The Design, Biomechanical Analysis And Clinical Application Of The Modular Diaphyseal Prosthesis Of Proximal Femur

objective To observe morphology of the proximal femoral canal and measure the morphological parameters. We designed the modular diaphyseal prosthesis system. To analysis the biomechanical characteristics of the reconstructed femur with the modular diaphyseal prosthesis by finite element method. To discuss the clinical effect of the diaphyseal prosthesis for femoral diaphyseal reconstruction after excision of malignant bone tumors.Methods (1)Fifty healthy adults were fit into this study. There were25males and25females, aged from20to60years. The height and BMI of these persons were from155to180cm and18to24. The distance of CT scanning was from femoral head to100mm beyond the lesser trochanter of the femur, and the thickness was lmm. The data of CT scanning was saved by Dicom format. Then these primitive CT dates were imported into professional digital orthopaedic platform (SuperImage system) in order to measure the diameter of the medullary cavity and the cross-sectional diameter of the femur for a total of11levels under the lesser trochanter. The result of measurement was imported into SPSS13.0in order to calculate mean value and standard deviation. The results were shown as (X±S) mm.(2) We imported CT scan databases of total femur into the Mimics10.0and Geomagic studio10.0for three-dimensional reconstruction, in order to gain the model of femur and femoral defects. Loads were established and applied on proximal femur to the largest strength when an adult of70kilogram under normal walking. To analysis the biomechanical characteristics of the reconstructed femur with the modular diaphyseal prosthesis by finite element method.(3) Between June2011and April2013,9patients with malignant bone tumors of femur were treated in our institution. There were3males and6females, aged from63to80(average,69years).There were8cases of bone metastasis. The other case was myeloma.8cases of9patients were suffered from pathological fracture, the other case was impending pathological fracture (Mirels scoring9points). Use the Musculoskeletal tumor society (MSTS) functional scoring system to evaluate limb function of patients two weeks after operation. Use VAS score (visual analogue scale, VAS) to evaluate pain assessment at preoperation and postoperation.Results (1)The result of measurement was shown in table1.1. The distance from the lesser trochanter of the femur to articular surface of proximal femur was69±9.91mm.(2) The compressive stress was concentrated on femoral calcar and1/3of middle and lower of femur, maximum99.93MPa, and the tensile stress was mainly located in the lateral femoral, maximum88.75MPa through Von Mises stress of the total normal femur model. The stress on characteristic observation area was found no significant difference between the normal femur and reconstructed femur (P>0.05). The extreme values of proximal femur reconstructed model did not exceed ultimate strength of titanium alloys and normal femur.(3) All the patients were successfully completed surgery, and average excision of bone was9.8cm (7-15cm). At final follow-up,5patients died of multiple organ metastasis of tumor or multiple organ failure, and the others were still alive. The mean time of the follow-up was6months (range;2-10months). The average MSTS score was25(range,23-28) two weeks after the surgery and limb functional recover to80%that of the original. All the patients began to avoid weight-bearing exercise for two weeks after operation. The preoperative VAS score and postoperative VAS scores were8points (range,7-10) VS2points (range,0-4). The pain remission rate was100%. In the follow-up period, there were no implant-related complications for patients, without any prosthesis revision case.1case was suffered from wound infection after operation, who achieved wound healing after debridement, anti infection and dressing change.Conclusion (1) Digital measurement is a precise, convenient and repeatable method for the morphological parameters of proximal femoral canal measurement.(2) Reconstruction with the modular diaphyseal prosthesis could recover the femoral biomechanics with rational mechanical design.(3) The diaphyseal prosthesis is an alternative method of reconstruction after the excision of femoral malignant bone tumors. It can allow patient early weight bearing, significantly relieve pain and the limb function is well.