Internal fixation retention for osseointegration

A combination prosthesis and osseointegrated fixture for the attachment of the prosthesis. A percutaneous osseointegrated fixture is provided with a bar of biocompatible material. The bar is formed into a plurality of loops and the prosthesis is molded to form a plurality of complementary mushroom-headed protuberances that fit snapwise into the loops.

BACKGROUND OF THE INVENTION 
The present invention relates to prosthetic devices, and in particular, to 
a combination prosthesis and osseointegrated internal fixation means. 
Prostheses, such as artificial eyes, ears, and the like, require some means 
of attachment to the patient. Such attachments should be both functional 
and aesthetic. Aesthetic considerations require that the prosthesis look 
as nearly as possible identical to the patients natural anatomy. 
Functional considerations include a comfortable and secure fit and 
restoration of normal uses associated with the lost or damaged anatomy. 
Desirably, the fit of the prosthesis is secure but the prosthesis is 
removable as required by the patient. 
One technique for attaching prostheses involves osseointegrated implants. 
Osseointegrated implants are surgically implanted into the patient's bony 
structure. These osseointegrated implants provide the anchoring point for 
the prosthesis. 
Osseointegrated implants for the attachment of prostheses are known in 
various applications, including the fixation of dental prostheses and 
orbital prostheses. Typically, these osseointegrated implants include 
certain common elements. Usually, a screw shaped fixture, typically of 
titanium, is surgically implanted and allowed to osseointegrate into the 
bone. A skin penetrating element, an abutment, also typically of titanium, 
is attached to the screw shaped fixture. A well known osseointegrated 
implant of this type (known as the Branemark system) developed by 
Per-Ingvar Branemark is available through Nobelpharma AB, P0 Box 5190 
S-402, Goteborg, Sweden. 
U.S. Design Pat. No. Des.294,295 issued to Branemark illustrates a typical 
implant of the type employed in the Branemark system. In the Branemark 
system a gold bar is fastened laterally between two osseointegrated 
implants and externally to the patient's skin. Metallic clips embedded in 
the prosthesis are employed to removable attach the prosthesis by clipping 
onto the gold bar. 
Another type of implant as used in conjunction with a spacing member for 
attaching a cranial facial prosthesis is disclosed in U.S. Pat. No. 
5,593,444 issued to Svensson et al. Svensson et al. discloses a spacing 
member arranged between a securing element implanted in the facial bone 
and an extraoral prosthesis. 
U.S. Pat. No. 5,064,374 issued to Lundgren discloses an implant structure 
comprising a central portion which can be attached to an implant fixed 
anchorage element and two projecting wing like structures to form a 
unitary bridge body. 
In another type of fixation method, a pair of strong magnets may be 
employed, one affixed to the prosthesis and the other affixed to the 
osseointegrated implant. U.S. Pat. No. 5,425,763 discloses such a magnet 
arrangement for attaching prostheses to an osseointegrated implant. 
There are a number of limitations to the prior art techniques for attaching 
a prosthesis to an osseointegrated implant. One is that the repeated 
attachment and removal of the prostheses can weaken the osseointegrated 
fixture. Another problem is that in some applications, such as orbital 
prostheses, limited space is available for fitting the prosthesis and fit 
is critical both for aesthetics and comfort. The prior art fixation 
techniques reduce the space available for the prosthesis. 
These and other limitations of the prior art are overcome by the present 
invention. 
SUMMARY OF THE INVENTION 
In the prior art gold wire bars are attached to percutaneous fixtures 
attached to bone anchored to titanium implants. Prostheses, mid-face, 
temporal, or thoracic, are attached to the gold wire bars with clips or 
magnets. In order to secure the prostheses to the gold wire bars, however, 
the clips or magnets exert considerable holding force, which renders 
attachment or removal of the prostheses liable to weaken the bone 
implants. Furthermore, the prior art techniques require the attachment of 
the prostheses to the external side of the gold wire bars. This leads to 
the loss of volume within which the prosthesis may fitted and may also 
render naturalistic fitting of the prosthesis difficult or impossible. 
The present invention is a combination prosthesis and fixture for the 
attachment of the prosthesis. The fixture comprises two or more 
osseointegrated implants and an attached bar. Each osseointegrated implant 
comprises an osseointegrated flange fixture to which an abutment, external 
to the patient's skin, is affixed. The bar is affixed to the abutments. 
The bar is formed into a plurality of loops. The prosthesis is formed of 
flexible synthetic material with "mushroom" headed protuberances that fit 
snapwise into the loops. With this approach, the prosthesis can be removed 
and reattached repeatedly without weakening the osseointegrated fixtures. 
The prosthesis may be formed by the method of U.S. Pat. No. 5,376,323. The 
prosthesis may be formed for a smooth close fit with the patient's 
anatomy. The formation of the "mushroom" does not significantly alter the 
surface contour of the portion of the prosthesis that contacts the 
patient. 
Conforming the prosthesis closely to the patient's anatomy has the 
advantage of preserving humidity which may be significant is certain 
applications, such as the replacement of an excised eye. Furthermore, the 
prior art attachment methods generally place the prosthesis completely 
exterior to the fixture thus losing space that may be desirable for 
accommodating the prosthesis itself. For example, correct aesthetic 
placement of a prosthetic eye is critically dependent on placing the 
prosthetic eye in the same plane as the natural eye. The space lost by 
other methods between the fixture and the surface of the patient's anatomy 
is regained with the present invention and may be usefully employed in the 
placement of the prosthesis. 
It is therefore an object of the present invention to provide for a 
prosthesis and osseointegrated fixture for the attachment of the 
prosthesis that is secure and repeatedly removable without weakening the 
osseointegrated implant. 
It is a further object of the present invention to provide for a prosthesis 
and osseointegrated fixture for the attachment of the prosthesis which 
preserves volume adjacent to the patient's anatomy for the placement of 
the prosthesis. 
These and other objects and advantages of the present invention will be 
apparent from a consideration of the following detailed description of the 
preferred embodiments in conjunction with the appended drawings as 
described following.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is a combination of a prosthesis and an 
osseointegrated fixture for the attachment of the prosthesis. 
Osseointegrated fixtures are integrated into the bone structure of the 
patient. Osseointegrated fixtures may be described with reference to FIGS. 
1 and 2. FIG. 1 shows the site 10 of an excised eye, which may have been 
lost due to, e.g., trauma, congenital defect, or surgical removal of a 
neoplasm. Although the preferred embodiment described herein is described 
with reference to a prosthetic eye and related fixture, the present 
invention is not so limited. Other types of prostheses would be suitable 
for the practice of the present invention, including, but not limited to, 
ears and other portions of the craniofacial anatomy. 
An osseointegrated implant typically comprises at least two parts, a flange 
fixture integrated into the bone and an abutment affixed to the flange 
fixture and external to the patient's skin. A typical flange fixture is 
disclosed in U.S. design Pat. No. Des.294,295, the disclosure of which is 
incorporated herein by reference. As used herein, the term 
"osseointegrated implant" refers to the combination of the flange fixture 
and the abutment. 
The implantation begins with a determination of the appropriate location 
for the implant. In the example of FIGS. 1 and 2, the locations are in the 
orbital rim 12. The location should be chosen to avoid any problems with 
the placement of the prosthesis and with due consideration for aesthetic 
factors in the contour of the prosthesis. After removal of a flap of the 
patient's skin over the chosen location for an implant, a hole is drilled 
and tapped in the orbital rim 12. A flange fixture 14 is screwed into the 
drilled and tapped hole in the orbital rim 12. After the flange fixture 14 
is inserted in the bone, it is allowed to integrate with the bone, i.e., 
the bone of the orbital rim 12 heals around the flange fixture 14. To 
assist in this process, the patient's skin is placed back over the top of 
the flange fixture 14 for a period of time. After healing and complete 
integration, the skin is removed and the second part of the 
osseointegrated implant 16, the abutment 18, is affixed to the flange 
fixture 14 by means of a screw (not shown). 
After a period of healing following placement of the abutment 18, the final 
steps in the preparation of the osseointegrated fixture 20 can commence as 
described with reference to FIGS. 3-5. Guide pins (not shown) are attached 
to the abutments 18 to locate the orientation of the axis of the implants 
16. An impression is taken of the site 10 including the implants 16 and 
the guide pins. After the impression is set, the guide pins are unscrewed 
and the impression is removed. A cast 26 is then made from the impression. 
A bar 22, preferably of gold alloy or other biocompatible material, is 
formed with at least two loops 24. The bar 22 may be fitted and shaped on 
the cast 26 prior to fitting it to the patient. Next the abutments 18 are 
removed from the flange fixtures 14 and welded to the bar 22 using the 
cast 26 as guide. Final fitting of the bar 22 may then be performed on the 
patient by attaching the welded bar 22 and abutments 18 to the flange 
fixtures 14 as shown in FIGS. 3 and 4. 
With the looped bar 22 and welded abutments 18 attached to the flange 
fixtures 14, the thin space immediately behind the bar 22 is filled with 
wax. The wax is undercut slightly so that when an impression is taken as 
described hereinafter, the impression of the looped bar 22 partially, but 
not completely wraps around the looped bar 22. 
The impression, using, for example, alginate, is then taken of the site 10 
on the patient where the prosthesis is to be fitted. As shown in FIGS. 
5-7, a cast in harder material, such as dental stone or plaster of paris, 
is taken from the impression and becomes the lower part 26 of a two-part 
mold 28 that is used to form the prosthesis. The lower part 26 may be seen 
to be an exact replica of the site 10 with a replica of the complete 
osseointegrated fixture 32 as it would appear on the patient. The 
osseointegrated fixture 32 comprises the flange fixtures 14 (although not 
appearing above the patient's skin), the abutments 18, and the looped bar 
22. 
The mold 28 also comprises an upper part 30 which forms the anterior 
portion of the prosthesis, including the superior and inferior eyelids 34, 
36 and the recess 38 for receiving a prosthetic eye. From the two-part 
mold 28 the prosthesis 40 is prepared as shown in FIG. 8. The prosthesis 
40 may be prepared using the room temperature vulcanizable (RTV) silicone 
method described in previous U.S. Pat. No. 5,376,323, the disclosure of 
which is incorporated herein by reference. 
As shown in FIGS. 9 and 10, a prosthesis 40 molded in this fashion has a 
pair of protuberances 41, 42 which are somewhat mushroom shaped as defined 
by a groove 43 formed from the cast image of the looped bar 22. The 
prosthesis, taken in RTV silicone or similar material, is somewhat 
elastic. The elastic protuberances 41, 42 fit snapwise into the two loops 
24 in the bar 22, thereby holding the prosthesis in position on the 
patient as shown in FIG. 14. 
Although the preferred embodiment is described herein with two loops 24, 
other applications may desirably employ a greater number of loops 24 and 
may employ a number of osseointegrated fixtures 32. 
It is significant that in the present invention the bar 22 may be attached 
to the fixtures posteriorly. In the prior art the placement is anteriorly 
which limits the space available to the prosthesis and thus complicates 
the task of duplicating the patient's anatomy. For example, in the case of 
orbital prostheses, the prosthetic eye must be in the same plane as the 
natural eye for a natural appearance. The approach of the present 
invention leads to a comfortable fit, good aesthetics, and in the case of 
orbital prostheses, the ability to maintain a tight fit which allows the 
maintenance of healthful humidity behind the prosthesis. 
Furthermore, as shown in FIGS. 12 and 13, the prosthesis 52 of the prior 
art method of attachment employs metallic clips 50 that snap over the bar 
22. The prior art prosthesis therefore is located entirely anteriorly to 
the bar 22 and thus looses the use of the space 54 located posteriorly to 
the bar 22. In the present invention by contrast, the prosthesis 40 is 
attached by snapwise fitting of a protuberance (for example protuberance 
42) into a loop 24 of the bar 22. As shown in FIG. 12, this allows full 
use to be made of the space that would normally be unused in the prior art 
method of attachment. The prosthesis 40 more closely conforms to the 
patient's anatomy, which may be significant where the prosthesis 40 is not 
employed for aesthetic purposes, but also provides a replication of 
function lost with the patient's natural anatomy. 
The loops 22 may be formed so as to lie in a single plane. Desirably, 
however, as shown in FIG. 11, the loops 22 are formed so the loops do not 
all lie in the same plane. This is advantageous in that the loops 22 
provide additional holding leverage. For example, if the prosthesis is an 
orbital prosthesis, it is desirable that the loops 22 are angled together 
so that the loops 22 act to hold the prosthesis 40 both in an 
anterior-posterior direction, but also medio-laterally as well. Not only 
is the holding power of the fixture 32 increased with respect to the 
prosthesis 40, but the hold is more evenly distributed so as to place less 
concentrated stress on the flange fixtures 14. 
The present invention has been described with reference to certain 
preferred and alternative embodiments that are intended to be exemplary 
only and not limiting to the full scope of the present invention as set 
forth in the appended claims.