta kolena.
Patellar tendon autografts are used daily by orthopedic surgeons for anterior cruciate ligament (ACL) reconstruction because they are known to give good and easily reproducible clinical results. The first surgeon who used a part of patellar ligament for ACL replacement was Langworthy in 1930s . Thirty years later, Jones  and Bruckner  refined the initial technique by using the central third of the patellar tendon. Following Franke's  publication, bone-patellar tendon-bone (BTB) became one of the most popular graft sources and gained further popularity both in Europe and the United States through the work of Eriksson  and Clancy .
The use of BTB graft is associated with excellent clinical results in 80-90% of cases, as well as some complications of the knee extensor mechanism, including BTB harvest site morbidity  and disruption of the knee extensor apparatus . Bone-patellar tendon-bone graft ensures strong initial graft fixation using interference screws, allowing direct bone-bone healing and consecutive bony integration at the fixation points of the reconstruction . The main disadvantage of BTB is a graft-tunnel mismatch  due to a smaller cross-section area and incomplete filling of the tunnel compared to hamstring tendon graft [10, 11].
Not much has changed in the way the BTB graft is prepared before implantation. Pujil et al.  described arthroscopic double-bundle ACL reconstruction technique using a rectangular patellar bone block, a double stranded patellar tendon, and a double tibial bone block. By simulating anatomical ACL reconstruction, Shino et al.  and Herbort et al.  tried to improve the BTB SB technique, creating a rectangular tunnel and bony part of the graft, neglecting the importance of the cross-sectional area of the classic BTB graft, with a width of 10 mm and the thickness of 3-5 mm, which ultimately depends on the individual patient's characteristics [15-17].
The aim of this study was to present the modified BTB graft preparation technique. We hypothesized that modified BTB graft preparation technique would increase the cross-sectional area of the graft, thus getting closer to the characteristics of the native ACL and/or hamstring tendon graft.
Material and Methods
The procedure of the study was approved by the Local Human Research Ethical Committee. A prospective study, conducted from July 1 to December 31, 2013, included 93 male patients of the average age 26 (15-44) in whom measurements of the patellar tendon and BTB graft were performed during the anterior cruciate ligament reconstruction. Only men were included in the study due to a small number of women operated in that period. The knee was approached through a vertical skin incision made from the middle of the patella to the inferior portion of the tibial tubercle, with the knee flexed. The skin flaps were created and the incision was sharply carried down through the transverse fibres of the paratenon. The paratenon was incised at its midpoint to expose the entire width of the patellar tendon. Next, while maintaining the tendon in a stretched position by flexing the knee, it was incised first on one side of the graft followed by the other side, obtaining 12-14 mm wide patellar tendon. Then, a chisel was used to create the tibial bone plug, approximately 25 mm long and 10mm wide, by scoring the tibial cortex and removing an equilateral triangle of bone with the saw. An osteotome was used to lift the tibial bone plug carefully from its bed onto a lap pad. The patellar tendon with a tibial bone plug was lifted up and cleaned off the remaining soft tissue attachments with the scissors. Using an oscillating saw, a patellar plug of trapezoidal shape, 25 mm long and 10 mm wide, was created and gently removed. The tendinous part of the BTB graft was measured (its width and thickness) and prepared on a side table by an assistant (Figure 1). The graft was then placed on the holder with a handle in a way which allowed sewing the edges of the patellar tendon in the shape of a tube (Figure 2). The diameter of the graft was determined by passing the folded graft through the sizing cylinders with incremental size changes of 1 mm. The circumference of the central part of the BTB graft was manually measured using a suture tightened around the graft. The suture was then cut and its length was measured in mm . The diameters of the circle and the cross-sectional areas were then calculated using a geometrical calculation (O = 2r[pi] and P = [r.sup.2][pi]) (Figure 3).
The standard anterolateral portal was used as a viewing portal and the anteromedial one as a working portal. The ACL stump was debrided. The femoral tunnel was created through the anteromedial portal to avoid excess fluid loss. The knee was placed at 110-120 degrees of flexion. The femoral guide with an appropriate offset was introduced into the joint through the anteromedial portal. With the help of a femoral guide, a drill-wire was placed into the centre of the anatomic ACL insertion which was then overdrilled with a 10-mm diameter reamer. A suture was retrieved after the guide pin had been drilled into the joint. Afterwards, a cannulated reamer with an equal diameter to the graft created the tibial tunnel. A grasper was then placed through the tibial tunnel to retrieve the suture. Then the graft was passed through the tibia into the femoral socket, and once the graft was properly positioned in the tunnel, it was fixed with round cannulated interference screws (RCI). Firm traction was applied to the tibial bone block while putting the knee through the full range of knee motion in order to pretense the graft and make sure that there is no impingement in full extension. The graft was then tensioned using 80 N force and the screws were additionally tightened if needed. Lachman test was used to check the knee stability. A drain was placed in the knee and the operative wound was closed in the usual fashion.
The width and the thickness of patellar tendon was 33 mm (28-43) and 4.05 mm (3-5), respectively. The width of the taken patellar tendon was 13.62 mm (12-14). After the preparation of the BTB grafts (Table 1), the following measures were recorded: the circumference of 30 mm, the diameter of 9.55, and the cross-sectional area of 71.59 [mm.sup.2] in 9 patients; the circumference of 31 mm, the diameter of 9.87 mm, and the cross-sectional area of 76.50 [mm.sup.2] in 15 patients, and the circumference of 32 mm, the diameter of 10.19 mm, and the cross-sectional area of 81.51 [mm.sup.2] in 69 patients.
The patellar tendon is the most distal part of the extensor mechanism which connects the inferior pole of the patella and the tibial tubercle. Technically, it is a ligament (connecting a bone to a bone), but it has often been referred to as a tendon because the patella is a sesamoid bone. The average length of the patellar tendon is 40-53 mm [15, 16, 18, 19]. The patellar tendon is wider proximally than distally because the fascicles tend to converge toward the midline . Yoo et al.  measured the width of the proximal and distal part of the tendon and they were 30 mm and 24 mm, respectively. In our study, the mean patellar tendon width measured in the middle of the tendon was 33 mm (28-43 mm). Regarding the thickness of the patellar tendon, it has been shown that the central third of the patellar tendon is significantly thicker than the medial and lateral thirds , and may be affected by long-term sports activity . The average patellar tendon thickness in our study ranged from 3 to 5 mm, similar to the average tendon thickness described in other studies using either magnetic resonance imaging (MRI) , or cadaveric [16, 17] knee measurements.
The goal of the anatomical ACL reconstruction is to restore the natural anatomy. The reconstructed ACL size is determined by the harvested graft size, not by the size of the native ACL insertion site. It is important to know the geometric characteristics of the graft including the length, cross-sectional area, and surface attachment of ACL in order to determine the optimal mechanical graft properties and obtain optimal ACL reconstruction results. The ACL has a "band-like" shape and does not have the same dimensions throughout its whole length . Harner et al.  measured the cross-sectional area of the ACL mid-substance in older cadavers, and found that cross-sectional ACL mid-substance area was approximately 3.5 times smaller than the ACL tibial and femoral insertions. The tibial insertion area in 2D (projected on the tibial plateau) ranged from 114 [mm.sup.2] to 229 [mm.sup.2] [17, 24, 25], while the calculated cross-section area of the native ACL ranged from 32 to 65 [mm.sup.2], also confirmed in cadaveric studies [12, 16, 25].
If a BTB graft has the thickness of 3 mm, the width of 10 mm and the cross-sectional area (CSA) of 30 [mm.sup.2], it is still significantly smaller than a cross-sectional area of the native ACL and/or 8 mm diameter hamstring tendon graft (with 50 [mm.sup.2] of cross-sectional area) . Shimizu et al.  and Yoshiya et al.  have reported that a 10-mm wide patellar tendon graft has an average CSA of 33 [mm.sup.2], while Staubli et al.  reported the average CSA of 36 [mm.sup.2] in a cadaveric study. For the patellar tendon graft of the average thickness (3-5 mm) [16-18] and the width of 10 mm, the CSA will be 30-50 [mm.sup.2]. Our modified BTB graft preparation technique made it possible to increase its cross-sectional area to 71-81 [mm.sup.2], and come close to the CSA of the native ACL and hamstring tendon graft (Table 2).
Regardless of whether the anatomic tunnel placement in the native footprint may be more important than a complete filling of the footprints , we believe that our modified BTB graft preparation allows better reconstruction of native ACL and/or hamstring tendon graft geometric characteristics. Geometric characteristics of the patellar tendon directly affect the BTB graft and the results of ACL reconstruction, and in an ideal anatomical ACL reconstruction, the geometry of the ACL graft should resemble that of the original ACL . The major finding in the present study is that the modified BTB graft preparation technique made it possible to increase its CSA.
One of the possible complications associated with our modified BTB graft preparation is a rupture of the patellar tendon. We have been using this modified BTB graft preparation technique since 2006, and out of 1750 ACL reconstructions we performed during this period, only two patients developed a patellar tendon rupture 8 months after surgery associated with an intense jump .
The main weakness of this study is the lack of mechanical and biological testing of our graft, which is going to be addressed in our future research.
For the average thickness (3-5 mm) and width (10 mm) of the patellar tendon graft, the cross-sectional area will be 30-50 [mm.sup.2]. The modified bone-patellar tendon-bone graft preparation technique made it possible to increase its cross-sectional area to 71-81 [mm.sup.2].
ACL--anterior cruciate ligament
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Rad je primljen 20. VI 2015.
Recenziran 29. VI 2015.
Prihvacen za stampu 30. VI 2015.
Miroslav MILANKOV (1,2), Mirko OBRADOVIC (1,2), Miodrag VRANJES (1,2) and Zlatko BUDINSKI (1,2)
University of Novi Sad, Faculty of Medicine (1)
Clinical Center of Vojvodina, Novi Sad
Department of Orthopedic Surgery and Traumatology (2)
Corresponding Author: Prof, Dr Miroslav Milankov, Klinicki centar Vojvodine, Klinika za ortopedsku hirurgiju i traumatologiju, 21000 Novi Sad, Hajduk Veljkova 1-7, E-mail: email@example.com
Table 1. Geometric characteristics of the modified BTB graft Tabela 1. Geometrijske karakterisitke modifikovanog kalema No of patients BTB graft circumference in mm Diameter Broj pacijenata (measured at the central part) in mm (O=2r[pi])/Obim kalema u mm Precnik (mereno u sredisnjem delu) u mm 9 30 9.55 15 31 9.87 69 32 10.19 No of patients Half-diameter Cross-sectional Broj pacijenata in mm area in [mm.sup.2] Poluprecnik (P=[r.sup.2][pi]). u mm Poprecni pesek u [mm.sup.2] 9 4.77 71.59 15 4.93 76.50 69 5.09 81.51 O circumference/obim; P surface/povrsina, r half-diameter/ poluprecnik, [pi] = 3,14
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|Title Annotation:||ORIGINAL STUDIES/ORIGINALNI NAUCNI RADOVI|
|Author:||Milankov, Miroslav; Obradovic, Mirko; Vranjes, Miodrag; Budinski, Zlatko|
|Date:||Nov 1, 2015|
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