Pioneering imaging methods from WMG at the University of Warwick have revealed how the surgical process impact bones and implant stability during hip replacements
Uncemented hip replacement surgery uses implants with roughened surfaces designed to allow the patient's bone to grow directly onto the implant, creating a strong, natural biological bond. Unlike cemented implants, which rely on bone cement that can degrade and fracture, uncemented implants depend on this natural bone integration for long-term stability.
With uncemented hip replacements expected to increase fivefold among younger adults by 2030, optimising surgical technique has become critical to meet growing demand and ensure lasting success.
In research from the University of Warwick, in collaboration with University Hospitals Coventry and Warwickshire (UHCW) NHS Trust, researchers have conducted in-depth studies using cadaver specimens, high-resolution micro-CT imaging, and digital volume correlation (DVC) to investigate how common surgical practices influence bone response during uncemented total hip arthroplasty (THA).
Vineet Seemala, PhD researcher, University of Warwick PhD who led this research, said: "Our research provides detailed insights into how bone microstructure changes during surgery. We demonstrated that surgical techniques such as broaching can increase bone density around the implant by causing the bone to deform and compact. This process leads to the formation of a three-point contact between the bone and implant, despite small overall surface contact due to the porous nature of trabecular bone."
Researchers have, for the first time, used these advanced imaging methods to show how bone changes during broaching- a near-universal step where surgeons prepare the femoral canal (inside of the femur bone) for the implant by gradually shaping and enlarging it with a series of metal broaches to achieve a precise implant fit. Standard scans and computer models can't capture these tiny changes because of their lower resolution.
The study revealed that while direct bone-to-implant contact was fairly low (3-5%), the implant was well seated within the bone geometry (82% of maximum fit). This suggests that surgeons should focus primarily on achieving the right fit, and preserving compacted bone debris, rather than simply trying to maximise the raw contact area to improve stability.
Broaching was also found to compact bone fragments into the surrounding area, increasing bone density by up to 21%. These fragments act like a natural bone graft, potentially strengthening the implant site. The researchers hope their findings will lead to more accurate surgical models and more personalised hip replacement planning, though further studies are needed to assess long-term effects, such as infection risk.
Dr Arnab Palit, Assistant Professor at WMG and senior author of this work added: "This research provides a greater insight into bone-broach and bone-implant interactions-specifically changes in bone density, achieved contact area, and induced strain during hip replacement. This fundamental study offers valuable insights that can inform the development of more accurate computational models for personalised surgical planning-an important advancement toward minimising implant failure and ensuring better long-term outcomes".
These mechanical insights may pave the way for more accurate, patient-specific pre-surgical planning tools. By predicting how individual bone types respond to implants, surgeons can optimise techniques and implant choices, potentially reduce complications and improve recovery times.
Professor Richard King, Consultant Orthopaedic Surgeon at UHCW NHS Trust and co-author of the study, said: "Although most patients who have a hip replacement have a great outcome, a few patients have problems. In many cases these problems relate to an uncemented femoral stem which either works loose over time, or the bone fractures around the implant, or the implant is not positioned perfectly during surgery.
"To prevent these problems, we need to better understand how the femur interacts with the implant, so that surgeons can use the right implant in the right way for each individual patient. We want our hip replacements to be perfect and never come loose, and research like this should help us to achieve this."
