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

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Radiology

Background:

• Total shoulder arthroplasty (TSA) use is rising, leading to increased revision surgeries.
• Aseptic loosening, often caused by stress shielding and proximal humeral osteolysis, is a key reason for TSA revision.
• Stress shielding occurs when altered load distribution around a prosthesis causes bone loss.

Purpose of the Study:

• To systematically review and compare stress shielding between traditional-length (TL) and short-stem (SS) humeral prostheses.
• To hypothesize that SS stems reduce stress shielding compared to TL stems.
• To analyze radiographic outcomes and bone remodeling patterns associated with different stem lengths.

Main Methods:

• A systematic literature search was performed across Cochrane, Embase, and Medline databases.
• Included studies reported radiographic outcomes of TL and SS stems from the past 10 years.
• Radiographic measures, including cortical thinning, osteopenia, condensation lines, and spot welds, were analyzed in a 5-zone proximal humerus model.

Main Results:

• Seven studies involving 620 patients (422 SS, 198 TL) were analyzed with a mean follow-up of 34.8 months.
• TL stems showed higher rates of cortical thinning and osteopenia (CNO) and spot welds (SW) in superior-lateral and medial zones.
• SS stems exhibited higher CNO in inferior-lateral and medial zones and SW in distal-lateral and medial zones; significant stem length effect on distal-lateral CNO was observed.

Conclusions:

• Radiographic differences indicate distinct bone remodeling patterns between SS and TL stems.
• SS stems may offer better proximal lateral bone preservation but require careful consideration due to increased distal cortical changes.
• TL stems might be preferable for cases requiring metaphyseal fixation or when bone quality is a concern.