Current state of 3D-printed custom-made spinal implants
Authors: Wen Jie Choy, Ralph J Mobbs
Journal: The Lancet Digital Health (2019)

3-dimensional (3D) printing of custom spinal implants for spinal surgery is a relatively new technique, with early case reports published over the past 5 years.1Phan K Sgro A Maharaj MM D'Urso P Mobbs RJ Application of a 3D custom printed patient specific spinal implant for C1/2 arthrodesis.J Spine Surg. 2016; 2: 314-318Crossref PubMed Google Scholar, 2Xu N Wei F Liu X et al.Reconstruction of the upper cervical spine using a personalized 3D-printed vertebral body in an adolescent with Ewing sarcoma.Spine. 2016; 41: E50-E54Crossref PubMed Scopus (196) Google Scholar 3D printing (also known as additive manufacturing), as the name suggests, involves layer-by-layer manufacturing of raw materials using a 3D printer, although different materials require slightly different manufacturing techniques.3Choy WJ Parr WCH Phan K Walsh WR Mobbs RJ 3-dimensional printing for anterior cervical surgery: a review.J Spine Surg. 2018; 4: 757-769Crossref PubMed Google Scholar Materials currently used for manufacturing custom spinal implants include medical-grade titanium3Choy WJ Parr WCH Phan K Walsh WR Mobbs RJ 3-dimensional printing for anterior cervical surgery: a review.J Spine Surg. 2018; 4: 757-769Crossref PubMed Google Scholar and poly-ether-ketone-ketone,4Amelot A Colman M Loret JE Vertebral body replacement using patient-specific three-dimensional-printed polymer implants in cervical spondylotic myelopathy: an encouraging preliminary report.Spine J. 2018; 18: 892-899Summary Full Text Full Text PDF PubMed Scopus (30) Google Scholar which have both been widely used for conventional off-the-shelf implants.5Rao PJ Pelletier MH Walsh WR Mobbs RJ Spine interbody implants: material selection and modification, functionalization and bioactivation of surfaces to improve osseointegration.Orthop Surg. 2014; 6: 81-89Crossref PubMed Scopus (167) Google Scholar The Article by Koen Willemsen and colleagues6Willemsen K Nizak R Noordmans HJ Castelein RM Weinans H Kruyt MC Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.Lancet Digital Health. 2019; (published online July 23.)http://dx.doi.org/10.1016/S2589-7500(19)30067-6Summary Full Text Full Text PDF Scopus (55) Google Scholar in The Lancet Digital Health addresses important questions around the regulatory processes involved in 3D printing. Few studies in the literature have discussed these issues to date, instead focusing mainly on surgical techniques and pathologies. However, completion of the regulatory requirements can be time consuming, taking 6 weeks even after streamlining following the first case in Willemsen and colleagues study.6Willemsen K Nizak R Noordmans HJ Castelein RM Weinans H Kruyt MC Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.Lancet Digital Health. 2019; (published online July 23.)http://dx.doi.org/10.1016/S2589-7500(19)30067-6Summary Full Text Full Text PDF Scopus (55) Google Scholar This delay presents as a barrier to cases in which 3D printing of a custom spinal implant is required for urgent fixation and immediate stabilisation, such as in cases of cancer pathologies. Separately, different countries outside Europe have different regulatory bodies (eg, the US Food and Drug Administration, or the Australian Therapeutic Goods Administration). Although not directly transferable, the details of regulatory process discussed in Willemsen and colleagues' Article6Willemsen K Nizak R Noordmans HJ Castelein RM Weinans H Kruyt MC Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.Lancet Digital Health. 2019; (published online July 23.)http://dx.doi.org/10.1016/S2589-7500(19)30067-6Summary Full Text Full Text PDF Scopus (55) Google Scholar could serve as a guide for surgeons from other countries in adopting this technology. 3D printing allows for the design of implants for conditions that are considered difficult to treat, or implants with additional features, such as pre-planned screw trajectories or conformities.7Choy WJ Mobbs RJ Wilcox B Phan S Phan K Sutterlin 3rd, CE Reconstruction of thoracic spine using a personalized 3D-printed vertebral body in adolescent with T9 primary bone tumor.World Neurosurg. 2017; 105: 1032.e13-1032.e117Crossref Scopus (80) Google Scholar, 8Mobbs RJ Parr WCH Choy WJ McEvoy A Walsh WR Phan K Anterior lumbar interbody fusion using a personalized approach: is custom the future of implants for anterior lumbar interbody fusion surgery?.World Neurosurg. 2019; (published online Jan 8.)DOI:10.1016/j.wneu.2018.12.144Crossref Scopus (32) Google Scholar However, the availability of this technology remains a substantial drawback. As Willemsen and colleagues highlight,6Willemsen K Nizak R Noordmans HJ Castelein RM Weinans H Kruyt MC Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.Lancet Digital Health. 2019; (published online July 23.)http://dx.doi.org/10.1016/S2589-7500(19)30067-6Summary Full Text Full Text PDF Scopus (55) Google Scholar having access to in-house 3D-specialised engineers will improve the process of implant design with the surgical team, but remains a logistical challenge at present. Specialised laboratories and 3D printers are required for the manufacture of implantable devices, leading to significantly higher costs than those associated with conventional off-the-shelf implants.1Phan K Sgro A Maharaj MM D'Urso P Mobbs RJ Application of a 3D custom printed patient specific spinal implant for C1/2 arthrodesis.J Spine Surg. 2016; 2: 314-318Crossref PubMed Google Scholar, 8Mobbs RJ Parr WCH Choy WJ McEvoy A Walsh WR Phan K Anterior lumbar interbody fusion using a personalized approach: is custom the future of implants for anterior lumbar interbody fusion surgery?.World Neurosurg. 2019; (published online Jan 8.)DOI:10.1016/j.wneu.2018.12.144Crossref Scopus (32) Google Scholar There might be a role for engineers, as well as a 3D printing laboratory, to be co-located with a medical facility to expediate the design and production of custom-made spinal implants. 3D printing, given its benefit in layer-by-layer manufacturing, allows the specialised design of spinal implants tailored to the individual patient. However, because of the higher costs associated with 3D printing, custom-made spinal implants are usually used for patients with severe anatomical abnormalities for which conventional off-the-shelf implants would be inadequate.6Willemsen K Nizak R Noordmans HJ Castelein RM Weinans H Kruyt MC Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.Lancet Digital Health. 2019; (published online July 23.)http://dx.doi.org/10.1016/S2589-7500(19)30067-6Summary Full Text Full Text PDF Scopus (55) Google Scholar Having an implant designed specifically on the basis of a patient's anatomy can negate the need for extensive bone and endplate preparation (ie, exposure of the weaker trabecular bone), which can result in poorer osseointegration and higher risk of subsidence.9Walsh WR, Pelletier M, Wang T, Lovric V, Morberg P, Mobbs RJ. Effect of anatomical location on bone ingrowth into 3D printed constructs. Spine Society of Australia 30th Annual Scientific Meeting; Gold Coast, Australia; April 5–7, 2019.Google Scholar The 3D printing literature remains sparse, with the majority of publications being case reports or review articles.3Choy WJ Parr WCH Phan K Walsh WR Mobbs RJ 3-dimensional printing for anterior cervical surgery: a review.J Spine Surg. 2018; 4: 757-769Crossref PubMed Google Scholar Although many spine companies have adopted 3D printing into their manufacturing processes, the question remains whether personalised implants provide significant benefits in terms of outcome and the recovery of the patient. Addressing this question will require studies with higher level of evidence, including prospective comparative studies to evaluate custom-made spinal implants and off-the-shelf implants. However, a major obstacle to carrying out comparative trials is that custom-made spinal implants are currently used for treatment on a case-by-case basis. Additionally, it is unlikely that two patients will present with the same pathology that results in a similar type of anatomical destruction requiring custom-made spinal implants, which makes direct comparative studies difficult. Overall, 3D printing is a promising manufacturing technique using currently available implant materials, as shown in Willemsen and colleagues' Article.6Willemsen K Nizak R Noordmans HJ Castelein RM Weinans H Kruyt MC Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case series.Lancet Digital Health. 2019; (published online July 23.)http://dx.doi.org/10.1016/S2589-7500(19)30067-6Summary Full Text Full Text PDF Scopus (55) Google Scholar In the right patient and with suitable indication, 3D printing of custom spinal implants can result in superior outcomes compared with off-the-shelf implants in terms of surgical efficiency,10Mobbs RJ Choy WJ Wilson P McEvoy A Phan K Parr WCH L5 en-bloc vertebrectomy with customized reconstructive implant: comparison of patient-specific versus off-the-shelf implant.World Neurosurg. 2018; 112: 94-100Crossref PubMed Scopus (28) Google Scholar stability,8Mobbs RJ Parr WCH Choy WJ McEvoy A Walsh WR Phan K Anterior lumbar interbody fusion using a personalized approach: is custom the future of implants for anterior lumbar interbody fusion surgery?.World Neurosurg. 2019; (published online Jan 8.)DOI:10.1016/j.wneu.2018.12.144Crossref Scopus (32) Google Scholar and potential osseointegration. We declare no competing interests. Challenges in the design and regulatory approval of 3D-printed surgical implants: a two-case seriesPatient-specific treatment approaches incorporating 3D-printed implants can be helpful in carefully selected cases when conventional methods are not an option. Comprehensive and efficient interactions between medical engineers and physicians are essential to establish well designed frameworks to navigate the logistical and regulatory aspects of technology development to ensure the safety and legal validity of patient-specific treatments. The framework described here could encourage physicians to treat (once untreatable) patients with novel personalised techniques. Full-Text PDF Open Access