Optimizing humeral stem fixation in revision shoulder arthroplasty with the cement-within-cement technique: A biomechanical evaluation

Abstract Background A previous clinical study suggested that a smaller stem with more cement may reduce humeral loosening. Our hypothesis is that utilizing a smaller stem diameter with more cement compared to a larger diameter stem will result in greater rotational stability. Materials and methods Two RSA humeral components of varying stem sizes were divided into the following testing groups: (I) 6 mm stem diameter with (2.5 cm bone loss [n=5], and 5 cm bone loss [n=5]) and (II) 10 mm stem diameter (2.5 cm bone loss [n=5], and 5 cm bone loss [n=5]). A 12 mm diameter humeral stem was instrumented using standard cementation technique into twenty, Sawbones humerii with either 2.5 cm or 5 cm of bone loss. The 12 mm stem was extracted and either a 6 mm or 10 mm stem was cemented -within-the existing cement mantle. Torque was applied for 1,000 cycles in increments of 2.5 N-m to 17.5 N-m on both revision stems. Results There was a decrease in rotational stability in the 10 mm diameter stems when compared with the 6 mm diameter stems (p Conclusions We disproved our hypothesis in this biomechanics model. Larger stems have greater resistance to torsional stress and are more stable even in cases of greater proximal bone loss whereas smaller stems were found to be unstable even with 2.5 cm of proximal bone loss. Level of evidence Basic Science Study.