Oral Presentation ANZBMS-MEPSA-ANZORS 2022

Time-elapsed micro-CT imaging of humeral implant failure in reverser shoulder replacement (#122)

Xiaolong Fan 1 , Egon Perilli 2 , Sophie Rapagna 2 , Ashish Gupta 1 , Saulo Martelli 1
  1. Queensland University of Technology, Brisbane City, QLD , Australia
  2. Medical Device Research Institute, College of Science and Engineering, Flinders University, , Adelaide, South Australia, Australia

Abstract

Reverse total shoulder arthroplasties can have complications due to adverse scenarios including mechanical failure of the humeral component1, resulting in the need for exploring the bone-implant interface. This study presents a novel time-elapsed microstructural imaging protocol for observing the volumetric deformation of a humerus implanted with a common reverse shoulder implant subjected to physiological loading, increased until fracture occurred.

Method

A left humerus from a male donor (age: 75 years) was used. The load applied on the proximal humerus head was based on the physiological glenohumeral joint force2. The specimen was mounted in a compressive stage described previously3 and scanned in a large-volume micro-CT (45µm/pixel). Micro-CT scans were performed for two scenarios: 1. pre-implantation: at 50N pre-load and after application of physiological load (650N); 2. implanted with an Aequalis reversed II stem (inlay technique): scanned at pre-load, physiological load (650N) and after load increased to fracture.

Results

A vertical displacement of the actuator by 1.5mm generated 650N compressive force. By increasing the displacement to 3mm, the force reached 2000 N, before dropping to 1000N (fracture). At 650N compression, most deformation occurred in the peri-prosthetic bone (Fig. 1c). A longitudinal fracture was accompanied by a significant distal migration of the implant stem with respect to the hosting bone (Fig. 1e).

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CONCLUSIONS
The protocol successfully displayed the relative displacement of the implant and the bone while under physiological load and after a fracture with micrometric detail. In this first test, the trabecular bone appears to mostly provide support for implant stability, while fracture likely occurred due to increased circumferential strain, caused by the implant migrating distally. The study is ongoing. The protocol can be used to study and optimize the effect on implant stability of different surgical procedures, and implant designs for maximal stability of the implant in the future.

  1. 1. Shah, Roche, Sullivan, et al. JSES Int. 2021;5(1):121. 2. Orthoload database, 2020 (https://orthoload.com). 3. Martelli, Perilli. J M. Behav Biomed Mater. 2018;84:265-272.