Additive Manufacturing of Patient-Specific Intervertebral Disc Models for Spinal Cord Compression Management

Over 90% of individuals over 50 years of age show signs of intervertebral disc degeneration, which can lead to spinal cord compression otherwise known as degenerative cervical myelopathy (DCM). DCM is a progressive condition, the leading cause of spinal cord injury, and affects patients’ mobility and quality of life. To enhance surgical planning and long-term management, this research focuses on the development of anatomically and mechanically accurate cervical intervertebral discs (IVDs). Consequently, additive manufacturing technologies were employed, specifically fused deposition modelling using VarioShore thermoplastic polyurethane (TPU) and PolyJet printing with Stratasys Vero. TPU samples were printed at temperatures from 200 °C to 240 °C, with flow ratios from 0.60 to 0.90, while Stratasys Vero samples were produced with Shore hardnesses between 30A and 95A. Compression tests were performed on 10 mm diameter, 50 mm gauge length samples at 1 mm min-1 to assess the modulus using the least squares method, in line with the ISO 604:2003. Here we show that (i) TPU’s compressive modulus aligns with existing literature for IVDs in the 31-80 age range, while Stratasys Vero fails to match the required modulus for ages 41-60; (ii) the increasing prevalence of DCM for individuals aged 40 years and above makes Stratasys Vero unsuitable; and (iii) TPU’s overall greater customisability, lower mechanical property variance, and 12-times lower cost than Stratasys Vero, makes it a well-suited material for patient-specific IVD modelling. These findings offer valuable insights for the development of patient-specific spinal models, enhancing personalised treatment strategies and improving DCM management. It is anticipated this research could improve clinical outcomes, reduce healthcare costs, and decrease reliance on testing using animal models.