Assessing proximal humerus cortical bone thickness for total shoulder arthroplasty: A cadaveric study.

Background: In reverse total shoulder arthroplasty, a humeral osteotomy is typically performed at the anatomic neck. The quality and quantity of cancellous and cortical bone impacts sizing of implants. Little-to-no information exists characterizing the transition of this bone quality at this location. This cadaveric study focused on measuring and analyzing the transition zone of the proximal humerus bone quality to better understand the implications of utilizing different implant sizes during reverse total shoulder arthroplasty. This assessment was conducted through the usage of a newly designed indentation depth probe. Methods: An Exactech, Inc. designed indentation depth probe was used to assess the transition from cancellous to cortical bone in 45 cadavers after a humeral osteotomy was performed. The thickness of the cortical rim was measured in regard to superior, inferior, anterior, and posterior quadrants. Linear regressions were utilized to evaluate the relationship between anatomic location in regard to cortical bone thickness. Independent sample two-tailed t-tests were also conducted to examine the relationship between spring force and bone thickness. Finally, independent sample two-tailed t-tests or Mann-Whitney U tests were utilized to examine the relationship between cortical thickness and variables including sex, age, osteoporosis, and a diagnosis of cancer. Results: All linear regressions were found to be insignificant excluding the relationships between inferior to anterior (p = 0.003) and inferior to posterior (p = 0.001). All t-tests and Mann-Whitney U tests were found to be insignificant, except for the relationship between age and the posterior aspect (p = 0.04). Conclusions: In our cohort, cortical bone thickness was not impacted by sex, diagnosis of osteoporosis, or diagnosis of cancer. Interestingly, age was found to only have an impact on the posterior aspect of the cortical bone rim. Differences in cortical bone thickness were also found in regard to both the inferior to anterior and inferior to posterior comparisons. Clinical relevance: This suggests that differences in cortical bone thickness can occur, and that one point of assessment might not be sufficient.