| Objective: Using finite element analysis,we analyzed the stability and effectiveness of the proximal femoral locking compression plate combined with the anteromedial minimally invasive screw rod internal fixation system after treatment of subtrochanteric fractures,and explored the mechanical advantages of the medial support of the anteromedial minimally invasive screw rod internal fixation system to provide a basis for the choice of clinical treatment.Referring to the existing anteromedial surgical approach to the proximal femur,a cadaveric anatomical study was performed to determine the optimal surgical approach for the placement of the anteromedial minimally invasive screw rod internal fixation system in the proximal femur.Methods:Part Ⅰ:By selecting the CT data of the right femur of the volunteer and using the finite element analysis method,we modeled the subtrochanteric fractures with the medial wall intact type and the medial wall fragmented type,as well as the internal fixation devices of proximal femoral locking compression plate(PFLCP),the anteromedial minimally invasive screw rod internal fixation system of the proximal femur,and reconstruction intramedullary nail,respectively.The assembly generates models of two types of fracture after fixation with PFLCP,PFLCP combined with the anteromedial minimally invasive screw rod internal fixation system of the proximal femur,and reconstruction intramedullary nail.The model was loaded with a vertical load of 750 N on the femoral head to simulate the force of an adult standing on one foot while weighing 75 kg by combining the data from the reference literature,constraining,setting,and assigning values to the model,the stress cloud and deformation displacement maps of the six groups of models were obtained.The displacement of the fracture block and the peak stress of each group of models were analyzed to compare the differences in the effects of the three internal fixation methods after treatment.Part II:Two male and two female adult cadaveric specimens with intact proximal femoral structures were dissected using anatomical study methods in accordance with existing anteromedial approaches to the proximal femur.We studied the distribution of nerves and blood vessels and the exposure of the anteromedial aspect of the proximal femur in different anteromedial surgical approaches,simulated the placement of an anteromedial minimally invasive screw rod fixation system,and investigated the effect of the fixation system on important blood vessels,nerves and other tissues.We combined the advantages of each surgical approach to determine the optimal surgical approach and screw placement strategy.Results:Part Ⅰ:When PFLCP fixing the intact medial wall type of subtrochanteric fracture,the peak stress situation: the peak of bone block 1 is 20.075 Mpa located in the medial wall,and the equivalent force of internal fixation is 235.9MPa,which is located at the junction of PFLCP and fracture as well as the distal position of the screw closer to the fracture line.The maximum displacement of each bone block and internal fixation: bone block 1 is 3.6868 mm,bone block Ⅰ is 1.4805 mm,bone block 2 is 1.5465 mm,and internal fixation is 3.1994 mm.When fixing the broken medial wall type of subtrochanteric fracture,the peak stress: the peak of bone block 1 is32.552 Mpa located at the medial wall,and the equivalent force of internal fixation is 168.1MPa,which is located at the position of the plate contact position with the fracture.The maximum displacement of each bone block and internal fixation: bone block 1 is 3.7167 mm,bone block II-1 is 1.7144 mm,bone block II-2 is 1.8298 mm,bone block II-3 is 2.2068 mm,bone block 2 is1.1962 mm,and internal fixation is 3.2887 mm.When PFLCP combined with the anteromedial minimally invasive screw rod internal fixation system fixing the intact medial wall type of subtrochanteric fracture,the peak stress situation: the peak of bone block 1 is 16.357 Mpa located in the medial wall,and the equivalent force of internal fixation is 160.3MPa,which is located at the rod of anteromedial minimally invasive screw rod internal fixation system,plate of PFLCP and fracture junction,PFLCP distal end is closer to the fracture line screw position.The maximum displacement of each bone block and internal fixation: bone block 1 is 3.4612 mm,bone block Ⅰ is 1.4688 mm,bone block 2 is1.4658 mm,and internal fixation is 3.0067 mm.When fixing the medial wall fragmentation type of subtrochanteric fracture,the peak stress situation: the peak of bone block 1 is 18.739 Mpa located in the medial wall,and the equivalent force of internal fixation is 113.38 MPa,located at the plate of PFLCP junction with the fracture,and the screw and rod of the anteromedial minimally invasive screw rod internal fixation system junction position.The maximum displacement of each bone block and internal fixation: bone block 1 is 3.0575 mm,bone block II-1 is 1.6923 mm,bone block II-2 is 1.7914 mm,bone block II-3 is 2.0915 mm,bone block 2 is1.1817 mm,and internal fixation is 3.4503 mm.When reconstruction intramedullary nail fixing the intact medial wall type of subtrochanteric fracture,the peak stress situation: the peak of bone block 1 is 15.881 MPa located in the femoral head and calcar femoris,and the equivalent force of internal fixation is219.5MPa,which is located at the lateral and medial side of the intramedullary nail at the fracture.The maximum displacement of each bone block and internal fixation: bone block 1 is3.7471 mm,bone block Ⅰ is 1.5773 mm,bone block 2 is 1.5643 mm,and internal fixation is3.5407 mm.When fixing the medial wall fragmentation type of subtrochanteric fracture,the peak stress situation: the peak value of bone block 1 is 21.616 MPa located in the medial wall,and the equivalent force of internal fixation is 135.19 MPa,which is located at the the medial side of the intramedullary nail at the fracture.The maximum displacement of each bone block and internal fixation: bone block 1 is 4.0632 mm,bone block II-1 is 1.7659 mm,bone block II-2 is 1.8914 mm,bone block II-3 is 2.2901 mm,bone block 2 is 1.1127 mm,and internal fixation is 3.8476 mm.When fixing subtrochanteric fractures in all three ways,for the medial wall intact type,the peak stress gradient of each bone mass is: reconstruction intramedullary nail < PFLCP combined with anteromedial minimally invasive screw rod internal fixation system < PFLCP;the gradient of displacement deformation level of each bone mass is: PFLCP combined with anteromedial minimally invasive screw rod internal fixation system < PFLCP < reconstruction intramedullary nail.For the medial wall fragmentation type,the peak stress gradient of the major bone block(bone block 1)is: PFLCP combined with anteromedial minimally invasive screw rod internal fixation system < reconstruction intramedullary nail < PFLCP;the gradient of displacement deformation of the major bone block is: PFLCP combined with anterior minimally invasive screw rod fixation system of the proximal femur < PFLCP < reconstruction intramedullary nail.Regardless of whether the medial wall was intact,the peak equivalent force and internal fixation displacement deformation of the PFLCP combined with anteromedial minimally invasive screw rod internal fixation system were significantly lower than those of the other two fixation methods.Part II:The Smith-Petersen approach(S-P)had a large incision and adequate exposure.During specimen manipulation on both sides,the lateral femoral cutaneous nerve was injured on one side,and the medial femoral vascular nerve was at a certain distance from the tail of the screw after simulated screw placement.The incision through the small rotor area of the femoral nerve and femoral vascular gap can be extended to both ends according to the situation,thus expanding the anteromedial exposure area of the proximal femur.During specimen manipulation on both sides,the medial femoral circumflex on one side was damaged during the upward extension of the incision and separation of the vascular nerve,and the medial femoral vascular nerve was located closer to the tail of the superior screw after simulated screw placement.The direct anterior approach(DAA)is a minimally invasive approach based entirely on the Heuter gap.Although there is some difficulty in revealing the medial wall due to the influence of the vastus intermedius muscle,adequate exposure of the proximal bone block of the subtrochanteric fracture can still be achieved.During specimen manipulation on both sides,the lateral femoral cutaneous nerve was injured on one side,and there was no obvious injury to the vessels,and the medial femoral vascular nerve was at a certain distance from the tail of the screw after simulated screw placement.The specimen of the lateral rectus femoris approach was successfully placed with a screw.The position of the screw was biased toward the anterior aspect of the femur,and there was still a possibility of injury to the lateral femoral cutaneous nerve during the operation.A minimally invasive operation was performed through the DAA approach,and the screw was successfully placed in specimen without dissection of the transverse branch of the lateral femoral circumflex artery and without neurovascular injury during the operation.Conclusions:(1)The PFLCP combined with the anteromedial minimally invasive screw rod internal fixation system has approximately similar fixation results to the reconstruction intramedullary nail in fixing medial wall intact subtrochanteric fractures,and the PFLCP combined with the anteromedial minimally invasive screw rod internal fixation system creates mechanical prerequisites for better fracture healing.In the case of medial wall fragmentation subtrochanteric fractures,the PFLCP combined with the anteromedial minimally invasive screw rod internal fixation system demonstrates more stable and effective fixation than reconstruction intramedullary nail and can be used as a treatment modality for medial wall fragmentation subtrochanteric fractures.(2)The anteromedial minimally invasive screw rod internal fixation system of the proximal femur is a viable approach to repair the medial wall of subtrochanteric fractures.After determining the exact location of the incision under x-ray fluoroscopy,the DAA approach and the small rotator area approach through the femoral nerve and femoral vascular gap are recommended for minimally invasive screw placement with small incisions,both of which can achieve satisfactory screw placement results with little interference to the surrounding important blood vessels and nerves tissues. |
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