Stress shielding following stemless anatomic total shoulder arthroplasty

Abstract

Background Finite element analysis has suggested that stemless implants may theoretically decrease stress shielding. The purpose of this study was to assess the radiographic proximal humeral bone adaptations seen following stemless anatomic total shoulder arthroplasty. Methods A retrospective review of 152 prospectively followed stemless total shoulder arthroplasty utilizing a single implant design was performed. Anteroposterior and lateral radiographs were reviewed at standard time points. Stress shielding was graded as mild, moderate, and severe. The effect of stress shielding on clinical and functional outcomes was assessed. Also, the influence of subscapularis management on the occurrence of stress shielding was determined. Results At 2 years postoperatively, stress shielding was noted in 61 (41%) shoulders. A total of 11 (7%) shoulders demonstrated severe stress shielding with 6 occurring along the medial calcar. There was one instance of greater tuberosity resorption. At the final follow-up, no humeral implants were radiographically loose or migrated. There was no statistically significant difference in clinical and functional outcomes between shoulders with and without stress shielding. Patients undergoing a lesser tuberosity osteotomy had lower rates of stress shielding, which was statistically significant ( p = 0.021) Discussion Stress shielding does occur at higher rates than anticipated following stemless total shoulder arthroplasty, but was not associated with implant migration or failure at 2 years follow-up. Level of evidence IV, Case series.

Stemless Reverse Shoulder Arthroplasty

“…[24][25][26] Still, rates of stress shielding range between 0 and 40% with different stemless implants in aTSA clinical studies, in part, because of heterogeneity in reported definitions and length of follow-up. 24,25,[27][28][29] FE modeling has also predicted how different stemless designs influence the location and concentration of stress experienced by surrounding bone. 21 This may affect not only the overall likelihood of stress shielding but the regions of the proximal humerus where stress shielding is most likely to occur.…”

“…Medial calcar and greater tuberosity resorptive changes have predominated with anchor fin and hollow screwtype stemless aTSA designs, respectively. 26,[28][29][30] While neither of these implants are available for use in RSA, the development, location, and effect of stress shielding with stemless RSA designs should be monitored going forward. Resorption of greater tuberosity and proximal humeral bone in RSA could lead to compromised external rotation function and instability due to loss of protective deltoid wrapping.…”

Porous versus solid shoulder implants in humeri of different bone densities: A finite element analysis

“…Furthermore, it is also important to consider the potential mechanobiological impact that porous stems may have on surrounding bone. Previous studies of proximal humeral implants for the shoulder have used computational models, radiographic and clinical outcomes postoperatively to examine the effects of stem length (Razfar et al, 19 Aibinder et al, 20 Denard et al, 21 ) hollow stems (Soltanmohammadi et al, 22 ) cementing (Denard et al, 23 Kim et al 24 ) and coatings (Tan et al 25 ) Porous humeral stems, however, have not been investigated.…”