How four weeks of implantation affect the strength and stiffness of a tendon graft in a bone tunnel: a study of two fixation devices in an extraarticular model in ovine

BACKGROUND: For a tendon graft to function as an anterior cruciate ligament, the tendon must heal to the bone tunnel. We studied the effect of 4 weeks of implantation on the strength and stiffness of a tendon in a bone tunnel using two different fixation devices in an ovine model. HYPOTHESIS: The type of fixation device in anterior cruciate ligament reconstruction may affect early healing, which can be measured as the strength and stiffness of a tendon in a bone tunnel. STUDY DESIGN: Controlled laboratory study. METHODS: An extraarticular tendon graft reconstruction was performed in ovine tibias. The graft was fixed with either a bioresorbable interference screw or a WasherLoc. After 4 weeks of implantation the strength and stiffness of the complex and the tendon graft-bone tunnel interface were determined by incrementally loading specimens to failure. RESULTS: For the interference screw, the strength deteriorated 63% and the stiffness deteriorated 40%. For the WasherLoc, the strength was similar and the stiffness improved 136%. CONCLUSIONS: The type of fixation device determines whether the strength and stiffness of a tendon in a bone tunnel increases or decreases after implantation. Clinical Relevance: The pace of rehabilitation may need to be adjusted based on the type of fixation device used to secure a soft tissue graft.     

Serial dilation versus extraction drilling in anterior cruciate ligament reconstruction: a biomechanical study

The hamstring tendon graft has become increasingly popular in anterior cruciate ligament reconstruction because of low donor-site morbidity. However, the tibial fixation is considered difficult, mainly because of low tibial mineral bone density. Therefore, we tested whether preparation of the tibial tunnel with compaction by serial dilation provided a stronger anchorage of the graft–fixation-device complex than does traditional extraction drilling of the tibial tunnel. In 20 bovine tibiae, the bone tunnels were created with either extraction drilling (group 1) or compaction by serial dilation (group 2). Twenty bovine digital extensor tendons were fixated in the bone tunnel with an Intrafix tibial fastener. The graft–fixation-device complexes were mounted in a hydraulic test machine. The fixation strength was evaluated after cyclic loading. The difference between the serial dilation group and the extraction drilling group ranged from a mean slippage of 0 mm at 70–220 N, to a mean slippage of 0.1 mm at 70–520 N. We found no significant difference in slippage of the graft–fixation-device complex after 1,600 cycles. This study failed to show a significant difference between compaction by serial dilation and extraction drilling of the tibia bone tunnel in anterior cruciate ligament reconstruction.     

Multistranded hamstring tendon graft fixation with a central four-quadrant or a standard tibial interference screw for anterior cruciate ligament reconstruction

BACKGROUND: Tibial fixation of hamstring tendon grafts has been the weak link in anterior cruciate ligament reconstruction. HYPOTHESIS: Use of a central four-quadrant sleeve and screw provides superior fixation when compared with standard interference screw fixation. STUDY DESIGN: Controlled laboratory study. METHODS: In eight pairs of cadaveric knees each anterior cruciate ligament was reconstructed using either an interference screw or a central sleeve and screw on the tibial side. The specimens were then subjected to cyclic loading followed by a load-to-failure test. RESULTS: The load required to cause 1 and 2 mm of graft laxity, defined as the separation of the femur and the tibia at the points of graft fixation, was significantly greater with the sleeve and screw than with the interference screw (at 2 mm: sleeve and screw, 216.1 +/- 30.1 N; interference screw, 167.0 +/- 33.2 N). The force at initial slippage for each of the graft strands was significantly higher with use of the central sleeve and screw. CONCLUSIONS: The four-quadrant sleeve and screw device may provide greater surface area for healing of hamstring tendon grafts and allow equal tensioning of graft strands before fixation. These factors are associated with increased strength of fixation and reduced laxity of the graft after cyclic loading. Clinical Relevance: Use of the central four-quadrant sleeve and screw system offers increased strength of fixation in anterior cruciate ligament reconstruction with hamstring tendon graft.     

Insertion of autologous tendon grafts to the bone: a histological and immunohistochemical study of hamstring and patellar tendon grafts

This study examined the structure of the insertion of autologous tendon grafts used for anterior cruciate ligament reconstruction. Biopsy specimens of the femoral ¶and tibial bone graft interface were obtained at revision surgery in 14 patients (6 with hamstring grafts, 8 with a patella tendon graft). The specimens were analyzed by light microscopy and immunohistochemistry (confirming type I, type II, and type III collagen). The insertions of hamstring autografts to the bone tunnel have three characteristic histological zones. Zone 1 is composed of the dense connective tissue of the graft. The collagen fibers of the graft enter the bone under oblique angles. Zone 2 is composed of woven bone with ¶a sharp transition to the lamellar bone of the tibia (zone 3). Immunohistochemistry revealed the presence of type I and type III collagen within the dense connective tissue of the graft. The woven and lamellar bone showed positive immunostaining for antibodies against type I collagen only. This structure resembled a fibrous ligament or tendon insertion. In the majority of patients with a patella tendon graft the structure of the insertion resembled a chondral enthesis. The chondral insertion of the graft to the bone is composed of four characteristic zones. Between the dense connective tissue of the graft (zone 1) and bone (zone 4) there is a zone of fibrocartilage (zone 2). Close to the bone the fibrocartilage is mineralized (zone 3). Within the fibrocartilage the immunohistochemical analysis confirmed type II collagen. This structure resembled the chondral enthesis of the normal anterior cruciate ligament. However, in cases in which the distal bone bloc has been fixated outside the tibial tunnel, the tibial insertion of the patellar tendon graft resembled a fibrous insertion. While both types of tendon grafts heal to the bone of femur and tibia, the insertion of patella tendon grafts healing by bone plug incorporation resembles the chondral insertion of the normal anterior cruciate ligament and may have a more physiological connection to the bone than hamstring grafts.     

MR evaluation of anterior cruciate ligament reconstruction with quadriceps tendon. Preliminary experience

PURPOSE: Anterior cruciate ligament reconstructions are becoming increasingly frequent, and MRI has been shown to be the best imaging modality for the non-invasive assessment of surgical outcome. Use of the quadriceps tendon as a biological replacement for injured cruciate ligament is a recent innovation. This study evaluated by MRI the results of anterior cruciate reconstruction in 27 consecutive patients who underwent arthroscopic reconstruction with homologous quadriceps tendon. MATERIAL AND METHODS: MRI was carried out on 27 patients who had undergone anterior cruciate ligament reconstruction with the middle third of the homolateral quadriceps tendon. The examinations were performed on two MRI units: a permanent 0.2-Tesla dedicated magnet (Artoscan, Esaote Italy) and whole-body 1.5-Tesla superconducting magnet (Signa, GE Medical Systems Milwaukee, Winsconsin USA). Axial, sagittal and coronal images were acquired with SE, GE and STIR fat suppression sequences. The examinations were performed 1, 3, and 6 months post-operatively in 16 patients, and 1 and 3 post-operatively in 11 patients. The same arthroscopic surgical technique was employed in all patients, with 20 cases of tibial mono-tunnel femoral semi-tunnel, and 7 cases with tibial bi-tunnel technique. All patients were assessed by arthrometric and clinical tests after surgery. Bioabsorbable interference screws were used for tibial fixation in all patients and metallic interference screws were used for femoral graft fixation in 8 patients. RESULTS: In all cases MRI correctly visualised the tunnel positions, the articular portion and the bone-portion of the graft inside the tibial and femoral tunnels. The absence of paramagnetic artefacts in the tibia allowed complete visualisation on the axial, sagittal and coronal MRI images with optimal spatial and contrast resolutions. In 6 cases, the presence of metal residues from the surgical cutter prevented correct evaluation of femoral tunnel content. No new graft or articular lesions were found. In 18/27 cases peri-focal marrow edema around the tibial tunnel had disappeared 3 months after surgery. The process of synovial incorporation was judged to be correct in all cases. DISCUSSION: The use of anterior cruciate ligament reconstruction with the quadriceps tendon is a important innovation given the size of the harvested material and the possibility of completely filling the osseous tunnels, without interposition of synovial proliferation or fluid collection between tendon and bone, as confirmed by MRI. Furthermore, the use of non-metallic screws allows MRI evaluation of tunnel content and oedema in the spongy bone around the tunnel. The study of the double tibial tunnel requires specific obliqueness in the coronal plane scans. CONCLUSIONS: This arthroscopic technique for anterior cruciate ligament reconstruction allows thorough MRI evaluation of all portions of the transplant, and in particular those coursing within the tibia and femur. The absence of bone oedema around the tunnels and synovial proliferation within the tunnels may be predictive of faster healing and complete bone incorporation of the grafts.     

Evolgate fixation of doubled flexor graft in anterior cruciate ligament reconstruction: biomechanical evaluation with cyclic loading

BACKGROUND: The weakest points in hamstrings anterior cruciate ligament reconstruction are its points of fixation, especially on the tibial side. Methods for graft fixation to bone should be strong enough to avoid failure, stiff enough to restore load-displacement response, and secure enough to resist slippage under cyclic loading. HYPOTHESIS: Biomechanical properties of the interference screw can be improved by reinforcing the walls of the tunnel with a metal spiral (Evolgate fixation). STUDY DESIGN: Controlled laboratory study. METHODS: Three paired tests were performed using common digital extensor bovine tendons fixed to porcine tibias with interference screw, Intrafix, and Evolgate; critical graft fixation conditions were simulated by applying subsequent cycles to the graft before loading the graft until failure. RESULTS: The strength, stiffness, and resistance to slippage of the Evolgate were significantly higher than those of the interference screw; the ultimate failure load of the Evolgate was significantly higher than that of the Intrafix (1058+/-130 N and 832+/-156 N, respectively; P=.02). No statistically significant differences were found between Evolgate and Intrafix regarding the stiffness and slippage under cyclic load. CONCLUSION: Evolgate fixation seems to be stronger, stiffer, and more resistant to slippage than is interference screw fixation of similar length, and it is stronger but not stiffer than Intrafix. CLINICAL RELEVANCE: The Evolgate provides structural properties that seem to be appropriate for an intensive rehabilitation after anterior cruciate ligament reconstruction using a doubled semitendinosus and gracilis graft.     

Compaction versus extraction drilling for fixation of the hamstring tendon graft in anterior cruciate ligament reconstruction

Initial strength of quadrupled hamstring tendon grafts fixed with titanium interference screws was assessed in 30 pairs of porcine tibiae. Bone tunnels were drilled with either compaction drilling (stepped routers) or conventional extraction drilling (cannulated drill bits). Fifteen pairs of specimens were subjected to a single-cycle load-to-failure test, while the rest underwent a cyclic-loading test to further assess the quality of the fixation. No significant difference between the two drilling techniques was found with regard to yield load, displacement at yield load, stiffness, or mode of failure. Porcine trabecular bone mineral density was determined using peripheral quantitative computed tomography and compared with that of young women and men at a site corresponding to that of the tibial bone drill hole of an anterior cruciate ligament reconstruction. There was a significant difference between the two species (210 +/- 45 mg/cm(3) in porcine tibial bone versus 129 +/- 30 mg/cm(3) in women and 134 +/- 34 mg/cm(3) in men), suggesting that porcine knee specimens may have limitations in studies of graft fixation in anterior cruciate ligament reconstruction. We found no difference between extraction and compaction drilling in initial fixation strength of a hamstring tendon graft for anterior cruciate ligament reconstruction using a porcine model.     

关节镜下膝关节腘肌腱重建的实验研究

目的:进一步研究膝关节后外复合体(posterolateral complex,PLC)与腘肌复合体的解剖特点,设计关节镜下重建腘肌腱的手术方法.方法:通过10例成人膝关节尸体标本进行两部分研究,每部分各取5例标本:第一部分进行大体解剖研究,对腘肌复合体(包括腘肌腱、肌腹、股骨附着点、肌腱-肌腹交界区)的解剖特点以及周围相邻解剖结构(包括胫骨平台、外侧半月板后角、后交叉韧带、胭腓韧带、血管)进行观察和测量.第二部分进行关节镜下手术重建技术的流程设计.设计显露腘肌腱的股骨附着点和肌腱-肌腹交界点的关节镜入路以及股骨和胫骨隧道的定位与制备方法,引入移植物并固定,完成腘肌腱的重建.结果:第一部分:腘肌腱的股骨附着点位于滑膜反折区,属滑膜外结构;止于股骨的腘肌腱沟的最近端,与关节软骨边缘紧邻,与外侧副韧带股骨附着点中心相距1.5～1.6cm.腘肌腱走行于腘肌腱浅沟内、肌腱-肌腹交界点位于胫骨后外侧平台的内、外中线与关节软骨面远侧1.0cm线的交点上,内侧距离后交叉韧带外侧边缘1.2～2.0cm、外侧与上胫腓关节的内侧缘紧邻.第二部分:进行膝关节镜下手术操作.采用前外入路及外侧辅助关节镜入路切除腘肌腱近端附着点周围滑膜反折,显露整个附着区,并利用克氏针确定中心点,自外向内制备股骨隧道.通过后外、后内及穿后间隔关节镜入路,沿腘肌腱走行局部切开与后关节囊的结合部,显露肌腱-肌腹交界点,并利用前交叉韧带重建胫骨导向器定位,自Gerdy结节向该交界点制备前后方向胫骨骨隧道.将移植物引入两隧道,并用挤压螺钉固定.5例标本手术均获成功,移植物可有效控制外旋稳定性.结论:根据解剖研究确定腘肌腱远近端的定位标志,通过关节镜技术进行显露及定位,在关节镜下完成腘肌腱的重建手术具有可行性.     

Porcine tibia is a poor substitute for human cadaver tibia for evaluating interference screw fixation

BACKGROUND: Animal tissues are commonly used in anterior cruciate ligament graft fixation studies. HYPOTHESIS: Porcine bones and tendons provide good surrogates for human cadaver tissues in the biomechanical evaluation of anterior cruciate ligament reconstruction. STUDY DESIGN: Randomized experimental study. METHOD: Three different tissue models-pure porcine (porcine graft fixed in porcine tibia, group 1), combination (human hamstring graft and porcine tibia, group 2), and pure human (human graft and tibia, group 3)-were compared using both cyclic-loading and subsequent single-cycle load-to-failure tests to assess the effect of graft and bone tissue source (porcine vs human) on the fixation strength of anterior cruciate ligament reconstruction. RESULTS: In the cyclic-loading test, the displacement (slippage) after 1500 cycles was 2.0 mm +/- 0.7 mm, 1.6 mm +/- 0.4 mm, and 4.4 mm +/- 1.9 mm for groups 1, 2, and 3, respectively (P <.001 between 1 and 2 vs 3). In the subsequent single-cycle load-to-failure test, the corresponding average yield loads were 668 N +/- 157 N, 962 N +/- 238 N, and 448 N +/- 98 N, all differences being statistically significant. CONCLUSIONS: In comparison to young human cadaver tibia, porcine tibia underestimate graft slippage and overestimate the failure load of the soft tissue graft in anterior cruciate ligament reconstruction. CLINICAL RELEVANCE: Porcine tibia does not provide a reasonable surrogate for human cadaver tibia for evaluating ACL reconstructions.     

Effect of screw length on bioabsorbable interference screw fixation in a tibial bone tunnel

Initial tibial fixation strength is the weak link after anterior cruciate ligament reconstruction with a quadrupled hamstring tendon graft fixed with bioabsorbable interference screws. The purpose of this study was to determine the biomechanical differences between 28-mm and tapered 35-mm interference screws for tibial fixation of a soft tissue graft in 16 young cadaveric tibias. Failure mode, displacement before failure, and ultimate failure load were tested with a testing machine aligned with the tibial tunnel to simulate a worst-case scenario. The mode of failure was graft slippage past the screw in all but one of the specimens. The mean maximum load at failure of the 28-mm screw was 594.9 +/- 141.0 N, with mean displacement at failure of 10.97 +/- 2.20 mm. The mean maximum load at failure of the 35-mm screw was 824.9 +/- 124.3 N, with a mean displacement to failure of 14.38 +/- 2.15 mm. The 38% difference in mean maximal load at failure was significant. Important variables in hamstring tendon graft fixation within a bone tunnel include bone mineral density, dilatation, gap size, screw placement, and screw width and length. Attention to these variables will help to provide secure graft fixation during biologic incorporation throughout the rehabilitation period.     

Foam-reinforced elderly human tibia approximates young human tibia better than porcine tibia: a study of the structural properties of three soft tissue fixation devices

BACKGROUND: Because there is an insufficient supply of young human knees, an alternative is needed for evaluating anterior cruciate ligament reconstructions. The authors determined whether an elderly human tibia reinforced with foam is a better substitute for a young human tibia than a porcine tibia in this study of the tibialfixation of a soft tissue anterior cruciate ligament graft using 3 devices. HYPOTHESIS: A foam-reinforced elderly human tibia more closely approximates the performance of a young human tibia than porcine tibia. STUDY DESIGN: Biomechanical study. METHODS: Failure mode, stiffness, yield, and slippage were determined for a double-looped tendon graft fixed with either an interference screw, WasherLoc, or tandem washers in young human tibiae, foam-reinforced tibiae from elderly humans, and porcine tibiae. RESULTS: The stiffness and yield of interference screw and WasherLoc fixation in foam-reinforced tibiae more closely approximate those in young human tibiae than in porcine tibiae. Slippage of all combinations of tibiae and fixation devices was similar CONCLUSIONS: A foam-reinforced human tibia more closely approximates the performance of a young human tibia than that of porcine tibia in this study. CLINICAL RELEVANCE: Fixation devices should be tested in foam-reinforced tibiae from elderly humans rather than tibiae from large farm animals when the supply of young human knees is insufficient.     

Compaction drilling does not increase the initial fixation strength of the hamstring tendon graft in anterior cruciate ligament reconstruction in a cadaver model

BACKGROUND: Compaction of the bone tunnel walls has been proposed to increase the fixation strength of soft tissue grafts fixed with an interference screw in anterior cruciate ligament reconstructions. HYPOTHESIS: Compaction drilling does not increase the initial fixation strength of the hamstring tendon graft in comparison with conventional extraction drilling. STUDY DESIGN: Randomized experimental study. METHODS: Initial fixation strength of quadrupled hamstring tendon grafts fixed with bioabsorbable interference screws was assessed in 22 pairs of human cadaveric tibiae. Bone tunnels were drilled with either a compaction drill or a conventional extraction drill. Specimens underwent a cyclic-loading test and the surviving specimens were then loaded to failure in a single-cycle load-to-failure test. Trabecular bone mineral density at the site corresponding to the actual site of the tibial bone tunnel was determined by using peripheral quantitative computed tomography. RESULTS: During the cyclic-loading test, no significant stiffness or displacement differences were observed between the two drilling techniques. Three specimens failed in the compaction-drilling group, whereas there were no failures in the extraction-drilling group. In the subsequent single-cycle load-to-failure test, no significant differences between the two drilling techniques were found with regard to displacement at yield load, stiffness, or mode of failure. There was no significant difference in trabecular bone mineral density between the two groups. CONCLUSIONS: Compaction drilling does not increase the initial fixation strength of the hamstring tendon graft compared with conventional extraction drilling.     

Tibial bone bridge and bone block fixation in double-bundle anterior cruciate ligament reconstruction without hardware: a technical note

Current techniques for tibial graft fixation in four tunnels double bundle (DB) anterior cruciate ligament (ACL) reconstruction are by means of two interference screws or by extracortical fixation with a variety of different implants. We introduce a new alternative tibial graft fixation technique for four tunnels DB ACL reconstruction without hardware. About 3.5 to 5.5 cm bone cylinder with a diameter of 7 mm is harvested from the anteromedial (and posterolateral) tibial bone tunnel (s) with a core reamer. The anteromedial (AM) and posterolateral (PL) hamstring tendon grafts (or alternatively tendon allografts) are looped over an extracortical femoral fixation device and cut in length according to the total femorotibial bone tunnel length. The distal 3 cm of each, the AM- and PL bundle graft are armed with two strong No. 2 nonresorbable sutures and the four suture ends of each graft are tied to each other over the 2 cm wide cortical bone bridge between the tibial AM and PL bone tunnel. In addition the AM- and/or PL bone block which was harvested at the beginning of the procedure is re-impacted into the two tibial bone tunnels. A dorsal splint is used for the first two postoperative weeks and physiotherapy is started the second postoperative day. The technique is applicable for four tunnels DB ACL reconstruction in patients with good tibial bone quality. The strong fixation technique preserves important tibial bone stock and avoids the use of tibial hardware which knows disadvantages. It does increase tendon to bone contact and tendon-to-bone healing and does reduce implant costs to those of a single bundle (SB) ACL reconstruction. Revision surgery may be facilitated significantly but the technique should not be used when bony defects are present. In case of insufficient bone bridge fixation or bone blocks hardware fixation can be applied as usual. Not supported by outside funding or grant(s): No benefits in any form have been received, or will be received, from a commercial party related directly or indirectly to the subject of this article. The study complies with the current laws of the country, in which it was performed.     

Close-looped graft suturing improves mechanical properties of interference screw fixation in ACL reconstruction

Purpose

In anterior cruciate ligament reconstruction with looped soft-tissue grafts, an interference screw is frequently used for tibial fixation. This study compared three alternatives thought to improve the initial mechanical properties of direct bioabsorbable interference screw fixation: suturing the graft to close the loop, adding a supplementary staple, or increasing the oversize of the screw diameter relative to the bone tunnel from 1 to 2 mm.

Methods

Twenty-eight porcine tibiae and porcine flexor digitorum profundus tendons were randomized into four testing groups: a base fixation using 10-mm-diameter screw with open-looped graft, base fixation supplemented by an extracortical staple, base fixation but closing the looped graft by suturing its ends, and base fixation but using an 11-mm screw. Graft and bone tunnel diameters were 9 mm in all specimens. Constructs were subjected to cyclic tensile load and finally pulled to failure to determine their structural properties.

Results

The main mode of failure in all groups was pull-out of tendon strands after slippage past the screw. The sutured graft group displayed significantly lower residual displacement (mean value reduction: 47–67 %) and higher yield load (mean value increase: 38–54 %) than any alternative tested. No other statistical differences were found.

Conclusions

Suturing a soft-tissue graft to form a closed loop enhanced the initial mechanical properties of tibial fixation with a bioabsorbable interference screw in anterior cruciate ligament reconstructions using a porcine model, and thus, this may be an efficient means to help in reducing post-operative laxity and early clinical failure. No mechanical improvement was observed for an open-looped tendon graft by adding an extracortical staple to supplement the screw fixation or by increasing the oversize of the screw to tunnel diameter from 1 to 2 mm.     

Pullout strength of tibial graft fixation in anterior cruciate ligament replacement with a patellar tendon graft: interference screw versus staple fixation in human knees

The endoscopic single incision technique for anterior cruciate ligament (ACL) reconstruction with a femoral half-tunnel may lead to a graft/tunnel mismatch and subsequent protrusion of the block from the tibial tunnel. The typical tibial fixation with an interference screw is not possible in these cases. Fixation with staples in a bony groove inferior to the tunnel outlet can be used as an alternative technique. Current literature does not provide biomechanical data of either fixation technique in a human model. This study was performed to evaluate the primary biomechanical parameters of this technique compared with a standard interference screw fixation of the block. Fifty-five fresh-frozen relatively young (mean age 44 years) human cadaver knee joints were used. Grafts were harvested from the patellar tendon midportion with bone blocks of 25 mm length and 9 mm width. A 10-mm tibial tunnel was drilled from the anteromedial cortex to the center of the tibial insertion of the ACL. Three different sizes of interference screws (7 × 30, 9 × 20, 9 × 30 mm) were chosen as a standard control procedure (n = 40). For tibial bone-block fixation the graft was placed through the tunnel, and the screw was then inserted on the cancellous or the cortical surface, respectively. Fifteen knees were treated by staple fixation. A groove was created inferior to the tunnel outlet with a chisel. The bone block was fixed in this groove with two barbed stainless steel staples. Tensile testing in both groups was carried out under an axial load parallel to the tibial tunnel in a Zwick testing machine with a velocity of 1 mm/s. Dislocation of the graft and stiffness were calculated at 175 N load. Maximum load to failure using interference screws varied between 506 and 758 N. Load to failure using staples was 588 N. Dislocation of the graft ranged between 3.8 and 4.7 mm for interference screw fixation and was 4.7 mm for staples. Stiffness calculated at 175 N load was significantly higher in staple fixation. With either fixation technique, the recorded failure loads were sufficient to withstand the graft loads which are to be expected during the rehabilitation period. Staple fixation of the bone block outside of the tunnel resulted in a fixation strength comparable to interference screw fixation. Received: 2 September 1996 Accepted: 30 January 1997     

Femoral fixation of hamstring grafts in posterior cruciate ligament reconstruction: biomechanical evaluation of different fixation techniques: is there an acute angle effect?

BACKGROUND: The literature provides little biomechanical data about femoral fixation of hamstring grafts in posterior cruciate ligament reconstruction. HYPOTHESIS: A hybrid fixation technique with use of an undersized screw has sufficient strength to provide secure fixation of posterior cruciate ligament grafts. Additional aperture fixation with a biodegradable interference screw can prevent graft damage that might be caused by an acute angle on the edge of the femoral tunnel. STUDY DESIGN: Controlled laboratory study. METHODS: In part 1, extracortical fixation of posterior cruciate ligament reconstructions with quadrupled porcine flexor digitorum grafts to simulate human hamstring grafts was compared with hybrid fixation methods using 6-, 7-, and 8-mm screws. Groups were tested in cycling loading with the load applied in line with the bone tunnel. In part 2, extracortical fixation was compared with hybrid fixation using a 1-mm undersized screw anterior and posterior to the graft. Structural properties and graft abrasion were evaluated after cyclic loading with the load applied at 90 degrees to the tunnel. In each group, 8 porcine knees were tested. RESULTS: In part 1, stiffness, maximum load, and yield load were significantly higher for hybrid fixation than for extracortical fixation. Hybrid fixation with an 8-mm screw resulted in higher yield load than with a 7-mm screw. In part 2, graft laceration was more pronounced in specimens with extracortical fixation than with hybrid fixation. Posterior screw placement was superior to the anterior position. CONCLUSION: For all parameters, hybrid fixation with an interference screw provided superior structural results. No relevant disadvantages of undersized screws could be found. Graft damage due to abrasion at the edge of the femoral bone tunnel was reduced by use of an interference screw. The posterior screw placement seems favorable. CLINICAL RELEVANCE: Hybrid fixation of hamstring grafts in posterior cruciate ligament reconstruction is superior to extracortical fixation alone with no relevant disadvantages of undersized screws. The results raise the suspicion of an acute angle effect of the femoral bone tunnel.     

前交叉韧带重建术中经胫骨的股骨隧道足迹定位方法改进及术后骨道评估

 目的 探讨前交叉韧带重建术中经胫骨的股骨隧道足迹定位方法的改进及术后骨道位置评估。 方法 分析2007 -06至2010-01于武警总医院行自体半腱肌腱和股薄肌腱单束重建前交叉韧带手术患者196例,应用改进的方法进行关节镜下经胫骨的股骨隧道足迹定位,并应用国际膝关节文献委员会（international knee documentation commitee, IKDC）评分及术后MRI行骨道位置评估的资料。 结果 经随访10～36个月,患者的前抽屉试验及Lachman试验均为阴性,IKDC评分情况均较术前差异有统计学意义( P <0.05) ,采用矢状位上关节线与移植肌腱的夹角(the angle between the joint line and the graft on the sagittal view,JGS)和冠状位上关节线与移植肌腱的夹角(the angle between the joint line and the graft  on the coronal image,JGC) ,对术后6个月及正常侧膝关节MRI行骨道位置评估,重建的前交叉韧带的位置与正常对照组的位置差异无统计学意义（ P >0.05）。 结论 单束重建前交叉韧带时,改进的经胫骨的股骨隧道的足迹定位方法是理想的股骨隧道定位方法,患者关节稳定性与功能均得到显著改善;采用JGS和JGC对骨道位置进行评估可较客观、准确地反映股骨隧道定位情况,骨隧道位置与临床效果相关。     

Effects of interference fit screw length on tibial tunnel fixation for anterior cruciate ligament reconstruction

Graft-tunnel mismatch during arthroscopically assisted anterior cruciate ligament reconstruction using the central-third patellar tendon results in less than 20 mm of bone plug remaining in the tibial tunnel. We decided to evaluate the strength of bone plug fixation using interference fit screws that were less than 20 mm in length. Biomechanical testing was performed on 48 porcine hindquarters using 9-mm diameter interference fit screws that measured 12.5, 15, and 20 mm in length. No significant difference was noted between the different-length screws for insertion torque, divergence, stiffness, displacement, or load to failure. We believe, therefore, that comparable graft fixation can be achieved in the tibial tunnel using 9-mm diameter interference fit screws that are less than 20 mm long, and that these shorter screws may be useful in cases of graft-tunnel mismatch.     

A biomechanical evaluation of transcondylar femoral fixation of anterior cruciate ligament grafts

BACKGROUND: Interference screw fixation of the graft in anterior cruciate ligament reconstruction is considered the gold standard, but limited clinical experience suggests that transcondylar fixation is equally effective. PURPOSE: To compare transcondylar and interference screw fixation. STUDY DESIGN: Ex vivo biomechanical study. METHODS: Twenty pairs of unembalmed knees underwent anterior cruciate ligament reconstruction with patellar tendon autografts. In 1 knee of each pair, the bone plug was stabilized in the femoral tunnel with standard interference screws; in the other knee, transcondylar screws were used. Testing to failure occurred immediately or after 1000 cycles of sinusoidal loading (30 to 150 N) (20 paired reconstructions each). Fixation stiffness, strength, graft creep, displacement amplitude, and change in amplitude were measured and compared (repeated measures anaylsis of variance with Tukey test; P <.05). RESULTS: There was no significant difference in acute strength, maximum load within 3 mm, or stiffness between transcondylar fixation (410 +/- 164 N, 183 +/- 93 N, and 49.6 +/- 28 N/mm, respectively) and interference fixation (497 +/- 216 N, 206 +/- 115 N, and 61 +/- 37.8 N/mm, respectively). Similarly, there was no significant difference in cyclic strength, maximum load within 3 mm, or stiffness between transcondylar fixation (496 +/- 214 N, 357 +/- 82.9 N, and 110 +/- 27.4 N/mm, respectively) and interference fixation (552 +/- 233 N, 357 +/- 76.2 N, and 112 +/- 26.8 N/mm, respectively). Predominant modes of failure were bone plug pullout (transcondylar fixation) and tendon failure or bone plug fracture (interference fixation). CONCLUSIONS: Transcondylar screw fixation of the patellar tendon autograft into the femoral tunnel performed mechanically as well as interference screw fixation. CLINICAL RELEVANCE: The results suggest that transcondylar and interference screws provide similar fixation for anterior cruciate ligament reconstruction.     

Interactive effects of tunnel dilation on the mechanical properties of hamstring grafts fixed in the tibia with interference screws

The effect of dilation of the tibial tunnel on the strength of hamstring graft fixation using interference screws was evaluated. In all, 28 RCI screws were tested in male human tibia-hamstring constructs with tibial tunnels reamed or dilated to the respective size of the graft diameter. Dilation of the tibial tunnel failed to significantly enhance hamstring fixation. Grafts secured in dilated tunnels displayed an 11% greater resistance to the initiation of graft slippage (174+/-112 N) compared to their undilated controls (156+/-77 N, P=0.63). Dilation of the tibial tunnel increased the failure load by an average of 4%, independent of screw diameter (dilated specimens: 360+/-120 N, controls: 345+/-88 N, P=0.74). Biomechanical research on the effect of tibial tunnel dilation in hamstring fixation has not provided satisfactory evidence as to the benefits of this additional surgical step during anterior cruciate ligament (ACL) reconstruction.