Vasileios Angelomenos: New CT-based technique can measure early implant motion and predict hip implant loosening

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VASILEIOS ANGELOMENOS
Dissertation defense: 13 February 2026  (click for details)
Doctoral thesis: Fixation and migration in total hip arthroplasty
Research area: Orthopaedics
Sahlgrenska Academy, The Institute of Clinical Sciences

Hip osteoarthritis is common and is usually treated with total hip arthroplasty (THA). A hip prosthesis consists of two main components: a femoral head (usually metal) and an acetabular cup (usually plastic). The components can be fixed to the bone either with or without cement. A new hip replacement typically provides excellent pain relief and improved function, but there is always a risk that the implant may loosen over time and require revision surgery.

“Implant loosening can be caused by infection, but it is more common for cemented implants to loosen without infection, says Vasileios Angelomenos, specialist physician in hand surgery and orthopedics at the Hand Surgery Department, Sahlgrenska University Hospital, and a doctoral student at the Institute of Clinical Sciences

Precise measurement methods and stepwise evaluation

Early movement in a cemented hip implant can occur relatively soon after surgery and is a well-known risk factor for future implant loosening. Detecting and measuring these small micromovements requires highly precise measurement methods and a safe, stepwise evaluation of new materials and techniques.

“The illustration above shows early micromovements at the interface between cement, bone, and implant. Fluid and particles are “pumped” between the bone and cement, driving inflammation that gradually leads to cement fatigue, bone resorption (osteolysis), and implant loosening.”

Micromovements in different bone cements

“I evaluated a newer low-dose CT-based method (CT RSA*) in comparison with traditional marker-based RSA (MBRSA*) to measure micromovements after hip replacement surgery. The methods differ in their requirements for markers, image acquisition, and quality control.”

In a cement study, Vasileios Angelomenos also investigated the fixation performance of a newer bone cement - Refobacin Bone Cement R - and compared it with the more commonly used Palacos R+G. He also examined how two different cement mixing techniques affected early micromovements and assessed patient-reported outcomes (PROMs) using standardized questionnaires in which patients rated their health, symptoms, function, and quality of life before and after surgery.

Early implant motion can be measured without implanted markers

Results from the four sub-studies included in the thesis show that CT RSA detected micromovements in both the acetabular cup and the femoral stem that were comparable to those measured with marker-based RSA, with very high reliability regardless of who performed the analysis. This means that early implant motion can be measured without surgically implanted markers, which are otherwise required in traditional methods—potentially simplifying both research studies and clinical follow-up.

“In the cement study, no significant differences were observed in implant migration or patient-reported outcomes between Refobacin and Palacos R+G two years after surgery. The mixing system had no measurable effect, suggesting that the two cements perform equally well.”

What has been the most rewarding and most challenging part of your doctoral project?

– The most rewarding aspect has been working at the intersection of clinical practice, imaging diagnostics, and method development, and seeing how precise measurements can contribute to safer implants and surgical procedures. The most challenging part has been optimizing and standardizing CT protocols and analyses, as well as managing motion and metal artifacts that can reduce image quality. Balancing clinical work with research also requires extensive logistics and careful prioritization.
 

 Text: Susanne Lj Westergren