Fracture Gap Motion Research Articles

EXPERIMENTALLY VALIDATED COMPUTER SIMULATIONS OF LOCKING PLATE FIXATIONS FOR SURGICAL EDUCATION

Surgical education of fracture fixation biomechanics relies mainly on simplified illustrations to distill the essence of the underlying principles. These mostly consist of textbook drawings or hands-on exercises during courses, both with unique advantages such as broad availability and haptics, respectively. Computer simulations are suited to bridge these two approaches; however, the validity of such simulations must be guaranteed to teach the correct aspects. Therefore, the aim of this study was to validate finite element (FE) simulations of bone-plate constructs to be used in surgical education in terms of fracture gap movement and implant surface strain.The validation procedure was conducted in a systematic and hierarchical manner with increasing complexity. First, the material properties of the isolated implant components were determined via four-point bending of the plate and three-point bending of the screw. Second, stiffness of the screw-plate interface was evaluated by means of cantilever bending to determine the properties of the locking mechanism. Third, implant surface strain and fracture gap motion were measured by testing various configurations of entire fixation constructs on artificial bone (Canevasit) in axial compression. The determined properties of the materials and interfaces assessed in these experiments were then implemented into FE models of entire fixation constructs with different fracture width and screw configurations. The FE-predicted implant surface strains and fracture gap motions were compared with the experimental results.The simulated results of the different construct configurations correlated strongly with the experimentally measured fracture gap motions (R2>0.99) and plate surface strains (R2>0.95).In a systematic approach, FE model validation was achieved successfully in terms of fracture gap motion and implant deformation, confirming trustworthiness for surgical education. These validated models are used in a novel online education tool OSapp (https://osapp.ch/) to illustrate and explain the biomechanical principles of fracture fixations in an interactive manner.

Augmentative Plating versus Exchange Intramedullary Nailing for the Treatment of Aseptic Non-Unions of the Femoral Shaft-A Biomechanical Study in a SawboneTM Model.

Non-unions after intramedullary nailing of femoral shaft fractures are a significant problem. Treatment options such as augmenting with plates or exchange nailing have been proposed. The ideal treatment remains controversial. Augmentative plating using a 4.5 mm LCP or a 3.2 mm LCP leaving the nail in situ was tested biomechanically and compared to exchange intramedullary nailing in a SawboneTM model of a femoral shaft non-union. The difference of fracture gap motion in axial testing was small. In rotational testing, the exchange nail allowed for the largest amount of motion. The 4.5 mm augmentative plate was the most stable construct in all loading conditions. Augmentative plating using a 4.5 mm LCP plate while leaving the nail in situ is biomechanically superior to exchange intramedullary nailing. A small fragment 3.2 mm LCP is undersized and does not reduce fracture motion sufficiently in a femoral shaft non-union.

Articular contact vs. embedding: Effect of simplified boundary conditions on the stress distribution in the distal radius and volar plate implant loading

Boundary conditions (BCs) are often simplified in experimental and numerical models simulating distal radius fractures and their treatments. The aim of this study was to investigate the effects of simplified BCs at the radiocarpal joint: (1) on the stress distribution in the intact distal radius, and (2) on the loading of a volar locking plate (VLP) used for distal radius fracture treatment. Finite element models of the distal radius with contact between carpals and cartilage were created as reference models for an intact bone and a fractured bone with VLP treatment. Four models with simplified BCs were compared to these reference models: One with embedding material instead of carpals, one with carpals tied to the radius; each loaded either uniaxially or with statically equivalent loading to the reference model. Differences in distal bone stress distributions and mechanical parameters of the VLP (fracture gap movement, plate peak stresses, distal screw loads) were generally largest for the uniaxially loaded, embedded model (up to 250 % in individual screw loads) and smallest for the model with tied carpals and statically equivalent loads (<25 % for all parameters). Differences were greatly reduced if statically equivalent loads were applied, but subchondral stress peaks were absent without carpals. In conclusion, implementing realistic resultant forces and moments is more important than the exact articular load distribution, but carpal bones should be included if subchondral bone stresses are analyzed. In this case, a tie constraint may replace articular contact modelling with acceptable accuracy if statically equivalent loading is applied.

Serklaj Kablolamada Farklı Subtrokanterik Kemik Kırılma Açılarının Biyomekanik Karşılaştırılması: Sonlu Eleman Çalışması

Cerclage wires are regularly hired as fixation gear to resource reposition, enhance alignment and growth fixation stability. In specific femoral shaft, subtrochanteric and periprosthetic fractures gain from cerclage fixation. Also in supracondylar femoral shaft fractures, extra cord cerclages proved to be extra than only a reposition device and accelerated the general power of the osteosynthesis construct. This study tests for the stabilizing effect of different bone fracture angles in with cerclage. Cerclage fixation of a oblique fractures were tested with fracture angles (45°, 55°, 65°). Construct stiffness and displacements were investigated under static loads and compared to the different bone fracture angles. With each of the tested bone fractures, stiffness wasn't significantly for a compare angles. Most reduction in fracture gap movement was achieved by 65° fracture angle, followed by 55° and 45° fractures. &#x0D; All cerclage wire fixation were generally superior with reduced fracture movements whereas in 65 degree fracture showing the greatest stabilizing effect. Cerclage wire application has emerged as a potential therapeutic for subtrochanteric fractures.

No more rattling: biomechanical evaluation of a hexapod ring fixator free of play.

Hexapod-ring-fixators have a characteristic rattling sound during load changes due to play in the hexapod struts. This play is perceived as unpleasant by patients and can lead to frame instability. Using slotted-ball-instead of universal-joints for the ring-strut connection could potentially resolve this problem. The purpose of the study was to clarify if the use of slotted-ball-joints reduces play and also fracture gap movement. A hexapod-fixator with slotted-ball-joints and aluminum struts (Ball-Al) was compared touniversal-joint-fixators with either aluminum (Uni Al) orsteel struts (Uni Steel). Six fixator frames each were loaded in tension, compression, torsion, bending and shear andmechanical performance was analyzed in terms of movement, stiffness and play. The slotted-ball-joint fixator wasthe only system without measurable axial play(<0.01mm) compared to Uni-Al (1.2±0.1)mm and Uni-Steel (0.6±0.2)mm (p≤0.001). In both shear directions the Uni-Al had the largest play (p≤0.014). The resulting axial fracture gap movements were similar for the two aluminum frames and up to 25% smaller for the steel frame, mainly due to the highest stiffness found for the Uni-Steel in allloading scenarios (p≤0.036). However, the Uni-Steel construct was also up to 29% (450g) heavier and had fewer usable mounting holes. In conclusion, the slotted-ball-joints of the Ball-Al fixator reduced play and minimized shear movement in the fracture while maintaining low weight of the construct. The heavier and stiffer Uni-Steel fixator compensates for existing play with a higher overall stiffness.

Biomechanical comparison of different cerclage types in addition to an angle stable plate osteosynthesis of distal tibial fractures

BackgroundDifferent stand-alone cerclage configurations and their optimal twisting techniques have been investigated over the years. This study tests for the stabilizing effect of different supplemental cerclage materials in combination with locked plating of distal tibia fractures. MethodsLocking plate fixation of a distal tibial spiral fracture was tested as stand-alone and with supplemental cerclage materials (one cable, two cables, wire, fiber tape). Construct stiffness and fracture gap movements were investigated under quasi-static and dynamic loads and compared to the stand-alone locking plate. ResultsWith each of the tested cerclages, stiffness was significantly higher than for a solitary plate osteosynthesis. Most reduction in fracture gap movement was achieved by cable cerclages, followed by double-looped wire and double-looped fiber tape cerclages. Under dynamic loading an additional cable cerclage reduces excessive gap movement. ConclusionCompared to solitary plate osteosynthesis all supplemental cerclage materials were generally superior with reduced fracture gap movements whereas cable cerclages showing the greatest stabilizing effect.

Single column plate plus other column lag screw fixation vs. both column plate fixation for anterior column with posterior hemitransverse acetabular fractures - a biomechanical analysis using different loading protocols.

Open reduction and internal fixation of both columns is considered the treatment of choice for displaced anterior column with posterior hemitransverse (ACPHT) fractures in non-geriatric patients. Plate fixation of one column combined with lag screw fixation of the other column allows to decrease operative time and approach-related morbidity compared to conventional both column plating. The aim of this biomechanical study was to evaluate whether single column plate plus other column lag screw fixation confers similar stability to both column plate fixation. Physiological loads were simulated using both the single-leg stance (SLS) as well as the sit-to-stand (STS) loading protocols. A clinically relevant ACPHT fracture model was created using fourth-generation composite hemipelves. Fractures were stabilized with three different fixation constructs: (1) anterior column plate plus posterior column screw fixation (AP+PCS), posterior column plate plus anterior column screw fixation (PP+ACS) and anterior column plate plus posterior column plate fixation (AP+PP). Specimens were loaded from 50 to 750N with a ramp of 100N/s. Fracture gap motion (FGM) and relative interfragmentary rotation (RIFR) between the three main fracture fragments were assessed under loads of 750N using an optical 3D measurement system. STS loading generally resulted in higher mean FGM and RIFR than STS loading in the AP+PCS and AP+PP groups, while no significant differences were found in the PP+ACS group. Compared to conventional both column plate fixation (AP+PP), PP+ACS displayed significantly higher FGM and RIFR between the iliac wing and the posterior column during SLS loading. No significant differences in FGM and RIFR were identified between the AP+PCS and the AP+PP group. Overall, single column plate plus other column lag screw fixation conferred similar stability to conventional both column plate fixation. From a clinical point of view, AP+PCS appears to be the most attractive alternative to conventional AP+PP for internal fixation of ACPHT fractures.

Biomechanical comparison of fixation techniques for transverse acetabular fractures – Single-leg stance vs. sit-to-stand loading

ObjectivesTo biomechanically compare five different fixation techniques for transverse acetabular fractures using both the single-leg stance (SLS) and the sit-to-stand (STS) loading protocols and to directly compare fracture gap motion (FGM) and relative interfragmentary rotation (RIFR). MethodsTranstectal transverse acetabular fractures were created on fourth-generation composite hemipelves in a reproducible manner. Five different fixation techniques were biomechanically assessed using both an SLS and STS loading protocol: anterior plate (AP) only, posterior plate (PP) only, anterior plate plus posterior column screw (AP+PCS), posterior plate plus anterior column screw (PP+ACS) and anterior plus posterior plate (AP+PP). After preconditioning, the specimens were loaded from 50 to 750 N with a ramp of 100 N/s. FGM and RIFR under loads of 750 N were measured using an optical 3D measurement system. ResultsIn the three groups of fixation techniques addressing both columns, STS loading resulted in higher mean FGM and in RIFR than SLS loading. No construct failure was observed. In the single plate groups (AP only and PP only), STS loading resulted in failure of all specimens before reaching loads of 750 N, while no failure occurred after SLS loading. No significant differences in FGM and RIFR were found between the double plate (AP+PP) and the single plate plus column screw (AP+PCS and PP+ACS) techniques. ConclusionSLS loading appeared to overestimate the strength of acetabular fracture fixation constructs and STS loading may be more appropriate to provide clinically relevant biomechanical data. Internal fixation of a single column might not provide adequate stability for transverse fractures, while strength of single plate plus column screw fixation and double plate fixation was comparable.

Low-profile double plating versus dorsal LCP in stabilization of the olecranon fractures

IntroductionProximal ulna fractures are common in orthopaedic surgery. Comminuted fractures require a high primary stability by the osteosynthesis, to allow an early functional rehabilitation as fast as possible, to reduce long-term limitations of range of motion. Classical dorsal plating is related to wound healing problems due to the prominence of the implant. New low-profile double plates are available addressing the soft tissue problems by positioning the plates at the medial and lateral side. This study analysed whether, under high loading conditions, these new double plates provide an equivalent stability as compared to the rigid olecranon locking compression plate (LCP).Materials and methodsIn Sawbones, Mayo Type IIB fractures were simulated and stabilized by plate osteosyntheses: In group one, two low-profile plates were placed. In group two, a single dorsal plate (LCP) was used. The bones was than cyclically loaded simulating flexion grades of 0°, 30°, 60° and 90° of the elbow joint with increasing tension forces (150 , 150 , 300 and 500 N). The displacement and fracture gap movement were recorded. In the end, in load-to-failure tests, load at failure and mode of failure were determined.ResultsNo significant differences were found for the displacement and fracture gap widening during cyclic loading. Under maximum loading, the double plates revealed a comparable load at failure like the single dorsal plate (LCP). The double plates failed with a proximal screw pull-out of the plate, whereas in the LCP group, in 10 out of 12 specimens the mode of failure was a diaphyseal shaft fracture at the distal plate peak.ConclusionBiomechanically, the double plates are a good alternative to the dorsal LCP providing a high stability under high loading conditions and, at the same, time reducing the soft tissue irritation by a lateral plate position.

Comparison of two reinforcement rings for primary total hip arthroplasty addressing displaced acetabular fractures: a biomechanical analysis

IntroductionAim of this study was to biomechanically compare two different acetabular cup fixation constructs in terms of fracture fixation for displaced acetabular fractures involving the anterior column with hemitransverse fracture under partial and full weight-bearing conditions.MethodsTwo different reinforcement rings designed as cages for primary THA were biomechanically tested in terms of managing a complex acetabular fracture. Single-leg stance cyclic loading was performed to assess fracture gap movement and fragment rotation. Twelve hemi pelvis Sawbones were divided into two groups: primary THA with acetabulum roof reinforcement plate (ARRP) (n = 6) and primary THA with Burch–Schneider reinforcement cage (BSRC) (n = 6).ResultsDuring loading under partial weight-bearing (250 N) fracture gap movement tended to be larger in the BSRC group as compared to the ARRP group. Under full weight-bearing conditions, the ARRP showed 60% significantly less motion (p = 0.035) of the os ilium to os ischii gap compared to BSRC. Fracture gap movements between the os ilium and spina iliaca fragments were significantly reduced by 76% (p = 0.048) for ARRP in contrast to BSRC. The ARRP group also demonstrated significantly less movement in the fracture gaps os ischii to quadrilateral plate (62% reduction, p = 0.009) and quadrilateral plate to spina iliaca (87% reduction, p < 0.001). Significantly less rotational movement of the quadrilateral plate to the os ilium was exhibited by the ARRP group (p = 0.015).ConclusionsThe presented acetabulum roof-reinforcement plate (ARRP) provides stable conditions at the acetabular component with adequate stabilization of a displaced acetabular fracture.

Locking plate constructs benefit from interfragmentary lag screw fixation with decreased shear movements and more predictable fracture gap motion in simple fracture patterns

BackgroundA mechanical characterisation of lag screw fixation plus locking plate – although clinically widely used as either “mixed fixation concept” or absolutely stable fixation – is so far missing. This study aimed to evaluate the influence of an interfragmentary lag screw on the resulting motion at the fracture site of locking plate constructs using a simple fracture at the distal femur. MethodsHuman cadaver femora were in vitro loaded in torsion and axial bending-compression with and without lag screw fixation next to a locking plate fixation. In addition, two plate working lengths were tested. Interfragmentary movement was measured optically. FindingsAxial interfragmentary movement is reduced with lag screw (102 mm plate working length, 1000 N, mean): 0.28 mm versus 0.82 mm. With lag screw, the fracture gap stays closed with mean normal interfragmentary movement ≤0.03 mm. Fracture gap tends to open without lag screw: normal interfragmentary movement up to −0.29 mm. Reduction of shear interfragmentary movement was observed throughout all tested loads and groups. Mean true shear remains generally low with lag screw (≤0.42 mm) compared to without lag screw (≤1.46 mm). We also found that interfragmentary movement variance decreases with lag screw, especially for longer plate working length. InterpretationAn interfragmentary lag screw next to locking bridge plating reduces fragment motion in vitro for a simple fracture pattern and provides a sufficient tool to decrease detrimental shear movements. Prospective clinical trials with interfragmentary lag screw fixation should prove these findings in wide clinical use to treat simple fracture patterns.

Screw fixation of ACPHT acetabular fractures offers sufficient biomechanical stability when compared to standard buttress plate fixation

BackgroundGeriatric acetabular fractures require fixation with sufficient primary stability to allow for immediate full-weight bearing. Minimally-invasive procedures would be desirable in order to keep perioperative morbidity low. The purpose of this study was to compare the biomechanical strength of lag screw-only fixation of anterior column posterior hemi-transverse (ACPHT) acetabular fractures to standard anatomical plate fixation.MethodsStandardized ACPHT fractures were created in fourth generation synthetic pelvis models and stabilized by either an anatomical buttress plate (n = 4) or by a screw-only construct (n = 4). In a validated setup, a cyclic loading protocol was applied with increasing axial force (3200 cycles, 175 N to 2250 N). Construct survival, acetabular fracture motion, and mode of failure were assessed.ResultsThe median number of cycles needed until failure of the construct occurred was 2304 cycles (range, 2020 to 2675) in the plate fixation group and 3200 cycles (range, 3101 to 3200) for the screw fixation constructs (p = .003). With regard to energy absorbed until failure, the plate fixation group resisted to 1.57 × 106 N*cycles (range, 1.21 × 106 to 2.14 × 106) and the screw fixation group to 3.17 × 106 N*cycles (range, 2.92 × 106 to 3.17 × 106; p = .001). All plate fixation specimens failed with a break-out of the posterior-column screw in the quadrilateral wing of the anatomical plate within a maximum load of 1750 N while the screw fixation constructs all survived loading of at least 2100 N. Acetabular fracture gap motion, acetabular rim angle, and medial femoral head subluxation as measures of fracture displacement were all not different between the two groups (p > 0.1).ConclusionsIn this in vitro biomechanical study, screw-only fixation of an ACPHT acetabular fracture resulted in at least as good construct survival as seen for standard buttress plate fixation. Both methods resisted sufficiently to forces that would be expected under physiologic conditions.

Biomechanical comparison of Gamma3 and InterTan nails for stable and unstable intertrochanteric fractures

Objective To compare the biomechanical properties of Gamma3 and InterTan nails in the fixation of femoral intertrochanteric fractures. Methods Twelve synthetic femora of 4th generation were randomized into 4 equal groups (n=3) for assessment of the 2 constructs of fracture fixation (Gamma3 versus InterTan nails). Groups A and B were made into models of stable femoral intertrochanteric fracture (AO/OTA type 31-A1.1) and groups C and D into unstable ones(AO/OTA type 31-A2.3). The biomechanical properties of Gamma3 and InterTan nails in the 4 models were tested and compared. Results For stable fracture models, the fracture gap movement increased with the increasing axial load and the torque increased with the increasing torsion angle. There were significant differences between groups A and B in fracture gap movement and torque (P 0.05). For unstable fracture models, there were no significant differences between groups C and D in fracture gap movement when the axial loads were 500 N, 600 N or 700 N (P >0.05), but there was a significant difference between the 2 groups when the axial load was larger than 800 N (P< 0.05). With the increasing torsion angle, the torque increased in groups C and D. There was a significant difference between the 2 groups in the torque at the same torsion angle (P< 0.05). There were a significant difference between groups C and D in failure load (2,781.5±600.6 N versus 3,150.5±633.8 N) (P=0.007). Conclusions For stable femoral intertrochanteric fractures, InterTan and Gamma3 nails may exhibit similar biomechanical properties. For unstable femoral intertrochanteric fractures, InterTan nails may provide obviously better biomechanical stability than Gamma3 nails. Key words: Hip fractures; Fracture fixation, intramedullary; Bone nails; Biomechanics

A sliding hip screw augmented with 2 screws is biomechanically similar to an inverted triad of cannulated screws in repair of a Pauwels type-III fracture

ObjectivePauwels 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. MethodsFourth 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). ResultsThe 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. ConclusionsThe 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.

Biomechanical effects of angular stable locking in intramedullary nails for the fixation of distal tibia fractures.

Treatment of distal tibia shaft fractures using intramedullary nailing requires stable fixation of the distal fragment to prevent malunion. Angular stable locking for intramedullary nails pledge to provide increased mechanical stability. This study tested the hypothesis that intramedullary nails with angular stable interlocking screws would have increased construct stiffness, reduced fracture gap movement and enhanced fatigue failure compared to nails with conventional locking having the same diameter. Biomechanical experiments were performed on 24 human cadaveric tibiae which obtained a distal fracture and were fixed by three different techniques: conventional locking with 8- and 10-mm-diameter nails and angular stable locking with 8-mm nails. Stiffness of the implant-bone construct and movement of the fragments were tested under axial loading and torsion. The constructs were tested to failure under cyclic fatigue loading. Analysis of variance and Kaplan-Meier survival analysis were used for statistical assessment. Axial stiffness of the 10-mm nail was about 50% larger compared to both 8-mm nail constructs independent of the type of locking mode (p < 0.01). No differences were found in axial performance between angular stable and conventional locking neither under static nor under cyclic testing conditions (p > 0.5). Angular stability significantly decreased the clearance under torsional load by more than 50% compared to both conventionally locked constructs (p = 0.03). However, due to the larger nail diameter, the total interfragmentary motion was still smallest for the 10-mm nail construct (p < 0.01). Although the 10-mm nail constructs survived slightly longer, differences between groups were minor and not statistically significant (p = 0.4). Our hypothesis that angular stable interlocking of intramedullary nails would improve mechanical performance of distal tibia fracture fixation was not confirmed in a physiologically realistic loading scenario. Whether minor mechanical advantages provided by angular stability of the locking screws would improve biological tissue response cannot be concluded from this biomechanical study.

Preliminary testing of a novel bilateral plating technique for treating periprosthetic fractures of the distal femur

BackgroundCurrent stabilization methods for periprosthetic fractures of the distal femur are inadequate in achieving fracture fixation, with complication rates as high as 29%. A major contributor to poor outcomes is that these methods rely only on screw purchase in the bone to maintain fracture reduction. We designed, manufactured and evaluated a novel plating method that utilizes the femoral prosthesis to enhance stability for treatment of distal femoral periprosthetic fractures. MethodsMedial and lateral plates were designed and manufactured based on geometry of a synthetic femur and femoral prosthesis. The two plates were linked via a compression screw and a small tab on each plate that inserted into pre-existing slots on the prosthesis. Mechanical tests (500N compression or 250N anterior directed cantilever bending), were performed on synthetic femurs with simple transverse fractures (3mm gap) just superior to the distal femoral prosthesis that were stabilized using either the prototype plates or a single lateral plate. Translational movements of the fracture site during loading were measured using 3D motion tracking. FindingsWith the single lateral plate, the distal fragment experienced a resultant displacement of 0.40mm under cantilever bending and 0.61mm under compression (13% and 20% respectively of fracture gap width). With the bilateral plates, fracture gap motion was significantly reduced to 0.13mm under bending and compression (4.3% of the fracture gap). InterpretationOur results indicate that a bilateral plating method is capable of improving stabilization of periprosthetic fractures compared to the traditional lateral plating technique.

The influence of distal locking on the need for fibular plating in intramedullary nailing of distal metaphyseal tibiofibular fractures

Using human cadaver specimens, we investigated the role of supplementary fibular plating in the treatment of distal tibial fractures using an intramedullary nail. Fibular plating is thought to improve stability in these situations, but has been reported to have increased soft-tissue complications and to impair union of the fracture. We proposed that multidirectional locking screws provide adequate stability, making additional fibular plating unnecessary. A distal tibiofibular osteotomy model performed on matched fresh-frozen lower limb specimens was stabilised with reamed nails using conventional biplanar distal locking (CDL) or multidirectional distal locking (MDL) options with and without fibular plating. Rotational stiffness was assessed under a constant axial force of 150 N and a superimposed torque of ± 5 Nm. Total movement, and neutral zone and fracture gap movement were analysed. In the CDL group, fibular plating improved stiffness at the tibial fracture site, albeit to a small degree (p = 0.013). In the MDL group additional fibular plating did not increase the stiffness. The MDL nail without fibular plating was significantly more stable than the CDL nail with an additional fibular plate (p = 0.008). These findings suggest that additional fibular plating does not improve stability if a multidirectional distal locking intramedullary nail is used, and is therefore unnecessary if not needed to aid reduction.

Die neue anatomische Flügelplatte für osteoporotische Azetabulumfrakturen: biomechanische Testung und erste klinische Erfahrungen

Acetabular fractures are rare injuries, but there is an increasing number of elderly people with ventral medial instability in cases of central subluxation of the femoral head in osteoporotic acetabular fractures. Common plate osteosynthesis cannot enable medial support of the quadrilateral surface. The new "acetabular wing plate" is anatomically shaped to fix the arcuate line and the quadrilateral surface. The plate pushes the femoral head back to lateral. The aim of this study was the biomechanical comparison with common plate concepts before clinical use of the new implant. For biomechanical testing eight artificial fracture models of the pelvis with anterior column fractures were used. They were implemented into a set-up of a one-leg stand model in the material test machine. Cyclical movements with axial pressure to the sacrum up to 250 N were given to the model. Fracture gap movement was measured with an optoelectronic 3D camera measuring system. In all pelvic models all screw holes were drilled by use of drill guides before first mechanical loading. The measurements were randomly done first with the new acetabular wing plate or with the pelvic low profile plate. Absolute and relative fracture gap movement and movements of the pelvic fragments were measured as well. The fracture gap movement and the fragment rotation were comparable in both groups. There was a slightly higher stability in the group of the acetabular wing plate but without statistical significance. In the pelvic low profile group two screw loosenings were found, but the models were able to be tested also with the acetabular wing plate. The new plate was clinically used in the first eight patients due to the good biomechanical results. In all cases the osteosyntheses were done by use of the Stoppa approach and the first window of the ilioinguinal approach. Application of the plate was mostly easy, the plate was also used as a reduction tool. Postoperative controls show anatomic reduction and correct implant position in all eight cases. The three month follow-up examinations confirm the continuing good reduction during fracture healing with the acetabular wing plate.

Distal radius fracture fixation with volar locking plates and additional bone augmentation in osteoporotic bone: a biomechanical study in a cadaveric model

Fractures of the distal radius represent the most common fractures in adults. Volar locked plating has become a popular method for treating these fractures, but has been subject to several shortcomings in osteoporotic bone, such as loss of reduction and screw purchase. In order to overcome these shortcomings, cement augmentation has been proposed. AO-type 23-A3.3 fractures were made in 8 pairs of fresh frozen osteoporotic cadaveric radial bones. All specimens were treated with volar plating, and divided into cement augmentation or non-augmentation groups (n = 8/group). Constructs were tested dynamically and load to failure, construct-stiffness, fracture gap movement and screw cutting distance were measured. Cement augmentation resulted in a significant increase in cycles and load to failure, as well as construct stiffness at loads higher than 325 N. When compared to the non-augmented group, fracture gap movement decreased significantly at this load and higher, as did screw cutting distance at the holes of the ulnar column. The cycles to failure depend on the BMD in the distal region of the radius. Cement augmentation improves biomechanical properties in volar plating of the distal radius.

Biomechanical comparison of intramedullar versus extramedullar stabilization of intra-articular tibial plateau fractures

Fractures of the proximal tibia occur very often and are a great challenge for trauma surgeons to stabilize. Although locked nails were developed to stabilize these fractures, this technique has not been sufficiently investigated. The purpose of this study was to biomechanically assess the stability of locked intramedullary nailing compared to locked plating. 16 fresh frozen human cadaveric tibiae were osteotomized in the meta-diaphyseal intersection with an osteotomy gap of 10 mm and a single osteotomy through the medial epicondyle to simulate a 41-C.2 fracture. Stabilization was performed with an angle stable locked Targon-TX nail (n = 8) and two additional canulated screws. The other testing group (n = 8) was treated with two canulated screws and a five-hole LCP-PLT. The bones were tested in a cyclic testing protocol with increasing loads under compression and a load sharing of 60 % through the medial tibial plateau and 40 % to the lateral side. Stiffness and fracture gap movement were measured and failure mode was assessed. No significant differences were found between the two implants regarding load until failure. The stiffness of the intramedullary nailing group (927 N/mm) was statistically significantly higher than the stiffness of the plating group (564 N/mm). No differences were found for fracture gap movement in the z-axis. However, differences were found for dislocation of the proximal-lateral and proximal-medial fragments, with absolute values of 0.099 mm in the plate group and 0.66 mm in the nailing group at 800 N. Prior to failure, fracture gap movement was 0.22 mm for the plating group and 1.66 mm for the nailing group, a difference that was also statistically significantly different. The nailing group failed by screw cut-out while the plating group failed by screw breakage. Nailing of proximal tibia fractures leads to a stiffer implant-bone construct than plating. Since no adverse effects were found after nailing it seems to be a good alternative to plating for intra-articular proximal tibia fractures, especially in patients with soft tissue problems.