The Effect of Stem Circumferential Grooves on the Stability at the Implant-Cement Interface

The application of stem surface treatments and finishes are common methods for improving stem-cement interface stability in joint replacement systems; however, success of these surfaces has been variable. As opposed to applying a treatment or finish, altering stem design through changing the surface topography of the base stem material may offer some advantages. This study compared the effect of stem circumferential grooving on the torsional and axial stability of cemented stems. Fifteen metal stems were machined from cobalt chrome to have smooth (n = 5) or circumferential-grooved surfaces, where groove depth and spacing was either 0.6 mm (n = 5) or 1.1 mm (n = 5). Stems were potted in aluminum tubes using bone cement, left 24 h to cure, and placed in a materials testing machine for testing using a cyclic staircase loading protocol at 1.5 Hz. All stems were tested independently in compression and torsion on separate testing days, using the same stems repotted with new cement. Motion of the stem was tracked, and failure was defined either as rapid increase in stem motion, or completion of the loading protocol. Statistical analysis was used to compare interface strength and stem motion prior to failure. Grooved stems demonstrated increased interface strength (p < 0.001) and reduced motion (p < 0.01) compared to smooth stems under compression. In torsion, no significant difference was found in strength among the grooved and smooth stems (p = 0.10); however, grooved 1.1 mm demonstrated greatest interface motion prior to catastrophic failure (p < 0.01). Overall, circumferential-grooved stems offered improved stability under compression, and comparable stability in torsion, relative to the smooth stems.