Boileau and Walch digitized 65 cadaveric humeri in 3D to precisely characterize proximal humeral geometry. They quantified four independently variable parameters: inclination, retroversion, medial offset, and posterior offset. The study asks whether contemporary prosthetic designs can actually reproduce that anatomy — and concludes they largely cannot.
Every shoulder arthroplasty textbook tells you to restore anatomy — this paper defines exactly what that means in three dimensions and why it is harder than it looks. The four parameters (inclination, retroversion, medial offset, posterior offset) each vary substantially between individuals and each vary independently. You cannot infer one from another.
When choosing a humeral component, a close-fitting cementless stem removes your ability to translate the head medially or posteriorly to match the patient's offsets. The paper is explicit: that stem design leaves you only depth of insertion and rotation as adjustable variables.
The recommended surgical retroversion of 30-40° (higher than the anatomical mean of ~18°) exists because surgeons have historically added retroversion to compensate empirically for uncorrected posterior offset. Knowing this, you can appreciate why truly adaptable third-generation systems (like the Aequalis, developed directly from this data) use an eccentric indexing mechanism to address offset independently rather than approximating it through version adjustments.
Boileau and Walch digitized 65 cadaveric humeri in 3D to precisely characterize proximal humeral geometry. They quantified four independently variable parameters: inclination, retroversion, medial offset, and posterior offset. The study asks whether contemporary prosthetic designs can actually reproduce that anatomy — and concludes they largely cannot.
Every shoulder arthroplasty textbook tells you to restore anatomy — this paper defines exactly what that means in three dimensions and why it is harder than it looks. The four parameters (inclination, retroversion, medial offset, posterior offset) each vary substantially between individuals and each vary independently. You cannot infer one from another.
When choosing a humeral component, a close-fitting cementless stem removes your ability to translate the head medially or posteriorly to match the patient's offsets. The paper is explicit: that stem design leaves you only depth of insertion and rotation as adjustable variables.
The recommended surgical retroversion of 30-40° (higher than the anatomical mean of ~18°) exists because surgeons have historically added retroversion to compensate empirically for uncorrected posterior offset. Knowing this, you can appreciate why truly adaptable third-generation systems (like the Aequalis, developed directly from this data) use an eccentric indexing mechanism to address offset independently rather than approximating it through version adjustments.