This cadaveric CT study simultaneously characterized the external geometry and intramedullary canal morphology of 60 human humeri using 3D computer modeling. It asked: what are the normative values for proximal humeral anatomy, and what do they demand from prosthetic design? The answer drove the shift from fixed-geometry to modular third-generation shoulder implants.
Shoulder arthroplasty implants of the 1980s and early 1990s used fixed geometry — one inclination angle, one version, one offset. Because the quantitative case for modularity had not been made. This paper made it: retroversion varies nearly fourfold across the population (9° to 31°) and cannot be predicted from anything else you can measure on the bone.
In practice, this means when you set humeral version intraoperatively, you cannot default to a fixed angle or estimate it from stem size. You must reference native anatomy. Typically the forearm axis with the elbow at 90°, or the posterior glenoid, depending on your surgeon's technique.
For implant selection, the finding that two inclination options (38° and 44°) capture 95% of patients within 3° is why modern modular systems offer at least two inclination angles rather than a single fixed neck-shaft geometry.
The intramedullary canal finding carries a direct implant design implication: the distal shaft of a cementless humeral stem should be cylindrical, not elliptical, because distal canal version diverges unpredictably from proximal canal version and from native head retroversion.
This cadaveric CT study simultaneously characterized the external geometry and intramedullary canal morphology of 60 human humeri using 3D computer modeling. It asked: what are the normative values for proximal humeral anatomy, and what do they demand from prosthetic design? The answer drove the shift from fixed-geometry to modular third-generation shoulder implants.
Shoulder arthroplasty implants of the 1980s and early 1990s used fixed geometry — one inclination angle, one version, one offset. Because the quantitative case for modularity had not been made. This paper made it: retroversion varies nearly fourfold across the population (9° to 31°) and cannot be predicted from anything else you can measure on the bone.
In practice, this means when you set humeral version intraoperatively, you cannot default to a fixed angle or estimate it from stem size. You must reference native anatomy. Typically the forearm axis with the elbow at 90°, or the posterior glenoid, depending on your surgeon's technique.
For implant selection, the finding that two inclination options (38° and 44°) capture 95% of patients within 3° is why modern modular systems offer at least two inclination angles rather than a single fixed neck-shaft geometry.
The intramedullary canal finding carries a direct implant design implication: the distal shaft of a cementless humeral stem should be cylindrical, not elliptical, because distal canal version diverges unpredictably from proximal canal version and from native head retroversion.