Primary stability of uncemented standard versus intermediate revision stems in hip arthroplasty: A biomechanical in vitro study.

Abstract

Standard uncemented (STD) stems are widely used in femoral revisions, while long conical revision stems provide distal diaphyseal fixation. Intermediate revision (REV) stems share the proximal design of STD stems but are longer. This study compares axial and rotational time-zero stability of STD and REV stems in-vitro using an artificial bone model. A biomechanical model using SYNBONE® femurs investigated uncemented, collared, fully coated 135° CCD Corail stems (STD, REV; DePuy Synthes, Warsaw IN, USA). Four groups (n = 6) were tested: (1) STD and (2) REV under axial loading (500 cycles at 20° adduction to 500 N at 1 Hz, followed by ramped catastrophic axial failure), and (3) STD and (4) REV under torsional loading (500 cycles to 10 Nm internal rotation at 1 Hz, followed by ramped catastrophic torsional failure). Stiffness and failure load/torque were evaluated. REV stems demonstrated significantly higher axial stiffness and failure load (302.3 ± 17.4 N/mm; 1173.7 ± 73.5 N) versus STD stems (217.4 ± 20.7 N/mm; 1032.0 ± 63.0 N), p ≤ 0.010. Torsional stiffness and failure torque with REV stems (2.42 ± 0.13 Nm/°; 46.6 ± 1.7 Nm) were significantly higher versus STD stems (1.90 ± 0.17 Nm/°; 40.9 ± 4.5 Nm), p ≤ 0.034. Failure patterns were consistent between REV and STD stems. REV stems provide higher axial and torsional stiffness, as well as higher failure load/torque than STD stems in artificial bone. The findings are limited to intact bone and reflect intrinsic biomechanical differences between stem designs at time-zero. Standard stems may warrant further consideration in selected revision cases.