Effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on tension of an anterior cruciate ligament graft: an in vitro study

BACKGROUND: High tension in an anterior cruciate ligament graft adversely affects both the graft and the knee; however, it is unknown why high graft tension in flexion occurs in association with a posterior femoral tunnel. The purpose of the present study was to determine the effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on the tension of an anterior cruciate ligament graft during passive flexion. METHODS: Eight cadaveric knees were tested. The angle of the tibial tunnel was varied to 60 degrees, 70 degrees, and 80 degrees in the coronal plane with use of three interchangeable, low-friction bushings. The femoral tunnel, with a 1-mm-thick posterior wall, was drilled through the tibial tunnel bushing with use of the transtibial technique. After the graft had been tested in all three tibial bushings with one femoral tunnel, the femoral tunnel was filled with bone cement and the tunnel combinations were tested. Lastly, the graft was replaced in the 80 degrees femoral and tibial tunnels, and the tests were repeated with excision of the lateral edge of the posterior cruciate ligament in 2-mm increments. Graft tension, the flexion angle, and anteroposterior laxity were recorded in a six-degrees-of-freedom load-application system that passively moved the knee from 0 degrees to 120 degrees of flexion. RESULTS: The graft tension at 120 degrees of flexion was affected by the angle of the femoral tunnel and by incremental excision of the posterior cruciate ligament. The highest graft tension at 120 degrees of flexion was 169 +/- 9 N, which was detected with the graft in the 80 degrees femoral and 80 degrees tibial tunnels. The lowest graft tension at 120 degrees of flexion was 76 +/- 8 N, which was detected with the graft in the 60 degrees femoral and 60 degrees tibial tunnels. The graft tension of 76 N at 120 degrees of flexion with the graft in the 60 degrees femoral and 60 degrees tibial tunnels was closer to the tension in the intact anterior cruciate ligament. Excision of the lateral edge of the posterior cruciate ligament in 2 and 4-mm increments significantly lowered the graft tension at 120 degrees of flexion without changing the anteroposterior position of the tibia. CONCLUSIONS: Placing the femoral tunnel at 60 degrees in the coronal plane lowers graft tension in flexion. Our results suggest that high graft tension in flexion is caused by impingement of the graft against the posterior cruciate ligament, which results from placing the femoral tunnel medially at the apex of the notch in the coronal plane.     

Reconstructive interventions of the posterior cruciate ligament--experimental studies of isometric aspects. Part II: Studies of the posterior cruciate ligament replacement model]

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 passive range of motion of the knee. In eight cadaveric knees the PCL was identified and cut. The specimens were mounted in a stabilizing rig. PCL reconstruction was performed using a 9-mm-thick synthetic cord that was 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 was described in part I of the 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 degree to 110 degrees, and the changes in the graft distance between the femoral attachment sites were measured in 10 degrees 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 placed tunnels produced considerable increases in femorotibial distance with knee flexion, e.g. about 8 mm at 110 degrees of flexion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of femoral tunnel placement on knee laxity and forces in an anterior cruciate ligament graft.

The purpose of this study was to measure the effects of variation in placement of the femoral tunnel upon knee laxity, graft pretension required to restore normal anterior-posterior (AP) laxity and graft forces following anterior cruciate ligament (ACL) reconstruction. Two variants in tunnel position were studied: (1) AP position along the medial border of the lateral femoral condyle (at a standard 11 o'clock notch orientation) and (2) orientation along the arc of the femoral notch (o'clock position) at a fixed distance of 6-7 mm anterior to the posterior wall. AP laxity and forces in the native ACL were measured in fresh frozen cadaveric knee specimens during passive knee flexion-extension under the following modes of tibial loading: no external tibial force, anterior tibial force, varus-valgus moment, and internal-external tibial torque. One group (15 specimens) was used to determine effects of AP tunnel placement, while a second group (14 specimens) was used to study variations in o'clock position of the femoral tunnel within the femoral notch. A bone-patellar tendon-bone graft was placed into a femoral tunnel centered at a point 6-7 mm anterior to the posterior wall at the 11 o'clock position in the femoral notch. A graft pretension was determined such that AP laxity of the knee at 30 deg of flexion was restored to within 1 mm of normal; this was termed the laxity match pretension. All tests were repeated with a graft in the standard 11 o'clock tunnel, and then with a graft in tunnels placed at other selected positions. Varying placement of the femoral tunnel 1 h clockwise or counterclockwise from the 11 o'clock position did not significantly affect any biomechanical parameter measured in this study, nor did placing the graft 2.5 mm posteriorly within the standard 11 o'clock femoral tunnel. Placing the graft in a tunnel 5.0 mm anterior to the standard 11 o'clock tunnel increased the mean laxity match pretension by 16.8 N (62%) and produced a knee which was on average 1.7 mm more lax than normal at 10 deg of flexion and 4.2 mm less lax at 90 deg. During passive knee flexion-extension testing, mean graft forces with the 5.0 mm anterior tunnel were significantly higher than corresponding means with the standard 11 o'clock tunnel between 40 and 90 deg of flexion for all modes of constant tibial loading. These results indicate that AP positioning of the femoral tunnel at the 11 o'clock position is more critical than o'clock positioning in terms of restoring normal levels of graft force and knee laxity profiles at the time of ACL reconstruction.     

Effect of tibial tunnel dilation on pullout strength of semitendinosus-gracilis graft in anterior cruciate ligament reconstruction

This biomechanical cadaver study evaluated the effect of tibial tunnel dilation on the pullout strength of semitendinosus and gracilis tendon grafts in anterior cruciate ligament reconstruction. Fourteen grafts were harvested, and the anterior cruciate ligament was reconstructed in the tibial and femoral tunnels. All femoral tunnels were reamed to the diameter of the graft. In seven knees, the tibial tunnels were reamed to the diameter of the graft. In the remaining seven knees, the tibial tunnels were reamed 2 mm smaller than the diameter of the graft and then serially dilated to the graft size using cannulated smooth dilators. Mechanical testing to graft failure was conducted. All grafts failed by graft pullout from the tibial tunnel. However, mean peak load was significantly higher for the dilated tibial specimens (616 +/- 263 N) than for the reamed specimens (453 +/- 197 N) (P = .0025).     

前交叉韧带解剖双束重建中股骨隧道建立路径的比较研究

目的前瞻性研究在关节镜下前交叉韧带（ACL）解剖双束重建术中,采用经胫骨隧道与经前内人路定位建立股骨隧道的可行性与准确性。方法在连续30例ACL患者的解剖双束重建术中,首先分别以45°、55°角钻取胫骨隧道,关节内出口分别在ACL胫骨解剖附丽区印记的前内和后外,保留1～2mm间隔骨桥;关节外入口分别位于胫骨结节内侧和内侧副韧带前缘的前方,间隔以两枚Washer不重叠为准,分别用于前内侧束和后外侧束的移植重建。然后分别经两胫骨隧道,将两根球头空心钻的钻杆自胫骨隧道插入关节内,观察两钻头杆能否到达理想的股骨隧道,录像记录并进行统计学分析。结果在本组30例患者中,经胫骨前内侧束隧道插入的钻头杆,在股骨侧的指向全部偏高、偏前,无一例能完全或部分到达股骨侧前内侧或后外侧束隧道口;而经胫骨后外侧束隧道的钻头杆,经屈或伸膝调整角度后,5例（16．7％）可完全到达、8例（26．7％）可部分到达股骨的前内侧束隧道口;有2例（6．7％）可完全到达、6例（20．0％）部分到达股骨的后外侧束隧道口。而经前内入路屈膝120°后,28例（93．3％）定位可达到理想位置。结论在ACL解剖双束移植重建中,经胫骨隧道定位钻取股骨隧道的方法不可靠、准确性差、变异较大、可重复性差;而经前内入路方法可调节性强、准确性好、股骨隧道短、不受胫骨隧道方向、角度和直径的影响、简便易行、重复性好;但应注意要在较大的屈膝角度下定位钻取。     

Radiological landmarks for placement of the tunnels in single-bundle reconstruction of the anterior cruciate ligament

There is little evidence examining the relationship between anatomical landmarks, radiological placement of the tunnels and long-term clinical outcomes following anterior cruciate ligament (ACL) reconstruction. The aim of this study was to investigate the reproducibility of intra-operative landmarks for placement of the tunnels in single-bundle reconstruction of the ACL using four-strand hamstring tendon autografts. Isolated reconstruction of the ACL was performed in 200 patients, who were followed prospectively for seven years with use of the International Knee Documentation Committee forms and radiographs. Taking 0% as the anterior and 100% as the posterior extent, the femoral tunnel was a mean of 86% (sd 5) along Blumensaat's line and the tibial tunnel was 48% (sd 5) along the tibial plateau. Taking 0% as the medial and 100% as the lateral extent, the tibial tunnel was 46% (sd 3) across the tibial plateau and the mean inclination of the graft in the coronal plane was 19 degrees (sd 5.5). The use of intra-operative landmarks resulted in reproducible placement of the tunnels and an excellent clinical outcome seven years after operation. Vertical inclination was associated with increased rotational instability and degenerative radiological changes, while rupture of the graft was associated with posterior placement of the tibial tunnel. If the osseous tunnels are correctly placed, single-bundle reconstruction of the ACL adequately controls both anteroposterior and rotational instability.     

Technical Note: Double tibial tunnel using quadriceps tendon in anterior cruciate ligament reconstruction

Summary: To avoid complications related to the use of patellar tendon and hamstring (semitendinosus and gracilis) tendon and to create a more anatomic reconstruction, we present a new technique based on the use of quadriceps tendon placed in a single half femoral tunnel and double tibial tunnels. The graft, harvested by a central longitudinal incision, possesses the following characteristics: (1) a bone plug 20 mm long and 10 mm in diameter; (2) a tendon component 7 to 8 cm long, 10 mm wide, and 8 mm thick; and (3) division of the tendon longitudinally into 2 bundles while maintaining the patellar insertion. Every bundle has a width and thickness of approximately 5 mm and 8 mm, respectively. The total length of the graft is 9 to 10 cm. A 10-mm half femoral tunnel is drilled through a low anteromedial portal with the knee flexed at 120°. A suture loop is left in place in the half tunnel. A double tibial tunnel is drilled in a convergent manner (from outside to inside) obtaining an osseous bridge between the 2 tunnels. Two suture loops are passed trough the tibial tunnels and retrieved in a plastic cannula (10 mm) positioned in the anteromedial portal to allow the passage of the 2 bundles in the tibial tunnels. The suture loop left in the half tunnel permits the transportation of the bone plug in the femoral tunnel. Fixation is achieved by an interference screw at the femoral side and by 2 absorbable interference screws (1 for each tunnel). The advantages of this technique are a more cross-sectional area (80 mm²), greater bone-tendon interface, and a more anatomic reconstruction. Theoretically, easier bone incorporation, decreased windshield wiper and bungee effect, fewer donor site problems, and less tunnel enlargement can also be possible.     

Biomechanical effects of medial-lateral tibial tunnel placement in posterior cruciate ligament reconstruction.

With most posterior cruciate (PCL) reconstruction techniques, the distal end of the graft is fixed within a tibial bone tunnel. Although a surgical goal is to locate this tunnel at the center of the PCL's tibial footprint, errors in medial-lateral tunnel placement of the tibial drill guide are possible because the position of the tip of the guide relative to the PCL's tibial footprint can be difficult to visualize from the standard arthroscopy portals. This study was designed to measure changes in knee laxity and graft forces resulting from mal-position of the tibial tunnel medial and lateral to the center of the PCL's tibial insertion. Bone-patellar tendon-bone allografts were inserted into three separate tibial tunnels drilled into each of 10 fresh-frozen knee specimens. Drilling the tibial tunnel 5 mm medial or lateral to the center of the PCL's tibial footprint had no significant effect on knee laxities; the graft pretension necessary to restore normal laxity at 90 degrees of knee flexion (laxity match pretension) with the medial tunnel was 13.8 N (29%) greater than with the central tunnel. During passive knee flexion-extension, graft forces with the medial tibial tunnel were significantly higher than those with the central tunnel for flexion angles greater than 65 degrees while graft forces with the central tibial tunnel were not significantly different than those with the lateral tibial tunnel. Graft forces with medial and lateral tunnels were not significantly different from those with a central tunnel for 100 N applied posterior tibial force, 5 Nm applied varus and valgus moment, and 5 Nm applied internal and external tibial torque. With the exception of slightly higher graft forces recorded with the medial tunnel beyond 65 degrees of passive knee flexion, errors in medial-lateral placement of the tibial tunnel would not appear to have important effects on the biomechanical characteristics of the reconstructed knee.     

Loss of knee extension after anterior cruciate ligament reconstruction: effects of knee position and graft tensioning

BACKGROUND: Loss of knee extension has been reported by many authors to be the most common complication following anterior cruciate ligament reconstruction. The objective of this in vitro study was to determine the effect, on loss of knee extension, of the knee flexion angle and the tension of the bone-patellar tendon-bone graft during graft fixation in a reconstruction of an anterior cruciate ligament. METHODS: The anterior cruciate ligament was reconstructed with use of tibial and femoral bone tunnels placed in the footprint of the native anterior cruciate ligament in ten cadavers. The graft was secured with an initial tension of either 44 N (10 lb) or 89 N (20 lb) applied with the knee at 0 degrees or 30 degrees of flexion. The knee flexion angle was measured with use of digital images following graft fixation. RESULTS: Tensioning of the graft at 30 degrees of knee flexion was associated with loss of knee extension in this cadaver model. Graft tension did not affect knee extension under the conditions tested. CONCLUSIONS: The results suggest that one of the common causes of the loss of full knee extension may be diminished if the graft is secured in full knee extension when the tibial and femoral tunnels are placed in the footprint of the native anterior cruciate ligament. More importantly, even when the femoral and tibial tunnels are placed in the femoral and tibial footprints of the native anterior cruciate ligament, fixing a graft in knee flexion can result in the loss of knee extension.     

In vitro comparison of elongation of the anterior cruciate ligament and single- and dual-tunnel anterior cruciate ligament reconstructions.

This study evaluated strain in the normal anterior cruciate ligament (ACL) and compared it to four different double-strand hamstring tendon reconstructive techniques. Seventeen fresh-frozen knees from 11 cadavers were tested. The strain in the anteromedial and posterolateral bands of the native ACL and their equivalents in four autograft techniques were measured using differential variable reluctance transducers. The anteromedial band of the intact ACL shortened from 0 degree -30 degrees of flexion, then lengthened to 120 degrees; the posterolateral band of the intact ACL shortened from 0 degree - 120 degrees of flexion. Following ACL excision, these knees underwent reconstruction with double-strand hamstring tendons with either single tibial and femoral tunnels, single tibial and dual femoral tunnels, dual tibial and single femoral tunnels, or dual tibial and dual femoral tunnels. With the exception of the dual-band, dual-tunnel technique, all of the procedures placed greater strain on the reconstructive tissues than was observed on the native ACL, after approximately 30 degrees of flexion. These results indicate that dual-band hamstring tendon reconstructions placed with single tibial and femoral tunnels do not address the complexity of the entire ACL. Rather, these procedures appear to only duplicate the effect of the anteromedial band, while perhaps overconstraining the joint as a result of its inability to reproduce the function of the posterolateral band. During rehabilitation following ACL reconstruction, therefore, only from 0 degree - 30 degrees of the graft tissues are not significantly strained. Dual tibial and femoral tunnel techniques should be evaluated further to more closely recreate knee kinematics following ACL reconstruction.     

Tunnel enlargement 5 years after anterior cruciate ligament reconstruction: a radiographic and functional evaluation

Purpose

The aetiology and clinical significance of enlargement of bone tunnels following anterior cruciate ligament (ACL) reconstruction remains controversial. This phenomenon has been attributed to biological factors and mechanical factors. We wanted to study the amount of femoral and tibial tunnel enlargement 5 years post-ACL reconstruction. By standardizing the type of femoral fixation, we also wanted to determine whether the type of tibial fixation had any bearing to the amount of tibial tunnel enlargement.

Methods

All patients who underwent arthroscopic hamstring autograft ACL reconstruction between January 2000 and December 2000 were identified. All grafts were fixed with close-looped endobutton proximally. The grafts were fixed on the tibial side with staples or bioabsorbable interference screws. At a minimum of 5 years after surgery, these patients were recalled. They were assessed with Lysholm knee, Tegner activity and the IKDC Subjective and Objective forms and a KT-1000 arthrometer. The diameter of the bone tunnels and tunnel positions in the anterior–posterior and lateral radiographs were measured using digital callipers by a two blinded researchers.

Results

We found that the femoral tunnel enlarged more than the tibial tunnel. At 5 years, the mean tibial tunnel enlargement was 2.46 mm and the mean femoral tunnel enlargement was 3.23 mm. All 54 patients had endobutton femoral fixation. Of them, 34 patients had tibial graft fixation with staples (extracortical fixation) and 20 patients had tibial graft fixation with bioabsorbable interference screws (aperture fixation). The mean enlargement as measured by the two independent observers in the extracortical group was 1.98 mm (24.7 %)* and 1.51 mm (18.2 %)**compared to 3.27 mm (40.4 %)* and 2.92 mm (30.0 %)** in the aperture fixation group. This difference in tibial tunnel enlargement between the groups was significant (p < 0.001, mean difference 1.29 mm). However, this was not correlated with any significant difference in clinical outcome at 5 years.

Conclusion

We, like some authors, have shown that the use of interference screws in tibial fixation despite being aperture fixation actually has a greater amount of tibial enlargement. This lends weight to the biological theory to tunnel enlargement.     

Simulated graft recession in endoscopic ACL reconstruction: influence on graft strain

Eight fresh cadaveric knee specimens underwent arthroscopic-assisted ACL reconstruction to examine the influence of femoral graft recession on graft strain pattern. Length changes between tibial origin and femoral insertion (simulating graft strain or isometry pattern) were measured throughout knee motion (0 degrees-90 degrees) with a simulated ACL construct. Measurements were taken at the "endo" position (replicating the normal endoscopic position) and in progressive 1.5-mm increments proximally within the femoral tunnel (mimicking femoral graft recession). After recession up to a maximum of 15 mm, a block was placed anterior to the "recessed" graft construct (simulating placement of bone graft anterior to the recessed graft) and strain patterns were remeasured. Graft strain patterns were altered with as little as 1.5 mm recession in two of eight specimens. Compared to the "endo" position, all specimens showed a statistically significant decrease in strain by 3 mm of graft recession (P<.001 for 7 of 8, and P=.0138 for 1 of 8). A direct relationship exists between graft placement and ACL strain patterns, with more proximal graft "recession" adversely influencing normal graft strain. Bone graft placement anterior to the recessed graft restores strain patterns to those seen at the normal "endoscopic" position.     

Reduction of femoral interference screw divergence during endoscopic anterior cruciate ligament reconstruction.

One of the complications of endoscopic anterior cruciate ligament (ACL) reconstruction is femoral interference screw divergence, usually occurring when the femoral screw insertion is different than the portal used for reaming the femoral tunnel. A new technique using a StraightShot graft passer (DePuy Orthopaedic Technology, Tracy, CA) allows the safe passage of a 7 mm M. Kurosaka Advantage cannulated femoral interference screw (DePuy) through the tibial tunnel with the patella tendon graft fully in position. This study compares femoral interference screw divergence in bone-patellar tendon-bone ACL reconstruction using two different screw insertion portals: the accessory anteromedial patella portal and the tibial tunnel portal (StraightShot technique). A radiographic analysis of 81 consecutive endoscopic ACL reconstructions was performed. The total divergence of each femoral screw was measured on both anteroposterior and lateral radiographs and then combined. Group I had the 7-mm femoral screw inserted through the accessory anteromedial patella portal; group II had the femoral screw inserted directly through the tibial tunnel. Group I showed more than 10 degrees of divergence in 50% of the cases, compared with only 4% percent in group II. The average divergence dropped from 11.3 degrees in group I to 1.2 degrees in group II. Femoral interference screw divergence can be virtually eliminated by inserting the femoral screw directly through the tibial tunnel using the StraightShot technique.     

Isolierter Bündelersatz bei Partialruptur des vorderen Kreuzbandes

Objective

Partial augmentation of isolated tears of the anteromedial and posterolateral bundle of the anterior cruciate ligament (ACL) with autologous hamstring tendons. The intact fibers of the ACL are preserved.

Indications

Symptomatic isolated tear of the anteromedial or posteromedial bundle of the ACL or rotational instability after ACL reconstruction with malplaced tunnels (e.g., high femoral position)

Contraindications

In revision cases: loss of motion due to malplaced ACL and excessive tunnel widening of the present tunnels with the risk of tunnel confluence.

Surgical technique

Examination of anterior–posterior translation and rotational instability under anesthesia. Diagnostic arthroscopy, repetition of the clinical examination under direct visualization of the ACL, meticulous probing of the functional bundles. Resection of ligament remnants, preparation/preservation of the femoral and tibial footprint. Harvesting one of the hamstring tendons, graft preparation. Positioning of a 2.4 mm K-wire in the anatomic center of the femoral anteromedial/posterolateral bundle insertion, cannulated drilling according to the graft diameter. Positioning of a 2.4 mm K-wire balanced according to the femoral tunnel at the tibia, cannulated drilling. Insertion of the graft and fixation.

Postoperative management

Analogous to that for ACL reconstruction.     

Comparisons of tunnel-graft angle and tunnel length and position between transtibial and transportal techniques in anterior cruciate ligament reconstruction

Purpose

Our aim was to evaluate tunnel-graft angle, tunnel length and position and change in graft length between transtibial (30 patients) and anteromedial (30 patients) portal techniques using 3D knee models after anterior cruciate ligament (ACL) reconstruction.

Methods

The 3D angle between femoral or tibial tunnels and graft at 0° and 90° flexion were compared between groups. We measured tunnel lengths and positions and evaluated the change in graft length from 0° to 90° flexion.

Results

The 3D angle at the femoral tunnel with graft showed a significant difference between groups at 0° flexion (p?=?0.01) but not at 90° flexion (p?=?0.12). The 3D angle of the tibial tunnel showed no significant differences between groups. Femoral tunnel length in the transtibial group was significantly longer than in the transportal group (40.7 vs 34.7 mm,), but tibial tunnel length was not. The relative height of the lateral femoral condyle was significantly lower in the transportal than the transtibial group (24.1 % vs 34.4 %). No significant differences were found between groups in terms of tibial tunnel position. The change in graft length also showed no significant difference between groups.

Conclusion

Even though the transportal technique in ACL reconstruction can place the femoral tunnel in a better anatomical position than the transtibial technique, it has risks of a short femoral tunnel and acute angle at the femoral tunnel. Moreover, there was also no difference in the change of the graft length between groups.     

Pullout strength of tibial graft fixation in ACL-replacement with a patellar tendon graft: Interference screw versus staple fixation in human knees

Summary The endoscopic single incision technique for 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 both fixation techniques in a human model. This study was performed to evaluate primary biomechanical parameters of this technique compared to a standard interference screw fixation of the block. 55 fresh-frozen human cadaver knee joints of a younger age (mean age: 44 years) 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. 3 different sizes of interference screws (7 × 30, 9 × 20 and 9 × 30 mm) were chosen as a standard control procedure (n = 40). For tibial bone-block fixation the graft was placed through the tunnel, the screw was then inserted on the cancellous or the cortical surface respectively. 15 knees were used for staple fixation. A groove was created inferior to the tunnel outlet with a chisel. The bone block was fixed in this groove with 2 barbed stainless steel staples. Tensile testing in both of the groups was carried out under axial load parallel to the tibial tunnel in a Zwick-testing-machine with a velocity of 1 mm/sec. 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 3.6 and 4.7 mm for interference screw fixation and was 4.2 mm for staples. With both fixation techniques, 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 fixation strength comparable to interference screw fixation.      

A Comparison of the Fixation Strengths Provided by Different Intraosseous Tendon Lengths during Anterior Cruciate Ligament Reconstruction: A Biomechanical Study in a Porcine Tibial Model

Background

The purpose of this study was to determine the tibial fixation strength provided by different intraosseous soft tissue graft lengths within the tibial tunnel.

Methods

Porcine tibial bones and digital flexor tendons were used for testing. Bone mineral densities of proximal tibial medial condyles were measured, and two-strand tendon bundles of 8 mm diameter were used. An intraosseous graft length of 2 cm was used in group 1 (n = 10), and a graft length of 4 cm was used in group 2 (n = 10). Tunnels were 4 cm in length and 8 mm in diameter. Tibial fixation was performed using a suture tied around a screw post with a washer and an additionally inserted 7 × 20 mm bioabsorbable screw. After applying preconditioning loading of 10 cycles, 1,000 cycles between 70-220 N were applied at a frequency of 1 Hz. Graft slippage and total graft movement were recorded. Ultimate tensile strength was measured by pull-out testing at an Instron crosshead speed of 1,000 mm/min.

Results

No significant intergroup difference was found for total graft movement after cyclic loading (slippage in group 1, 1.2 mm and group 2, 1.2 mm, respectively, p = 0.917; and total graft movement in group 1, 3.3 mm and group 2, 2.7 mm, respectively, p = 0.199). However, mean ultimate tensile strength in group 2 was significantly higher than that in group 1 (group 1, 649.9 N; group 2, 938 N; p = 0.008).

Conclusions

In a porcine model, ultimate tensile strength was greater for a 4 cm long intraosseous flexor tendon in the tibial tunnel. However, no intergroup difference in graft slippage or total graft movement was observed. The results show that a 2 cm intraosseous graft length in the tibial tunnel is safe and has sufficient strength (> 450 N) for adequate rehabilitation after anterior cruciate ligament reconstruction.     

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     

A New Technique for Femoral and Tibial Tunnel Bone Grafting Using the OATS Harvesters in Revision Anterior Cruciate Ligament Reconstruction

Revision anterior cruciate ligament (ACL) reconstruction is becoming more frequent, especially in specialized centers, because of the large numbers of primary ACL procedures performed. In 2-stage revisions, bone grafting of the tunnels may be undertaken if the primary position was inaccurate or if osteolysis has caused widening of the tunnels. This will allow the desired placement of the new tunnels without the risk of loss of structural integrity. It is technically difficult to deliver and impact bone graft into the femoral tunnel with the standard surgical and arthroscopic instruments. We describe a new technique for femoral and tibial tunnel impaction grafting in 2-stage ACL revisions, using the OATS grafting instruments (Osteochondral Autologous Transfer System; Arthrex, Naples, FL). The appropriately sized OATS harvester is chosen 1 mm larger than the tunnel size and is used to harvest bone graft from the iliac crest through a percutaneous approach. This provides a cylindrical graft, which is delivered to the femoral tunnel through the arthroscopic portal. The inside punch of the harvester is tapped and this allows delivery of the graft in a controlled manner and its impaction into the tunnel. The same is repeated for the tibial tunnel while providing support for the proximal end of the tunnel.     

Simplified MRI sequences for postoperative control of hamstring anterior cruciate ligament reconstruction

Introduction Usually, standard radiographs are used for postoperative quality follow-up after ACL reconstruction. However, with the use of hamstring grafts and bioabsorbable implants, accurate assessment of the tunnel and implant position is impossible. The graft and its relation to anatomical landmarks cannot be evaluated directly. MRI is an alternative to radiography, permitting direct graft visualization and 3-dimensional assessment of the tunnel position, but it is expensive and time consuming for routine use. The aim of this study was to develop a simplified MRI protocol and to evaluate it for routine postoperative quality follow-up after ACL reconstruction.Materials and methods Various scanning protocols were tested in a series of 105 patients and evaluated for image sharpness, clarity of the structures, susceptibility to artefacts, applicability regarding precise analysis of graft and tunnel position, and time consumption. One simplified specific scan protocol was then defined and applied in a series of 60 consecutive patients after hamstring ACL replacement. The position of the femoral and tibial tunnels was measured in the sagittal, coronal and axial sections and classified according to Harner (femoral) and Stäubli (tibial). Impingement of the graft in the intercondylar roof was analysed according to Howell. The position of the bioabsorbable interference screws was assessed.Results Scan protocol: T2-weighted gradient-echo sequences (GRE) with TR 246 ms, TE 11 ms, flip angle 25°, 2 mm sections and a 256×256 matrix yielded the best image quality of tendon grafts and bone tunnels with tolerable time consumption (average scanning time per patient 1 min 40 s). Altogether 8–16 sections were obtained for every patient. Tunnel placement: 46/60 (77%) of the femoral tunnels were in zone 4, 13/60 (21%) at the border of zones 3 to 4, 1/60 (2%) in zone 3 in the sagittal plane (Harner). The femoral tunnels in the axial plane were at 10:30 oclock in 32/60 (53%), at 11:00 oclock at 24/60 (40%) and at 10:00 oclock in 4/60 (4%) patients. The mean distance of the anterior border of the tibial tunnel from the anterior cortex was 39% (± 4.9%) related to the total sagittal diameter of the tibia. There was no graft impingement. The position of the interference screws was anterior to the grafts in all cases.Conclusion Simplified MRI sequences can be used for postoperative quality follow-up after ACL replacement and are an alternative to standard radiographs giving more specific and precise information regarding tunnel position and screw placement. Analyzing the bone tunnels in a series of 60 patients demonstrated that correct assessment of tunnel placement after arthroscopic ACL reconstruction is feasible using this simplified MRI technique.