Abstract
Introduction
As population grows older, and patients receive primary joint replacements at younger age, more and more patients receive a total hip prosthesis nowadays. Ten-year failure rates of revision hip replacements are estimated at 25.6%. The acetabular component is involved in over 58% of those failures. From the second revision on, the pelvic bone stock is significantly reduced and any standard device proves inadequate in the long term [Villanueva et al. 2008]. To deal with these challenges, a custom approach could prove valuable [Deboer et al. 2007].
Materials and methods
A new and innovative CT-based methodology allows creating a biomechanically justified and defect-filling personalized implant for acetabular revision surgery [Figure 1].
Bone defects are filled with patient-specific porous structures, while thin porous layers at the implant-bone interface facilitate long-term fixation. Pre-operative planning of screw positions and lengths according to patient-specific bone quality allow for optimal fixation and accurate transfer to surgery using jigs.
Implant cup orientation is anatomically analyzed for required inclination and anteversion angles. The implant is patient-specifically analyzed for mechanical integrity and interaction with the bone based upon fully individualized muscle modeling and finite element simulation.
Results
Ten clinical severe pelvic bone defects, classified Parosky IIIb, have benefited from this methodology so far. Implant outline, thickness, fixation and cup orientation was adapted to the anatomical situation. Stress shielding of the bone was eliminated by taking into account personalized muscle anatomy, bone quality and patient weight while evaluating the design performance. All implants were applied smoothly intra-operatively because of personalized case documentation provided and jig technology for accurate pre-drilling of screw holes. Postoperative imaging showed excellent results. Short term follow-up indicates good outcome for the patients treated, restoring mobility and functionality, and showing solid anchorage to the bone.
Conclusion
Complex acetabular bone defects can be treated adequately and efficiently, using a personalized solution which addresses both patient's and surgeon's needs.
