Apparatus for trialing a modular humeral head
The present disclosure is directed to a modular shoulder prosthesis measuring device having an adjustable radial offset provided by relative rotation of an adapter interdisposed between the stem and the head. Specifically, the interface configuration between the stem and the adapter, as well as between the adapter and the head are designed such that relative positioning of these components provides a continuous adjustment in the radial offset. Indicia are provided to precisely determine the magnitude and direction of the adjustment being made.
1. An adjustable prosthesis comprising:
a stem having a proximal face;
a humeral head having an articulation surface and a bottom face opposite the articulation surface, the bottom face defining an elongated aperture having first and second ends defining a generally flat interface surface; and
an adapter interposed between the proximal face and the bottom face, the adapter defining a cylindrical coupling tapered portion having a centerline which is generally perpendicular to the interface surface, the adapter having a generally planar bearing surface configured to engage the interface surface so as to allow continuous linear movement of the generally planar bearing surface with respect to the interface surface and of the humeral head with respect to the adapter from a first position to a second position in a direction perpendicular to the centerline and within the elongated aperture, the adapter and elongated aperture defining a variable sized cavity therebetween when the generally planar bearing surface is engaged with the interface surface.
2. The adjustable prosthesis of claim 1 , wherein the adapter is rotationally positionable on the stem to provide a first adjustment and relatively linearly positionable to the head to provide a second adjustment so as to couple the head to the stem in a fixed orientation within a range of orientations defined by the first and second adjustments.
3. The adjustable prosthesis of claim 2 , wherein the range of orientations is a 1-5 mm radial offset.
4. The adjustable prosthesis of claim 1 , wherein the adapter is rotationally coupled to the stem such that relative angular positioning of the adapter on the stem will effect a first radial offset, and the adapter is linearly coupled to the head such that relative positioning of the adapter with respect to the head will effect a linear offset.
5. The adjustable prosthesis of claim 1 , wherein the adapter and the humeral head each include indicia that indicate a relative position of the humeral head with respect to the adapter.
6. The adjustable prosthesis of claim 1 , wherein the humeral head includes rotational indicia along the articulation surface for determining a relative rotation of the humeral head with respect to the stem.
7. The adjustable prosthesis of claim 1 , wherein a through bore is defined through the articulation surface of the head and is in communication with the elongated aperture to receive a coupling member to couple the humeral head to the adapter.
8. The adjustable prosthesis of claim 7 , wherein the through bore has a slot portion and a circular portion that facilitates transverse movement of the coupling member within the through bore.
9. The adjustable prosthesis of claim 1 , wherein the stem further comprises a taper coupling feature.
10. The adjustable prosthesis of claim 9 , wherein the cylindrical coupling tapered portion of the adapter is positionable within the taper coupling feature of the stem to couple the adapter to the stem.