Lateralization in reverse shoulder arthroplasty: a descriptive analysis of different implants in current practice

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Implant Design

Background:

• The concept of lateralization in reverse shoulder arthroplasty (RSA) lacks a clear, standardized definition.
• Existing RSA implants exhibit varied degrees of lateralization on the glenoid, humeral, or both sides.
• This ambiguity complicates the selection and application of RSA devices.

Purpose of the Study:

• To establish a precise definition for lateralization in reverse shoulder arthroplasty.
• To quantify the lateralization provided by commonly utilized RSA implant designs.
• To categorize implants based on their degree of global lateral offset.

Main Methods:

• Analysis of 28 configurations from 22 distinct RSA implants using digitized templates.
• Measurement of glenoid, humeral, and global lateralization, normalized to a reference implant (Delta III).
• Classification of implants into defined categories based on glenoid (medialized/lateralized) and humeral (medialized/minimally lateralized/lateralized) components, and global offset increments.

Main Results:

• Global lateral offset varied significantly across analyzed RSA designs, ranging from 13.1 mm to 35.8 mm.
• Implants were categorized into five groups based on global lateral offset: medialized RSA (M-RSA), minimally lateralized RSA (ML-RSA), lateralized RSA (L-RSA), highly lateralized RSA (HL-RSA), and very highly lateralized RSA (VHL-RSA).
• Specific counts for each category were provided (e.g., five M-RSA, six HL-RSA).

Conclusions:

• A substantial heterogeneity exists in the lateralization achieved by current RSA implants on the market.
• This quantitative analysis provides a framework for understanding implant lateralization features.
• Surgeons can utilize this information to tailor surgical techniques based on the specific lateral offset characteristics of the chosen RSA implant.