Biomechanical Analysis of two fixation methods for proximal chevron osteotomy of the first metatarsal Doctoral thesis at the Medical University of Vienna for obtaining the academic degree Doctor of Medical Science Submitted by Priv. Doz. Dr. Reinhard Schuh Supervisor: Prof. Reinhard Windhager Dept. of Orthopaedics Medical University of Vienna Waehringer Guertel 18-20 1090 Vienna Vienna, 03/2015 FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 2 Declaration This study was performed at the Adolf Lorenz Lab for Biomechanics of the Department of Orthopaedics of the Medical University of Vienna (Head: Prof. Reinhard Windhager, MD). The author herby confirms that planning of the study, experimental testing, statistical analysis of results and preparation of the manuscript were exclusively performed by himself under the guideance of his supervisor. Madeleine Willegger, MD and Emir Benca, MSc assisted in preparation of the specimens, surgeries and experimental testing. Shahin Zandieh, MD helped in the assessment of bone mineral density. Wolfgang Schuh, MSc assisted in proofreading of the manuscritpt. FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 3 Content Declaration…………………………..ii Table of contents…………...………..iii List of figures………………………..v List of tables……………………...…vi Abstract…………………………..…vii Kurzfassung………………..……….ix List of Abbrevations………………..xi Acknowledgements………………...xii CHAPTER 1 INTRODUCTION: 1.1. Hallux valgus deformity………………………………..13 1.2. Pathobiomechanics……………………………………..15 1.3. Treatment Options……………………………………...16 1.4. First Metatarsal Osteotomies…………………………...17 1.4.1. Distal Metatarsal Osteotomies………………………..18 1.4.2. Midshaft Osteotomies………………………………...18 1.4.3. Proximal Metatarsal Osteotomies…………………….19 1.5. Proximal Chevron Ostetomy……………………………21 1.6. Locking plate technology……………………………….22 1.6.1. Historical Perspective…………………………………22 1.6.2. Biomechanical Aspects………………………………..22 1.6.3. Locking Mechanism…………………………………...25 1.7. Load distribution of the first metatarsal…………………26 1.8. Fixation of first metatarsal ostetomies…………………..27 1.9. Aims……………………………………………………..29 CHAPTER 2 MATERIAL AND METHODS: 2.1. Specimens……………………………………………….31 2.2. Measurement of Bone Mineral Density…………………32 FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 4 2.3. Surgical technique………………………………………34 2.3.1. Variable locking plate fixation………………...............35 2.3.2. Screw fixation…………………………………………37 2.4. Biomechanical testing…………………………………..38 2.4.1. Servohydraulic testing system………………………..38 2.4.2. Motion capture system………………………………..40 2.4.3. Testing Protocol………………………………………40 2.5. Outcome parameters……………………………………41 2.6. Statistical Analysis……………………………………..44 CHAPTER 3 RESULTS: 3.1. Load to failure………………………………………….45 3.2. Bending stiffness……………………………………….46 3.3. Dorsal angulation………………………………………47 3.4. Mode of failure………………………………………....48 3.5. Bone mineral Density…………………………………..50 CHAPTER 4 DISCUSSION: 4.1. Limitations……………………………………………...59 4.2. Conclusion……………………………………………...60 REFERENCES…………………………………………….61 CURRICULUM VITAE…………………………………..66 LIST OF PUBLICATIONS……………………………….73 FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 5 List of Figures FIGURE 1: Pathomechanism in the development of hallux valgus deformity FIGURE 2: Regions of first metatarsal osteotomies FIGURE 3: Schematic drawing of different first metatarsal osteotomies FIGURE 4: Priciples and failure mechanism of conventional plates FIGURE 5: Priciples and failure mechanism of locking plates FIGURE 6: locking mechanism of conventional and locking screws FIGURE 7: human first metatarsal FIGURE 8: DXA scan of first metatarsal wih determined region of interest FIGURE 9: first metatarsal with marked osteotomy FIGURE 10: transfixation of first metatatsal after ostetomy FIGURE 11: application of variable locking plate FIGURE 12: final construct after variable locking plate fixation FIGURE 13: insertion of wood screws in a specimen where screw fixation was used FIGURE 14: servohydraulic testing device FIGURE 15: experimental setup FIGURE 16: mode of failure of plate and screw constructs FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 6 List of tables TABLE 1: Maximum tolerated load untitl construct failure occured TABLE 2: Bending stiffness of screw and variable locking plate construct TABLE 3: Boxplots of dorsal angulation of the distal fragment TABLE 4: Mode of failure of screw constructs TABLE 5: Mode of failure of variable locking plate constructs TABLE 6: Boxplots of BMD FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 7 Abstract Biomechanical analysis of two fixation methods for proximal chevron osteotomy of the first metatarsal. Reinhard Schuh1, MD; Jochen Gerhard Hofstaetter1,MD; Emir Benca1, MSc.; Madeleine Willegger1, Gobert von Skrbensky1,MD, Assoc.-Prof.; Shahir Zandieh2,MD; Axel Wanivenhaus1,MD, Prof.; Johannes Holinka1, MD; Reinhard Windhager1, MD, Prof. 1Dept. of Orthopaedics, Medical University of Vienna, Waehringer Guertel 18-20, 1090 Vienna 2 Dept. of Radiology, Hanusch Krankenhaus, Heinrich-Collin-Strasse 20, 1140 Vienna Background Recent attention has been focussed on plate for proximal first metatarsal osteotomies due to the advent of locking plate systems and their considerable success elswhere in the body. Also, a number of authors provided clincial and biomechanical data for these implants in foot and ankle surgery. However, to the best of our knowledge, there does not exist any biomechanical data regarding plate fixation for proximal chevron osteotomy. Therefore, the aim of present study is to compare biomechanical properties of fixation of proximal chevron osteotomies with two different fixation methods. Methods Ten matched pairs of fresh-frozen cadaveric first metatarsals are used for the study.. Both metatarsal of each specimn undergo proximal chevron osteotomy. The osteotomy is fixed with eighter a 3.5 mm cannulated compression screw (Synthes) or a medial locking plate (variable angle-stable foot plate, Königsee Implantate GmbH). Each group contains an equal number of left and right metatarsals. Construct stiffness and the amount of distal fragment angulation at the peak load of 31 N are documented on the first, 10th, 50th, 100th, 200th, 300th 400th, 500th, 600th, 700th, 800th, 900th, and 1000th load cycles. The slope oft he latter one-quarter oft he ascending load-displacement curve, a region that was consistently linear, is utilized to measrue the stiffnesss in newtons per millimeter of deflection of the distal metatarsal head. The screw and plate groups are compared in pairwise fashion. FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 8 Results The bending stiffness of the constructs fixed with the variable locking plate exceeded that of the constructs fixed with the compression screw at all measurement points between the load cycle. We investigated a statistically significant higher number of construct failures in the screw construct Conclusions Based on the results of the present study variable locking plates perform superior to screw fixation for proximal metatarsal osteotomies. This implants might be promising in the clinical setting in terms of reduction of complication rate related to dorsiflexion malunion after these procedures. 2 FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 9 Kurzfassung Biomechanische Analyse zweier Fixationsmethoden bei proximaler Chevronostetotmie zur Hallux valgus Korrektur Hintergrund Die proximale Chevronosteotomie stellt eine Operationsmethode mit hohem Korrekturpotential bei Hallux valgus Deformität dar. Nachteilig ist die aufgrund der Lokalisation relativ hohe Rate an Fehlverheilungen in Dorsalextensionstellung, welche bis zu 17% betragen können. Dies führt zu Insuffizienz des ersten Strahls unter Belastund und bedingt dadurch Metatarsalgie. Rezente biomechanische und klinische Studien belegen die Wichtigkeit der Fixationsmethode proximaler Metatarsalosteotomien. Das Ziel der vorliegenden Arbeit war ein Vergleich der biomechanischen Eigenschaften von variabel winkelstabiler Platten- respektive Schraubenosteosynthesen bei proximaler Chevronosteotomie. Methodik Zehn humane Ossa Metatarsalia 1 wurden einer proximalen Chevronosteotomie unterzogen. Die Osteosynthese erfolgte mittels varibel winkelstabiler Platte (2.7 mm variable angle-stable T arthrodesis plate, Königsee Implantate GmbH, Aschau, Deutschland) respektive kannülierter Zugschraube (DepuySynthes, Salzburg, Austria). Repititive zyklische Belastungen wurden mithilfe einer servohydraulischen Testapperatur (858 Mini Bionix® MTS® Systems Corporation, Eden Prairie, MN, USA) von plantar nach dorsal appliziert. Die dorsale Angulation des distalen Fragments wurde mittels optoelektronischen Stystem gemessen. Ergebnisse Die Konstrukte mit variabel winkelstabiler Plattenfixation wiesen eine statistisch signifikant höher Biegesteifigkeit und eine geringere dorsale Angulation des distalen Fragments als jene mit Schraubenfixation. Ferner bestand eine statistisch signifikante Korrelation zwischen Knochendichte und maximal tolerierter Belastung bis zum Konstruktversagen bei Schraubenosteosynthese. (r=0.640, p=0.041) FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 1 0 Konklusion Aufgrund der Resultate der vorliegenden Studie empfehlen wir variable winkelstabile Plattenosteosynthesen bei proximaler Chevronosteotomie, speziell bei Patienten mit geringer Knochenqualität. 2 FIXATION OF PROXIMAL CHEVRON OSTEOTOMY 1 1 List of abbreviations aBMD areal bone mineral density AOFAS American Orthopaedic Foot and Ankle Society BA bone area BMC bone mineral content BMD bone mineral density cm Centimeter CORA center of rotation angulation CT computed tomography DMAA distal metatarsal