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Biomechanical Evaluation of Cross-Pin Versus Interference Screw Tibial Fixation Using a Soft-Tissue Graft During Transtibial Posterior Cruciate Ligament Reconstruction
Biomechanical Evaluation of Cross-Pin Versus Interference Screw Tibial Fixation Using a Soft-Tissue Graft During Transtibial Posterior Cruciate Ligament Reconstruction Yong Seuk Lee, M.D., Joon Ho Wang, M.D., Ji Hoon Bae, M.D., Hong Chul Lim, M.D., Jung Ho Park, M.D., Jin Hwan Ahn, M.D., Tae Soo Bae, Ph.D., and Bee-Oh Lim, Ph.D.
Purpose: This article reports the biomechanical demonstration of a technique for transtibial posterior cruciate ligament (PCL) reconstruction using a soft-tissue graft with cross-pin fixation in the tibia and compares this with the biomechanical properties achieved with other methods. Methods: We used 5 paired cadaveric knees and another 10 tibias. Soft-tissue grafts were randomized. The femoral side of the anterior cruciate ligament was fixed with a Bio-TransFix device (Arthrex, Naples, FL) (group I), and the tibial side of the PCL was fixed with a Bio-TransFix device (group II). In another 10 tibias, tibial fixations were performed by use of a bio-interference screw (group III). Biomechanical testing was carried out on a testing machine, and maximal failure load, stiffness, and displacement were analyzed. The lengths of the slots of the TransFix device (Arthrex) from the near cortex were measured to compare the proper length of the device. Results: Maximal mean failure loads in groups I, II, and III were 549.3 ⫾ 55.4 N, 570.8 ⫾ 96.9 N, and 371.3 ⫾ 106.2 N, respectively, showing a significant difference (P ⫽ .0003). Stiffnesses were 47.52 ⫾ 16.84 N/mm, 59.14 ⫾ 17.09 N/mm, and 27.60 ⫾ 16.73 N/mm, respectively, showing a significant difference (P ⫽ .01). Mean displacements were 19.99 ⫾ 5.79 mm, 19.09 ⫾ 8.51 mm, and 17.58 ⫾ 7.10 mm, respectively, showing no significant difference (P ⫽ .7535). The mean lengths of the slots of the TransFix device of the femurs and tibias were similar at 20.3 ⫾ 1.25 mm and 20.2 ⫾ 1.32 mm, respectively, showing no significant difference (P ⫽ .8637). Conclusions: The transtibial technique by use of cross-pin tibial fixation with a Bio-TransFix device in PCL reconstruction provides stable fixation that is comparable to that achieved by use of conventional bio-interference screw fixation and femoral fixation in an anterior cruciate ligament reconstruction, an already well-established technique. Clinical Relevance: Biomechanically, tibial cross-pin fixation compares favorably with interference screw fixation and is useful when a graft is short. However, safety issues have not yet been resolved. Key Words: Posterior cruciate ligament—Transtibial technique—Cross-pin fixation—Bio-TransFix—Biomechanics.
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or transtibial double-bundle posterior cruciate ligament (PCL) reconstruction, most surgeons use an Achilles allograft because the available graft length
is longer than those of other graft materials.1,2 Recently, soft-tissue grafts, in particular, a 4-stranded hamstring autograft or 2-stranded tibialis allograft,
From Korea University Ansan Hospital (Y.S.L., J.H.W., J.H.P.), and Korea University Guro Hospital (J.H.B., H.C.L.), Anam-dong Seongbuk-Gu, Seoul, Korea, Samsung Medical Center (J.H.A.), Gangnam-gu, Seoul, Korea, Korea Orthopedics & Rehabilitation Engineering Center (T.S.B.), Bupyung-ku Incheon, Korea, and Sports Science Institute, Seoul National University (B.-O.L.), Gwanak-gu, Seoul, Korea. The authors report no conflict of interest. Received July 18, 2008; accepted February 11, 2009. Address correspondence and reprint requests to Yong Seuk Lee, M.D., Department of Orthopaedic Surgery, Korea University Ansan Hospital, 516 Gozan-dong, Danwon-gu, Ansan 425-707, South Korea. E-mail: [email protected] © 2009 by the Arthroscopy Association of North America 0749-8063/09/2509-8418$36.00/0 doi:10.1016/j.arthro.2009.02.006
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have provided other graft options, and they offer advantages and clinical results that are almost equivalent to anterior cruciate ligament (ACL) reconstruction with bony fixation.3-6 However, often, a 4-stranded hamstring or 2-stranded tibialis graft is short with bio-interference fixation at the anterior orifice of the tibial tunnel. Therefore we proposed a new surgical technique for arthroscopic double-bundle PCL reconstruction that is stronger and not restricted by graft type and length and that uses mainly a 4-stranded hamstring autograft or 2-stranded tibialis allograft with TransFix (Arthrex, Naples, FL) tibial fixation.7 The TransFix implant was originally used for the ACL femoral fixation of a soft-tissue graft and is considered to be a safe option.8-12 However, tibial fixation of a TransFix implant is not well established, and unpredictable complications can occur.7,13,14 The aim of this study was to demonstrate the surgical technique of transtibial PCL reconstruction with cross-pin fixation (Bio-TransFix device [Arthrex], 50 mm in length and 5 mm in diameter) by comparing the biomechanical properties obtained by use of those achieved with ACL cross-pin femoral fixation and PCL tibial fixation with bio-interference screws. METHODS Cadaveric Model Hamstring (semitendinosus and gracilis) and tibialis (tibialis anterior and posterior) grafts were harvested from an initial sample of 5 paired cadaveric knees (total of 10 cadaveric knees). Another 10 tibias were also used. All soft tissues were dissected and removed, and the femur and tibia were reduced to a residual length of 15 cm. Bones were submerged in warm normal saline solution, and density determinations were obtained. Bone mineral density (BMD) of the proximal human cadaveric tibias were determined
with a dual-energy x-ray absorptiometry scanner (Hologic QDR-2000 Whole-Body X-ray Bone Densitometer; Hologic, Bedford, MA). Measurements were made at metaphyseal portions because this is the area of interference and cross-pin fixation in the tibia. The mean age of the experimental models was 52.2 years (range, 37 to 63 years), and there were 6 men and 4 women. The bone-graft complexes were randomly divided into 3 subgroups. We did not consider BMD during the allocation of specimens if it was over 0.6 g/cm2 because a previous study showed that a BMD over 0.6 g/cm2 is acceptable for testing specimens.15,16 The femoral sides for ACL reconstruction were fixed with a Bio-TransFix device (group I), and the tibial sides for transtibial PCL reconstruction were fixed with a Bio-TransFix device (group II). Tibial fixation for transtibial PCL reconstruction in another 10 tibias was performed by use of a bio-interference screw of 10 mm in diameter and 30 mm in length (Inion Hexalon, Tampere, Finland) (group III). Surgical Technique All tunnels were made at 1 cm in diameter and were prepared with a 10-mm reamer. Grafts were arranged randomly with the 3 different graft materials. Grafts were adjusted to tunnel diameters by longitudinal minimal cutting when a diameter was too large or by additional suturing when too small until the surgeon felt modest resistance during passage.14 For single-bundle ACL reconstruction for the anteromedial bundle,5 the femoral tunnel of the anteromedial bundle was located at the posterior proximal corner of the ACL footprint commensurate with graft diameter. A 6-mm over-the-top guide was placed on the posterior cortex of the notch between the 10:00and 10:30-o’clock positions (right knee), and the femoral tunnel was reamed to a length of approximately 4 cm. A tunnel hook matching the tunnel diameter was assembled and was inserted into a femoral socket. The
FIGURE 1. In vivo arthroscopic operation. The implant is inserted at the lateral side of the tibia for tibial fixation and fixed with a Bio-TransFix device 2 cm from the posterior orifice.
TRANSTIBIAL PCL RECONSTRUCTION
FIGURE 2. (A) The specimen was secured in polymethyl methacrylate bone cement. A tunnel was made in the direction of the applied tensile force, and the specimen was fixed rigidly to the testing system. (B) Biomechanical testing of the tibias was carried out with a testing machine (Instron 8511).
guide pin sleeve was positioned on the lateral aspect of the lateral femoral condyle. A 5-mm broach, with a depth stop collar, was drilled over a 3-mm guide pin to broach the cortex for Bio-TransFix implant fixation. The wire was then pulled out, and the midsection of the graft was positioned over the passing wire with the graft end lengths equalized. Needle holders were used to secure the free ends of the wire and to assist graft passage. After graft passage, the Bio-TransFix dilator was inserted over the wire to engage the implant. For PCL reconstruction,7 a tibial tunnel was made by use of a transtibial technique and fixed with a Bio-TransFix device at 2 cm from the posterior orifice (Fig 1). The tip of the guide was positioned on the PCL backside of the tibia, 1 cm below the articular surface and just lateral to the midline. The drill guide angle of the tibia was oriented at 55° to 60°, and all tunnels were 1 cm in diameter. Grafts were adjusted to the tunnel diameter for ACL femoral fixation. The TransFix tunnel hook was inserted through the tibial tunnel and positioned approximately 2 cm proximal to the tibial posterior orifice, and a 3-mm drill pin was then drilled through the guide sleeve and TABLE 1.
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tunnel hook, exiting the tibia medially. During the in vivo arthroscopic operation, we check the C-arm for this procedure and we routinely check the proper graft length in the tibial tunnel indirectly. The 5-mm broach, with a depth stop collar, was drilled over the 3-mm guide pin to broach the cortex for the TransFix implant. The graft-passing wire was inserted and hooked. The graft was then passed to the tibial tunnel and fixed with a Bio-TransFix implant. The TransFix implant operates by use of a corticocancellous suspension mechanism and must pass the tunnel sufficiently to hang the graft. Therefore the length from the near cortex to the tunnel through the slot of the TransFix implant was measured to compare the proper length of the device. For tibial bio-interference screw fixation, a 10-mm tibial tunnel was made and a looped portion of the hamstring or tibialis graft was adjusted to a diameter of 10 mm with a whipstitch and fixed with a biointerference screw of 10 mm in diameter and 30 mm in length. This screw was positioned at the anterior orifice of the tibial tunnel and was engaged in hard cortical bone. Biomechanical Testing Ten cadaveric knees and ten tibias were thawed for 24 hours at room temperature before testing. They were moistened with saline solution during mounting and testing. Femurs and tibias were then secured in polymethyl methacrylate bone cement. A tunnel was made parallel to the direction of the applied tensile force, and the specimen was fixed rigidly to the testing system (Fig 2A). Biomechanical testing was performed with a testing machine (Instron 8511; MTS, Minneapolis, MN) (Fig 2B). The free graft portion was secured directly by use of a custom-made jig. The graft length was adjusted to 12 to 13 cm with a 4-stranded hamstring and 2-stranded tibialis. Constructs were then cycled 20 times at approximately 10 N to pre-tension them, and a load was then applied at 30 mm/min to failure. Resulting load-elongation curves and maximal loads were documented, and stiff-
Maximal Loads, Stiffnesses, and Displacements in 3 Study Groups Mean ⫾ SD (95% confidence interval)
Maximal load (N) Stiffness (N/mm) Displacement (mm)
Group I
Group II
Group III
549.3 ⫾ 55.4 (514-583.7) 47.5 ⫾ 16.8 (37.1-57.9) 19.9 ⫾ 5.8 (16.4-23.4)
570.8 ⫾ 96.9 (510.7-630.9) 59.1 ⫾ 17.1 (48.5-69.7) 19.1 ⫾ 8.5 (13.8-24.4)
371.3 ⫾ 106.2 (305.4-437.2) 27.6 ⫾ 16.7 (17.2-38) 17.6 ⫾ 7.1 (13.2-22)
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Y. S. LEE ET AL. TABLE 2.
Failure Modes in Study Groups
Cadaver No.
Group I
Group II
Group III
1 2 3 4 5 6 7 8 9 10
Deformation* Breakage Deformation Deformation Deformation Deformation Deformation Breakage Deformation Breakage
Deformation* Deformation* Deformation Deformation Deformation Breakage Breakage Deformation Deformation† Breakage
Pullout Pullout Pullout Pullout Pullout Pullout Pullout Pullout Pullout Pullout
*With pullout at proximal portion. †With a split in tibial plateau.
nesses, displacements, and failure modes were evaluated. Maximal load was defined as the highest load sustained, and displacement was defined as the distance from the initial position to the maximal load in the load-elongation curve. Stiffness was defined as the linear region of the early load-elongation curve. Statistical Methods A power analysis was performed. A difference in maximal load between the 3 different fixation methods of greater than 200 N was assumed to be clinically significant. The standard deviation (SD) of the maximal load was 106.25, with ␣ and power values of .05 and 0.8, respectively. The required sample size was calculated to be 7 cases. Testing was carried out by use of the SPSS statistical package, version 12.0 (SPSS, Chicago, IL); 95% confidence intervals were used to determine statistical significance. We used the Kruskal-Wallis test to compare the 3 groups and t test to compare the 2 groups. In groups I, II, and III, the Kruskal-Wallis test by use of the least significant difference test with ranks was
used to compare the maximal loads, stiffnesses, and displacements. In groups I and II, lengths from the near cortex to the tunnel were compared by use of the t test. P ⬍ .05 was considered significant. RESULTS Mean BMD was 0.84 g/cm2 (range, 0.73-0.94 g/cm2). Maximal loads at failure for groups I, II, and III are listed in Table 1. The strengths of group I and group II were superior to that of group III (P ⫽ .003 and P ⬍ .001, respectively). There was no significant difference between groups I and II (P ⫽ .124). The stiffnesses of groups I, II, and III are listed in Table 1. The mean stiffnesses of group I and group II were greater than that of group III (P ⫽ .014 and P ⬍ .001, respectively). No significant difference was observed between groups I and II (P ⫽ .135). Displacement in groups I, II, and III is listed in Table 1. The mean lengths of the TransFix implant slots of the femurs and tibias were 20.3 ⫾ 1.25 mm and 20.2 ⫾ 1.32 mm, respectively, which was not significant by t test (P ⫽ .8637). Table 2 summarizes failure modes. Regarding the Bio-TransFix implant, the failure modes varied and resembled those of femoral and tibial fixation (Fig 3). However, all grafts in group III failed because of graft pullout at tibial fixation sites and, in most cases, the screw was left in position. DISCUSSION The principal findings of our study showed that the surgical technique for a transtibial PCL reconstruction using cross-pin fixation with a Bio-TransFix device was favorable through a comparison of the biomechanical properties with those of the well-established ACL femoral fixation and PCL tibial fixation with a
FIGURE 3. (A) Mode of failure with Bio-TransFix device showing breakage and (B) deformation in tunnel portion.
TRANSTIBIAL PCL RECONSTRUCTION
FIGURE 4. The superficial peroneal nerve at the entrance area of the Bio-TransFix device can be protected if the insertion point is positioned at the anterior and superior region of the fibular neck.
bio-interference screw. The results confirmed that the biomechanical properties of tibial cross-pin fixation with a Bio-TransFix device were comparable to those of femoral fixation by use of the well-established ACL reconstruction.8-12 Furthermore, tibial cross-pin fixation with a Bio-TransFix implant has superior maximal load and stiffness compared with tibial bio-interference screw fixation for PCL reconstruction, similar to femoral fixation with ACL reconstruction.6,8,10,17,18 Therefore it is a good alternative option for cases with a relatively short soft-tissue graft. For transtibial PCL reconstruction, we described a surgical technique for arthroscopic double-bundle PCL reconstruction that was not restricted by the
FIGURE 5. Follow-up magnetic resonance imaging scans showing (A) lateral entry portion, (B) mid portion, and (C) medial exit portion of BioTransFix device (arrows).
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type and length of graft and that was found to be stronger using mainly a 2-stranded tibialis allograft or 4-stranded hamstring autograft with TransFix tibial fixation and effective graft passage without graft damage.7 However, tibial fixation by use of the TransFix implant is not completely understood, and unpredictable problems can occur. Nevertheless, our follow-up studies showed that the superficial peroneal nerve at the entrance area of the Bio-TransFix device can be protected if the insertion point of the implant is positioned at the anterior and superior portion of the fibular neck (Fig 4). Furthermore, posterior neurovascular structures are protected because the TransFix implant is inserted in the intramedullary portion of the posterior cortex of the tibia (Fig 5). The implant’s proper placement can also be confirmed by insertion of an arthroscope into the tibial tunnel (Fig 6). The medial side is also protected because the tip of the TransFix implant does not perforate the medial cortex (Fig 7). We have performed the described operation in more than 15 patients, and the following complications occurred. The femoral staple was elevated in one patient, and he showed grade 2 laxity. Another patient showed breakage of the tendon on the tibial loop at 2 months postoperatively by follow-up magnetic resonance imaging. Subsequently, we have always performed soft-tissue anchoring with No. 5 Ethibond (Ethicon, Somerville, NJ) or post-tie fixation. However, this experimental study shows a lower maximal load at failure than the other series.6,8,10,18 Previous studies have reported that the BMD strongly influences initial tendon graft fixation strength.19-21 Ahmad et al.8 used a porcine model and reported a maximal failure load of 746 N. Becker et al.22 also used a porcine model and reported a maximal failure load of 1,303 N. Fabbriciani et al.10 used a sheep model and reported a maximal failure load of 889 N. Milano et al.18 used a porcine model and reported a maximal failure load of 1,491 N. This discrepancy might be because of the old cadaveric specimens used in our series. However, a previous study indicated that
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FIGURE 6. The TransFix device is inserted into the intramedullary portion of the posterior cortex of the tibia, and its proper placement can be confirmed by insertion of an arthroscope into the tibial tunnel.
a BMD of greater than 0.6 g/cm2 is suitable for testing specimens.15,16 These specimens were suitable for testing, but the BMDs of these cadaveric specimens were lower than those in other animal series. This study has several limitations. First, the BMDs were low and variable because of the ages of the cadaveric specimens used, and it is possible that specimens were unevenly distributed, because we did not consider the BMD during specimen allocation. Second, this study showed a lower mean load and higher SDs than previous animal studies. We believe that the high SDs originated from differences in the quality of the cadaveric bones. Third, this was only a time 0 study without healing, and the strength may change over time in vivo. Finally, further studies are needed to assess the safety of the TransFix approach to the tibia with a particular focus on the superficial peroneal nerve of the entry area and on neurovascular structures in the popliteal
FIGURE 7. The medial side is protected because the tip of the Bio-TransFix device (arrow) does not perforate the medial cortex.
area during implant insertion because of the possibility of posterior cortex perforation. CONCLUSIONS The transtibial technique by use of cross-pin tibial fixation with a Bio-TransFix device in PCL reconstruction provides stable fixation that is comparable to femoral fixation in ACL reconstruction, an already well-established technique. REFERENCES 1. Ahn JH, Yoo JC, Wang JH. Posterior cruciate ligament reconstruction: Double-loop hamstring tendon autograft versus Achilles tendon allograft—Clinical results of a minimum 2-year follow-up. Arthroscopy 2005;21:965-969. 2. Yoon KH, Bae DK, Song SJ, Lim CT. Arthroscopic doublebundle augmentation of posterior cruciate ligament using split Achilles allograft. Arthroscopy 2005;21:1436-1442. 3. Ahn JH, Park JS, Lee YS, Cho YJ. Femoral bioabsorbable cross-pin fixation in anterior cruciate ligament reconstruction. Arthroscopy 2007;23:1093-1099. 4. Fu FH, Bennett CH, Ma CB, Menetrey J, Lattermann C. Current trends in anterior cruciate ligament reconstruction. Part II. Operative procedures and clinical correlations. Am J Sports Med 2000;28:124-130. 5. Lee YS, Kim SK, Park JH, et al. Double-bundle anterior cruciate ligament reconstruction using two different suspensory femoral fixation: A technical note. Knee Surg Sports Traumatol Arthrosc 2007;15:1023-1027. 6. Kousa P, Jarvinen TL, Vihavainen M, Kannus P, Jarvinen M. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part II: Tibial site. Am J Sports Med 2003;31:182-188. 7. Lee YS, Ahn JH, Jung YB, et al. Transtibial double bundle posterior cruciate ligament reconstruction using TransFix tibial fixation. Knee Surg Sports Traumatol Arthrosc 2007;15: 973-977. 8. Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med 2004;32:635-640. 9. Espejo-Baena A, Ezquerro F, de la Blanca AP, Serrano-Fer-
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10.
11.
12.
13. 14.
15.
nandez J, Nadal F, Montanez-Heredia E. Comparison of initial mechanical properties of 4 hamstring graft femoral fixation systems using nonpermanent hardware for anterior cruciate ligament reconstruction: An in vitro animal study. Arthroscopy 2006;22:433-440. Fabbriciani C, Mulas PD, Ziranu F, Deriu L, Zarelli D, Milano G. Mechanical analysis of fixation methods for anterior cruciate ligament reconstruction with hamstring tendon graft. An experimental study in sheep knees. Knee 2005;12:135-138. Harilainen A, Sandelin J, Jansson KA. Cross-pin femoral fixation versus metal interference screw fixation in anterior cruciate ligament reconstruction with hamstring tendons: Results of a controlled prospective randomized study with 2-year follow-up. Arthroscopy 2005;21:25-33. Misra R, Strover A, El-Shazly M. Intra-articular protrusion of malpositioned Transfix implant following anterior cruciate ligament reconstruction. Arthroscopy 2006;22:226.e1-226.e4. Available online at www.arthroscopyjournal.org. Choi NH, Son KM, Victoroff BN. A pitfall of transfix fixation during anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2008;16:479-481. Lee YS, Ahn JH, Kim JG, et al. Analysis and prevention of intra-operative complications of TransFix fixation in anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 2008;16:639-644. Mendes DG, Iusim M, Angel D, et al. Histologic pattern of biomechanic properties of the carbon fiber-augmented ligament tendon. A laboratory and clinical study. Clin Orthop Relat Res 1985:5160.
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16. Yoo JC, Ahn JH, Kim JH, et al. Biomechanical testing of hybrid hamstring graft tibial fixation in anterior cruciate ligament reconstruction. Knee 2006;13:455-459. 17. Scheffler SU, Sudkamp NP, Gockenjan A, Hoffmann RF, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: The impact of fixation level and fixation method under cyclic loading. Arthroscopy 2002;18:304-315. 18. Milano G, Mulas PD, Ziranu F, Piras S, Manunta A, Fabbriciani C. Comparison between different femoral fixation devices for ACL reconstruction with doubled hamstring tendon graft: A biomechanical analysis. Arthroscopy 2006;22:660-668. 19. Gibson LJ. Biomechanics of cellular solids. J Biomech 2005; 38:377-399. 20. Pena F, Grontvedt T, Brown GA, Aune AK, Engebretsen L. Comparison of failure strength between metallic and absorbable interference screws. Influence of insertion torque, tunnelbone block gap, bone mineral density, and interference. Am J Sports Med 1996;24:329-334. 21. Zantop T, Weimann A, Wolle K, Musahl V, Langer M, Petersen W. Initial and 6 weeks postoperative structural properties of soft tissue anterior cruciate ligament reconstructions with cross-pin or interference screw fixation: An in vivo study in sheep. Arthroscopy 2007;23:14-20. 22. Becker R, Voigt D, Starke C, Heymann M, Wilson GA, Nebelung W. Biomechanical properties of quadruple tendon and patellar tendon femoral fixation techniques. Knee Surg Sports Traumatol Arthrosc 2001;9:337-342.
Purpose: This article reports the biomechanical demonstration of a technique for transtibial posterior cruciate ligament (PCL) reconstruction using a soft-tissue graft with cross-pin fixation in the tibia and compares this with the biomechanical properties achieved with other methods. Methods: We used 5 paired cadaveric knees and another 10 tibias. Soft-tissue grafts were randomized. The femoral side of the anterior cruciate ligament was fixed with a Bio-TransFix device (Arthrex, Naples, FL) (group I), and the tibial side of the PCL was fixed with a Bio-TransFix device (group II). In another 10 tibias, tibial fixations were performed by use of a bio-interference screw (group III). Biomechanical testing was carried out on a testing machine, and maximal failure load, stiffness, and displacement were analyzed. The lengths of the slots of the TransFix device (Arthrex) from the near cortex were measured to compare the proper length of the device. Results: Maximal mean failure loads in groups I, II, and III were 549.3 ⫾ 55.4 N, 570.8 ⫾ 96.9 N, and 371.3 ⫾ 106.2 N, respectively, showing a significant difference (P ⫽ .0003). Stiffnesses were 47.52 ⫾ 16.84 N/mm, 59.14 ⫾ 17.09 N/mm, and 27.60 ⫾ 16.73 N/mm, respectively, showing a significant difference (P ⫽ .01). Mean displacements were 19.99 ⫾ 5.79 mm, 19.09 ⫾ 8.51 mm, and 17.58 ⫾ 7.10 mm, respectively, showing no significant difference (P ⫽ .7535). The mean lengths of the slots of the TransFix device of the femurs and tibias were similar at 20.3 ⫾ 1.25 mm and 20.2 ⫾ 1.32 mm, respectively, showing no significant difference (P ⫽ .8637). Conclusions: The transtibial technique by use of cross-pin tibial fixation with a Bio-TransFix device in PCL reconstruction provides stable fixation that is comparable to that achieved by use of conventional bio-interference screw fixation and femoral fixation in an anterior cruciate ligament reconstruction, an already well-established technique. Clinical Relevance: Biomechanically, tibial cross-pin fixation compares favorably with interference screw fixation and is useful when a graft is short. However, safety issues have not yet been resolved. Key Words: Posterior cruciate ligament—Transtibial technique—Cross-pin fixation—Bio-TransFix—Biomechanics.
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or transtibial double-bundle posterior cruciate ligament (PCL) reconstruction, most surgeons use an Achilles allograft because the available graft length
is longer than those of other graft materials.1,2 Recently, soft-tissue grafts, in particular, a 4-stranded hamstring autograft or 2-stranded tibialis allograft,
From Korea University Ansan Hospital (Y.S.L., J.H.W., J.H.P.), and Korea University Guro Hospital (J.H.B., H.C.L.), Anam-dong Seongbuk-Gu, Seoul, Korea, Samsung Medical Center (J.H.A.), Gangnam-gu, Seoul, Korea, Korea Orthopedics & Rehabilitation Engineering Center (T.S.B.), Bupyung-ku Incheon, Korea, and Sports Science Institute, Seoul National University (B.-O.L.), Gwanak-gu, Seoul, Korea. The authors report no conflict of interest. Received July 18, 2008; accepted February 11, 2009. Address correspondence and reprint requests to Yong Seuk Lee, M.D., Department of Orthopaedic Surgery, Korea University Ansan Hospital, 516 Gozan-dong, Danwon-gu, Ansan 425-707, South Korea. E-mail: [email protected] © 2009 by the Arthroscopy Association of North America 0749-8063/09/2509-8418$36.00/0 doi:10.1016/j.arthro.2009.02.006
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have provided other graft options, and they offer advantages and clinical results that are almost equivalent to anterior cruciate ligament (ACL) reconstruction with bony fixation.3-6 However, often, a 4-stranded hamstring or 2-stranded tibialis graft is short with bio-interference fixation at the anterior orifice of the tibial tunnel. Therefore we proposed a new surgical technique for arthroscopic double-bundle PCL reconstruction that is stronger and not restricted by graft type and length and that uses mainly a 4-stranded hamstring autograft or 2-stranded tibialis allograft with TransFix (Arthrex, Naples, FL) tibial fixation.7 The TransFix implant was originally used for the ACL femoral fixation of a soft-tissue graft and is considered to be a safe option.8-12 However, tibial fixation of a TransFix implant is not well established, and unpredictable complications can occur.7,13,14 The aim of this study was to demonstrate the surgical technique of transtibial PCL reconstruction with cross-pin fixation (Bio-TransFix device [Arthrex], 50 mm in length and 5 mm in diameter) by comparing the biomechanical properties obtained by use of those achieved with ACL cross-pin femoral fixation and PCL tibial fixation with bio-interference screws. METHODS Cadaveric Model Hamstring (semitendinosus and gracilis) and tibialis (tibialis anterior and posterior) grafts were harvested from an initial sample of 5 paired cadaveric knees (total of 10 cadaveric knees). Another 10 tibias were also used. All soft tissues were dissected and removed, and the femur and tibia were reduced to a residual length of 15 cm. Bones were submerged in warm normal saline solution, and density determinations were obtained. Bone mineral density (BMD) of the proximal human cadaveric tibias were determined
with a dual-energy x-ray absorptiometry scanner (Hologic QDR-2000 Whole-Body X-ray Bone Densitometer; Hologic, Bedford, MA). Measurements were made at metaphyseal portions because this is the area of interference and cross-pin fixation in the tibia. The mean age of the experimental models was 52.2 years (range, 37 to 63 years), and there were 6 men and 4 women. The bone-graft complexes were randomly divided into 3 subgroups. We did not consider BMD during the allocation of specimens if it was over 0.6 g/cm2 because a previous study showed that a BMD over 0.6 g/cm2 is acceptable for testing specimens.15,16 The femoral sides for ACL reconstruction were fixed with a Bio-TransFix device (group I), and the tibial sides for transtibial PCL reconstruction were fixed with a Bio-TransFix device (group II). Tibial fixation for transtibial PCL reconstruction in another 10 tibias was performed by use of a bio-interference screw of 10 mm in diameter and 30 mm in length (Inion Hexalon, Tampere, Finland) (group III). Surgical Technique All tunnels were made at 1 cm in diameter and were prepared with a 10-mm reamer. Grafts were arranged randomly with the 3 different graft materials. Grafts were adjusted to tunnel diameters by longitudinal minimal cutting when a diameter was too large or by additional suturing when too small until the surgeon felt modest resistance during passage.14 For single-bundle ACL reconstruction for the anteromedial bundle,5 the femoral tunnel of the anteromedial bundle was located at the posterior proximal corner of the ACL footprint commensurate with graft diameter. A 6-mm over-the-top guide was placed on the posterior cortex of the notch between the 10:00and 10:30-o’clock positions (right knee), and the femoral tunnel was reamed to a length of approximately 4 cm. A tunnel hook matching the tunnel diameter was assembled and was inserted into a femoral socket. The
FIGURE 1. In vivo arthroscopic operation. The implant is inserted at the lateral side of the tibia for tibial fixation and fixed with a Bio-TransFix device 2 cm from the posterior orifice.
TRANSTIBIAL PCL RECONSTRUCTION
FIGURE 2. (A) The specimen was secured in polymethyl methacrylate bone cement. A tunnel was made in the direction of the applied tensile force, and the specimen was fixed rigidly to the testing system. (B) Biomechanical testing of the tibias was carried out with a testing machine (Instron 8511).
guide pin sleeve was positioned on the lateral aspect of the lateral femoral condyle. A 5-mm broach, with a depth stop collar, was drilled over a 3-mm guide pin to broach the cortex for Bio-TransFix implant fixation. The wire was then pulled out, and the midsection of the graft was positioned over the passing wire with the graft end lengths equalized. Needle holders were used to secure the free ends of the wire and to assist graft passage. After graft passage, the Bio-TransFix dilator was inserted over the wire to engage the implant. For PCL reconstruction,7 a tibial tunnel was made by use of a transtibial technique and fixed with a Bio-TransFix device at 2 cm from the posterior orifice (Fig 1). The tip of the guide was positioned on the PCL backside of the tibia, 1 cm below the articular surface and just lateral to the midline. The drill guide angle of the tibia was oriented at 55° to 60°, and all tunnels were 1 cm in diameter. Grafts were adjusted to the tunnel diameter for ACL femoral fixation. The TransFix tunnel hook was inserted through the tibial tunnel and positioned approximately 2 cm proximal to the tibial posterior orifice, and a 3-mm drill pin was then drilled through the guide sleeve and TABLE 1.
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tunnel hook, exiting the tibia medially. During the in vivo arthroscopic operation, we check the C-arm for this procedure and we routinely check the proper graft length in the tibial tunnel indirectly. The 5-mm broach, with a depth stop collar, was drilled over the 3-mm guide pin to broach the cortex for the TransFix implant. The graft-passing wire was inserted and hooked. The graft was then passed to the tibial tunnel and fixed with a Bio-TransFix implant. The TransFix implant operates by use of a corticocancellous suspension mechanism and must pass the tunnel sufficiently to hang the graft. Therefore the length from the near cortex to the tunnel through the slot of the TransFix implant was measured to compare the proper length of the device. For tibial bio-interference screw fixation, a 10-mm tibial tunnel was made and a looped portion of the hamstring or tibialis graft was adjusted to a diameter of 10 mm with a whipstitch and fixed with a biointerference screw of 10 mm in diameter and 30 mm in length. This screw was positioned at the anterior orifice of the tibial tunnel and was engaged in hard cortical bone. Biomechanical Testing Ten cadaveric knees and ten tibias were thawed for 24 hours at room temperature before testing. They were moistened with saline solution during mounting and testing. Femurs and tibias were then secured in polymethyl methacrylate bone cement. A tunnel was made parallel to the direction of the applied tensile force, and the specimen was fixed rigidly to the testing system (Fig 2A). Biomechanical testing was performed with a testing machine (Instron 8511; MTS, Minneapolis, MN) (Fig 2B). The free graft portion was secured directly by use of a custom-made jig. The graft length was adjusted to 12 to 13 cm with a 4-stranded hamstring and 2-stranded tibialis. Constructs were then cycled 20 times at approximately 10 N to pre-tension them, and a load was then applied at 30 mm/min to failure. Resulting load-elongation curves and maximal loads were documented, and stiff-
Maximal Loads, Stiffnesses, and Displacements in 3 Study Groups Mean ⫾ SD (95% confidence interval)
Maximal load (N) Stiffness (N/mm) Displacement (mm)
Group I
Group II
Group III
549.3 ⫾ 55.4 (514-583.7) 47.5 ⫾ 16.8 (37.1-57.9) 19.9 ⫾ 5.8 (16.4-23.4)
570.8 ⫾ 96.9 (510.7-630.9) 59.1 ⫾ 17.1 (48.5-69.7) 19.1 ⫾ 8.5 (13.8-24.4)
371.3 ⫾ 106.2 (305.4-437.2) 27.6 ⫾ 16.7 (17.2-38) 17.6 ⫾ 7.1 (13.2-22)
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Y. S. LEE ET AL. TABLE 2.
Failure Modes in Study Groups
Cadaver No.
Group I
Group II
Group III
1 2 3 4 5 6 7 8 9 10
Deformation* Breakage Deformation Deformation Deformation Deformation Deformation Breakage Deformation Breakage
Deformation* Deformation* Deformation Deformation Deformation Breakage Breakage Deformation Deformation† Breakage
Pullout Pullout Pullout Pullout Pullout Pullout Pullout Pullout Pullout Pullout
*With pullout at proximal portion. †With a split in tibial plateau.
nesses, displacements, and failure modes were evaluated. Maximal load was defined as the highest load sustained, and displacement was defined as the distance from the initial position to the maximal load in the load-elongation curve. Stiffness was defined as the linear region of the early load-elongation curve. Statistical Methods A power analysis was performed. A difference in maximal load between the 3 different fixation methods of greater than 200 N was assumed to be clinically significant. The standard deviation (SD) of the maximal load was 106.25, with ␣ and power values of .05 and 0.8, respectively. The required sample size was calculated to be 7 cases. Testing was carried out by use of the SPSS statistical package, version 12.0 (SPSS, Chicago, IL); 95% confidence intervals were used to determine statistical significance. We used the Kruskal-Wallis test to compare the 3 groups and t test to compare the 2 groups. In groups I, II, and III, the Kruskal-Wallis test by use of the least significant difference test with ranks was
used to compare the maximal loads, stiffnesses, and displacements. In groups I and II, lengths from the near cortex to the tunnel were compared by use of the t test. P ⬍ .05 was considered significant. RESULTS Mean BMD was 0.84 g/cm2 (range, 0.73-0.94 g/cm2). Maximal loads at failure for groups I, II, and III are listed in Table 1. The strengths of group I and group II were superior to that of group III (P ⫽ .003 and P ⬍ .001, respectively). There was no significant difference between groups I and II (P ⫽ .124). The stiffnesses of groups I, II, and III are listed in Table 1. The mean stiffnesses of group I and group II were greater than that of group III (P ⫽ .014 and P ⬍ .001, respectively). No significant difference was observed between groups I and II (P ⫽ .135). Displacement in groups I, II, and III is listed in Table 1. The mean lengths of the TransFix implant slots of the femurs and tibias were 20.3 ⫾ 1.25 mm and 20.2 ⫾ 1.32 mm, respectively, which was not significant by t test (P ⫽ .8637). Table 2 summarizes failure modes. Regarding the Bio-TransFix implant, the failure modes varied and resembled those of femoral and tibial fixation (Fig 3). However, all grafts in group III failed because of graft pullout at tibial fixation sites and, in most cases, the screw was left in position. DISCUSSION The principal findings of our study showed that the surgical technique for a transtibial PCL reconstruction using cross-pin fixation with a Bio-TransFix device was favorable through a comparison of the biomechanical properties with those of the well-established ACL femoral fixation and PCL tibial fixation with a
FIGURE 3. (A) Mode of failure with Bio-TransFix device showing breakage and (B) deformation in tunnel portion.
TRANSTIBIAL PCL RECONSTRUCTION
FIGURE 4. The superficial peroneal nerve at the entrance area of the Bio-TransFix device can be protected if the insertion point is positioned at the anterior and superior region of the fibular neck.
bio-interference screw. The results confirmed that the biomechanical properties of tibial cross-pin fixation with a Bio-TransFix device were comparable to those of femoral fixation by use of the well-established ACL reconstruction.8-12 Furthermore, tibial cross-pin fixation with a Bio-TransFix implant has superior maximal load and stiffness compared with tibial bio-interference screw fixation for PCL reconstruction, similar to femoral fixation with ACL reconstruction.6,8,10,17,18 Therefore it is a good alternative option for cases with a relatively short soft-tissue graft. For transtibial PCL reconstruction, we described a surgical technique for arthroscopic double-bundle PCL reconstruction that was not restricted by the
FIGURE 5. Follow-up magnetic resonance imaging scans showing (A) lateral entry portion, (B) mid portion, and (C) medial exit portion of BioTransFix device (arrows).
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type and length of graft and that was found to be stronger using mainly a 2-stranded tibialis allograft or 4-stranded hamstring autograft with TransFix tibial fixation and effective graft passage without graft damage.7 However, tibial fixation by use of the TransFix implant is not completely understood, and unpredictable problems can occur. Nevertheless, our follow-up studies showed that the superficial peroneal nerve at the entrance area of the Bio-TransFix device can be protected if the insertion point of the implant is positioned at the anterior and superior portion of the fibular neck (Fig 4). Furthermore, posterior neurovascular structures are protected because the TransFix implant is inserted in the intramedullary portion of the posterior cortex of the tibia (Fig 5). The implant’s proper placement can also be confirmed by insertion of an arthroscope into the tibial tunnel (Fig 6). The medial side is also protected because the tip of the TransFix implant does not perforate the medial cortex (Fig 7). We have performed the described operation in more than 15 patients, and the following complications occurred. The femoral staple was elevated in one patient, and he showed grade 2 laxity. Another patient showed breakage of the tendon on the tibial loop at 2 months postoperatively by follow-up magnetic resonance imaging. Subsequently, we have always performed soft-tissue anchoring with No. 5 Ethibond (Ethicon, Somerville, NJ) or post-tie fixation. However, this experimental study shows a lower maximal load at failure than the other series.6,8,10,18 Previous studies have reported that the BMD strongly influences initial tendon graft fixation strength.19-21 Ahmad et al.8 used a porcine model and reported a maximal failure load of 746 N. Becker et al.22 also used a porcine model and reported a maximal failure load of 1,303 N. Fabbriciani et al.10 used a sheep model and reported a maximal failure load of 889 N. Milano et al.18 used a porcine model and reported a maximal failure load of 1,491 N. This discrepancy might be because of the old cadaveric specimens used in our series. However, a previous study indicated that
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Y. S. LEE ET AL.
FIGURE 6. The TransFix device is inserted into the intramedullary portion of the posterior cortex of the tibia, and its proper placement can be confirmed by insertion of an arthroscope into the tibial tunnel.
a BMD of greater than 0.6 g/cm2 is suitable for testing specimens.15,16 These specimens were suitable for testing, but the BMDs of these cadaveric specimens were lower than those in other animal series. This study has several limitations. First, the BMDs were low and variable because of the ages of the cadaveric specimens used, and it is possible that specimens were unevenly distributed, because we did not consider the BMD during specimen allocation. Second, this study showed a lower mean load and higher SDs than previous animal studies. We believe that the high SDs originated from differences in the quality of the cadaveric bones. Third, this was only a time 0 study without healing, and the strength may change over time in vivo. Finally, further studies are needed to assess the safety of the TransFix approach to the tibia with a particular focus on the superficial peroneal nerve of the entry area and on neurovascular structures in the popliteal
FIGURE 7. The medial side is protected because the tip of the Bio-TransFix device (arrow) does not perforate the medial cortex.
area during implant insertion because of the possibility of posterior cortex perforation. CONCLUSIONS The transtibial technique by use of cross-pin tibial fixation with a Bio-TransFix device in PCL reconstruction provides stable fixation that is comparable to femoral fixation in ACL reconstruction, an already well-established technique. REFERENCES 1. Ahn JH, Yoo JC, Wang JH. Posterior cruciate ligament reconstruction: Double-loop hamstring tendon autograft versus Achilles tendon allograft—Clinical results of a minimum 2-year follow-up. Arthroscopy 2005;21:965-969. 2. Yoon KH, Bae DK, Song SJ, Lim CT. Arthroscopic doublebundle augmentation of posterior cruciate ligament using split Achilles allograft. Arthroscopy 2005;21:1436-1442. 3. Ahn JH, Park JS, Lee YS, Cho YJ. Femoral bioabsorbable cross-pin fixation in anterior cruciate ligament reconstruction. Arthroscopy 2007;23:1093-1099. 4. Fu FH, Bennett CH, Ma CB, Menetrey J, Lattermann C. Current trends in anterior cruciate ligament reconstruction. Part II. Operative procedures and clinical correlations. Am J Sports Med 2000;28:124-130. 5. Lee YS, Kim SK, Park JH, et al. Double-bundle anterior cruciate ligament reconstruction using two different suspensory femoral fixation: A technical note. Knee Surg Sports Traumatol Arthrosc 2007;15:1023-1027. 6. Kousa P, Jarvinen TL, Vihavainen M, Kannus P, Jarvinen M. The fixation strength of six hamstring tendon graft fixation devices in anterior cruciate ligament reconstruction. Part II: Tibial site. Am J Sports Med 2003;31:182-188. 7. Lee YS, Ahn JH, Jung YB, et al. Transtibial double bundle posterior cruciate ligament reconstruction using TransFix tibial fixation. Knee Surg Sports Traumatol Arthrosc 2007;15: 973-977. 8. Ahmad CS, Gardner TR, Groh M, Arnouk J, Levine WN. Mechanical properties of soft tissue femoral fixation devices for anterior cruciate ligament reconstruction. Am J Sports Med 2004;32:635-640. 9. Espejo-Baena A, Ezquerro F, de la Blanca AP, Serrano-Fer-
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16. Yoo JC, Ahn JH, Kim JH, et al. Biomechanical testing of hybrid hamstring graft tibial fixation in anterior cruciate ligament reconstruction. Knee 2006;13:455-459. 17. Scheffler SU, Sudkamp NP, Gockenjan A, Hoffmann RF, Weiler A. Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: The impact of fixation level and fixation method under cyclic loading. Arthroscopy 2002;18:304-315. 18. Milano G, Mulas PD, Ziranu F, Piras S, Manunta A, Fabbriciani C. Comparison between different femoral fixation devices for ACL reconstruction with doubled hamstring tendon graft: A biomechanical analysis. Arthroscopy 2006;22:660-668. 19. Gibson LJ. Biomechanics of cellular solids. J Biomech 2005; 38:377-399. 20. Pena F, Grontvedt T, Brown GA, Aune AK, Engebretsen L. Comparison of failure strength between metallic and absorbable interference screws. Influence of insertion torque, tunnelbone block gap, bone mineral density, and interference. Am J Sports Med 1996;24:329-334. 21. Zantop T, Weimann A, Wolle K, Musahl V, Langer M, Petersen W. Initial and 6 weeks postoperative structural properties of soft tissue anterior cruciate ligament reconstructions with cross-pin or interference screw fixation: An in vivo study in sheep. Arthroscopy 2007;23:14-20. 22. Becker R, Voigt D, Starke C, Heymann M, Wilson GA, Nebelung W. Biomechanical properties of quadruple tendon and patellar tendon femoral fixation techniques. Knee Surg Sports Traumatol Arthrosc 2001;9:337-342.