NZ728884B2 - Femoral stem and post system for hip prosthesis - Google Patents

Abstract

femoral stem for use in hip replacement surgery, specifically hip replacement surgery in dogs and similar animals or humans, and a process of implanting the same when used on animals. More particularly, the invention is directed to a femoral stem that includes a lateral bolt or post that protrudes through the cortex or wall of bone opposite the neck of the femoral stem. The lateral bolt or post reduces the occurrence of subsidence in implanted femoral stems. The lateral bolt or post provides an anchor point on the cortex or wall of bone as opposed to relying solely on the compression of the femoral stem against the wall of the bony canal of the femur being implanted. The lateral port further comprising a tapering diameter in the region of the femoral neck and where the first end of the insertion tip also has a tapering body that matches the tapering diameter of the lateral port. through the cortex or wall of bone opposite the neck of the femoral stem. The lateral bolt or post reduces the occurrence of subsidence in implanted femoral stems. The lateral bolt or post provides an anchor point on the cortex or wall of bone as opposed to relying solely on the compression of the femoral stem against the wall of the bony canal of the femur being implanted. The lateral port further comprising a tapering diameter in the region of the femoral neck and where the first end of the insertion tip also has a tapering body that matches the tapering diameter of the lateral port.

Description

FEMORAL STEM AND POST SYSTEM FOR HIP PROSTHESIS DESCRIPTION BACKGROUND OF THE INVENTION [Para 1] The present invention relates to a femoral stem for hip prosthesis used for replacing the natural joint of a hip joint with an cial device. More particularly, the invention relates to a modified l stem to prevent subsidence.

[Para 2] It is well known that in the orthopaedic field, surgery of the hip joint is generally carried out to treat pathologies such as arthrosis, tis, hip luxation, femoral head and neck fractures, or similar conditions generating a ssive wear, pain, or dysfunction of the hip joint. The hip joint connects the femur to the pelvis and comprises the femur head engaged in the acetabulum which is a joint cavity on the outer face of the pelvic bone. In the femur, in addition to said femoral head, there is the neck connecting the head to the femoral body, having a rather udinal pment.

[Para 3] On the basis of the natural shape of the hip, the prosthesis to be implanted comprises therefore of a femoral part and a pelvic part. The femoral part called a femoral stem is typically made of surgical grade metal, i.e., titanium alloy or stainless steel, and the pelvic part called acetabular cup is typically made of Ultra High Molecular Weight Polyethylene (UHMWP) and /or surgical grade metal, i.e., titanium alloy or ess steel. The femoral stem Page 1 of 18 17316789_1 (GHMatters) P105185.NZ comprises a main body also known as the stem, which is implanted into a udinal cavity of bone made in the natural femoral shaft. The acetabular cup is implanted into the bony bed made in the natural pelvic ulum. Such femoral stem ends at the top of the natural l shaft with a er which blends into a femoral neck projecting from the shoulder and having a terminal cone. A spherical femoral head also made of metal or ceramics is inserted on to the above mentioned terminal cone and forms the pivot ball of the artificial ball and socket joint after placing it into the acetabular cup.

[Para 4] The surgical ion to the patient's hip begins with cutting the femoral neck to remove the femoral head and neck. Such operation is called a femoral neck ion or osteotomy. The resected natural l head and neck are removed to expose the top of the femoral canal. Subsequent preparation of the femur by proper pins, drills, and rasps prepares the internal canal of the femoral bone where the prosthetic stem will be inserted. The acetabulum is then prepared by removing cartilage and bone with spherical mill to form a seat into which the acetabular cup is then inserted. The femoral stem is then inserted into the prepared femoral canal. A spherical head is placed onto the terminal cone of the femoral prosthesis neck. After the femoral stem and head are assembled, the head is reduced into the implanted acetabular cup restoring the original configuration of the hip joint.

[Para 5] Once implanted, the femoral prosthesis and the acetabular cup recreate almost identically the original shape and function of the hip joint.

Page 2 of 18 89_1 (GHMatters) P105185.NZ Such provides pain relief and recovery of the joint on so as to allow the patient to have a normal life for many years.

[Para 6] The stem is anchored in the femur through three main methods. The first consisting of fication of a liquid polymer around the stem that acts as a cement, ting stem firmly to the bone. Most modern methods use a natural process whereby the femoral stem is press fit or compressed into the bony bed of the femoral canal. The direct contact of bone to stem allows for bone integration into the metal of the stem. The anchoring ability of the bone growth into the metal implant is ed by a roughened or textured outer surface of the metal. The final and less common method of stem fixation uses several screws that anchor the stem to the wall of the femoral canal.

[Para 7] One major disadvantage of press fit bony ingrowth method is subsidence. Subsidence is the ssive post-operative nt or migration of the implanted femoral stem down the bony canal of the l shaft. In certain patients, particularly active patients or animals that cannot understand instructions to minimize activity, the femoral stem may be impacted further into the femur prior to bony integration h repeated impacts from normal activity. Subsidence may result in: 1) a decreased ability of the bone to grow into the metal surface resulting in a loose femoral stem, 2) a significant change in position of the stem resulting in an increased incidence of dislocation of the femoral head out of the cup, and 3) fracturing of the femoral shaft as the implant gets pushed down the canal. Fracturing or breaking of the femur bone Page 3 of 18 17316789_1 (GHMatters) P105185.NZ particularly in non-human patients, such as dogs or cats may be due to the r bone cortical walls of the bones compared to humans.

[Para 8] The present invention addresses these needs and provides other d advantages.

SUMMARY OF THE INVENTION [Para 9] The present invention is directed to a femoral stem for a hip joint esis. The femoral stem has a femoral base with a generally elongated shape having a proximal end and a distal end. The l stem also has a femoral neck with a generally tubular shape extending from the proximal end of the femoral base and having a concentric axis. A lateral port is on a side of the femoral base generally opposite the femoral neck and in alignment with the concentric axis. The l stem also has a lateral post with a first end removably secured within the lateral port and a second end ing a ermined distance from the side of the femoral base.

[Para 10] The femoral base preferably has a longitudinal axis along the elongated shape with the longitudinal axis and the concentric axis form an operating angle therebetween. The operating angle may be between 30 degrees and 60 degrees, preferably imately 45 degrees.

[Para 11] The femoral neck preferably includes a guide hole passing concentrically through the femoral neck along the central axis. The guide hole preferably connects to the lateral port. The lateral post preferably includes a guide rod extending from the first end of the lateral post in alignment with a long axis of the lateral post. The guide rod preferably has an outer diameter Page 4 of 18 17316789_1 (GHMatters) P105185.NZ substantially equal to an inner diameter of the guide hole, such that the guide rod snugly but easily slides through the guide hole.

[Para 12] The predetermined distance from the side of the femoral base is such that when the lateral post is secured within the l port, the second end thereof extends imately 2mm beyond a lateral cortex of a femur bone into which the femoral stem is implanted.

[Para 13] A process for implanting a lateral stem as described above begins with preparing an end of a femur bone for implantation of the femoral stem.

The femoral stem preferably includes a femoral neck that replicates a neck on a femur bone of a t, wherein the femoral stem has a lateral port on a side generally opposite the l neck in-line with a concentric axis of the femoral neck. The femoral stem is then implanted in the prepared femur bone.

A lateral hole is drilled through a lateral cortex of the femur bone adjacent to the lateral port on the femoral stem. The lateral post is then installed through the l hole and into the lateral port such that a n of the lateral post protrudes from the lateral cortex of the femur bone.

[Para 14] In this process, the preparing step may e exposing a hip joint of a patient comprising a femur bone connected to a hip socket. The femur bone is separated from the hip socket and a head and neck of the femur bone is cut off so as to expose an interior of the femur bone. The exposed interior of the femur bone is rasped out to create a cavity for receiving the femoral stem.

Page 5 of 18 17316789_1 (GHMatters) P105185.NZ [Para 15] The drilling step may include inserting a first drill bit through the guide hole along the concentric axis of the femoral neck and through the lateral port to contact the femur bone adjacent to the lateral port. A pilot hole is drilled h the l cortex of the femur bone using the first drill bit, where the pilot hole is aligned with the lateral port and the concentric axis. A guide wire is inserted through the guide hole, the lateral port, and the pilot hole in the l cortex such that the guide wire protrudes from the femur bone. A second drill bit is aligned with the guide wire protruding from the pilot hole. The lateral hole is drilled through the lateral cortex using the second drill bit in-line with the concentric axis of the femoral neck. The first drill bit is preferably a pilot hole drill bit on the order of about 1.5 mm. The second drill bit is a ably cannulated drill bit to fit over the guide wire. The process may further include cleaning the lateral port and lateral hole after the ng step to remove any bone debris.

[Para 16] The lateral post is ably secured within the lateral port, as by screw threads or a comparable securing ism. The implanting step may include inserting the femoral stem into the cavity in the prepared end of the femur bone and impacting the femoral stem into the cavity.

[Para 17] The process may further include measuring a depth of the lateral hole and selecting the lateral post based upon the measured depth of the lateral hole such that the lateral post protrudes from the lateral cortex by at least 2mm.

Page 6 of 18 17316789_1 (GHMatters) P105185.NZ [Para 18] Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the ion.

BRIEF DESCRIPTION OF THE DRAWINGS [Para 19] The accompanying drawings illustrate the invention. In such drawings: [Para 20]