The Walch type B humerus: glenoid retroversion is associated with torsional differences in the humerus

Area of Science:

• Orthopedic surgery
• Radiology
• Biomechanics

Background:

• Walch type B glenoid is characterized by retroversion, subluxation, and erosion.
• The corresponding humeral morphology, particularly torsion, is not well understood.
• This study addresses the knowledge gap regarding humeral torsion in Walch type B shoulders.

Purpose of the Study:

• To investigate and quantify humeral torsion in Walch type B shoulders using 3D computed tomography models.
• To compare humeral torsion between Walch type B shoulders and a control group of non-osteoarthritic shoulders.
• To explore potential differences in humeral torsion based on sex and subtypes of Walch type B glenoids.

Main Methods:

• Generated 3D humerus models from CT scans of 59 Walch type B shoulders and 59 controls.
• Defined humeral torsion relative to the epicondylar axis using an anatomic head-neck plane.
• Assessed inter-rater reliability and performed subgroup analysis for Walch types B2 and B3.

Main Results:

• Walch type B humeri showed significantly less retrotorsion (14° ± 9°) than controls (36° ± 12°) (P < .001).
• Sex-based differences in humeral torsion were observed in controls but not in the type B group.
• Excellent inter-rater reliability (ICC = 0.962) was achieved for humeral torsion measurements.

Conclusions:

• Walch type B humeri possess significantly reduced retrotorsion compared to non-osteoarthritic shoulders.
• The causal relationship between altered humeral retrotorsion and the type B glenoid remains undetermined.
• Further research is needed to guide surgical reconstruction of type B2 humeral component version for optimal arthroplasty survivorship.