Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2001-08-20
2004-05-25
Snow, Bruce (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S908000, C623S023330
Reexamination Certificate
active
06740120
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to femoral prostheses and methods for their implantation.
Total hip replacement became a clinical reality for the first time in November, 1962. The femoral head and neck were removed, the upper marrow canal of the femur was cleaned out (i.e., marrow contents removed), and the metal femoral component was inserted into the femur. Total hip replacement using a femoral component or implant is generally successful for the short term (ten years), however in the long run, deterioration of the bone occurs and the implant may loosen.
Bone deterioration adjacent femoral implants is a multi-factored process which includes at least two elements, strain deprivation and osteolysis. Bone loss due to strain deprivation (or what is commonly but incorrectly referred to as “stress shielding”) occurs in association with substantially all conventional intramedullary femoral components and is caused by the implant splinting the upper femur, preventing the upper femur from being subjected to natural bending. My prior application, PCT Application Serial No. US97/14233, includes features directed to alleviating splinting. Osteolysis is a late complication of joint replacement surgery in which the bone adjacent the implant develops lesions, either “scooped out” (focal) or diffuse (linear) areas. Osteolysis is somewhat less common than bone loss due to strain deprivation, and depends on the type of implant used. Several factors are known to contribute to osteolysis, including access of joint wear debris to a joint space JS above the collar of the component and to the area between the implant and the bone (the implant-bone interface IB). Joint wear debris carried by the fluid remains in the joint space JS and becomes concentrated. The synovial lining of the joint has limited ability to absorb and encapsulate the wear debris, resulting in osteolysis of the exposed bone. Another factor is joint fluid pressure in the implant-bone interface IB. The latter factor commonly occurs in prior art implants because fluid is able to enter the implant-bone interface IB. As the person walks, high fluid pressures are generated at the interface and within the bone cells. Recent research suggests that joint fluid pressure is a significant factor in osteolysis.
Although much less common than strain deprivation or osteolysis, the most disastrous cause of bone deterioration adjacent a femoral implant is infection. Infection may occur shortly after the total hip replacement operation (acute infection), or may occur months or years after the operation (late infection). Acute infections may be caused by bacterial contamination of the incision by airborne bacteria or from bacteria from the patient's skin. Late infections usually are caused by bacteria going through the patient's circulatory system and lodging in the bone adjacent the femoral implant.
Infection adjacent a femoral implant is a serious problem because of the pain, fever and disability it causes. The bacteria (or other organisms) cause infection in the bone and soft tissues around the implant and begin to multiply (osteomyelitis). The body's attempt to fight the infection tends to damage the bone as well.
The diagnosis of deep infection of a total joint replacement is often delayed because of the inaccessibility of the hip joint within the body. The diagnosis of infection of a total hip replacement requires aspiration of joint fluid (inserting a needle into the joint space JS (
FIG. 34
) and drawing infected fluid out of the joint with a syringe) or alternatively, obtaining deep tissue specimens from the joint. Tissue specimens are obtained by open surgery at the joint, or, much less commonly, by arthroscopic surgery (exploration of the joint through small incisions using fiberoptic telescopes).
An infection may be present at the implant-bone interface IB and not manifest itself in the joint fluid (false negative aspiration). It can be technically difficult to obtain fluid from the hip joint because of scarring from the previous surgery. The scar tissue which forms around a femoral implant may also make arthroscopic visualization of the joint difficult. Surgically exposing the hip to obtain tissue samples carries with it the pain and disability of open surgery as well as the risk of introducing bacteria around the implants.
Infrequently, the infection can be treated without removing the implant. The hip joint is surgically exposed and cleaned (debrided) through removal of dead and infected tissue. However, it is not possible to clean everywhere around the implant. Moreover, the interface between the bone and implant is generally inaccessible, which inhibits the introduction of antibiotics into the implant-bone interface IB. As shown in
FIG. 34
, antibiotics introduced into the joint space JS will generally remain in the joint space and will not flow down into the implant-bone interface IB. Intravenous systemic antibiotics are administered for several weeks or months following surgery. This method of treating an infection adjacent an implant usually is attempted only on early infections (less than three or four weeks) and is not always successful in eradicating the infection.
More commonly, infection adjacent a femoral prostheses requires complete removal of the implant and removal of bone cement (if present). The removal of cemented or non-cemented intramedullary stem femoral implants will destroy some amount of bone. In the case of removal of porous ingrowth (non-cemented) femoral implants, the destruction of bone is extensive. These components frequently require cutting the upper thigh bone (femur) in half longitudinally (extended trochanteric osteotomy), cutting the metal stem in half transversely, and using a hollow coring drill to remove the lower half of the stem (trephining). The extent of bone loss associated with removal of total hip replacement femoral implants is aggravated in cases where pre-existing bone loss from strain deprivation and osteolysis is present. Once the implant is removed, the patient is given systemic (intravenous or oral) antibiotics for two months or more. When there is evidence that the infection has been cleared, a new total hip replacement is installed in a second operation. Fixation of the new implant in the bone is frequently compromised by loss of bone stock.
In some patients, the joint replacement implants are permanently left out (Girdlestone procedure). This option is considered for patients having a weakened immune system, such as those with diabetes, rheumatoid arthritis or who require steroids. A Girdlestone procedure is also considered for patients who are too ill to withstand an additional major operation. With the hip implant absent, the hip joint tissues contract and the leg becomes significantly shorter. With no bony or mechanical connection or support, the hip is unstable and frequently painful. Most patients require the use of crutches, walker or wheelchair after a Girdlestone procedure.
Another problem in the treatment of infection is presented by the systemic administration of antibiotics, taken orally or intraveneously. Systemic antibiotics expose the entire body to the antibiotic. Potential side effects of antibiotics limit the amount that can be given. Side effects of systemic antibiotics include allergic reactions, impairment of kidney function, damage to the nerves which allow hearing and balance, gastrointestinal complications, and other problems. Additionally, bone has a relatively poor blood supply compared with other tissues, e.g., muscles or internal organs, so that achieving high enough concentrations of antibodies in the bone to eradicate the bacterial infection is difficult. The implant, acrylic bone cement (if present), nonviable bone and scar tissue may also harbor deep seated bacteria which may again begin to multiply once antibiotics are discontinued.
An alternative method of delivering antibiotics to an infected hip implant employs an antibiotic cement spacer. The infected hip replacement components are removed and the b
Pellegrino Brian E.
Senniger Powers Leavitt & Roedel
Snow Bruce
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