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PURPOSE: It was hypothesized that using a Patient-Specific Cutting Guide (PSCG) would allow the creation of sawbones model osteotomies, identical in the 3 planes and the hinge parameters, that can be used for biomechanical studies. The aim of the study was to evaluate the accuracy of the PSCG system and to introduce and assess the new hinge parameter; the hinge area. METHODS: Six identical sawbones tibia models were identically set up for identical osteotomy cuts by the same surgeon in the same session and with identical instruments. A medical scanner was used to evaluate the 3D configuration of all the specimens. The analyzed parameters included the cutting angles in both the coronal and sagittal planes (degrees) and the hinge and the slicing areas (cm2), and the hinge thickness (mm). The values were statistically evaluated for average, standard deviation, 95% confidence index, and delta to the expected values were calculated. RESULTS: The mean values for the coronal and sagittal angles were 110.5̊±1̊ and 89.8̊±0.8̊, respectively. The 95% confidence index level ranged between 0.1̊, and 0.8̊ in both the coronal & the sagittal planes. The mean values for the hinge thickness, the hinge area, and the slicing area were 12.7±1.5mm, 4.2±0.9 cm2, and 18.3±1.2 cm2, respectively. CONCLUSION: In the presented study, it can be demonstrated that mechanically identical osteotomy specimens, with regard to the cutting planes and hinge parameters, can be reliably created using the PSCG. The identical specimens can be used for biomechanical research purposes to further expand our knowledge of the factors affecting osteotomy outcomes. LEVEL OF EVIDENCE: IV.

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Background: Shoulder arthroplasty is becoming increasingly common. With evolving implant designs, multiple humeral stem options exist for the surgeon to choose from. New stemless and short-stem systems are modular, remove less native bone stock, and better adapt to patient anatomy. It has been suggested that shorter stem implants may be protective against periprosthetic fracture; however, this has not been mechanistically evaluated. Therefore, this study aimed to biomechanically test synthetic humeri with long-stem, short-stem, and stemless arthroplasty components in a torsional manner to evaluate their response to loading and characterize failure. Methods: Twenty-four synthetic humeri were implanted with long stem, short stem, or stemless uncemented prosthesis, 8 in each group. Humeri were mounted in a custom testing jig with a morse taper interfacing with a mechanical testing system. After a 20N axial force, specimens were torsionally loaded to failure at 15 degrees/sec, with 50 Hz collection. Torque vs. rotation curves were generated for each specimen, and stiffness, yield, ultimate strength, and failure load were measured. ANOVA and post hoc pairwise comparisons were used to assess effect of stem type on mechanical test variable. The association of the stem type with fracture type was analyzed by a Fisher's Exact test. Statistical significance was set at P < .05. Results: During torsional loading, long-stem implants were significantly stiffer than short or stemless implants. The angle of implant yielding was similar across stem designs; however, stemless implants had a lower yield torque. This correlated with a decreased yield energy in stemless compared to short stems as well. Maximum torque and failure torque was also significantly higher in short-stem and long-stem implants compared to stemless. Discussion: Periprosthetic fractures in shoulder arthroplasty are a concern in low-energy trauma, and stem design likely plays a significant role in early implant-bone failure. Our results suggest stemless implants under torsional load fail at lower stress and are less stiff than stemmed implants. The failure mechanism of stemless implants through metaphyseal cancellous bone emphasizes the effect bone quality has on implant fixation. There is likely a balance of torsional stability to survive physiologic loads while minimizing diaphyseal stress and risk of diaphyseal periprosthetic fracture. This combined with revision and fixation options represent decisions the surgeon is faced with when performing shoulder arthroplasty.

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Biomedical engineers and physicists frequently use human or animal bone for orthopaedic biomechanics research because they are excellent approximations of living bone. But, there are drawbacks to biological bone, like degradation over time, ethical concerns, high financial costs, inter-specimen variability, storage requirements, supplier sourcing, transportation rules, etc. Consequently, since the late 1980s, the Sawbones® company has been one of the world's largest suppliers of artificial bones for biomechanical testing that counteract many disadvantages of biological bone. There have been many published reports using these bone analogs for research on joint replacement, bone fracture fixation, spine surgery, etc. But, there exists no prior review paper on these artificial bones that gives a comprehensive and in-depth look at the numerical data of interest to biomedical engineers and physicists. Thus, this paper critically reviews 25 years of English-language studies on the biomechanical properties of these artificial bones that (a) characterized unknown or unreported values, (b) validated them against biological bone, and/or (c) optimized different design parameters. This survey of data, advantages, disadvantages, and knowledge gaps will hopefully be useful to biomedical engineers and physicists in developing mechanical testing protocols and computational finite element models.

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Background Since posterior cervical fixation with lateral mass screws was introduced in 1979, multiple techniques have been described in the literature. However, no study to date has determined whether pre-drilling all lateral masses prior to screw insertion has a benefit over the traditional sequential drilling and screw insertion on the alignment of the screw-rod construct. This study sought to determine the efficacy and efficiency in achieving alignment with a novel pre-drilling technique compared to the traditional sequential drilling technique. The authors hypothesized that the novel pre-drilling technique could be applied more quickly and precisely than the traditional sequential drilling technique. Methods Eight cervical spine sawbones models were utilized to place 64 lateral mass screws by two surgeons. The pre-drilling technique was utilized to place 32 screws in four models, and the sequential drilling technique was utilized to place the 32 screws in the remaining four models. In the traditional sequential drilling technique, each lateral mass underwent screw tract preparation and insertion before proceeding to the subsequent vertebra. In the pre-drilling technique, all lateral masses were marked and drilled sequentially before screw placement. CT imaging with 3D reconstructions was generated for all models. Variability in screw placement and time taken to fully instrument the models were compared.  Results The mean time to completion of the pre-drilling technique was 337 ± 22 seconds compared to 490 ± 22 seconds with the traditional technique (p<0.01). There was a significantly higher variability in the coronal plane within the traditional group between C5 and C6 compared to other adjacent vertebrae (p<0.05). There was no significant difference in the start point variability and the overall tightness of line fit between the techniques. Conclusions Our study suggests that a novel pre-drilling technique for lateral mass screw insertion may be more efficient and reliable than the traditional sequential drilling technique. In addition, this technique may reduce the need for rod contouring or additional implants to optimize the alignment of cervical instrumentation. However, further clinical studies are necessary to validate the potential clinical and radiologic benefits of this described technique.

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BACKGROUND: In sawbones with proximal humerus fracture model, three different fixation configurations, Parallel-Straight K-wires, Cross-Straight K-wires and Palm-Tree Method, were biomechanically compared. METHODS: A total of 36 anatomical pediatric humerus sawbones models were used. They were divided into three equal groups; parallel fixation with straight K-wires (Group PS), cross fixation with straight K-wires (Group CS), and Palm-Tree Method (Group PT). Models were tested in abduction and torsional at a speed of 0.5 mm/s and a 0-5 mm displacement range. Loading (N) and Stiffness (N/mm) data were calculated and compared statistically. RESULTS: Group PS was significantly higher than the other two groups in abduction bending cyclic load values (P<0.001). It was also significantly higher in Group CS than in Group PT (P < 0.001). No significant differences were detected between the three different fixation groups' cyclic torsional load values (p < 0.05). CONCLUSION: The parallel configuration with straight K-wires will provide a more stable fixation than the cross configuration with straight or Palm-Tree Method in pediatric proximal humeral sawbones fracture modeling.

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Background: Olecranon fractures are common in motorcycle accidents, falls, or in direct elbow injury. In cases of transverse olecranon fracture, surgery is frequently required in adults. The aim of this study is to compare the biomechanical durability of suture anchor fixation in olecranon fractures to conventional tension band wiring technique in saw bones. Methods: 12 plastic saw bones were divided into 3 groups: tension band wiring fixation, modified Cha-Batman method, and a modified simple suture method using a suture anchor. After fixation, cyclic load tests were conducted for 1,000 cycles, at 5 Hz with a force of 10 N to 250 N. After cycling loading, the extent of displacement was measured using a non-contact coordinate measuring instrument, and statistical analysis performed. Results: The average displacement was significantly smaller in the modified Cha-Bateman method (1.4 mm) than in the tension band wiring method (3.8 mm, p = 0.007) and the modified simple suture method using suture anchor (3.3 mm, p = 0.012). There was no significant difference in displacement between tension band wiring fixation and the modified simple suture method (p = 0.564). Conclusions: This study provides a biomechanical basis for the hypothesis that the suture anchor technique in weak bone model could obtain results comparable to those of conventional tension band wiring. In particular, the modified Cha-Bateman method, showed stronger biomechanical properties than the tension band wiring method and modified simple suture method using a suture anchor. The current study could also provide pilot data that can be used in future experiments.

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BACKGROUND: The purpose of this study is to compare compression generated by a Precice magnetic lengthening intramedullary nail and a 5.0 mm limited contact dynamic compression plate. METHODS: Transverse osteotomy sites were created in the femoral shaft of ten Sawbones fourth generation composite femurs. Antegrade 10-degree trochanteric Precice nails and 8-hole, 5.0 mm plates were used for fixation. The plates were compressed by placing a neutral screw and three eccentrically drilled compression screws on alternating sides of the osteotomy. Average compression and distribution of compression were compared, and P-values <0.05 were considered statistically significant. FINDINGS: The Precice nail generated an average of 2.38 megapascal across the osteotomy sites. The plate generated an average of 0.70 megapascal (P < 0.001) with the initial compression screw, 0.93 megapascal (P < 0.001) after the second screw, and 1.04 megapascal (p < 0.001) after the final screw. The distribution of compression was assessed utilizing a polar transformation to compare pressure values. We found that the distribution of compression was more circumferentially uniform in the Precice nail group (P = 0.046). INTERPRETATION: This study demonstrates that an electromagnetic intramedullary device is capable of generating significantly higher compression, in a more uniform distribution, than a 5.0 mm limited contact dynamic compression plate in a Sawbones model. The results indicate that electromagnetic intramedullary nail systems may be an ideal alternative to compression plating for treatment of at-risk fractures, nonunions, delayed unions, and intercalary allograft reconstruction.

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The study utilized finite element method to determine displacements and stresses in a set of Pauwels Type III femoral neck fractures repaired using 3 techniques (cannulated screws (Triad), sliding hip screw (SHS), and a Hybrid (SHS + cannulated screws). The research found that shear displacement doubled between the 65° and 75° fracture angles regardless of fixation construct. The SHS alone was the least stable construct, with highest construct stresses and shear displacement along the fracture plane. The stability of the Hybrid and Triad constructs were similar, but stress in the Hybrid was lower suggesting it would provide a higher load to failure than the Triad.

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PURPOSE: The aim of this study was to investigate the biomechanical properties of the InternalBrace for lisfranc injuries. METHODS: A Sawbone model was developed comparing screw, suture button and InternalBrace. RESULTS: When loaded in axial tension at 0.5 mm/s, the screw was stiffest (2,240 N/mm), while the InternalBrace (200 N/mm) was stiffer than the suture button (133 N/mm). Cyclic loading with 10,000 cycles of 69 N, 138 N, and 207 N showed the InternalBrace maintained stiffness, but fatigued earlier than the suture button. CONCLUSION: The mechanical properties of the InternalBrace support clinical use, but further studies are needed regarding early weight bearing.

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BACKGROUND: Trauma can fracture the scapular neck. Typically, a single plate along the lateral scapula border affixes the glenoid fragment to the scapula. This method is limited by difficulty in screw placement, frequent excessive soft tissue dissection, and risk for neurovascular injury. Substituting 2 smaller plates bridging the scapular neck mitigates these limitations, but no comparative mechanical data between techniques exists. Therefore, we compared the mechanical properties of two constructs securing a simulated scapular neck fracture. METHODS: Twenty synthetic human scapulae underwent a templated scapular neck fracture. Repairs were performed with a single plate on the lateral scapular border (Column method), or two small plates parallel to the lateral border (Neck method). Measures of displacement, force, and stiffness were quantified during cyclic testing (20-150 N, 1 Hz, 1000 cycles) and loading to failure. Statistical comparisons were made with t-tests (p ≤ 0.050). FINDINGS: The column constructs had higher displacements than neck constructs after 1000 cycles, but differences were small (mean) 0.18 (SD 0.01) vs. 0.15 (0.02) mm (p ≤ 0.004). Cyclic stiffness was 655 (43) and 790 (88) N/mm for the column and neck constructs, respectively (p ≤ 0.003). Both techniques performed comparably in failure loading: at 1 mm of gap reduction the compressive loads were 426 (61) N and 428 (48) N and stiffness was 354 (129) and 334 (80) N/mm for the column and neck constructs, respectively. INTERPRETATION: Given the surgical advantages, the neck fixation may be more suitable without biomechanical compromise compared to traditional lateral column fixation.

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PURPOSE: The transversely oriented fracture lines are very difficult to reduce during operations, even after clear exposure of the fracture site, in acetabular fractures. The purpose of this study is to verify the quality of reduction between the different subtypes (transtectal, juxtatectal, and infratectal) of transverse fractures. This study also determined the proper type of clamps to use and the proper zone for achieving accurate reductions in Sawbones models. MATERIALS AND METHODS: Six fractures in 3 different subtypes of transverse fractures were artificially created. Ten different reduction clamps were applied for reduction of the fractures. Twelve holes around the fracture were drilled for the maintenance of the clamps. The fracture displacements were measured at the extra-articular area and the intra-articular joint portion. The pictures of the intra-articular fracture displacements were taken by a camera and these were uploaded and analyzed by the TraumaCad® computer program (Brainlab). RESULTS: The reduction quality was poor in order of transtectal, juxtatectal and infratectal. The intraarticular opening was more prominent in the transtectal subtype. The safe zone, when giving consideration of the neurovascular bundles, was a quadrilateral surface of the ilium. Drill holes are useful for maintenance of the reduction clamps. Reduction clamps with points (Weber clamp) were the best for maintenance and accurate reduction. Regarding the concerns of placement of clamps, the middle to posterior combination was the best. The upper hole among the posterior holes in the ilium was the most likely to well reduce the intra-articular opening. CONCLUSION: Transtectal was the more complicated subtype in the aspect of reduction quality. The Weber type reduction clamp was the best for reduction by centrally located holes in the quadrilateral surface and posteriorly located iliac holes in transverse acetabular fractures. The upper hole, among the posterior holes in the ilium, was the best for reduction of the fracture displacements in the intraarticular portion of acetabulum.

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STUDY DESIGN: Prospective randomized study. OBJECTIVES: To define the impact of an inexpensive, user-friendly, and reproducible lumbar pedicle screw instrumentation bioskills training module and evaluation protocol. METHODS: Participants were randomized to control (n = 9) or intervention (n = 10) groups controlling for level of experience (medical students, junior resident, or senior resident). The intervention group underwent a 20-minute bioskills training module while the control group spent the same time with self-directed study. Pre- and posttest performance was self-reported (Physician Performance Diagnostic Inventory Scale [PPDIS]). Objective outcome scores were obtained from a blinded fellowship-trained attending orthopedic spine surgeon using Objective Structured Assessment of Technical Skills (OSATS) and Objective Pedicle Instrumentation Score metrics. In addition, identification of pedicle breach and breach anatomic location was measured pre- and posttest in lumbar spine models. RESULTS: The intervention group showed a 30.8% improvement in PPDIS scores, compared with 13.4% for the control group (P = .01). The intervention group demonstrated statistically significant 66% decrease in breaches (P = .001) compared with 28% decrease in the control group (P = .06). Breach identification demonstrated no change in accuracy of the control group (incorrect identification from 32.2% pre- to posttest 35%; P = .71), whereas the intervention group's improvement was statistically significant (42% pre- to posttest 36.5%; P = .0047). CONCLUSIONS: We conclude that a concise lumbar pedicle screw instrumentation bioskills training session can be a useful educational tool to augment clinical education.

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In order to facilitate the learning of distal radius shortening osteotomy by junior surgeons, the main assumption was that using a three-dimensional procedural simulator was better than a bone procedural simulator. After viewing a video, ten junior surgeons performed a distal radius shortening osteotomy: five with a bone procedural simulator (Group 1) and five with a three-dimensional procedural simulator (Group 2). All subsequently performed the same surgery on fresh cadaveric bones. The duration of the procedure, shortening of the radius, and the level of osteotomy were significantly better in Group 2. The three-dimensional procedural simulator seems to teach distal radius osteotomy better than a bone model and could be useful in teaching and learning bone surgery of the wrist.

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Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in fixation failure. While numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw pull-out force, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of high strength calcium phosphate cements (hsCPCs, specifically dicalcium phosphate) affected the corresponding orthopedic screw pull-out force in urethane foam models of "healthy" and "osteoporotic" synthetic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R2 = 0.79) was weaker than correlation with total cement porosity (R2 = 0.89). In open pore Sawbone that mimics "healthy" cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). High strength, low porosity cements also produced higher pull-out forces (50-190% increase) in "healthy" Sawbones with cortical fixation if the failure strength of the cortical material was similar to, or greater than (a metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell, thereby increasing the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5mL (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity calcium phosphate cement (CPC) may still produce a significant improvement in screw pull-out force. When the correlation strength of all the tested models were compared both cement porosity and compressive strength accurately predicted pull-out force (R2=1.00, R2=0.808), though prediction accuracy depended upon the strength of the material surrounding the Sawbone. The correlations strength was low for bone with no, or weak, cortical fixation (R2=0.56, 0.36). Higher strength and lower porosity CPCs also produced greater pull-out force (1-1.5kN) than commercial CPC (0.2-0.5kN), but lower pull-out force than PMMA (2-3kN). The results of this study suggest that the likelihood of screw fixation failure may be reduced by selecting calcium phosphate cements with lower porosity and higher compressive strength, in patients with healthy bone mineral density and/or sufficient cortical thickness. This is of particular clinical relevance when fixation with metal plates is indicated, or where the augmentation volume is limited.

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BACKGROUND: A fracture through the proximal radius is a theoretical concern after cortical button distal biceps fixation in an active patient. The permanent, nonossified cortical defect and medullary tunnel is at risk during a fall eliciting rotational and compressive forces. We hypothesized that during simulated torsion and compression, in comparison with unaltered specimens, the cortical button distal biceps repair model would have decreased torsional and compressive strength and would fracture in the vicinity of the bicipital tuberosity bone tunnel. METHODS: Sixteen fourth-generation composite radius Sawbones models were used in this controlled laboratory study. A bone tunnel was created through the bicipital tuberosity to mimic the exact bone tunnel, 8 mm near cortex and 3.2 mm far cortex, made for the BicepsButton distal biceps tendon repair. The radius was then prepared and mounted on either a torsional or compression testing device and compared with undrilled control specimens. RESULTS: Compression tests resulted in average failure loads of 9015.2 N in controls versus 8253.25 N in drilled specimens ( P = .074). Torsional testing resulted in an average failure torque of 27.3 Nm in controls and 19.3 Nm in drilled specimens ( P = .024). Average fracture angle was 35.1° in controls versus 21.1° in drilled. Gross fracture patterns were similar in compression testing; however, in torsional testing all fractures occurred through the bone tunnel in the drilled group. CONCLUSION: There are weaknesses in the vicinity of the bone tunnel in the proximal radius during biomechanical stress testing which may not be clinically relevant in nature. CLINICAL RELEVANCE: In cortical button fixation, distal biceps repairs creates a permanent, nonossified cortical defect with tendon interposed in the bone tunnel, which can alter the biomechanical properties of the proximal radius during compressive and torsional loading.

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STUDY DESIGN: Randomized, prospective study within an orthopedic surgery resident program at a large urban academic medical center. OBJECTIVES: To develop an inexpensive, user-friendly, and reproducible lumbar laminectomy bioskills training module and evaluation protocol that can be readily implemented into residency training programs to augment the clinical education of orthopedic and neurosurgical physicians-in-training. METHODS: Twenty participants comprising senior medical students and orthopedic surgical residents. Participants were randomized to control (n = 9) or intervention (n = 11) groups controlling for level of experience (medical students, junior resident, or senior resident). The intervention group underwent a 40-minute bioskills training module, while the control group spent the same time with self-directed study. Pre- and posttest performance was self-reported by each participant (Physician Performance Diagnostic Inventory Scale [PPDIS]). Objective outcome scores were obtained from a blinded fellowship-trained attending orthopedic spine surgeon using Objective Structured Assessment of Technical Skills (OSATS) and Objective Decompression Score metrics. RESULTS: When compared with the control group, the intervention group yielded a significant mean improvement in OSATS (P = .022) and PPDIS (P = .0001) scores. The Objective Decompression Scores improved in the intervention group with a trend toward significance (P = .058). CONCLUSIONS: We conclude that a concise lumbar laminectomy bioskills training session can be a useful educational tool for to augment clinical education. Although no direct clinical correlation can be concluded from this study, the improvement in trainee's technical and procedural skills suggests that Sawbones training modules can be an efficient and effective tool for teaching fundamental spine surgical skills outside of the operating room.

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OBJECTIVE: The purpose of the present study was to compare inter-fragmentary compression pressures after fixation of a simulated type II odontoid fracture with the headless compression Herbert screw and a half threaded cannulated lag screw. METHODS: We compared inter-fragmentary compression pressures between 40- and 45-mm long 4.5-mm Herbert screws (n=8 and n=9, respectively) and 40- and 45-mm long 4.0-mm cannulated lag screws (n=7 and n=10, respectively) after insertion into rigid polyurethane foam test blocks (Sawbones, Vashon, WA, USA). A washer load cell was placed between the two segments of test blocks to measure the compression force. Because the total length of each foam block was 42 mm, the 40-mm screws were embedded in the cancellous foam, while the 45-mm screws penetrated the denser cortical foam at the bottom. This enabled us to compare inter-fragmentary compression pressures as they are affected by the penetration of the apical dens tip by the screws. RESULTS: The mean compression pressures of the 40- and 45-mm long cannulated lag screws were 50.48±1.20 N and 53.88±1.02 N, respectively, which was not statistically significant (p=0.0551). The mean compression pressures of the 40-mm long Herbert screw was 52.82±2.17 N, and was not statistically significant compared with the 40-mm long cannulated lag screw (p=0.3679). However, 45-mm Herbert screw had significantly higher mean compression pressure (60.68±2.03 N) than both the 45-mm cannulated lag screw and the 40-mm Herbert screw (p=0.0049 and p=0.0246, respectively). CONCLUSION: Our results showed that inter-fragmentary compression pressures of the Herbert screw were significantly increased when the screw tip penetrated the opposite dens cortical foam. This can support the generally recommended surgical technique that, in order to facilitate maximal reduction of the fracture gap using anterior odontoid screws, it is essential to penetrate the apical dens tip with the screw.

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OBJECTIVE: Pauwels III femoral neck fractures are highly unstable. These fractures are commonly treated with three cannulated screws or sliding hip screw (SHS) implants, however high rates of non-union persist. A hybrid SHS construct has recently been proposed. The objective of the study was to compare this construct to the familiar inverted triad of cannulated screws and to a single SHS. METHODS: Fourth generation biomechanical femur analogs were used to create a highly repeatable injury model. The hybrid SHS construct contained a SHS with two superior cannulated screws in an inverted triangle configuration. Eight samples for each construct were biomechanically evaluated and the results compared using ANOVA (p<0.05). RESULTS: The cannulated triad and hybrid SHS provided similar stiffness and fracture gap motion. The single SHS exhibited significantly lower stiffness and larger fracture plane diastasis than either the inverted triangle of cannulated screws or hybrid SHS (p<0.05). None of the constructs exhibited catastrophic failure during cyclic loading nor under loading up to 2.5 times body weight. CONCLUSIONS: The single SHS provided the least stable fracture fixation, while the inverted triad and hybrid SHS constructs were mechanically similar. The fracture repair simulated here illustrates how these repairs have the potential to return near pre-fracture strength in ideal conditions with young, healthy bone. However; in clinical situations where comminution impairs load transfer through the cortices the hybrid SHS may be the most favorable option.

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PURPOSE: Metacarpal fractures are commonly treated by a variety of means including casting or open reduction internal fixation when unacceptable alignment is present following attempted closed reduction. Dorsal plating with either single-row 2-dimensional or double-row 3-dimensional plates has been proposed. This study's purpose was to determine if there are any differences in fixation construct stability under cyclic loading and subsequent load to failure between the lower profile 3-dimensional and the larger 2-dimensional plates in a metacarpal fracture gap sawbone model. METHODS: Thirty metacarpal cortico-cancellous synthetic bones were cut with a 1.75-mm gap between the 2 fragments simulating mid-diaphyseal fracture comminution. Half of the metacarpals were plated with 2.0-mm locking 2-dimensional plates and half with 1.5-mm locking 3-dimensional plates. The plated metacarpals were mounted into a materials testing apparatus and cyclically loaded under cantilever bending for 2,000 cycles at 70 N, then 2,000 cycles at 120 N, and finally monotonically loaded to failure. Throughout testing, fracture gap sizes were measured, failure modes were recorded, and construct strength and stiffness values were calculated. RESULTS: All 3-dimensional constructs survived both cyclic loading conditions. Ten (67%) 2-dimensional constructs survived both loading conditions, whereas 5 (33%) failed the 120-N loading at 1377 ± 363 cycles. When loaded to failure, the 3-dimensional constructs failed at 265 N ± 21 N, whereas the 2-dimensional constructs surviving cyclic loading failed at 190 N ± 17 N. CONCLUSIONS: The shorter, thinner 3-dimensional metacarpal plates demonstrated increased resistance to failure in a cyclic loading model and increased load to failure compared with the relatively longer, thicker 2-dimensional metacarpal plates. CLINICAL RELEVANCE: The lower-profile 3-dimensional metacarpal plate fixation demonstrated greater stability for early postoperative resistance than the thicker 2-dimensional fixation, whereas the smaller size and lower profile of the 3-dimensional plates potentially reduces soft tissue stripping, implant prominence, and risk of extensor tendon irritation.

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OBJECTIVE: The purpose of the present study was to compare inter-fragmentary compression pressures after fixation of a simulated type II odontoid fracture with the headless compression Herbert screw and a half threaded cannulated lag screw. METHODS: We compared inter-fragmentary compression pressures between 40- and 45-mm long 4.5-mm Herbert screws (n=8 and n=9, respectively) and 40- and 45-mm long 4.0-mm cannulated lag screws (n=7 and n=10, respectively) after insertion into rigid polyurethane foam test blocks (Sawbones, Vashon, WA, USA). A washer load cell was placed between the two segments of test blocks to measure the compression force. Because the total length of each foam block was 42 mm, the 40-mm screws were embedded in the cancellous foam, while the 45-mm screws penetrated the denser cortical foam at the bottom. This enabled us to compare inter-fragmentary compression pressures as they are affected by the penetration of the apical dens tip by the screws. RESULTS: The mean compression pressures of the 40- and 45-mm long cannulated lag screws were 50.48±1.20 N and 53.88±1.02 N, respectively, which was not statistically significant (p=0.0551). The mean compression pressures of the 40-mm long Herbert screw was 52.82±2.17 N, and was not statistically significant compared with the 40-mm long cannulated lag screw (p=0.3679). However, 45-mm Herbert screw had significantly higher mean compression pressure (60.68±2.03 N) than both the 45-mm cannulated lag screw and the 40-mm Herbert screw (p=0.0049 and p=0.0246, respectively). CONCLUSION: Our results showed that inter-fragmentary compression pressures of the Herbert screw were significantly increased when the screw tip penetrated the opposite dens cortical foam. This can support the generally recommended surgical technique that, in order to facilitate maximal reduction of the fracture gap using anterior odontoid screws, it is essential to penetrate the apical dens tip with the screw.

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