Design,Biomechanical Analysis And Application Of The Novel Quadrilateral Anatomical Plates For Complex Acetabular Fractures

Part Ⅰ Design and finite element analysis of the novel quadrilateral anatomical plates for complex acetabular fracturesObjective: With the development of orthopedic doctors’ understanding of acetabular fracture,more and more attention has been paid to the quadrilateral surface(QLS)and QLS fracture.At present,there is still a lack of special apparatus for the QLS fracture in the domestic market.Hence,our team designed a set of QLS anatomical plates for the treatment of complex acetabular fractures.The study was aimed to compare the biomechanical properties and stability,using a finite element model,of four fixation constructs used for the treatment of anterior column and posterior hemi-transverse(ACPHT)acetabular fractures under two physiological loading conditions(standing and sitting).Methods: A finite element model simulating ACPHT acetabular fractures was created based on the CT data of a healthy male adult.Then the following four fixation techniques were applied:(A)a special infrapectineal quadrilateral surface buttress plate(IQP);(B)a special suprapectineal quadrilateral surface buttress plate(SQP);(C)a suprapectineal plate combined with posterior column and infra-acetabular screws(SP-PS-IS);and(D)an infrapectineal plate combined with posterior column and infra-acetabular screws(IP-PS-IS).Three-dimensional finite element stress analysis was performed on these models with a load of 700 N in standing and sitting positions.Biomechanical stress distributions and fracture displacements were analysed and compared between these fixation techniques.Results: In models simulating the standing position,high displacements and stress distributions were observed at the infra-acetabulum regions.The degree of these fracture displacements was lowest in the SQP(0.076 mm),followed by the IQP(0.078 mm)and the largest was the SP-PS-IS(0.087 mm)fixation constructs.However,the IP-PS-IS fixation construct had the highest effective stiffness.In models simulating the sitting position,high fracture displacements and stress distributions were observed at the regions of the anterior column.The degree of these fracture displacements was low in the SP-PS-IS(0.101 mm),as compared to the SQP(0.105 mm)and the IQP(0.13 mm)fixation constructs.And the highest effective stiffness was observed in the IQP fixation construct.Conclusion: In both standing and sitting positions,the stability and stiffness index were comparable between these four fixation techniques.In standing position,stress concentrations at the regions of infra-acetabulum and QLS suggest that the infra-acetabular screw or QLS plate fixation was required,and the novel SQP or IQP has a higher stability as compared with the reconstruction plate combined with long periacetabular lag screws fixation.However,in sitting position,stress concentrations at the regions of anterior column suggest that the supra-or infra-pectineal anterior column plate fixation was required,and the former is more stable.Part Ⅱ Biomechanical comparison of four different fixations for acetabular fractures involving quadrilateral surfaceObjective: Anterior column-posterior hemitransverse(ACPHT)fractures are prevalent in the elderly and often associated with quadrilateral surface(QLS)comminution.The traditional fixation methods couldn’t commendably meet the requirements of the treatment,therefore researches of special apparatuses for the fixation of acetabular quadrilateral surface fractures have been the hotspot in recent years.This biomechanical study aimed to compare the biomechanical properties and stability,using composite Sawbones models,of two special QLS buttress plates with traditional fixation devices using pelvic brim reconstruction plates combined with periarticular long screws for the treatment of ACPHT fractures.Methods: ACPHT fractures with an isolated QLS fragment were created on 24 composite hemipelves(fourth-generation Sawbones models)and allocated to 4 groups:(1)infrapectineal QLS buttress plate(Group A);(2)suprapectineal QLS buttress plate(Group B);(3)suprapectineal reconstruction plate with 3 periarticular long screws(Group C);and(4)infrapectineal reconstruction plate with 3 screws the same as Group C(Group D).Specimens were loaded to simulate partial(35-350 N)or full(75-750 N)weight-bearing.A universal testing machine was synchronized with a 3-dimensional video tracking system to optically track displacement at the interest points along fracture lines and calculate construct stiffness.The fixation systems were compared using the Kruskal-Wallis and Mann-Whitney U tests.Results: The experimental results of the partial and full weight-bearing simulations were surprisingly similar.During 290 loading cycles,the maximum displacement on the 6 predetermined points did not exceed 1.1 mm.Multiple comparisons among groups of relative displacements on each predetermined measurement point did not differ significantly(p > 0.05).Group C demonstrated the greatest construct stiffness and significantly greater stiffness than Group D(p < 0.017).However,no significant difference in stiffness was identified between Group A and B,particularly Group A and C(p > 0.017).Conclusion: All 4 constructs maintained stable fixation under simulated partial or full weight-bearing activity.The suprapectineal pelvic brim plate with 3 periarticular long screws remains the gold standard.The 2 special QLS buttress plates,particularly infrapectineal,provided stiffness and stability comparable to standard fixation.However,moving the pelvic brim plate from the suprapectineal to infrapectineal border is not recommended because it significantly decreases fixation strength.Part Ⅲ Application of novel quadrilateral surface anatomical plates for the treatment of complex acetabular fracturesObjectives: To explore the clinical effectiveness,advantages and disadvantages of the novel quadrilateral surface(QLS)anatomical plates in the treatment of complex acetabular fractures,and to elaborate the points for attention in the operation.Methods: Thirty-six cases of acetabular fractures treated in our department were retrospectively analyzed from January 2017 to June 2019.Among them 27 cases were male and 9 were female.The mean age was 48.9 years(range,27-74 years).According to the Letournel-Judet’s classification,there were 5 cases anterior column fractures(involving quadrilateral surface),5 cases "T" shaped,2 case transverse associated with posterior wall,12 cases anterior column and posterior hemi-transverse(ACPHT)and 12 cases double columns fractures.Before operation,all patients were taken pelvic anterior-posterior X-ray and CT scan.To record surgical time,intraoperative blood loss and postoperative complications.After operations all patients were taken pelvic X-ray in anterior-posterior and Judet position,as well as CT scan.To evaluate the radiographic quality of reduction by Matta criteria and hip functions by Modified Merle D’Aubigné scoring system.Results: The average surgical time was 140 min(range,100-180 min).The average blood loss was 600 ml(range,300-1200 ml).An additional shaping was unnecessary in 36 patients who were implanted with the anatomical QLS buttress plate and all patients were operated successfully.All patients were followed for an average time of 12 months(range,6-18 months).The quality of fracture reduction was evaluated according to Matta standard,of which there were 21 cases excellent,8 cases good,and 7 cases poor,with an excellent rate of 80.6%(29/36).At the last follow-up,the function of the hip joint was graded according to the Modified Merle D’Aubigné scoring system for a mean 16.2 scores(13-18 scores),of which there were 20 cases excellent,11 cases good,5 cases fair and 0 case poor,with an excellent rate of 86.1%(31/36).All patients recovered well,in addition to 1 case of obturator nerve paralysis and 2 cases of lateral femoral cutaneous nerve injury happened postoperative one day(recovered one month later).None other postoperative complications.Conclusions: The three novel QLS anatomical plates could meet the needs of the treatment of complex acetabular fractures,especially for the acetabular fractures involving the quadrilateral surface.There is no need to re-shape the plates intraoperatively as its anatomical design.Moreover,it is more likely to obtain a satisfactory clinical effectiveness by using these special QLS plates with lower complications and rigid fixation,which is worthy of clinical promotion in the treatment of complex acetabular fractures.