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Objectives and questions: While many femoral revisions may be performed using primary stems, there is a wide range of revision stems available. Most of them are long and have a conical design with a round shape in cross-section. They typically aim for distal diaphyseal fixation. The DePuy Synthes CORAIL^® revision stem (REV) offers an intermediate option. Unlike the standard CORAIL^® stem (STD), it is 39 mm longer and slotted distally to adapt to the femoral diaphysis’s anterior bowing. This study aims to compare the axial and rotational stability of STD and REV stems in an artificial bone model.

Material and methods: Using a SYNBONE^®-model, 12 STD (size 11, 135°) and 12 REV (size 11, 135°) collared hip stems were implanted. Neck osteotomies were performed 20mm above the lesser trochanter, and the femoral canal was prepared with compaction broaches. Four groups (n=6 each) were evaluated: (1) STD and (2) REV with axial loading (500 cycles at 20° adduction, up to 500 N at 1 Hz (50/s), and quasi-static loading to failure); and (3) STD and (4) REV with torsional loading (500 cycles up to 10 Nm internal rotation at 1 Hz, and quasi-static loading to failure). Based on acquired machine data, stiffness at final loading ramp (axial N/mm; torsional Nm/°) and peak load (N)/torque (Nm) at failure were measured. Statistical evaluation as explorative data analysis (mean ± standard deviation (SD)) using One-Way ANOVA with Bonferroni/Games-Howell post-hoc analysis (p≤0.05 considered significant).

Results: REV demonstrated significantly higher axial stiffness (302.3 ± 17.4 N/mm) compared to STD (217.4 ± 20.7 N/mm, p<0.001) and was more resistant to peak axial force (1173.7 ± 73.5 N vs. STD 1032.0 ± 63.0 N, p=0.061). Torsional stiffness was also higher for REV (2.42 ± 0.13 Nm/° vs. STD 1.90 ± 0.17 Nm/°, p=0.002). However, peak torque at failure was comparable (STD: 40.9 ± 4.5 Nm, REV: 46.6 ± 1.7 Nm, p=0.206). Axial failure occurred at the distal stem tip, while torsional failure involved proximal rotation and spiral fracture distally.

Discussion and conclusions: The REV stem’s extended distal length improved axial and torsional stiffness and increased peak load compared to STD in artificial bone models. However, peak torque remained unaffected, and the advantages of the REV stem may not be critical in primary arthroplasty. These findings align with the excellent clinical performance of the standard stem. In revision cases with osteolysis or osteotomies, the biomechanical benefits of REV warrant further evaluation.