When stemless fixation is put to the test: what bone-density modelling suggests about AETOS◊ Stemless Shoulder System

Key takeaways

• AETOS Stemless is designed to prioritize dense peripheral metaphyseal fixation and full circumferential cancellous support within 15–20 mm of the resection plane.
• In CT-based virtual implantation, AETOS Stemless demonstrated higher average cancellous bone density at the implant interface versus a comparator stemless implant (reported ~20% higher).¹
• In the highest-density cancellous regions (>0.20 g/cm³), AETOS Stemless showed a reported ~12% higher average density at the interface.¹
• Results were consistent across the full implant size range, including both small and large anatomy cohorts.¹
  

Why it matters: literature links higher local cancellous density to lower micromotion (primary stability) and suggests excessive micromotion can compromise osseointegration (secondary stability).^2,3

So what do these modelling data mean when you’re choosing a stemless strategy?

Stemless implants pose the question: “Is the metaphysis strong enough—exactly where I’m anchoring?” Bone-density modelling helps answer that question by estimating the quality of bone actually contacting the implant after preparation. Modelling data summarized in the Evidence in Focus demonstrated that AETOS stemless shoulder was associated with higher-density cancellous bone at the interface versus a comparator—mechanically meaningful if you’re targeting stability without a diaphyseal stem.¹

What’s the challenge with stemless fixation?

Primary stability depends on achieving adequate press-fit and resisting micromotion in the early phase. One cadaveric analysis of a press-fit stemless implant reported lower micromotion under load in higher-density cancellous bone (p<0.0005).³ 

Secondary stability depends on osseointegration. Finite element modelling across multiple press-fit stemless designs suggests that micromotion >20 μm may be more likely to compromise osseointegration, and bone density plays a central role in that risk profile.^2,3

So the practical dilemma becomes: how do you reliably engage the highest density cancellous regions available—across different anatomies—without over-complicating technique?

In this Evidence in Focus study, “higher density” refers to cancellous bone at the implant interface, including the highest-density regions defined as >0.20 g/cm³ based on CT radiodensity categorization aligned with published proximal humerus density literature.⁴

Evidence in focus: modelling study at a glance

Objective: model and compare the volume and approximate density of humeral bone in contact with AETOS Stemless versus a comparator stemless implant across small and large anatomy.¹

Design: preoperative CT scans were used for virtual implantation using recommended surgical techniques (Small cohort: females aged 47–70 years, n=32; Large cohort: males aged 55–74 years, n=42).¹

Radiodensity categories were selected to align with proximal humerus radial density reported in prior literature.⁴

What the results are really saying

Across both small and large cohorts, AETOS Stemless was reported to contact higher-density cancellous bone than the comparator. Two numbers capture the headline: approximately 20% higher average cancellous density at the interface, and approximately 12% higher average density within the highest-density regions (>0.20g/cm³).¹

Mechanically, this matters because higher-density cancellous bone is associated with lower micromotion in cadaveric testing, which supports primary stability.⁴ 

And if secondary stability is threatened by excess micromotion, engaging denser cancellous bone may help keep the interface in a more favorable range for osseointegration.^2,4 

Connecting the result back to design intent

The Evidence in Focus summary describes AETOS Stemless as designed for stability using anterior/posterior cruciate fins, a proximal tapered inlay collar, and press-fit plasma spray. The stated aim is dense peripheral metaphyseal engagement with circumferential cancellous support close to the resection plane (15–20 mm).

Consistent with that design intent, the CT-based virtual implantation/density modelling reported higher cancellous bone density at the implant interface for AETOS Stemless versus a comparator (≈20% higher overall; ≈12% higher in the highest-density regions >0.20 g/cm³).¹

Take-home question

When you’re considering stemless fixation, ask: “Am I anchoring in the densest cancellous ring available, with circumferential support?” Modelling can’t replace intraoperative judgement (thumb test), but it can indicate whether a system is designed (and appears, in silico, to behave) in a way that consistently targets higher-density bone across anatomies.

About the AETOS Stemless Shoulder System 

AETOS Stemless is intended for anatomic TSA and is designed for peripheral metaphyseal engagement using cruciate fins, a proximal tapered inlay collar, and press-fit plasma spray coating.

 

Find out more about the AETOS Shoulder System:

 

This information is for educational and informational purposes only and may not be appropriate for all jurisdictions. This information does not constitute and is not intended to be medical advice. Smith+Nephew does not provide medical advice. It is the treating health care provider’s responsibility to determine the best course of treatment for their patient based upon their professional medical judgment. For detailed information, including indications for use, contraindications, effects, precautions and warnings, please consult the product’s Instructions for Use (IFU) prior to use.