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Tomasz Poboży

A neck-fixated short stem and bone preservation after hip arthroplasty

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Tomasz Poboży

Polish version: Krótki trzpień szyjkowo-fiksowany a zachowanie kości po endoprotezoplastyce biodra

Short stems do not all preserve bone in the same way. A Danish randomized trial found that the neck-fixated, non-diaphyseal Primoris stem was associated with higher bone mineral density (BMD) in selected Gruen zones at 2 years than the conventional Echo stem in younger patients with primary hip osteoarthritis. Patient-reported function did not show a measurable advantage.

Why this study matters

Stress shielding and periprosthetic bone loss remain concerns after uncemented total hip arthroplasty (THA), particularly when considering bone stock for future revision. Short stems aim to reduce distal load transfer and load the proximal femur more physiologically, but the category includes distinct biomechanical concepts. Tjønneland and colleagues compared two specific designs: neck-fixated Primoris and conventional Echo, which achieves metaphyseal fixation with diaphyseal engagement.

Study design

At Aalborg University Hospital in Denmark, 61 patients with primary hip osteoarthritis were randomized: 31 to Primoris and 30 to Echo. One Primoris patient was excluded after a periprosthetic fracture was identified at the 6-week review, leaving 60 in the final analysis.

The population was deliberately young and selected: women were no older than 55 and men no older than 65. Exclusions included osteoporosis, diabetes, rheumatoid arthritis, smoking and medication affecting bone metabolism. The primary outcome was periprosthetic BMD measured by DXA before surgery and at 6 weeks, 12 months and 24 months. EQ-5D, Oxford Hip Score and Forgotten Joint Score-12 were also assessed.

Main results

At 24 months, BMD was significantly higher with Primoris in three Gruen zones:

  • Zone 3: difference 0.40 g/cm² (95% CI 0.26–0.53; P < 0.001).
  • Zone 5: difference 0.20 g/cm² (95% CI 0.07–0.33; P = 0.003).
  • Zone 7: difference 0.27 g/cm² (95% CI 0.14–0.41; P < 0.001).

The authors expressed these differences as approximately 19.1%, 9.1% and 14.3%, respectively, relative to Echo. The increase in zone 7 BMD from 6 weeks to 24 months was also greater with Primoris. Patient-reported outcomes improved similarly, with no significant between-group differences in EQ-5D, Oxford Hip Score or FJS-12.

Clinical interpretation for an orthopaedic surgeon

This trial separates a biological effect from a benefit perceived by patients. Greater proximal bone preservation could matter over many years and potentially assist future revision, but the 2-year trial did not demonstrate better function or quality of life. The results support proximal load transfer with this neck-fixated design, not superiority of every short stem over every conventional stem.

Limitations

  • The study was small and conducted at one centre.
  • Participants were younger and healthier than typical THA recipients; osteoporosis, diabetes and smoking were excluded.
  • Only two stem models were compared.
  • BMD is a surrogate endpoint. The trial was not designed to assess revision, aseptic loosening or late periprosthetic fractures.
  • One Primoris patient was excluded after a periprosthetic fracture detected at 6 weeks.

Implications for practice

For selected younger patients, a neck-fixated design may preserve bone in parts of the proximal femur, which is of interest when long implant service and future bone stock matter. The study does not establish fewer revisions, fractures or loosening, demonstrate functional superiority, or determine safety in older patients with osteoporosis or poor bone quality. Larger studies and substantially longer follow-up are required.

References

Tjønneland A, Christiansen JD, Jakobsen T, Nielsen PT. Preservation of periprosthetic bone with a collum-fixated short stem versus conventional metaphyseal-fixated stems in total hip arthroplasty: a randomized controlled trial with 2-year follow-up in 61 patients. Acta Orthop. 2026;97:510–516. DOI: 10.2340/17453674.2026.46481. PubMed · Full text in PubMed Central.

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For Doctors and Physiotherapists · Research Updates, Literature and Evidence-Based Medicine

Content prepared by: Tomasz Poboży - orthopaedic surgeon.

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