It is known that arthroprostheses used to reconstruct the shoulder joint can be the anatomical or inverse type. Anatomical humeral prostheses are provided with a hemispherical head that artificially reconstructs the human anatomy and are suitable to articulate in the glenoid cavity of the shoulder blade or possibly in a mating artificial seating attached to the glenoid cavity. On the contrary, inverse prostheses provide a concave articular insert able to allow the rotation of an artificial spherical body attached to the glenoid seating, commonly called glenosphere.
It is known that humeral prostheses, whether anatomical or inverse, generally include a distal joint element, also called rod or pin, inserted inside the humerus along the diaphyseal axis, to support the humeral head in anatomical humeral prostheses or the concave articular insert in inverse prostheses.
Distal joint elements of various types are known, for example with an elongated tubular shape, to define an elongated rod, or a small-sized pin, typically used for mini-invasive humeral prostheses. The shape and size of the distal joint element can also depend on the type and size of the humeral prosthesis, for example inverse humeral prostheses can need a distal joint element that is bigger than anatomical ones.
It is possible, for example due to degeneration of the tissues of the shoulder, that operations may have to be carried out to revise the prosthesis, for example to replace the prosthesis, or operations to convert an anatomical prosthesis into a inverse prosthesis or vice versa.
It is known, for example from the patent application EP-A-1.472.999, to make a modular humeral prosthesis, comprising an adapter body, which functions as a metaphyseal module, to be positioned in a seating made under the head of the humerus and connectable on one side to a rod inserted in the humerus and on the other side to the semi-spherical humeral head, in the case of anatomical prostheses, or to the concave articular insert in the case of inverse prostheses. Indeed, by varying the adapter body, the known modular humeral prosthesis can be made as anatomical or inverse. Moreover, in the field of the same type of prosthesis, anatomical or inverse, it may be possible to change the shape or size of the adapter body, releasing it from the rod and keeping the latter inserted in the humerus, whenever its sizes or characteristics are suitable for the humeral prosthesis to be grafted.
However, one possible disadvantage of this known modular humeral prosthesis is that it cannot be converted from anatomical to inverse without having to replace the adapter body. This latter operation, which entails extracting the adapter body from the bone seating, can be invasive and destructive.
Another possible disadvantage of the known humeral prosthesis is that it does not allow to completely replace the rod with another element inserted in the humerus, such as a rod with a different conformation or size, or a nail for osteosynthesis, preserving the adapter body already inserted, that is, without extracting the adapter body from the humerus which, as we said above, can be difficult and invasive.
It is known for example that, in the event of fractures of the humerus, for the purposes of osteosynthesis, it may be necessary to introduce inside the humerus a humeral nail that reproduces the correct alignment of the bone fragments to allow reciprocal welding thereof. The humeral nail can be introduced in antegrade fashion, with a passage through the proximal part of the humerus (antegrade nail), or retrograde, through an aperture in the olecranon fossa (retrograde nail). The antegrade solution is generally preferable, since it is less invasive and less complex.
However, in the state of the art and with the humeral prostheses available, if there is a fracture of the humerus and there is a humeral prosthesis present, it may be necessary to completely remove the prosthetic implant, or alternatively to use external synthesis means, such as osteosynthesis plates which in any case do not always guarantee a successful synthesis.
One disadvantage of known solutions is therefore that it it is not possible to act in an antegrade manner to remove the rod or pin and insert the nail without removing the adapter body, in the event of fractures of the humerus where there is a humeral prosthesis present.
Document US-A-2005/0125067 describes a modular prosthesis of the known type, provided with a head and a rod coupled to the head. The rod has a proximal portion coupled with the head and a distal portion configured to extend in a long bone of the patient. The distal portion can be removed from the rod after the prosthesis has been implanted, without removing the proximal portion.
Document WO-A-99/47081 also describes a modular orthopedic prosthesis having a body that has a through hole that receives a connection bushing that in turn receives a rod having a proximal neck and a distal shaft. The connection bushing can be expanded radially in order to clamp the rod and the body together.
Purpose of the present invention is to obtain a modular humeral prosthesis that allows revisions or conversions of the prosthesis, keeping the adapter body of the humeral prosthesis in the humeral seating and allowing to replace the distal joint element, either rod or pin.