Biomechanical evaluation of patellar- and hamstring tendon graft fixation for anterior cruciat ligament reconstruction using a poly-(D, L-lactide) interference screw

Anterior cruciate ligament (ACL) reconstruction using autologous hamstring tendons are being performed more frequently and satisfactory results have been reported. Advantages such as low donor site morbidity and ease of harvest as well as disadvantages like low initial construct stiffness have been described. Recently, it has been demonstrated that graft fixation close to the original ACL insertion sites increases anterior knee stability and graft isometry. Hamstring tendon fixation techniques using interference screws offer this possibility. To reduce the risk of graft laceration, a round threaded titanium interference screw (RCI) was developed. To improve initial fixation strength, fixation techniques for hamstring tendons with separate or attached tibial bone plugs were introduced. However, data on fixation strength do not yet exist. With respect to the proposed advantages of biodegradable implants, like undistorted magnetic resonance imaging, uncompromised revision surgery and a decreased potential of graft laceration during screw insertion, we performed pullout tests of round threaded biodegradable and round threaded titanium interference screw fixation of semitendinosus (ST) grafts with and without distally attached tibial bone plugs. Data were compared with bone-tendon-bone (BTB) graft fixation using biodegradable and conventional titanium interference screws. We used 56 proximal calf tibiae to compare maximum pullout force, screw insertion torque, and stiffness of fixation for biodegradable direct ST tendon and bone plug fixation (group I: without bone plug, group II: with bone plug) versus titanium interference screw fixation (group III: without bone plug, group IV: with bone plug). A round threaded biodegradable poly-(D, L-lactide) (Sysorb) and a round threaded titanium interference screw (RCI) were used. As a control calf bone-tendon-bone (BTB) grafts fixed with either poly-(D, L-lactide) (group V) or conventional titanium (group VI) interference screws were used. ST tendons were harvested either with or without their distally attached tibial bone plugs from human cadavers and were folded to a three-stranded graft. Specimen were loaded in a material testing machine with the applied load parallel to the long axis of the bone tunnel. Maximum pullout force of ST bone plug (group III: 717 N +/- 90, group IV: 602 N +/- 117) fixation was significantly higher than that of direct tendon (group I: 507 N +/- 93, group III: 419 N +/- 77) fixation. Maximum pullout force of biodegradable screw ST fixation was higher than that of titanium screw fixation in both settings. There was no significant difference in pullout force between biodegradable (713 N +/- 210) and titanium (822 N +/- 130) BTB graft fixation or between ST fixation with bone plug and biodegradable screw with BTB fixation. Pullout force of hamstring tendon interference screw fixation can be improved by using a biodegradable implant. In addition, initial pullout force can be greatly improved by harvesting the hamstring tendon graft with its distally attached tibial bone plug. This may be important, especially in improving tibial graft fixation. This study encourages further research in tendon-bone healing with direct interference screw fixation to confirm the potential of this advanced method.     

Tendon healing in a bone tunnel. Part II: Histologic analysis after biodegradable interference fit fixation in a model of anterior cruciate ligament reconstruction in sheep

Purpose: Tendon-to-bone healing of soft-tissue grafts has been described to progress by the development of a fibrous interzone that undergoes a maturation process leading to the development of an indirect type of ligament insertion. Previous studies used extra-articular models or fixation far away from the joint line; thus, no data are available investigating tendon-to-bone healing of a soft-tissue graft fixed anatomically. Therefore, we studied the tendon-to-bone healing of the anatomic soft-tissue graft interference fit fixation in a model of anterior cruciate ligament (ACL) reconstruction in sheep. Type of Study: Animal study. Methods: Thirty-five mature sheep underwent ACL reconstruction with an autologous Achilles tendon split graft. Grafts were directly fixed with biodegradable poly-(D,L-lactide) interference screws. Animals were euthanized after 6, 9, 12, 24, and 52 weeks and histologic evaluations were performed. Undecalcified specimens were evaluated under normal and polarized light. Additionally, animals received a polychrome sequential labeling (tetracycline, xylenol orange, and calcein green) to determine bone growth per time under fluorescent light. Results: Intratunnel histologic findings at 6 weeks showed a tendon-bone junction with only a partial fibrous interzone between the graft tissue and the surrounding bone. A mature intratunnel tendon-bone junction with a zone of fibrocartilage was found at 9 to 12 weeks. At the tunnel entrance site a wide regular ligamentous insertion site was seen in all specimens after 24 weeks. This insertion showed regular patterns such as the direct type of insertion of a normal ligament with a dense basophilic transition zone consisting of mineralized cartilage. Conclusions: A fibrous interzone between the graft tissue and the bone tunnel was only partially developed, which is in contrast to all previous studies in which nonanatomic fixation was used. Thus, it is reasonable to assume that the tendon-to-bone healing in the present study may progress partially by direct-contact healing without the development of a fibrous interzone. To our knowledge, this is the first report describing the development of a direct type of ligament insertion after ACL replacement with a soft-tissue graft. This is in contrast to previous studies reporting the development of an indirect type of insertion when using nonanatomic fixation far away from the joint line. Thus, histologic data strongly indicate that anatomic interference fit fixation is beneficial for tendon-to-bone incorporation by leading to the development of a direct type of ligament insertion.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 2 (February), 2002: pp 124–135     

Interference screw divergence in femoral tunnel fixation during endoscopic anterior cruciate ligament reconstruction using hamstring grafts

Purpose:To compare the divergence angles between bioabsorbable interference screws inserted into the femoral tunnel with the screwdriver placed through the anteromedial portal to those inserted with the screwdriver placed through the tibial tunnel and to examine the effect of the femoral tunnel interference screws’ divergence angles on fixation strength of hamstring grafts after anterior cruciate ligament (ACL) reconstruction using hamstring grafts. Type of Study:Cadaveric biomechanical pullout study. Methods:ACL reconstruction was performed in 8 pairs of fresh-frozen human cadaveric knees using hamstring grafts fixed within the femoral tunnels using bioabsorbable interference screws. Within matched pairs, 1 screw was placed into the femoral tunnel using a screwdriver placed through the tibial tunnel (group 1), and in the other knee it was placed into the femoral tunnel using a screwdriver placed through the anteromedial portal (group 2). Radiographs were taken to measure the degree of divergence between the interference screw and the femoral tunnel. After disarticulation, pullout strength was then measured using a cyclic-loading model. Results:In group 2, there was significantly more divergence between the screw and the femoral tunnel compared with group 1, particularly in the sagittal plane (average 14.4° compared with 3.4°, P =.00014). With the number of specimens available for comparison, no significant difference was detected between the 2 groups with regard to 3 mm and 5 mm of pullout when cyclically loaded (P =.77 and.74, respectively). Conclusions: The increased technical difficulty, combined with the potential risks of tibial tunnel widening and graft damage, with placement of the screwdriver through the tibial tunnel for the purpose of decreasing femoral interference screw divergence in ACL reconstruction using hamstring grafts may not be justified.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 5 (May-June), 2002: pp 510–514     

Hamstring tendon fixation using interference screws: a biomechanical study in calf tibial bone

It has recently been shown that graft fixation close to the ACL insertion site is optimal in order to increase anterior knee stability. Hamstring tendon fixation using interference screws offers this possibility and a round threaded titanium interference screw has been previously developed. The use of a round threaded biodegradable interference screw may be equivalent. In addition, to increase initial fixation strength, graft harvest with a distally attached bone plug may be advantageous, but biomechanical data do not exist. This study compares the initial pullout force, stiffness of fixation, and failure modes of three strand semitendinosus grafts in 36 proximal calf tibiae using either biodegradable poly-(D,L-lactide) (Sysorb; Sulzer Orthopaedics Ltd, Munsingen, Switzerland) or round threaded titanium (RCI; Smith & Nephew DonJoy, Carlsbad, CA) interference screws, harvested either without (biodegradable: group I, titanium III) or with (biodegradable: group II, titanium: group IV) attached tibial bone plugs. Maximum pullout force in group I (507 ± 93 N) was significantly higher than in group III (419 ± 77 N). Pullout force of bone plug fixation was significantly higher than that of direct tendon fixation (717 ± 90 N in group II and 602 ± 117 N in group IV). Pullout force of biodegradable fixation was significantly higher in both settings. These results indicate that initial pullout force of hamstring-tendon graft interference screw fixation can be increased by using a biodegradable interference screw. In addition, initial pullout force of hamstring-tendon graft fixation with an interference screw can be greatly increased by harvesting the graft with its distally attached tibial bone plug.Arthroscopy 1998 Jan-Feb;14(1):29-37     

Graft failure versus graft fixation in ACL reconstruction: histological and immunohistochemical studies in rabbits

The causes of graft failure after anterior cruciate ligament (ACL) reconstruction are multifactorial including the methods of graft fixation. The purpose of this study was to examine the ACL graft failure in three different methods of graft fixations including interference screw fixation, suture-post fixation and combined interference screw and suture-post fixation. We hypothesized that the fixation method after ACL reconstruction can affect the graft healing in tibial tunnel. Eighteen New Zealand white rabbits were categorized into three groups according to the method of fixation in unilateral ACL reconstruction with long digital extensor autograft. Histological examination demonstrated that the combined fixation and suture-post fixation groups showed significantly better integration between tendon and bone (P = 0.04). In immunohistochemical analysis, the combined fixation and suture-post fixation groups showed significantly higher BMP-2 and VEGF expressions than interference screw (P < 0.01). The tendon–bone healing after ACL reconstruction was affected by the method of graft fixation. Combined fixation with interference screw and suture-post reduced graft-tunnel micromotion and improved the graft healing in tibial tunnel.     

Initial fixation strength of modified patellar tendon grafts for anatomic fixation in anterior cruciate ligament reconstruction.

Recently it has been shown that anatomic tibial graft fixation in anterior cruciate ligament (ACL) reconstruction is preferable in order to increase isometry and knee stability. To facilitate anatomic patellar tendon graft fixation, customized graft length shortening is necessary. The purpose of this study was to compare the initial fixation strength of four different shortened patellar tendon grafts including three bone plug flip techniques and direct patellar tendon-to-bone interference fit fixation in a model with standardized bone density. Ninety calf tibial plateaus (22 to 24 weeks old) with adjacent patella and extensor ligaments were used. Tendon grafts were shortened by flipping the bone plug over the tendon leaving a tendon-tendon-bone (TTB) construct and, as the first modification in the opposite direction resulting in a tendon-bone-tendon (TBT) construct. The second modification consisted of the TBT construct with interference screw position at the lateral aspect of the bone plug (TBTlat). As the fourth modification the tendon graft was directly fixed (Tdirect) with an interference screw. In addition, a round-threaded titanium (RCI; Smith & Nephew DonJoy, Carlsbad, CA), a round-threaded biodegradable screw (Sysorb; Sulzer Orthopedics, Münsingen, Switzerland), and a conventional titanium interference screw (Arthrex Inc, Naples, FL) were compared. We found that TTB (mean 441 N for biodegradable screw, 357 N for RCI screw, 384 N for conventional screw) and TBT (mean 407 N for biodegradable screw, 204 N for RCI screw, 392 N for conventional screw) construct fixation achieves comparable fixation strength, although failure in the TTB was due to tendon strip off at its ligamentous insertion. The highest failure load was found in TBTlat fixation (mean 610 N for biodegradable screw, 479 N for RCI screw). Therefore, this technique should be recommended when using a tendon flip technique. The failure load for Tdirect fixation (mean 437 N for biodegradable screw, 364 N for RCI screw) was similar to that of TTB and TBT fixation, which may indicate that a patellar-tendon graft harvested without its patellar bone plug and directly fixed with an interference screw is equivalent to a flipped graft. This may additionally reduce harvest site morbidity and eliminates the risk of patellar fracture. The fixation strength of round-threaded biodegradable and conventional titanium interference screws was similar, whereas that of round-threaded titanium screws was significantly lower in the patellar tendon flip-techniques. However, it should be taken into consideration that round-threaded titanium screws are proposed for direct tendon-to-bone fixation.     

Interference screw position and hamstring graft location for anterior cruciate ligament reconstruction

Anterior cruciate ligament reconstruction with hamstring tendon graft and interference screw fixation has recently been considered. Concerns for the use of interference screws with soft tissue grafts include damage to the graft during screw insertion, decreased fixation strength, and a decrease in the bone-tendon contact area for healing within the tunnel when the screw is placed in an eccentric position. This last concern could be addressed by placing the interference screw centrally between the four limbs of the hamstring graft. The purpose of this study was to determine the mode of failure, the pullout force, and graft slippage before graft fixation failure of hamstring tendons fixed with an interference screw positioned eccentrically in relation to the hamstring tendons verses an interference screw positioned centrally between the four graft limbs. The semitendinosus and gracilis tendons were harvested from six, fresh cadaveric specimens. Each tendon was divided into two segments of equal length. Both the semitendinosus and gracilis tendon segments were looped to form four strands. The specimens were then fixed with a bioabsorbable interference screw in the two different positions and pulled from a standardized polyurethane foam. All tendons in both groups failed by pulling out from between the interference screw and tunnel, regardless of the screw position. No tendon was cut by the screw in either group. There was no significant difference between the forces required to produce specific amounts of graft slippage between the two fixation techniques tested. There was no significant difference between the average total slippage at maximum pullout, 11.8 mm for the screw placed in the eccentric position and 13.7 mm for the screw placed in the central position. The maximum pullout force averaged 265.3 N for the screw placed in the eccentric position, and 244.7 N for the screw placed in the central position; these values were not significantly different. Placement of the interference screw in the central position did not compromise strength and it improves graft contact within the bone tunnel. Interference screw fixation, when applied against a bone plug, has been shown to consistently have a pullout force of more than 400 N.Arthroscopy 1998 Jul-Aug;14(5):459-64     

Bioabsorbable polyglyconate interference screw fixation in anterior cruciate ligament reconstruction: a prospective computed tomography-controlled study.

PURPOSE: It was the purpose of the study to evaluate a new polyglyconate bioabsorbable interference screw for graft fixation in anterior cruciate ligament (ACL) reconstruction. TYPE OF STUDY: Prospective randomized. MATERIALS AND METHODS: Forty patients who underwent endoscopic ACL reconstruction were included in the study and randomized intraoperatively. Group A consisted of 20 patients (6 women, 14 men; mean age, 29.6 years) who had femoral bone block fixation with a bioabsorbable interference screw and tibial fixation with a titanium interference screw. Group B included 20 patients (5 women, 15 men; mean age 29.6 years) who had fixation of both femoral and tibial bone blocks with titanium interference screws. There was no significant difference between the groups with regard to age, gender, height, weight, time from injury to surgery, activity level, and concomitant injuries. RESULTS: Clinical results (using IKDC, Lysholm, Tegner scores) of the 2 groups as well as instrumented laxity measurements (KT-1000) did not show significant (P >.05) differences at any stage of follow-up. No complications with respect to graft fixation could be found. Computed tomography scans, performed within the first postoperative week, at 6 weeks, and at 3, 6, 12, and 24 months postoperatively revealed a uniform picture for all patients within the groups, showing completed screw degradation at 12 months in group A. CONCLUSION: Polyglyconate interference screw fixation for patellar tendon grafts has not been found to be associated with increased clinical complications or significant osteolysis. It provided equivalent fixation and clinical results compared with titanium screws. However, replacement of the screw with bone did not take place for up to 3 years postoperatively.     

The evolgate: a method to improve the pullout strength of interference screws in tibial fixation of anterior cruciate ligament reconstruction with doubled gracilis and semitendinosus tendons

Purpose:The goal of the study was to investigate the biomechanical properties of a new device for tibial fixation in arthroscopic anterior cruciate ligament reconstruction using doubled semitendinosus and gracilis tendons.Type of Study:Biomechanical study.Methods:This study compares the initial pullout strength, stiffness, and failure modes of 7 pairs of 4-strand human semitendinosus and gracilis grafts fixed to porcine tibias using either the Evolgate (Citieffe, Bologna, Italy) or 1 round threaded titanium interference screw. Structural tests of the graft fixation method tibia complexes were performed using a materials testing machine (MTS Bionix 855, Minneapolis, MN) at a strain rate of 50 mm/second.Results:The mean failure load was 1,237 ± 191 N for the Evolgate and 537 ± 65 N for the interference screw (P < .05) and the mean stiffness was 168 ± 37 N/m for the Evolgate and 105 ± 17 N/m for the interference screws (P ≤ .05). Although in all the cases fixed with the Evolgate failure occurred because of tendon rupture inside the tibial tunnel close to the fixation device, in 4 of the 7 cases fixed with interference screws, failure occurred because of tendon slippage at the fixation site.Conclusions:These results indicate that initial pullout strength of hamstring tendon graft interference screw fixation can be significantly increased using the Evolgate. In fact, because the screws purchase only in the cancellous bone, the Evolgate reinforces the walls of the tibial tunnel with a titanium involute, avoiding the loss of fixation strength related to the low density of the cancellous bone of the proximal metaphysis of the tibia.     

前十字韧带重建中的移植物位置偏移

目的 计算可吸收界面螺钉导致的移植物偏离隧道位移,探讨其对前十字韧带重建产生的影响.方法 19个新鲜尸体膝关节标本,随机选取5个,采用7 mm、8 mm、9 mm界面螺钉固定自体肌腱,测定偏移距离.另外14个膝关节分为等长组和解剖组,等长组膝关节测量界面螺钉固定后及校正位置的移植物拉长距离;解剖组膝关节于膝关节生物力学测试仪上分别测定ACL完整组、ACL缺失组、偏移组和校正组在134 N前向负荷下膝关节屈曲0°、15°、30°、60°和90°位的胫骨前向位移.结果 (1)肌腱偏移:直径7mm、8 mm、9mm的界面螺钉分别使移植物偏移(2.36±0.11)mm、(2.72±0.06)mm、(3.00±0.06)mm.(2)等长性:初始拉长小于3 mm,偏移拉长大于3 mm,校正拉长小于3 mm.(3)生物力学:屈膝0°、15°位,ACL完整组与偏移组、校正组差异无统计学意义.屈膝30°、60°、90°位ACL完整组与其他各组比较差异均有统计学意义,屈膝30°、60°位偏移组与校正组比较差异有统计学意义.结论 无论等长重建还是解剖重建,界面螺钉均影响移植物的股骨隧道口位置.前十字韧带重建预先校正股骨隧道口位置,移植物基本会处于预先的理想位置.

Abstract：

Objective To investigate the impact of graft position shift on anterior cruciate ligament reconstruction induced by femoral fixation of interference screw. Methods Nineteen fresh cadaveric knees were used and assigned to three groups. 1) Study of graft position shift: 5 knees were randomly selected, interference screws of 7 mm, 8 mm and 9 mm were used in autologous tendon fixation, then the graft position shift were measured. 2) Study of isometry: 7 knees were randomly divided into the isometric reconstruction group (D group). In the D group, Retrobutton, interference screw and interference screw in location-corrected bone tunnel were used respectively as fixation. The isometry of grafts was evaluated. 3) Study of tibia anterior translation: 7 knees were randomly divided into the anatomic reconstruction group (J group). In the J group,the tibia anterior translation was measured in four different conditions in the same joint: intact knee joint,knee joint without ACL, ACL anatomic reconstruction by interference screw fixation, and ACL anatomic reconstruction by interference screw fixation with corrected bone tunnel location. Results 1) With 7 mm, 8mm and 9 mm interference screw fixation, graft position shift were (2.36±0.11) mm, (2.72±0.06) mm and (3.00±0.06) mm respectively. 2) Graft length change: graft length change in Retrobutton group and corrected bone tunnel group were less than 3 mm, while graft length change in those fixed with interference screw were stretched in more than 3 mm. 3) Study of tibia anterior translation: there was no difference among the intact group, the anatomic group and the corrected group at 0° and 15°. However, the difference was found between the intact group and other groups at 30°、60° and 90° of flexion, as well as between these two reconstructed methods at 20° joint flexion (P＜0.05). Conclusion In both isometric and anatomic ACL reconstruction with interference screw, the graft is pushed tightly toward the femoral tunnel wall, which shifts the graft away from the desired position. In our study we find out that the corrected location of the femoral bone tunnel significantly improves the isometry of ACL reconstruction and anatomic reconstruction.     

Fixation strength of a biodegradable interference screw and a press-fit technique in anterior cruciate ligament reconstruction with a BPTB graft

The objective of this study was to evaluate the fixation strength of a biodegradable interference screw (Arthrex, Naples, FL) compared with press fit fixation and a titanium interference screw in anterior cruciate ligament (ACL) reconstruction using a bone-patellar tendon-bone (BPTB) graft. Porcine lower limbs were used. Ultimate failure loads of the biodegradable screw (805.2 N; range 680 to 995 N) did not differ significantly from ultimate failure loads of titanium interference screws (768.6 N; range 544 to 1094 N). Press fit fixation provided significant (P < .01) lower fixation strength (462.5 N; range 80 to 825 N). These results support the conclusion that biodegradable interference screws are a reasonable alternative in terms of primary fixation strength.     

Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: The impact of fixation level and fixation method under cyclic loading

Purpose: To mechanically test different reconstruction techniques of the anterior cruciate ligament (ACL) under incremental cyclic loading and to evaluate the impact of the level and method of graft fixation on tensile properties of each technique. Type of Study: In vitro biomechanical study. Methods: Four hamstring and 1 patellar tendon reconstruction techniques were performed on 40 young to middle-aged human cadaveric knees (average age, 39 years). An anterior drawer with increasing loads of 20 N increments was applied at 30° of knee flexion. Anatomic, direct interference screw fixation was tested in 2 hamstring and in the patellar tendon groups. Nonanatomic (extracortical) graft anchorage was tested in the remaining 2 hamstring groups with indirect graft fixations on both sides and the combination of indirect tibial and direct femoral fixation. Structural properties were determined throughout the cyclic loading test. Results: The more anatomic reconstruction techniques provided significantly higher structural properties and smaller loss of fixation compared with nonanatomic, extracortical fixation, with indirect repair on both fixation sites resulting in the lowest structural properties. The tibial fixation site was the weakest link in all of the anatomic reconstructions. Patellar tendon fixation with attached bone blocks in both bone tunnels significantly improved construct stiffness and decreased graft slippage. Conclusions: The results of this study suggest that anatomic fixation should be preferred for anchorage of hamstring tendons and linkage materials should be avoided. Direct soft-tissue fixation with interference screws still allows considerable graft slippage, which can be limited by using a bone block or application of a backup or hybrid fixation, especially on the tibial fixation site.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 18, No 3 (March), 2002: pp 304–315     

Histological findings of tendon-bone healing following anterior cruciate ligament reconstruction with hamstring grafts

BACKGROUND: The purpose of the study was the histological examination of tendon-bone healing of hamstring grafts after anterior cruciate ligament (ACL) reconstruction. METHODS: During five arthroscopies done 6-14 months after ACL reconstructions, biopsies of the wall of the former drilled femoral canal were obtained. Four patients were primarily operated on using a suspending device (Endobutton, Acufex Microsurgical, Mansfield, MA, USA, and Transfix, Arthrex, Naples, FL, USA) for femoral fixation, one patient was reconstructed with a biodegradable interference screw directly inserted between the tendon and the wall of the canal. Biopsies were obtained using a tube harvester during re-arthroscopy. Three grafts were stable, two grafts were unstable, and revision of the ACL was performed. RESULTS: Histologically, in the four cases of reconstruction with a button or a rectangular pin, biopsies resembled granulation tissue without insertion of fibers between the tendon tissue and the bony wall. A wide area of woven bone was noted adjacent to the pre-existing lamellar bone. In contrast, the tendon-bone junction in the knee reconstructed with a biodegradable interference screw resembled a zone of metaplastic fibrous cartilage between the tendon graft and the lamellar bone. Collagen fibers connecting the tendon-bone interface occurred under polarized light microscopy. CONCLUSION: We conclude that the use of hamstring grafts for ACL reconstruction can lead to different histological pattern of tendon-bone healing. Micromotion of the hamstring graft inside the drilled canal can be play a role in tendon-bone healing.     

Comparisons of intraosseous graft healing between the doubled flexor tendon graft and the bone–Patellar tendon–Bone graft in anterior cruciate ligament reconstruction

Purpose: The purpose of this study was to compare intraosseous graft healing between the doubled flexor tendon (FT) graft and the bone–patellar tendon–bone (BPTB) graft in anterior cruciate ligament (ACL) reconstruction. Type of Study: Randomized trial. Methods: A biomechanical and histologic study was conducted with 24 adult beagle dogs. Bilateral ACL reconstructions were performed in each animal. Autogenous doubled FT and BPTB grafts were used for the left and right knees, respectively. Each end of the 2 grafts was tethered with a polyester suture to a screw post with a washer. The animals were then allowed unrestricted activities in their cages. Eight animals were killed at 3, 6, and 12 weeks, respectively. Results: Histologically, the FT graft was anchored to the tunnel wall with newly formed collagen fibers resembling Sharpey’s fibers by 12 weeks. These fibers were more abundant in the anterior (ventral) gap than in the posterior (dorsal) gap. In the BPTB graft, the bone plug was anchored with newly formed bone at 3 weeks, although osteocytes in the plug trabeculae were necrotic for 12 weeks. Degeneration of the tendon-bone junction in the plug progressed at 6 weeks. Tensile testing showed that the weakest site was different not only between the 2 grafts but also between the observation periods. In the FT graft, the weakest site was the graft-wall interface at 3 weeks and the intraosseously grafted tendon at 6 weeks. In the BPTB graft, the weakest site was the graft-wall interface at 3 weeks and the proximal site in the bone plug at 6 weeks. The ultimate failure load of the FT graft was significantly inferior (45.8%) to that of the BPTB graft at 3 weeks (P =.021). At 6 weeks, the load of the FT graft was 85% that of the BPTB graft without a significant difference (P =.395). Conclusions: As to the clinical relevance, the fixation device chosen for soft-tissue fixation appears to be more important than comparing it to the BPTB graft, although this has yet to be conclusively proven.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 5 (May-June), 2001: pp 461–476     

Primary stability of bone-patellar tendon-bone graft fixation with biodegradable pins

Purpose: We evaluated the initial bone-patellar tendon-bone (BPTB) graft fixation strength of biodegradable pins compared with interference screws in anterior cruciate ligament reconstruction using bovine knees. Type of Study: Biomechanical in vitro study. Methods: Ten BPTB grafts from human donors fixed with 2 biodegradable 2.7-mm pins (Rigid Fix; Ethicon, Mitek Division, Norderstedt, Germany) crossing the bone block perpendicular and 10 BPTB grafts fixed with conventional biodegradable interference screws (Absolute Absorbable Interference Screw; Innovasive Devices, Marlborough, MA) underwent ultimate single-cycle failure loading at a rate of 200 mm/min. The grafts were fixed to bovine tibia to simulate young human femoral bone density. Failure mode, displacement before failure, and ultimate failure load were tested with a testing machine. The pullout force was in line with the bone tunnel to simulate a worst case scenario. Results: The failure mode for cross pins was either fracture of the bone block (5 specimens) or fracture of the articular pin (5 specimens). The failure mode for interference screws was slippage past the screw in all specimens. In the single cycle loading test, the mean yield load for the biodegradable pins was 400.2 (± 122.4) N, maximum load, 524.6 (± 136.6) N, with a mean stiffness of 155.2 (± 32.4) N/mm. The yield load at failure for the interference screw was 402.7 (± 143.9) N, maximum load 515.7 (± 168.5) N with a mean stiffness of 168 (± 42) N/mm. Conclusions: Fixation of a BPTB graft with 2 biodegradable 2.7-mm pins (Rigid Fix) leads to primary stability that is comparable to fixation with biodegradable interference screws.     

Interference screw divergence in endoscopic anterior cruciate ligament reconstruction

Interference screws are commonly used for graft fixation in bone-tendon-bone patellar tendon anterior cruciate ligament (ACL) reconstruction. The clinical significance of graft screw divergence has not been well studied. This report retrospectively reviews our initial experience in 73 consecutive endoscopic (single-incision) ACL reconstructions using interference screw fixation. Femoral divergence occurred more frequently in the lateral plane (29%) than the anteroposterior (AP) plane (15%). No early graft failures were noted clinically or by KT-1000 arthrometer testing. If properly tested at the time of operation, it does not appear that divergence of femoral screws < 30° leads to early clinical failure in endoscopic ACL reconstruction. We propose that stresses on the graft-screw-tunnel construct will concentrate distally when placed in a divergent fashion, resulting in a wedge effect. No changes in early range of motion protocols or rehabilitation are recommended if screw divergence is noted and provided intraoperative stability is noted.     

Enveloping the tendon graft with periosteum to enhance tendon-bone healing in a bone tunnel: A biomechanical and histologic study in rabbits

Purpose: Fixing and incorporating the tendon graft within the bone tunnel is a major concern when using grafts for ligament reconstruction. The periosteum contains multipotent stem cells and has the potential to form osteogenic and chondrogenic tissues. This study uses histologic and biomechanical analyses to examine the effect of periosteum on tendon-bone healing within a bone tunnel. Type of Study: Experimental study in an animal model. Methods: In this study, 36 adult New Zealand White rabbits were used. The long digitorum extensor tendon was transplanted into a bone tunnel of the proximal tibia. The periosteum from the proximal tibia was sutured on the surface of the tendon portion. The tendon was pulled through a drill-hole in the proximal tibia and attached to the medial aspect of the tibia. Histologic examination of the tendon-bone interface and biomechanical test for maximal pullout load were evaluated at 4, 8, and 12 weeks after operation. Results: Histologic analysis of the tendon-bone interface showed a fibrous layer formed between the tendon and the bone by the periosteum. This layer became progressively integrated with the tendon and bone surface during the healing process. At 4 weeks, the cancellous bone lining in the bone tunnel was interdigitated with the fibrous interface tissue. At 8 weeks, progressive new bone grew into the interface fibrous layer. At 12 weeks, collagen fibers anchored to the bone and organization with fibrocartilage formation developed between the tendon and bone. Biomechanical testing revealed higher maximal pullout strength in the periosteum-enveloped group at all time points, with a statistically significant difference at 8 and 12 weeks. The periosteum-treated group had a higher interface strength-to-length ratio and significant increase at 8 weeks and 12 weeks. Conclusions: The histologic and biomechanical studies demonstrated that, if periosteum was sutured on the tendon that was transplanted within a bone tunnel, it resulted in a superior healing process and better healed strength. When doing ligament reconstruction with a tendon graft, the periosteum can be sutured to the graft to enhance tendon-bone healing.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 19, No 3 (March), 2003: pp 290–296     

骨-髌腱-骨自体移植重建前十字韧带的研究

目的探讨使用骨-髌腱-骨自体移植重建前十字韧带(ACL)术后1年内重建物生物力学性能和组织学变化。方法在39只成年犬单侧后肢行骨-髌腱-骨自体移植重建ACL手术。术后分别在4、8、12、26和52周时处死动物,对正常对照侧ACL和手术侧重建物在屈膝90°行拉力试验直到完全断裂,记录断裂位置,计算横断面积、强度、刚度和应力,观察关节内和隧道内韧带转化过程及隧道内骨块-隧道壁、髌腱-隧道壁和骨块-髌腱三个界面的组织学愈合过程。结果术后隧道内骨块-隧道壁界面4周时愈合;髌腱-隧道壁界面52周时有Sharpey样纤维跨过,出现潮线,软骨细胞有成行排列的趋势;术后骨块-髌腱界面未钙化的纤维软骨层消失,52周时仍未重现;韧带在关节内和隧道内部分的转化过程相似,其结构均于26周时与正常ACL相似。生物力学试验显示所有重建物均在韧带部断裂。52周时,移植髌腱的强度、刚度和应力分别为对照侧的38%、58%和50%,差异有统计学意义。骨隧道内的骨-骨界面术后4周时愈合,早于骨-腱界面;骨-腱界面52周时表现为间接止点,界面出现成行排列趋势的软骨细胞,界面的愈合过程仍在继续。结论用挤压螺钉固定的重建物在手术4周以后,力学薄弱处始终位于韧带本身,在指导患者进行康复锻炼时不必担心固定止点的力学性能。挤压螺钉固定的止点不仅在术后即刻稳定,而且在止点愈合、韧带化过程中仍然保持力学性能可靠。术后1年时虽然韧带在组织学上与正常ACL相似,但力学性能显著低于正常,在剧烈活动时患者需配带支具等进行保护。     

Structural properties of a new device for graft fixation in cruciate ligament reconstruction: the shim technique

Introduction  

In ACL reconstruction using a soft tissue graft, aperture fixation with interference screws (IFS) can lacerate and rotate the graft and cause primary tunnel widening. To overcome these downsides, a new wedge-shaped implant (MegaShim, Karl Storz, Germany) was developed. We hypothesized that aperture fixation of hamstring ACL reconstruction using the MegaShim technique shows comparable structural properties when compared to interference screw fixation.     

Kniegelenklaxizität beim vorderen Kreuzbandersatz

Background

The use of interference screws for femoral graft fixation in anterior cruciate ligament (ACL) reconstruction with hamstring grafts can result in rotation of the graft around the screw leading to changes in the final position of the graft within the bone tunnel.

Material and methods

In a prospective study 107 patients (54 right and 53 left knees) underwent ACL reconstruction with a hamstring tendon autograft. Femoral fixation of the graft was performed with a standard right-thread screw in all cases. Patients were assessed at 6 months postoperatively with the international knee documentation committee (IKDC) standard evaluation including instrumented laxity measurements and the results were compared between right and left knees.

Results

A significantly higher postoperative anterior laxity was observed in left knees with a negative Lachman test in only 64 % of the cases compared with 87 % in the group of right knees. Accordingly, instrumented laxity measurements of the reconstructed knee compared with the contralateral knee revealed significant differences between left and right knees (left knees 1.8±1.2 mm and right knees 1.0±1.4 mm)

Conclusions

This study demonstrates the importance of femoral graft positioning and its sensitivity to multiple influencing factors. The use of standard right-thread interference screws for femoral graft fixation in the mirrored situation of right and left knees may produce a systematic error in ACL reconstruction. Due to a possible rotation of the graft around the screw, the final position of the transplant may vary thus leading to significant changes in anterior translation of the operated knee.