BlOMECHANlCS OF THE ACETABULAR LABRUM by Stephen John Ferguson A thesis submitted to the Department of Mechanical Engineering in conformity with the requirements for the degree of Doctor of Philosophy Queen's University Kingston, Ontario, Canada March, 2000 copyright Q Stephen John Ferguson, 2000 National Library Bibliothèque nationale 1+1 dca"ada du Canada Acquisitions and Acquisitions et Bibliographie Services services bibliographiques 395 Wellington Street 395. rue Wellington Ottawa ON KIA ON4 Ottawa ON K1A ON4 Canada Canada YOM fi& Votre réference Our lile Notre rdfdmee The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sell reproduire, prêter, dishibuer ou copies of this thesis in microfom, vendre des copies de cette thèse sous paper or electronic formats. la forme de microfiche/nlm, de reproduction sur papier ou sur format électronique. The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts kom it Ni la thèse ni des extraits substantiels may be printed or othenvise de celle-ci ne doivent être imprimés reproduced without the author' s ou autrement reproduits sans son permission. autorisation. Biomechanics of the Acetabular Labrum Abstract The goal of this research was to determine the fünctional role of the acetabular Iabrum in the normal hip joint, and its possibIe role in the development of osreoarthrosis. Despite clinical evidence of a Iink between labrum patholom and osteoarthrosis, there have been few studies of the function of the acetabular Iabrurn. An investigation of the tensile and compressive material properties of labrum tissue showed that the labrum, with its highly onented collagen fibre structure, was much stiffer and stronger than the adjoining cartiIage- The resistance to fluid flow through the labrum was also higher than through cartilage. One can infer that the strength and imperrneability of the labrum enhance its ability to seal and stabilise the hip joint. Poroelastic finite-element models of the hip joint demonstrated that the labrum could seal a presswised fluid layer within the hip joint under physiologica1 loading. Consequently, cartilage stresses and contact pressures were reduced. The models also indicated that, with its Iow perrneability, the labrum added an important resistance to the flou. path for fluid expressed fiom the cartiIage layers. Cartilage stresses and strains calculated by the mode1 were up to 30% higher following removal of the labrurn. Contact pressures, and hence fnction between the cartilage surfaces, were also signilicantly higher foilowing fabrum removal. The predictions of the finite-eIement models were evaluated through a series of in vitro whole-joint creep consolidation experiments on hurnan hips. The overall compression of the cartitage layers under a variety ofstatic and dynamic Ioads was measured. Removal of the labrum resulted in a quicker cartilage consolidation rate. Peak intra-articular fluid pressures of over 500 Wa were measured during loading in joints with a well-forrned labrum. The results OF the experiments agreed with the predictions of the finite element models and lend further support to hypotheses about labrum sealing. S J. Ferguson Queen's University Biornechanics of the Acetabular Labrum . - -- - Co-Authorship This thesis represents the results of the candidate 's independent investigation, with exceptions as noted. The technical assistance of sthers has been acknowledged in the individual chapters, as necessary. Each chapter of this thesis is the original work of the candidate. The CO-authorsof the manuscripts corntained in this thesis, Dr. J.T. Bryant, Dr. K. Ito and Dr. R. Ganz, provided supervision of the individual studies, as well as advice with respect to the analysis of study results and manuscript revision. S J . Ferguson iii Queen's University Biomechanics of the Acetabular Labrum Acknowledgements Several years ago in Toronto, as I sat designing gas-tempering loops for steel- rnaking plants, 1 would never have imagined the path ahead, which would eventually lead me to the rarefied air of the Swiss Alps. On a typical Ontario February morning I visited Queen's University to consider returning to school for pduate studies. 1 followed Dr. Tim Bryant al1 over the campus, running to keep up with this animated individual on his seerningly never-ending agenda. Tim's enthusiasm for his work made his classes on soft tissue biomechanics a pleasure, and when the time came to find a supewisor for this doctoral thesis, the choice for me was obvious. My introduction to the A0 Institute in Davos was through a fortunate choice of location for a research intemship. Towards the end of this internship, 1 met Dr. Keita ho, and together we began to draw an outhe of the work presented here. We also began a fi-iendship that extends beyond the doors of the Institute. I could not have hoped for two better supervisors- Their objective evaluation of my work throughout the project has been invaluable, although having an ocean between the two institutions has presented some logistical challenges. Thank you to both for supporting my desire to wnte manuscripts as the project progressed. I would also like to thank Dr. ReinhoId Ganz for providing the inspiration for this research through his clinical investigations of labrum pathology, and also Dr. Slobodan Tepic for his expert advice during a particularly hectic planning session one blustery day in Boston, and whenever my head started to hurt thinking about cartilage mechanics, For technical assistance at the A0 Institute I am indebted to Benno Dicht and Peter Ambühl in the machine shop, Iris KeIler and Kati Kampf for histological preparation, Emir Schluep for photography and Gethin Owen for electron microscopy. S.J. Fermouson Queen's University Biornechanics of the Acetabular Labrum My time at the A0 Institute and at QueenysUniversity has been made much more enjoyable by the rnany people whose paths 1have crossed. Too many good fiiends to name individual 1y; thank you al1 for the c ycling adventures, winter tours, Wok-In curries, Schtvyzertuutsch lessons and the occasional Weizenbier in sorne cosy pub or another. Three individuals deserve special mention. Geoff Richards provided a hearty rnkture of mischief and humour, and tireIessl y pursued the establishment of a student community. ZouZou Kuzyk kept me sane through my comprehensive exams and I have truly missed Our conversations since leaving Kingston. With Nick Bishop 1 have shared an office, a mountaintop, an apartment and, most importantly, a Iasting friendship. It will be a profound change to lose the daily banter and brainstorming- I wish hirn al1 the best with his owresearch, and with his devilish contraption of pipes, bearïngs and cornputers. I have been blessed with the support of two families throughout my studies. To my mother, father and sisters 1 owe a debt of +ptitude for al1 the helpful words when 1 hit the lows and the praise when things went rny way, No matter where you go in life, you never leave home. Ich rnochte auch meiner '-Adoptivw-familie in Davos, den Ettingers, herzlich danken. Ohne ihre Unterstutzung ware ich Iangsam verrückt geworden. Danke auch, dass ihr immer einen PIatz fur mich am Tisch hattet. Finally. to Ladina, thank you for the patience that you showed when the lab stole our time, the encouragement that you gave me to always look ahead, and the confidence that you expressed in my abilities. Every man needs sorneone special, and I'm fortunate to have found that person. This research was conducted at the A0 ASiF Research hstitute, Davos, Switzerland and in the Department of Mechanical Engineering, Queen's University, Kingston, Ontario, Canada. Funding was provided in part by a NaturaI Sciences and Engineering Research Council (Canada) Post Graduate Scholarship and by an A0Research Foundation Grant, SJ. Ferguson Queen's University Biomechanics of the Acetabular Labrum for Jeianette Srone S.J. Ferguson Queen's University Biomechanics of the Acetabular Labrum Table of Contents .. Abstract .................................................................................................................. ii ... Co-Authorship ..... ...... ............................................................................................. iir Acknowledgements ................................................................................................ iv .. Contents ................................................................................................................. vrl List of Tables ........................................................................................................... x List of Figures and Illustrations ..... ........................................................................ x Chapter One .Introduction ......................................... .... ........................................ 1 Hypotheses ................................................................................................ 5 Re ferences ................................................................................................. 8 Chapter Two .Background ...........................*............................................*......... 10 Labrum Anatomy .................................................................................