Does stem length affect proximal humeral stress shielding? A systematic review

Total shoulder arthroplasty (TSA) has increased in use, with revision surgeries also increasing. One cause of revision is aseptic loosening driven by stress shielding-a condition where altered load distribution leads to proximal humeral osteolysis surrounding the humeral prosthesis. This systematic review compares stress shielding between traditional-length (TL) and short-stem (SS) humeral prostheses, hypothesizing that SS stems reduce stress shielding.

A systematic search of Cochrane, Embase, and Medline databases was conducted. Inclusion criteria targeted studies from the last 10 years reporting radiographic outcomes of TL and SS stems. Pooled radiographic measures were stratified into a 5-zone analysis of the proximal humerus for comparison. These included cortical thinning and osteopenia (CNO), condensation lines (CL), spot welds (SW), and an overall adaptive change score. An additional GLIMMIX procedure was performed to evaluate the effect that technique and stem length had on radiographic outcomes using random effects modeling.

A total of 7 studies were included, and 620 patients were analyzed, with 422 receiving SS and 198 receiving TL humeral prostheses. The weighted average follow-up was 34.8 months. TL showed higher rates of CNO around the superior-lateral humeral prosthesis, and SS showed higher rates of CNO around the inferior-lateral and medial prosthesis. TL showed higher rates of SW around the superior-lateral and medial prosthesis, but SS showed higher rates of SW around the distal-lateral and medial prosthesis. No differences were found in CL for any group or for any measure under the stem. A significantly greater proportion of TL patients had low adaptive change scores, with more SS patients possessing high adaptive change scores. Technique did not show any significant effects on radiographic outcomes while stem length showed a significant effect on CNO in the distal-lateral zone (F-Value = 19.72, p = 0.04, OR = 0.106, 95 % CI [0.012-0.932]).

This study demonstrated radiographic differences between short and traditional-length stems that suggest unique patterns of bone remodeling. While short stems may better preserve proximal lateral bone, the higher incidence of distal cortical changes warrants careful patient selection, and traditional-length stems may remain preferable when metaphyseal fixation or bone quality is a concern.