| Background: Supracondylar humerus(SCH)fracture is a commonly encountered pediatric trauma,which accounts for about 60% of all elbow fractures in children.Management strategy is usually directed according to fracture patterns and characteristic.Many surgeons are faced with the question of how to accurately and anatomically reduce the fracture and maintain that reduction in order to prevent complications.Difficulty in achieving and maintaining anatomic alignment have be attributed to many factors especially with the use of closed reduction and pinning fixation method.Percutaneous pinning is currently regarded as the gold standard for managing displaced SCH fractures.Although it has not completely eliminated the incidence of intra-operative or postoperative complications,it has helped reduce these complications significantly,when compared to closed reduction and immobilization with cast or splint alone and other methods.However,the incidence of loss of reduction is still a major concern to many pediatric orthopedic surgeon.Causes of loss of reduction with pinning techniques have been attributed to pinning configuration,pin size,pin number and pin spread.Technical errors causing loss of reduction can be avoided by maximizing separation of the pins at fracture site,engaging sufficient bone in both proximal and distal fragments,engaging the medial and lateral columns proximal to the fracture,and addition of a third lateral entry pin if there is concern about fracture stability after placement of two lateral pins.Both crossed pins and divergent lateral pins are said to have comparable stiffness in numerous clinical and biomechanical studies.However,the favorable height of intersection or exit point of crossed pins and the entry point of lateral pins required to achieve optimal stability of fractures have not been adequately explored.Although their efficacy have not been compared,other fixation techniques such as lateral external fixation and elastic stable intramedullary nails have all also been used with these fractures with acceptable outcomes.The objective of our studies was to find out the most suitable fixation technique for various fracture characteristics of supracondylar fractures in children.Methods: The study was divided into four parts.Part one was a biomechanical study designed to compare Kirschner wires,lateral external fixation and elastic stable intramedullary nailing system fixation techniques used in high SHFs(MDJ distal humeral fractures),using composite bone models.Three positions of the fracture lines,high,mid and low were analyzed respectively in order to best simulate clinical circumstances.For optimal stabilization,all lateral entry pins in the pinning configurations assumed a divergent orientation.Both models were tested in flexion,extension,valgus,varus,internal rotational and external rotation.Stiffness for each model was then calculated in the six directions.In part two,we hypothesized that posterior lateral column(PLC)entry pins improve stability of transverse high supracondylar fractures when used in combination with directly placed lateral or medial pins.A typical,high transverse extension-type fracture in the coronal plane with a sagittal obliquity of 20 degrees was created in the MDJ region in 36 sawbone humeri models.The humeri were reduced anatomically and fixated with two or three 2.0mm Kirschner wires(KWs)as follows: two-conventional crossed pins(2CC),two-conventional lateral pins(2CL),two-conventional crossed pins plus one-posterior lateral column pin(3PC),two-conventional lateral pins plus one-posterior lateral column pin(3PL),one-conventional medial pin plus one-posterior lateral column pin(2PC)and one-conventional lateral pin plus one-posterior lateral column pin(2PL).The fixated bones were tested in flexion,extension,valgus,varus,internal rotational and external rotation.Stiffness for each model was then calculated in the six directions.The aim of part three was to compare crossed and lateral-only pinning techniques using an anatomically accurate computational 3D pediatric humeral model.Our working hypotheses were that stability of pins is affected by the distal humeral structures;that capitellar entry pins are more stable than direct lateral entry pins;and that highly intersecting crossed pins are more stable than low ones..Elbow CT data of a 6yo child was used to model an anatomically,accurate pediatric humerus model in simpleware software.The humerus model had an intact capitellar ossific nucleus and distal humeral cartilage.The reconstructed surface model of the humerus was then imported into solidworks for solid model generation.Through a series of three-dimensional modeling tools in solidworks,a typical,transverse supracondylar fracture,with a 20 degrees sagittal obliquity was created at the level of the olecranon fossa.Five models of varying heights crossed pins,with pins exiting in 5 different zones(CP1 to CP5)and 3 models of lateral-only pins were generated.The entry points of the medially lying pin in the lateralonly pins were altered with respect to the ossific nucleus of the capitellum to generate a total of 3 configurations with the 2-lateral pins-2LCap,2LP,2LD..The fixated models were tested in the six loading directions of flexion,extension,valgus,varus,internal and external rotations in Abaqus.Stiffness data for the models and stress level distributions on the pins were analyzed.Part four aimed at retrospectively analyzing the characteristics of the exit points,entry points of the most lateral pins and possible influencing factors and prospectively investigating whether the position of the exit points could be artificially controlled;and finding out how to achieve a high exit point with the most lateral pin,in order to ensure maximum divergence.Data of patients admitted for extension-type supracondylar fractures of the humerus between March 2016 and December 2017 were recorded.Between March 2016 and December 2016 all the surgeons were doing the operation freely and data during that period were collected and analyzed as the retrospective group.Demographic data relating to age,sex,side of injury,type of fracture,Gartland’s classification,location and pattern of fracture line and pin size used,were recorded.The last anterior-posterior(AP)and lateral images before the application of casts were used for observation.Entry points of the lateral pins were recorded in reference to the ossification center of the capitellum in both views.To determine the exit point of the most lateral pin,we first determined and marked the upper border of the metaphyseal diaphyseal junction(MDJ)region by drawing two perpendicular and tangential lines along the shaft of the humerus on the AP radiograph.A horizontal line passing through the more proximal point of the two points where the lines intersected the humeral shaft was regarded as the upper boundary of the MDJ region.The regions below and above the line were further divided into four equal zones(-4 to +4)as exit zones,based on the distance from the intra-epicondylar line to the upper boundary of the MDJ region.The coronal pin angles α,formed by the pin and a line traversing the maximum diameter of the olecranon fossa were measured on the AP images;while the sagittal pin angles β formed by the pin and a line at the most distal ossified humeral bone edge,perpendicular to the anterior humeral line were also measured on the lateral images.All measurements were done using measurement tools available on the hospital’s Picture Archiving and Communication System(PACS)software.The prospective part of this study started from January 2017 and ended in December 2017.Based on the findings of the retrospective study,two of the surgeons started to insert the lateral pins from lateral and posterior to the ossification center of the capitellum and intentionally aimed at exiting in zone +1 or higher and data collected as the random group.The other surgeons who were unaware of this protocol were grouped as random.Demographic data and fracture characteristics and measurement data were also collected and recorded as in the retrospective study.Results: Results of part one showed that,in high MDJ fractures,ESIN had better overall stiffness than the other techniques.In the mid groups,3-crossed pinning(1-medial and 2-lateral pins)had the best overall stiffness,followed by 2-crossed pinning(1-medial and 1-lateral pins).In the low fractures,3-crossed pinning was superior to all other techniques.Two crossed pinning and 3-lateral pinning techniques yielded comparable stiffness in the low fracture model.Results from part two showed the three-pin configurations to have increased stiffness in all directions of testing.Overall,the 3PL configuration had statistically significant higher stiffness in all directions except in valgus,where the 3PC configuration was significantly stiffer.Pair-wise comparison however found no significant difference between the two techniques in all loading directions.Among the two-pins configurations,2CC was significantly stiffer in valgus and internal rotation but insignificantly stiffer in flexion;2PC was significantly stiffer in external rotation while 2CL was insignificantly stiffer in extension and varus loadings.Between the two crossed pins,2CC was insignificantly stiffer than 2PC in all directions except in external rotation where 2PC was significantly stiffer.Between the two lateral pins,2CL pins were insignificantly stiffer than 2PL in extension,valgus and varus loadings while 2PL was insignificantly stiffer in flexion,internal and external rotations.Difference in stiffness between 2CC and 2PL were insignificant in all directions except in internal rotation.Results of part three showed a positive trend for higher stiffness as the intersection and exit heights of pins increased,in all loading directions.CP4 and CP5 showed similar stiffness values in all compressive loadings.However,in torsional loadings,CP4 was stiffer than CP5.Stiffness among the pins did not change much in both flexion and extension for all crossed pins.For valgus and varus loadings,huge change in stiffness was observed as the pins crossed and exited higher,with CP4 and CP5 exhibiting the greatest stiffness in those directions.A significant change in stiffness values was also observed starting with the CP3 pins in both internal and external rotations.Among the 2-lateral pins,the direct capitellar entry pinning(2LCap)technique had the best stiffness in all loading directions.The posterior capitellum entry pinning(2LP)technique was the second best in all directions,except in flexion and extension where stiffness values for both 2LP and 2LD were similar.When compared with crossed pins,2LCap had the best stiffness among all 2 pins techniques in compressive loadings.However,CP3-CP5 crossed pins were all stiffer than 2LP and 2LD lateral pins in compressive loadings.In torsional loadings,CP4 was the stiffest among all the techniques2 LP and 2LD lateral pins were however superior to CP1 and CP2 crossed pins in torsional loading.It was observed that the stress distribution regions were mainly concentrated around the fracture sites in all loading directions.The lowest and highest stress in crossed pins were experienced in sagittal and coronal loadings respectively.CP4 crossed pins generated the lowest overall stress levels while CP1 generated the highest overall stress levels.The highest stress levels were mostly found to be located on the lateral pins in compressive loadings,except in CP4 and CP5 were they were located on the medial pins.In torsional loadings however,the highest stresses were all located on the medial pins.Among the 2-lateral pins,2LD pinning technique generated the lowest overall maximal stress levels,while 2LP generated the highest overall stress levels.The lowest and highest stress in the lateral pins were experienced in sagittal and rotational loadings respectively.The medial(capitellar)lateral pins experienced the highest stress levels individually in the lateral pins.In the retrospective and prospective study of part four,there were altogether 161 patients participated in the retrospective study of study four.The average age was 5.2 years(range: 1-13 years).One hundred and twelve patients(69.6%)were younger than 6 years while 49(30.4%)were over age 6.There were 89(55.3%)males and 72(44.7%)females.Sixty-three(39.1%)were injured on the right arm and 98(60.9%)on the left arm.Fifty-two(32.3%)were classified as Gartland type Ⅱ and 109(67.7%)as type la One-hundred fractures(62.1%)were fixed with 1.6mm pins and 61(37.9%)with 2.0mm pins.The coronal pin angle averaged 58.4(range: 40.7 to 75.0)°,and the lateral pin angle averaged 90.5(range: 74.3 to 102.0)°.As to the exit points,88(54.7%)were in the-1 region,26(16.1%)in the-2 region,38(23.6%)in the +1 region and 9(5.6%)in the +2 region.In the AP view,151(93.8%)of the lateral pins entered from lateral to or lateral third of the ossification center of the capitellum(using “capitellum” to represent “the ossification center of the capitellum” for the lateral entry in the following text),and the other 10(6.2%)went through the capitellum.In the lateral view,143(88.8%)entered from posterior to or within the posterior third of the capitellum(the posterior entry)and 18(11.2%)went through the anterior two thirds of the capitellum.In the AP view,the medial entry pins made slightly larger coronal angles than that of lateral entry(63.9±6.43 vs.58.0±6.26,p=0.005).In the lateral view,the posterior entry pins were tilted more anteriorly than those inside the capitellum(89.8±5.96 vs.96.2±3.38,p<0.001).However,all the above-mentioned had no significant difference with regards to the pin distribution in the exit zones.Although the majority of the pins entered from lateral to the capitellum on the AP view and posterior to the capitellum on the lateral view(85.1%),the statistical difference was insignificant(p=0.308).Altogether there were 161 cases in the prospective study of study four.There was no difference in the constitution of the two groups except in the pin size and sagittal angles of pins.In the coronal view,the angle of the most lateral pins averaged 57.9(range: 34.9 to 70.7)°(range: 34.9 to 70.7)in the random group,compared to 59.7(range: 46.0 to 71.6)°in the intended group.Difference in the comparison of pin angles was not significant statistically.Distribution of the most lateral pins in the exit zones was significantly different between the random and intended groups(p=0.006).In the sagittal view,the angle of the most lateral pins averaged 90.4(range: 78.5 to 109.4)°in the random group,compared to 88.5(range: 75.0 to 101.0)°in the intended group.Difference was statistically(p=0.031).Then we tried to find out possible factors influencing the exit point distribution of the pins in the intended group.Age group and pin size seemed to have some influence,with p values of 0.046 and 0.012 respectively.Gender and Gartland typing had no influence,with p values of 0.965 and 0.647 respectively.Conclusions: Study one demonstrated that the most suitable fixation for MDJ fractures from a biomechanical point of view would be ESIN for fractures located in the upper region of the MDJ region.Pinning fixation can provide sufficient stiffness and resistance to rotation in all directions in the mid and low MDJ fractures of the distal humerus.Crossed pinning would yield better overall stiffness than ESIN and LEF in these groups,especially against torsional forces.Two lateral and 1 medial pins make the most stable construct and is recommended as the pinning technique of choice for lower MDJ fractures.Study two demonstrated that posterior lateral column entry pins used in combination with other direct pins would be more stable than only direct lateral entry pins in high supracondylar fractures.PLC pins can improve stability in both crossed and lateral-only configurations.Two-posterior lateral(2PL)pinning technique would be as stable as twocrossed pins(2CC)due to the more proximal entry and higher exit points of the pin,it may serve as an alternative to crossed pins for SCH fractures as it poses no risk to iatrogenic ulnar nerve injury.If stability is in doubt,three-posterior lateral pins(3PL: two-conventional lateral pins plus one-posterior lateral column pin)is preferred.Study three provides a preliminary computational results of pinning techniques for displaced,transverse supracondylar fracture from a biomechanical perspective.Two lateral pins in divergent configuration with the medial/inner lateral pin going through the capitellar ossific nucleus,may provide the best stability for supracondylar fractures against compressive forces.For torsional forces,2-crossed pins exiting at the upper border of the metaphyseal-diaphyseal junction provides the best stability.Study four analyzed the distribution of the exit points of the most lateral pins used in lateral pinning protocol.The ideal entry point for a high exit lays lateral and posterior to the ossification center of the capitellum.With intention,the exit points of the most lateral pin could be elevated from below to above the MDJ line.Aiming at the +1 region above the MDJ would result in higher pin exits.The most lateral pins in lateral pinning can achieve an average angle of about 60°in the coronal plane with the intra-epicondylar line.Younger patients and patients fixed with 1.6mm pins may have higher exit points. |
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