Comprehensive Biomechanical And Clinical Analysis Of AP,PA Lag Screws And Posterior Plate For Fixation Of Posterior Malleolar Fractures

Ankle joint is the most commonly injured joint that is treated by the orthopaedic surgeons.Simply,the fractures involving the ankle are categorized according to the involvement of the malleoli as;medial malleolar,lateral malleolar or with concomitant involvement of the posterior malleolus named tri malleolar fractures.Posterior malleolar fractures have relatively low incidence of 7-14%as compared to the medial or lateral malleolar fractures.In majority of the cases,the posterior malleolar fractures occur as a part of tri malleolar fractures.Though isolated posterior malleolar fractures do exist but are rare.Posterior malleolar fractures range in size from an extra articular flake to a 50%involvement of the entire tibial plafond.The morphology of the posterior malleolar fragment also varies from a Volkmann or posterolateral fracture fragment to the fractures termed as posterior variant pilon fractures involving the entire posterior tibial corner or with two separate posterolateral and posteromedial fragments.In the most commonly occurring posterolateral type fractures,the injury is caused by an avulsive force generated by the posterior inferior tibiofibular ligament(PITFL)and is usually presented in association with medial and lateral malleoli fractures.The combination of axial loading and rotational deformation is considered as the underlying mechanism of injury in the posteromedial dislocations and posterior pilon fractures.Meanwhile the hyper plantar flexion with axial loading is proposed as the causative agent for the isolated posterior malleolar fractures.Treatment standards for the posterior malleolar fractures are still controversial.But most of the surgeons consider the posterior fragment of more than 25%as a candidate for surgical fixation.Several fixation methods are used in the recent clinical practice but the best fixation strategy is not clear.The involvement of the posterior malleolus shows the poor prognosis.We hypothesized that the different fixation constructs may affect the outcomes in means of biomechanical efficacy and the size of the fracture fragment may influence the various fixation implants.According to our experience,the fixation constructs used for the fixation of posterior variants pilon fractures with two separate posteromedial and posterolateral fracture fragments are not convenient to use.And the biomechanical analyses of these fixation methods are also lacking in the recent literature.In an effort to solve these issues,we have conducted a detailed experimental and clinical work.In the first part of the study,a comprehensive comparative finite element analysis(FEA)was done using the three dimensional(3D)fracture models of the posterior malleolus.Fixation of PMF with anteroposterior(AP),posteroanterior(PA)lag screws and posterior plating was simulated.Outcome measures in form of stress distribution and displacement changes were analyzed.We further studied the relative effects of the fixation constructs on the size of the fracture.In the second part of the experiment a further biomechanical comparison was performed using the cada-veric specimens.The causative forces were noted which produced the 0.5mm,1 mm,1.5 mm and 2 mm vertical displacements of the fracture fragments in the three fixation strategies.The third part of this work was composed of the retrospective clinical study.We retrospectively compare the clinical outcomes of AP,PA lag screws fixation with posterior buttress plate.At last,we designed a new L-shaped buttress plate to deal with the posterior pilon fractures in a better way.We further analyzed the biomechanical efficiency of this new plate and compared it with commonly used fixation methods.In short we concluded that the posterior plating is biomechanically the most stable fixation construct.The larger sized fracture fragments demands more vigorous and efficient fixations than the smaller sized fractures.On clinical follow up,patients treated with posterior plates showed better results comparing to the patients treated with AP lag screws.3D printed model of the newly designed pre-contoured L plate precisely delineates the regional morphological characteristics of the posterior plafond.Moreover,its biomechanical fixation strength is superior to other fixation implants.Authors suggest posterior plating to treat the posterior malleolar fractures especially in large sized fracture fragments.Surgeons should consider the results of this comprehensive work when operative decision is made to treat posterior malleolar fractures.Objectives:Clinically there are different fixation methods used for fixation of the posterior malleolar fractures(PMF),but the best treatment modality is still not clear.Few studies have concentrated on this issue,least of all using a biomechanical comparison.The purpose of this study was to carry out a comparative biomechanics of three different commonly used fixation constructs for the fixation of PMF by finite element analysis(FEA)and to compare the effect of fixation constructs on the size of the fracture computationally.Materials and methods:Computed tomography(CT)images were used to reconstruct three dimensional(3D)model of the tibia.Computer aided design(CAD)software was used to design 3D models of 30%,40%and 50%sizes.Finally,3D PMF models fixed with two antero-posterior(AP)lag screws,two postero-anterior(PA)lag screws and posterior plate were simulated through computational processing.In the first half of experiment,simulated loads of 500 N,1000 N and 1500 N were applied to the PMF and proximal ends of the 30%sized fracture models were fixed in all degrees of freedom.Whereas in the second half of the experiment,the distal ends of the models(30%,40%and 50%)were fixed and simulated loads of 350 N and 700 N were applied to the proximal tibial end.Results:The mean vertical displacement value in the posterior plate group(0.52 mm)was lower than AP(0.68 mm)and PA(0.69 mm)lag groups.Statistically significant low amount of the relative micro-motion(P<0.05)was observed in the posterior plate group.The results of the second half of the experiment showed that in single limb standing condition(700 N),the posterior plate group produced the lowest relative displacement(RD)among all the groups(0.01,0.03 and 0.06 mm).Further nodal analysis of the highest RD fracture group showed a higher mean displacement of 4.77 mm and 4.23 mm in AP and PA lag screws model(p= 0.000).The amounts of stress subjected to these implants,134.36 MPa and 140.75 MPa were also significantly lower(p= 0.000).There was a negative correlation(p= 0.021)between the implant stress and displacement which signifies a less stable fixation using AP and PA lag screws.Conclusions:It was concluded that the posterior plate is biomechanically the most stable fixation method for fixation of PMF.Progressively increasing fracture size demands more stable fixation construct because RD increases significantly.Posterior buttress plate produces superior stability and lowest RD in PMF models irrespective of the fragment size.Objective:Clinically there are different fixation methods used for fixation of the posterior malleolar fractures(PMF),but the best treatment method is still unknown.Only a few studies have concentrated on this issue,least of all using a biomechanical comparison.The purpose of this study was to carry out a comparative biomechanical analysis of three different commonly used internal fixation constructs used for the fixation of PMF in cadaveric specimens.Materials and methods:15 human cadaveric ankle specimens were used to simulate the posterior malleolar fracture models with a 30%size of the tibial plafond,according to clinically obtained data.All the models were randomly divided into three groups.The specimens in the Group A were fixed with two antero-posteriorly(AP)directed lag screws,Group B with two postero-anterior(PA)lag screws and Group C used a posterior plate for fixation of the fracture fragment.Then each model was subjected to axial loads.Final outcomes included loads for 0.5 mm,1 mm,1.5 mm and 2 mm(failure load)vertical displacement of the posterior fragment,were noted.Results:Significantly higher amounts of compressive loads were noted to cause the vertical displacement in the posterior plate group than AP and PA lag screws.Conclusions:It was concluded that the posterior plating is biomechanically the most stable fixation construct for the PMF fixation.Objective:The purpose of this retrospective study was to evaluate the post operative clinical outcomes and to report the radiographical findings of posterior malleoloar fractures surgically fixed either with antero-posterior(AP)lag screws,postero-anterior(PA)lag screws or with posterior plating in setting of posterior malleolar fractures.Patients and methods:From January 2013 to January 2016,47 patients with involvement of the posterior malleolus were recognized.Pre and post operative x-rays and computer tomography CT-scan images were compared using the Picture Archiving and Communication System(PACS).Medical charts review was also performed.Open reduction and internal fixation(ORIF)of the posterior maleolar fractures were done using the posterior plate(18 patients),and in 15 patients by PA lag screws.AP lag screws were used in 14 patients.We used the modified Weber's criteria,range of motion(ROM)of the ankle,and Bargon's radiographical grading system for posttraumatic arthritis as the main outcome measurements.The mean follow-up time period was 12 months(range,8-36).Results:All the patients in the posterior plate group showed statistically significant good results as compared to the AP lag group(p=0.003).There was no case of malunion or nonunion.Patients in PA lag group also showed good results.Three patients in the AP lag group showed radiographical evidence of post traumatic osteoarthritis(OA).Malunion was noted in 2 cases in AP group.Conclusions:Posterior buttress plate showed the better clinical outcomes on follow up as compared to AP lag screws.There was no significant difference between PA lag group and posterior plate group(p=0.05).Objectives:The posterior malleolus fractures with two distinguished posterolateral(PLF)and posteromedial(PMF)fragments are termed as posterior pilon variant fractures.The optimal surgical fixation method for these challenging fractures is still unknown.The purpose of this study was(1)to design a new posterior L-shaped plate,(2)to conduct a comparative biomechanical analysis to compare its mechanical strength with the routinely used fixation methods by using the non linear finite element analysis(FEA)and(3)to make a 3 dimensional(3D)model of the new plate using the of 3D printing technology.Materials and methods:Initially,the 3D model of the distal tibia was reconstructed form the computed tomography(CT)images.Computer aided design(CAD)software was used to design 3D models of the posterior pilon variant fractures.One fracture model was simultaneously fixed with two posteroanterior(PA)lag screws and posterior buttress plate.In another model,the posterior L-shaped plate was used to fix the both posterior fragments.Both fixation models were simulated through computational processing.Simulated loads of 750 N and 1500 N were applied to the fracture fragments while the proximal ends of the models were fixed.The stereo-lithography(Stl)format of the posterior L plate was used to print the 3D structure.Output results representing the implant von Mises stress,relative fracture displacement(RD)and vertical displacement of the fracture fragments were analyzed.The contour of the 3D printed L plate was compared with cadaveric specimen of distal posterior tibia in relation to the regional morphological characteristics of the posterior plafond.Results:3D printed L plate model exactly matched the surface variations in the posterior malleolus.The statistically significant lower amount of RD(P<0.05)was observed in the posterior L plate group.Conclusion:It was concluded that the newly designed posterior L plate is biomechanically more stable fixation construct for fixation of the posterior pilon variant fractures.3D printed pre-contoured plate model is exactly fitted with the precise morphology of the posterior plafond.It can be used as an alternative fixation method in the posterior pilon variant fractures.