Suture anchor fixation strength in the Latarjet procedure: a biomechanical study in cadavers.

BACKGROUND: The use of metallic screws for graft fixation during the Latarjet procedure is not devoid of complications. The purpose of the present cadaver study was to determine the initial strength of coracoid graft fixation using suture anchors and compare it to that of the traditional screw fixation of the graft using a fresh frozen human shoulder cadaver model. MATERIALS AND METHODS: Twelve unpaired fresh frozen cadaver shoulders were utilized. In the first group, suture anchor fixation of the graft was used, while 3.75-mm cannulated screws were used in the second group. The specimens were then cyclically loaded from 5 to 150 N at a speed of 0.05 mm/s for 100 cycles. After cyclic loading, each specimen was then loaded at a constant rate of 0.5 mm/s until 7 mm of displacement. Cyclic elongation, peak-to-peak displacement, stiffness and maximum load were measured. RESULTS: There were no significant differences between the traditional screw fixation and fixation using suture anchors in elongation, peak-to-peak displacement, stiffness and maximum load. CONCLUSIONS: In this study, traditional screw fixation and fixation using suture anchors did not significantly affect biomechanical performance in a classic Latarjet procedure.

Subtrochanteric shortening in total hip arthroplasty: biomechanical comparison of four techniques.

Safe reduction of the femoral head into the true acetabulum requires a certain amount of femoral shortening in patients with high dislocation of the hip. In subtrochanteric shortening applications, to reduce complications it is necessary to maintain a stable fixation at the osteotomy line. The purpose of this study is to investigate frequently used methods from a biomechanical point of view. Four osteotomy groups were created with composite femurs to investigate subtrochanteric osteotomies; transverse, oblique, z-subtrochanteric and double Chevron. All loading tests were carried out with two implant types both with and without strut graft and cable fixation. No single inherent feature increasing the stability of the investigated osteotomy types was found. Additionally graft application did not have a significant contribution to stability.

A Novel Electromechanical Intramedullary Nail System for Limb Lengthening.

Background/Purpose of the Study: Many methods have been developed to treat leg length discrepancies. Extensible intramedullary nails are the most commonly used systems. However, complications such as excessive distraction, blockage of the nail, aditional surgery, uncontrolled lengthening and much pain occur during the use of these systems, and the desired success rate cannot be achieved. This study aims to develop a new extensible intramedullary system with two mechanisms (electronical and mechanical) for femur and tibia that treats leg length inequalities in a way that allows lengthening without complications as much as possible and does not require a second surgical intervention. It was planned to perform basic mechanical and cadaver functional tests of the new system, which will be designed and developed for this purpose. Methods: The 3D design of the system has been completed with 3D computer software. A compact system has been developed that is mechanically activated by sudden axial loading and electronically activated by a controllable electric motor. Basic mechanical and functional tests of the new system have been performed within a cadaver. Results: The rapid prototype of the system with electronical and mechanical units has been produced. As a result of the mechanical tests (axial loading), the nail was found to be resistant to compression forces. Its application to the cadaver and function tests was successfully performed. Conclusions: We believe that the system we have developed will have advantages, such as working principle, ease of application, controlled lengthening, patient mobility compared to existing leg lengthening methods. The success of the system in practice will be evaluated by in-vivo animal experiments after more detailed mechanical experiments on cadavers. According to the results, it will be ready for human use by performing necessary restorations.

Comparison of five percutaneous pinning methods for unstable extra-articular distal radius fractures: A mechanical study using sawbones.

OBJECTIVES: This study aims to mechanically compare five different extra-focal bi-cortical pin configurations (using two and three pins) employed for fixation of a simulated unstable extra-articular distal radius fracture with dorsal comminution using a sawbone model. MATERIALS AND METHODS: This in vitro mechanical study was conducted between June 2019 and July 2019. A standard fracture model (Arbeitsgemeinschaft für Osteosynthesefragen [AO] type 23-A3.3) was created using a fourth generation composite artificial radius bone. Five groups with two- and three-pin configurations were tested under axial, volar, and dorsal loading with a universal test device. Mean stiffness values were compared statistically. RESULTS: Comparison of stiffness values from axial and volar loading tests between groups in paired comparison showed no statistically significant difference (p=0.194 and p=0.086, respectively). Dorsal loading tests showed statistically significant difference between the groups in pairwise comparison (p=0.002). Three-pin groups (Groups 3, 4, and 5) had higher stiffness values compared to two-pin groups (Groups 1 and 2) in dorsal loading tests (p=0.001). Three-pin configuration test groups with two divergent or convergent pins from the radial styloid performed better compared to both two-pin groups (p=0.01, p=0.002) in dorsal loading tests. CONCLUSION: Our data demonstrated that the three-pin configuration with two divergent or convergent Kirschner wires from the styloid and a third wire from the dorsal/ulnar cortex had higher stiffness values compared to two-pin configurations in dorsal loading tests. When indicated, we suggest the use of a three-pin construct. Particularly in cases with a risk of volar angulation, we recommend a three-pin configuration with two divergent or convergent bi-cortical Kirschner wires.

Comparison of two different screw trajectories in the treatment of oblique scaphoid fractures: A mechanical study on composite bone models.

OBJECTIVES: In this mechanical study, we aimed to compare two different screw trajectories in terms of durability against axial loads on oblique scaphoid fractures using composite bone models. MATERIALS AND METHODS: Oblique osteotomies were made along the dorsal sulcus of 14 composite scaphoid bone models. Following this, all bone models were randomly classified. One group of bones were fixed with a screw placed perpendicular to the osteotomy line and the other group was fixed with a screw placed centrally down the long axis of the scaphoid bone. Each scaphoid bone model was positioned on a mechanical testing machine. Subsequently, axial loading tests were applied on each bone model to measure the amount of loading required to cause 2-mm displacement and failure on the osteotomy side and maximum displacement at the time of failure on scaphoid bone models. RESULTS: There was no statistically significant difference in load to 2-mm displacement and failure between the two groups (p>0.05). Also, there was no statistically significant difference between the two groups in terms of maximum displacement seen on failure (p>0.05). CONCLUSION: In our study, we found that the stability of the screws which laid perpendicular to the fracture line and parallel to the long axis of the scaphoid was the same in fixing oblique scaphoid fractures.

Biomechanical comparison of tigecycline loaded bone cement with vancomycin and daptomycin loaded bone cements.

OBJECTIVE: The objectives of this study were "1" to analyze the compressive and tensile mechanical strength characteristics of tigecycline loaded bone cement and "2" to compare them with those of vancomycin and daptomycin loaded bone cements which are used in prosthetic joint infections complicated with resistant microorganisms. METHODS: In this study, three experimental groups, which consisted of vancomycin (subgroups containing 1 g, 2 g, and 3 g vancomycin), daptomycin (subgroups containing 0.5 g, 1 g, and 1.5 g daptomycin), and tigecycline (subgroups containing 50 mg, 100 mg, and 150 mg tigecycline) and one control group without antibiotics were used. Using a standardized protocol, all antibiotic loaded bone cements were prepared. For each antibiotic group, including the control group, 10 samples were tested. All samples were biomechanically tested in terms of compressive strength and tensile strength. RESULTS: Compression tests showed that all determined antibiotic concentrations resulted in a significant decrease when compared with the control group (p<0.0011). Vancomycin and daptomycin study groups demonstrated lower tensile strength than the control group (p<0.0011). However, comparison of tensile values of tigecycline study groups with the control group revealed no significant difference (p>0.0011). In addition, all statistically significant results from between groups comparisons revealed higher tensile and compressive mechanical strength values for the tigecycline groups (p<0.0011). CONCLUSION: Evidence from this study has demonstrated that tigecycline loaded bone cement may have no mechanical disadvantage compared with vancomycin and daptomycin loaded bone cements in terms of mechanical strength when used at defined concentrations.

Which is the best fixation method for lateral cortex disruption in the medial open wedge high tibial osteotomy? A biomechanical study.

When performing a medial opening wedge upper tibial osteotomy, a fracture into the lateral cortex can lead to loss of stability of the construct. The aim of this study was to assess different intra-operative techniques to overcome this problem, and test the stability under axial compression. Twenty eight calf tibias had a medial opening wedge osteotomy and lateral cortical fracture created and then were tested in four groups depending on how this fracture was fixed; none, a plate and screws, two staples, and a circular external fixator. Loss of medial height of the osteotomy line and lateral cortex micromotion was evaluated under maximal axial loading of 2,500 N. No fixation had significantly inferior results compared with the other three types. The plate and screws and staples showed better results than circular external fixation in terms of preserving the medial height, whereas the plate and screws and circular external fixator showed better results compared with staples in terms of lateral cortex stability. This study suggests that plate and screw fixation for lateral cortex disruption during the medial opening wedge upper tibial osteotomy has better stability under axial compression than staples or a circular external fixator.

Straight-Forward versus Bicortical Fixation Penetrating Endplate in Lumbosacral Fixation-A Biomechanical Study.

OBJECTIVE: Many lumbosacral fixation techniques have been described to offer a more screw-bone purchase. The forward anatomical fixation parallel to the endplate is still the most preferred method. Literature revealed little knowledge regarding the mechanical stability of lumbosacral trans-endplate fixation compared to the traditional trans-pedicular screw fixation method. The aim of this study is to assess the pull-out strength of lumbosacral screws penetrating the end plate and comparing it to the conventional trans-pedicular screw insertion method. METHODS: Eight lumbar and eight sacral vertebrae, with average age 69.4 years, Left pedicles of the 5th lumbar vertebrae were used for trans-endplate screw fixation, group 1A, right pedicles were used for anatomical trans-pedicular screw fixation, group 1B. In the sacral vertebrae, the right side S1 pedicles were used for trans-endplate fixation, group 2A, left side pedicles were used for anatomical trans-pedicular screw fixation, group 2B. The biomechanical tests were performed using the axial compression testing machine. All tests were applied using 2 mm/min traction speed. RESULTS: The average pull-out strength values of groups 1A and 1B were 403.78±11.71 N and 306.26±17.55 N, respectively. A statistical significance was detected with p=0.012. The average pull-out strength values of groups 2A and 2B were 388.73±17.03 N and 299.84±17.52 N, respectively. A statistical significance was detected with p=0.012. CONCLUSION: The trans-endplate lumbosacral fixation method is a trustable fixation method with a stronger screw-bone purchase and offer a good alternative for surgeons specially in patients with osteoporosis.

Hexagonal grafts in mosaicplasty: Biomechanical comparison of standard cylindrical and novel hexagonal grafts in calf cadaver model.

OBJECTIVE: Cylindrical grafts are currently used to cover defected area in mosaicplasty. However, there are some difficulties with cylindrical grafts, such as potential dead space between grafts and insufficient coverage. Hexagonal graft (honeycomb model) was created and evaluated in this biomechanical study. Hypothesis was that harvesting grafts with hexagonal shape, which has the best volume geometry characteristics in nature, would be biomechanically advantageous and provide superior pull-out strength. METHODS: Total of 24 fresh calf femurs were divided into 3 equal groups. In the first group, 1 cylindrical and 1 hexagonal graft were compared. Second group consisted of 3 cylindrical and 3 hexagonal grafts. Third group was designed to evaluate effect of graft depth; hexagonal graft implanted at 5 mm depth was compared with 20-mm-deep hexagonal graft. All specimens were subjected to pull-out test. Friction field and graft surface area were also evaluated. RESULTS: Pull-out strength comparison of 15-mm-deep triple cylindrical grafts and 15-mm-deep triple hexagonal grafts in second group revealed statistically significant difference in favor of hexagonal grafts (p < 0.05). Surface area of cylindrical graft with 9-mm diameter was calculated to be 50.27 mm2, while hexagonal graft surface area was 55.425 mm2. Volume ratio of cylindrical and hexagonal grafts was 753.98 mm3 and 831.375 mm3, respectively. CONCLUSION: This biomechanical study demonstrated that graft geometry, especially in multiple graft applications, is a factor that influences stability. Hexagonal grafts appear to be more stable than cylindrical grafts in multiple applications, and they may be used to cover a larger defected area.

Central defect type partial ACL injury model on goat knees: the effect of infrapatellar fat pad excision.

BACKGROUND: The mid-substance central defect injury has been used to investigate the primary healing capacity of the anterior cruciate ligament (ACL) in a goat model. The sagittal plane stability on this model has not been confirmed, and possible effects of fat pad excision on healing have not been evaluated. We hypothesize that excising the fat pad tissue results in poorer ligament healing as assessed histologically and decreased tensile strength of the healing ligament. We further hypothesize that the creation of a central defect does not affect sagittal plane knee stability. METHODS: A mid-substance central defect was created with a 4-mm arthroscopic punch in the ACLs of right knees of all the subjects through a medial mini-arthrotomy. Goats were assigned to groups based on whether the fat pad was preserved (group 1, n = 5) or excised completely (group 2, n = 5). The left knees served as controls in each goat. Histopathology of the defect area along with measurement of type I collagen in one goat from each group were performed at 10th week postoperatively. The remaining knees were evaluated biomechanically at the 12th week, by measuring anterior tibial translation (ATT) of the knee joints at 90° of flexion and testing tensile properties (ultimate tensile load (UTL), ultimate elongation (UE), stiffness (S), failure mode (FM)) of the femur-ACL-tibia complex. RESULTS AND DISCUSSION: Histopathology analysis revealed that the central defect area was fully filled macroscopically and microscopically. However, myxoid degeneration and fibrosis were observed in group 2 and increased collagen type I content was noted in group 2. There were no significant differences within and between groups in terms of ATT values (p = 0.715 and p = 0.149, respectively). There were no significance between or within groups in terms of ultimate tensile load and ultimate elongation; however, group 2 demonstrated greater stiffness than group 1 that was correlated with the fibrotic changes detected microscopically (p = 0.043). CONCLUSIONS: The central defect type injury model was confirmed to be biomechanically stable in a goat model. Resection of the fat pad was noted to negatively affect defect healing and increase ligament stiffness in the central defect injury model.

Biomechanical evaluation of different internal fixation methods for humerus shaft fractures with medial butterfly fragment.

OBJECTIVE: The aim of this study was to compare the biomechanical strength of three fixation methods in humerus shaft fractures with medial butterfly fragment. METHODS: An AO 12B2 fracture with butterfly fragment was created in 21 synthetic cortical shell humeri. Humeri were divided into 3 groups which underwent bridge plating, antegrade intramedullary nailing or retrograde intramedullary nailing. Rotational and four-point bending test displacement curves were obtained. RESULTS: Mean displacement values in the torsion tests were 37.38 (range: 25.75 to 55.69) mm in the bridge plating group, 26.55 (range: 21.25 to 41.81) mm in the antegrade nailing group, and 33.23 (range: 27.50 to 46.45) mm in the retrograde nailing group. Mean displacement values in the four-point bending test were 3.27 (range: 2.54 to 3.73) mm in the bridge plating group, 3.17 (range: 2.69 to 3.55) mm in the antegrade nailing group, and 3.15 (range: 2.10 to 4.03) mm in the retrograde nailing group. No significant difference was found among the groups (p>0.05). CONCLUSION: The biomechanical stability of bridge plating, antegrade intramedullary nailing and retrograde intramedullary nailing appears to be similar in the fixation of humerus shaft fractures with medial butterfly fragment.

Comparison of screw-fixation stabilities of first metatarsal shaft osteotomies: a biomechanical study.

OBJECTIVES: Although metatarsal shaft osteotomies have become popular in the surgical treatment of moderate or advanced hallux valgus owing to better reduction and stability, they present fixation problems as the angular correction increases. The purpose of this biomechanical study was to evaluate the effects of widely used metatarsal shaft osteotomies and a newly defined osteotomy modification on the stability of screw fixation at greater angular corrections. METHODS: Upon evaluation of known problems of shaft osteotomies, a new osteotomy type was designed that might provide an adequate contact area while allowing a greater angular correction, increased stability, and safer osteosynthesis. In our new modification of the Mau osteotomy, the proximal plantar notch that was defined for the Sammarco's modification to increase the contact area was created more proximally making an angle of about 50 degrees with the osteotomy, and the osteotomy was extended until 5 mm to the distal joint surface, aiming to increase the contact area and intrinsic stability. For biomechanical analysis, 30 standard metatarsal bone models (Sawbones) were divided into five groups equal in number for the following osteotomy methods: Myerson's modification of the Ludloff osteotomy, Mau osteotomy, scarf osteotomy, offset V osteotomy, and the new modification of the Mau osteotomy. Osteotomies were performed with a standard correction of 10 degrees in the intermetatarsal angle, followed by appropriate osteosynthesis with fixation by two Acutrak compression screws. The relationship between osteotomies and osteosynthesis in terms of stability was assessed by the three-point bending test. RESULTS: The mean stiffness of the Ludloff osteotomy was significantly lower than all the other osteotomy groups (p<0.05). Stiffness of the Mau group was significantly greater than three groups (p<0.05), but the difference from the offset V group did not reach significance. Stiffness of the new Mau modification was significantly greater than the scarf group (p=0.016), but did not differ significantly from the offset V group. Osteotomy groups with and without notching had similar stiffness values (p=0.582), whereas single notching was associated with a significantly greater stiffness compared to double notching (p=0.031). CONCLUSION: Our findings suggest that the new modification to the proximal shaft osteotomies moves the center of rotation of angulation more proximally and provides sufficient stability of screw fixation.

[Investigation of radioulnocarpal joint load distribution effects of radial shortening osteotomy for the treatment of Kienböck disease: a biomechanical study]. / Kienböck hastaligi tedavisinde kullanilan radyal kisaltma osteotomisinin radioulnokarpal ekleme binen yükler üzerindeki etkilerinin arastirilmasi: Biyomekanik çalisma.

OBJECTIVES: We evaluated the effects of radial shortening osteotomy on the radiolunate joint load distribution. MATERIALS AND METHODS: This biomechanical study used standard left wrist models made of solid foam (Sawbones, Malmö, Sweden). The radioulnocarpal joint load distribution was investigated in the normal wrist model and 2 mm and 4 mm radial shortening osteotomy models under 14 kgf and 25 kgf loads when the wrist position was neutral. RESULTS: In the normal wrist group, the comparison of the average pressure distributions under the 14 kgf and 25 kgf loads shows that the increase at the ulnocarpal joint loading and the decrease at the radiolunate joint loading were statistically significant (p=0.012, p=0.036, respectively). When we compared the respective average pressure distributions after 14 kgf and 25 kgf loading, there were no significant differences between the normal wrist and the osteotomy groups. CONCLUSION: Consequently, radial shortening osteotomy is not effective in decreasing radiolunate joint loading when the wrist is in neutral position.