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How can we make hip replacements even better and safer? Thom Snijders and Joost van Erp looked for answers during their PhD research. Thom looked at how to place the hip cup to lower the risk of dislocation. Joost added to this by studying the hip stem and how the spine, pelvis, and hip move together. They successfully defended their thesis in the past week.

Q: You both did research into hip arthroplasty, also known as hip replacement, a surgical procedure where damaged parts of the hip joint are removed and replaced with artificial implants. Could you both briefly explain what you researched during your PhD?

 

Thom: My PhD explores the challenges in current research aimed at how to achieve optimal acetabular cup placement to prevent dislocation.  A key finding is that inconsistencies across studies—such as varying definitions, reference planes, and the predominance of static assessments—complicate progress, despite the fact that dislocations typically occur during dynamic activities.

Joost: My thesis adds on to Thoms research and includes the femoral stem of the hip prosthesis in the quest to solve total hip instability. Moreover, it explores the etiology of degenerative diseases of the lower extremities in relation to spinopelvic mobility and the optimal materials used for polyethylene in the acetabular cup.

Q: How did your projects connect or build on each other? And did you collaborate a lot during your PhDs?

 

Thom: My research mainly focusses on the acetabular cup of the total hip arthroplasty. It seemed only logic to use the 3-D solution for the cup for the stem as well. That’s were Joost picked up.

Joost: I continued with the 3-D model Thom made for the stem, after I performed a systematic review about the current knowledge about the orientation about the femoral stem.

Q: What was the most impactful or surprising finding in your work?

 

Thom: What stands out to me is the research community’s reluctance to move beyond traditional measures like anteversion and adopt sagittal anteinclination (SAI) instead. Most femoral and pelvic motion occurs around the same axis that defines SAI, and importantly, it can be measured across different positions. While I understand the historical context behind the preference for anteversion, current advancements—particularly the reduced concern over radiation exposure—make it increasingly difficult to justify this persistence.

Joost: I think several findings in multiple researches, for example: the higher prevalence of knee degeneration in high pelvic incidence, finding the solution about how to implement the 3-D model in the femoral stem and the lower wear rates in vitamin E acetabular cups.

Q: Looking forward: how do you see your research contributing to improving hip replacement surgery in practice?

 

Thom: 80% of the people with coxarthrosis have normal spino-pelvic-femoral parameters and the THA is already very successful. Therefore, we need to recognize the patients who fall out of these 80%. These are the ones at risk for a dislocation and we need to pick them out by physical examination and some lateral radiographs of the pelvis. We need to check for the mobility, morphology and the position of the pelvis.  

Joost: I think our studies are already quite practical and could be important for future hip-spine surgery. Knowledge-gaps are identified and partially solved, and a part of the recommendations could be directly implemented in daily clinical practice.

Q: How do you look back on your time in Utrecht? What else are you proud of, or are cherished memories of the RMCU?   

 

Thom: Our headquarters were in the Diakonessenhuis, the Clinical orthopedic Research Center – mN in Zeist. However, we went to the UMCU many times to gather with other researchers for some brainstorm sessions. This brought our research to a higher level and we always left with new enthusiasm, new ideas and of course more questions than answers. 

Joost: Indeed, our PhD is a unique collaboration between the Diakonessenhuis and the UMCU, which enables us to perform research in high-volume THA cohorts, which are smaller in a tertiary center as the UMCU, but with the research facilities established and acedamic knowledge in the UMCU as backing

Q: What skills or experiences did you gain that surprised you?

 

Thom: That cooperation leads to much more possibilities and solutions. 75% of my thesis wasn’t there if I had not met someone that could help me with a problem when I did not know how to continue. 

Joost: Indeed, in clinical studies, the best way to perform quick and high-quality research is to seek help and ask for advice. Connect the right people with each other and your research and new ideas will develop.

Q: What are your plans after the PhD?

 

Thom: I’m an orthopedic surgeon and I’m doing a fellowship in spine orthopedics. I’m hoping that after this fellowship, I will find a nice orthopedic group were I can work as a Hip-Spine surgeon.

Joost: For the next 1,5 years I’ll finish my residency in orthopedic surgery in the St. Antonius Hospital. I have several ongoing research projects besides this PhD which I’ll finish. After this period I probably want to follow on fellowship, for example, in hip and/or knee arthroplasty.