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

Femoral interference screw divergence as a result of anteromedial portal insertion and outside-in FlipCutter femoral tunnel drilling: A cadaveric study

Aims and objectives

To investigate whether interference screw fixation through an anteromedial portal into an outside-in drilled femoral tunnel via a flip cutter results in acceptable hardware position.

Materials & methods

10 cadaveric knees underwent ACL-reconstruction with patellar BTB autograft. Femoral tunnel drilling was performed utilizing an outside-in flip cutter drill and interference screws for femoral fixation. Lateral and anterior-posterior (AP) fluoroscopic images were taken to measure screw divergence within the femoral tunnel. The means of AP and lateral divergence angles were compared using two-tailed t-tests.

Results

Using the flip cutter, the AP and lateral divergence angles were 7.3° ± 4.5° and 9.3° ± 9.3°, respectively, while the total divergence angles were 16.6° ± 11.8°. Divergence angles using a cannulated reamer were found to be 14.4° ± 2.5° and 6.8° ± 2.8° for AP and lateral, respectively and 21.1° ± 5.2° for the total divergence. The AP divergence angles using the flip cutter were significantly less than those reported using a cannulated reamer (p = 0.001).

Conclusions

The flip cutter method resulted in significantly reduced divergence angle between the screw and graft when compared to previous cadaveric studies in the coronal plane. There was no significant difference in divergence angle in the sagittal plane. Both methods appear to result in divergence angles below the threshold which would be considered to significantly decrease pull-out strength. Large standard deviations also reflect limited sample size but may also suggest more variability in divergence when compared to historical control set. This study clearly establishes the outside-in technique using a retrograde reamer as a viable independent femoral drilling solution for ACL reconstruction when using a BTB autograft with a femoral interference screw.

Comparison of mechanical properties in interference screw fixation technique and organic anterior cruciate ligament reconstruction method: a biomechanical study

Background

Bone and Site Hold Tendon Inside (BASHTI) technique is an organic implant-less technique for anterior cruciate ligament (ACL) reconstruction with some clinical advantages, such as speeding up the healing process, over implantable techniques. The study aims to compare the mechanical properties of BASHTI technique with the conventional interference screw technique.

Methods

To investigate the mechanical properties, 20 in-vitro experimental tests were conducted. Synthetic dummy bone, along with fresh digital bovine tendons, as a graft, were used for experiments. Three loading steps were applied to all specimens, including a preconditioning, a main cyclic, and a pull-out loading.

Results

The mechanical characters of an interference screw technique using an 8 mm tendon diameter, including fixation strength, average cyclic stiffness (ACS), and average pull-out stiffness (APS) were found to be 439 ± 132 N, 10.3 ± 5.3 kN/mm, and 109 ± 40 N/mm, respectively. In the case of an interference screw using a 9 mm tendon, the fixation strength, ACS, and APS were obtained 549 ± 87 N, 10.3 ± 4.7 kN/mm, and 91 ± 13 N/mm, respectively. In parallel, the fixation strength, APS, and ACS of BASHTI technique using an 8 mm tendon were 360 ± 123 N, 3.3 ± 0.6 kN/mm, and 79 ± 27 N/mm, respectively, while, for 9 mm tendon 278 ± 103 N, 2.4 ± 1.2 kN/mm, and 111 ± 40 N/mm, were reported for fixation strength, APS, and ACS respectively when BASHTI technique was used.

Conclusion

About 50% of interference screw samples showed superior mechanical properties compared to BASHTI technique, but in another half of the samples, the differences were not significant (N.S.). However, due to organic advantages of BASHTI technique and lower cost, it could be used as a substitute for interference screw technique, especially where fast recovery is expected.

Developing an organic implant-less technique which has numerous clinical advantages

Comparing this novel technique with interference screw technique

Implementing synthetic Sawbones blocks to have a controlled study

Selecting the best fixation condition for this novel technique

Hyperflexion and Femoral Interference Screw Insertion in ACL Reconstruction

Background:

In anatomic anterior cruciate ligament (ACL) reconstructions produced with flexible reamers and no knee hyperflexion, it is unknown whether knee hyperflexion is necessary for femoral interference screw insertion.

Purpose:

To compare femoral screw-graft divergence in anatomic ACL reconstructions with endoscopic interference screws placed without knee hyperflexion and with the use of flexible versus rigid screwdrivers.

Study Design:

Controlled laboratory study.

Methods:

Ten matched pairs of cadaveric knees had bone-tendon-bone graft ACL reconstructions with anatomic femoral tunnels. The knees were flexed to 90°. Femoral interference screws (7 × 20 mm) were placed in pairs of knees: in 1 knee with a flexible screwdriver and in the opposite knee with a rigid screwdriver. Graft-screw divergence was imaged with computed tomography scans and tested with cyclic and static biomechanical tests.

Results:

The mean screw-graft divergence was 12.07° ± 4.04° with the rigid screwdriver and 10.68° ± 3.23° with the flexible screwdriver (P = .35). The cyclic tests with screws placed by a rigid screwdriver had a mean increase in displacement of 0.56 ± 0.20 mm. For screws placed with the flexible screwdriver, the mean increase in displacement was 0.58 ± 0.32 mm (P = .66). Yield load was 393.3 ± 95.1 N for screws placed by a rigid screwdriver and 408.2 ± 119.0 N for screws inserted with the flexible screwdriver (P = .78). Maximum load was 523.1 ± 88.7 N for screws placed by a rigid screwdriver and 467.1 ± 107.3 N for screws inserted with the flexible screwdriver (P = .09).

Conclusion:

With either a rigid or a flexible screwdriver, there were no significant effects on screw divergence or fixation strength.

Clinical Relevance:

Knees can be kept at 90° during endoscopic femoral interference screw insertion. The use of a traditional rigid or flexible screwdriver will not affect screw-graft divergence or fixation strength.

Femoral Screw Divergence via the Anteromedial Portal Using an Outside-In Retrograde Drill in Bone-Patella Tendon-Bone Anterior Cruciate Ligament Reconstruction: A Cadaveric Study

PURPOSE

To assess screw divergence when inserting an interference screw for a bone-patellar tendon-bone graft using an outside-in technique with a retrograde drill to create the femoral tunnel.

METHODS

Ten cadaver specimens underwent anterior cruciate ligament reconstruction with a bone-patellar tendon-bone autograft, with 23-mm-deep tunnels created by a retrograde drill outside-in technique. Drilling angles were based on a previous study that established the optimal angles to recreate the anterior cruciate ligament footprint. To ensure that screw insertion angles matched the angle of socket drilling, a marking pen was used to transpose 2 lines on the skin of the anterior knee corresponding to the drill in both the coronal and axial planes with the knee held at 90° of flexion. The femoral-sided bone plug was affixed with a 7 × 23 mm interference screw through an anteromedial portal. Computed tomography scans were used to calculate coronal and sagittal screw-tunnel divergence.

RESULTS

The median screw divergence in the coronal plane was 2.79°, with a range of 1.1° to 17.2°. Of 10 specimens, 8 had no divergence (0° to 5°), 0 screws were between 5° and 10°, 1 screw was between 10° and 15°, and 1 screw was between 15° and 20°. The 95% confidence interval was 3.73° to 11.69°. No screws had ≥20° of divergence. In the sagittal plane, the median screw divergence was 5.68°, with a range of 1.2° to 18.7°. Five specimens had no divergence (0° to 5°), 3 screws were between 5° and 10°, 0 screws were between 10° and 15°, and 2 screws were between 15° and 20° of divergence. The 95% confidence interval was 3.73° to 11.69°. No screws had ≥20° of divergence.

CONCLUSIONS

The results of this study showed that 80% of screws diverted less than 5° in the coronal plane. In the sagittal plane, only 50% of screws were found to have divergence of 5° or less. No screw in either plane had divergence of greater than or equal to 20°.

CLINICAL RELEVANCE

When using a retrograde drill, a skin marking technique is a useful aid in placing interference screws with acceptable angles of divergence when using an inside-out technique.

Fixation strength of the interference screw in the femoral tunnel: The effect of screw divergence on the coronal plane

Clinical studies to examine the effect of screw divergence have not been applied to the fixation of hamstring grafts. A few previous reports have addressed the correlations between the loss of pullout strength and divergence on hamstring tendon fixation in biomechanical tests. The purpose of this study was to examine the effect of interference screw divergence on the coronal plane when digital flexor tendons were fixed with an interference screw. Twenty fresh porcine hindlimb specimens were chosen. The grafts were fixed using titanium soft tissue interference screws. The hindlimbs were divided into two groups according to the insertion method of the screw. The screw was placed along the graft parallel to the long axis of the femoral tunnel in 10 specimens (parallel placement group), and the others were placed laterally at a 15° divergent angle from the bone tunnel on the coronal plane (divergence group). The cyclic-loading test was loaded for 1500cycles. Five specimens failed because of a pull-out of the tendon in divergence group. The number of specimens that failed before the completion of cycles in the divergence group was significantly greater than that in the parallel placement group. Although the residual displacement after 1500cycles for the divergence group was greater than that for the parallel placement group, no statistically significant difference was found between the groups. This study suggests that the screw placed laterally at a 15° divergent angle on the coronal plane decreases the fixation strength of the digital flexor tendons fixed with an interference screw.

Fixation strength of biocomposite wedge interference screw in ACL reconstruction: effect of screw length and tunnel/screw ratio. A controlled laboratory study

Background

Primary stability of the graft is essential in anterior cruciate ligament surgery. An optimal method of fixation should be easy to insert and provide great resistance against pull-out forces.

A controlled laboratory study was designed to test the primary stability of ACL tendinous grafts in the tibial tunnel. The correlation between resistance to traction forces and the cross-section and length of the screw was studied.

Methods

The tibial phase of ACL reconstruction was performed in forty porcine tibias using digital flexor tendons of the same animal. An 8 mm tunnel was drilled in each specimen and two looped tendons placed as graft. Specimens were divided in five groups according to the diameter and length of the screw used for fixation. Wedge interference screws were used. Longitudinal traction was applied to the graft with a Servohydraulic Fatigue System. Load and displacement were controlled and analyzed.

Results

The mean loads to failure for each group were 295,44 N (Group 1; 9 × 23 screw), 564,05 N (Group 2; 9 × 28), 614,95 N (Group 3; 9 × 35), 651,14 N (Group 4; 10 × 28) and 664,99 (Group 5; 10 × 35). No slippage of the graft was observed in groups 3, 4 and 5. There were significant differences in the load to failure among groups (ANOVA/P < 0.001).

Conclusions

Longer and wider interference screws provide better fixation in tibial ACL graft fixation. Short screws (23 mm) do not achieve optimal fixation and should be implanted only with special requirements.

Soft tissue tendon graft fixation in serially dilated or extraction-drilled tibial tunnels: a porcine model study using high-resolution quantitative computerized tomography

BACKGROUND

Tibial tunnel preparation may contribute to improved soft tissue graft fixation.

HYPOTHESIS

Step dilation produces greater tunnel wall bone volume than does extraction drilling and increases fixation strength. Bioabsorbable interference screw divergence decreases fixation strength, regardless of tunnel preparation method.

STUDY DESIGN

Controlled laboratory study.

METHODS

Twenty porcine tibias were divided into 2 groups of 10 with matching mean apparent bone mineral density. One group received 9-mm-diameter extraction-drilled tunnels, and the other group received 7-mm-diameter extraction-drilled tunnels followed by step dilation to 9 mm. High-resolution quantitative computerized tomography scans and voxel analysis techniques determined tunnel wall bone volume fraction. Screws secured 8.5-mm-diameter porcine grafts in the tunnels. Repeat scans were used to determine screw divergence. Cyclic loading was performed in a servohydraulic device before load to failure testing.

RESULTS

The step dilation group had greater tunnel wall bone volume/total volume than did the extraction drilled group; however, a significant increase in fixation strength was not detected. Specimens with screw divergence angles less than 15 degrees had superior fixation and insertion torques compared with specimens with angles 15 degrees or more. Screw divergence correlated more strongly with fixation strength than did mean apparent bone mineral density or screw insertion torque.

CONCLUSION

Step dilation increased tunnel wall bone volume/total volume, but fixation strength did not improve. Screw divergence >or=15 degrees decreases graft-bone tunnel fixation whether or not step dilation is performed.

CLINICAL RELEVANCE

Screw alignment plays a greater role in anterior cruciate ligament graft fixation than does extraction drilling or step dilation tunnel preparation methods in healthy bone.

Bioabsorbable screw divergence angle, not tunnel preparation method influences soft tissue tendon graft-bone tunnel fixation in healthy bone

Bone tunnel fixation of a soft tissue tendon graft is the weak link immediately following ACL reconstruction. This biomechanical study evaluated the influence of extraction drilled or step dilated bone tunnels and bioabsorbable screw divergence on soft tissue tendon graft fixation. From an initial group of 50 available specimens, similar apparent bone mineral density porcine tibiae (1.2 +/- 0.24 g/cm2) were divided into two groups of ten specimens each. Group 1 (extraction drilled) received 9 mm diameter tunnels. Group 2 (step dilated) received 7 mm diameter tunnels that were dilated to 9 mm. Grafts were secured in tunnels using 10 mm diameter, 35 mm long tapered screws. After high resolution CT scanning to evaluate screw divergence, constructs were pretensioned on a servo hydraulic device between 10 and 50 N for 10 cycles, and isometric pretensioned at 50 N for 1 min, prior to 500 sub-maximal loading cycles (50-200 N) and load to failure testing at 20 mm/min. Wilcoxon Signed Rank tests and Mann-Whitney U-tests were used to evaluate group differences. Coefficient of determination values (r2) were calculated to further delineate statistically significant relationships. Tunnel preparation method did not display statistically significant effects on insertion torque, displacement during cyclic testing, relative stiffness during cyclic testing, load at failure, stiffness during load to failure testing or displacement during load to failure testing. Screw divergence < 15 degrees produced lower displacement and greater relative stiffness during cyclic testing and greater load at failure and stiffness during load to failure testing. Screw divergence angle displayed moderate relationships with construct displacement during cyclic testing (r2 = 0.54), stiffness during load to failure testing (r2 = 0.60), and load at failure (r2 = 0.41). Tunnel dilation does not enhance soft tissue tendon graft fixation strength in healthy bone. Bioabsorbable screw divergence of > or = 15 degrees significantly reduces soft tissue tendon graft-bone tunnel fixation.

Femoral interference screw placement through the tibial tunnel: a novel method without graft damage

A frequently encountered problem in endoscopic 1-incision anterior cruciate ligament (ACL) reconstruction is the difficulty involved in accurately inserting the femoral interference screw without significant and undesirable divergence between the screw and the graft when a femoral interference screw is fixed through the anteromedial portal. To minimize divergence, the authors demonstrated a modified, easy, and reproducible procedure that can be performed without causing graft injury or requiring special instrumentation. A ligament reconstruction route is created with the use of an ACL guide system. Lead graft sutures are pulled through the anteromedial portal by way of the femoral tunnel and out the anterolateral thigh first. The tendon graft is then inserted through the anteromedial portal and up into the femoral tunnel. A guidewire is introduced through the tibial tunnel into the femoral tunnel. An appropriately sized BioScrew (Linvatec, Largo, FL) is inserted, with the use of a guidewire inside the screw, through the tibial tunnel into the femoral tunnel. The graft is then retrieved through the anteromedial portal and is inserted through the tibial tunnel. Finally, the tendon graft in the tibial tunnel is similarly fixed with a BioScrew of the same size. Moreover, this novel approach is feasible for all tendon grafts (bone-patellar tendon-bone grafts, quadriceps tendon-patellar bone grafts, and hamstring tendon grafts).

Expansion anchors for use in anterior cruciate ligament (ACL) reconstruction: establishing proof of concept in a benchtop analysis

The current method for graft fixation in bone tendon-bone anterior cruciate ligament (ACL) reconstruction is the interference screw. Although this method of fixation provides for adequate graft fixation with respect to strength, intraoperative placement is difficult and the failure rate is high. To address these concerns, we have designed and fabricated prototype expansion anchors that could be expanded to anchor the graft in the bone tunnel. As a first step in assessing the validity of this concept, in the current work, we demonstrate that these systems are of comparable fixation strength (biomechanical pullout testing) to the standard interference screw, are smaller at the time of insertion and thus provide for increased visibility and ease of placement. The increased visibility should result in better placement and reduced failure rates. The increased ease of placement should result in significant savings in decreased OR time.

Femoral interference screw divergence after anterior cruciate ligament reconstruction provoking severe anterior knee pain

An unusual case of anterior knee pain after anterior cruciate ligament reconstruction secondary to femoral screw divergence is described. We hypothesize that a contracture of the lateral head of the gastrocnemius, caused by irritation from the femoral screw, could increase the patellofemoral joint reaction. This would contribute to increasing the overload of the subchondral bone, which could explain the anterior knee pain. Conversely, tight gastrocnemius may lead to an increase in foot pronation of the subtalar joint, resulting in an increased valgus vector force at the knee, which can cause anterior knee pain. Finally, dorsiflexion of the talocrural joint will also decrease if the gastrocnemius is tight, provoking biomechanical limitations and possible knee problems during walking and running.