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].

Fibroblast Growth Factor Soaked Collagen Membrane Shows No Biomechanical or Histological Advantages in the Treatment of Chronic Rotator Cuff Tears in a Rabbit Model.

PURPOSE: To investigate the histological and biomechanical effects of a fibroblast growth factor (FGF-2)-soaked collagen membrane used to treat a full-thickness chronic rotator cuff (RC) rupture in a rabbit model. METHODS: Forty-eight shoulders from 24 rabbits were used. At the beginning of the procedure, 8 rabbits were killed to assess the control group (Group IT) with intact tendons. To establish a chronic RC tear model, a full-thickness subscapularis tear was created on both shoulders of the remaining 16 rabbits and left for 3 months. The transosseous mattress suture technique was used to repair tears in the left shoulder (Group R). The tears in the right shoulder (Group CM) were treated using the same approach, with an FGF-soaked collagen membrane inserted and sutured over the repair site. Three months after the procedure, all rabbits were killed. Biomechanical testing was performed on the tendons to determine failure load, linear stiffness, elongation intervals, and displacement. Histologically, the modified Watkins score was used to evaluate tendon-bone healing. RESULTS: There was no significant difference among the three groups in terms of failure load, displacement, linear stiffness, and elongation (P > .05). The total modified Watkins score was not affected by applying the FGF-soaked collagen membrane to the repair site (P > .05). Fibrocytes, parallel cells, large-diameter fibers, and the total modified Watkins score were significantly lower in both repair groups when compared to the intact tendon group (P < .05). CONCLUSIONS: In addition to tendon repair, FGF-2 soaked collagen membrane -application at the repair site provides neither biomechanical nor histological advantages in the treatment of chronic RC tears. CLINICAL RELEVANCE: FGF-soaked collagen membrane augmentation provides no impact on the chronic RC tear healing tissue. The need to investigate alternative methods that may have a positive effect on healing in chronic RC repairs continues.

Three-Dimensional Finite Element Analysis of a Notched Insert Design for Reverse Total Shoulder Arthroplasty to Prevent Scapular Notching.

Purpose: Reverse total shoulder arthroplasty (RSA) is an effective treatment option for rotator cuff arthropathy. Scapular notching following RSA remains a major complication and has a high incidence. This finite element analysis (FEA) study provides a future reference for the optimal design of the insert component of RSA. This study aims to clarify the effect of a new design RSA with a notched insert on the range of adduction, scapular notching, and stress variation of its insert component using three-dimensional (3D) FEA. Methods: 3D nominal Grammont-type monobloc RSA implant components are modeled on the sawbones glenohumeral joint. The polyethylene insert is redesigned with notching of the inferior part. The comparison of standard and notched designs was performed by FEA for stress pressure of scapular notching and the degree of adduction. 3D mesh models are created for stress analysis to compare the results between standard and notched inserts for the adduction. Results: The redesigned notched inserts had an additional ~ 11.2° on adduction and prevented scapular notching. The stress analysis results for the notched insert design were lower than the standard ones (4.7 vs 22.4 Kpa). Conclusions: Notched insert design of Grammont-type RSA could provide additional adduction with lower stress on the glenoid, leading to less scapular notching. Further experimental and clinical studies on different RSA types are needed to verify this effect. Study Design: Basic Science Study; Biomechanics and Computer Modeling.

Biomechanical comparison of fixation methods on third-generation femoral composite bone models in Pauwels type 3 femoral neck fractures: Contribution of the medial buttress plate to fixation.

OBJECTIVE: To compare the use of cannulated screws in an inverted triangular configuration, medial buttress plates, and the combination of these 2 fixation methods in the treatment of Pauwels type 3 femoral neck fractures. METHODS: Twenty-eight anatomical composite third-generation femoral bone models were divided into 4 groups. The control group (group 1) was formed with 7 third-generation intact bone models. The fracture model was created with a 70° cutting block to fit 21 Pauwels type 3 fracture configurations. Seven models were fixed with an isolated 3.5 mm one-third semi-tubular medial buttress plate (group 2), 7 were fixed in an inverted triangular configuration with 6.5 mm cannulated screws (group 3), and 7 were fixed using a combination of 6.5 mm cannulated screws and a medial buttress plate (group 4). Cyclic loading was applied using axial forces ranging from 60 N to 600 N and moments ranging from 0.7 Nm to 7.0 Nm for 500 cycles. Once the cyclic loading stage was completed, the loads were removed from the system, and the quasi-static loading stage was employed to determine the stiffness and failure forces of the system under both axial and torsional forces. Quasi-static tests were performed with an axial speed of 1.8 mm/min and a torsional speed of 4.5°/min. The biomechanical properties of all groups were examined in terms of axial stiffness, torsional stiffness, and maximum axial force parameters. RESULTS: The stiffness values of groups 1, 2, 3, and 4 were 303 ± 35.8 N/mm, 159.6 ± 25 N/mm, 232 ± 35.9 N/mm, and 366.9 ± 58 N/mm, respectively, under axial forces (P < .01); 2172.7 ± 252.1 Nmm/°, 1225.3 ± 238.6 Nmm/°, 2123 ± 359.4 Nmm/°, and 2721.85 ± 304 Nmm/°, respectively, under torsional moments (P < .01); and 2072.1 ± 256.1 N, 1379.9 ± 290.6 N, 2099.1 ± 454.2 N, and 2648.4 ± 364.6 N, respectively, under the maximum force (P < .01). CONCLUSION: This study showed that in the fixation of Pauwels type 3 fractures formed on third-generation bone models, the utilization of half-thread cannulated screws in an inverted triangle configuration, along with a medial buttress plate, provided stronger fixation compared to the remaining implant groups and the control group. According to the evaluation of the parameters, the isolated application of a medial buttress plate had poorer biomechanical properties than other fixation methods.

Evaluation of Unicortical Locking Screw Placement for Torsional Loads in Distal Radius Fractures: A Biomechanical Study in Cadavers.

Background We aimed to compare bio-mechanical outcomes of short-length 75%-length uni-cortical screw (SL75UCS) and full-length 100%-length screws (FL100S) under axial compression (AXC) and torsional compression (TRC) in cadaveric distal radius volar plate model. Methodology A total of 20 wrists from 10 fresh frozen cadavers were included. A 2.5 mm titanium alloy distal radius anatomical plate was placed to the distal radii in full anatomical position, just proximal to the watershed line. Three bi-cortical screws to the shaft of the radius, followed by uni-cortical drilling for distal screwing were placed. Measurement by pulling the drill once it reached the opposite cortex was applied. We selected the screw lengths such that they corresponded to the SL75UCS. In the same configuration for each of the cadavers, we delivered six screws from distal radius holes of the anatomical plate. An oscillating handsaw was used to create an extra-articular distal radius fracture model (AO 23-A3.2). We created a dorsal AP model by performing a 1-cm wedge osteotomy from the dorsal aspect. Complete separation of the volar cortex was achieved. Potting was performed by embedding the shaft of the prepared radius into the polyurethane medium. We placed aluminum apparatus into the distal end to ensure applying of AXC and TRC in bio-mechanistic tests. Results No statistically significant difference of stiffness between the SL75UCS and FL100S both under AXC (p=0.88) and TRC (p=0.82). SL75UCS and FL100S groups did not differ in elastic limit under AXC (p=0.71) and TRC (p=0.71). Maximal force on SL75UCS and FL100S groups were also similar under both AXC (p=0.71) and TRC (p=0.50). Conclusions Our study findings suggest that drilling the dorsal cortex may not be necessary in the management of distal radius fractures. Instead, utilizing SL75UCS could serve as a viable alternative. This approach offers potential advantages in reducing the risk of extensor tendon complications associated with drilling or screw protrusion. It is a safe method under torsional load to avoid drilling of the dorsal cortex and SL75UCS could be performed in order to prevent from extensor tendon complications secondary to drilling or screw protrusion.

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 four different fixation methods in the management of Pauwels type III femoral neck fractures: Is there a clear winner?

BACKGROUND: Cannulated screws augmented with the medial buttress plate could confer greater biomechanical stability and higher union rates than the screw fixation alone for treating young patients with Pauwels type III femoral neck fractures (FNFs). No study has evaluated the effects of distal bicortical screw fixation and biomechanical properties of buttress plate augmentation under simultaneous vertical and rotational forces, physiologically acting on the hip joint. This study aimed to compare the biomechanical properties of four methods of three cannulated screw fixation under the combined axial and torsional loading in a synthetic femur model of type III FNF. METHODS: Twenty-four third-generation composite femora were divided into four groups (6 femora in each group) based on the screw fixation configuration: inverted triangle configuration (Group A),  Pauwels' configuration (Group B), inverted triangle configuration combined with medial buttress plate using distal unicortical (Group C), and distal bicortical screw placement (Group D). A Pauwels type III FNF was simulated on the sawbones. Each model was subjected to the combined axial and torsional cyclic loading and subsequently tested to failure. RESULT: Significant differences were determined in axial stiffness (AS) among the four groups (p = 0.024), whereas there was no significant difference in torsional stiffness (p = 0.147). The mean AS was higher in group D (639.5 ± 86.2 N/mm) than in group A (430.6 ± 94.8 N/mm), group B (426.2 ± 41.9 N/mm), and group C (451.2 ± 156.7 N/mm). Failure forces (FFs) were significantly different among four groups (p = 0.007), while there was no considerable difference in failure moment values (p = 0.555). The mean FF was significantly higher in group D (1307.1 ± 96.4 N) than in group A  (1076.9 ± 371.2 N) and group B (1075.5 ± 348.3 N) (p = 0.014 and p = 0.018, respectively). There was no significant difference in the mean FF between groups D and C. CONCLUSION: Regardless of the medial plate use, multiple cannulated systems could provide similar biomechanical results regarding torsional stiffness and failure moments. Bicortical placement of the most distal screw in medial buttress plate application could improve axial stability but not significantly affect the rotational stability of the inverted triangle screw fixation system in managing type III FNFs.

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.

EFFECT OF TRANEXAMIC ACID ON FRACTURE HEALING IN RATS.

Introduction: In this study we investigated the effect of tranexamic acid (TXA) on fracture healing in an established animal model, when used to stop bleeding in orthopedic trauma surgery. Materials and Methods: This study was a randomized, controlled, laboratory study. Eighteen Sprague-Dawley rats were randomly assigned to three groups, either receiving TXA intravenously (Group 1), TXA topically (Group 2), or isotonic TXA intravenously and TXA topically in the same amounts for the control group (Group 3). First, a Kirschner wire was inserted retrogradely into the femoral intramedullary canal. Then the femurs were fractured at the midshaft region with blunt guillotine. After 4 weeks, the rats were sacrified and the femurs harvested. Cortical bone volume, callus volume, and bone mineral density were calculated using computer tomography scans. Torsion tests were performed. Groups were compared by maximum torque to failure and callus stiffness. Results: There were no statistical differences in torque to failure and stiffness between the 3 groups. There were no differences in mean total bone volume, callus volume, percent bone volume, or callus density between the groups. Conclusions: A single dose of topical or intravenous TXA has no negative effect on fracture healing when used in traumatic femur fracture surgery in an animal model. Evidence level II; Randomized controlled experimental study.

Introdução: Neste estudo, investigamos o efeito do ácido tranexâmico (TXA) sobre a consolidação de fraturas em um modelo animal estabelecido, quando é usado para estancar o sangramento em cirurgias de trauma ortopédico. Materiais e Métodos: Trata-se de estudo de laboratório randomizado e controlado. Dezoito ratos Sprague-Dawley foram atribuídos randomicamente em três grupos, que receberam TXA por via intravenosa (Grupo 1), TXA tópico (Grupo 2) ou isotônico por via intravenosa e tópico na mesma quantidade como grupo controle (Grupo 3). Primeiro, foi inserido um fio de Kirschner por via retrógrada no canal intramedular femoral. Em seguida, o fêmur dos animais foi fraturado na região média do corpo do fêmur com guilhotina romba. Depois de quatro semanas, os ratos foram sacrificados e os fêmures foram retirados. O volume do osso cortical, o volume do calo e a densidade mineral óssea foram calculados por meio de tomografia computadorizada e foram realizados testes de torção. Os grupos foram comparados de acordo com o torque máximo até a falha e a rigidez do calo. Resultados: Não houve diferença estatística no torque até a falha e rigidez entre os três grupos nem diferenças entre os grupos quanto ao volume médio total do osso, volume e densidade do calo e percentual de volume ósseo. Conclusões: Uma dose única de TXA tópico ou intravenoso não tem efeito negativo sobre a consolidação da fratura quando usada em cirurgia de fratura traumática de fêmur em modelo animal. Nível de evidência II; Estudo experimental controlado randomizado.

The efficacy of angiotensin-converting enzyme inhibitors in preventing postoperative tendon adhesion formation: An experimental study in rats.

OBJECTIVE: The aim of this study was to investigate the efficacy of angiotensin-converting enzyme inhibitors (ACEIs) in preventing postoperative tendon adhesion formation in a rat model of Achilles tendon repair. METHODS: In this study, 60 Sprague-Dawley male rats weighing 300 to 350 g were used. Rats were randomly divided into six groups (n = 10 per group): control-1, control-2, sham-1, sham-2, experiment-1, and experiment-2. The same surgical procedure was performed in all rats; a full thickness Achilles tenotomy was performed, and the tendon was repaired using a modified Kessler suture. Enalapril (10 mg/kg/day) was orally given to the Experiment-1 and Experiment-2 groups for three and six weeks, respectively. Thirty rats were sacrificed at three weeks (Control-1, Sham-1, Experiment-1); the remaining 30 rats were sacrificed at six weeks (Control-2, Sham-2, Experiment-2). Then, macroscopic, biomechanical, and histologic investigations were performed. RESULTS: Adhesion degree was found macroscopically lower in the Experiment-1 and 2 groups than others. In the histologic examination, the fibrosis level was found the lowest in the Experiment-2 group. Biomechanical evaluation indicated that mean maximum resistance before tendon rupture was significantly higher in the Experiment-2 group than in other groups. CONCLUSION: Evidence from this study has shown that ACEIs can decrease fibrosis and tendon adhesion during tendon recovery in rats due to their antifibrotic effects as the result of Angiotensin-II suppression.

Evaluation of a novel semicircular locking external fixator for treating fractures of long bones: Biomechanical comparison with a circular external fixator.

PURPOSE: This study aimed to investigate the biomechanical properties of a novel semicircular locking external fixator with locking screw mechanism, shape of trapezoidal corrugations, half- ring designed for greater stability. MATERIALS AND METHODS: The novel external fixator had a half-ring with the shape of trapezoidal corrugations and locking screws fixing the bone at different angles in all three planes (sagittal, axial, and coronal). The biomechanical properties of the semicircular locking external fixator (group 1) were compared with those of a standard Ilizarov-type circular external fixator (group 2) (TST, Istanbul, Turkey) in an experimental study design. Five frames were used in each group. Standard PE 1000 (polyethylene) rod models (n = 10) simulating the tibia bone model were used. Both systems were compared biomechanically by applying axial and torsional loads simultaneously. RESULT: Two samples in group 2 were damaged before the test ended during axial loading. All of the samples in group 1 completed the tests without damage after 150,000 cycles. The axial stiffness of the semicircular locking external fixator was found to be significantly higher than that of the Ilizarov-type circular external fixator (p < 0.05). No statistically significant difference was found between the two fixators in torsional loading. The application time of semicircular locking external fixator was significantly shorter than Ilizarov-type circular external fixator (p < 0.05). CONCLUSION: The novel semicircular locking external fixator was biomechanically stronger than the Ilizarov-type external fixator for treating fractures of long bones. It can be used as a permanent external fixator for the definitive treatment of long bone fractures with soft tissue damage in terms of stability and application time.

An oblique osteotomy is better for subtrochanteric shortening in total hip arthroplasty for high hip dislocation: a mechanical comparison of four techniques.

BACKGROUND: Subtrochanteric femoral shortening is used during total hip arthroplasty for high hip dislocation in developmental dysplasia of hip patients. METHODS: We mechanically tested the stability of various commonly used subtrochanteric osteotomy techniques. As the equivalent of a femoral stem placed in a shortened femur without any stable fixation at the osteotomy line, 2 polyvinylchloride pipes were loosely intertwined. 4 different osteotomies (Z-subtrochanteric osteotomy, oblique-45° osteotomy, double Chevron-90° and 120° subtrochanteric osteotomy) were simulated. Torsional and axial loads were applied, and torsional stiffness was calculated for each test model. RESULTS: Z, double Chevron-90° and 120° subtrochanteric osteotomy models demonstrated lower mean torsional stiffness than oblique-45° osteotomy. With the highest torsional stiffness oblique-45° provides the best stability for treatment of high dislocation hips when a subtrochanteric osteotomy is added. CONCLUSIONS: This matches our previous clinical experience. Oblique osteotomy may also provide higher contact surfaces in the osteotomy lines to promote bone healing.

Effect of tranexamic acid on fracture healing in rats / Efeito do ácido tranexâmico na cura de fratura em ratos

ABSTRACT Introduction In this study we investigated the effect of tranexamic acid (TXA) on fracture healing in an established animal model, when used to stop bleeding in orthopedic trauma surgery. Materials and Methods This study was a randomized, controlled, laboratory study. Eighteen Sprague-Dawley rats were randomly assigned to three groups, either receiving TXA intravenously (Group 1), TXA topically (Group 2), or isotonic TXA intravenously and TXA topically in the same amounts for the control group (Group 3). First, a Kirschner wire was inserted retrogradely into the femoral intramedullary canal. Then the femurs were fractured at the midshaft region with blunt guillotine. After 4 weeks, the rats were sacrified and the femurs harvested. Cortical bone volume, callus volume, and bone mineral density were calculated using computer tomography scans. Torsion tests were performed. Groups were compared by maximum torque to failure and callus stiffness. Results There were no statistical differences in torque to failure and stiffness between the 3 groups. There were no differences in mean total bone volume, callus volume, percent bone volume, or callus density between the groups. Conclusions A single dose of topical or intravenous TXA has no negative effect on fracture healing when used in traumatic femur fracture surgery in an animal model. Evidence level II; Randomized controlled experimental study.

RESUMO Introdução Neste estudo, investigamos o efeito do ácido tranexâmico (TXA) sobre a consolidação de fraturas em um modelo animal estabelecido, quando é usado para estancar o sangramento em cirurgias de trauma ortopédico. Materiais e Métodos Trata-se de estudo de laboratório randomizado e controlado. Dezoito ratos Sprague-Dawley foram atribuídos randomicamente em três grupos, que receberam TXA por via intravenosa (Grupo 1), TXA tópico (Grupo 2) ou isotônico por via intravenosa e tópico na mesma quantidade como grupo controle (Grupo 3). Primeiro, foi inserido um fio de Kirschner por via retrógrada no canal intramedular femoral. Em seguida, o fêmur dos animais foi fraturado na região média do corpo do fêmur com guilhotina romba. Depois de quatro semanas, os ratos foram sacrificados e os fêmures foram retirados. O volume do osso cortical, o volume do calo e a densidade mineral óssea foram calculados por meio de tomografia computadorizada e foram realizados testes de torção. Os grupos foram comparados de acordo com o torque máximo até a falha e a rigidez do calo. Resultados Não houve diferença estatística no torque até a falha e rigidez entre os três grupos nem diferenças entre os grupos quanto ao volume médio total do osso, volume e densidade do calo e percentual de volume ósseo. Conclusões Uma dose única de TXA tópico ou intravenoso não tem efeito negativo sobre a consolidação da fratura quando usada em cirurgia de fratura traumática de fêmur em modelo animal. Nível de evidência II; Estudo experimental controlado randomizado.

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.

Tear Completion Versus In Situ Repair for 50% Partial-Thickness Bursal-Side Rotator Cuff Tears: A Biomechanical and Histological Study in an Animal Model.

BACKGROUND: Tear completion followed by repair (TCR) and in situ repair (ISR) have been widely used for bursal-side partial-thickness rotator cuff tears (PTRCTs). Both techniques have shown favorable results; however, controversy continues in terms of the best management. PURPOSE: To compare the histological and biomechanical outcomes of these 2 techniques for 50% partial-thickness bursal-side rotator cuff tear repair in a rabbit model. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 27 rabbits were used in this experimental study. Seven rabbits were sacrificed at the beginning of the study to form an intact tendon control group. A chronic 50% partial-thickness bursal-side tear model was created in 20 rabbits, and 5 rabbits were sacrificed for biomechanical testing of chronic partial-thickness tears (control group) without repair. In 15 rabbits, partial-thickness tears were repaired after 8 weeks. Partial-thickness tears in the right shoulders were completed to full thickness and repaired; in contrast, left shoulders were repaired in situ. All rabbits were euthanized 8 weeks after the repair. The tendons were tested biomechanically for ultimate failure, linear stiffness, and displacement. Histological evaluations of tendon-to-bone healing were performed via the modified Watkins score. RESULTS: Macroscopically, all repaired tendons were attached to the greater tuberosity. The TCR group had a higher failure load than the ISR group, with mean values of 140.4 ± 13.8 N and 108.1 ± 16.6 N, respectively (P = .001). The modified Watkins score was significantly higher in the TCR group (23.5; range, 22-27) than in the ISR group (19.5; range, 16-22) (P = .009). CONCLUSION: Both repair techniques are effective for 50% partial-thickness bursal-side rotator cuff tears; however, TCR yields significantly superior biomechanical and histological characteristics compared with ISR. CLINICAL RELEVANCE: Tear completion and repair technique may increase tendon-to-bone healing and thereby reduce re-rupture rate in the partial thickness bursal side rotator cuff tears.

Evaluation of two interforaminal implants and implant-assisted removable dentures on stress distribution: an in vitro study.

OBJECTIVES: In mandibular edentulism, the treatment option with a two-interforaminal implant-retained bridge and a removable partial denture is rarely evaluated in literature. The aim of this in vitro study was to evaluate the stress distribution of this treatment option by comparing it with traditional treatment options with interforaminal implants in the edentulous mandible. MATERIALS AND METHODS: Two interforaminal implants were placed in a formalin-fixed cadaver mandible, and overdentures with three different types of attachments were fabricated: (1) two ball attachments and an overdenture, (2) a Dolder bar and an overdenture, and (3) screw-retained two-implant inter-canine porcelain fused to a metal bridge and an implant-assisted removable denture (IARD) with precision attachments. Three biting conditions were generated for each denture type, and the strains were documented under vertical loading of 100 N. RESULTS: The calculated strain values from measured strains in all measurement sites and loading conditions for the screw-retained two-implant inter-canine porcelain fused to a metal bridge and a cast framework partial denture with precision attachments situation were lower than in the other scenarios (P<0.05). CONCLUSION: Within the limitations of the present study, it can be concluded that an IARD may be a reasonable and valuable alternative to ball attachments or a bar in two interforaminal implants, especially when the patients prefer to be able to show their teeth even when they take out their removable dentures.

Effects of Denture Base Thicknesses and Reinforcement on Fracture Strength in Mandibular Implant Overdenture with Bar Attachment: Under Various Acrylic Resin Types.

OBJECTIVE: This study aimed to assess the effect of reinforcement, denture base thickness, and acrylic resin types on dynamic and static fracture strength in mandibular implant overdentures with bar attachment. MATERIALS AND METHODS: One hundred and eight experimental mandibular implant overdentures with bar attachments were fabricated in three main groups, namely unreinforced (control: C), reinforced with unidirectional glass fibers (FR), and Co-Cr cast metal (MR). Each group included denture bases of 2-, 3-, and 4-mm thicknesses and produced with conventional (CA) and high-impact acrylic (HIA) resins. Specimens were thermocycled (5,000 times, 5-55°C) then subjected to a 400,000 cyclic load regime. Unbroken specimens were then loaded until fracture by a universal testing machine. Differences in mean fracture resistance among the groups were compared using the one-way analysis of variance (with post hoc Tukey's honestly significant difference test) and Student's t-tests (α = 0.05). RESULTS: Fracture strength increased significantly when the denture base thickness was increased (p = 0.001). The 2-mm denture base thickness was not enough for reinforcement. The fracture strength of the FR groups was significantly higher than other groups for 3- and 4-mm thicknesses (p = 0.001). The fracture strength of the HIA resin was significantly higher than CA resin in FR groups (p = 0.029 and p = 0.001). MR groups showed the weakest fracture strength. CONCLUSIONS: The 2-mm denture base thickness had sufficient fracture strength without reinforcement and a positive relationship between acrylic resin thickness and fracture resistance was found.

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).

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.

Decellularization of Trachea With Combined Techniques for Tissue-Engineered Trachea Transplantation.

OBJECTIVES: The purpose of this study is to shorten the decellularization time of trachea by using combination of physical, chemical, and enzymatic techniques. METHODS: Approximately 3.5-cm-long tracheal segments from 42 New Zealand rabbits (3.5±0.5 kg) were separated into seven groups according to decellularization protocols. After decellularization, cellular regions, matrix and strength and endurance of the scaffold were followed up. RESULTS: DNA content in all groups was measured under 50 ng/mg and there was no significant difference for the glycosaminoglycan content between group 3 (lyophilization+deoxycholic acid+de-oxyribonuclease method) and control group (P=0.46). None of the decellularized groups was different than the normal trachea in tensile stress values (P>0.05). Glucose consumption and lactic acid levels measured from supernatants of all decellularized groups were close to group with cells only (76 mg/dL and 53 mg/L). CONCLUSION: Using combination methods may reduce exposure to chemicals, prevent the excessive influence of the matrix, and shorten the decellularization time.