Humeral short stem varus–valgus alignment affects bone stress

• Published in: Journal of orthopaedic research 2022-09, Vol.40 (9), p.2169-2178
• Main Authors: Tavakoli, Amir, Spangenberg, Gregory, Reeves, Jacob M., Faber, Kenneth J., Langohr, G. Daniel G.
• Format: Article
• Language: English
• Subjects: Arthroplasty, Replacement, Shoulder - instrumentation; bone resorption; Elbow Joint; Humans; humeral short stem; Humerus - diagnostic imaging; Humerus - surgery; implant positioning; Male; Prosthesis Design; shoulder arthroplasty; stress shielding
• ISSN: 0736-0266; 1554-527X
• DOI: 10.1002/jor.25239

The use of uncemented humeral stems in total shoulder arthroplasty (TSA) is associated with stress shielding. Shorter length stems have shown to decrease stress shielding; however, the effect of stem varus–valgus alignment is currently not known. The purpose of this study was to quantify the effect of short stem distal humeral endosteal contact due to varus–valgus angulation on bone stresses after TSA. Three‐dimensional models of eight male cadaveric humeri were constructed from computed tomography data. Bone models were reconstructed with a short stem humeral component implant in three positions (standard, varus, and valgus). Modeling was performed at 45° and 75° of abduction and the resulting differentials in bone stress compared to the intact state and the expected time‐zero bone response were determined. In cortical and trabecular bone, the standard position (STD) altered bone stress less than the valgus (VAL) and varus (VAR) positions relative to the intact state. For both cortical (p = 0.033) and trabecular (p = 0.012) bone, the VAL position produced a larger volume of bone with resorbing potential compared to the STD position. Statement of Clinical Significance The results of this study show that central positioning of a short stem humeral implant produces the smallest changes in bone stresses compared to the intact state and produces the smallest volume of bone expected to resorb due to stress shielding. If distal contact must occur, valgus malposition resulting in distal medial stem cortical contact may be worse than varus malposition resulting in distal lateral stem contact.