Tibia Bone Support in Total Ankle Arthroplasty is Maximized Through Use of Anatomic Cuts

Transcription

1 Tibia Bone Support in Total Ankle Arthroplasty is Maximized Through Use of Anatomic Cuts Jeffrey E. Bischoff Extremities Research, Zimmer, Inc., Warsaw IN 1 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

2 Disclosure Tibia Bone Support in Total Ankle Arthroplasty is Maximized Through Use of Anatomic Cuts Jeffrey E. Bischoff My disclosure is in the Final AOFAS Program Book. I have a potential conflict with this presentation due to: I am a Zimmer employee. 2 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

3 Introduction Designs and techniques associated with contemporary total ankle replacement (TAR) involve distal tibia cuts that vary in both shape and depth of resection. Initial stability (micromotion) and long-term stability (stress shielding) of the placed prosthesis may depend on the density of the bone at the resulting bone/implant interface. Stability of contemporary prostheses has been evaluated through cadaveric testing [1] and finite element analysis [2,3], using a limited number of cadavers or patient specific models, respectively. Cadaveric test setup for implant stability [1] The effect of the resection shape and depth on bone density in the distal tibia has not specifically been quantified. 3 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

4 Objective The goal of this study was to assess the extent to which resection shape and resection depth impact the density of bone immediately adjacent to TAR prostheses. Method Image-based analysis of tibial bone density in the vicinity of TAR resections using the ZiBRA TM Anatomical Modeling System [4]. 4 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

5 Data Acquisition CT scans obtained of the tibia were obtained from cadavers or individuals with no indications of arthritis or previous surgeries of the tibiotalar joint Ethnicity Number of samples Caucasian 14 Korean 24 Japanese 22 Indian 28 Digital models of the tibia constructed via image segmentation 5 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

6 Tibial Resection A series of flat and anatomic (radius 40mm) TAR resection cuts were performed on each model Cut depth (6-16mm) was measured from the high point of the articular surface in the tibial plafond. The tibial malleolus was retained, as it is generally preserved during TAR Cut depth Illustration of flat and round tibial resections Representative bone density maps for flat (left) and round (right) tibial cuts 6 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

7 Bone Density Assessment Across each resection, the Hounsfield unit (HU) data from the CT image were extracted with a spatial resolution of approximately 1mm HU data were normalized based on the peak HU for each individual specimen, and averaged across the resection to determine a value of normalized density for each resection on a specimen-specific basis. An estimate of total available bone support was calculated for each resection as the product of the average density and the area of the resection. For each resection level, differences between flat and round cuts were evaluated using a paired Student s t-test, with significance defined at P < AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015 Illustration of HU assignment, with hotter colors representing denser bone

8 Results Bone Density Statistically significant differences in average bone density between flat and round cuts were found at resection depths greater than 10mm The average density for round cuts decreased by 4%, 10%, and 18% for resection depths of 8, 10, and 12mm, relative to the 6mm cut; and for flat cuts, by 6%, 17%, and 25%, respectively. Bone density Round Flat * * * 6mm 8mm 10mm 12mm 14mm 16mm Depth of cut 8 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

9 Results Bone Support Statistically significant differences in bone support between flat and round cuts were found at resection depths greater than 8mm Bone density Round Flat * * * * 6mm 8mm 10mm 12mm 14mm 16mm Depth of cut 9 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

10 Discussion Use of an anatomic curved resection of the distal tibia within TAR results in a tibial bone bed of greater density than for flat resections at comparable depths. The effect of decreasing density of bone with greater resection depth is mitigated by use of an anatomic cut. Clinical Significance: The bone density of the tibia directly adjacent to the prosthesis in total ankle replacement can be maximized through the use of anatomic curved cuts, and may result in improved biomechanical performance of the prosthesis 10 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

11 References 1. McInnes KA, Younger ASE, Oxland TR. Initial Instability in Total Ankle Replacement: A Cadaveric Biomechanical Investigation of the STAR and Agility Prostheses. Journal of Bone and Joint Surgery 2014;96;e147(1-8). 2. Terrier A, Guilemin M, Fernandes CS, Crevoisier X. Comparative Analysis of Fixed and Mobile Bearing Total Ankle Prostheses: Effect on Tibial Bone Strain and Tibial Component Fixation. ORS 2015 Annual Meeting, Las Vegas, NV. 3. Hamilton MA, Diep P, Nunley J, DeOrio J, Easley M, Valderrabano V. Predicting Tibial Stress Fields Around Total Ankle Replacements. ORS 2015 Annual Meeting, Las Vegas, NV. 4. Bischoff JE, Davis B, Seebeck J, Henderson A, Zuhars J, Marion P, Goodlett C. Verification and Validation of an Open Source Based Morphology Analysis Platform to Support Implant Design. Proceedings of the ASME Conference on Frontiers in Medical Devices: Applications of Computer Modeling and Simulation, Washington, DC, Sept 11-13, Thank You. 11 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015