Femoral hip prosthesis

-1- PRO 6677 FEMORAL HIP PROSTHESIS The present invention relates to a femoral hip prosthesis, and more particularly to a femoral hip stem component.

Hip arthroplasty procedure includes anesthesia and patient placement on a table in proper orientation. The patient's body is then stabilized, scrubbed, prepared and draped. An inchsoon is made and the subcutaneous tissue is divided. Appropriate soft tissue is excised and/or divided for exposure and dislocation of the hip. After the Eemoral head is dislocated from its assess lug axed acetabulum, the head is rotated for better exposure. Afemoral neck osteotomy is then performed wherein the head and neck are cut away from the femur shaft. Next, the intermeddler canal is prepared to accommodate the hip stem component of the prosthesis and, ultimately, the stem is anchored within the inter muddler canal.

Prior to the present invention, numerous femoral inserts have been proposed for use in hip joint prostheses. Generally, each includes a polished spherical head or capitulum mounted upon a stem, which is inserted into the intermeddler canal of the femur. Often, the inserts are cemented within the canal to hold them fast against the applied forces and loads. Such inserts are described, for example, in US.

Patents 3,102,536, 3,320~951, 3,818,512, 3,874,003, 3,875,593, 3,965,490, 4~012,796 and 4,080,666.

~.3~2 The characteristics of the spacing or interface between the exterior surface of the femoral stem and the interior contour of the prepared cavity in the intermeddler canal play an important role in properly anchoring the insert to the femoral bone. A stem of sufficient length has long been recognized as desirable since it provides increased surface area for cementing within the canal and increased resistance to rotation however, long stems require large intermeddler cavities, particularly at the caulker leading into the canal since the overall surface thereof makes it impossible for the insert to pass into the canal without a significantly oversized entrance.

Such cavities result in large gaps or voids between the outside surface of the inserted stem and the inside surface of the cavity. heretofore, a glove fit between a femoral stem and the intermeddler cavity together with superior anchoring of the stem and resistance to rotation have been considered difficult to achieve.

Accordingly, an object of the present invention is a femoral hip prosthesis having a stem component that forms a glove fit when inserted into the intermuddler canal of a femur, the stem being properly anchored in place and having significant resistance to rotation.

In accordance with the present invention, a femoral hip prosthesis comprises a stem component generally divided into a proximal portion and a substaunchly longer distal portion. the stem has a slight posterior bow along its length.

The proximal portion has a slight twist of from about 5 to 15, the twist extending in a direction from the anterior to the posterior face of the stem through the medial face thereof.

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I Preferably, the length of the distal portion is from about 2 to 3 times that of the proximal portion, as measured along the medial face, and generally commences at the boundary of the distal and proximal portions.

Moreover, the twist priorly extends throughout the proximal portion and is about 9. The exterior surface so the proximal portion preferably includes a porous coating to stimulate in growth of bone.

The proximal portion ox the stem may be generally equally divided into proximal, central and distal segments, with a lateral flare provided on the distal segment for wedge-engaging action with the femoral zone when the stem is inserted therein. A neck extends from the proximal segment of the proximal portion of the stem, the neck having an axis at an angle of about 45 to the general orientation of the stem. Preferably, the neck is antevented at the angle of from about 5 to 15, and a capitulum may be secured to the neck by a Morse fit.

Novel features and advantages of the present invention in addition to those mentioned above will become apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawing wherein:

Figure 1 is a front elevation Al or anterior view of a left femoral hip prosthesis, according to the present invention;

Figure 2 is a top plan view of the prosthesis shown in Figure l;

Figure 3 is a right side elevation Al or lateral view of the prosthesis shown in Figure l;

Figure 4 is a rear elevation Al or posterior view of the prosthesis shown in Figure l;

Figure 5 is a let size elevation Al or medial view of the prosthesis shim in Figure l;

Figure 6 is a bottom plan view of the prosthesis shown in Figure l;

Figure 7 is an exploded view of the prosthesis shown in Figure 1 with the capitulum shown in section;

Figure 8 is a bottom plan view of the capitulum;

Figure 9 is a sectional view taken along line 9-9 of Figure l;

Figure 10 is a sectional view taken along line 10-10 of Figure l;

Figure 11 is a sectional view taken along line 11-11 of Figure l; and Figure 12 is a sectional view taken along line 12~12 of Figure lo Referring in more particularity to the drawing a femoral hip prosthesis 10 includes a stem component 12 having a neck 14 to which a capitulum 16 is secured.

Figures 1-6 illustrate a left hip prosthesis having an anterior face (Figure 1), a posterior face figure 4), a lateral face figure 3) and a medial face (Figure 5).

As explained more full below, the stem 12 tightly fits within a prepared in~ermedullary cavity 18 in the left femur or femoral bone 20.

The fit of stem 12 within cavity 18 is glove-like without any void or gap therebetween.

me stem 12 is generally David into a proximal portion I and a substantially longer distal portion 26.

The length of the distal portion 26 is preferably froDl about 2 to 3 times the length of the proximal portion 22 as measured along the medial face (Figure 5).

As shown best in Figures 3 and 5, stem 12 has a --5- slight posterior bow 28 along its length.

The posterior bow 28 may be a curve having a radius of about 16 inches, for example, and aids in securing the stem 12 to femur 20 while preventing rotation relative to the femoral bone 20.

The proximal portion 22 includes a slight twist which generally commences at the boundary between distal portion 26 and proximal portion 22 and continues in an upward direction to the shoulder I forming the upper boundary of proximal portion 22.

This total twist of generally from about 5 to 15, preferably from about 7 to 12 and especially about 9, in proximal portion 22 extends in a direction from the anterior face to the posterior face of stem 12 through the medial face thereof.

This is best shown in the sectional views of Figures 9-12 wherein it can be seen that distal portion 26 has no twist.

Figure 1 together with the sectional views of Figures 9-12 show that the horizontal Y and Z I axes cross each other at 90, and that the point of intersection forms the vertical axis X.

Utilizing these coordinates, it is readily apparent from Figures 9 and 10 that distal portion 26 of stem 12 is without twist.

However Figure 11 clearly shows that the twist has commenced in the proximal portion 22 amounting to angle a of about 4 at that elevation.

Continuing, the upper extreme of proximal portion 22 exhibits the especially preferred total twist angle b of about 9, and such is shown in Figure 12.

The proximal portion 22 of stem 12 may be generally equally divided into a proximal segment 32, a central segment 34 and a distal segment 36.

For reasons ISLE --6- explained Gore fully below, distal segment 36 includes a flare 38 on the lateral side thereof. When stem 12 is inserted into femur 20, flare 38 wedgingly engages the adjacent bone to thereby load and stress the bone, which promotes bone growth into and around prosthesis 10.

In this regard, the entire outside surface of proximal portion 22 includes a porous coating 40 for the inyrowth of bone and tissue.

As shown best in Figures 1 and 4, neck 14 of prosthesis 10 is at an angle A of about 45 to the general orientation of stem 12. The neck 14 has a tapered free end portion 42 which cooperates with a tapered internal socket 44 in the capitulum 16.

The tapering characteristics of end portion 42 and socket 44 are such that a Morse fit results when the capitulum 16 is secured onto the neck 14. As is well known, the capitulum 16 is in the form of a polished spherical element which articulates with the natural acetabulum, or an ace tabular prosthesis if the natural acetabulum has been replaced.

Neck 14 and its associated capitulum 16 are anteverted at an angle B, generally of from about 5 to 15 and preferably from about 9 to 15. As shown in Figures 2 and 3, this ante version is about 9; as such, capltulum 16 is angled slightly toward the anterior by about 9. Such ante version places capitulum 16 in the best possible position for articulation with the natural acetabulum or ace tabular prosthesis.

Femoral hip prosthesis 10 is implanted within the femur 20 following femoral neck osteotomy and proper formation of the intermeddler cavity 18 into which stem 12 of the prosthesis 10 is to be inserted. In Jo --7- forming the intermeddler cavity 18, a portion of the counsels tissue near the end of the femur 20 initially is cut away with an appropriate cutting tool Into shown). Following such removal, a rasp (not shown having the same general shape as stem 12 is driven into the intermeddler canal of femur 20. The rasp is then withdrawn from the femur 20 and the stem 12 introduced into the thus formed in~ramedullary cavity 18. Stem 12 passes into intermeddler cavity 18 without violating or interrupting the newly formed contour shaped by the rasp The posterior bow 28 together with the twist in the proximal portion 22 enables such insertion of the stem into intermeddler cavity 18 and results in a glove fit substantially free of gaps or voids between the exterior surface of the stem 12 and the interior contour of the prepared cavity 18.

Porous coating 40 on proximal portion 22 stymiefates in growth of bone, and the lateral flare 38 acrelegates this anchoring process. Since tensile loading is greatest at the lateral surface of proximal portion 22, lateral flare 38 increases the surface area at that location to load and stress the adjacent bone and thereby promote ingrowthO Additionally, the wedge engaging action of the lateral flare 38 against the femoral bone 20 significantly contributes to the anchoring of the stem 12 within the intermeddler cavity 18, and bone cement is not needed.

With prosthesis 10 in two pieces comprising stem 12 and capitulum 16, multiple neck lengths can be obtained with each stem 12 by using capitulums 16 with different internal sockets 44. For example, when a 3~C~ long neck length is desired, the internal socket 44 in the capitulum 16 may be short, and with a long internal socket 44 a shorter neck length is achieved with the same stem 12. Both stem 12 and capitulum 16 may be 5 fabricated of, for example, cobalt/chromium/molybdenum or titanium by techniques known in the art.