Conventional Interference Screw Research Articles

Mechanical properties of a bioabsorbable magnesium interference screw for anterior cruciate ligament reconstruction in various testing bone materials

Tears of the anterior cruciate ligament (ACL) negatively impact the stability and kinematics of the knee. Interference screws (ISs) are used for graft fixation in ACL reconstruction and provide sufficient fixation strength to withstand the patients' activities during the graft-to-bone integration process. Magnesium is a novel material used to manufacture IS given its strength and bioabsorbability. In previous studies, the selected magnesium IS design showed a better fixation performance in comparison to the conventional IS design due to its shape design and surface condition. In this study, bioabsorbable magnesium ISs were tested for their insertion (insertion torque and a number of turns to implement the IS) and fixation performance (pull-out and dynamic test). To obtain a reliable initial assessment of IS performance, ISs were implanted in 15 per cubic foot (PCF) Sawbones polyurethane foam blocks, Sawbones biomechanical tibia models with 17 PCF foam cores, and human cadaveric tibiae. Porcine tendons were used in the foam block pull-out test, and nylon ropes were used in all other test setups to prevent influences of the ligament graft material itself. In the pull-out test, the graft was subjected to tensile stress at a rate of 6 mm/min. For the dynamic test, 1000 cycles between 0 and 200 N were performed, followed by a final pull-out test. After each test, the tunnel widening pattern was observed by measuring the aspect ratio of the tunnel at the insertion site. The insertion torque lies within the normal insertion torque of the ISs as well as the average ligament tension before the insertion. In the foam block setup, the nylon rope showed a higher pull-out force than the porcine tendon. The comparison of each setup using nylon rope for both pull-out and pull-out after the dynamic test showed no significant difference between the foam block and cadaver setup. However, all tibia model setup shows unexpectedly high pull-out force due to the influence of its cortical layer. There were no statistically significant differences in tunnel widening between foam block-porcine tendon and foam block-nylon rope constructs. The pull-out resistance of magnesium ISs falls within the typical ACL tension range during daily activities. Even though the test results of the magnesium ISs are different in each bone material, the magnesium IS shows adequate fixation ability and workability during insertion without material failure.

In Vitro Investigation of the Fixation Performance of a Bioabsorbable Magnesium ACL Interference Screw Compared to a Conventional Interference Screw.

An anterior cruciate ligament (ACL) reconstruction is a common treatment for patients with ACL rupture that aims to regain pre-injury knee stability and kinematics. During the ACL reconstruction, one method to fix the graft is the use of an interference screw (IS). The IS should provide initial stability and secure the graft during the healing period. In recent years, magnesium has emerged as an alternative material to permanent metal and polymer ISs. In addition, differences in designs, such as the shape of the IS, can influence the fixation performance of the IS. Therefore, in this biomechanical experiment, two different screw designs with two ligament materials were compared in an insertion and a pull-out test at a rate of 1 mm/s. The screw designs were a conventional polymer screw and a magnesium screw. Porcine tendon and nylon rope were used as ligament materials. All tests were performed in polyurethane foam blocks with 15 PCF density (Synbone AG, Switzerland). As a result, both screw designs required an insertion torque of less than 3 Nm. There was a significant difference between the porcine and nylon rope in pull-out tests for each screw design. The magnesium screw had the highest pull-out force at 412.14 ± 50.00 N for porcine tendon and 707.38 ± 21.81 N for nylon rope. There were no significant differences in tunnel widening (narrow-wide ratio) between each ligament material. The magnesium screw showed the lowest narrow-wide tunnel ratio, implying a better ability to compress the graft to the tunnel. In conclusion, a more optimized magnesium IS design resulted in better graft fixation and an improved ACL reconstruction outcome.

Biomechanical evaluation of an allograft fixation system for ACL reconstruction.

The purpose of this study was to compare the biomechanical stability, especially graft slippage of an allograft screw and a conventional interference screw for tibial implant fixation in ACL reconstruction. Twenty-four paired human proximal tibia specimens underwent ACL reconstruction, with the graft in one specimen of each pair fixed using the allograft screw and the other using the conventional interference screw. Specimens were subjected to cyclic tensile loading until failure. The two fixation methods did not show any statistical difference in load at graft slippage (p = 0.241) or estimated mean survival until slippage onset (p = 0.061). The ultimate load and the estimated mean survival until failure were higher for the interference screw (p = 0.04, and p = 0.018, respectively). Graft displacement at ultimate load reached values of up to 7.2 (interference screw) and 11.3mm (allograft screw). The allograft screw for implant fixation in ACL reconstruction demonstrated comparable behavior in terms of graft slippage to the interference screw but underperformed in terms of ultimate load. However, the ultimate load, occurring at progressive graft slippage, may not be considered a direct indicator of clinical failure.

The double-lasso loop technique of Biceps tenodesis has lower displacement after cyclic loading, compared to interference screw fixation: Biomechanical analysis in an ovine model.

Biceps tenodesis is an effective treatment for symptomatic long head of biceps tendon pathology. Recently the arthroscopic "double lasso-loop" suture anchor (DLSA) technique was described, advantaged by reduced cost, complexity, and operative time. We aimed to compare the in vitro strength of DLSA with conventional interference screws (IS). A biomechanical analysis was conducted on 14 sheep shoulders (8 DLSA, 6 IS), consisting of a 500-cycle cyclic loading experiment of 5-70 N and ultimate failure load (UFL) test where each specimen was pulled until failure. Displacement (mm) was recorded every 100 cycles, while stiffness and UFL were observed. Cyclic displacement was significantly lower with DLSA at 100 cycles, but not above. During the UFL test, IS was stiffer (27.68 ± 6.56 N/mm versus 14.10 ± 5.80 N/mm, p = .005) and had higher UFL (453.67 ± 148.55 N versus 234.22 ± 44.57 N, p = .001) than DLSA. All DLSA failures occurred with suture/anchor pull-out, while all IS constructs failed at the muscle/tendon. Comparison of the novel DLSA technique with a traditional IS method found lower initial displacement. While our IS constructs could withstand higher UFL, peak load characteristics of DLSA were similar to previous ovine studies. Hence, the DLSA technique is a viable alternative to IS for biceps tenodesis with its purported non-biomechanical advantages.

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

BackgroundBone 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.MethodsTo 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.ResultsThe 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.ConclusionAbout 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.

Increased Load to Failure in Biceps Tenodesis With All-Suture Suture Anchor Compared With Interference Screw: A Cadaveric Biomechanical Study

To compare the biomechanical characteristics of a single radially expanding all-suture anchor with an interference screw for open subpectoral long head of biceps tendon (LHBT) tenodesis. Eighteen fresh-frozen matched-pair human cadaveric humeri were used for this biomechanical study. The matched pair humeri were randomly assigned into 2 experimental biceps tenodesis groups: conventional interference screw (CIS) or all-suture suture anchor (ASSA). Open subpectoral LHBT tenodesis was then performed and biomechanical testing was performed using a servohydraulic test frame. A preload of 5 N was applied for 2 minutes before cyclic loading. Displacement was recorded at cycle 300 (D300) and cycle 500 (D500) and at ultimate failure. Data recorded included displacement, load to failure, displacement at failure. Paired t test was used for analysis. Decreased displacement was observed for the CIS group at D300 (1.67 ± 0.57 mm vs 3.35 ± 2.24 mm; P= .04), D500 (2.00 ± 0.76 mm vs 3.87 ± 2.20 mm; P= .04), and at failure (5.17 ± 3.05 mm vs 10.76 ± 2.66 mm; P < .001). Load to failure was lower in CIS specimens (170 ± 24.5 N vs 217.8 ± 51.54 N; P= .02). Failure in each case was tendon pullout for all CIS specimens; in ASSA 6 specimens failed as the suture pulled through the tendon, 2 specimens failed by suture breakage. No difference in stiffness was observed between the 2 groups (CIS= 98.33 ± 22.98 N/m vs ASSA= 75.94 ± 44.83 N/m; P= .20). Our study found that open subpectoral biceps tenodesis performed with an ASSA construct results in increased load to failure as compared with CIS. However, the CIS did demonstrate decreased displacement as compared to ASSA in this cadaveric biomechanical study. ASSA and CIS at time zero provide fixation as indicated by the provider intraoperatively for LHBT tenodesis. ASSA, however, does remove less cortical bone than does CIS and therefore produces a smaller stress riser in the proximal humerus. Further testing as to the integrity of ASSA is warranted to determine the integrity of the tenodesis with cyclical loading.

Biomechanical Analysis of All-Suture Suture Anchor Fixation Compared With Conventional Suture Anchors and Interference Screws for Biceps Tenodesis

To compare the biomechanical properties of all-suture suture anchors (ASSAs) with conventional interference screws (CISs) and conventional suture anchors (CSAs) for long head of the biceps tendon fixation during proximal biceps tenodesis (BT). We randomized 21 fresh-frozen human cadaveric shoulders into 3 subpectoral BT treatment groups: ASSA, CSA, and CIS. Each construct was cyclically loaded from 5 to 70N for 500 cycles (1Hz). All specimens that survived cyclic loading were then pulled to failure (1mm/s). Elongation, maximum load, energy, and failure mode were recorded. The humerus was stripped of tissue and then subjected to torsional displacement at a rate of 1°/s until fracture occurred. Maximum load, displacement, stiffness, and energy were recorded. During tendon testing, 3 specimens (43%) in the CIS group failed early during cyclic testing by the tendon tearing at the screw-tendon interface. All other specimens in the CIS group, as well as all specimens in the ASSA and CSA groups, survived cyclic testing and failed during pull-to-failure testing. Failure occurred at the tendon-anchor or -screw interface in all specimens (100%), with no anchor or screw pullout. The CIS group had significantly decreased elongation (8.9 ± 2.23mm) at maximum load compared with the ASSA (19.2 ± 5.2mm) and CSA (18.9 ± 2.23mm) groups (P= .001). During torsional testing, the ASSA group was able to withstand significantly greater torsional displacement (9.22° ± 0.86°) before failure and had greater energy to failure (497.3 ± 45 Nmm-degrees) than the CIS group (6.13° ± 1.24° and 256.6 ± 70.3 Nmm-degrees, respectively; P= .005). This study shows that the biomechanical properties of ASSA, CSA, and CIS constructs are similar. The interference screw group had lower tendon elongation at maximum load but had several early failures compared with the suture anchor groups. The use of suture anchors results in maximum tendon and torsional bone loads similar to interference screws for the long head of the biceps tendon. Torsional testing of the CIS resulted in spiral fractures traversing the screw tunnel in 100% of the specimens, which was not found in the suture anchor groups. The ASSA is a viable fixation method for BT in comparison with the CSA and CIS.

Biomechanical analysis of an interference screw and a novel twist lock screw design for bone graft fixation

BackgroundMalpositioning of an anterior cruciate ligament graft during reconstruction can occur during screw fixation. The purpose of this study is to compare the fixation biomechanics of a conventional interference screw with a novel Twist Lock Screw, a rectangular shaped locking screw that is designed to address limitations of graft positioning and tensioning. MethodsSynthetic bone (10, 15, 20lb per cubic foot) were used simulating soft, moderate, and dense cancellous bone. Screw push-out and graft push-out tests were performed using conventional and twist lock screws. Maximum load and torque of insertion were measured. FindingsMax load measured in screw push out with twist lock screw was 64%, 60%, 57% of that measured with conventional screw in soft, moderate and dense material, respectively. Twist lock max load was 78% and 82% of that with conventional screw in soft and moderate densities. In the highest bone density, max loads were comparable in the two systems. Torque of insertion with twist lock was significantly lower than with conventional interference screw. InterpretationBased on geometric consideration, the twist lock screw is expected to have 35% the holding power of a cylindrical screw. Yet, results indicate that holding power was greater than theoretical consideration, possibly due to lower friction and lower preloaded force. During graft push out in the densest material, comparable max loads were achieved with both systems, suggesting that fixation of higher density bone, which is observed in young athletes that require reconstruction, can be achieved with the twist lock screw.

A novel, hydroxyapatite-based screw-like device for anterior cruciate ligament (ACL) reconstructions

BackgroundRupture of the anterior cruciate ligament (ACL) is one of the most common injuries of the knee. Common techniques for ACL reconstruction require a graft fixation using interference screws. Nowadays, these interference screws are normally made of titanium or polymer/ceramic composites. The main challenge of application of a fixation device made entirely of bioactive ceramic is in relation to the low strength of such materials. The purpose of this study was to evaluate a novel geometry for a fixation device made of pure hydroxyapatite for ACL reconstructions that can overcome some problems of the titanium and the polymer/ceramic screws. MethodsFinite Element Analysis was used for optimization of the stress distribution in conventional interference screw geometry. For experimental evaluation of the new fixation device, ex vivo tests were performed. ResultsThe innovative screw-like fixation device is characterized by multiple threads with a large thread pitch. The novel design enabled the insertion of the screw into the bone without the application of an external torque or a screwdriver. In turn, it also allowed for the use of low-strength and high-bioactivity materials, like hydroxyapatite. Ex vivo tests showed that the novel screw can sustain pull-out forces up to 476 N, which is comparable to that of the commercially available BioComposite™ interference screws (Arthrex Inc., Germany), as a reference. ConclusionsIn summary, the novel screw design is a promising strategy to develop all-ceramic fixation devices for ACL reconstructions, which may eliminate some drawbacks of the current interference screws.

The fixation strength of a novel ACL soft-tissue graft fixation device compared with conventional interference screws: a biomechanical study in vitro

Anterior cruciate ligament reconstruction using autologous hamstring tendons is an established surgical procedure but some grafts fail due to poor fixation. This study compared the fixation of a new ACL graft fixation device (the EZ KneeSpan) to conventional soft-tissue threaded titanium interference screws (IS). The EZ device was designed to provide secure fixation while avoiding soft-tissue graft damage associated with use of an IS. Eight paired fresh-frozen cadaveric human knees and bovine digital extensor tendons were used. Two tunnels were placed in each tibia and femur, and grafts were fixed using the EZ device and the IS in each bone. Cyclic tensile loading and pull-out testing measured graft slippage (mm) and ultimate strength (N) of the fixation. The results were compared using the non-parametric Wilcoxon signed-rank test. Graft slippage after cyclic loading was significantly lower in the EZ group at 2.4±0.1mm versus 9.5±6.2mm for the IS group in the femur and 3.3±1.4mm versus 17.7±13.6mm in the tibia. The mean ultimate load for the femoral EZ group was significantly higher than the IS group (769±223N versus 468±60N), but they did not differ significantly in the tibia (518±48N versus 546±139N). Our results indicate that with the EZ device the initial fixation of cyclically loaded hamstring grafts could be superior to that with an IS. The EZ KneeSpan device also had similar tibial and higher femoral ultimate fixation strength than an IS.

Design Review &amp; Preliminary Testing for a Biomimetic Absorbable Ligament Anchor

Review of current Anterior Cruciate Ligament (ACL) anchor technologies indicates that many devices facilitate osteointegration but not soft tissue in-growth. The design and preliminary testing of a novel biomimetic in-situ dilating bioabsorbable ACL anchor for simultaneous soft and hard tissue attachment is the subject of this study. The anchor method for this concept has been developed to mimic the mechanical-key configuration observed in a hair root. Reviewed anchor devices are typically interference screw-based. Screw anchors can lead to unnecessary ligament pre-stress, tearing during deployment and poor graft-bone contact. This work demonstrates a new fixation concept specifically developed for use with devices consisting of temperature-sensitive glass-reinforced-glass (GRG) soft tissue conductive biomaterial. Ligament anchorage is accomplished by dilation of the device into the base of a hair-root shaped osteotomy where a ligament with a collar and self tightening knot is inserted beforehand. This method facilitates full ligament-to-bone contact at the osteotomy zone where critical physiological ligament anchorage develops. Ligament pull-out loads equivalent to published results for conventional anchors were achieved using graft analogue. Testing with porcine ligaments resulted in a substantial reduction in ligament pull-out loads. Tibia bone sample constraints combined with the unraveling of the ligament knot were identified as primary factors for low pull-out loads for the porcine ligament tests. Subsequent design iterations will employ a reduction in prototype dimensions in addition to the use of a suture to lock the ligament knot. The hair-root shaped osteotomy and ligament anchor knot elements of this approach may be translated to other fixation systems and methods. By improving macro-mechanical-key interaction between the anchor, bone and ligament, further increase in pull-out forces may be achieved without unnecessary ligament pre-stress and tear damage caused by conventional interference screw threads.

A bioabsorbable plug in bone-tendon-bone reconstruction of the anterior cruciate ligament: Introduction of a novel fixation technique

Purpose: Our aim was to compare the fixation strength of a novel plugging technique with that of the conventional interference technique in bone–patellar tendon–bone reconstruction of the anterior cruciate ligament. Type of Study: Randomized experimental study. Methods: Twenty matched pairs of porcine knees were randomly assigned to 2 groups. The bone block of the graft was secured in the femoral drill hole with either the new bioabsorbable poly-L-lactide/D-lactide (PLA 96/4) copolymer plug (plugging technique) (n = 20) or a conventional interference screw (interference technique) (n = 20). Ten pairs were subjected to a single cycle loading test at a rate of 50 mm/min while the remaining 10 pairs underwent a cyclic loading test to further assess the quality of the fixation. The cyclic loading test consisted of 1,500 loading cycles between 50 and 200 N at half-hertz frequency, after which the specimens were loaded to failure at a rate of 50 mm/min. Results: In the single cycle loading test, the average ultimate failure load was 1,061 ± 342 N in the plugging technique group and 971 ± 260 N in the interference technique group (P =.57). Significant group differences were found neither in the yield loads nor in the stiffness of the fixations. In the cyclic loading, significant displacement difference was not observed between the 2 fixation techniques. There were neither significant group differences with regard to the ultimate failure load (plugging technique 994 ± 376 N versus interference technique 1,001 ± 343 N, P =.97) nor yield load of the fixations in the subsequent single cycle loading. Conclusions: The results of this study indicate that, in anterior cruciate ligament reconstruction, the new plugging technique is a reasonable alternative for fixation of the femoral site of a bone–patellar tendon–bone graft.Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 17, No 2 (February), 2001: pp 144–150

Experimental stability of a new implant-free fixation technique in ACL replacement

The purpose of the study is to establish data on the stability of an ACL replacement. In 40 human cadaver knees, either a mid patellar ligament third with a trapezoid bone block on one side was fixed on the femoral side in a 2-diameter drill hole, or a conventional interference screw fixation was applied. Average primary stability amounted to 570 N (+/- 100 N) for the bone-blocking technique, and to 402 N ( +/- 79 N) for the interference screw fixation. When statistically tested by variance analysis, stability was significantly higher for the bone blocking technique than with interference screw fixation (p < 0.05). Thus, when using a mid-patellar ligament third for ACL reconstruction, the new implant-free technique described here appears to be a practical and reliable method for femoral graft fixation.