Significant Difference In Failure Load Research Articles

Medial Patellofemoral Ligament Augmented With a Reinforced Bioinductive Implant Is Biomechanically Similar to the Native Medial Patellofemoral Ligament at Time Zero in a Cadaveric Model

To biomechanically compare primary medial patellofemoral ligament (MPFL) repair (MPFLr) augmented with a reinforced bioinductive implant (RBI) to the native MPFL ligament and a semitendinosus (semi-T) MPFL reconstruction (MPFLR) at time zero. Four fresh-frozen matched pair cadavers (8 knees) were used to biomechanically compare the native MPFL to augmented MPFLr (n= 4) and semi-T MPFLR (n= 4). The native MPFL (n= 8) was isolated, preserving the femoral and patellar attachments, and pulled to failure. The semi-T was harvested from 1 of the matched pairs and whipstitched, as was a 250-mm× 5-mm RBI. A standard double-bundle docking technique was utilized. The patella was potted and mechanically pulled parallel to the transverse axis until failure in both cohorts. Cyclic creep, load and displacement at failure, failure mode, and stiffness were recorded. Failure load was highest in the RBI with repair group (287 ± 130 N) compared to the native MPFL (219 ± 64 N) and the semi-T group (84 ± 29 N). No statistically significant difference in failure load between the RBI augmentation with repair group and the native ligament (P= .19) were found. The semi-T reconstruction group failed at the least amount of displacement (7.93 ± 3.4 mm) compared to the native MPFL (20.9 ± 9 mm) (P < .01) and the RBI with repair group (33.2 ± 17.7 mm) (P < .02). At 10 mm of displacement, the RBI group (8.3 ± 1.2 N/mm) demonstrated stiffness in the midrange compared to the native MPFL (14.1 ± 7.1 N/mm). Early anchor/tendon pullout failure on the patella side was noted in the semi-T group compared to the RBI group. One reconstruction was excluded from analysis due to poor bone quality. No statistically significant difference was seen between the augmented MPFL repair and the native MPFL in load-to-failure testing. The augmented MPFL repair was observed to have biomechanical properties similar to the native MPFL. MPFLr with RBI augmentation provided consistent stiffness at clinically relevant displacement. Primary MPFL repair and reconstruction using the semi-T graft, while effective, are nevertheless imperfect procedures. MPFL repair has been shown to have higher instability recurrence rates, while the stiffness profile of MPFLR with semi-T is higher than the native MFPL and may lead to knee stiffness, loss of motion, or cartilage damage. The results of this time-zero biomechanical study indicate that the use of an RBI for augmentation of a primary MPFL repair may be a viable alternative to traditional MPFL repair or reconstruction using a semi-T graft.

The effect of number of knots per throw, knot technique, and suture type on strength properties of suspensory fixation button surgical procedures

Previous studies of the cortical suspensory button (CSB) implant have analyzed fixation strength as a function of suture type and surgical technique, but knot configuration remains an area of interest. This study investigates 4-strand knot configurations in CSB suspensory fixation, specifically comparing the use of 2 separate knots with a single knot. We hypothesize that using 2 knots on the distal side of the CSB with #2 suture will yield the strongest and stiffest suspensory fixation. Two types of knot configurations were compared: a single knot with all 4 suture strands versus 2 independent knots with 2 suture strands each (1 knot from inner strands and 1 knot from outer strands). They were tested using #2 or 2-0 suture, and at distal (on top of the button) or proximal (underneath the button) knot positions. Mechanical testing on the Instron measured ultimate failure load, elongation at failure, and stiffness. Statistical analyses (Shapiro-Wilk, unpaired Student's t-tests, and Chi-square tests) assessed differences in strength, stiffness, elongation, and failure mode between knot configurations within each CSB construct combination. With #2 suture, 2 knots across the CSB resulted in higher load to failure compared to 1 knot in both proximal (467.00 N vs. 554.66 N, P= .026) and distal (395.18 N vs. 526.51 N, P < .001) locations. Furthermore, 2 knots provided higher stiffness than 1 knot in both proximal (53.24 N/mm vs. 67.89 N/mm, P < .001) and distal (47.08 N/mm vs. 56.73 N/mm, P= .041) knot locations. However, using 2-0 suture showed no significant differences in failure load and stiffness regardless of knot location. Using #2 suture and tying 2 independent knots across the CSB increased load to failure and stiffness compared to using only 1 knot regardless of knot position. Thus, if using #2 suture, it is recommended to tie 2 knots to enhance construct strength. However, with 2-0 suture, the number of knots did not impact construct strength. Therefore, if using 2-0 suture, 1 knot can be used to save time. Knot position did not significantly affect the strength or stiffness of the CSB construct, emphasizing the importance of considering knot prominence and surgical approach for determining knot location.

Novel bisphosphonate-based cathepsin K-triggered compound targets the enthesis without impairing soft tissue-to-bone healing.

Background: Osteoadsorptive fluorogenic sentinel 3 (OFS-3) is a recently described compound that contains a bone-targeting bisphosphonate (BP) and cathepsin K (Ctsk)-triggered fluorescence signal. A prior study in a murine Achilles repair model demonstrated its effectiveness at targeting the site of tendon-to-bone repair, but the intrinsic effect of this novel bisphosphonate chaperone on tendon-to-bone healing has not been previously explored. We hypothesized that application of this bisphosphonate-fluorophore cargo conjugate would not affect the biomechanical properties or histologic appearance of tendon-bone repairs. Materials and Methods: Right hindlimb Achilles tendon-to-bone repair was performed on 12-week old male mice. Animals were divided into 2 groups of 18 each: 1) Achilles repair with OFS-3 applied directly to the repair site prior to closure, and 2) Achilles repair with saline applied prior to closure. Repaired hindlimbs from 12 animals per group were harvested at 6 weeks for biomechanical analysis with a custom 3D-printed jig. At 4 and 6 weeks, repaired hindlimbs from the remaining animals were assessed histologically using H&E, immunohistochemistry (IHC) staining for the presence of Ctsk, and second harmonic generation (SHG) imaging to evaluate collagen fibers. Results: At 6 weeks, there was no significant difference in failure load, stiffness, toughness, or displacement to failure between repaired hindlimbs that received OFS-3 versus saline. There was no difference in tissue healing on H&E or Ctsk staining on immunohistochemistry between animals that received OFS-3 versus saline. Finally, second harmonic generation imaging demonstrated no difference in collagen fiber parameters between the two groups. Conclusion: OFS-3 did not significantly affect the biomechanical properties or histologic appearance of murine Achilles tendon-to-bone repairs. This study demonstrates that OFS-3 can target the site of tendon-to-bone repair without causing intrinsic negative effects on healing. Further development of this drug delivery platform to target growth factors to the site of tendon-bone repair is warranted.

Biomechanical analysis of two medial buttress plate fixation methods to treat Pauwels type III femoral neck fractures

BackgroundFemoral neck fractures in young people are usually Pauwels Type III fractures. The common treatment method are multiple parallel cannulated screws or dynamic hip screw sliding compression fixation. Due to the huge shear stress, the rate of complications such as femoral head necrosis and nonunion is still high after treatment. The aim of our study was to compare the stabilities of two fixation methods in fixating pauwels type III femoral neck fractures.MethodsAll biomimetic fracture samples are fixed with three cannulated screws combined with a medial buttress plate. There were two fixation groups for the buttress plate and proximal fracture fragment: Group A, long screw (40 mm); Group B, short screw (6 mm). Samples were subjected to electrical strain measurement under a load of 500 N, axial stiffness was measured, and then the samples were axially loaded until failure. More than 5 mm of displacement or synthetic bone fracture was considered as construct failure.ResultsThere were no significant differences in failure load (P = 0.669), stiffness (P = 0.842), or strain distribution (P > 0.05) between the two groups.ConclusionsUnicortical short screws can provide the same stability as long screws for Pauwels Type III Femoral Neck Fractures.

Fixation of intraoperative proximal femoral fractures during THA using two versus three cerclage wires - a biomechanical study

BackgroundIntraoperative proximal femoral fractures (IPFF) are relevant complications during total hip arthroplasty. Fixation using cerclage wires (CW) represents a minimally-invasive technique to address these fractures through the same surgical approach. The goal of treatment is to mobilise the patient as early as possible, which requires high primary stability. This study aimed to compare different cerclage wire configurations fixing IPFF with regard to biomechanical primary stability.MethodsStandardised IPFF (type II, Modified Mallory Classification) were created in human fresh frozen femora and were fixed either by two or three CW (1.6 mm, stainless steel). All cadaveric specimens (n = 42) were randomised to different groups (quasi-static, dynamic) or subgroups (2 CW, 3 CW) stratified by bone mineral density determined by Dual Energy X-ray Absorptiometry. Using a biomechanical testing setup, quasi-static and dynamic cyclic failure tests were carried out. Cyclic loading started from 200 N to 500 N at 1 Hz with increasing peak load by 250 N every 100 cycles until failure occurred or maximum load (5250 N) reached. The change of fracture gap size was optically captured.ResultsNo significant differences in failure load after quasi-static (p = 0.701) or dynamic cyclic loading (p = 0.132) were found between the experimental groups. In the quasi-static load testing, all constructs resisted 250% of the body weight (BW) of their corresponding body donor. In the dynamic cyclic load testing, all but one construct (treated by 3 CW) resisted 250% BW.ConclusionsBased on this in vitro data, both two and three CW provided sufficient primary stability according to the predefined minimum failure load (250% BW) to resist. The authors recommend the treatment using two CW because it reduces the risk of vascular injury and shortens procedure time.

Effects of Veneering Ceramic and Methods on Failure Load of Veneered Zirconia

Background: A variety of veneering options to zirconia frameworks are now available. The purpose of this study is to evaluate the effect of veneer materials, veneering methods, cement materials, and aging on the failure load of bilayered veneer zirconia. Material and methods: Zirconia bars (20 × 4 × 1 mm) were veneered to 2 mm total thickness (n = 10/group). Veneering method groups included: 1. Hand-layered feldsparthic porcelain (VM = Vita VM9, Vident) and fluorapatite glass–ceramic (CR = IPS e.max Ceram, IvoclarVivadent); 2. Pressed feldspathic porcelain (PM = Vita PM9, Vident) and fluorapatite glass–ceramic (ZP = IPS e.max ZirPress, IvoclarVivadent); 3. CAD-/CAM-milled feldspathic ceramic (TF = Vitablocs Triluxe Forte, Vident) and lithium-disilicate glass–ceramic (CAD = IPS e.max CAD, IvoclarVivadent). CAD/CAM veneers were either cemented with resin cements (P = Panavia21, KurarayDental), (R = RelyX Ultimate, 3M ESPE), (M = Multilink Automix, Ivoclar Vivadent) or fused with fusion glass–ceramic (C = CrystalConnect, IvoclarVivadent). A three-point bending test (15 mm span, zirconia on tension side) was performed on Instron universal testing machine (ISO 6872) recording load-to-failure (LTF) of first veneer cracks or catastrophic failure. For group VM, PM, TF-M, TF-C, CAD-M, CAD-C, ten more bars were prepared and aged with cyclic loading (100,000 cycles, 50% LTF) and thermocycling (2000 cycles) before testing. Data were analyzed by ANOVA, Tukey HSD post hoc tests, and t-test (α = 0.05). Zirconia veneered with IPS e.max CAD by fusing had significantly higher failure load compared with zirconia veneered with other veneering materials (p ≤ 0.05). For cemented veneers, the cement type had a significant effect on the failure load of the veneer zirconia specimens. Specimens cemented with Panavia 21 had a lower resistance to loading than other cements. The aging experiment revealed a significant difference in failure load between non-aged and aged bars in groups VM and PM, but not in the groups with CAD-/CAM-milled veneers. In conclusion, veneer materials, veneering methods, and cement materials have a significant effect on the failure load of bilayered veneer zirconia. CAD-/CAM-milled veneer zirconia is not susceptible to aging performed in this study.

Does skin preparation alter suture strength characteristics? Assessing the effect of chlorhexidine and isopropyl alcohol on common skin closure suture material.

Sutures are essential to approximate tissues and enable healing by first intention until a wound regains its original tensile strength. The mechanical properties of sutures are well documented, but the effects of exposing sutures to skin preparation solutions used in surgery are not. This study was performed to investigate whether 2% chlorhexidine and 70% isopropyl alcohol skin preparation, commonly used prior to incision and prior to closure, has any effect on the mechanical properties of several commonly used surgical suture types. Four suture types were soaked in either 2% chlorhexidine and 70% isopropyl alcohol or Hartmann's solution for 5 minutes. All sutures were left to dry for 11 days before being tested to failure using an Instron 3367 tensile testing machine. Testing revealed significant differences in failure load, ultimate tensile stress, and Young's modulus between suture types (P < .05). No significant differences in failure load (P = .98), ultimate tensile stress (P = .21), or Young's modulus (P = .22) were observed between the test group and the control group when comparing sutures of the same type. This study demonstrates that chlorhexidine/isopropyl skin preparation solutions do not significantly change the mechanical properties of suture materials exposed to them.

Unicortical Versus Bicortical Button Fixation For Distal Biceps Brachii Tendon Rupture: A Cadaveric Biomechanical Study

Objectives: Acute distal biceps tendon rupture is an increasingly common and more recognized injury affecting active adults. Operative repair is the preferred treatment, particularly for restoration of elbow function and strength. No prior study has biomechanically compared unicortical versus bicortical distal biceps button fixation under cyclic loading, which is most representative of postoperative physiologic conditions. We hypothesized there would be no difference in loss of force, tendon gap formation, or ultimate failure load following cyclic loading between unicortical and bicortical button techniques for the repair of distal biceps tendon rupture. Methods: Experimental testing with 13 fresh-frozen matched paired cadaver elbows was conducted. One specimen from each pair was randomized to either unicortical or bicortical distal biceps button fixation techniques, with contralateral specimen assigned to the alternate technique. In both arms of the experiment, the distal 2.5 cm of the biceps tendon was whipstitched and the free suture ends threaded in opposite directions through a 2.6 x 12 mm titanium cortical button. A 3.2 mm guide pin was drilled through the central aspect of the radial tuberosity from anterior to posterior, aiming approximately 20° in the ulnar direction. The button was inserted and deployed for either unicortical or bicortical fixation and the free suture limbs tensioned to advance tendon down to bone for final fixation. Loading was performed using an MTS servohydraulic actuator. A 25-N distal biceps preload was applied and each specimen cycled from full extension to 90° of flexion at 0.5 Hz for 3000 cycles using a displacement controlled protocol. All specimens were subsequently loaded to failure at 2 mm/s to simulate an acute postoperative load. Outcome measures were a loss of force from cycle 5 to cycle 3000, tendon gapping during cyclic loading, and ultimate failure load. Results: During cyclic loading, the mean change in force from cycle 5 to cycle 3000 was -0.33 N for the unicortical fixation group and 0.36 N for the bicortical fixation group (p=0.21). The increase in tendon gap for the unicortical fixation group was 1.02 mm and for the bicortical fixation group was 1.83 mm (p=0.37). During failure loading, the unicortical button fixation group had a mean failure load of 170.45 N and the bicortical button fixation group a mean failure load of 181.25 N (p=0.89). Conclusion: No significant differences exist between the two techniques in loss of force and tendon gap formation under cyclic loading conditions. This indicates that both unicortical and bicortical distal biceps button techniques maintained an equivalent stabilization during a simulated 3 month postoperative healing period. Additionally, there was no significant difference in failure load between the two groups indicating an equivalent response in the event of an acute injury. Clinical Relevance: Distal biceps button fixation strength and tendon gap behavior under physiologic cyclic load support the implementation of early postoperative elbow range of motion, imperative in the prevention of elbow stiffness. Unicortical fixation may be sufficient in facilitating optimal bone-tendon apposition and healing, while minimizing risk of iatrogenic injury associated with bicortical fixation.

Bone block augmentation from the iliac crest for treatment of deep osteochondral defects of the knee resembles biomechanical properties of the subchondral bone.

Bone block augmentation from the iliac crest can be used for reconstruction of the osteochondral unit to restore the underlying subchondral bone upon restoration of the cartilaginous layer via matrix-induced chondrocyte transplantation. To critically understand the successful restoration of the defect, biomechanical and histological analysis of the implanted bone blocks is required. The aim of the study was to analyse the ability of the bone block technique to restore huge bone defects by mimicking the physiological subchondral zone. The experiments were performed using lateral femoral condyles and iliac crest bone grafts from the same cadavers (n = 6) preserved using the Thiel method. CT scans were made to evaluate bone pathology. Bone mineral density of all specimens was evaluated in the femoral head prior to testing. A series of tests were conducted for each pair of specimens. A static compression test was performed using an electro dynamic testing machine with maximal strength and failure behavior analyzed. Biomechanical tests were performed in the medial-lateral direction for iliac crest and for femoral condyles with and without removal of the cartilage layer. Histological analysis was performed on decalcified specimens for comparison of the condyle at lesion site and the graft. No significant difference in failure load could be found for iliac crest (53.3-180.5N) and femoral condyle samples upon cartilage removal (38.5-175.1N) (n.s.). The femoral condyles with an intact cartilage layer showed significantly higher loads (118.3-260.4N) compared to the other groups indicating that native or regenerated cartilage can further increase the failure load (p < 0.05). Bone mineral density significantly influenced failure load in all study groups (p < 0.05). Histological similarity of the cancellous bone in the femoral condyle and in the iliac crest was observed. However, within the subchondral zone, there was a higher density of sponge like organized trabeculae in the bone samples from the iliac crest. Tide mark was only detected at the osteochondral interface in femoral condyles. This study demonstrated that, bone blocks derived from the iliac crest allow a biomechanical appropriate and stable restoration of huge bony defects by resembling the subchondral zone of the femoral condyle. Therefore, bone augmentation from the iliac crest combined with matrix-induced autologous chondrocyte transplantation seems to be a reasonable method to treat these challenging injuries.

Fracture Strength and Retention of All-Ceramic Endocrowns Luted Using Two Different Resin Cements

Purpose: The purpose of this in vitro study was to evaluate and compare the fracture resistance and retention of CAD/CAM endocrowns and conventional glass fiber post supported crowns. Materials and Methods: Sixty-four (N=64) sound mandibular molars were endodontically treated and randomly assigned into 2 groups (n=32 each) according to the type of restoration constructed; Group (E): Endodontically treated teeth restored with IPS e.max CAD, lithium disilicate based, endocrowns and Group (P): Endodontically treated teeth restored with glass-fiber posts, composite cores and IPS e. max CAD crowns. Samples of each group were further subdivided into 2 subgroups (n=16 each) according to the type of adhesive resin cement used. the samples were thermocycled (2000 cycle, between 5oC-55oC). Samples were mountedin a universal testing machine and loaded to failure at a crosshead speed of 1.0 mm / min. The failure loads were recorded. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey’s post hoc significance difference tests. Differences were considered significant at P<0.05. The pull-out test was performed on a universal testing machine and the values obtained were statistically analyzed by analysis of variance using one-way analysis of variance (ANOVA)) and multiple comparison test of Tukey, with level of significance at P<0.05. Results: Statistical analysis using twowayanalysis of variance (ANOVA) test revealed no statistically significant difference in failure load among the four tested subgroups (at P< 0.05). Endocrowns recorded statistically significant mean higher fracture load values (1729.91N±407.9) compared to post retained crowns, (1435.84±405.2). Statistical analysis using two ways analysis of variance (ANOVA) test revealed a statistically significant difference in debonding load among the four tested subgroups (at P<0.05). Tukey’s post hoc test revealed a significant difference between each two subgroups. The highest mean debonding loadwas recorded in the subgroup (PR) (96.98N±4.47), whereas the least value was recorded in the subgroup (EM) (49.48N±3.81). Conclusions: lithium disilicate based endocrown restorations increase the fracture resistance of endodontically treated molars compared to conventional crowns associated with glass fiber posts and resin composite filling cores.

Impact of Arthroscopic Lateral Acromioplasty on the Mechanical and Structural Integrity of the Lateral Deltoid Origin: A Cadaveric Study

To determine whether a 5-mm and/or 10-mm arthroscopic lateral acromioplasty (ALA) would weaken the structural and mechanical integrity of the lateral deltoid. The acromion and lateral deltoid origin were harvested from 15 pairs (n= 30) of fresh-frozen human cadaveric shoulder specimens. One side of each specimen pair (left or right) was randomly assigned to either a 5-mm (n= 7) or 10-mm (n= 8) ALA group, and the contralateral sides (n= 15) were used as matched controls. Acromion thickness and width were measured pre- and postoperatively. After ALA, specimens were inspected for damage to the lateral deltoid origin. Each specimen was secured within a dynamic testing machine, and the deltoid muscle was pulled to failure. Statistical analysis was performed to determine whether ALA reduced the lateral deltoid's failure load. There was no significant difference in failure load between the 5-mm ALA group (661 ± 207N) and its matched control group (744 ± 212N; mean difference= 83N; 95% confidence interval [CI], -91 to 258; P= .285) nor between the 10-mm ALA group (544 ± 210N) and its matched control group (598 ±157N; mean difference= 54N; 95% CI, -141 to 250; P= .532). There was no correlation found between the amount of bone resected (measured by percent thickness and width of the acromion after ALA) and the failure load of the deltoid. Visual evaluation of the acromion after ALA revealed the lateral deltoid origin had no damage in any case. ALA did not weaken the structural or mechanical integrity of the lateral deltoid origin. Neither a 5-mm nor a 10-mm ALA significantly reduced the deltoid's failure load. The lateral deltoid origin was not macroscopically damaged in any case. ALA can be performed without the potential risk of macroscopically damaging the lateral deltoid origin or reducing its failure load.

Interfragmentary motion assessment for three different fixation techniques of femoral neckfractures in young adults.

Vertical femoral neck fractures in the youth could be happened in high-energy accidents, and because of dominant shearing forces, this fracture is considered as a troublesome injury with a controversy regarding selection of the best fixation method. The long term goal of this quasi-experimental study was to find the more stable fixation method among cannulated screws (CSs), proximal femoral locking plate (PFLP), and dynamic hip screw with derotational screw (DHS+DS) for this kind of fracture. Twelve fresh-frozen cadaveric femurs were assigned to three groups that were matched for mean bone mineral density and stiffness of intact bone. Vertical fractures were artificially mimicked in the specimens and fixed using three different implants, i.e. CSs, PFLP, and DHS+DS. Then, the samples were tested under incremental, cyclic, and failure loading phases. The differences in all biomechanical parameters were statistically significant among tested groups (p<0.05). All biomechanical parameters for the DHS+DS method of fixation are significantly different from those corresponding to CSs (p<0.05). There were no significant differences in failure load and failure energy between the PFLP and CSs techniques (p>0.05). Also, there were no significant differences in relative stiffness and femoral head displacement between the PFLP and DHS+DS groups (p>0.05). Based on the clinical assumption that restricted weight-bearing regimen is recommended in the postoperative rehabilitation protocol, the results of this study suggest that the priority order of selection for the stable fixation implant of vertical femoral neck fracture in young patients is DHS+DS, then PFLP, and finally CSs.

The effect of zirconia framework design on the failure of all-ceramic crown under static loading.

PURPOSEThis in vitro study aimed to compare the failure load and failure characteristics of two different zirconia framework designs of premolar crowns when subjected to static loading.MATERIALS AND METHODSTwo types of zirconia frameworks, conventional 0.5 mm even thickness framework design (EV) and 0.8 mm cutback of full contour crown anatomy design (CB), were made for 10 samples each. The veneer porcelain was added on under polycarbonate shell crown made by vacuum of full contour crown to obtain the same total thickness of the experiment crowns. The crowns were cemented onto the Cobalt-Chromium die. The dies were tilted 45 degrees from the vertical plane to obtain the shear force to the cusp when loading. All crowns were loaded at the lingual incline of the buccal cusp until fracture using a universal testing machine with cross-head speed 0.5 mm/min. The load to fracture values (N) was recorded and statistically analyzed by independent sample t-test.RESULTSThe mean and standard deviations of the failure load were 1,170.1 ± 90.9 N for EV design and 1,450.4 ± 175.7 N for CB design. A significant difference in the compressive failure load was found (P<.05). For the failure characteristic, the EV design was found only cohesive failures within veneering porcelain, while the CB design found more failures through the zirconia framework (8 from 10 samples).CONCLUSIONThere was a significant difference in the failure load between two designs, and the design of the framework influences failure characteristic of zirconia crown.

Effect of immediate and delayed high-strain loading on tendon-to-bone healing after anterior cruciate ligament reconstruction.

We previously demonstrated, in a rat anterior cruciate ligament (ACL) graft reconstruction model, that the delayed application of low-magnitude-strain loading resulted in improved tendon-to-bone healing compared with that observed after immediate loading and after prolonged immobilization. The purpose of this study was to determine the effect of higher levels of strain loading on tendon-to-bone healing. ACL reconstruction was carried out in a rat model in three randomly assigned groups: high-strain daily loading beginning on either (1) postoperative day one (immediate-loading group; n = 7) or (2) postoperative day four (delayed-loading group; n = 11) or (3) after prolonged immobilization (immobilized group; n = 8). Animals were killed two weeks after surgery and micro-computed tomography (micro-CT) and biomechanical testing of the bone-tendon-bone complex were carried out. The delayed-loading group had greater tissue mineral density than either the immediate-loading or immobilized group (mean [and standard deviation], 813.0 ± 24.9 mg/mL compared with 778.4 ± 32.6 mg/mL and 784.9 ± 26.4 mg/mL, respectively; p &lt; 0.05). There was a trend toward greater bone volume per total volume fraction in both the immobilized and the delayed-loading group compared with the immediate-loading group (0.24 ± 0.03 and 0.23 ± 0.06 compared with 0.20 ± 0.05; p = 0.06). Trabecular thickness was greater in the immobilized group compared with the immediate-loading group (106.5 ± 23.0 μm compared with 72.6 ± 10.6 μm; p &lt; 0.01). There were no significant differences in failure load or stiffness between the immobilized group and either high-strain cyclic-loading group. Immediate application of high-strain loading appears to have a detrimental effect on healing in this rat model. Any beneficial effects of delayed loading on the healing tendon-bone interface (after a brief period of immobilization) may be offset by the detrimental effects of excessive strain levels or by the detrimental effects of stress deprivation on the graft. The timing and magnitude of mechanical load on a healing rat ACL reconstruction graft may have important implications for postoperative rehabilitation. Avoidance of exercises that cause high graft strain in the early postoperative period may lead to improved tendon-to-bone healing in humans.

Comparison of Pull-out Strength for Different Bone Block Length in a Porcine Anterior Cruciate Ligament Model.

Background:Bone block length for bone–patellar tendon–bone (BPTB) anterior cruciate ligament (ACL) reconstruction has traditionally been 25 mm in length. The previous surgical technique did not require the surgeon to pay particular attention to the length of the bone block, and therefore, there is scant evidence in the literature describing ideal lengths. With the gaining popularity of accessory medial portal drilling of the femoral tunnel, concerns with tunnel length and graft shuttling have surfaced. Newer techniques have advised shortening of the femoral bone block to accommodate the shorter tunnel and for ease of bone block manipulation into the aperture of the tunnel.Purpose:To compare the effects of bone block length on the pull-out strength of patellar tendon grafts using metal interference screws in a porcine ACL reconstruction model. The hypothesis was that the pull-out strength of each length of bone block under cyclic and ultimate load to failure testing would surpass the physiologic loads experienced by a normal ACL.Study Design:Controlled laboratory study.Methods:This study used 27 unmatched porcine femurs and BPTB constructs. Specimens were randomly assigned to a 10-, 15-, or 20-mm bone block reconstruction and a cycle load of 100, 500, or 1000 cycles. This resulted in 9 specimen groups with 3 specimens in each group. A central composite design (CCD) for the test matrix was selected, as this was optimum for requiring relatively few experiments while still exploring the complete range of interest for 2 independent variables. Each reconstruction used a 7 × 20–mm titanium interference screw. All reconstructions were performed on the femoral side using 10-mm-wide patellar tendon grafts, and tensile tests were performed. The loading protocol started with a 20-N preload, then cyclic testing to the appropriate number of cycles in the elastic region between 50 and 150 N at a strain rate of 200 mm/min, and then ended with ultimate load-to-failure testing. Ultimate load to failure, peak stress, elongation, and stiffness were all recorded. The patellar tendon graft mode of failure was measured by visual inspection.Results:During load-to-failure testing, 5 of 9 graft constructs in the 10-mm group failed at the bone block, while 2 of 9 failed in the 15-mm group at this interface. In the 20-mm group, all 9 specimens failed at the tendon, and none failed at the bone block. There was a statistically significant difference in modes of failure between the bone block length groups in the reconstructed ACL grafts. Analysis indicates that a smaller bone block length graft is more likely to fail due to a bone block failure than a tendon failure. The average ± standard deviation failure load for all specimens was 573 ± 171 N. The mean failure loads for the 10-, 15-, and 20-mm groups were 614 ± 110, 658 ± 92, and 540 ± 203 N, respectively. There was no statistical significance between the groups in any of these measurements.Conclusion:Bone blocks of 20 to 25 mm in length are normally used in surgical practice. Thus, the purpose of this study was to explore the effects of a smaller bone block length in the fixation strength of a graft. This study could not yield a significant difference in failure load for differently sized bone blocks. There was a significant tendency of shorter bone block lengths to fail due to bone block failure.Clinical Relevance:Bone block failure was defined as slippage of the bone block or interference screw. These results show that using a smaller bone block may increase the likelihood of a graft failure in an ACL reconstruction.

In Vitro Evaluation Of The Ferrule Effect And Post Material On Failure Load And Mode In Endodontically Treated Teeth

Aim: To compare the ferrule effect and two types of bonded post material on failure load and mode of crowned endodontically treated teeth. Methods: Sixty eight extracted human maxillary central incisors were sectioned 15 mm coronal to the root apex using hard tissue cutter. They were then endodontically treated with master apical file size 45 and obturated with gutta percha and AH 26 sealer using lateral condensation technique. Samples were randomly divided into four groups of 17 where Group A was placed with titanium post without ferrule preparation; Group B placed with titanium post and 2 mm ferrule preparation; Group C placed with fiber white post without ferrule preparation and Group D placed with fiber white post and 2 mm ferrule preparation. Next, the core was built with Paracore and Ni-Cr crowns cemented before held in a metal base for the testing using universal testing machine. A compressive load at a crosshead speed of 1mm/ min at an angle of 135o to the long axis of the sample was applied until failure. Results: Kruskal-Wallis test indicated no significant difference in failure load between groups at α=0.05. Chisquare test for independence showed a significant difference in failure mode between the groups at α=0.05. Conclusion: Ferrule effect preparation and type of bonded post materials give no difference on failure load of endodontically treated teeth. Fiber reinforced composite posts have a more favourable failure mode when compared to metallic posts.

Evaluation of the Fatigue Performance and Degradability of Resorbable PLDLLA-TMC Osteofixations

The fatigue performance of explanted in-situ degraded osteofixations/osteosyntheses, fabricated from poly (70L-lactide-co-24DL-lactide-6-trimethylane-carbonate or PLDLLA-TMC) copolymer was compared to that of virgin products. The fatigue test was performed on 21 explants retrieved from 12 women and 6 men; 16-46 years by a custom-designed three-point bend apparatus using a staircase method and a specified failure criterion (an increase of the deflection of the specimen > 1 mm) with run-out designated as “no failure” after 150,000 loading cycles. While all the virgin products showed run-out at 38N, all of the specimens fabricated from explants failed at this load level. For the explant specimens, although there was a trend of decreased failure load with increased in-situ time, this decrease was pronounced after 4 months in-situ, however, not yet statistically significant, while a 6-month in-situ explant had significantly less failure load. Three and four month in-situ explants had highly significant differences in failure load between measurements close and distant to the osteotomy line: p=0.0017 (the region of maximum load in-situ). In the virgin products, there were only traces of melt joining and cooling, left from a stage in the manufacturing process. For the implants retrieved after 4.5 months in-situ, the fracture surfaces showed signs of degradation of the implants, possibly caused by hydrolysis, and for those retrieved after 9 months in-situ, there were cracks and pores. Thus, the morphological results are consistent with those obtained in the fatigue test. The present results suggest that resorbable osteofixations fabricated from PLDLLA-TMC are stable enough to allow loading of the healing bone and degrade reliably

Effectiveness of Low-Profile Supplemental Fixation in Anterior Cruciate Ligament Reconstructions With Decreased Bone Mineral Density

The purpose of this study was to compare anterior cruciate ligament (ACL) fixation using a bioabsorbable interference screw (BIS) and a supplemental low-profile suture anchor (PushLock 4.5-mm polyetheretherketone anchor; Arthrex, Naples, FL) with a standard BIS fixation to determine if fixation methods were dependent on tibial bone mineral density (BMD). Ten matched pairs of fresh-frozen human female knee specimens (20 total) were harvested with specimen ages ranging from 40 to 65 years. The BMD for each specimen was determined with a dual-energy x-ray absorptiometry scanner. The specimens were divided into 2 groups, 1 with a BIS and the other with a BIS plus a PushLock. Tibial-sided ACL fixation with hamstring tendon grafts was performed on all the specimens. Then, load to failure and stiffness were biomechanically tested. The BIS-plus-PushLock specimens had a significantly higher mean yield load compared with specimens with the BIS alone (702 N v 517 N, P= .047). However, in samples with lower bone density, there was no statistically significant difference in failure loads between fixation techniques (P= .8566 at BMD of 0.5 g/cm(2)). As the bone density of the samples increased, the failure loads increased for both techniques (P < .0001 for PushLock and P= .0057 for BIS). This BMD-associated increase was greater for the PushLock (P= .0148), resulting in a statistically significant difference in failure load at the upper range tested (P= .0293 at BMD of 0.9 g/cm(2)). Supplemental fixation of ACL reconstructions with a PushLock is beneficial in persons with a normal BMD of the proximal tibia, but at a lower BMD, there was no difference in our study. Individuals with normal BMDs may benefit from this supplemental fixation. However, caution should be used in postmenopausal women or individuals with chronic ACL injuries when using this fixation strategy.

Comparison of ACL Fixation Devices Using Cadaveric Grafts

We evaluated two newer forms of femoral fixation of hamstring grafts for anterior cruciate ligament reconstruction, the Endobutton direct (Smith and Nephew, Andover, MA) and Femoral intrafix (Depuy Mitek, Raynham, MA), and compare them to devices that have been evaluated in the literature, the AXL Crosspin (Biomet, Warsaw, IN) and Biotransfix II (Arthrex, Naples, FL). Paired hamstring tendon allografts were fixed in the femoral tunnel of 24 cadaveric bovine knees (6 per group) according to each device's specifications. The free ends (tibial sides) were fixed to the materials testing machine via custom-made cryo-clamps. In Phase I, single load to failure and stiffness were evaluated, and in Phase II, peak displacement was evaluated while cyclic loading was performed over 1000 cycles. One-way analyses of variance were performed to test for differences between groups. There were no significant differences in failure load (p = 0.42) or stiffness (p = 0.39) between the fixation devices. There was also no significant difference in peak displacement measured during the cyclic loading phase (p = 0.32). Our findings suggest that the newer generation devices, Endobutton direct and Femoral intrafix, have similar strength in single load to failure and similar peak displacement during cyclic loading as compared with clinically proven Crosspin techniques. These newer devices, which are designed to accommodate for more anatomic femoral tunnel placement, may provide a reasonable alternative without compromising biomechanical properties.

Core Weave Versus Krackow Technique for Achilles Tendon Repair: A Biomechanical Study

The Krackow stitch, commonly used for Achilles tendon repair, leaves the bulk of the stitch on the surface of the tendon as a possible nidus for adhesion. The proposed core weave stitch leaves a minimal amount of suture material on the tendon surface. The functional strength of the core weave stitch compared with the Krackow and the optimal number of throws, or stitches crossing the surface of the tendon, with this stitch are not known. Twenty-one matched pairs of fresh-frozen cadaveric Achilles tendons were transected and randomly assigned to receive a 4-stranded stitch, either Krackow or core weave, with three, five, or seven throws. The samples were cyclically loaded to 75, 125 and 175 N for 1000 cycles at each load until failure, defined as 5 mm of elongation. No significant difference in failure load was observed between the Krackow and core weave groups at any number of throws or within the groups based on number of throws. Failure load for the different number of throws in the Krackow group approached significance (p = 0.10), with higher failure load with three throws. Functional strength of the core weave stitch and the Krackow stitch did not differ between groups with three, five, and seven throws. There was no significant difference in strength based on throws in either group. The proposed core weave stitch provides functional strength similar to that of the Krackow stitch for tendon repair with reduced suture material on the tendon surface.