Surgical staff spin a wheel of fortune with twelve different types of stems for a hip joint prosthesis.
Cover image of Karin Rilby’s doctoral thesis. Does choice of stem influence outcome after total hip arthroplasty?

Karin Rilby: How hip prosthesis design affects functionality


The increasing need for hip replacements has prompted innovations in implant design. Are shorter stems, anchoring in the proximal femoral bone, truly more effective? Karin Rilby’s doctoral thesis provides increased understanding of different implants, potentially contributing to wiser choices for each patient.

Dissertation defense: 3 May 2024 (click for details)
Doctoral thesis: Influence of stem design on Total Hip Arthroplasty. Clinical and radiological assessment based on randomized controlled trials and register data
Research area: Orthopaedics
Sahlgrenska Academy, The Institute of Clinical Sciences

Arthritis in the hip joint is a growing concern due to aging populations and rising obesity rates. Consequently, more individuals require hip replacements. Since the advent of modern hip prostheses in the 1960s, numerous types of implants have been introduced and withdrawn from the market.

Karin Rilby, orthopaedic specialist and researcher at the Institute of Clinical Sciences.

I have also become more skeptical about how scientific results are presented and interpreted

“In recent years, there has been a trend to make the part anchored in the femoral bone, called the stem, shorter. This evolution occurs despite that there is little evidence supporting the use of short stems,” says Karin Rilby, an orthopedic specialist and a researcher at the Institute of Clinical Sciences.

Comparing different stems

What is the focus of your research?
”In my thesis, we compare newly introduced or short stems with a reference stem. We have compared how patients experience the functionality of the hip prosthesis and what radiologic changes we can see in the bone tissue surrounding the implant,” says Karin Rilby, and continues:

“We have also conducted a registry study where short stems have been compared with standard ones to detect any differences between the implants. There is a theory that a short stem might be easier to replace if one is forced to undergo a revision surgery, and we attempted to confirm this with data from three national joint replacement registries.”

A young woman and an elderly man, both using crutches.
Figure 9 in the thesis. Patients have different demands and expectations on total hip arthroplasty.

“Important for making choices”

What are the key findings?
“We have found minimal differences between the implants studied. Patients aren’t more satisfied with new or shorter stems compared to established ones. In the registry study, we see that there may be some support for the short stems being easier to revise.”

What value does this research offer patients?
“For me as a clinician, it is important to understand how different implants work to make informed clinical choices together with patients.”

Challenging new methods

What has been rewarding about your doctoral project?
“It has been enjoyable to really understand how different implants behave, such as what changes occur in the surrounding bone mass. I have also become more skeptical about how scientific results are presented and interpreted.”

And what has been difficult?
“Learning new methods has been challenging. Some of the radiological methods we have used require very high precision. Otherwise, errors can easily creep in.”

Text: Jakob Lundberg