Comminuted talar neck fractures: a mechanical comparison of fixation techniques

OBJECTIVE: To compare the mechanical performance of 3 fixation techniques for comminuted talar neck fractures. DESIGN: In vitro biomechanical study. SETTING: Bioengineering research laboratory. PARTICIPANTS: Thirty previously frozen human cadaveric tali were osteotomized across the talar neck. A wedge of bone 2 cm long and extending 50% of the medial to lateral and superior to inferior dimension of the talus was removed to create an unstable, comminuted fracture. INTERVENTION: The specimens were randomized to one of 3 fixation groups. The first group was fixed with 3 anterior-to-posterior screws. The second group was fixed with 2 cannulated screws inserted from posterior to anterior. The third group was fixed with 1 screw from anterior to posterior and a medially applied blade plate. Specimens were embedded in acrylic cement and mounted on an Instron mechanical testing machine. Loading was applied in the dorsal-medial direction to failure. MAIN OUTCOME MEASURES: For each specimen, the load-displacement curve, yield point, and 3 mm displacement point were recorded in response to controlled dorsal-medial loading to failure. Stiffness was calculated as the linear portion of the slope of the load (kN) versus displacement (mm) curve. Statistical analysis of the data was conducted using analysis of variance. RESULTS: The mean yield point of each of the fixation techniques tested exceeded 1.4 kN. No statistically significant difference was found between the fixation methods, even when variations in age and sex were considered. CONCLUSIONS: The mean yield point of the fixation techniques tested exceeds the theoretical stress across the talar neck during active motion. Anterior plate fixation provided equivalent stability to posterior screw fixation.     

双切口接骨板内固定治疗距骨颈粉碎性骨折的临床效果

背景：距骨颈骨折是距骨骨折中最常见的类型,采用切开复位螺钉内固定是经典的手术方式,但总体疗效仍不尽人意,尤其是采用单切口时,内翻畸形愈合率较高,且对于粉碎性骨折,螺钉固定效果也不佳。双切口是目前临床推崇的手术入路,结合接骨板固定,可获得良好的疗效。目的：探讨双切口接骨板内固定治疗距骨颈粉碎性骨折的手术技巧及疗效。方法：2010年5月至2011年5月,我院共收治13例闭合距骨颈粉碎性骨折患者。根据Hawkins分型：II型8例,III型5例。所有患者入院后行常规X线检查及CT扫描以明确骨折类型和粉碎程度,待肿胀消退后择期行双切口接骨板内固定术。术后定期复查X线片,并采用直观模拟量表（VAS）、美国骨科足踝外科协会（AOFAS）踝与后足评分系统及简明健康状况调查表（SF-36）综合评估最终治疗效果,同时记录相关并发症情况。结果：本组11例获得随访,随访时间12-24个月,平均18．7个月。患者术后均无切口感染,边缘和皮瓣坏死及内固定失败等并发症发生。X线结果显示,术后骨折端愈合的时间为8～12周,平均10．4周。末次随访时VAS评分0～5分,平均1．09±1．64分。AOFAS踝与后足评分为72-95分,平均84．55±7．29分。SF．36评分为70-96分,平均85．00±7．84分。未见畸形愈合发生。结论：采用双切口接骨板内固定治疗距骨颈骨折技术要求简单,在获得稳定固定的同时,还可维持距骨颈力线,避免畸形愈合,是治疗距骨颈粉碎性骨折有效的治疗方法。     

Intramedullary screw fixation of Jones fractures: a biomechanical study.

The management of proximal fifth metatarsal ("Jones") fractures in athletes has become increasingly more aggressive, despite a lack of biomechanical data in the literature. A cadaver biomechanical study was conducted to evaluate the strength of intramedullary fixation of simulated Jones fractures loaded to failure via three-point bending on a Materials Testing System machine. In a series of eight intact fifth metatarsal control specimens, the force to failure (fracture) was measured for comparison with repaired specimens. Acute fractures were simulated in 10 pairs of feet via osteotomy at the typical fracture location and were fixed with either a 4.5-mm malleolar screw or a 4.5-mm partially threaded, cancellous, cannulated screw, both placed using conventional intramedullary techniques. Force at initial displacement averaged 73.9 N (SD, 64.7 N) for the malleolar screws and 72.5 N (SD, 42.3 N) for the cannulated screws. Force at complete displacement averaged 519.3 N (SD, 226.2 N) for the malleolar screws and 608.4 N (SD, 179.7 N) for the cannulated screws. The force to failure of the intact specimens was significantly greater than the initial and complete forces to failure for the fixed specimens (P < 0.05, independent measures analysis of variance). There was no statistical difference between the average forces at initial displacement or at complete displacement in the fixed metatarsal specimens for the two different types of screws, but the forces at complete displacement for each screw type were significantly greater than the forces at initial displacement (P < 0.05). On the basis of literature review and data generated from this study, it is apparent that the forces necessary to cause displacement of the stabilized Jones fracture are above what would be transmitted within the lateral midfoot during normal weightbearing. The choice of screw and intramedullary technique of fixation is a matter of surgeon preference, because the choice of screw makes no biomechanical difference.     

Vertically oriented femoral neck fractures: mechanical analysis of four fixation techniques

OBJECTIVE: Femoral neck fractures in young individuals are typically high angled shear fractures. These injuries are difficult to stabilize due to a strong varus displacement force across the hip with weight bearing. The purpose of this study was to compare the biomechanical stability of four differing fixation techniques for stabilizing vertical shear femoral neck fractures. METHODS: Vertical femoral neck fracture stability was assessed using 4 surgical constructs in 32 cadaveric femurs: 7.3 mm cannulated screws placed in a triangular configuration (group 1), a 135-degree dynamic hip screw (group 2), a 95-degree dynamic condylar screw (group 3), and a locking proximal femoral plate (group 4). The 4 groups were matched for mean bone density and each specimen was tested under incremental loading, cyclical loading, and loading to failure. The modes of fixation failure were recorded for each specimen and the mean group stiffness, failure loads, and failure energies were calculated. RESULTS: All 8 specimens failed during incremental loading in group 1. Five of 8 constructs failed with incremental loading, and 3 failed with cyclical testing in group 2. The combined 16 specimens in groups 3 and 4 survived both incremental and cyclical loading. The differences in stiffness, failure loads, and failure energies between the 4 groups were statistically significant (P < 0.001). The strongest construct was the locking plate and the weakest construct was the 7.3-mm cannulated screw configuration. The cannulated screw configuration group failed as the screws backed out of the femoral head and by varus collapse of the osteotomy; the fixed angled devices all failed at the bone-implant interface. CONCLUSIONS: The strongest construct for stabilizing a vertical shear femoral neck fracture is the proximal femoral locking plate, followed in descending order by the dynamic condylar screw, the dynamic hip screw, and the 3 cannulated screw configuration.     

Intramedullary screw fixation of proximal fifth metatarsal fractures: a biomechanical study

Intramedullary screw fixation is a popular technique for treatment of proximal fifth metatarsal fractures. The purpose of this study was to compare the fixation rigidity of a 5.5 mm partially threaded cannulated titanium screw, with presumed superior endosteal purchase, to a similar 4.5 mm screw. Acute fifth metatarsal fractures were simulated in cadavers, stabilized with intramedullary screws, and loaded to failure in three-point bending. The initial failure loads for the metatarsals fixed with 4.5 mm and 5.5 mm screws were not significantly different (332.4 N vs. 335.2 N, respectively), nor were the ultimate failure loads (849.8 N vs. 702.2 N, respectively). Based upon our results, maximizing screw diameter does not appear to be critical for fixation rigidity and may increase the risk of intraoperative or postoperative fracture.     

Fixed-angle plate fixation in simulated fractures of the proximal humerus: a biomechanical study of a new device

This study was performed to evaluate the biomechanical properties of a new device for displaced fractures of the proximal humerus. The device is a low-profile, fixed-angle plate specially designed for percutaneous application. With the use of embalmed cadaveric humeri, we simulated both noncomminuted and comminuted 2-part surgical neck fractures of the proximal humerus. Each humerus of a pair was then randomly fixed with either the new experimental device or the Association for the Study of Internal Fixation (ASIF) T-plate and mechanically tested to failure in an axial shear-loading model. The two fixation devices were evaluated in paired humeri with regard to mode of failure, stiffness, displacement at physiologic loads, and displacement, load, and energy at the point of ultimate load before failure. In the noncomminuted fracture trials the experimental device exhibited significantly greater stiffness (P <.001; P =.002 for normalized values) and ultimate load before failure (P =.015) and significantly less displacement at higher physiologic loads (P =.031). In the comminuted fracture trials the experimental device exhibited significantly greater stiffness (P =.048), ultimate load (P <.001) and energy absorbed (P =.048) before failure, and significantly less displacement at higher (P =.004) and lower physiologic loads (P =.011). The study demonstrates improved biomechanical properties for the new experimental device over the T-plate in simulated fractures of the proximal humerus. We extrapolate that these improved biomechanical properties may prove advantageous in future clinical investigation.     

Biomechanical properties of off-axis screw in Pauwels III femoral neck fracture fixation: Bicortical screw construct is superior to unicortical screw construct

ObjectivesThe purpose of this study is to determine the biomechanical properties of the bicortical off-axis screw fixation for stabilizing of Pauwels III femoral neck fractures compared with other fixation methods.MethodsEighteen synthetic femurs (Sawbones Pacific Research Laboratories, Vashon, WA) were divided into three groups. The osteotomy was made vertically to mimic the Pauwels type III femoral neck fracture. Group A (n = 6) was fixed with traditional inverted triangle cannulated screws. Group B (n = 6) was fixed with a unicortical off-axis screw and two parallel cannulated screws. Group C (n = 6) was fixed with a bicortical off-axis screw and two parallel cannulated screws. Each group was tested with a nondestructive axial compression test at a 7° of valgus followed with 1000 cycles of cyclic loading test from 100 N to 1000 N. Finally, a destructive axial compression test was applied until catastrophic failure.ResultsThe average axial stiffness from group A to group C was 856.5, 934, and 1340 N/mm, respectively. The average ultimate failure load from group A to group C was 2612.7, 2508.8, and 3706 N, respectively. Group C exhibited significantly greater axial stiffness and a higher ultimate failure load than the other two groups (P < 0.05). Regarding the interfragmental displacement, the values from group A to group C were 0.41, 0.83, 0.36, respectively, and group B exhibited significantly larger fracture gap formation after the cyclic loading test.ConclusionsThe results of this biomechanical study show statistically significant increases in axial stiffness and ultimate failure load for the off-axis screw placed in bicortical fashion. Once the off-axis screw was positioned unicortically, the largest fracture diastasis was observed as compared to the other two methods.     

Anterior screw fixation for an odontoid fracture using an Acutrak 4/5 screw: a case report

The direct anterior screw fixation of odontoid fractures by a single cancellous screw, especially for osteoporotic vertebrae, has a potential risk of leading to insufficient stability and implant failures. We experienced good results following surgery using a single Acutrak 4/5 screw to obtain sufficient stability for an odontoid fracture in a patient with osteopenia. The screw is a cannulated self-tapping headless screw and has a tapered profile and full threads with variable pitches, and it can yield sufficient compression force as the screw is inserted. The preoperative severe neck pain of the patient was diminished immediately after the surgery. The patient achieved bone union in a short time and had a good clinical result for at least 3 years. Some biomechanical studies showed that the compression force of Acutrak standard screws was stronger than that of both 4.0-mm cancellous screws inserted with the lag screw technique and Herbert screws, and other studies showed that the compression force of Acutrak 4/5 screws was equivalent to that of 4.5-mm cortical screws. However, there has been no clinical report of surgery using an Acutrak 4/5 screw for odontoid fractures. This is the first clinical report of fixation by an Acutrak 4/5 screw.     

Clinical results of minimal screw plate fixation of forearm fractures

Traditional plating technique for forearm fractures specifies implant selection based on achieving a minimum number of "cortices" of screw fixation on either side of the fracture. Recent biomechanical data suggest that plates with fewer screws provide equivalent strength of fixation compared with standard compression plating techniques in forearm fractures. As described in this article, we retrospectively reviewed a surgeon's experience at a regional level I trauma center to evaluate the clinical outcome of this newer fixation strategy. Seventy-eight fractured bones were plated using "minimal" screw technique--less than the traditionally recommended 6 cortices of screw purchase. Nonunion or fixation failure occurred in 7 fractures (5 patients), producing a union rate of 91% (71/78). All nonunions were atrophic and occurred in open fractures with bone loss. No construct failed because of fixation loss caused by having too few screws. Minimal screw plate technique was stable fixation, despite not having 6 cortices on both sides of the fracture. Technical emphasis should be on adequate plate length rather than number of cortices of fixation in each segment.     

Clinical results of minimal screw plate fixation of forearm fractures.

Traditional plating technique for forearm fractures specifies implant selection based on achieving a minimum number of "cortices" of screw fixation on either side of the fracture. Recent biomechanical data suggest that plates with fewer screws provide equivalent strength of fixation compared with standard compression plating techniques in forearm fractures. As described in this article, we retrospectively reviewed a surgeon's experience at a regional level I trauma center to evaluate the clinical outcome of this newer fixation strategy. Seventy-eight fractured bones were plated using "minimal" screw technique--less than the traditionally recommended 6 cortices of screw purchase. Nonunion or fixation failure occurred in 7 fractures (5 patients), producing a union rate of 91% (71/78). All nonunions were atrophic and occurred in open fractures with bone loss. No construct failed because of fixation loss caused by having too few screws. Minimal screw plate technique was stable fixation, despite not having 6 cortices on both sides of the fracture. Technical emphasis should be on adequate plate length rather than number of cortices of fixation in each segment.     

Stability of radial head and neck fractures: a biomechanical study of six fixation constructs with consideration of three locking plates

PURPOSE: Open reduction and internal fixation of radial neck fractures can lead to secondary loss of reduction and nonunion due to insufficient stability. Nevertheless, there are only a few biomechanical studies about the stability achieved by different osteosynthesis constructs. METHODS: Forty-eight formalin-fixed, human proximal radii were divided into 6 groups according to their bone density (measured by dual-energy x-ray absorptiometry). A 2.7-mm gap osteotomy was performed to simulate an unstable radial neck fracture, which was fixed with 3 nonlocking implants: a 2.4-mm T plate, a 2.4-mm blade plate, and 2.0-mm crossed screws, and 3 locking plates: a 2.0-mm LCP T plate, a 2.0-mm 6x2 grid plate, and a 2.0-mm radial head plate. Implants were tested under axial (N/mm) and torsional (Ncm/ degrees ) loads with a servohydraulic materials testing machine. RESULTS: The radial head plate was significantly stiffer than all other implants under axial as well as under torsional loads, with values of 36 N/mm and 13 Ncm/ degrees . The second-stiffest implant was the blade plate, with values of 20 N/mm and 6 Ncm/ degrees . The weakest implants were the 2.0-mm LCP, with values of 6 N/mm and 2 Ncm/ degrees , and the 2.0-mm crossed screws, with values of 18 N/mm and 2 Ncm/ degrees . The 2.4-mm T plate, with values of 14 N/mm and 4 Ncm/ degrees , and the 2.0-mm grid plate, with values of 8 N/mm and 4 Ncm/ degrees came to lie in the midfield. CONCLUSIONS: The 2.0-mm angle-stable plates-depending on their design-allow fixation with comparable or even higher stability than the bulky 2.4-mm nonlocking implants and 2.0-mm crossed screws.     

Torque resistance after fixation of Jones fractures with intramedullary screws

BACKGROUND: Intramedullary screws frequently are used for fixation of Jones fractures of the fifth metarsal. While the ability of intramedullary screw fixation in fifth metatarsals to resist bending and tensile forces is well known, the ability to withstand torsion has not been studied. This paper compares the torsional stiffness of Jones fractures treated with 6.5-mm short- threaded intramedullary screws to those treated with 5.0-mm cannulated short-threaded intramedullary screws. METHODS: Nine fresh-frozen, matched pairs of cadaver fifth metatarsals had an acute Jones fracture simulated with an osteotomy. They were stabilized with intramedullary screws and then loaded to failure. RESULTS: The torsional stiffness of the metatarsals fixed with the 6.5-mm did not differ significantly from that using 5.0-mm screws. However, to achieve stability, the 5.0-mm screw had to be long enough to reach the metatarsal head and neck. This tended to straighten the normally curved fifth metatarsal bone and caused lateral gapping at the fracture site. CONCLUSION: Both 5.0-mm or 6.5-mm screws provide equal torsional rigidity, but 5.0-mm screws may need to be longer, which could potentially straighten the fifth metatarsal shaft in patients who have a curved fifth metatarsal.     

Comparison of Pullout Strength between 3.5-mm Fully Threaded,Bicortical Screws and 4.0-mm Partially Threaded,Cancellous Screws in the Fixation of Medial Malleolar Fractures

Displaced medial malleolus fractures are considered unstable and typically require open reduction and internal fixation for anatomic reduction and early joint range of motion. These fractures are usually fixated with either compression lag screws or tension band wiring depending on the fracture pattern, size of the distal fragment, and bone quality. When fracture fixation fails, it is typically in pullout strength. Failure of primary bone healing can result in nonunion, malunion, and need for revision surgery. The current study wished to explore a potentially stronger fixation technique in regard to pullout strength for medial malleolar fractures compared with traditional cancellous screws. This was a comparative study of the relative pullout strength of 2 fully threaded 3.5-mm bicortical screws versus 2 partially threaded 4.0-mm cancellous screws for the fixation of medial malleolar fractures. Ten fresh-frozen limbs from 5 cadavers, mean age 79 years (range of 65–97 years), were tested using the Instron 8500 Plus system. The median force recorded at 2 mm of distraction using unicortical partially threaded cancellous screws was 116.2 N (range 70.2 to 355.5N) compared with 327.6 N (range 117.5 to 804.3 N) in the fully threaded bicortical screw (P = .04). The unicortical screw fixation displayed only 64.53% of the median strength noted with the bicortical screw fixation at clinical failure. The current study demonstrated statistically significantly greater pullout strength for 3.5-mm bicortical screws when compared with 4.0-mm partially threaded cancellous screws used to fixate medial malleolar fractures in a cadaveric model.     

Effect of screw placement on fixation in the humeral head

The objectives of this study were (1) to determine the most advantageous screw locations within the humeral head when plate and screw fixation is to be used and (2) to determine the effect of positioning the screw tip abutting the subchondral bone. Ten paired humeral heads were harvested with a monoplanar cut through the anatomic neck. Through use of a standardized template, 7 holes were drilled and tapped in each specimen for insertion of 6.5-mm fully threaded cancellous screws perpendicular to the plane of the cut. Paired specimens were randomized into 2 groups, one with the screw purchase in central cancellous bone and the other with the screw purchase up to the subchondral bone. Each screw was pulled out axially at a displacement rate of 10 mm/min through use of a servohydraulic testing machine. The length of thread purchase, position within the head, and screw pullout load to failure were recorded. The normalized pullout force to failure was calculated by dividing absolute pullout force to failure by length of screw purchase. Data were analyzed by means of a 2-way repeated measures analysis of variance and post hoc Student-Newman-Keuls test. The central position had a significantly higher absolute pullout force to failure than all other sites (P < .05). By virtue of the humeral head shape, the central position also had a significantly greater length of screw purchase than all other positions (P < .05). The central position had a significantly higher relative pullout force to failure than all other positions (P < .05). Subchondral bone abutment positioning improved both the absolute and the relative pullout forces to failure (P < .05). When screws and plates are used in open reduction and internal fixation of a proximal humerus fracture, a major mode of failure is loss of fixation within the humeral head. On the basis of this study, optimal screw purchase with respect to bone fixation can be achieved by including screws located in the center of the humeral head in the subchondral abutment position. To minimize screw fixation failure, the anterosuperior position should be avoided. The pattern of distribution of the relative pullout force as measured in this study is consistent with previous observational studies of patterns of trabecular density within the humeral head.     

Intramedullary screw fixation of Jones fractures

BACKGROUND: Jones fractures of the fifth metatarsal can be stabilized using intramedullary screw fixation techniques. A range of screw diameters from 4.5 mm to 6.5 mm can be used, but the optimal screw for this procedure has yet to be defined. In clinical practice, we have observed that failure is more likely when smaller diameter screws are used. METHODS: Experimental Jones fractures were created in 23 pairs of human cadaver fifth metatarsals, which were fixed using either 5.0 mm or 6.5 mm screws. Fracture stiffness and pull-out strengths were measured for either screw type and their relationships with bone mineral density and medullary canal diameter were determined. RESULTS: There was no significant difference in the bending stiffness of fractures stabilized with 5.0 mm and 6.5 mm screws; however, different mechanisms of failure were noted for either screw type. Poor thread purchase within the medullary canal was noted with the 5.0 mm screws, while excellent purchase was noted with 6.5 mm screws. Pull-out strength testing revealed significantly higher pullout strengths for the larger 6.5 mm screws. There was no significant difference in bone mineral density or medullary canal diameter between right and left metatarsals. CONCLUSIONS: Fifth metatarsals can often accommodate a 6.5 mm screw for the stabilization of Jones fractures. Larger diameter screws did not result in greater fracture stiffness in our model, but did result in significantly greater pull-out strengths. CLINICAL RELEVANCE: Larger diameter screws may be more appropriate for intramedullary screw fixation of Jones fractures.     

Comparison of two headless screw designs for fixation of capitellum fractures

In order to determine the effects of two different headless screw designs on fixation of simulated capitellum fractures six matched pairs of embalmed humeri had simulated capitellum fractures created. Fixation with Acutrac compression screws was compared to Herbert screws in a matched pair experimental design. All specimens were cyclically tested with simulated physiologic loading. Both displacement of the capitellum as a function of the number of cycles and failure loads were determined. Fixation by the Acutrac screws was significantly more stable than Herbert screws at 2000 cycles, 0.17 mm wersus 1.57 mm (p < 0.02) The Acutrac fixation also had a higher failure load, 154 N versus 118 N (p < 0.05). The Acutrac screws tested in this biomechanical study provided more stable fixation of simulated capitellum fractures than Herbert screws. This appears to be related to the design of these screws.     

Mechanical characteristics of locking and compression plate constructs applied dorsally to distal radius fractures

PURPOSE: Locking plates are thought to have many advantages such as a decreased incidence of loss of reduction secondary to screw toggling and improved bone healing due to an increased periosteal blood supply. We hypothesized that locking plates will also provide increased stiffness and increased load to failure when they are applied dorsally to stabilize dorsally comminuted distal radius fractures. This study compared the stiffness and strength of dorsally applied locking and standard (nonlocking) T-plates applied to a dorsally comminuted distal radius fracture model. METHODS: Sixteen pairs of embalmed cadaveric human radii were potted, and a standard wedge osteotomy was performed simulating a dorsally comminuted distal radius fracture. The radii were randomized into 2 groups, so that 8 pairs received a 3.5-mm dorsal locking T-plate over the osteotomy on the right radius and 8 pairs received the same on the left radius. A dorsal 3.5-mm standard T-plate was placed over the osteotomy on the contralateral radius in each group. An axial load was used to test the strength and stiffness of each construct. Paired t tests were then used to compare the strength and stiffness of the locking plate with those of the standard plate. RESULTS: A significant difference was found in both the stiffness and the strength between the locking and standard nonlocking plates. The locking T-plate was 33% stiffer than the standard T-plate. The locking T-plate had a 91% increase in the load to failure. Failure for both locking and standard T-plates occurred via volar cortex bone fracture. CONCLUSIONS: Locking T-plates increased both the stiffness and strength of dorsally comminuted distal radius fractures compared with standard nonlocking T-plates by a statistically significant margin.     

Lag screw only fixation of the lateral malleolus

OBJECTIVES: To evaluate the use of lag screw only fixation of noncomminuted oblique fractures of the lateral malleolus in patients younger than fifty years of age. DESIGN: Prospective evaluation. SETTING: Level I trauma center. PATIENTS AND PARTICIPANTS: Forty-seven ankle fractures with simple oblique patterns and no comminution that were long enough to accept two lag screws placed at least 1 centimeter apart were prospectively evaluated. All patients were younger than fifty years of age. There were twenty-three ligamentous SE4, eighteen bimalleolar SE4, and six PE4 fractures. INTERVENTION: Open reduction and internal fixation with lag screw only fixation of the lateral malleolus. MAIN OUTCOME MEASUREMENTS: Radiographic and clinical outcome parameters were compared with those of a cohort of patients previously treated at the same institutions using different techniques. RESULTS: Thirty-five patients' ankles were fixed with two lag screws, ten with three lag screws, and two with four lag screws. The incision for lag screw placement was 30 percent shorter and slightly more anterior than that in the comparison group. No patient lost reduction and there were no soft-tissue complications in the group. Follow up averaged 1.6 years for forty-two patients. One patient (2 percent) had complaints of lateral pain in the study, compared with 17 percent in the plate group. No patient fixed with lag screws had palpable hardware, as compared with 56 percent in the plate group. None had any restrictions in shoe wear, as compared with 15 percent in the plate group. No patient required screw removal, as compared with 31 percent in the plate group. There was no difference in radiographic outcome between the two groups. CONCLUSIONS: Lag screw only fixation is a useful and successful method for appropriately selected lateral malleolar fractures.     

Schuhli augmentation of plate and screw fixation for humeral shaft fractures: a laboratory study

OBJECTIVES: Schuhli locking nuts provide a mechanism to lock 4.5-millimeter bone screws to a standard dynamic compression plate (DCP plate). It has been proposed that Schuhlis can provide increased fixation stability in areas of a proximal cortical defect or osteopenic bone and may keep screws from loosening and backing out from the plate. A biomechanical study was performed to investigate the effect of Schuhli augmentation of a ten-hole broad DCP plate for fixation of a simulated humeral shaft fracture versus standard DCP plate fixation. DESIGN: Biomechanical cadaver study. INTERVENTION: Six pairs of cadaveric humeri from elderly individuals were tested in offset axial loading, torsion, and four-point bending to obtain load versus deformation curves and baseline mechanical properties. Each pair of humeri was then instrumented with a ten-hole broad DCP plate on one side and a DCP plate augmented with Schuhlis at each screw hole on the contralateral side. All screws were placed in cortical bone. The constructs were retested in all three modalities. The humeri were then cycled in torsion for 1,000 cycles and retested in all three modalities. Each humerus was then loaded to failure in torsion to determine the ultimate load and rotational displacement. MAIN OUTCOME MEASUREMENTS: Resistance to displacement was determined from the load versus deformation curves in each testing modality before and after cycling; these data were normalized to the intact values determined prior to instrumentation. Paired Student's t tests were performed to determine statistically significant differences between the two modes of fixation. RESULTS: There were no significant differences in stability between the two fixation techniques in all three testing modalities both before and after cycling. However, the Schuhli augmented constructs sustained significantly greater loads and rotational deformations prior to failure. CONCLUSIONS: In this model of humeral shaft fractures in the elderly, the addition of Schuhlis did not significantly change the mechanical stability of plate and screw fixation. However, load and angular deformation at failure were significantly greater in the Schuhli augmented specimens.     

Percutaneous screw configuration versus perimeter plating of calcaneus fractures: a cadaver study

BACKGROUND: Percutaneous screw configuration has been used clinically to reduce the high rate of wound complications associated with the extensile approach of standard open reduction and internal plate fixation. The aim of this cadaveric biomechanical study was to compare the strength of the standard perimeter plating with that of the percutaneous screw configuration for a Sanders type-2B calcaneus fracture. MATERIALS AND METHODS: Ten pairs of fresh-frozen cadaveric lower limbs were prepared and osteotomized to create a Sanders type-2B fracture. Of each pair, one specimen underwent open reduction and internal fixation with standard perimeter plating; the other was stabilized with the percutaneous screw configuration. Each foot was compressed axially via the talar dome (1 mm/sec) until failure occurred. Differences in treatment groups were analyzed for significance (p < 0.05) using paired t-tests. RESULTS: Construct stiffness was 158 +/- 85 and 113 +/- 60 N/mm for the plate and percutaneous fixation, respectively (p = 0.18). Failure occurred at an average of 1156 +/- 513 and 1064 +/- 540 N for the plate and percutaneous construct, respectively (p = 0.65). CONCLUSION: The results suggest that open reduction and internal fixation with percutaneous screw configuration for Sanders type-2B calcaneus fractures provides a strength similar to that of perimeter plating. CLINICAL RELEVANCE: Percutaneous screw fixation of calcaneus fractures may provide fracture reduction similar to plate fixation.