Comparison of two different superior capsule reconstruction methods in the treatment of chronic irreparable rotator cuff tears: a biomechanical and histologic study in rabbit models.

BACKGROUND: In the treatment of irreparable rotary cuff (RC) tears, the superior capsule of the shoulder is reconstructed using tensor fascia lata (TFL) or several allografts to prevent progressive joint degeneration. This study compared the healing qualities of acellular human dermal graft (HDG) and the TFL autograft in superior capsule reconstruction (SCR) from biomechanical and histologic perspectives. METHODS: Chronic retracted RC tear models were created bilaterally in 9 rabbits, and 7 rabbits with intact RC were used as a control group. SCR was performed 8 weeks after the tear using HDG in right shoulders and TFL in left shoulders. At 12 weeks after SCR, 2 shoulders from each experimental group were investigated for histologic healing, and 7 samples from the experimental and control groups were biomechanically tested. RESULTS: Complete healing was observed macroscopically in the glenoid and humeral sides of both groups. No difference was observed in the enthesis maturation scores between the experimental groups. Collagen fiber density was higher and the orientation was better in TFL group. Inflammatory cell infiltration was not seen in the TFL group, but inflammatory cell infiltration was pronounced in the HDG group. The mean pullout strengths of the TFL group, HDG group, and intact RC group were 139.7 ± 40.5 N, 123.9 ± 47.9 N, and 105.1 ± 11.8 N (P = .187), respectively. The mean stiffness values (P = .711), yield forces (P = .404), and displacements (P = .135) were also statistically not different between the groups. CONCLUSION: In SCR, the healing qualities of HDG and TFL were similar in rabbit models.

Evaluation of strain distribution on an edentulous mandible generated by cobalt-chromium metal alloy fixed complete dentures fabricated with different techniques: An in vitro study.

STATEMENT OF PROBLEM: Fixed complete dentures (FCDs) have been used in the treatment of completely edentulous patients for over 40 years. However, few reports have investigated misfit values and strain distribution in the context of FCDs fabricated with new technologies. PURPOSE: The purpose of this in vitro study was to evaluate misfit values and strain distribution in FCDs and their relation to the fabrication technique of the cobalt-chromium (Co-Cr) metal framework. MATERIAL AND METHODS: Four implants were placed in the interforaminal region of a mandibular cast at the bone level. The Co-Cr metal alloy frameworks were fabricated using the following techniques: computer-aided design and computer-aided manufacturing (CAD-CAM), milling from hard blocks, CAD-CAM milling from soft blocks, and direct metal laser sintering (DMLS). The superstructures of equal sizes with acrylic resin bases and acrylic resin denture teeth were fabricated on the Co-Cr metal alloy framework, and a digital microscope was then used to measure the misfit between the abutments and the implants. The stress formed after the application of torque was measured with a strain-gauge stress analysis technique. Data were statistically analyzed using 1-way ANOVA and the Tukey Honestly Significant Difference test (α=.05). The correlation between the misfit and the strain values was evaluated with the Pearson Correlation test (α=.001). RESULTS: The lowest mean misfit values (99 ±17 µm) were observed in the hard block group (P<.05) and the highest in the DMLS group (139 ±29 µm). A statistically significant positive relationship was found between the misfit and the stress distribution after torque application (P<.05). Moreover, the lowest misfit group, hard blocks, had the lowest mean strain values (81.1 ±54 MPa) after torque application. CONCLUSIONS: Within the limitations of this in vitro study, the fabrication technique used for Co-Cr metal alloy frameworks appears to influence the passive fit significantly (P<.05). The hard-block technique was found to be the most precise fabrication technique for Co-Cr metal alloy frameworks. A significant relationship was observed between the amount/distribution of misfit and the strain on the FCD (P<.05).

Biomechanical comparison of oblique and step-cut osteotomies used in total hip arthroplasty with femoral shortening.

BACKGROUND: Various types of shortening osteotomies and prosthesis are used for femoral reconstruction in total hip arthroplasty of the high hip dislocation. This biomechanical study investigates whether step-cut osteotomies result in better stability than oblique osteotomies and cylindrical femoral stems enhance stability of the osteotomy more than conical stems, and which osteotomy and prosthesis type maintain the stability better after cyclical loading. METHODS: Oblique and step-cut shortening osteotomies were compared under axial and rotational forces, using synthetic femur models and conical or cylindrical femoral prostheses. The models underwent cyclic loading for 10,000 cycles at 3 Hz (100-1000 N axial bending or 0.5-10 Nm torque). After the completion of cyclic loading, the models were loaded until failure. Stiffness values before and after cyclical loading, and failure loads were the outcome parameters. Relative displacements at the osteotomy sites were also measured using 3-Dimensions Digital Imaging Correlation System. RESULTS: The mean failure load was significantly higher in conical prosthesis groups under axial forces. In torsion tests, the mean stiffness of conical prosthesis groups after cyclical loading was higher in oblique osteotomies. The other parameters were similar between the groups. CONCLUSIONS: According to the results of the study, although some individual statistically significant parameters were obtained, step-cut osteotomies, which are technically challenging procedures, were not found biomechanically superior to oblique osteotomies, with neither conical nor cylindrical prostheses.

A New Mini-External Fixator for Treating Hallux Valgus: A Preclinical, Biomechanical Study.

Proximal metatarsal osteotomy is the most effective technique for correcting hallux valgus deformities, especially in metatarsus primus varus. However, these surgeries are technically demanding and prone to complications, such as nonunion, implant failure, and unexpected extension of the osteotomy to the tarsometatarsal joint. In a preclinical study, we evaluated the biomechanical properties of the fixator and compared it with compression screws for treating hallux valgus with a proximal metatarsal osteotomy. Of 18 metatarsal composite bone models proximally osteotomized, 9 were fixed with a headless compression screw and 9 with the mini-external fixator. A dorsal angulation of 10° and displacement of 10 mm were defined as the failure threshold values. Construct stiffness and the amount of interfragmentary angulation were calculated at various load cycles. All screw models failed before completing 1000 load cycles. In the fixator group, only 2 of 9 models (22.2%) failed before 1000 cycles, both between the 600th and 700th load cycles. The stability of fixation differed significantly between the groups (p < .001). The stability provided by the mini-external fixator was superior to that of compression screw fixation. Additional testing of the fixator is indicated.

Retention and surface changes of zirconia primary crowns with secondary crowns of different materials.

OBJECTIVES: To evaluate zirconia as a substitute for gold alloy in primary crowns facing secondary crowns manufactured with different materials, in terms of long-term retention force changes, wear, and phase transformation was aimed. MATERIALS AND METHODS: A total of 12 groups, each containing six samples, consisting of gold alloy primary crown-electroformed gold secondary crowns (AA), zirconia primary crown-electroformed gold secondary crowns (ZA) and zirconia primary crown-casted non-precious alloy secondary crowns (ZC) with conus angles of 0°, 2°, 4°, and 6° were evaluated. Samples were subjected to 10,000 insertion-separation cycles in artificial saliva and retention force was measured. X-ray diffraction and scanning electron microscope analysis were performed on the sample surfaces. RESULTS: The highest retention forces were obtained from ZC-0° group (72.09-71.26 N) and the lowest were obtained from ZA-4° (12.73-19.44 N) and ZA-6° (5.36-19.73 N) groups in the beginning and after 10,000 cycles, respectively. Retention force increased as the conus angle decreased. The monoclinic phase ratio of the zirconia primary crowns decreased after the experiments. No wear was observed in zirconia primary crowns except for the ZC-0° and ZC-2° groups. The use of zirconia primary crowns resulted in a less excursive retention force. CONCLUSIONS: A more predictable and less excursive retention force can be obtained using a hard and rigid primary crown material like zirconia. CLINICAL RELEVANCE: Despite a lack of knowledge about the aging of zirconia without a veneer layer in the oral environment, zirconia primary crowns are more advantageous in terms of retention force development and wear.

The effect of strut allograft and its position on Vancouver type B1 periprosthetic femoral fractures: a biomechanical study.

The aim of this study is to assess the biomechanical advantage of adding strut allograft and the effect of its position on the construct in Vancouver type B1 fractures. Fifteen forth-generation synthetic femurs were used and created a fracture model at the tip of prosthesis, and subsequently fixated with a lateral plate only, lateral plate and medial strut, lateral plate and anterior strut. Rotational and axial tests were performed. In all loading tests, the plate with medial strut group was stiffer than the other constructs and had higher failure load values and had less displacement in the fracture site. A combination of a plate with a medial strut allograft provides more mechanical stability on periprosthetic femoral fractures near the tip of a total hip arthroplasty.

A new configuration of lateral-pin fixation for pediatric supracondylar humeral fracture: A biomechanical analysis.

OBJECTIVE: The aim of this study was to biomechanically compare a new lateral-pinning technique, in which pins engage the medial and lateral columns of the distal humerus in a divergent configuration in both the axial and sagittal planes instead of the coronal plane, with the cross-pin, and with 2 and 3 coronally divergent lateral-pin techniques in a synthetic humerus model of supracondylar humerus fractures. METHODS: Thirty-six identical synthetic models of the humerus simulating a standardized supracondylar humerus fracture were included in this study. They were divided into 4 groups based on the pin configuration of fixation: the new 3-lateral pin-fixation technique (group A), 2 crossed pins (group B), 3 divergent lateral pins (group C), and 2 divergent lateral pins (group D). Each model was subjected to combined axial and torsional loading, and then torsional stability and torsional stiffness (Nmm/°) were recorded. RESULTS: Group A had greater rotational stability than groups C and D but had no statistically significant additional rotational stability compared with group B (P=.042, P=.008, P=.648, respectively), whereas group B had greater rotational stability than only group D (P=.020). Furthermore, group A demonstrated higher internal rotational stiffness compared with groups C and D (P=.038, P=.006, respectively). Group B had better internal rotational stiffness than group D (P=.015). There was no significant difference in internal rotational stiffness between groups A and B (P=. 542), groups B and C (P=.804), and groups D and C (P=.352). Although no statistically significant differences existed between groups A and B, the modified pin configuration exhibited the highest torsional stability and stiffness. Group D showed the lowest values in all biomechanical properties. CONCLUSION: This study has shown us that this new lateral-pinning technique may provide torsional resistance to internal rotational displacement as strong as the standard technique of crossed-pin configuration of fixation. Furthermore, with this new pin configuration, greater torsional resistance can be obtained than with either the standard 2- or the standard 3-lateral divergent pin configuration. Cite this article as: Bilgili F, Demirel M, Birisik F, Balci HI, Sunbuloglu E, Bozdag E. A new configuration of lateral-pin fixation for pediatric supracondylar humeral fracture: A biomechanical analysis. Acta Orthop Traumatol Turc., 2023 10.5152/j.aott.2024.21091 [Epub Ahead of Print].

Horizontal suture placement influences meniscal repair fixation strength.

PURPOSE: This in vitro biomechanical study investigated the influence of horizontal suture placement distance from the medial meniscal lesion repair site on fixation characteristics during submaximal cyclic and load to failure test conditions. METHODS: Eighteen cadaveric (20-45 years of age) medial menisci with intact joint capsules were harvested within 24-48 h after death and divided into two groups of 9 specimens each for biomechanical testing. A 2.0-cm-long antero-posterior vertical longitudinal lesion was created with a #15 scalpel 2.0-3.0 mm from the outer edge of each meniscus. Menisci were repaired using #2-0 suture material with two horizontal suture loops placed either 1.0 mm (Group 1) or 3.0 mm (Group 2) from the lesion site. Following repair, the lesion was extended completely through the meniscal horns so that no tissue secured the repair, only the two horizontal suture loops representing a "worst-case" testing scenario. Following repair, specimens were placed in a servo hydraulic device using a pair of 1.2-mm-diameter steel wire loops and underwent submaximal cyclic loading between 5 and 50 N (1 Hz) for 500 cycles prior to load to failure testing (5 mm/min crosshead speed, 20 Hz data collection). An alpha level of P < 0.05 was selected to indicate statistical significance. RESULTS: Five of nine (55.6 %) Group 1 specimens did not complete submaximal cyclic testing. All Group 2 specimens completed submaximal cyclic testing (Fisher's exact test P = 0.029). Statistically significant mean group differences were not observed for displacement during submaximal cyclic loading (Group 1 = 5.0 ± 1.5 mm and Group 2 = 5.7 ± 1.6 mm) or for construct stiffness during load to failure testing (Group 1 = 50.1 ± 6.3 N/mm and Group 2 = 52.6 ± 11.9 N/mm). Group 2 displayed greater mean load at failure (112.1 ± 40.8 N vs. 72.7 ± 11.2 N, P = 0.02) and mean displacement at failure (11.1 ± 2.2 mm vs. 7.6 ± 1.4 mm, P = 0.03) than Group 1. CONCLUSIONS: Horizontal sutures placed slightly farther away from the meniscus lesion displayed superior repair fixation than sutures placed closer to the lesion. The superior biomechanical meniscal repair fixation provided by capturing greater tissue volume may enable safe earlier participation in functional exercise activities. Studies are needed to verify these findings in vivo.

The influence of the attachment type and implant number supporting mandibular overdentures on stress distribution: an in vitro study, part I.

OBJECTIVES: The main goal of this study was to compare the stress distribution of mandibular overdentures (OVD) with different numbers of supporting implants and single versus splinted attachment types. MATERIALS AND METHODS: Four different biting situations were simulated for the 2-, 3-, and 4-implant retentive anchor as well as bar attachment OVDs on a formalin-fixed cadaver mandible, and strains were recorded under vertical loading of 100 N. RESULTS: The calculated von Mises values from measured strains in all measurement sites and loading conditions for nonsplinted attachments (retentive anchor) were higher than splinted (bar) attachments. CONCLUSIONS: It may be concluded that in cases with low quality and quantity of bone, the increase in number of implants and the use of a splinted attachment should be preferred to reduce forces emerging around the implants during function. The use of 2 single attachments in cases with good bone quality and ideal size implants still seems to be a safe and sufficient solution for the treatment of mandibular edentulism with OVDs.

The Effects of Cross-Linking Agents on the Mechanical Properties of Poly (Methyl Methacrylate) Resin.

Cross-linking agents are incorporated into denture base materials to improve their mechanical properties. This study investigated the effects of various cross-linking agents, with different cross-linking chain lengths and flexibilities, on the flexural strength, impact strength, and surface hardness of polymethyl methacrylate (PMMA). The cross-linking agents used were ethylene glycol dimethacrylate (EGDMA), tetraethylene glycol dimethacrylate (TEGDMA), tetraethylene glycol diacrylate (TEGDA), and polyethylene glycol dimethacrylate (PEGDMA). These agents were added to the methyl methacrylate (MMA) monomer component in concentrations of 5%, 10%, 15%, and 20% by volume and 10% by molecular weight. A total of 630 specimens, comprising 21 groups, were fabricated. Flexural strength and elastic modulus were assessed using a 3-point bending test, impact strength was measured via the Charpy type test, and surface Vickers hardness was determined. Statistical analyses were performed using the Kolmogorov-Smirnov Test, Kruskal-Wallis Test, Mann-Whitney U Test, and ANOVA with post hoc Tamhane test (p ≤ 0.05). No significant increase in flexural strength, elastic modulus, or impact strength was observed in the cross-linking groups compared to conventional PMMA. However, surface hardness values notably decreased with the addition of 5% to 20% PEGDMA. The incorporation of cross-linking agents in concentrations ranging from 5% to 15% led to an improvement in the mechanical properties of PMMA.

Biomechanical comparison of tibial eminence fracture fixation with high-strength suture, EndoButton, and suture anchor.

PURPOSE: To biomechanically compare anterior cruciate ligament (ACL) tibial bony avulsion fixation by suture anchors, EndoButtons (Smith & Nephew, Andover, MA), and high-strength sutures subjected to cyclic loading. METHODS: Type III tibial eminence fractures were created in 49 ovine knees, and 7 different types of repairs were performed. Each repair group contained 7 specimens. The repair groups were as follows: No. 2 FiberWire (Arthrex, Naples, FL); No. 2 UltraBraid (Smith & Nephew); No. 2 MaxBraid (Arthrotek, Warsaw, IN); No. 2 Hi-Fi (ConMed Linvatec, Largo, FL); No. 2 OrthoCord (DePuy Mitek, Raynham, MA); Ti-Screw suture anchor (Arthrotek); and titanium EndoButton. These constructs were cyclically loaded (500 cycles, 0 to 100 N, 1 Hz) in the direction of the native ACL and loaded to failure (100 mm/min). Endpoints included ultimate failure load (in Newtons); pullout stiffness (in Newtons per millimeter); cyclic displacement (in millimeters) after 100 cycles, between 100 and 500 cycles, and after 500 cycles; and mode of failure. Bone density testing was performed in all knees. RESULTS: Bone density was not different among the groups. The EndoButton group had a higher ultimate failure load than the FiberWire, UltraBraid, Hi-Fi, and suture anchor groups (P < .05). The MaxBraid and OrthoCord groups had higher failure loads than the suture anchor group (P < .05). The MaxBraid group also had a higher failure load than the Hi-Fi group (P < .05). Stiffness was not statistically different for the various tested constructs. After 100 cycles, the EndoButton group had less displacement than the FiberWire, UltraBraid, MaxBraid, and Hi-Fi groups (P < .05). The suture anchor group had less displacement than the Hi-Fi and FiberWire groups (P < .05). The displacements of the different tested constructs between 100 and 500 cycles and total displacements after 500 cycles were not statistically different. The predominant failure mode was suture rupture. CONCLUSIONS: Under cyclic loading conditions in an ovine model, EndoButton fixation of tibial eminence fractures provided greater initial fixation strength than suture anchor fixation or fixation with various high-strength sutures except for OrthoCord. CLINICAL RELEVANCE: During initial cyclic loading of ACL tibial eminence fractures, the strength of the repair construct should be taken into consideration because conventional suture repair even with ultrahigh-molecular-weight polyethylene sutures may not provide enough strength.

Aperture fixation instead of transverse tunnels at the patella for medial patellofemoral ligament reconstruction.

PURPOSE: Medial patellofemoral ligament (MPFL) reconstruction is an effective option for the treatment of recurrent patellar instability. Most techniques utilize the passage of a tendon graft through tunnels at the patella with the risk of patellar fracture. The purpose of this study was to investigate the strength of the recent MPFL reconstruction techniques (transverse tunnel, interference screw, anchor, and docking technique). METHODS: Thirty-six saw bones were divided into four groups (transverse tunnel, interference screw, anchor fixation, and docking technique) with nine patellae in each. Patella-tendon constructs were pre-loaded to 10 N and cyclically loaded for 20 cycles from 2 to 30 N under load control at a rate of 5 N/sec. The construct was then tested to failure at a constant displacement rate of 6 mm/sec. Ultimate load (N), stiffness (N/mm), and failure mode were recorded for each specimen. RESULTS: The docking group had lower ultimate load [106 (SD 41) N] and stiffness [14 (SD 2) N/mm] values than the other groups tested (P = 0.007). The anchor group had lower stiffness [21 (SD 6) N/mm] values than the tunnel group [28 (SD 3) N/mm (P = 0.01)] and the interference screw group [31 (SD 6) N/mm, (P = 0.004)]. There was no significant difference in the ultimate load between anchor [299 (SD 116) N], tunnel [304 (SD 140) N], and interference screw groups [241 (SD 103) N] (n.s.). CONCLUSION: Aperture fixation techniques, especially interference screw fixation, were as strong as the technique utilizing tunnels in the patella for MPFL reconstruction.

The effect of onlay cortical fibula strut grafts on biomechanical features of Vancouver type B1 periprosthetic femoral fractures.

OBJECTIVE: This study aimed to investigate biomechanically the effects of onlay fibula grafts on Vancouver Type B1 Periprosthetic Femoral Fractures (PPFs). METHODS: Vancouver Type B1 PFF models were created in 25 fourth-generation synthetic femurs and fixed with locking plates using bicortical, unicortical screws, and cables. While no graft was used in group 1, onlay fibula grafts were placed anteriorly in group 2 and medially in group 3. In group 4, the cortical strut allograft was placed on the medial femoral cortex, and a locking compression plate (LCP) was applied to the lateral femoral cortex. In group 5, the strut allograft was placed over the anterior cortex of the femur and fixed with the same technique as in group 4. All models were then subjected to rotational and axial cyclical stiffness tests and load to failure to measure and compare the mechanical strengths of the constructs. RESULTS: The mean stiffness values of group 4 with medial allograft, before and after cyclical loading, were higher than all other groups, under both rotational and axial forces. The mean stiffness values of fibula autografts (groups 2 and 3) were similar to that of anterior allografts (group 5) in each test except that the mean initial axial stiffness of group 5 was higher than group 2. Failure loads were also not different between the groups. CONCLUSION: Although the rigidity of Vancouver type B1 periprosthetic femur fractures is highest if allografts are placed medially, fibula autografts can also provide similar fixation strengths to allografts if locking plates with unicortical and bicortical screws and cables are used.

Loop security and tensile properties of polyblend and traditional suture materials.

Tensile and knot properties of new generation (polyblend) and traditional suture materials in orthopedic surgery were investigated in standard laboratory conditions. Study focused on Fiberwire No. 5 and 2, Ethibond No. 5, 2 and 00, Orthocord No. 2, MaxBraid No. 2, Prolene No. 0 and 00, PDS No. 0 and 00, and Vicryl No. 2, 0 and 00. A 27-cm suture loop was fastened with 10 knots for ten samples for each type. Test parameters were tensile load to failure, elongation at failure point and knot slippage, and volume of 10-fold knots. Results were compared using ANOVA test. Failure load of No. 5 Fiberwire (625.0 ± 30.0 N) was significantly higher compared to all other suture types. Tensile strengths of MaxBraid No. 2 (287 ± 11 N) was significantly stronger compared to two other No. 2 polyblend sutures types and Ethibond No. 5. Knot slippage of Fiberwire No. 5 (14 ± 1.9 mm) was significantly higher compared to all other suture types. Ethibond No. 2 (0.1 ± 0.3 mm) had the lowest knot slippage. Elongation at the failure point of Fiberwire No. 2 (5%) was significantly lower than all other suture types. Mean calculated knot volume of #5 Fiberwire (73 ± 6.9 mm(3)) was significantly higher compared to #5 Ethibond (53 ± 4.8 mm(3)). Results of the study proved presence of significant differences between tensile and knot properties of various suture types and sizes. Loop security of larger diameter sutures is not always higher than thinner sutures. Suture elongation and knot slippage are important failure modes for high-diameter sutures and short-suture loops.

Meniscal repair using large diameter horizontal sutures increases fixation strength: an in vitro study.

PURPOSE: the purpose of this study was to compare the mechanical characteristics of meniscal repair fixation using horizontal sutures and two different diameter sutures under submaximal cyclic and load to failure test conditions. METHOD: a 2-cm long anteroposterior vertical longitudinal incision was created in two groups of bovine medial menisci. Lesions were repaired using either #2-0 (Group 1), or #2 (Group 2) Fiberwire suture. Following repair, the lesion was extended through the posterior and anterior meniscal horns so that no tissue secured the repair site. Specimens underwent submaximal cyclic (5-50 N at 1 Hz for 500 cycles) and load to failure testing (5 mm/min crosshead speed) in a servo hydraulic device. Specimen failure mode was verified by the primary investigator. An alpha level of P < 0.05 was selected to indicate statistical significance. RESULTS: group 2 displayed greater load at failure (132.1 ± 54.4 N) than Group 1 (91.9 ± 26.2 N) (P = 0.02). Group 2 also displayed greater stiffness (47.1 ± 8.3 N/mm) than Group 1 (38.5 ± 10.2 N/mm) (P = 0.03). The failure mode for all specimens was suture pull-through the meniscal tissue. Larger diameter suture provided superior mechanical meniscal fixation. CONCLUSION: if horizontal suture would be used in meniscal repair, the most suitable larger diameter suture should be used.

Tendon-grasping strength of various suture configurations for rotator cuff repair.

PURPOSE: The purpose of the present study is to evaluate the mechanical performance and initial strength of the arthroscopic Mason-Allen, double mattress, inclined Mason-Allen, and lasso loop stitch configurations. METHODS: Using 36 sheep infraspinatus tendons, tendon widths and thicknesses were measured with a digital caliper to confirm standardization of the tendons. Four different stitch configurations (Mason-Allen, inclined Mason-Allen, double mattress, and lasso loop) were biomechanically tested with cyclic loading followed by load to failure testing. The cyclic elongation, peak-to-peak displacement, ultimate tensile strength, stiffness, and mode of failure were recorded. RESULTS: Mean tendon widths and thicknesses were statistically the same. The lasso loop (0.7 ± 0.1 mm) demonstrated a mean cyclic elongation greater than the Mason-Allen (0.5 ± 0.3 mm) and double mattress (0.5 ± 0.3 mm) groups (P = 0.011; P = 0.013). No differences were found in ultimate failure load, stiffness, and peak-to-peak displacement for the Mason-Allen (mean 99 ± 42 N, 39 ± 9 N/mm, 0.6 ± 0,1 mm), inclined Mason-Allen (113 ± 52 N, 44 ± 14 N/mm, 0.5 ± 0.1 mm), double mattress stitch (119 ± 68 N, 45 ± 10 N/mm, 0.5 ± 0.1 mm), or lasso loop (100 ± 38 N, 42 ± 7 N/mm, 0.5 ± 0.1 mm) groups (n.s.). Each specimen failed at the suture-tendon interface. Three specimens (two Mason-Allen and one inclined Mason-Allen) failed during cyclic testing. CONCLUSION: Conventional Mason-Allen configuration can be applied with double-loaded suture anchor safely. Recent modifications of the configurations offer no biomechanical advantage.

An in-silico approach to modeling orthodontic tooth movement using stimulus-induced external bone adaptation.

Bone remodeling process has been used in orthodontics to treat malposition of teeth in patients by applying stimuli outside of usual everyday loads to promote tooth movement by affecting equilibrium state of the surrounding bone tissue. Accurate modeling of long term orthodontic tooth movement (OTM) is crucial in the field of dental biomechanical research since it allows to predict the behavior and interaction of bone-tooth environment in a non-destructive way, and helps to gain more insight on how exactly tooth motion progresses over time. Existence of such predictive tools might help to avoid the adverse effects of OTM on teeth and the surrounding tissues during this clinical procedure. In this study a new numerical approach to simulating long-term OTM is proposed, that involves external bone adaptation with strain energy density of the bone taken as the stimulus parameter and bone adaptation modeled by nodal movements at the bone-tooth interface using Abaqus UMESHMOTION subroutine. Contrary to conventional re-meshing algorithms, where the mesh of resorbed-apposed bone region is constantly updated and element deletion/creation is performed for each increment, the proposed method only moves nodes without changing the initial mesh topology. For this study, a 3D model of right central maxillary incisor tooth and its surrounding maxillary bone was used for the modeling of OTM for a duration of 1 week. Two test cases were performed and the results from induced tooth motion were investigated. Results indicate tooth movement values that were quite close to clinical values provided in the literature and this method is easily applicable to validate various postulates of OTM via adapting the stimulus-adaption rate relation and patient-specific planning of orthodontic patients as well.

The Effects of Different Screw Combinations on the Initial Stability of Ankle Arthrodesis.

Background: The literature is scanty regarding the biomechanical effects of different thread configurations on the initial stability of ankle arthrodesis. This study aims to compare the initial stability of tibiotalar fusion site in ankle arthrodesis using cannulated screws with different thread designs. Methods: We biomechanically tested under cyclic loading the effects of different screw combinations on the initial stability of ankle arthrodesis. A total of 28 synthetic ankle models were divided into four groups: two partially threaded cancellous screws (group A), partially and fully threaded cancellous screws (group B), a partially threaded cancellous screw with a headless compression screw (group C), and a fully threaded cancellous screw and a headless compression screw (group D). Biomechanical variables including ultimate failure load, initial stiffness, ultimate stiffness, and failure angulation were analyzed. Results: There were no differences in any of the biomechanical variables among the four groups (P = .41 for ultimate failure load, P = .079 for initial stiffness, P = .084 for ultimate stiffness, and P = .937 for failure angulation). Conclusions: Combinations of different cannulated screws showed similar results in terms of the stability and stiffness of the tibiotalar fusion site.

Biomechanical analysis of multilevel discectomy and excision of posterior longitudinal ligament: an in vitro study in sheep.

AIM: This experimental biomechanical study was performed to determine the effects of multilevel anterior cervical discectomy and excision of posterior longitudinal ligament (PLL) to stabilize the cervical spine using an in vitro animal model. MATERIALS AND METHODS: Fifty fresh cadaveric C3-C6 sheep spine specimens were divided into five experimental groups: Group A was the control group; Group B, one-level discectomy; Group C, two- level discectomy, Group D, three-level discectomy, and Group E, three-level discectomy and excision of PLL, respectively. The specimens were subjected to non-destructive loads cycled from zero to five Newton-meter for flexion, extension, right and left lateral bending, and axial rotation on an electrohydraulic test machine. Load displacement curves were obtained via collected data using strain gauges. The values were obtained for all five groups, statistical differences were determined respectively (P<0.05, ANOVA). RESULTS: One-level discectomy was less stable than the control group, two-level discectomy was less stable than one-level discectomy and three-level discectomy was less stable than two-level discectomy, respectively (P<0.05). Excision of PLL did not seem to affect stability (P>0.05). CONCLUSION: Our data suggested that cervical discectomy decreases stability of sheep spine pieces.

[The effect of debridement performed before capsular plication on biomechanical properties of the knee joint capsule: an experimental study in rabbits]. / Plikasyondan önce debridman uygulamasinin diz kapsülünün biyomekanik özelliklerine etkisi: tavsanda deneysel çalisma.

OBJECTIVES: The purpose of this study was to evaluate early postoperative biomechanical changes in plicated joint capsules and to determine the effect of debridement to create a bleeding inner capsular surface on the healing process. METHODS: Fifty-four mature New Zealand white rabbits were used. Plication was performed in unilateral medial knee joint capsules of 48 rabbits either alone (n=24) or following debridement (n=24) to create a bleeding inner capsular surface. Six rabbits remained untreated for the control group. The operated knee joints were immobilized in flexion postoperatively. The rabbits from the two study groups were sacrificed in groups of six immediately after operation, in the first, second, and third weeks, of which five were evaluated in tensile tests and one was evaluated histologically. RESULTS: Compared to the controls, tensile strengths were significantly higher in both study groups until the third week (p<0.01), after which the difference became insignificant (p>0.05). The strength of the plicated capsules was significantly higher in the first week in both study groups than those measured in subsequent weeks (p<0.01), whereas similar tensile strengths were recorded in the second and third weeks (p>0.05). Compared to its absence, the use of debridement was associated with a significantly lower strength in the first week (p<0.01), but this difference was not observed afterwards (p>0.05). Histological findings were similar in the two study groups and were characterized by healing with increased fibrosis starting from the first week. CONCLUSION: A plicated capsule would not be weaker than an intact one. Our findings do not favor debridement for a more rapid and better healing process. Rather, it might have adverse effects on the biomechanical properties of the capsule.