Evaluation of the Effect of Rail Hole Over- Drilling on the Trabecular Metal Total Ankle

Transcription

1 Evaluation of the Effect of Rail Hole Over- Drilling on the Trabecular Metal Total Ankle Mehul A. Dharia 1, Duane Gillard 1, 1 Research & Development, Zimmer, Inc., Warsaw IN 1 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

2 Disclosure Evaluation of the Effect of Rail Hole Over-Drilling on the Trabecular Metal Total Ankle Mehul A. Dharia 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 During implantation of the Zimmer Trabecular Metal Total Ankle (ZTMTA) total ankle replacement (TAR) system, the tibia and talus are prepared by drilling rail holes such that the implanted components have equal interference fit on both anterior (A) and posterior (P) sides of each rail. Rail Hole Drill Guide Tibia Rail Holes P A Tibia P Talus Rail Holes Talus A/P View Lateral View Implanted ZTMTA If the provisional does not properly seat into the rail holes, adjustments may be made per the surgical technique by over-drilling one of the affected rail holes. 3 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

4 Objective The objective of this study was to determine whether these adjustments in rail hole preparation may compromise the functional strength of either the cement mantle or the implant. Method 2-D plane stress* finite element analysis (FEA) models of the TAR were created to simulate: press-fit conditions without over-drilling of rail holes Several over-drilling scenarios for the anterior and posterior rail holes for the tibia and talus: 2mm anterior for tibia, talus 2mm posterior for tibia, talus 1mm anterior and 1mm posterior for tibia and talus * Loading in the ankle joint is primarily directed in AP and proximal-distal directions [1], and thus coronal-plane stresses are expected to be relatively small. 4 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

5 Model Tibia and talus components were oriented at 41% and 45% gait position, respectively, as these orientations have been shown to result in the highest stresses in the implant [2]. An axial compressive force representing physiological load was applied from the articulating component. Peak stresses predicted in the cement mantle and in the trabecular metal part of the implant components were examined, as indicators of the expected functional strength of the device in vivo. 5 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

6 Results For both tibia and talus, peak stresses were normalized using peak Von-Mises stress value predicted in the bone cement and peak Maximum Principal stress value predicted in trabecular metal (TM) part of the implant*. Adjustment Tibia Cement Tibia Implant Talus Cement Talus Implant interference fit mm anterior mm posterior mm anterior-posterior * Implant stresses reported in this study are for the trabecular metal part of the implant. 6 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

7 Results - Tibia Peak stresses in both the tibia cement mantle and the TM part of the tibia implant were predicted for 2mm anterior adjustment in the anterior rail. Combined 1mm anterior and 1mm posterior adjustment in the anterior rail. Lowest stresses in both the tibia cement mantle and the TM part of the tibia implant were predicted for 2mm posterior adjustment in the anterior rail. 7 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

8 Results - Tibia 2mm anterior adjustment in the anterior rail Anterior Posterior Normalized Von-Mises Stress in bone cement Normalized Maximum Principal Stress in Trabecuar Metal part of the Implant 8 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

9 Results - Talus Peak stresses in the talus cement mantle were not affected significantly by any of the adjustment configurations considered in this study. Peak stresses in the TM part of the talar component were predicted for 2mm anterior adjustment of the posterior rail followed by Combined 1mm anterior and 1mm posterior adjustment of the posterior rail. Lowest stresses in the TM part of the talus implant were predicted for 2mm posterior adjustment in the posterior rail. 9 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

10 Results - Talus 2mm anterior adjustment in the posterior rail Posterior Anterior Normalized Von-Mises Stress in bone cement Normalized Maximum Principal Stress in the Trabecuar Metal part of the Implant 10 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

11 Discussion The functional strength of the talar component (TM part of the implant and cement) is not compromised by any of drilling adjustments examined here. The functional strength of the tibia component (TM part of the implant and cement) decreases marginally with 2mm anterior adjustment of the anterior rail hole. Clinical Significance: The functional strength of the tibial component (TM part of the implant and cement) with a 2mm posterior adjustment of the anterior rail is equivalent to or better than for the other rail hole adjustments. The functional strength of the talar component (TM part of the implant and cement) with a 2mm posterior adjustment of the posterior rail is equivalent to or better than for the other rail hole adjustments. 11 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015

12 References 1. Bell CJ, and Fisher J, Simulation of Polyethylene Wear in Ankle Joint Prostheses. Journal of Biomedical Materials Research Part B: Apllied Biomaterials 81B-1, 162 (2007). 2. Dharia MA, Bischoff JE, Biomechanical Evaluation of Total Ankle Arthroplasty, Proceedings of World Congress of Biomechanics 2014, July 6-11, 2014, Number 14-IS-3788-WCB, Session 5-20WCB (3788), Boston, MA. Thank You. 12 AOFAS Annual Meeting, Long Beach, CA, July 15-18, 2015