[Comparison of filling ratio, alignment, and stability between ABG short-stem and Corail long-stem in total hip arthroplasty for Dorr type C femur].

Objective: Using the mono-energy reconstruction images and X-ray films to investigate whether the ABG Ⅱ short-stem could improve the filling ratio, stability, and alignment in the Dorr type C femur, compared with the Corail long-stem.

Methods: Among patients who were with Dorr type C femurs and treated with total hip arthroplasty between January 2006 and March 2012, 20 patients with a Corail long-stem (Corail group) and 20 patients with an ABG Ⅱ short-stem (ABG Ⅱ group) were randomly selected. The differences in gender, age, body mass index, and preoperative diagnoses between the two groups were not significant ( >0.05). The ABG Ⅱ group was with a mean follow-up of 142 months (range, 102-156 months), and the Corail group was with a mean follow-up of 107 months (range, 91-127 months). There was no significant difference in the Harris score and subjective satisfaction score between the two groups at last follow-up ( >0.05). At last follow-up, dual-energy CT scans with mono-energy image reconstruction were used to calculate the prosthetic filling ratio and to measure the alignment of the prosthesis in the coronal and sagittal positions. Stability assessment was performed based on X-ray films, and the subsidence distance was measured using EBRA-FCA software.

Results: X-ray film observation showed that the prostheses in the two groups were stable and no signs of loosening was found. The incidence of pedestal sign was significantly lower in the ABGⅡ group than in the Corail group ( <0.05), and the incidence of heterotopic ossification was significantly higher in the ABGⅡ group than in the Corail group ( <0.05). The subsidence distance of femoral stem in ABG Ⅱ group was significantly greater than that in Corail group ( <0.05), and the subsidence speed of femoral stem in ABG Ⅱ group was also greater than that in Corail group, but the difference was not significant ( >0.05). The overall prosthesis filling ratio was significantly higher in the ABG Ⅱ group than in the Corail group ( <0.05), while the coronal filling ratio at the lesser trochanter, 2 cm below the lesser trochanter, and 7 cm below the lesser trochanter were not significant ( >0.05). The results of prosthesis alignment showed that there was no significant difference in the sagittal alignment error value and the incidence of coronal and sagittal alignment error >3° between the two groups ( >0.05), while the coronal alignment error value in the ABG Ⅱ group was significantly greater than that in the Corail group ( <0.05).

Conclusion: Although the ABG Ⅱ short-stem avoids the distal-proximal mismatch of the Corail long-stem in the Dorr type C femur and thus achieves a higher filling ratio, it does not appear to achieve better alignment or stability.