A modified Gruen classification for comparing short and conventional Zweymüller-type stems: A three-dimensional...

Area of Science:

• Orthopedic surgery
• Biomedical engineering
• Radiology

Background:

• The original Gruen classification is standard for assessing femoral stems in total hip arthroplasty (THA).
• Comparing stems of varying lengths with the original classification can lead to inaccurate interpretations of regional fixation.
• A modified classification is needed for precise comparison of different stem lengths.

Purpose of the Study:

• To propose and evaluate a modified Gruen classification for comparing short and conventional Zweymüller-type stems.
• To assess the utility of the modified classification using 3D CT scans.
• To compare stem-cortex contact, bone reactions, and thigh pain between short and conventional stems.

Main Methods:

• Retrospective review of 519 primary THAs using the direct anterior approach.
• Propensity score matching to compare 91 MIRFY short stems and 91 Profemur Z conventional stems.
• Assessment of stem-cortex contact using original and modified Gruen classifications on 3D CT, alongside evaluation of bone reactions and thigh pain at 2 years.

Main Results:

• The modified classification reallocated distal contacts to more proximal regions, correcting potential misinterpretations from the original classification.
• The MIRFY short stem demonstrated a more proximal contact distribution compared to the conventional stem under the modified classification.
• No significant difference in radiographic bone reactions was observed, but the MIRFY group reported less thigh pain.

Conclusions:

• The modified Gruen classification provides a complementary and more anatomically accurate framework for comparing femoral stems of different lengths.
• This approach enhances the interpretation of regional stem-cortex contact in total hip arthroplasty.
• The modified classification aids in understanding fixation patterns and clinical outcomes like thigh pain.