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Branislav Jaramaz - The Western Pennsylvania Hospital - Pittsburgh, USA*Email: mhafez@msn.comIntroduction: Dislocation following total hip replacement (THR) remains a significant clinicalproblem and can occur even with optimal implant alignment. Our hypothesis was that differentpatterns of pelvic flexion / extension during daily activities could influence acetabularalignment and contribute to impingement and instability following THR. Methods: This studyaimed at identifying different patterns of pelvic flexion / extension xthat could be predictive forinstability following THR. A range of motion (ROM) simulator was used to demonstrate theeffects of different patterns of pelvic flexion / extension on ROM and impingement. The findingswere applied to pelvic flexion / extension measurements obtained from 84 patients in standingand sitting positions. Results: Three different categories of pelvic flexion / extension wereidentified; normal, hypermobile and stiff. ROM simulator revealed that changes in pelvicflexion / extension had significant effects on ROM and impingement. Patients in the stiff pelviscategory, even with “optimal” implant alignment, were more susceptible to implantimpingement. Conclusions: The different patterns of pelvic flexion/ extension during dailyactivities could affect acetabular alignment and stability following THR. We propose aclassification system that can identify different types of pelvic flexion / extension and predicttheir effects on the stability of THR. Patients with unfavourablevccc pelvic flexion / extensionwho are susceptible to impingement may require modified cup alignment.Table I: Classification of pelvic flexion / extension with suggestions for acetabular cupalignment.Type I Type II Type IIIName NormalHypermobile pelvis(Exaggerated response)Stiff pelvisMobileII-aII-bIII-aIII-bExtensionFlexion TypeExtension TypeFlexion TypePelvic flexion /extension instandingPelvic flexion /extension in sittingTypeFlex Flex Excessive Flex Lack of Flex FlexExt Excessive Ext Ext Ext Lack of ExtStability Stable StableUnstablebut sensitive to malalignment even with optimal acetabularalignmentWeak Weak posteriorly Anterior PosterioranteriorlyFlex = flexion Ext = extension Ant = anterior Post = posteriorExt Rot = external rotation Int Rot = internal rotation ADL = activities of daily livingfile:///E|/ISTA2010-Abstracts.htm[12/7/2011 3:15:47 PM]