Ultimate Pullout Strength Research Articles

Muscle Belly Repair: Biomechanical Assessment of the Anchor Suture and the Modified Kessler Techniques.

Background: Treatment of muscle belly lacerations remains a problem for surgeons. Inadequate repair of lacerations can cause functional disability. To date, there is no consensus on the method of repair for these injuries. We have previously described a technique of repairing mid-substance muscle belly lacerations. The aim of this study was to determine the ultimate strength of an intact muscle belly and to compare the anchor suture (AS) technique with the modified Kessler (MK) technique. Methods: Fifteen fresh frozen hind-legs from adolescent pigs were divided into three groups and used for the testing. Each group consisted of five specimens. Group one was the intact control group, group two was repaired with the MK technique and group three was repaired with the AS technique. Following repair, the muscles were secured in a custom-made fixation apparatus and underwent linear tensioning at a rate of 25 mm/min, generating a load-displacement curve for each specimen. The data regarding ultimate strength, modes of failure and number of intact suture/anchor constructs (for groups 2 and 3) was calculated. Results: The ultimate strength of the intact muscle group of was found to be 608.1 ± 107.9 N. This was significantly (p < 0.05) higher than the pull-out strength of the MK and AS groups. The pull-out strength of the AS group was 143.1 ± 36.7 N, nearly twice that of the MK group 69.8 ± 16.4 N (p = 0.11). Suture pull-out was the most common mode of failure. Conclusions: The AS technique was found to have both higher strain and nearly twice the ultimate pull-out strength compared to the MK repair group. We suggest the AS technique as a viable technique for mid-substance muscle belly repairs.

Investigation of Interfacial Bonding Properties of Polyurethane Concrete and Cement Concrete/Steel Reinforcement

To solve the problem that the repair material of the bridge's expansion joint anchorage area is prone to debonding from the other bridge components, polyurethane concrete was designed and prepared, and the bonding performance of polyurethane concrete was tested by the bond splitting test, bond direct shear test, bond oblique shear test, and steel reinforcement pull-out test. The results show that the interfacial bond strength of polyurethane concrete and cement concrete can be improved by increasing the interfacial roughness. The bond splitting strength increases by up to 91.4%, the bond direct shear strength increases by up to 55.2%, and the bond oblique shear strength increases by up to 28.9%. The bond strength between polyurethane concrete and cement concrete are minimally influenced by temperature. An increase in the diameter of the reinforcement or the length of the bonded anchorage can increase the ultimate pull-out strength of the polyurethane concrete and the steel reinforcement. Polyurethane concrete is a novel composite material with excellent bonding performance with cement concrete and steel reinforcement, which can be widely used in practical projects, such as repairing bridge expansion joint anchorage areas in the future.

Pull-out Strength of Suture Anchor and Torque of Buddy Anchor for an Osteoporotic Humeral Head in Rotator Cuff Repair: Parallel Versus Divergent Insertion

Background: The buddy anchor technique is useful to reinforce loose anchors in the osteoporotic humeral head during arthroscopic rotator cuff repair. However, theoretical parallel insertion of the buddy anchor to index a loose anchor is challenging in arthroscopy and can widen the entry site and decrease structural integrity. Purpose: To investigate and compare the biomechanical stability between 2 buddy anchor insertion techniques (parallel insertion vs divergent insertion) in the osteoporotic humeral head. Study Design: Controlled laboratory study. Methods: A total of 24 paired fresh-frozen cadaveric shoulders were used, and each pair was randomly assigned to either the parallel insertion group or the divergent insertion group. In the parallel insertion group, the buddy anchor was inserted parallel to the index loose anchor. In the divergent insertion group, the buddy anchor was inserted at a 20° angle in the medial direction to the index loose anchor. The insertion torque of the buddy anchor and ultimate pull-out strength of the index anchor were measured and compared between the 2 groups. Results: The mean maximum insertion torque was significantly higher in the parallel insertion group (16.1 ± 1.8 cN·m) compared with the divergent insertion group (12.0 ± 1.5 cN·m) (P < .001). The mean ultimate pull-out strength was significantly higher with divergent insertion (192.2 ± 28.6 N) than with parallel insertion (147.7 ± 23.6 N) (P < .001). Conclusion: For application of the buddy anchor system in the cadaveric osteoporotic humeral bone model, divergent insertion showed better ultimate pull-out strength than conventional parallel insertion, despite inferior maximum insertion torque. Clinical Relevance: The results of this study widen the applicability and accessibility for the buddy anchor system.

Anchorage of Perfobond Leiste shaped shear connector composite dowel with carbon fibre reinforced polymer

This study focuses on the pullout behaviour of composite structures having closed shape geometry Perfobond Leiste (PBL) shear connectors wrapped with carbon fibre reinforced polymer (CFRP). Eight test specimens having PBL connectors with and without CFRP were used to perform the pullout tests. These tests were performed under static loading, and the concrete thickness and the embedment depth were the parameters used to evaluate the effects of CFRP jacketing on the pullout strength. The responses, that is, the initial cracking load, the ultimate pullout capacity and the displacement, were investigated. Failure modes were analysed, and a new model was proposed because of the unavailability of suitable models for PBL shear connectors with CFRP. The diagonally bonded CFRP jackets significantly delayed the onset of cracking and showed superior performance in terms of deformation capacity and ultimate pullout strength. A strength model was proposed to predict the ultimate pullout capacity of CFRP-confined PBL composite dowels. Overall, the study demonstrated that it is more efficient to use the proposed CFRP-confined PBL shear connectors than other connectors in practical engineering applications, given the improved deformation capacity and the ultimate shear strength.

Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study

To compare the response to cyclical loading and ultimate pull-out strength of threaded suture anchor with and without calcium phosphate bone void filler augmentation in a polyurethane foam block model and invitro proximal humerus cadaveric model. This controlled biomechanical study consisted of 2 parts: (1) preliminary polyurethane foam block model, and (2) invitro cadaveric humeri model. The preliminary foam block model intended to mimic osteoporotic bone using a 0.12 g/mL foam material. Half of the foam block models were first filled with injectable calcium phosphate bone substitute material (CP-BSM), whereas the other half were not augmented with CP-BSM. Each specimen was then instrumented with a threaded suture anchor. The same technique and process was performed in a matched cadaveric humeri model. Testing then consisted of a stepwise, increasing axial load protocol for a total of 40 cycles. If the anchor remained intact after cyclic loading, the repair was loaded to failure. The number of completed cycles, failure load, and failure modes were compared between groups. Average pull-out strength for suture anchor with CP-BSM in the osteoporotic foam block model was significantly higher at 332.68 N ± 47.61 compared with the average pull-out strength of suture anchor without CP-BSM at 144.38 N ± 14.58 (P= .005). In the matched cadaveric humeri model, average pull-out strength for suture anchor with CP-BSM was significantly higher at 274.07 N ± 102.07 compared with the average pull-out strength of suture anchor without CP-BSM at 138.53 N ± 109.87 (P= .029). In this time zero, biomechanical study, augmentation of osteoporotic foam block and cadaveric bone with calcium phosphate bone substitute material significantly increases pull-out strength of threaded suture anchors. Considering concerns about suture anchor pull-out from osteoporotic bone, augmentation with calcium phosphate bone substitute material increases load to failure resistance.

Optimization of Mix Ratio of Epoxy Mortar with Super-Early Strength Based on Orthogonal Test

Through adding accelerator to common epoxy mortar and optimizing its mix ratio by orthogonal test, the influences of the contents of filler, diluent, curing agent and accelerator on the early strength of epoxy mortar were studied respectively. Results showed that the filler content has the most significant influence on the compressive strength and splitting strength of epoxy mortar, and the optimum combination of these four contents is A2B2C3D2, on which condition compressive strength of epoxy mortar can reach 71.4 MPa and splitting strength 6.72 MPa at super-early stage (4h, at nursing temperature 25 C). Pull-out test on the anchor bolts with optimum-mix-ratio epoxy mortar as anchorage agent was carried out, and compared to tests with quick setting cement as anchorage agent, proving that the pull-out strength with epoxy mortar as anchorage agent was much higher than that of quick-setting cement. The ultimate pull-out strength of the anchor increased with anchorage depth at pull-out bonding failure, which indicates that the optimized epoxy mortar with super-early strength can meet the needs of emergency repair and other special projects, and can be applied in the fields of structural reinforcement and rapid repair of traffic engineering.

Predicting bond behavior of HB FRP strengthened concrete structures subjected to different confining effects

This paper presents an analytical model to predict the bond behavior of hybrid bonded (HB) fiber reinforced polymer (FRP) strengthened concrete structures considering different confining effects. The bond strength of HB-strengthened concrete structures subjected to uniaxial loading is attributed to the friction-type bond from steel plate and the chemical bond provided by epoxy-based resin. The friction-type bond is assumed to develop before any interfacial slip occurs, and remain constant when the interfacial slip is nonzero; for the chemical bond between FRP and concrete, a tri-linear bond-slip relation is adopted. The loading process of HB-strengthened structures consists of three stages, and the stage-wise solution to slip, bond stress, and axial force of HB FRP are derived based on a governing ordinary differential equation (ODE). In this study, the experimental program includes twelve HB-strengthened concrete specimens, using different confining effects (twisting moments on the steel bolts). Test results indicated that the ultimate pullout strength increases and the failure mode switches from debonding to FRP rupture as the twisting moment increases. Moreover, by comparison to three series of experimental results, the proposed model can precisely predict failure mode, ultimate strength, load-slip relation and bond stress distribution. The twisting moment on bolts is found to have the most significant improvement on the ultimate tensile strength. Finally, the critical twisting moment without yielding FRP rupture is derived.

Effect of pedicle screw diameter on screw fixation efficacy in human osteoporotic thoracic vertebrae

The selection of an ideal screw size plays a crucial role in the success of spinal instrumentation as larger diameter screws are thought to provide better fixation strength but increase the risk of pedicle failure during insertion. On the other hand, smaller diameter screws are with lesser risk of pedicle breakage but are thought to compromise the stability of the instrumentation. By investigating the relationship between screw diameter and the pullout strength of pedicle screws after fatigue loading, this study seeks to find quantitative biomechanical data for surgeons in determining the most ideal diameter size screws when performing surgical implementations on osteoporotic vertebrae.Twenty-seven osteoporotic (BMD ranged: 0.353–0.848 g/cm2) thoracic vertebrae (T3-T8) were harvested from 5 human cadavers. Two sizes of poly-axial screws (5.0 mm × 35 and 4.35 mm × 35) were implanted into each pedicles of the vertebrae by an experienced surgeon. Specimens were randomly distributed into control group, fatigue group of 5000 and 10,000 cycles with peak-to-peak loadings of 10–100 N at 1 Hz. Each specimen was then axial pullout tested at a constant rate of 5 mm/min. The ultimate pullout strength (N) & stiffness (N/mm) were obtained for analysis.The results showed that although the larger diameter screws achieved superior pullout strength immediately after the implantation, both sizes of screws exhibited comparable pullout strengths post fatigue loading. This indicates that the smaller diameter screws may be considered for surgical techniques performed on osteoporotic vertebrae for reduced risk of pedicle breakage without sacrificing fixation strength.

A Combination of a Polycaprolactone Fumarate Scaffold with Polyethylene Terephthalate Sutures for Intra-Articular Ligament Regeneration.

Intra-articular ligamentous injuries are typically unrepairable and have limited outcomes after graft reconstruction. A combination of porous polycaprolactone fumarate (PCLF) scaffolds with polyethylene terephthalate (PET) sutures was developed with the goal of regenerating intra-articular ligaments. Scaffolds were fabricated by injecting PCLF over three-dimensional-printed molds containing two strands of PET suture down its central pore followed by cross-linking. Scaffolds were seeded with human mesenchymal stem cells (MSCs) from adipose tissue. To demonstrate cell attachment and proliferation in culture, we performed live/dead staining and cell proliferation assays. These experiments showed that MSCs remain viable and continue to proliferate on the scaffolds in culture for at least 2 weeks. Bare scaffolds were then used to reconstruct the rabbit anterior-cruciate ligament (ACL), while control rabbits underwent semitendinosus autograft reconstruction. The specimens underwent micro-computed tomography (CT) imaging, histological examination, and biomechanical testing at 8 weeks. The ultimate pull-out strength of the PCLF-PET scaffolds and tendon autografts was initially 72 ± 30 N and to 45 ± 10 N, respectively (p < 0.06). On inspection after 8 weeks in vivo, the intra-articular portion of the PCLF-PET scaffolds was fragmented while the tendon autografts remained intact. Cross-sectional areas of bone tunnels in the PCLF-PET scaffolds (11.3 ± 1 mm2) were enlarged compared to tendon autografts (3.8 ± 0.5 mm2) (p < 0.004) as measured by micro-CT. These studies show that PET-reinforced PCLF scaffolds are capable of initial ACL reconstruction and supports stem cell growth. The intra-articular portion of the scaffold may need to be re-engineered to support their use in ligament regeneration.

Evaluation of Load Transfer in Geogrids for Base Stabilization Using Transparent Soil

The design of roadways with geosynthetic-stabilized base layers requires proper evaluation of the load-transfer mechanisms between soil particles and geosynthetics. In the case of geogrid reinforcements, the resistances mobilized on rib elements are key factors that determine the mechanical responses for both: (1) the ultimate pullout strength; and (2) the in-plane stiffness. Geogrids with different aperture shapes have rib elements along different orientations, and different rib orientations could generate different load transfer mechanisms. In this study, a new experimental testing program using transparent soil was conducted to visualize the load transfer of geogrids with different aperture shapes (e.g. rectangular, triangular). Specifically, small-scale soil-geosynthetic interaction tests were conducted using high-definition cameras. Consequently, image-processing techniques were used to obtain the displacements and deformations of geogrid specimens from digital images. The soil-geogrid interaction behaviors for geogrid specimens with different aperture shapes were evaluated and compared. Overall, multiple mechanisms for load transfer between soil and geogrids with different geometric characteristics could be characterized and quantified using new techniques involving transparent soil and digital image analysis.

Statistical analysis of the effective stress method and modifications for prediction of ultimate bond strength of soil nails

Uncertainty in the predicted ultimate pullout strength of soil nails can be significant due to the complexity of nail–soil interactions, inherent variability in soil properties and the effects of nail installation. The paper first presents a statistical evaluation of the accuracy of ultimate bond strength of soil nails using the effective stress method (ESM) equation that has been adopted in Hong Kong. A total of 113 ultimate nail capacity data points from field pullout tests were collected from the literature and used to estimate the accuracy of the current ESM. Based on the available data, the current ESM default pullout model is found to be excessively conservative (on average) by at least a factor of three. The spread in prediction accuracy measured by the coefficient of variation (COV) of bias is in the range of 36–43 % after removing anomalous test data. Here, bias is the ratio of measured to predicted pullout load capacity. In addition, the accuracy of the current ESM equation for prediction of nail bond strength is shown to be dependent on the magnitude of predicted ultimate bond strength and magnitude of nominal vertical effective stress which is undesirable. The paper examines four candidate-modified bond strength equations with empirical coefficients that have been back-fitted to measured bond strengths to improve the overall accuracy of the equation and to reduce or remove the undesirable dependencies noted above. One equation with an empirically corrected stress-dependent term is judged to be the best candidate model based on the mean of bias values, spread (COV) of bias values, lack of dependencies and simplicity. Finally, the relative contributions of random variability in soil shear strength to measurement bias in bond strength (prediction accuracy) for each soil type are computed for the best bond strength model. Analysis of the contribution of soil shear strength to prediction accuracy showed that the combination of variability due to factors other than soil shear strength was greater than the variability in soil shear strength alone, where the latter is defined by the soil secant friction coefficient.

Glucosamine-chondroitin sulphate accelerates tendon-to-bone healing in rabbits.

This study aims to investigate the contribution of glucosamine-chondroitin sulphate (GlcN-CS) to the healing of tendons within the bone tunnel. Tendon-to-bone healing was investigated in 28 New Zealand rabbits by re-attaching the extensor digitorum longus tendon into bone tunnel which was created in the proximal tibia. Rabbits were separated into two groups as treatment and control groups. Treatment group (n=14) received 210-250 mg/kg/day glucosamine sulphate and 170-200 mg/kg/day chondroitin sulphate, whereas control group (n=14) received equivalent dose of vehicle. Treatment and control groups were compared at sixth and 12th week after the procedure according to histological and biomechanical analysis. Yamakado scoring system was used to evaluate the histological changes. According to histological analysis, scores were significantly higher at both sixth and 12th week evaluations in the treatment group (p=0.029). Although not statistically significant, the ultimate pullout strength was higher in the treatment group at the 12th week evaluation (35.3 N/mm2 vs. 24.3 N/mm2) (p>0.05). However, stripping occurred at the muscle-tendon junction in the treatment group whereas tendons stripped from the bone tunnels in the control group. While no tendons in the treatment group stripped from the bone tunnels, we observed at sixth and 12th week evaluations that tendons in the control group stripped from the tunnels. Glucosamine-chondroitin sulphate treatment enhances tendon-to-bone healing by increasing hyaline cartilage formation and decreasing formation of capillary vessels.

The First Shot is Your Best Shot! Detrimental Biomechanical Effects of Revising Suboptimally Placed Pedicle Screws

everal factors affect the ultimate pullout strength of a pedicle screw. Features inherent to the screw design (its S format—conical or cylindrical, its thread width and pitch length, as well as its outer and inner diameter, just to mention a few) have a strong influence upon the distribution of forces on the metal/bone interface and, therefore, upon the overall pullout strength of the screw (Figure 1). As a general rule, a larger outer diameter (the most important factor), a smaller inner diameter, and a shorter pitch interval, by increasing the total contact area between the bone and the screw, improve its overall pullout strength (4). However, it has already been demonstrated that in osteoporotic patients a screw with larger diameter may not necessarily increase its ultimate pullout strength, and may even result in increased rates of pedicle fractures, as the outer cortex of osteoporotic pedicles has been shown to be significantly thinner than those of normal vertebrae (8).

The Effect of Insertion Angle on the Pullout Strength of Threaded Suture Anchors: A Validation of the Deadman Theory

To determine the effect of insertion angle, from 45° to 135° in 15° increments, on the number of cycles withstood, the ultimate pullout strength, and the stiffness of threaded suture anchors subjected to load. Threaded anchors were inserted into polyurethane foam at angles from 45° to 135°, in 15° increments, relative to the direction of pull. Five anchors were tested at each angle. The anchors were first cycled for 30 cycles (10 each at 100 N, 150 N, and 200 N). The surviving specimens were then tensioned to failure. The McNemar test was used to compare cyclic failure rates. Paired-samples t tests were used to compare load-to-failure (LTF) and stiffness data. All P values are multiplicity adjusted by the Hommel procedure. Four of 5 anchors inserted at 45° failed during cyclic testing at a mean of 27 cycles (P= .13). One of 5 anchors placed at 60° failed after 29 cycles (P= .99). All other anchors survived cyclic testing. Mean LTF was 234 N, 243 N, 297 N, 373 N, 409 N, 439 N, and 417 N at insertion angles of 45°, 60°, 75°, 90°, 105°, 120°, and 135°, respectively. LTF was significantly less for the 60° group when compared with the 90°, 105°, 120°, and 135° groups (P < .05). LTF was significantly less for the 75° group when compared with the 105°, 120°, and 135° groups (P < .05). For the 90° group, LTF was only significantly less when compared with the 135° group (P= .022). Thedifferences in LTF between the 105°, 120°, and 135° groups were not significant. Stiffness increased from 28.13 N/mm at 90° to 43.4 N/mm at 105° (P= .03), 61.48 N/mm at 120° (P= .003), and 86.83 N/mm at 135° (P= .008). Anchors placed at more acute angles, that is, anchors placed closer to the so-called deadman's angle, failed at lower loads and provided less construct stiffness than anchors placed at angles greater than 90°. Stiffness also increased sequentially from an angle of insertion of 90° up to our maximum angle tested of 135°. For threaded metallic suture anchors, an obtuse insertion angle of 90° to 135° in relation to the line of pull of the suture and rotator cuff withstands a greater LTF and provides a stiffer construct than the more acute insertion angle advocated by the "deadman theory." This study offers a biomechanical validation for optimal placement of threaded suture anchors at an angle of 90° or more, as anatomic restraints allow, from the vector of pull of the attached suture and rotator cuff, rather than the 45° angle recommended by the deadman theory.

Strength and Creep Characteristics of Reclaimed Asphalt Pavement–Sand Blend Backfill in Mechanically Stabilized Earth Walls

Using reclaimed asphalt pavement (RAP) as a backfill for mechanically stabilized earth (MSE) walls provides both environmental and economic benefits by allowing in situ recycling for road widening projects. RAP, a well-drained granular material, has lower reinforcing strip pullout strength than A-3 sand and creeps under constant load. The objective of this research was to determine whether blending RAP with A-3 sand would improve RAP's performance in MSE applications. Laboratory specimens of 100% RAP, 100% A-3 sand, and 50% RAP–50% sand blends were compacted by the modified Proctor method and tested for vertical creep with one-dimensional oedometer compression tests at three stress levels to simulate different depths behind an MSE wall. Large-scale test pit testing was performed to determine reinforcing strip ultimate lateral pullout strength; pullout creep at 25%, 50%, and 75% of ultimate pullout; and vertical creep at the three overburden stress levels used in laboratory testing. RAP–sand blends had higher density, friction factors, and pullout strength and developed ultimate pullout strength at lower displacements than either 100% sand or 100% RAP. The RAP–sand blends exhibited more horizontal and vertical creep than 100% sand but significantly less creep than 100% RAP.

The Strength and Effects of Humeral Rotation on Single-Versus Double-Row Repair Techniques in Small Rotator Cuff Tears

With advanced surgical techniques, instrumentation, and implants, arthroscopic rotator cuff repair has become increasingly popular. As the techniques continue to evolve, so do the methods by which the repairs are tested. Cyclic loading has shown to better replicate postoperative motion after cuff repair. Recently, cyclic loading with dynamic external rotation has been studied for large rotator cuff repairs. Our study applies this concept to small, isolated supraspinatus tears, comparing single- vs double-row repair techniques. A 1.5-cm rotator cuff tear was created in cadaveric specimens and repaired with single-and double-row repair techniques. With cyclic loading and dynamic external rotation, gap formation and ultimate pullout strength were determined and found to be equivalent. This study demonstrates no significant difference in single- vs double-row repairs for small, isolated supraspinatus tears when tested with cyclic loading and dynamic external rotation.

Holding power of variable pitch screws in osteoporotic, osteopenic and normal bone: Are all screws created equal?

Introduction Biomechanical properties of four different commercially available small fragment cannulated screws (Twin fix (Stryker, Freiburg, Germany), Herbert, (Zimmer, Warsaw, USA), Omnitech (Unimedical, Torino, Italy), Barouk (Depuy, Warsaw, USA)), with variable pitch, used for fracture fixation were compared. Materials and methods Polyurethane foam blocks of three different densities with mechanical properties similar to osteoporotic, osteopenic and normal bones were used to conduct the tests. Each screw was tested for pushout and pullout holding power after a primary insertion and for pullout after a repeated insertion into the respective foam blocks. Results The mean pullout and pushout strengths of all screws correlated to the foam density, and were significantly ( p < 0.001 and <0.001, respectively) better in foam with higher density. The mean pullout strength of each screw was consistently lower after reinsertion into the osteoporotic, osteopenic and normal bone densities by 4–30%, when compared to the index insertion (Fig. 4b). Yet, this difference was not found to be statistically significant ( p = 0.23). The Barouk screw performed significantly ( p < 0.0001) better than the other screws in all three different densities of foam for both for pushout and pullout after index insertion as well as for pullout tests after reinsertion. Conclusion The holding power of screws is directly correlated to bone density, thread design and number of threads engaging the bone. Reinsertion through the same hole could reduce the ultimate pullout strength. The surgeon should consider the advantages and disadvantages of each implant, depending on the clinical situation and choose accordingly.

Pullout strength for cannulated pedicle screws with bone cement augmentation in severely osteoporotic bone: Influences of radial hole and pilot hole tapping

Background Pedicle screw fixation in a severely osteoporotic spine remains a challenge for orthopedic surgeons. The previous literature does not adequately address the effects of radial holes for cannulated screws with cement injection and pilot hole tapping on the bone/screw interfacial strength. Methods Specially designed cannulated pedicle screws, with or without radial holes, were installed in tapped and untapped pilot holes and then injected with cement. A uniform synthetic bone (test block) was used to provide a platform for each screw design. Specimens with inserted screws were then tested for axial pullout failure. Findings (1) Cannulated screws with cement augmentation significantly increased the pullout strength in comparison to solid screws. Additionally, the amount of cement exuded from the cannulated screws increased with an increasing number of radial holes, leading to an increase in the average ultimate pullout strength for cannulated screws with a large number of radial holes. (2) Radiological examination indicated that the cement was exuded from the most proximal holes at the very beginning of its flow path, whereas no cement exudation was found at the remaining distal holes. (3) Cement exudation from the holes of cannulated screws into the open cell of the test block led to a composite (cement/bone) structure at the area of cement exudation. Observations of the failed specimens indicated that failure occurred at the composite/bone interface, while the composite was well bonded to the screws. This implies that the screw/composite interfacial strength was much higher than the composite/bone interfacial strength. (4) Tapping pilot holes decreased the pullout strength of the screws. Generally, larger standard deviations were found for the tapped cases, implying that untapped cases results are more repeatable than tapped cases results. Interpretation Cannulated pedicle screws with radial holes combined with PMMA cement augmentation but without tapping may be a viable clinical option for achieving fixation in severely osteoporotic bone.

Cervical anterior transpedicular screw fixation (ATPS)—Part II. Accuracy of manual insertion and pull-out strength of ATPS

Reconstruction after multilevel decompression of the cervical spine, especially in the weakened osteoporotic, neoplastic or infectious spine often requires circumferential stabilization and fusion. To avoid the additional posterior surgery in these cases while increasing rigidity of anterior-only screw-plate constructs, the authors introduce the concept of anterior transpedicular screw (ATPS) fixation. We demonstrated its morphological feasibility as well as its indications in a previous study in Part I of our project. Consequently, the objectives of the current study were to assess the ex vivo accuracy of placing ATPS into the cervical vertebra as well as the biomechanical performance of ATPS in comparison to traditional vertebral body screws (VBS) in terms of pull-out strength (POS). Twenty-three ATPS were inserted alternately to two screws into the pedicles and vertebral bodies, respectively, of six cadaveric specimens from C3-T1. For insertion of ATPS, a manual fluoroscopically assisted technique was used. Pre- and post insertional CT-scans were used to assess accuracy of ATPS insertion in the axial and sagittal planes. A newly designed grading system and accuracy score were used to delineate accuracy of ATPS insertion. Following insertion of screws, 23 ATPS and 22 VBS were subjected to pull-out testing (POT). The bone mineral density (BMD) of each specimen was assessed prior to POT. Statistical analysis showed that the incidence of correctly placed screws and non-critical pedicles breaches in axial plane was 78.3%, and 95.7% in sagittal plane. Hence, according to our definition of "critical" pedicle breach that exposes neurovascular structures at risk, 21.7% (n = 5) of all ATPS inserted showed a critical pedicle breach in axial plane. Notably, no critical pedicle perforation occurred at the C6 to T1 levels. Pull-out testing of ATPS and VBS revealed that pull-out resistance of ATPS was 2.5-fold that of VBS. Mean POS of 23 ATPS with a mean BMD of 0.566 g/cm(2) and a mean osseus screw purchase of 27.2 mm was 467.8 N. In comparison, POS of 22 VBS screws with a mean BMD of 0.533 g/cm(2) and a mean osseus screw purchase of 16.0 mm was 181.6 N. The difference in ultimate pull-out strength between the ATPS and VBS group was significant (p < 0.000001). Also, accuracy of ATPS placement in axial plane was shown to be significantly correlated with POS. In contrast, there was no correlation between screw-length, BMD, or level of insertion and the POS of ATPS or VBS. The study demonstrated that the use of ATPS might be a new technique worthy of further investigation. The use of ATPS shows the potential to increase construct rigidity in terms of screw-plate pull-out resistance. It might diminish construct failures during anterior-only reconstructions of the highly unstable decompressed cervical spine.

Evaluation of Tendon Graft Fixation Using α-BSM Calcium Phosphate Cement

Many ligament reconstruction procedures require tendon healing within a surgically prepared bone tunnel. The interface between the graft and tunnel wall is the "weak link" in the initial phase of this process. By providing additional fixation and serving as a carrier for bone-derived growth factors, calcium phosphate cements may augment healing. The purpose of this study was to evaluate alpha-BSM calcium phosphate cement as the sole method of fixation for tendon and bone-tendon-bone grafts in an in vitro porcine model. Ten tendon grafts and ten bone-tendon-bone grafts were fixed within porcine femoral and tibial bone tunnels by use of alpha-BSM calcium phosphate cement. The grafts were then loaded to failure. The ultimate pullout strength and the site of failure were recorded for each specimen. The bone-tendon-bone grafts achieved a mean pullout strength of 224.8 N (+/-79.9 N). Of the grafts, 6 failed at the cement-bone plug interface, 2 failed because of fracture of the bone plug, and 2 failed at the tendon-bone plug interface. The tendon grafts had a mean load to failure of 81.2 N (+/-23.7 N), and all 10 failed at the tendon-cement interface. The difference in fixation strength between these graft types was significant (P < .05). Though inadequate as the sole means of graft fixation, alpha-BSM calcium phosphate cement can help to augment bone plug fixation during the early phase of tendon-bone healing. In addition, alpha-BSM may provide added graft fixation and increased stiffness and act as a growth factor carrier for both tendon grafts and bone-tendon-bone grafts in ligament reconstruction surgery. This study evaluated the ability of alpha-BSM cement to augment tendon-bone healing because it may play a role as a growth factor carrier in future tendon healing models.