| Pertrochanteric fractures have been one of the most common fractures in clinical practice,and are especially frequent in elderly women diagnosed with osteoporosis.The fracture mechanism is dominated by low-energy injury.To reduce complications and improve the living quality of the patients,surgery has become the consensus of orthopedists.However,due to the special anatomical structure of the proximal femur,such as neck-shaft angle,anteversion angle,etc.,it is difficult to obtain standard anatomical reduction with the closed reduction.Positive/neutral reduction of anteromedial cortical support is a non-anatomical functional reduction,which is easier to achieve than anatomical reduction during surgery.The mutual restraint of the anteromedial cortex can help control the sliding of head-neck fragment under stress,thereby promoting fracture healing.However,there are pertrochanteric fractures confirmed as positive or neutral reduction during the operation would shift into negative after surgery,which maybe related to the instability after cephalomedullary nailing.However,the risk factors lead to the alteration of anteromedial cortical support status remain unanswered.With the in-depth understanding of the imaging characteristics of pertrochanteric fractures using three-dimensional CT,the coronal plane and lateral wall fractures that could not observed on X-ray have gradually attracted the attention of orthopedists.However,the regularity and corresponding proportion of the involved range of posterior coronal fractures have not investigated.At the same time,the effect of the involvement of posterior coronal fragments on the biomechanics of pertrochanteric fractures after cephalomedullary nailing has not verified.This dissertation includes four parts:Part One: Analysis of risk factors for loss of anteromedial cortical support reduction after cephalomedullary nailing for pertrochanteric fractures Objective: The reduction of anteromedial cortical support plays an important role in the stability of pertrochanteric fractures after cephalomedullary nailing.However,during follow-up,we found that some patients with positive/neutral cortical support confirmed intraoperatively would convert to negative support.This part aimed to investigate the risk factors for loss of anteromedial cortical support reduction after cephalomedullary nailing.Methods: Patients diagnosed with pertrochanteric fractures who met the inclusion criteria between January 2017 and December 2019 were retrospectively analyzed.The ages,sex,side,fracture type,ASA score,TAD,Cal-TAD,Parker ratio,fracture reduction quality,NSA,the filling ratio of the distal nail in the medullary cavity in the anteroposterior(AP)and lateral views were collected.According to the anteromedial cortical alignment shown by postoperative 3D CT,the patients were divided into two groups: anteromedial cortical maintenance support(Group 1,positive/neutral support),and loss of support(Group 2,negative support).Univariate and multivariate logistic regression analyses were conducted to explore the risk factors for the change of anteromedial cortical support after cephalomedullary nailing.Results: A total of 122 patients were included in this study,including 88 females and34 males;the mean age was 83.0 years old,the mean postoperative NSA was 130.7°,and the mean TAD was 22.5 mm.According to the postoperative 3D CT imaging,84cases(69%)were in Group 1 and 38 cases(31%)in Group 2.Univariate analysis found that fracture classification,fracture reduction quality,distal filling ratio of cephalomedullary nails in the AP and lateral views,and lateral Parker ratio were statistically significant.Multivariate logistic regression analysis found that fracture reduction quality(P < 0.001)and distal filling ratio of cephalomedullary nail in the lateral view(P < 0.001)were risk factors for loss of anteromedial cortical support.The best cut-off value of the lateral filling ratio for predicting changes in anteromedial cortical support was 53%(sensitivity 89.3%,specificity 78.9%).Conclusions: Fracture reduction quality and lateral distal filling ratio of the cephalomedullary nail are risk factors for predicting loss of postoperative anteromedial cortical support.To improve the stability after cephalomedullary nailing of pertrochanteric fractures,the diameters of the proximal femoral medullary should evaluated before operation,and the cephalomedullary nail with larger distal diameter should be selected as far as possible without reaming.Part Two: Finite element analysis of the relationship between the distal filling ratio of the cephalomedullary nail and postoperative stability of pertrochanteric fractures Objective: The influence of the distal filling ratio of the cephalomedullary nail on the postoperative stability of unstable pertrochanteric fractures was investigated through finite element analysis,which provides a theoretical basis for selecting cephalomedullary nail with appropriate distal diameter during surgery.Methods: The unstable pertrochanteric fracture model(A2.3)was established from the CT scan data of a healthy elderly female volunteer.The cephalomedullary nail models were established according to the parameters of PFNA-II.There are three types of distal diameters of the cephalomedullary nails,which were 10 mm,11 mm and 12 mm respectively.Two models with different medullary canal diameters were set up according to the data of the anteromedial cortical support maintained group and changed group in the previous part.The relevant parameters were set to simulate the stress of the single foot standing during walking.The distributions of stress and displacement in the femur and cephalomedullary nail were compared among the models with different distal nail diameters.Results: For the groups with the same medullary cavity diameter,the von-Mises stress on the femur,the maximum displacement of the femur and the cephalomedullary nail decreased as the diameter of the distal end of cephalomedullary nail was increased.In the anteromedial cortical support maintained group,when the cephalomedullary nail with a distal diameter of 10 mm was used,the von-Mises stress on the femur was 184.64 MPa,and the maximum femoral displacement was 17.52 mm.When the nail with a distal diameter of 12 mm was used,the von-Mises stress reduced to 165.91 MPa,and the maximum displacement reduced to 16.87 mm.The von-Mises stress on the femur was 178.68 MPa and the maximum displacement of the femur was 19.21 mm when the nail with a distal diameter of 10 mm was used in the anteromedial cortical support changed group.When the nail with a distal diameter of12 mm used,the von-Mises stress reduced to 156.73 MPa,and the maximum displacement reduced to 18.22 mm.When using cephalomedullary nails with the same distal diameter,the maximum displacements of the femur and cephalomedullary nail were greater in the group with a larger medullary cavity.The von-Mises stress on the femur in all models was concentrated in the anteromedial cortical region.Conclusions: In the unstable pertrochanteric fracture models fixed by cephalomedullary nails,the von-Mises stress and displacement on the femur decreased with the increase of the distal filling ratio of the cephalomedullary nails.The increased filling ratio was benefit for improving the postoperative stability.Part Three: 3D-CT morphological study of posterior coronal fractures in pertrochanteric fractures Objective: Pertrochanteric fractures with posterior coronal fractures are common.In this part,a 3D CT morphological analysis was conducted to explore the distribution and corresponding proportion of posterior coronal fractures.We also proposed a classification method to analyze the involvement of the lateral femoral wall.Methods: Patients diagnosed with pertrochanteric fractures in our hospital between October 2018 and December 2021 were analyzed.Three-dimensional reconstruction was performed on the CT scan data of the included patients,and the regularity of the involved range of posterior coronal fractures was observed and grouped.According to the anatomy,the posterior coronal structure was divided into the following four parts:the greater trochanter,intertrochanteric ridge,lesser trochanter,and posteromedial cortex.Patients were divided into seven groups according to the extent of involvement shown by posterior coronal 3D CT,irrespective of whether the fracture fragment as a whole or comminuted.The patients were divided into the lateral wall intact group,lateral wall partial fractured group,and complete lateral wall fractured group according to the involvement of the posterior border of the lateral wall.Finally,the patients were divided into five groups according to the number of fragments in the posterior coronal plane between the femoral head and the femoral shaft,regardless of the extent of fracture fragments.Results: A total of 211 patients were included in this study,including 83 males and128 females,with an average age of 82.1 years old.The proportion of fractures in the posterior coronal plane was 94.79%.The proportion of large banana-like fractures was 23.70%.In terms of lateral wall involvement,the proportion of the lateral wall intact was 52.60%,the proportion of posterior border of the lateral wall partially fractured was 21.33%,and the proportion of posterior border of the lateral wall completely fractured was 26.07%.Four-part fractures accounted for a relatively small proportion of 4.27%.Conclusions: For pertrochanteric fractures,the proportion of fractures in the posterior coronal plane reached up to 94.79%,and the proportion of the posterior border of the lateral wall completely fractured was 26.07%.Therefore,the protection of the blade insertion area should ensured during operation to prevent the lateral wall rupture.Part Four: Effect of fracture levels in the coronal plane on the stability of pertrochanteric fractures fixed with cephalomedullary nails: a finite element analysis Objective: This finite element analysis was conducted to explore the influence of different involvement ranges of coronal fracture fragments on the stability of pertrochanteric fractures after cephalomedullary nailing,and to provide a theoretical basis for the clinical management of coronal fracture fragments.Methods: According to the study on the posterior coronal fracture in the previous part,the CT scan data of a healthy elderly female volunteer were used to establish the pertrochanteric fracture models with different involved ranges of posterior coronal fracture fragments.The cephalomedullary nail model was constructed according to the parameters of PFNA-II.The relevant parameters were set to simulate the stress of the single foot standing during walking.The von-Mises stress and maximum displacement for the femur and cephalomedullary nail were compared among the models with different involved ranges in the posterior coronal plane.Results: The von-Mises stress and maximum displacement on both the femur and the cephalomedullary nail increased with the extent of the posterior coronal fragment in pertrochanteric fractures.From group one to group eight,the von-Mises stress on the femur increased from 105.73 MPa to 145.03 MPa.When the fractures involved the lesser trochanter,there was a significant stress concentration on the femur,which was located in the anteromedial cortex.The von-Mises stress on the cephalomedullary nail also increased from 317.29 MPa to 550.32 Mpa.When the fractures involved more than the lesser trochanter,the von-Mises stress on the cephalomedullary nail changed from the inner side of the lag screw insertion hole to the outer side.The maximum displacement of the femur increased from 12.48 mm to 13.40 mm,and the maximum displacement of the cephalomedullary nail increased from 12.17 mm to 13.00 mm.Conclusions: The involvement extent of the posterior coronal fragment has an impact on the biomechanics of the femur and cephalomedullary nail,and the integrity of the lesser trochanter and the posteromedial cortex have a greater impact on the stability of the internal fixation.When the posteromedial cortex involved with a large range,banding and fixation are suggested to improve the stability. |
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