A modular humeral head system includes a housing having an outer surface
and an inner surface. A hemispherical socket formed on one end of the
inner surface and threads formed on the other end of the inner surface. A
cap is attached at the threaded end of the housing. The cap has one or
more threaded holes that run from the top surface to bottom surface of
the cap. A screw may be inserted in each hole. The modular humeral head
system also includes an intermediate piece having a hemispherical head at
one end of a tapered shaft. The tapered shaft is inserted in a humeral
stem. The hemispherical head and the hemispherical socket form a ball and
socket coupling. A trial head may be impacted on the housing. The trial
head has one or more holes that are aligned with the screws inserted in
the cap.
In use, the assembly of the trial head, cap and housing can be adjusted to
be in any angular orientation about hemispherical head. The tightening of
the one or more screws fixes the angular position of the trial head. An
optimum position for the trial head is established via trial reduction,
the one or more screws tightened to fix the position of the head and the
trial head is replaced with a humeral head of corresponding size and
shape. The maximum adjustment of the angular position may be limited by a
limiting mechanism. In another embodiment, bone cement or other
bio-compatible material is introduced in a chamber formed between the cap
and the hemispherical head.