| Objective: To investigate the curative effect of cemented long stem and short stem prosthetic replacement in comminuted intertrochanteric fracture of aged patients, and to compare it between long and short prothesis, meanwhile, to reserch the influence on the curative effect of different methods to deal with the calcar femorale; To analyze the stress of rest femur, long and short stem prothesis, cement by establishing 3-D FE model then to provide rational suggestions for clinic.Materials and methods : 54 cases (54 hips ) with comminuted intertrochanteric fracture were performed cemented prothetic replacement in Shandong university Qilu hospital during 2002-5 to 2007-5, who are divided into 2 groups, one is long stem prothesis group(4#) including 31 cases, the other is short stem prothesis group (3#) including 23 cases. All patients underwent the similar Surgical method with the conventional replacement, but the only difference is that there are three ways to deal with the calcar femorale in the operation of comminuted intertrochanteric fracture including reconstruction with cement, transfixion with titanium wire, and cerclage with titanium wire. The followed-up content include the first year and the recent function evaluated by Harris scores, and the X-rays of hips. In the base of satisfactory curative effect, we use graphics processing software Mimics to deal with the CT digital image file, and reconstruct the three-dimensional entity of femur with CAD modeling software Unigraphics. After that we establish the 3-D modle of long stem and short stem prothesis and mantle layer of cement. Finally we establish the three-dimensional finite element model of those materials, and then impose the boundary conditions of force, set up the material parameters, accordingly we do finite element analysis on these model in stress .Result:①31 cases in long stem group except 1 died were followed up for an average of 28 months. The first year Harris score was 66-95, average 83.7, and the rate of excellent and good was 83.7 percents . 23 cases in short stem group were all followed up for an average of 31 months. The first year Harris score was 57-91, average 78.2, and the rate of excellent and good was 83.7 percents . The first year Harris score of two groups had no significant difference.②The follow-up X-ray showed three cases of heterotopic ossification in the long stem prosthetic replacement group, all of them were Brooker I, and two cases occurred radiolucent zone around the prothesis, but the width was less than 2mm; In addition to a case of malunion, the fractures of calcar femorale healed well. In the short stem group, there were 2 cases of heterotopic ossification and both were Brooker I, and 1 cases occurred radiolucent zone around the prothesis, but the width was less than 2mm; and all of fractures of calcar femorale healed well.③After repalcing with long stem prothesis, we found the method of cement reconstruction to calcar femorale was significantly longer than the other two methods in bed time , but there was no significant difference in short-time curative effect.④In the prothetic finite element model, there were two stress concentration areas on neck, one appeared on the superior, the other was on the inferior middle part of neck and near to the conjunction of femoral neck and shaft, the peak value was 3#169.9Mpa, 207.5Mpa; 4# 191.5Mpa, 227.4Mpa respectively; and there were three stress concentration areas on stem, one appeared on the conjunction of femoral neck and shaft, and the other two are on the bilateral distal part of stem, the peak value was 3#85.91Mpa, 56.11Mpa, 121.83Mpa; 4#108.52Mpa, 94.13Mp, 182.426Mpa respectively.⑤On the FEM of rest femur, the rule of distribution was that stress gradually rised from proximal to distal, it got to concentration on bilateral lower 1 / 3 of femoral shaft, then once again reduced to the end, and the peak value was 3#83.35Mpa, 96.86Mpa; 4#82.11Mpa, 95.88Mpa respectively.⑥The stress distribution of interface between bone cement and prothetic stem was different between long and short stem.The distribution of short stem was that there were only two stress concentration areas which were in the the correlative area with distal end of the prothesis, the medial peak value was 10.9Mpa and the lateral peak value was21.3 Mpa. The distribution of long stem was that there was a stress-concentration peakin the middle of medial interface, and there were two stress concentration areas in thedistal end of bilateral interface. The peak value was 4.78Mpa, 2.48 Mpa, 14.83 Mparespectively.⑦The interior and exterior interfaces of bone cement which was used toreconstruct the calcar femorale had the similar rule of stress distribution, there was astress concentration zone in the transition region between thick and thin cement, itwas just in the medial posterior of cement which was correlative to the fracturesurface of calcar femorale, and the peak value was 3#4.31Mpa, 10.06Mpa,4#6.03Mpa ,13.67Mpa respectively.Conclusion: 1.The short-term currative effect of prothetic replacement for treatingcomminuted intertrochanteric fracture of aged patients is satisfactory, there is nosignificant difference between long and short stem, but the long-term follow up needto be done.2. The short-term currative effect is not affected whatever the calcar femorale is dealtwith for long stem prothetic replacement.3.The stress distribution of rest femur after prothetic replacement is similar to thenormal femur. But the peak value and the range of the concentration area are higherthan normal femur. We find that long stem replacement effects stress distributionsmaller and it is consistent with the biomechanical requirements of human femur bycontrast.4.There is no significant difference between long and short stem in the rule of stressdistribution.of prothesis, and the rule is similar to normal replacement, but there is anadditional small stress concentration area in the medial of proximal end of prothesison the FEM of comminuted intertrochanteric fracture.5.The calcar femorale reconstruction with bone cement is consistent withbiomechanical requirment, because it dosen't change the rule of stress distribution offemur and the cement will not rupture, prosthesis will not loosen for this reason.6.The interface stress distribution between cement and prothetic stem changes acutelyin short stem prothetic replacement, the peak value of the stress-concentrationoversteps the fatigue strength of bone cement, so the loosening rate will be higher. However, interface stress distribution between cement and prothetic stem is similar to normal arthroplasty, so its loosening rate may be lower than the short stem in treating comminuted intertrochanteric fracture of aged patients.
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