Randomised trial comparing bone remodelling around two uncemented stems using modified Gruen zones

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Radiology

Background:

• Assessing bone remodelling around total hip arthroplasty (THA) is crucial for implant longevity.
• Current methods using dual-emission X-ray absorptiometry (DEXA) and standard Regions of Interest (ROI), like Gruen zones, limit comparative analysis of different uncemented stem designs.
• Standardized ROI definitions are needed for accurate evaluation of implant-induced bone mineral density (BMD) changes.

Purpose of the Study:

• To compare the efficacy of a modified Gruen zone approach versus standard Gruen zones for assessing BMD changes around two uncemented THA stems.
• To determine if the modified ROI method can reveal significant differences in bone preservation between Symax(TM) and Omnifit(®) stems.
• To evaluate the impact of proximal coating on bone remodelling using DEXA over a two-year follow-up.

Main Methods:

• A randomized clinical trial involving 49 patients comparing Symax(TM) (n=25) and Omnifit(®) (n=24) uncemented stems with proximal coating.
• DEXA scans were used to measure BMD at two-year follow-up.
• BMD analysis was performed using both standard Gruen zones and a modified approach ensuring equal ROI length and position (zones 1 and 7) for direct comparison of cancellous and cortical bone.

Main Results:

• The modified Gruen zones yielded lower BMD values for the Omnifit(®) stem in zone 7 (3.6% decrease, p<0.05) compared to standard zones.
• The modified ROI analysis revealed a statistically significant difference in bone preservation favouring the Symax(TM) implant, a difference not apparent with standard Gruen zones.
• This adaptation highlighted significant bone preservation differences between the two stem designs in zone 7.

Conclusions:

• The modified Gruen zone method provides a more accurate and sensitive assessment of bone remodelling around THA implants.
• This adaptation is essential for valid comparisons of bone preservation between different uncemented stem designs.
• The study recommends the use of modified Gruen zones for future DEXA-based assessments of bone remodelling in THA research.