| Dislocation remains a significant clinical problem occurring in between2%and4%of cases and has been associated with malalignment of the acetabular component(cup). Dislocation of an implant following total hip replacement is painful and disabling for patients and expensive for the health service as the final way to solve the problem is to do revision surgery.Generally,30-50°is the safe range for Abduct,10-25°is that for anteversion to site the acetabular component.The incidence rate for dislocation will increase four times while beyond this safe range.Malposition of the acetabular component increases the occurrence of impingement,reduces the safe range of motion,and increases the risk of dislocarlon and wear.The orientation of the cup is connected with the experience of the surgeon in some degree,but a more precise and more simple locator will make it more secure.A lot of attempts had been made by some scholars at home and abroad to improve the accuracy of implantation of the cup over traditional methods. Someone uses a little head device which can decrease the dodge,others use laser technique to site the acetabular component.The Improvement can increase the accuracy rate in some degree, but they can not demonstrate the position of acetabular continuously,the orientation for location can not be modulated.The Hip Nav system is a computer assisted and image guided clinical system used to assist precise planning and placement of the acetabular component in total hip replacement surgery.But it is too expensive and too complicated to make it popular in our country currently.The aim of this research was to invent a reliable,simple and affordable method to assist the orthopaedic surgeon in assessing the angle of cups at Implantation and hence reduce the incidence of dislocation.The precision and clinical practicability of the MEMS goyroscope locator has been tested in an emulated environment and cadavers.Chapter one:The study of in the precise of the MEMS gyroscope in the emulated environmentMaterials and method1.1MaterialsOne male identical plastic models,one Digital protractor,one MEMSGyroscope,one notebook computer,one hand shank, one protractor,one pencil, some profile-papers.1.2MethodIn the male identical plastic models of the pelvis,left side,the center of rotation is fixed in the acetabulum(图.1).Lateral approach is used in the study,5doctors(2with10years experience and3with5years) make100times acetabular cup location altogether.Each participant performed20times45°abductions and15°anteversions spectively(图.1.2.3.4). Then, the fixed arm of digital protractor is placed in the horizontal plane,and the hand shank(wego,weihai city,china) fixed with the rotating arm(the precise of the angle had been proved by geometry,whether the rotating arm is parallel with the hand shank or not).We get the abduction angle through elevation of the hand shank(the real angle can be read in the screen,图.2),and get the anteversion through the reverse movement of the fixed arm(图.3).The real angle of the anteversion can be got through the angle drawed in the profile-papers by protractor(图.4). The the MEMS gyroscope(chongqing bingren technology co,ltd,chongqing city,china) makes60times45°abductions and15°anteversions respectively (图.5,6,7,8).The gyroscope is connected with the hand shank through a plastic clip(in order to eliminate the effect of the magnetism of the hand shank to the gyroscope).The gyroscope is connected to the notebook and the real time angle change can be read visa the screen(图.9).Keep a record of degree numbers,then the abduction and anteversion angles are simulated by us.All the process are supervised by one investigator.Participants were told to operate in accordance with the standard requirements and all of the participants were told that the purpose of this study.Result1.1The subjects number analysisAll the participants are divided into three groups:10years experience group with2participants to make20locations eachl;5years experience group with3participants to make20locations each;MEMS gyroscope group with60locations. The predetermined Angle difference is the testing standard.1.2The baseline data of each group(Tablel,2,3). 1.3Compare results (Table4?6) 1.3Analysis320angle degree deferences have been analysed totally.Compare to the traditional technique,the gyroscope’s reproducibility(mean of standard deviations for each surgeon) of the abduction decrease from5.63to0.15and anteversion from7.64to0.29(Table.l);compare to10years experience group,the gyroscope’s precision (difference between planned and achieved orientations) of the abduction decrease from6.13to0.29and anteversion from5.29to0.15(Table.2).Moreover the antervesions have never be beyond0.8and the abductions never be beyond0.3in the gyroscope group.The defference for5years group reach13.9°for anteversion and13.3°for abduction;13.9°for anteversion and12.7°for abduction in10years group.Compare to traditional group,the anteversion decrease to0.8°from13.9°and abduction from13.3°to0.3°.There are significant difference in anteversion and abduction between gyroscope and traditional technique(p<0.05).(Table.3)(Student t’test is used to evaluate the correlation,p<0.05).Conclusion1.Compare to surgeons with less experience,the error of the experience surgeons is relatively small.We can speculate that the patient might be less at risk for dislocation whom were operated by the experienced surgeons。2.Compare to traditional technique,the gyroscope can make the orientation of acetabula component more precise in the total hip arthroplasty and be worthy of promotion. Chapter two The precise study and clinical significance of the MEMS gyroscope on the cadaverThe result of gyroscope in simulate environment are encouraging.Then we test it in the human pelvis anatomy model and cadaver respectively,and measure the abduction and anteversion angles.The results are wonderful,too. Presently reports as follows:Materials and method1. Materials8human pelvis anatomy model and4fresh frozen cadaver(male2,female2;one whole cadaver, two are divided between the Lumbar4,5intervertebra and the limb is completed,one is divided between the Lumbars and sacrum1intervertebra),one cement aeetabular cups(Wego,Weihai city,china).The inner diameter of the cup is28mm;external diameter is46mm.The plasticine is used to fix the cup.2. Method2.1The measurement of the real angles of the cup’s abduction and anteversion.2.1.1The8human pelvis anatomy model were fixed in the fixator.The fixator could keep the anteversion angle of pelvis holding60°.After the cup was implanted,the pelvis was three dimensional reconstructed with spiral CT,the angle of cup was measured while rotating the3-D image.2.1.2Once the cup is implanted in the acetabulum,the anteversion of the pelvis is fixed.The pelvis of cadaver was three dimensional reconstructed with CT,the true orientation of cup was measured while rotating the3-D image.2.2Siting the acetabutar cup to the human pelvis anatomy model.2.2.1Site the cup in the8human pelvis anatomy model with the traditional mechanical inserter.The angle of the inserter was set constantly:abduction45°,anteversion15°.Dental base acrylic powder was used to fix the cup.2.2.2Site the cup in the8human pelvis anatomy model with the MEMS gyroscope inserter.The gyroscope inserter in made from MEMS gyroscope,power line,data connecting line,screen,plastic clip,hand shank(图.5,6,7,9).The step is that the pelvis model is fixed in a fixate and flat on a table,the anteversion of the pelvis is60°.Then the hand shank parallel with the hypothetical body vertical axis and press the tare,the adbduction and anteversion in the screen will return to zero.The appropriate cup will be choosed to insert into the acetabulum,elevate the hand shank to45°for abduction and rotate to get the15°anteversion.At last,hammer the hand shank to fix the cup.2.3Site the cup in the4fresh frozen cadaver with the MEMS gyroscope inserter.The cadavers are laid on the table and fixed. Site the cup in cadaver through posterior lateral incision.The process for using with gyroscope were as same as2.2.2.2.4Measurement2.4.1Site the cup by traditional cup inserter and new device under single orientation setting.The setting angle is abduction45°anteversion15°.Site the cup by traditional cup inserter and gyroscope.Each side twice implantation.The pelvis of cadaver was three dimensional reconstructed with CT,the true orientation of cup was measured while rotating the3-D image. 2.4.2Duplicate testSite the cup by traditional cup inserter and gyroscope for two times.The two processes were independent.2.4.3Site the cup by gyroscope to human pelvis anatomy model under muti-orientation setting.The muti-orientation setting include four groups:(1)abduction45°,anteversion15°;(2)abduction45°,anteversion30°;(3)abduction45°,anteversion60°;(4)abduction60°,anteversion15°.Use the gyroscope to lead siting the acetabular cup and have the repeatability test. he pelvis of cadaver was three dimensional reconstructed with CT,the true orientation of cup was measured while rotating the3-D image.2.4.4Site the cup by new device in cadaver under muti-orientation setting.The muti-orientation setting was as same as2.4.3.Site the cup by the gyroscope.The pelvis,of cadaver was three dimensional reconstructed with CT,the true orientation of cup was measured while rotating the3-D image.Result1. Site the cup in the8humman pelvis anatomy model by the traditional mechanical inserter and the gyroscope(setting angles abduction45°,anteversion15°)(Table.l). Conelusion1. Compare to traditional method,the MEMS gyroscope can be set from0°to90°freely to site the acetabular cup.2. The new device is a reliable one which can set abduction/anterversion angle freely and lead siting cup punctually.3. Using the new device to lead siting cup,angular deviation was within5°.The new device is more accurate than the traditional mechanical cup inserter.4. Using the gyroscope to lead siting cup,the duplicate test demonstrates that the repeatability is better than that of traditional inserter. |
