Fixation of custom 3D metal printed pelvic implants. A Clinical RSA study

Patient specific custom designed and 3D metal printed implants (3DPI) offer an innovative alternative approach to the management of large bone defects in the pelvic area. The latter are a challenge for reconstruction after extended bone tumour resections or after revision of failed implants at the hip region. Furthermore, high failure rates are reported with current available reconstructions methods. Due to technological advances, large and complex 3DPI designs are now readily available to be used as a reconstructive alternative in pelvic tumour and total hip arthroplasty revision surgery. Early results are promising and multiple centers worldwide have adopted this new technique in recent years (1–10).

Since no innovation should be done without evaluation, the new medical device regulations (MDR) in Europe, impose strict / high standards using clinical evidence on existing implants and on new orthopaedic implant before their market introduction. In the past, the ODEP (Orthopaedic Data Evaluation Panel) and the Dutch Orthopaedic Association (NOV) defined benchmarks, with maximum rates of revision for any hip (cup or stem) and knee implant. This has been adopted by The European Federation of National Associations of Orthopaedics and Traumatology (EFORT) recently. The benchmark of excellent implant performance is defined as a revision percentage, for any reason, below or equal to 10% after 10 year. Because a period of 10 years is too long to introduce new implants in a safe way, other methods can be used which on short term have a high predictive value for long-term failure. Measurements of early micromotion of the implant within the bone, with an accuracy of 0.1mm has such predictive value. The current gold standard for micromotion measurements is RSA (11,12). A safer way of introducing new implants to the market was already proposed in 1995, where RSA studies are performed after pre-clinical testing, but before general market introduction (13). The short-term RSA results are a prognostic value for long term failure for a-septic loosening (14–17). For that matter, the NOV issued a guideline in 2011 that new hip arthroplasty designs should only be used if clinical Radio Stereometric Analysis (RSA) data are available, or when the new design is part of a clinical RSA study (18–21).

In the light optimal patient care, development of new techniques and innovations like 3DPI’s should obviously be encouraged, but the introduction also closely monitored and evaluated with techniques available for this purpose. Custom 3D metal printed implants are not, but will be subjected to more strict implant criteria set by the EU (MDR effective since July 2018 with transition up to May 2020). In order to improve patient safety, the new MDR anticipates to regulate and quantify the quality of custom 3D metal printed implants. In the light of implant fixation and long-term survival, there is a need to assess primary and secondary fixation by evaluating three-dimensional migration patterns of these implants within the bone by means of RSA. This ought to be done in addition to and in combination with the evaluation of clinical, standard radiological and patient reported outcome measures.

Study objectives: The primary objective of this clinical study is to determine and evaluate the short-, mid- and long-term migration patterns of custom 3D metal printed pelvic implants by means of Radio Stereometric Analysis combined with clinical, standard radiological and patient reported outcome measures (PROMS) results.

Study design: single center prospective cohort study

Study population: all patients eligible for treatment with a custom 3D metal printed pelvic implant (3DPI).

Intervention: Evaluation of a custom 3D metal printed pelvic implant (3DPI) with RSA (i.e. implant migration software using tantalum markers as bone markers) t.

Main study parameters:
Primary Objective:
The primary objective of this study is to evaluate the short, mid and long-term migration patterns, of custom 3D printed pelvic implants and mechanical loosening patterns.

Secondary Objective:
The secondary objective is to evaluate clinical (e.g complications), radiological (CT) and PROMS outcome of 3D printed pelvic implants.

Similar or better fixation, migration and functional outcomes compared to other existing techniques

Investigation Pre-operative Pre-discharge 6w 3m 6m 12m 24m yearly thereafter
RSA X-ray x (*) x (*) x (*) x (*) x (*) x (*) x (*)
Pelvic CT scan x x
Standard pelvic/hip X-ray
AP + Lateral x x x
Anchor question x (*) x (*)
NRS rest + activity x (l) x (l) x (*) x(l) x (*) x (*)
EQ-5D-5L x (l) x (l) x (*) x (l) x (*) x (*)
Tumour pts:
MSTS x (*) x (*) x (*) x (*) x (*) x (*)
All other pts:
HOOS-PS, OHS X (L) X (L) x (*) X (L) x (*) x (*)

3d titanium printed pelvic implant