The Biomechanical Research And Clinical Application Of Prosthesis Position In Total Hip Arthroplasty

The positioning of acetabular component and femoral stem is playing an important rolein total hip arthroplasty (THA) for recovery of hip function or releasing of pain. Many studieson the hip biomechanics and clinical outcome of THA have been published, in which variablestem or acetabular anteversion and inclination were still controversial. A combinedanteversion technique (CAT) is a new concept, which was proposed by Professor ChristopherAmuwa from Nigeria in2008. Combined anteversion technique considered35°as an optimalsum of stem and cup, which ranging from25°-50°. Although some clinical trials ofcombined anteversion technique have been reported, the biomechanical properties of this skillare still unknown. The main purpose of the present research is to explore the strain and stressof hip bone or prosthesis after total hip arthroplasty with different combined anteversiontechnique. Clinical trials were designed and performed according to the basic researchoutcome. The present research consists of three major parts, finite element analysis, cadaver tests andclinical trials, aiming to provide biomechanical basic theories and evidence for further clinicalapplications.The first section is the finite element analysis of combined anteversion technique in THA.The objective of the study is to explore the biomechanical traits of hip prosthesis after totalhip replacement with combined anteversion technique. A pelvic three-dimensional model wasestablished based on computer-tomography scanning data. Six virtual total hip arthroplastywere performed by this advanced surgery. The stem anteversions were settled as0°,5°,10°,15°,20°and25°, which combined with the cup anteversion of35°,30°,25°,20°,15°and10°,respectively. The inclination of acetabular component is designed for40°in all the six models.The pelvic movement and peak Von Mises stress of acetabular component, prosthetic cup,ceramic liner, femoral head, femoral stem or cortical bone were evaluated after virtualsurgeries. The results showed that stem anteverted20°combined with cup anteverted15°skillis an optimal technique, because it could protect against stress concentration on hip bone, cup, liner, femoral head, prosthetic stem and cortical bone maximatily. It could decrease thepossibility of prosthetic fatigue break and friction between cup liner and femoral head. Inaddition, a slight pelvic internal movement could ensure the physiological status utmost whenthe hip is loaded.The second section is the cadaver tests of combined anteversion technique in THA. Theaim of the study is to explore the strain of hip or femoral bone after THA with CAT andprovide a mutual verification with the above computer simulation. Three techniques wereused in the present study. The stem were anteverted0°-10°,11°-20°and21°-25°, combiningwith cup antervsersion of35°-25°,24°-15°and14°-10°, respectively. The cup inclinationranged from35°to45°. The strain of posterior or anterior wall of acetabula and femoralperipheric cortical bone was compared with normal hip after loading by600N forces.Compared with the other two skills, stem anteverted11°-20°combined with cup24°-15°is areasonable technique, due to its slight change strain of femoral cortical bone and acetabularelative to normal hip. The present result is similar to the results of finite element analysis tosome extent, by which a mutual verification was addressed.The final section of the present research is the clinical trial of combined anteversiontechnique in THA. According to the results of the above two investigations, three combinedanteversion techniques were used in the clinical trial, in which stem anteverted0°-10°,11°-20°and21°-25°, combining with cup antervsersion of35°-25°,24°-15°and14°-10°,respectively. The cup inclination was addressed at40°in THA procedure. The radiographicresults were estimated pre-or postoperatively, including moment arm of gravity, femoraloffset, height of rotation center and continuity of shenton's line. All the patients werefollowed up for postoperative complications by telephone communication. In addition, Harrisscoring system was performed to estimate the hip function. We found that femoral neckfracture, avascular necrosis of femoral head, developmental dysplasia or hip arthritis could betreated by these three kinds of surgical skills. The poor moment arm of gravity, femoral offset,height of rotation center and shenton's continuity were improved after THA. All the hips showed a good function after six months postoperatively, whereas there was no significantdifference between all the three combined anteversion techniques.According to the three investigations, stem anteverted20°combined with cup anteverted15°is considered as a suitable CAT in the research of combined anteversion of35°. It couldavoid excess stress concentration on prosthesis or bone, which could decrease the prostheticfatigue break and friction. In addition, this technique could not only certify the similarphysiological situation paralleled to normal pelvis, but also provided a good outcome ofradiology, postoperative complications and hip function.