Public defence: Rasmus Dehli Thorkildsen

MD Rasmus Dehli Thorkildsen at Institute of Clinical Medicine will be defending the thesis “Uncemented Metal-on-metal Arthroplasty for Trapeziometacarpal Osteoarthritis” for the degree of PhD (Philosophiae Doctor).

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Photo: Øystein Horgmo.

Trial Lecture – time and place

See Trial Lecture.

Adjudication committee

  • First opponent: Professor Torben Bæk Hansen, Aarhus University
  • Second opponent: Professor Søren Kold, Aalborg Universitetshospital
  • Third member and chair of the evaluation committee: Professor Berit Flatø, University of Oslo

Chair of the Defence

Professor II Olav Røise, University of Oslo

Principal Supervisor

Professor II Magne Røkkum, University of Oslo


Osteoarthritis of the trapeziometacarpal joint of the thumb can cause pain and lead to reduced hand function. Surgically, many techniques are in use, but as yet, no method has been proven superior.

The main aim of the thesis was to study a modern, uncemented metal-on-metal (MoM) joint replacement and its place in the treatment of this condition. To this end we compared two uncemented MoM screw cups (the Motec® and the Elektra™) in a finite element model to determine potential advantages or problems with the designs. The problem of metal wear was assessed in a joint simulator to study whether the rate of wear could be reduced by coating the articulation with Chrome Nitride (CrN). Furthermore, we compared an uncemented MoM joint replacement with trapeziectomy with ligament reconstruction and interposition (LRTI) in a randomized controlled trial. Lastly, in cases where joint replacements were revised, we examined the trapezia histologically to study mechanisms responsible for the prosthetic failure.

 We found that the Motec® design distributed load to the surrounding bone more evenly, and to a lesser extent than the Elektra™. However, the former design was more sensitive to angular loading. We demonstrated that wear from a small MoM articulation could be reduced by coating the articulation with CrN. We found no statistical difference between joint replacement (the Elektra™) and trapeziectomy with LRTI at two years as assessed by subjective- and objective outcome measures. However, there were more complications and reoperations in the joint replacement group. Finally, we found large amounts of metal wear and osteolytic regions in the tissues surrounding the prosthetic cups. The predominant cells seen were macrophages in various stages of activation.

Despite similar results in a randomized controlled trial, we cannot recommend the use of the joint replacement. The MoM articulation and cup design seem to be the main obstacles to longer function and improved results.


Additional information

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Published Feb. 21, 2020 9:35 AM - Last modified Feb. 21, 2020 9:35 AM