Biomechanical Investigation And Clinicalapplication Of The Distal Femoral Socket-type Prosthetic Revision System.

Objective:Analysis the reason of the tumor prosthetic revision surgery of the knee joint.Provide a new solution for the revision of extramedullary stem fracture of the distal femoral custom-made tumor prostheses,the SPRS(socket-type prosthetic revision system)system.Test the biomechanical stability of the socket part and evaluate its clinical effect retrospectively.Determine its application field initially and provide theoretical basis for further clinical use.Methods:Produce 6sets of simulated experiment specimens and divide into six groups according to different fixed length.Fix with bone cement and strengthen with pointed extrusion locking screw on the 41ateral side 3times.Biomechanical tests were made of each specimen respectively with computer controlled electronic universal testing machine,and the software of it installed on the computer collect the data automatically.Make analysis of the shift/angle changes in different direction and determine the shortest effective fixed length initially.Retrospectively study the two clinical cases performed limited revision operations with SPRS.The stability of it and the function of the involved limbs were observed in follow-up.During August 2005-November 2015,there were 2 patients with extramedullary stem fracture after custom-made tumor prostheses replacement in our department.1 male and 1 female.The age was 25 and 51 years old respectively.The pathological diagnosis and involved locations were osteosarcoma of distal femur and recurrent giant cell tumor of distal femur.The interval between replacement operation and extramedullary stem fracture were 26 months and 128 months respectively.The fracture occurred when they were walking without obvious history of trauma.The fracture sites both located at the conjunction of the extramedullary stems in distal femoral prostheses.According to the firm fixation of the intramedullary stem and the enough length of the residual extramedullary stem.Limited revision operation was designed with SPRS in order to avoid removing the firmly fixed intramedullary stem and bone cement which is very difficult.The wearing fittings were replaced at the same time.Patients took regularly functional exercises postoperatively.The stability of revision prosthesis and the function of the involved limbs were observed in follow-up.Results:Under the 2500N static axial tension(compression)loading and 16N.m torsional loading the average maximum displacement were(3.34±0.14)×10-1mm?(2.00±0.09?×10-1mm?(1.53±0.05)×10-1mm?(1.37±0.03)×10-1mm?(1.00±0.04)×10-1mm?(0.63±0.02)×10-1mm respectively.The average tensional(compressional)stiffness of the socket part of SPRS with different length(10mm?20mm?30mm?40mm?50mm?70mm)were 7.50±0.31(KN/mm)?12.49±0.56(KN/mm)?16.34±0.51(KN/mm)?18.28±0.44(KN/mm)?25.11±0.88(KN/mm)?39.51±0.94(KN/mm)respectively.There is statistically significant differences among the group(P<0.05).The average maximum torsionalangle were 3.20± 0.11(deg)?2.69±0.11(deg)?1.62±0.03(deg)?1.07±0.02(deg)?0.90±0.02(deg)?0.45 ±0.01(deg).The average torsional stiffness were 5.01±0.17(N.m/deg)?5.95±0.22(N.m/deg)?9.87±0.21(N.m/deg)?14.98±0.32(N.m/deg)?17.84± 0.40(N.m/deg)?35.38 ± 1.01(N.m/deg)respectively.There is statistically significant differences among the group(P<0.05).The specimen of fixed length at 30mm was made three point bending fatigue test with the setting of 10cm span,loading range between 120-1200N,performed 3million circulations,and was examined to found that no loosening and damage were happened after the test.The average fatigue bending stiffness was7.01±0.12KN/mm,and bending changes was 1.54×10-1mm.After the axial tension(compression)the specimens of fixed length at 10mm?20mm were found apparent bone cement debonding both from the internal metal-cement surface and the average maximum displacement were(3.34±0.14)×10-1mm?(2.00±0.09)×10-1mm respectively.After the torsional test the specimen of fixed length at 10mm the average maximum torsional angle was 3.20±0.11(deg)and that is larger than the experimental parameter,didn't satisfy the requirement of experiment.The two cases made limited revision operation with SPRS postoperative followed up 26months and 128months respectively,still with the firm fixation and no loosening were occurred,MSTS limb function score were 63.3%?83.7%at last follow-up.Conclusions:The specimens of fixed length 30mm and longer met all of the experimental parameters,and can provide a firm stability for the SPRS.In our clinical use the SPRS the length of the residual extramedullary stem were both 70mm.The SPRS system allows a limited revision operation with preserving the firmly fixed intramedullary stem,which reduces the difficulty of operation and makes the recovery of the limb function as soon as possible.Although clinical cases are few,nearly 11 years of follow-up confirmed its reliability of the prosthesis,worthy of further clinical application.