The antiglide plate for distal fibular fixation. A biomechanical comparison with fixation with a lateral plate

Posterior antiglide plates recently have been introduced as a method of fixation for the short oblique fracture (Type B, as defined by the AO Group) of the distal part of the fibula. This method has several advantages over the more commonly used lateral plate for the fixation of this type of fracture, including dissection of a smaller area and less operative time, minimum bending of the plate, and no potential for penetration of a screw into the joint. The system can also be applied without insertion of a screw into the distal fragment. This prompted us to compare the biomechanical properties of fixation with the antiglide and lateral plating systems. Short oblique fractures of the distal part of the fibula were produced mechanically in cadaveric legs by supination and external rotation of the foot. The torque that was necessary to produce the fracture in each of twenty-four fibulae was recorded. After fracture, each fibula was reduced anatomically and fixed internally with a lateral plate or antiglide plate applied posteriorly. The strength of fixation was measured by restressing the legs until failure of fixation occurred. The stiffness of the fixation system and the amount of energy required to produce failure of fixation were also calculated. The system using the lateral plate for fixation failed when the torque reached an average of 64.3 per cent of the torque that produced the fracture.(ABSTRACT TRUNCATED AT 250 WORDS)     

A biomechanical evaluation of locked plating for distal fibula fractures in an osteoporotic sawbone model

BackgroundSupination external rotation (SER) injuries are commonly fixed with a one third tubular neutralization plate. This study investigated if a combination locked plate with additional fixation options was biomechanically superior in osteoporotic bone and comminuted fracture models.MethodsUsing an osteoporotic and a comminuted Sawbones model, SER injuries were fixed with a lag screw for simple oblique fibula fractures, and either a one third tubular neutralization plate or a locking plate. Samples were tested in stiffness, peak torque, displacement at failure, and torsion fatigue.ResultsThere was no statistically significant difference in biomechanical testing for fractures treated with a lag screw and plate. For comminuted fractures, locked plating demonstrated statistically significant stiffer fixation.ConclusionA combination locked plate is biomechanically superior to a standard one third tubular plate in comminuted SER ankle fractures. There was no biomechanical superiority between locked and one third tubular plates when the fracture was amenable to a lag screw.     

Fibula pro-tibia vs standard locking plate fixation in an ankle fracture saw bone model

BACKGROUNDLocking plate fixation in osteoporotic ankle fractures may fail due to cut-out or metalwork failure. Fibula pro-tibia fixation was a technique prior to the advent of locking plates that was used to enhance stability in ankle fractures by achieving tri or tetra-cortical fixation. With locking plates, the strength of this fixation construct can be further enhanced. There is lack of evidence currently on the merits of tibia-pro-fibula augmented locking plate fixation of unstable ankle fractures.AIMTo assess if there is increased strength to failure, in an ankle fracture saw bone model, with a fibula pro-tibia construct when compared with standard locking plate fixation.METHODSTen osteoporotic saw bones with simulated supination external rotation injuries were used. Five saw bones were fixed with standard locking plates whilst the other 5 saw bones were fixed with locking plates in a fibula pro-tibia construct. The fibula pro-tibia construct involved fixation with 3 consecutive locking screws applied across 3 cortices proximally from the level of the syndesmosis. All fixations were tested in axial external rotation to failure on an electromagnetic test frame (MTS 858 Mini-Bionix test machine, MTS Corp, Eden Praire, MN, United States). Torque at 30 degrees external rotation, failure torque, and external rotation angle at failure were compared between both groups and statistically analyzed.RESULTSThe fibula pro-tibia construct demonstrated a statistically higher torque at 30 degrees external rotation (4.421 ± 0.796 N/m vs 1.451 ± 0.467 N/m; t-test P = 0.000), as well as maximum torque at failure (5.079 ± 0.694N/m vs 2.299 ± 0.931 N/m; t-test P = 0.001) compared to the standard locking plate construct. The fibula pro-tibia construct also had a lower external rotation angle at failure (54.7 ± 14.5 vs 67.7 ± 22.9).CONCLUSIONThe fibula pro-tibia locking plate construct demonstrates biomechanical superiority to standard locking plates in fixation of unstable ankle fractures in this saw bone model. There is merit in the use of this construct in patients with unstable osteoporotic ankle fractures as it may aid improved clinical outcomes.     

A contoured locking plate for distal fibular fractures in osteoporotic bone: a biomechanical cadaver study

ObjectiveFixation of ankle fractures in elderly patients is associated with reduced stability conditioned by osteoporotic bone. Therefore, fixation with implants providing improved biomechanical features could allow a more functional treatment, diminish implant failure and avoid consequences of immobilisation.Materials and methodsIn the actual study, we evaluated a lateral conventional contoured plate with a locking contoured plate stabilising experimentally induced distal fibular fractures in human cadavers from elderly. Ankle fractures were induced by the supination-external rotation mechanism according to Lauge-Hansen. Stage II fractures (AO 44-B1) were fixed with the 2 contoured plates and a torque to failure test was performed. Bone mineral density (BMD) was measured by quantitative computed tomography to correlate the parameters of the biomechanical experiments with bone quality.ResultsThe locking plate showed a higher torque to failure, angle at failure, and maximal torque compared to the conventional plate. In contrast to the nonlocking system, fixation with the locking plate was independent of BMD.ConclusionFixation of distal fibular fractures in osteoporotic bone with the contoured locking plate may be advantageous as compared to the nonlocking contoured plate. The locking plate with improved biomechanical attributes may allow a more functional treatment, reduce complications and consequences of immobilisation.     

Dual Nonlocked Plating as an Alternative to Locked Plating for Comminuted Distal Fibula Fractures: A Biomechanical Comparison Study

The purpose of this cadaveric study was to compare the biomechanical properties of dual nonlocked plating and single-locked plating using matched pairs of isolated fibula specimens. Fractures were simulated in 10 matched pairs of isolated cadaveric fibulae and plated with a single lateral locking plate for right-sided specimens, or with a one-third tubular plate and a 7-hole 2.4-mm minifragment adaption plate for left-sided specimens. An external rotation torque was applied at a rate of 1°/second, and torque at 10° was measured. Each fibula specimen was evaluated using a micro computed tomography scanner, and bone mineral density was calculated as milligrams of bone per cubic centimeter of volume. Dual nonlocked plating and locked plating specimens demonstrated torque measurements that were not significantly different at 10° of external rotation (1.48 N·m and 1.92 N·m, respectively; p = .093). The stiffness of the dual nonlocked plated and locked plating constructs were not significantly different (p = .228 and p = .543, respectively). The effect of bone mineral density on maximum torque at failure was not a reliable predictor of maximum torque in either the dual nonlocked plating or locked plating specimens (R² = 0.548 and R² = 0.096, respectively). We found no differences in torque at 10° of external rotation or stiffness between locking plate and dual nonlocking plate fixation constructs. This study provides evidence that dual nonlocked plating likely constitutes adequate fixation in situations in which a locking plate is being considered for comminuted distal fibula fractures.     

Comparison of Locking Versus Nonlocking Plates for Distal Fibula Fractures

Locking plates might offer a biomechanical fixation advantage for distal fibula fractures with comminution or osteoporotic bone. In January 2011, our unit introduced a bone-specific locking plate for the distal fibula. The aim of the present study was to compare it against more conventional plating system implants for lateral malleolar fixation in terms of outcomes, crude costs, and complications. We retrospectively reviewed a consecutive cohort of patients with closed ankle fractures who presented within a 24-month period. The clinical and radiographic outcomes were compared among conventional plating using a one-third semitubular plate, a 3.5-mm limited-contact dynamic compression plate, and a 2.7-mm/3.5-mm locking compression distal fibula plate. A total of 145 patients with ankle fractures underwent surgical fixation: 87 (60.0%) with the semitubular plate, 22 (15.2%) with the limited-contact dynamic compression plate, and 36 (24.8%) with the locking compression distal fibula plate. A greater proportion of patients with established osteoporosis or osteoporosis risk factors were in the locking compression distal fibula plate group (27.8% versus 2.3% and 0%). Four patients (2.8%) required washout for infection. No significant differences were found between the sex distribution within the 3 groups (p?=?.432). No significant difference was found in the complication rate (p?=?.914) or the reoperation rate (p?=?.291) among the 3 groups. Although costing >6 times more than a standard fibula fixation construct (implant cost), bone-specific locking compression distal fibula plates add to the portfolio of implants available, especially for unstable fractures with poor bone quality.     

Locked plate fixation of the comminuted distal fibula: a biomechanical study

Background

The purpose of this study was to compare the biomechanical properties of locked versus nonlocked lateral fibular bridge plating of comminuted, unstable ankle fractures in a mode of catastrophic failure.

Methods

We created comminuted Weber C fractures in 8 paired limbs from fresh cadavers. Fractures were plated with either standard or locked one-third tubular bridge plating techniques. Specimens were biomechanically evaluated by external rotation to failure while subjected to a compressive load approximating body weight. We measured the angle to failure, torque to failure, energy to failure and construct stiffness.

Results

There was no significant difference in construct stiffness or other biomechanical properties between locked and standard one-third tubular plating techniques.

Conclusion

We found no difference in biomechanical properties between locked and standard bridge plating of a comminuted Weber C fibular fracture in a model of catastrophic failure. It is likely that augmentation of fixation with K-wires or trans-tibial screws provides a construct superior to locked bridge plating alone. Further biomechanical and clinical analysis is required to improve understanding of the role of locked plating in ankle fractures and in osteoporotic bone.     

Preliminary Biomechanical Proof of Concept for a Hybrid Locking Plate/Variable Pitch Screw Construct for Anterior Fixation of Type II Odontoid Fractures

STUDY DESIGN.: A human cadaveric biomechanical proof-of-concept study. OBJECTIVE.: To test whether adding a locking plate to the anterior surface of C2 attaching directly to the interfragmentary screw may reduce potential for anterior screw cutout and improve construct strength. SUMMARY OF BACKGROUND DATA.: The most common mode of failure for screw fixation of dens fractures is via cutout at the anterior body of C2. METHODS.: A human, cadaveric model of type II dens fractures was created and fixed using either a headless, fully threaded variable pitch screw (FTVPS) or a screw with an attachable locking plate construct (LPC). Following quasistatic loading to failure, stiffness and load to failure were compared using t tests. Mode of failure was determined from radiographical and gross inspection. RESULTS.: Load to failure was greater for the LPC than for the FTVPS alone (498 N vs. 362 N, P = 0.04). The LPC consistently failed via compression of cancellous bone posterior to the lag screw, whereas the FTVPS constructs failed via cutout of the screw from the anterior C2 body. CONCLUSION.: Locking plate supplementation of anterior screw fixation of type II odontoid fractures improves construct strength and changes the failure mechanism from anterior screw cutout to posterior displacement of the screw. An attachable locking plate/interfragmentary screw construct may improve clinical outcomes for these fractures.     

The dorsal antiglide plate in the treatment of Danis-Weber type-B fractures of the distal fibula

The results of 93 of 107 consecutive antiglide plate internal fixations of Danis-Weber Type-B fractures of the distal fibula are reported with a follow-up period of just over one year. Using the ankle evaluation scale of Weber, 66.7% excellent, 27.9% good, and only 5.4% poor results were found. The method of dorsal antiglide plate fixation is possible in most of the frequent Type-B ankle fractures. Stabilization is better with the antiglide plate, especially in older patients with osteoporotic bone. Because of these advantages and the biomechanically sound technique, the antiglide plate is recommended for stabilization of the Danis-Weber Type-B fracture of the distal fibula.     

Locking plates increase the strength of dynamic hip screws

INTRODUCTION: Failure of a dynamic hip screw (DHS) fixation leads to decreased mobility of the patient and frequently to a decrease in general health. The most common mode of failure of a DHS is cut out of the lag screw from the femoral head. The second most common mode of failure is lift-off of the plate from the femur. The aim of this laboratory-based experimental study was to determine whether a DHS secured to an osteoporotic femur with a locking screw plate would provide a stronger construct than the standard DHS plate. METHOD: The standard DHS design was compared to a DHS with fixed angle locking screws holding the DHS plate to the femur. Standard dynamic compression plates (DCP) and locking compression plates (LCP) were attached to synthetic, osteoporotic bone. A load was applied to replicate the forces occurring following the fixation of unstable, intertrochanteric hip fractures. A bracket on the proximal end of the plate replicated the lag screw in the femoral head. The constructs were cyclically loaded by a screw-driven material-testing machine and the number of cycles before failure occurred was determined. RESULTS: The mean number of cycles to failure for the locking plate construct was 2.6 times greater than for the standard screw construct (285 versus 108 cycles, respectively p=0.016). CONCLUSION: A dynamic hip screw with fixed angle locking screws would reduce the risk of DHS failure. A locking screw DHS would be particularly useful in patients with osteoporotic bone, and in patients with less stable fracture configurations.     

Biomechanical comparison of a lateral polyaxial locking plate with a posterolateral polyaxial locking plate applied to the distal fibula

BackgroundPolyaxial locking plates are becoming popular for the fixation of distal fibula fractures. This study establishes how construct stiffness and plate loosening, measured as range of motion, differs between lateral and posterolateral plate location.MethodsSeven matched pairs of cadaver fibulae were osteotomized in standardized fashion to produce a Weber type B distal fibula fracture. The fragments were fixated with an interfragmentary lag screw and polyaxial locking plates, with one fibula in each pair receiving a posterolateral anti-glide-plate, and the other a lateral neutralization-plate. In a biomechanical test, the bending and torsional stiffnesses of the constructs and the ranges of motion (ROM) were measured and subjected to a paired comparison.ResultsThe laterally plated group had a higher median (interquartile range) bending stiffness (29.2 (19.7) N/mm) and a smaller range of motion (2.06 (1.99) mm) than the posterolaterally plated group (14.6 (20.6) N/mm, and 4.11 (3.28) mm, respectively); however, the results were not statistically significant (p_bending = 0.314; p_ROM = 0.325). Similarly, the torsional stiffness did not differ significantly between the two groups (laterally plated: 426 (259) N mm/°; posterolaterally plated: 248 (399) N mm/°; p_torsion = 0.900). The range of motion measurements between the two groups under torsional loading were also statistically insignificant (laterally plated: 8.88 (6.30) mm; posterolaterally plated: 15.34 (12.64) mm; p_ROM = 0.900).ConclusionIn biomechanical cadaver-model tests of Weber type B fracture fixation with polyaxial locking plates, laterally plated constructs and posterolaterally plated constructs performed without significantly difference. Therefore, other considerations, such as access morbidity, associated injuries, patient anatomy, or surgeon's preference, may guide the choice of plating pattern. Further clinical studies will be needed for the establishment of definitive recommendations. Clinical relevance: Information on the behavior of polyaxial locking plates is relevant to surgeons performing internal fixation of distal fibula fractures.     

Comparative strength of three methods of fixation of transverse acetabular fractures.

With the advent of percutaneously placed lag screws for fixation of acetabular fractures, this study evaluated the strength of lag screw fixation compared with traditional fixation techniques of transverse acetabular fractures. Ten formalin-treated human, cadaveric pelvic specimens with bilateral, transtectal transverse acetabular fractures were used for this study. The right acetabular fractures were fixed with a five-hole plate and four screws with the central hole spanning the posterior fracture site. The left acetabular fractures were fixed with two lag screws, one each in the anterior and posterior columns, or with a screw and wire construct stabilizing both columns. The specimens were loaded to implant failure. Stiffness, yield strength, maximum load at failure, and site of failure was recorded. The plate and screw construct showed significantly greater yield and maximum strength when compared with the two lag screws. The stiffness of the lag screw method was 39% higher than that of the plating method, but this result was not statistically significant. In addition, the plate and screw method provided significantly greater maximum strength than the screw and wire technique. The quadrilateral plate seemed to be the weakest area of fixation because 83% of the implant failures occurred in this region. In patients in whom the risks of formal open reduction and internal fixation of acetabular fractures outweigh the possible benefits, such as in patients with burns or degloved skin, the advent of computer-assisted and fluoroscopically guided percutaneous surgical techniques have been instrumental. This study showed there is greater strength of fixation with a plate and screw construct, possibly secondary to supplementary fixation distal to the quadrilateral plate. However, lag screw fixation provided relatively greater stiffness, which may account for its clinical success. Percutaneous lag screw fixation of appropriate transverse acetabular fractures is a viable option.     

Biomechanical properties of orthogonal plate configuration versus parallel plate configuration using the same locking plate system for intra-articular distal humeral fractures under radial or ulnar column axial load

IntroductionPrevious reports have questioned whether an orthogonal or parallel configuration is superior for distal humeral articular fractures. In previous clinical and biomechanical studies, implant failure of the posterolateral plate has been reported with orthogonal configurations; however, the reason for screw loosening in the posterolateral plate is unclear. The purpose of this study was to evaluate biomechanical properties and to clarify the causes of posterolateral plate loosening using a humeral fracture model under axial compression on the radial or ulnar column separately. And we changed only the plate set up: parallel or orthogonal.Materials and methodsWe used artificial bone to create an Association for the Study of Internal Fixation type 13-C2.3 intra-articular fracture model with a 1-cm supracondylar gap. We used an anatomically-preshaped distal humerus locking compression plate system (Synthes GmbH, Solothurn, Switzerland). Although this is originally an orthogonal plate system, we designed a mediolateral parallel configuration to use the contralateral medial plate instead of the posterolateral plate in the system. We calculated the stiffness of the radial and ulnar columns and anterior movement of the condylar fragment in the lateral view.ResultsThe parallel configuration was superior to the orthogonal configuration regarding the stiffness of the radial column axial compression. There were significant differences between the two configurations regarding anterior movement of the capitellum during axial loading of the radial column.DiscussionThe posterolateral plate tended to bend anteriorly under axial compression compared with the medial or lateral plate. We believe that in the orthogonal configuration axial compression induced more anterior displacement of the capitellum than the trochlea, which eventually induced secondary fragment or screw dislocation on the posterolateral plate, or nonunion at the supracondylar level. In the parallel configuration, anterior movement of the capitellum or trochlea was restricted because of the angular stability of the plate and locking screws in the condyle.ConclusionsThe posterolateral plate tended to bend anteriorly under axial compression of the radial column in the orthogonal configuration, which led to secondary displacement of the posterolateral plate and eventual screw loosening.     

Locking plate technology: current concepts

The management of fractures with traditional plating techniques has undergone a paradigm shift over the past 20 years. For many fractures, anatomic reduction using a dynamic compression plate has been the gold standard. However, minimally invasive approaches combined with biologically friendly internal fixation have become accepted methods of complex fracture treatment. The orthopedic literature has demonstrated advantages when comparing locking plate techniques with traditional compression plating techniques, particularly in fractures about the knee. The advantages of locking plates apply most directly to cases of highly comminuted fractures, unstable metadiaphyseal segments, and osteoporotic fractures. The biomechanical properties of locking plates have distinguished and defined their clinical use compared to traditional plates. A thorough understanding of these properties will assist the orthopedic surgeon in choosing the appropriate construct when faced with a difficult fracture. Compression plating requires absolute stability for bone healing. In contrast, locking plates function as "internal fixators" with multiple anchor points. This type of fixed-angle device converts axial loads across the bone to compressive forces across fracture sites, minimizing gap length and strain. The strain theory demonstrates that anatomic reduction is not required for bone healing, and that tolerable strain (2%-10%) can promote secondary bone healing. Callus formation is further promoted when biologically friendly surgical approaches are combined with locking plate "internal fixators". In contrast, conventional plates function by creating an environment where primary bone healing occurs. This plate provides "absolute rigidity" and requires anatomic reduction fixed in compression. Primary bone healing occurs in this manner. In highly comminuted, segmentally deficient, or porotic bone, bone quality is poor and "absolute rigidity" does not exist. Furthermore, soft-tissue stripping adds a biologic insult to the poor bone quality. These disadvantages may lead to poor outcomes such as nonunion, implant failure, malunion, or even infection. These disadvantages remain theoretical, as no prospective studies clearly demonstrate a difference between plating methods in difficult metadiaphyseal or osteoporotic fractures. However, the overwhelming biomechanical evidence has led to a more biologically friendly approach to these fractures. The indications for use of locking plates are evolving. The literature demonstrates low rates of nonunion and overall complication rates with locking plates in difficult metaphyseal and diaphyseal fractures. Anatomic reduction of the articular surface remains paramount. Hybrid techniques that combine the benefits of compression plate fixation with the biological and biomechanical advantages of locking plates are the most likely end result of current locking plate applications.     

Plate selection for fixation of extra-articular distal humerus fractures: A biomechanical comparison of three different implants

Operative fixation of extra-articular distal humerus using a single posterolateral column plate has been described but the biomechanical properties or limits of this technique is undefined. The purpose of this study was to evaluate the mechanical properties of distal humerus fracture fixation using three standard fixation constructs.Two equal groups were created from forty sawbones humeri. Osteotomies were created at 80 mm or 50 mm from the tip of the trochlea. In the proximal osteotomy group, sawbones were fixed with an 8-hole 3.5 mm LCP or with a 6-hole posterolateral plate. In the distal group, sawbones were fixed with 9-hole medial and lateral 3.5 mm distal humerus plates and ten sawbones were fixed with a 6-hole posterolateral plate. Biomechanical testing was performed using a servohydraulic testing machine. Testing in extension as well as internal and external rotation was performed. Destructive testing was also performed with failure being defined as hardware pullout, sawbone failure or cortical contact at the osteotomy.In the proximal osteotomy group, the average bending stiffness and torsional stiffness was significantly greater with the posterolateral plate than with the 3.5 mm LCP. In the distal osteotomy group, the average bending stiffness and torsional stiffness was significantly greater with the posterolateral plate than the 3.5 mm LCP. In extension testing, the yield strength was significantly greater with the posterolateral plate in the proximal osteotomy specimens, and the dual plating construct in the distal osteotomy specimens. The yield strength of specimens in axial torsion was significantly greater with the posterolateral plate in the proximal osteotomy specimens, and the dual plating construct in the distal osteotomy specimens.Limited biomechanical data to support the use of a pre-contoured posterolateral distal humerus LCP for fixation of extra-articular distal humerus exists. We have found that this implant provided significantly greater bending stiffness, torsional stiffness, and yield strength than a single 3.5 mm LCP plate for osteotomies created 80 mm from the trochlea. At the more distal osteotomy, dual plating was biomechanically superior. Our results suggest that single posterolateral column fixation of extra-articular humerus fractures is appropriate for more proximal fractures but that dual plate fixation is superior for more distal fractures.     

A biomechanical study of conventional acetabular internal fracture fixation versus locking plate fixation

Background

Conventional internal fixation entails the use of an interfragmentary lag screw along with a plate. Not all acetabular fractures are amenable to the placement of an interfragmentary lag screw, and the fracture may be displaced during tightening of the interfragmentary lag screw. Locking plates are a possible solution. We sought to determine whether a locking plate construct can provide stability equivalent to that provided with a conventional construct for transverse acetabular fractures.

Methods

We used 5 paired fresh-frozen cadaveric acetabula. We fixed one side with the conventional technique and the other side with a locking plate. We subjected each fixation to a cyclic compressive force up to 500 cycles, followed by compressive force until failure. We monitored 3-dimensional motion of the fracture.

Results

The average fracture gap at 50 N compressive force after 500 loading cycles was 0.41 (standard deviation [SD] 0.49) mm for the conventional plate and lag screw construct compared with 0.76 (SD 0.62) mm for the locked plate construct (p = 0.46). The force to failure, as defined by 2 mm of fracture gap, was 848 (SD 805) N for the conventional plate and lag screw construct compared with 506 (SD 277) N for the locked plate fixation (p = 0.34).

Conclusion

The locking plate construct is as strong as the conventional plate plus interfragmentary lag screw construct for fixing transverse acetabular fractures. Locking plates may improve management of acetabular fractures by eliminating the need for placement of an interfragmentary lag screw. Furthermore, they may be helpful in revision hip arthroplasty in patients with pelvic discontinuity.     

肱骨近端骨折3种不同固定方式重建内侧柱的有限元分析

目的 采用有限元分析肱骨近端骨折锁定钢板联合内侧支撑螺钉、锁定钢板联合腓骨支撑及外侧锁定钢板联合内侧钢板重建内侧柱3种内固定模型的生物力学稳定性.方法 选取1名健康女性志愿者进行肱骨近端CT扫描,按照肱骨解剖颈下5 mm截骨,建立肱骨近端内侧柱缺失型骨折模型,按不同内固定方式分为PC组、PF组、PP组.PCO组单纯应用...     

Comparison of plate and screw fixation and screw fixation alone in a comminuted talar neck fracture model

BACKGROUND: Talar neck fracture fixation has been studied in noncomminuted fracture models, but no large clinical series of comminuted fracture patterns have been published and no biomechanical studies have compared plate fixation with screw fixation in comminuted talar neck fractures. METHODS: Nine matched pairs of fresh frozen talar specimens were stripped of soft tissue and mounted in a cylindrical jig. The talar neck was fractured using a dorsally directed shear force at a rate of 200 mm/min, and dorsal comminution was simulated by removing a 2-mm section of bone from the distal fracture fragment. One specimen from each pair was fixed with either two solid 4.0-mm partially threaded cancellous screws posterior-to-anterior just lateral to the posterior process of the talus or with a four-hole 2.0-mm minifragment plate contoured to the lateral surface of the talar neck and secured with 2.7-mm screws. A 2.7-mm fully threaded cortical screw was placed medially using a lag technique. The specimens were then loaded to failure with a dorsally directed force at a rate of 200 mm/min. Failure was defined as the load producing 2 mm of displacement. A Student's t-test analysis was used with significance set at p < or = 0.05. RESULTS: Posterior-to-anterior screw fixation had a statistically significant higher load to failure than plate fixation (p < 0.05). Mean load to failure for the screw group was 120.7 +/- 68.5 N and 89.7 +/- 46.6 N for the plating group. CONCLUSIONS: Plate fixation may offer substantial advantages in the ability to control the anatomic alignment of comminuted talar neck fractures, but it does not provide any biomechanical advantage compared with axial screw fixation. Further, the fixation strength of both methods was an order of magnitude lower than those found in previous studies of noncomminuted fractures.     

Die Stabilität von distalen Radiusfrakturen mit volaren winkelstabilen Plattenosteosynthesen

Background

Distal radius fractures continue to show significant complication rates after operative treatment with locked plating. Failure occurs by screw loosening or screw penetration in the distal fragment. Placement of additional screws may enhance the stiffness of fracture fixation. The aim of this study was to determine the fatigue properties of different screw configurations in distal radius plate osteosynthesis with biomechanical tests and finite element analysis (FEA).

Material and methods

Unstable distal radius fractures were created in 12 human cadaveric bone specimens and were fixed with volar locking plates. Group 4SC was fixed with four screws in the distal row and group 6SC with two additional screws the row below. Dynamic loading was applied physiologically. The radial shortening, the angulation of the distal fragment and the failure mechanism were determined by experimental tests and were further elucidated by FEA.

Results

Group 6SC showed a significantly lower radial shortening and inclination. Breakage of the screws within the plate was noted in group 4SC, while moderate screw penetration was observed in group 6SC. FEA confirmed the biomechanical tests. In group 4SC elevated von Mises strain in the locking mechanism explained the inclination of the screws and the distal fragment. The elastic strain in group 6SC was increased at the screw-bone interface which explained the resulting screw penetration.

Conclusion

The failure mechanism in volar plating of distal radius fractures depended on the number of screws and their configuration. Using two more screws increases construct stiffness and angular stability under dynamic loading. However, increased stiffness also promoted screw penetration mainly in osteoporotic bone. Compared to screw penetration, loss of reposition and inclination of the distal fragment observed in the 4SC configuration is more likely to result in clinical complications.     

An internal locking plate to study intramembranous bone healing in a mouse femur fracture model

In most murine fracture models, the femur is stabilized by an intramedullary implant and heals predominantly through endochondral ossification. The aim of the present study was to establish a mouse model in which fractures heal intramembranously. Femur fractures of 16 SKH‐mice were stabilized by an internal locking plate. Femur fractures of another 16 animals were stabilized by an intramedullary screw. Bone repair was analyzed by radiographic, biomechanical, and histological methods. At 2 weeks, histological analysis showed a significantly smaller callus diameter and callus area after locking plate fixation. Cartilage formation within the callus could only be observed after screw fixation, but not after fracture stabilization with the locking plate. Radiological and biomechanical analysis after 2 and 5 weeks showed a significantly improved healing and a higher bending stiffness of fractures stabilized by the locking plate. Fractures stabilized by the locking plate healed exclusively by intramembranous ossification, which is most probably a result of the anatomical reduction and stable fixation. The fractures that healed by intramembranous ossification showed an increased stiffness compared to fractures that healed by endochondral ossification. This model may be used to study molecular mechanisms of intramembranous bone healing. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:397–402, 2010