Boileau and Walch mapped the three‑dimensional shape of the cadaveric proximal humerus to see how much it varies between people and whether humeral components of the time could reproduce it.
Cadaveric study of 65 humeri from 19 male and 20 female donors aged 67 to 95 (mean 86), excluding arthritic or previously fractured bones.
Methods
Specimens
65 cadaveric humeri
Donor age 67 to 95 years, mean 86
Method
Computer‑linked digitizing device to map the bone surface
Measurements
Inclination (neck‑shaft angle)
Retroversion relative to the transepicondylar axis
Medial offset of the head
Posterior offset of the head
Sphericity of the articular surface
Articular diameter vs head thickness
Hinge point: where the stem axis meets the anatomical neck plane, relative to the top of the articular surface
Key Findings
The proximal humerus differed from person to person in size and shape, with individual variation in the head's inclination, retroversion, medial offset and posterior offset.
Mean retroversion was only 17.9°, and the authors found that part of what is called retroversion is actually posterior offset of the head.
In 88.2% of specimens, the largest and smallest diameters of the head differed by less than 1 mm, so most heads were true spheres.
Articular surface diameter correlated strongly with head thickness (r = 0.96).
In 72.3% of humeri, the stem axis met the anatomical neck plane within 1 mm of the top of the articular surface, a landmark the authors used to guide reaming.
From these data the authors designed a modular, third‑generation humeral component that adjusts for all four parameters and seats the prosthetic head on the patient's own anatomical neck once marginal osteophytes are removed.
Board pearl
Humeral retroversion averaged 17.9° but ranged from −6.7° to 47.5°, so the authors concluded the head cut should follow each patient's anatomical neck.
Authors' conclusion
Although good clinical results can be achieved with current modular and non-modular components their relatively fixed geometry prevents truly anatomical restoration in many cases.
Boileau and Walch mapped the three‑dimensional shape of the cadaveric proximal humerus to see how much it varies between people and whether humeral components of the time could reproduce it.
Cadaveric study of 65 humeri from 19 male and 20 female donors aged 67 to 95 (mean 86), excluding arthritic or previously fractured bones.
Methods
Specimens
65 cadaveric humeri
Donor age 67 to 95 years, mean 86
Method
Computer‑linked digitizing device to map the bone surface
Measurements
Inclination (neck‑shaft angle)
Retroversion relative to the transepicondylar axis
Medial offset of the head
Posterior offset of the head
Sphericity of the articular surface
Articular diameter vs head thickness
Hinge point: where the stem axis meets the anatomical neck plane, relative to the top of the articular surface
Key Findings
The proximal humerus differed from person to person in size and shape, with individual variation in the head's inclination, retroversion, medial offset and posterior offset.
Mean retroversion was only 17.9°, and the authors found that part of what is called retroversion is actually posterior offset of the head.
In 88.2% of specimens, the largest and smallest diameters of the head differed by less than 1 mm, so most heads were true spheres.
Articular surface diameter correlated strongly with head thickness (r = 0.96).
In 72.3% of humeri, the stem axis met the anatomical neck plane within 1 mm of the top of the articular surface, a landmark the authors used to guide reaming.
From these data the authors designed a modular, third‑generation humeral component that adjusts for all four parameters and seats the prosthetic head on the patient's own anatomical neck once marginal osteophytes are removed.
Board pearl
Humeral retroversion averaged 17.9° but ranged from −6.7° to 47.5°, so the authors concluded the head cut should follow each patient's anatomical neck.
Authors' conclusion
Although good clinical results can be achieved with current modular and non-modular components their relatively fixed geometry prevents truly anatomical restoration in many cases.