By Paul Roberts

Paul Roberts is a recently retired Consultant hip and knee arthroplasty surgeon. For most of his consultant career he was based at the Royal Gwent Hospital, Newport. He has a long-standing interest in the design and development of orthopaedic implants and instruments, and held numerous UK and foreign patents.

Corresponding author e-mail: [email protected]

By early 1996, my friend and colleague Peter Grigoris and I had been involved in hip resurfacing for several years, both in the UK and abroad. Based on this experience we concluded that a hip resurfacing based on Sulzer’s Metasul bearing could offer considerable advantages with respect to bearing wear compared to the implants available at the time. We decided to design a new hip resurfacing system incorporating the Metasul bearing, which by then had been in clinical use for eight years as a small diameter articulation. I should stress that whilst between us we had a reasonable grasp of biomechanics and tribology, our knowledge was not comprehensive. A crash course in these subjects was required.    

By mid-1997 we had finalised the major design parameters of the prototype cup and head. The specifics of the bearing we intended to leave to Sulzer’s experts. With the help of contacts in the local engineering faculty, we were able to produce detailed drawings demonstrating the critical design features of the implants.  We were then ready to approach industry with our ideas. Obviously in our case we had only one option; Sulzer Medica. At the time Sulzer’s hip portfolio did include a metal on metal hip resurfacing with a Metasul bearing, which had been developed by Heinz Wagner in 1991. However, this system had many problems, particularly the difficulty of insertion of the acetabular component, and only small numbers had been inserted. We hoped therefore, that Sulzer would be open to a new hip resurfacing project.

With the help of the MD of Sulzer Medica UK, a meeting was arranged with the CEO and hip team at Sulzer Medica’s headquarters in Switzerland. Naively, we attended this meeting without any protection of our Intellectual Property; no Confidentiality Agreement, no Non-disclosure Agreement. This was an error. We made our presentation, which included the detailed design drawings – another potential error. As was expected, the CEO was non-committal, but a further meeting with the hip engineering team was arranged. Eventually, after 12 months and several more meetings, Sulzer agreed to proceed with the project. We had a 'generic contract' prepared by a local competent but non-specialist Solicitor- a third error, and then the 'fun' began. The next three years was a roller coaster of excitement, optimism, frustration and anger, including contract disputes and threats of litigation. 

The complexity of development and production of a new implant should not be underestimated. Despite a relatively large and well-funded team, progression through the various development stages was slow, with multiple forms of analysis and regulatory oversight required:

  • Design modification

FE Analysis

Material testing

  • Testing

Hip simulator studies

Material testing

Animal tests (for plasma coating)

  • Instruments

Material testing

Dry bone and cadaveric surgery

  • Operative technique
Cadaveric surgery
  • Manufacture

New machines, quality control and production runs

  • Regulation
Lawyers, compliance officers etc.
  • Outcome analysis

Clinical follow-up studies

RSA study

By early 2001, the MHRA had given approval for a limited implantation study: 125 cases in two UK centres, and 25 cases for RSA analysis in Sweden. Appropriate Research Ethical Committee approval was obtained in each of the three centres and the first implantation was in May 2001. Implantations had to cease after 150 cases until a sub-cohort of 50 cases had a minimum of 12 months clinical and radiological outcome data. These data were analysed by the MHRA and approval for unrestricted sales in Europe (CE mark) was granted in 2002.

All in all, it took almost seven years from concept to full regulatory approval. This timeline is apparently typical for the development an orthopaedic implant. The time commitment during this period was substantial. We attended dozens of meetings during each phase of development, usually occupying two days. This time had to be taken as annual leave from the NHS. The time commitment does not cease once the implant has been approved for sale. If the product is successful, it is likely you will be asked to attend multiple scientific meetings around the world to present the design rationale and outcome data of the prosthesis, and to run teaching symposia based on the implant. Once again, this time has to be taken as annual leave; it is unlikely to be approved as study leave as it is not enhancing your own personal development. Practically, the only way I could meet these demands on my time, without foregoing completely family holidays, was to move to a part-time contract in the NHS, with the obvious implications for salary and pension.

In 2010 Peter and I designed a monobloc hip resurfacing acetabular component with trans-articular screw fixation, for use in the 'difficult acetabulum'. On this occasion we decided not to involve the implant industry until after we had obtained a patent. We commissioned a bio-engineering laboratory in a Swiss Technical University to carry out the appropriate laboratory tests to obtain the data needed to support our concept and there-by the patent application. This was surprisingly cost-effective and overall proved to be an excellent collaboration, which I would recommend. Interestingly, the lab was prepared to carry out the work on a no-fee basis for a share of the patent or a share of future royalties. A potentially attractive option if funds are tight.

The experience gained during these two projects is the basis for the rest of this article on page 38 in the March edition of the JTO.