A HISTOMORPHOMETRIC ANALYSIS OF MUSCULAR INSERTION REGIONS: UNDERSTANDING ENTHESIS ETIOLOGY DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of The Ohio State University By Stephen Harold Schlecht, M.Sc. Graduate Program in Anthropology **************** The Ohio State University 2012 Dissertation Committee: Sam D. Stout, Advisor Clark Spencer Larsen Paul W. Sciulli Copyright by Stephen Harold Schlecht 2012 ABSTRACT The purpose of this study is to explore the relationship between tendon insertions, or entheses, and mechanically induced bone remodeling. Previous research suggests size and complexity of entheses are indicative of strain magnitude resulting from habitual physical activity. However, degree differences in the morphological expression of entheses has never been explicitly linked to activity intensity. Additional factors such as age, sex, and genetics potentially influence insertion morphology. This study investigates the relationship between enthesis location and mechanical loading, quantifying histomorphometric evidence for targeted remodeling related to applied strains in the non-weight bearing human radius. Thin sections from three diaphyseal regions of the radius associated with four muscle bodies responsible for forearm rotation were harvested from 14 human cadavers and prepared for histologic analysis. Specifically, cross-sections were removed from the right and left proximal, midshaft, and distal diaphysis where the biceps brachii, supinator, pronator teres, and pronator quadratus muscles respectively insert. Osteon population densities (OPD), or number of intact and fragmentary osteons per unit area, and osteon area (On.Ar) were quantified from eight cross-sectional zones defined by the principal anterioposterior and mediolateral axes, and their intersecting planes; ii encompassing all potential regions of tendon insertion. OPD reflects the visible remodeling history of compacta along each ray, and On.Ar reflects strain level. Interval mean plots confirm associations between OPD and On.Ar, demonstrating elevated bone turnover along rays aligned with three of the four considered entheses. The biceps brachii enthesis was not associated with increased remodeling, reflecting reduced cortical volume and calcified fibrocartilage present within the radial tuberosity, demonstrating composite and etiological differences between fibrous and fibrocartilaginous entheses. Findings from this investigation confirm a potential relationship between entheses and mechanical strain. However, other contributing factors remain elusive. Biological profiles that attribute enthesial morphology to general activity levels should be employed cautiously. Before the validity of their use can be confirmed, further investigation into additional mechanical and systemic influences is recommended. iii DEDICATION Dedicated to my father Glenn A. Schlecht, and brother Peter N. Schlecht, who were not here to witness the conclusion of my formal education. You were always supportive of my dreams and I hope I have made you proud. You are loved and missed dearly. iv ACKNOWLEDGEMENTS I would first and foremost like to thank my advisor, Dr. Sam Stout, for introducing me to a histologic method of exploration that I had previously never considered. Most of all he provided me with the independence to pursue my ideas, while nurturing an appreciation for theoretical and critical analysis. My dissertation committee, Dr. Sam Stout, Dr. Clark Larsen, and Dr. Paul Sciulli were instrumental in the ultimate development and completion of this project with their constructive comments and assistance. Additionally, I would like to thank Dr. Kenneth Jones and Dr. Robert DePhilip for expanding my knowledge and passion for human anatomical form and function. The National Science Foundation via a doctoral dissertation improvement grant provided financial support for this project. The Ohio State University Bioarchaeological Laboratory provided the facilities and equipment for specimen preparation and analysis. Specimen procurement would not have been possible without the assistance of Mark Whitmer, Michelle Whitmer, and Dr. Amanda Agnew. I would also like to thank colleagues Corey Maggiano, Giuseppe Vercellotti, Britney Kyle McIlvaine, and Dr. Deborrah Pinto for their assistance in conceptualizing and developing this project. I also owe a debt of gratitude to my undergraduate advisor, v Dr. James Theler, for he instilled in me a passion for anthropological inquiry that has remained with me through the years. It is he who I strive to emulate in the classroom, and I only hope I can become half the educator and mentor that he was throughout my undergraduate career. Finally I would like to thank my family for their undying love and support through all the trials and tribulations experienced over the last few years. Without them I would never have had the drive to continue pursuing my goals, and I only hope that through the years I may repay the devotion and support laid upon me. vi VITA 2002 B.Sc., University of Wisconsin-La Crosse 2004 M.Sc. with Distinction, University of Sheffield 2005-2006 Adjunct Instructor, Department of Behavioral and Social Sciences, Chaffey College, Rancho Cucamonga, CA 2006-2012 Graduate Teaching Associate, Department of Anthropology, The Ohio State University, Columbus, OH 2010 Adjunct Instructor, Department of Anthropology, Ohio University, Athens, OH 2010-2012 Adjunct Instructor, Department of Social Sciences and Anthropology, Columbus State Community College, Columbus, OH 2011-2012 Adjunct Instructor, Department of Biological Sciences, Columbus State Community College, Columbus, OH FIELDS OF STUDY Major Field: Anthropology Area of Emphasis: Biological Anthropology vii TABLE OF CONTENTS ABSTRACT ……………………………………………………………………………………………………………………ii DEDICATION......................................................................................................................iv ACKNOWLEDGEMENTS …………………...………………………………………………………………….…...v VITA …………………………………………………………...……………………………………………………………......vii LIST OF TABLES ……………………………………………………...…………………………………………….….....xi LIST OF FIGURES ……………………………………………………………………………………………………….xiii CHAPTERS 1. Introduction……………………………………………………………………………………………………….1 1.1 Rationale for study……………………………………………………………………………………..6 1.2 Overview of sample and methods..……...…….……………………………………………….7 1.3 Specific hypotheses…………………………………………………………….....……………………9 1.4 Use of the human radius………………………………………………..……………….…………..10 1.5 Use of human cadavers…………………………………………………………………………….11 2. Bone Biology and Physiology…………………………………………………………………………..12 2.1 The osteoclast………………………………..……………….…………………………...………….13 2.2 The osteoblast and its lineage………..………………………………………….………...….15 2.3 Regulators of bone cell activation and function………………….…………........…….....17 2.4 Bone modeling…………………………………………………..………..…………...……...…...22 2.5 Bone remodeling…………………….……………………….....……………………….…………..24 2.5.1 Primary purpose of remodeling…………………………...………………………27 2.6 The mechanostat………………………………………………...………………………………….31 2.7 Role of the lacunocanalicular network……………………..…....……...………………..34 2.8 BMU response to microdamage……………………………….........…...…………………37 2.9 Detecting mechanical strain levels in bone……………………..………...……………39 viii 2.9.1 Macrostructure………………………….………………………..……………………….39 2.9.2 Microstructure……………………………………………………………………………..41 3. Tendon and Biology and Physiology…………………...……………………….…………………45 3.1 Tendon development…………………………………………….……..……....………………..46 3.2 Structural properties………………………….……..………………………...…...…..…….………..…..47 3.3 Mechanical properties……………………………………...………..……....…………………49 4. Entheses…………………...…………………………………………………………………………………..53 4.1 Fibrous attachments……………………………………………..…...…………………………55 4.2 Fibrocartilaginous attachments……………………..………..…...………………………..57 4.3 Osteologic enthesial remnants…………………………………….......………………….60 4.4 Entheses and activity-related studies……………………….…...…………...........……...65 5. Materials and Methods………………………………………………...………………………………72 5.1 Materials…………………………..………………..………………...……………………………….….72 5.1.1 Human radius………..………………………………………………...…….…………….72 5.1.2 Population selection….…...………………………………....………………………..73 5.1.3 Population sample demographics………………....…………………..…........73 5.1.4 Specimen selection..........................................................................74 5.1.5 Muscle actions.................................................................................75 5.2 Methods.....................................................................................................78 5.2.1 Specimen preparation....................................................................78 5.2.2 Histomorphometric field sampling...............................................79 5.2.2.1 Observed and derived variables for microstructural . analysis..........................................................................82 5.2.3 Data analysis..................................................................................83 6. Results...............................................................................................................86 6.1 Proximal cross-sections............................................................................86 6.2 Midshaft cross-sections.............................................................................91 6.3 Distal cross-sections..................................................................................94 6.4 Additional