Tibial fixation comparison of semitendinosus-bone composite allografts fixed with bioabsorbable screws and bone-patella tendon-bone grafts fixed with titanium screws

Tibial fixation remains the weak link of ACL reconstruction over the first 8–12 weeks postoperatively. This study compared the biomechanical properties of tibial fixation for a bone-patellar tendon-bone (BPTB) graft and a novel semitendinosus-bone composite (SBC) allograft with mixed cortical-cancellous bone dowels at each end. Seven paired, fresh frozen cadaveric knees (20–45 years) were stripped of all soft tissue attachments and randomly assigned to receive either the BPTB graft or SBC allograft. Grafts were placed into tibial tunnels via a standard protocol and secured with either a 10 mm×28 mm bioabsorbable (SBC) or titanium (BPTB) screw. Grafts were cycled ten times in a servo hydraulic device from 10–50 N prior to pull to failure testing at a rate of 20 mm/min with the force vector aligned with the tibial tunnel ("worst case scenario"). Wilcoxon Signed Rank Tests were used to evaluate biomechanical differences between graft types (p<0.05). Tibial bone mineral density and interference screw insertion torque were statistically equivalent between graft types. The mode of failure for all constructs was direct screw and graft construct pullout from the tibial tunnel. Significant differences were not observed between graft types for maximum load at failure strength (BPTB=620.8±209 N vs. SBC=601.2±140 N, p=0.74) or stiffness (BPTB=69.8 N/mm±29 N/mm vs SBC=47.1±31.6 N/mm, p=0.24). The SBC allograft yielded significantly more displacement prior to failure than the BPTB graft (15.1±4.9 mm vs 9.2±1.3 mm, p=0.04). Increased construct displacement appeared to be due to fixation failure, with some evidence of graft tissue tearing around the sutures: Bioabsorbable screw (10×28 mm) fixation of the SBC allograft produced unacceptable displacement levels during testing. Further study is recommended using a titanium interference screw or a longer bioabsorbable screw for SBC graft fixation under cyclic loading conditions.Arthrex Inc., Naples, FL, USA sponsored this study     

单束重建前交叉韧带骨道位置对临床效果影响的研究

目的:探讨前交叉韧带重建术骨道位置对临床效果的影响。方法:2005年5月至12月于我所行自体腘绳肌腱单束重建前交叉韧带手术患者72例,采用其侧位X线平片测量骨道位置,结合膝关节功能评分、KT-2000测试结果进行分析。结果:患者的IKDC、Lysholm和Tegner评分以及KT-2000在134N下屈膝30度和90度位膝关节前后位移情况均较术前显著改善(P<0.01)。股骨骨道位于Blumensaat’s线的后23.87%,胫骨骨道位于胫骨平台全长的前38.25%。膝关节伸直受限患者胫骨骨道位于胫骨平台前34.19%,伸直正常患者胫骨骨道位于胫骨平台的前38.91%,二者相比具有显著性差异(P<0.05〉。KT-2000屈膝30度位膝关节前后位移值大于等于3mm患者的胫骨骨道位于胫骨平台的前44.78%,位移小于3mm患者胫骨骨道位于胫骨平台的37.39%,二者相比具有显著性差异(P<0.01)。结论:单束重建前交叉韧带手术使患者关节稳定性与功能均得到显著改善。X线测量可较客观、准确地反映骨道定位情况,骨道位置与临床效果相关;本次研究显示比较理想的骨道位置在X线侧位片上位于胫骨平台的前34~37%。     

Bone tunnel enlargement following anterior cruciate ligament reconstruction: a randomised comparison of hamstring and patellar tendon grafts with 2-year follow-up

Radiographic tibial and femoral bone tunnel enlargement has been demonstrated following anterior cruciate ligament (ACL) reconstruction. This study investigated whether bone tunnel enlargement differs between four-strand hamstring (HS) and patellar tendon (PT) ACL reconstructions over the course of a 2-year follow-up. Patients undergoing primary ACL reconstruction (n = 65) were randomised to receive either a PT or HS autograft. Femoral fixation in both groups was by means of an Endobutton. On the tibial side the PT grafts were fixed using a metallic interference screw, and the HS tendons by sutures tied to a fixation post. The PT grafts were inserted such that the proximal end of the distal bone block was within 10 mm of the tibial articular surface, resulting in a portion of free patellar tendon in the femoral tunnel immediately proximal to the articular surface. Patients were reviewed after 4 months and 1 and 2 years. Tunnel enlargement was determined by measuring the widths of the femoral and tibial tunnels with a digital caliper in both lateral and anteroposterior radiographs. Because of the presence of the interference screw and the proximity of the bone block to the tibial articular surface, the tibial tunnel could not be reliably measured in the PT group. Measurements were corrected for magnification, and changes in tunnel width were recorded relative to the diameters drilled at surgery. Standard clinical measures were also noted. In 32% of patients in the PT group there was femoral tunnel obliteration from 4 months onwards. For the other patients there was a significantly greater increase in femoral tunnel width in the HS group than in the PT group at each follow-up, but no significant change with time. There was also a marked increase in tibial tunnel width in the HS group at 4 months but not thereafter. There was no relationship between tunnel enlargement and clinical measurements. Although tunnel enlargement is more common and greater with HS grafts, it does not appear to affect the clinical outcome in the first 2 postoperative years. Femoral suspensory fixation does not in itself appear to be the principal cause of femoral tunnel enlargement, at least for PT grafts.     

Tibial tunnel widening after anterior cruciate ligament reconstructions with hamstring tendons using Rigidfix femoral fixation and Intrafix tibial fixation

The purpose of this study was to evaluate tibial tunnel widening prospectively after anterior cruciate ligament (ACL) reconstruction with hamstring tendon grafts using Rigidfix (DePuy Mitek, Raynham, MA) femoral fixation and Intrafix (DePuy Mitek) tibial fixation. Fifty-six consecutive patients who underwent ACL reconstruction with a minimum of 2 years’ postoperative evaluation were reviewed. On the anterior–posterior (AP) and lateral radiographs, the diameter of the tibial tunnel was measured at proximal, middle, and distal positions, and the shape of the tibial tunnels were classified. Tunnel widening was defined as widening of greater than 2 mm. Group I was defined as cases with no tunnel widening, and group II was defined as cases with tunnel widening. Postoperative laxity evaluations were performed using Lachman test, pivot-shift test, and instrumented laxity testing using the KT-1000 arthrometer. On the AP radiographs, the average diameter of the tibial tunnel increased 8.8% at 6 months and 8.5% at 12 months postoperatively compared to the immediate postoperative day. On the lateral radiographs, the average diameter of the tibial tunnel increased 7.2% at 6 months and 8.1% at 12 months year postoperatively compared to the immediate postoperative day. The tunnel shape evaluation revealed predominantly linear type in 53 patients (95%). Group I was 42 patients (75%), and group II was 14 (25%). The average KT-1000 measurement was 1.0 ± 1.8 mm in group I and 2.1 ± 2.8 mm in group II (n.s.). The Lachman and pivot-shift tests showed no significant differences between the two groups. In conclusion, hamstring ACL reconstruction using Rigidfix and Intrafix fixation showed less widening of the tibial tunnels than observed in previously published studies.     

不同固定方法重建前交叉韧带后骨道变化的对比临床观察研究

目的:对比研究胫骨端不同固定方法采用半腱肌腱和股薄肌腱重建前交叉韧带后骨道增宽情况。材料和方法:我所2005年3月到12月的64名患者(65例膝关节)单束前交叉韧带重建患者,采用自体半腱肌腱和股薄肌腱为移植物,根据胫骨端固定方法不同分为门形钉组(36例),联合固定组(可吸收挤压螺钉+门形钉,14例),Intrafix组(Intrafix固定螺钉,15例),术后平均15.8个月(11~20个月)随访时拍X线片进行骨道测量,股骨端测量骨道关节入口处直径,胫骨端分别测量胫骨骨道关节线水平(T1)、骨道中点部位(T2),及骨道胫骨皮质出口处(T3),取胫骨骨道最宽处作为衡量骨道增宽的标准,所得数据进行统计分析。结果:门形钉组、联合固定组和Intrafix组三组股骨骨道增宽发生率,正位分别为97.22%、92.86%、93.33%,侧位为94.44%、85.71%、93.33%,胫骨骨道增宽发生率,正位为91.67%、92.86%、93.33%,侧位为91.67%、92.86%、100%。各组股骨、胫骨骨道增宽发生率相比无明显差别。门形钉组、联合固定组和Intrafix组三组骨道增宽程度,股骨正位分别为55.71%、47.60%、56.40,侧位为55.52%、53.00%、51.30%;胫骨正位为47.14%、52.60%、66.20%,侧位为51.85%、63.50%、72.50%。胫骨骨道形状以O型(正位片)及V型(侧位片)最常见。Intrafix组术后随访时胫骨骨道关节入口处骨道扩大不明显,和术后即刻相比此处直径正位片上无明显差别,侧位片上仅1例骨道扩大超过2mm。结论:术后随访时门形钉组、联合固定组和Intrafix组三组骨道增宽发生率无明显差别。Intrafix组胫骨骨道关节入口处增宽不明显。     

Optimal screw diameter for interference fixation in a bone tunnel: a porcine model

The study investigates the optimal interference screw dimensions required to secure a tendon graft in a bone tunnel. A standard 8 mm pig flexor-tendon graft was inserted into a standard open-ended 8 mm bone tunnel of a porcine distal femur and secured using either 7 mm, 8 mm or 9 mm diameter metal interference screws (Arthrex Inc, Naples, FL). The construct was tested to failure using a Shimadzu ASG 10KN Universal Material Testing Machine (Shimadzu, Tokyo, Japan). Load and mode of construct failure were recorded for 37 individual constructs. There was no significant difference in the load at failure between the 7 mm screw (192 N; range 151–232) and 8 mm screw (181 N; range 150–212) (p>0.05). There was a significant difference between the 7 mm screw and the 9 mm screw (109 N; range 67–151) (p=0.006) and between the 8 mm screw and the 9 mm screw (p=0.015). When using a 9 mm screw, 100% of the constructs failed by cut out of the graft at the tunnel opening. The 7 mm constructs failed by slippage of the tendon from the bone tunnel in 83% of cases, with only 17% failing by cut out at the tunnel opening. The 8 mm constructs demonstrated a mixture of failure modes, with slippage occurring in 58% of cases, cut out in 38% and failure of the graft substance in one case (4%). In this model, screw diameters equal to or 1 mm less than the tunnel/tendon diameter provides better fixation than using a screw 1 mm larger. The mode of failure differs for each of these screws.     

Mechanical evaluation of a soft tissue interference screw with a small diameter: significance of graft/bone tunnel cross-sectional area ratio

The purpose of this study is to evaluate the mechanical properties of a graft fixation using a small diameter soft tissue interference screw and analyze the factors affecting the fixation strength. Forty porcine knees were used. A bone tunnel, either 4.5 mm (n=40) or 5.0 mm (n=40) in diameter, was created in the bone block obtained from the proximal tibia or the distal femur. A patella–patellar tendon specimen with varied width was harvested, and the distal end of the patellar tendon was fixed within the bone tunnel using a small diameter soft tissue interference screw (4×15 mm). Then, the patella–patellar tendon-bone block complex was loaded until failure occurred and the maximum load was measured. As potential influential factors on the fixation strength, the insertion torque, bone mineral density of the bone block, and graft/tunnel cross-sectional area ratio (GTR) of each specimen were calculated. A significant correlation between the maximum failure load and the insertion torque was demonstrated. The quadratic regression analysis showed a statistically significant correlation between the failure load and the GTR. Optimal GTR for achieving high fixation strength was approximately 80%. When used in appropriate conditions, the mean failure load was 177 N for the 4.5 mm screw and 180 N for the 5 mm screw. The use of a small diameter interference screw for the fixation of a tendon graft to a bone is clinically feasible. Our research showed that the selection of appropriate fitting conditions is an important factor for optimizing the properties of the fixation.     

Tibial attachment area of the anterior cruciate ligament in the extended knee position

Knowledge of the anatomy of the anterior cruciate ligament (ACL), including its course and orientation in relation to the roof of the intercondylar fossa, is a prerequisite for successful intra-articular ACL reconstruction. To attain precision placement of the tibial attachment site and to avoid graft/roof conflict in the extended knee position, we assessed the anteroposterior tibial insertion of the ACL in the midsagittal plane of the extended knee. We measured the anterior-posterior (AP) limits and the center of the tibial attachment area of the ACL from the anterior tibial margin. The inclination angle of the intercondylar fossa roof was measured with respect to the shaft axis of the femur. The tibial attachment area of the ACL was determined in ten cadaveric knees. Using the cryoplaning technique, we determined the tibital attachment of the ACL in five knees. Using contrast magnetic resonance arthrography (MRA), we measured the tibial insertion of the ACL in 35 patients (23 male and 12 female) with intact ACLs. The total AP midsagittal diameter of the tibia averaged 51.0±5.8 mm in the cadaveric knees, 49 mm on cryosections, and 53.7 mm in men and 49.0 mm in women with MRA. The average anterior limit of the ACL, measured from the anterior tibial margin, was 14±4.2 mm in the cadaveric knees, 12.1 mm at cryosectional anatomy, and 15.2 mm in men and 13.4 mm in women with MRA. The center of the tibial attachment area was located at 21±2.6 mm in cadaveric knees, at 21.2 mm on cryosections, and at 23.7 mm in men and at 21.4 mm in women with MRA. The posterior limit of the tibial attachment area of the ACL was 29.0±4.1 mm in cadaveric knees, 30.6 mm on cryosections, 32.1 mm in male and 29.4 mm female patients with MRA. The roof inclination angle measured on average 39.8° on cryosections and 36.8° in men and 35.2° in women on MRA. Based on these morphometric data and to avoid notch/graft conflict in knee extension, we advocate placing the center of the tibial tunnel at 44% of the tibia diameter posterior and parallel to the individual intercondylar roof inclination angle.     

The influence of tibial fixation on tunnel enlargement after hamstring tendon anterior cruciate ligament reconstruction

The retrospective study was designed to evaluate tibial-tunnel enlargement after anterior cruciate ligament reconstruction with hamstring autograft. Forty-three patients (43 knees) were enrolled, among whom a spiked washer was used for the tibial side fixation in 20 knees (Group SW) and the WasherLoc was used in 23 knees (Group WL). After an average 16 (range 12–32) months follow-up, the distance between the sclerotic margins of the tibial tunnel was measured at the joint level, and 1 and 2 cm distal to the joint level on the lateral view radiographs, from which the tibial-tunnel enlargement at each point (E1, E2, and E3 respectively) was determined. Anterior knee laxity was also measured using a KT-1000 or KT-2000 arthrometer at follow-up. E1, E2, and E3 were 2.3±1.3 mm (mean±standard deviation), 1.8±0.8 mm, and 1.5±0.8 mm respectively in Group SW, and 2.6±1.0 mm, 2.6±1.2 mm, and 2.9±1.6 mm in Group WL. Group WL had a larger mean value than Group SW at each level of measurement, with a statistically significant difference in E2 and E3. Fifty percent of the tunnels were the cone type in Group SW, whereas reversed cone-type tunnels were the most common (39%) in Group WL. The side-to-side difference in anterior knee laxity was –0.6±5.2 mm in Group SW and 1.8±9.0 mm in Group WL, which was significantly different between the groups. No statistical relationship was found between tunnel enlargement and side-to-side difference in anterior knee laxity in Group SW, whereas there was a slight negative correlation between E1 or E2 and anterior knee laxity in Group WL. It is possible that there is greater tension applied to the graft when the WasherLoc is used, which creates larger compressive forces on the posterior wall of the tibial tunnel by the graft. This was probably the reason for the greater tunnel enlargement and the high incidence of the reversed cone-type tunnel in Group WL.     

Tibial tunnel area changes following arthroscopic anterior cruciate ligament reconstructions with autogenous patellar tendon graft

We investigated radiographic changes in tibial tunnel area after ACL reconstructions with autogenous patellar tendon grafts on anteroposterior and lateral radiographs over 3 years. Fifty patients followed up for at least 1 year were included in the study. Radiographs were taken on the day of surgery and 3, 6, 9, 12, 24, and 36 months postoperatively. Tibial tunnels on both radiographs were divided into proximal, middle, and distal one-third. The area of each one-third and the greatest diameter of the tibial tunnel on both radiographs was measured using an image-processing software. According to the tunnel area changes, the shape of tibial tunnel was classified into one of four shapes; cylinder, mallet, reverse bottle, and reverse triangle. The correlations between area, diameter and shape of the tunnel, and clinical variables including arthrometer measurement and clinical score were determined. The areas of each one-third of the tibial tunnels on lateral radiographs was always greater than that on anteroposterior radiographs, although the diameters on the two radiographs did not differ significantly. The area of proximal one-third largest and that of distal one-third smallest on both radiographs at any time point. The enlargement and reduction occurred within 3 months and tended to continue for 9 months. Thereafter the tunnel change stabilized on both radiographs. The most common shape of the enlarged tunnels was cylindrical on anteroposterior radiographs reverse triangle on lateral radiographs. No negative effects of enlarged area, diameter, or tunnel shape on clinical results were found in our study.     

Cyclic pull-out strength of hamstring tendon graft fixation with soft tissue interference screws. Influence of screw length

Blunt-threaded interference screws used for fixation of hamstring tendons in anterior cruciate ligament reconstructions provide aperture fixation and may provide a biomechanically more stable graft than a graft fixed further from the articular surface. It is unknown if soft tissue fixation strength using interference screws is affected by screw length. We compared the cyclic and time-zero pull-out forces of 7 x 25 mm and 7 x 40 mm blunt-threaded metal interference screws for hamstring graft tibial fixation in eight paired human cadaveric specimens. A four-stranded autologous hamstring tendon graft was secured by a blunt-threaded interference screw into a proximal tibial tunnel with a diameter corresponding to the graft width. Eight grafts were secured with a 25-mm length screw while the other eight paired grafts were secured with a 40-mm length screw. During cyclic testing, slippage of the graft occurred as the force of pull became greater with each cycle until the graft-screw complex ultimately failed. All grafts failed at the fixation site, with the tendon being pulled past the screw. There were no measurable differences in the mean cyclic failure strength, pull-out strength, or stiffness between the two sizes of screws. Although use of the longer screw would make removal technically easier should revision surgery be necessary, it did not provide stronger fixation strength than the shorter, standard screw as had been postulated.     

The influence of screw geometry on hamstring tendon interference fit fixation

We used a standardized model of calf tibial bone to investigate the influence of screw diameter and length on interference fit fixation of a three-stranded semitendinosus tendon graft for anterior cruciate ligament reconstruction. Biodegradable poly-(L-lactide) interference screws with a diameter of 7, 8, and 9 mm and a length of 23 and 28 mm were used. We examined results in three groups of 10 specimens each: group 1, screw diameter equaled graft diameter and screw length was 23 mm; group 2, screw diameter equaled graft diameter plus 1 mm and screw length was 23 mm; group 3, screw diameter equaled graft diameter and screw length was 28 mm. The mean pull-out forces in groups 1, 2, and 3 were 367.2+/-78 N, 479.1+/-111.1 N, and 537.4+/-139.1 N, respectively. The force data from groups 2 and 3 were significantly higher than those from group 1. These results indicate that screw geometry has a significant influence on hamstring tendon interference fit fixation. Increasing screw length improves fixation strength more than oversizing the screw diameter. This is important, especially for increasing tibial fixation strength because the tibial graft fixation site has been considered to be the weak link of such a reconstruction.     

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     

Posterior cruciate ligament (PCL) reconstruction-an in vitro study of isometry

Isometric positioning of the posterior cruciate ligament (PCL) graft is important for successful reconstruction of the PCL-deficient knee. This study documents the relationship between graft placement and changes in intra-articular graft length during a passive range of motion of the knee. In eight cadaveric knees the PCL was identified and cut. The specimens were mounted in a stabilising rig. PCL reconstruction was performed using a 9-mm-thick synthetic cord passed through tunnels 10 mm in diameter. Three different femoral graft placement sites were evaluated: (1) in four specimens the tunnel was located around the femoral isometric point, (2) in two specimens the tunnel was positioned over the guide wire 5 mm anterior to the femoral isometric point, (3) in two specimens the tunnel was positioned over the guide wire 5 mm posterior to the isometric femoral point. In all knees only one tibial tunnel was created around the isometric tibial point. The location of the isometric points is described in part I of this study. The proximal end of the cord was fixed to the lateral aspect of the femur. Distally, the cord was attached to a measuring unit. The knees were flexed from 0° to 110°, and the changes in the graft distance between the femoral attachment sites were measured in 10° steps. Over the entire range of motion measured, the femoral tunnels positioned around the isometric point produced femorotibial distance changes of within 2 mm. The anteriorly and posteriorly placed tunnels produced considerable changes in femorotibial distance with knee flexion, e.g. about 8 mm at 110° of flexion.     

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.     

Graft-tunnel mismatch in endoscopic anterior cruciate ligament reconstruction Intraoperative and cadaver measurement of the intra-articular graft length and the length of the patellar tendon

The results of a study conducted on 50 knees endoscopically reconstructed for an anterior cruciate ligament (ACL) lesion with a free bone-patellar tendon-bone graft and 9 cadaver knees are reported. The mean lengths of the patellar tendon (45.48 ± 4.71 mm) and intra-articular ACL graft (20.44 ± 1.98 mm) were measured in the operated knees. The mean length of the tibial bone tunnel (51.62 ± 2.60 mm) was also measured with a tibial guide at 55°. No statistically significant correlation was found between these three measurements. The length of the patellar tendon was weakly correlated with body height. Measurement of the tibial tunnel on the cadaver knees with increasing degrees of inclination revealed a mean length increase of 0.68 mm per degree (confidence limits: 0.49–0.86). Comparison between the tunnel lengths obtained with the guide and those measured with a Kirschner wire showed a mean difference of 2.3 mm. It is thus desirable to make the tunnel about 53 mm long to ensure excellent fixation of a 28 mm bone block with a 25 mm interference screw. Correct measurement of the anatomical structures involved is in any event an essential requirement for proper execution of the surgical technique. Received: 26 June 1997 Accepted: 12 November 1997     

A prospective evaluation of tunnel enlargement in anterior cruciate ligament reconstruction with hamstrings: extracortical versus anatomical fixation

Changes in the femoral and tibial bone tunnel were studied prospectively after arthroscopic ACL reconstruction with quadruple hamstring autograft. To determine whether tunnel enlargement can be decreased by fixing the graft close to the joint line having a stiffer fixation construct we compared "anatomical" (one absorbable interference screw femorally, and bicortical fixation with two absorbable interference screws tibially) and extracortical fixation techniques (Endobutton femorally, and two no. 6 Ethibond sutures over a suture washer tibially). Over a 2-year period we evaluated 60 patients clinically (IKDC scale, Cincinnati Knee Score, KT-1000) and radiographically (confirmed by MRI). The operated knee was radiographed immediately postoperatively and 6 and 24 months postoperatively. The femoral and tibial bone tunnel diameter was measured on anteroposterior and lateral images, and the tunnel area was calculated and compared to the initial area calculated from the perioperative drill size. In the "anatomical" group the immediately postoperative bone tunnel area was 75% larger than the initial tunnel area, after 6 months it was increased another 31%, and between 6 and 24 months it remained basically unchanged. In the "extracortical" group there was no significant enlargement immediately postoperatively, but after 6 months it was 65% larger than the initial area of drill and graft size, and between 6 and 24 months it decreased to 47%. There was no correlation between the amount of tunnel enlargement and clinical scores or KT-1000 measurement. Arthroscopic ACL reconstruction with quadruple hamstring autograft is associated with bone tunnel enlargement. Using a purely extracortical fixation technique thus significantly increased the tibial and femoral tunnel area during the first 6 postoperative months, while it decreased slightly thereafter. The insertion of large interference screws apparently not only compresses the graft in the bone tunnel but also significantly enlarges the bone tunnel itself. The immediate enlargement at the time of the operation is followed by a reduced further enlargement at 6 months and then stabilization. Tunnel widening did not influence clinical outcome over a 2-year period.     

Pretibial ganglion-like cyst formation after anterior cruciate ligament reconstruction: a consequence of the incomplete bony integration of the graft?

We report a case of subcutaneous pretibial ganglion, with direct communication to the tibial tunnel after an autologous reconstruction of the anterior cruciate ligament with hamstring tendons. The tibial graft fixation was with a 9 mm poly-L-lactide interference screw 5 years earlier. The screw had undergone complete resorption at the time the cyst occurred. No joint inflammatory reaction or graft insufficiency was detected. The patient underwent cyst excision and curettage of the tibial tunnel with full recovery. This complication seems to be the consequence of a direct communication between the joint and the pretibial subcutaneous tissue through a fibrous tibial tunnel and would have occurred, as there is no full osteointegration of the graft due to the resorption of the bioabsorbable interference screw.     

Bone tunnel enlargement after anterior cruciate ligament reconstruction using hamstring tendons

We retrospectively reviewed 87 anterior cruciate ligament reconstructions using autogenous hamstring tendons with the Endobutton technique to investigate the relationship between bone tunnel enlargement and clinical outcome and to identify factors that contribute to the enlargement. The clinical outcome was evaluated using the Lysholm score and KT-1000 arthrometer. The location of the femoral tunnel with respect to Blumensaat's line, the tibial tunnel with respect to the tibial plateau, and the angle between the femoral tunnel and Blumensaat's line (femoral tunnel angle) were measured. Bone tunnel enlargement was observed in 32 patients (37%). Enlargement occurred in 22 of the femoral tunnels and 26 of the tibial tunnels. Enlargement of both tunnels occurred in 16 knees. There was no statistical difference in Lysholm scores or KT-1000 arthrometer measurements between the enlarged group and the unenlarged group. The femoral tunnel was placed more anteriorly in the enlarged femoral tunnel group than in the unenlarged femoral tunnel group. The tibial tunnel was placed more anteriorly in the enlarged tibial tunnel group than in the unenlarged tibial tunnel group. The femoral tunnel angle was significantly smaller in the enlarged femoral tunnel group than in the femoral unenlarged group. Gender, patient age, intraoperative isometricity, and graft size were not significant factors. Bone tunnel enlargement was not correlated with the clinical outcome measures. We conclude that the main factor associated with tunnel enlargement are the locations and angles of the tunnels. The windshield-wiper motion of the graft may be enhanced by changing tension in the graft due to tunnel malposition. An acute femoral tunnel angle may increase the mechanical stress on the anterior margin of the femoral tunnel.     

The use of a mono-fluted reamer results in decreased enlargement of the tibial tunnel when using a transtibial ACL reconstruction technique

Purpose

To evaluate whether femoral tunnel preparation using a mono-fluted reamer rather than an acorn reamer would result in less tibial tunnel deformation when using a transtibial technique for anterior cruciate ligament reconstruction.

Methods

Tibial and femoral tunnel preparation was performed in four matched pairs of cadaveric knees. The tibial tunnel was drilled using a standard acorn reamer. The femoral tunnel was prepared using a transtibial technique with a mono-fluted reamer, and then, the same femoral tunnel was re-reamed using an acorn reamer. The anterior–posterior (AP) and medial–lateral (ML) dimensions of the tibial tunnel were recorded after each reamer. We then compared the measurements following the use of each reamer using a paired two-sample t test.

Results

There was a significantly larger degree of tibial tunnel deformation following femoral tunnel preparation with the acorn reamer when compared with the mono-fluted reamer. The initial tibial tunnel measured 10.5 and 10.1 mm in the AP and ML dimensions, respectively. The resultant AP diameter of the tibial tunnel after femoral reaming was 16.7 mm (p < 0.001) for the acorn reamer compared with 11.6 mm (p < 0.001) for the mono-fluted reamer. The ML diameters were 11.3 mm (p = 0.003) versus 10.2 mm (p = 0.07) for the acorn and mono-fluted reamer, respectively.

Conclusion

The use of a mono-fluted reamer for femoral tunnel preparation results in less tibial tunnel deformation during transtibial reaming.