Systems and methods for monitoring wear and/or displacement...

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Reexamination Certificate

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C324S653000, C324S639000

Reexamination Certificate

active

06583630

ABSTRACT:

FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to systems and methods for monitoring wear of, and/or displacement between, artificial joint members, vertebrae, segments of fractured bones, and dental implants. More specifically, embodiments of the present invention relate to detection systems capable of determining a distance between, for example, joint members of an artificial joint or between vertebrae, thus enabling to determine, for example, relative displacement therebetween.
Artificial Joints
Total joint arthroplasty is an operation involving the replacement of a damaged joint with an artificial joint assembly in order to restore motion to the joint and function to the muscles and ligaments and other soft tissue structures that operate and control the joint.
The operation is typically performed on individuals with a painful, disabling arthritic joint that is no longer responsive to conservative treatment regimens. This operation typically entails implantation of two or more artificial joint members into respective natural joint members so as to replace deteriorated natural articulating surfaces with artificial equivalents.
Artificial joint assemblies have been devised for a variety of joints including hips, knees, ankles, shoulders, elbows, fingers, toes and wrists. Typically, components of artificial joints such as that shown in, for example, U.S. Pat. No. 4,068,324 to Townley et al. mimic the structure and function of joint members of a natural joint, thus providing as natural as possible articulation motion.
While artificial joint components are designed to provide stable and permanent attachment to the natural adjacent body tissue(s), at attachment interfaces, motion and/or loosening of the artificial joint member can occur, resulting in artificial joint relocation, which can lead to a loss of function, bone deterioration and tissue debris generation.
Such relocation can lead to an increase in wear to the articulating surfaces of the artificial joint. Such wear typically results in reduced function of the artificial joint and, in addition, produces joint debris which are expelled from the joint area to the surrounding tissues and may cause adverse reactions, such as inflammatory granulatoma, in these tissues.
The debris expelled from the artificial joint includes microscopic particles typically measuring up to a few microns in size. These particles provoke various tissue reaction, which affect the bones hosting the artificial joint implant.
The type and severity of the biological reaction to wear generated particles depend mainly on the physical properties and to a lesser degree also on the chemical properties of the wear particles. For example, in joints which include polyethylene component three types of particles are observed, chunks, flakes and granules. The granules, which are approximately one micron in size, are responsible for an intense inflammatory reaction. The histology is characterized by phagocytosis of the particles, resulting in large conglomerations of macrophages due to their inability to digest the polyethylene. The inflammatory process is accompanied by release of biochemical mediators such as prostaglandins and interleukins that cause absorption of the host native bone. Wear particles of other plastics, such as acetyl-copolymer, are of similar physical shapes but may cause an even more intense reaction.
Wear in metallic and ceramic joints is typically characterized by small granules which are taken in by macrophages, leading to a similar biochemical reaction to that caused by plastics.
As a wear of a joint progresses and larger amount of particles are expelled to the surrounding tissues, further bone absorption and loosening of the joint implant may occur. Such loosening of a prosthetic joint implant and damage to surrounding tissues is often left undetected in a patient even if regularly checked by a physician. Most modern methods currently employed for determining the extent of loosening and/or wear of an artificial joint, rely upon either X-ray, computer tomography, isotope bone scan or magnetic resonance to image the implanted joint and are of insufficient accuracy or technically difficult to perform and/or interpret even by highly skilled professionals. In fact, the most modern joint replacement assemblies incorporate metal backed plastic components, metallic components, or ceramic components within metallic shells and as such the available imaging methods cannot produce sufficient contrast in order to determine artificial joint loosening and/or articulating surface wear.
As a result of inefficient detection methods, oftentimes the only indication of early joint loosening is the pain and discomfort suffered by the patient. Oftentimes bone absorption progresses to a stage necessitating replacement surgery using larger implants, and/or bone grafts to accommodate for the lost bone tissue. The prognosis for success and service life of the implant after such a corrective operation is less predictable and depends, among other factors, on the extent of bone absorption suffered. If performed relatively early on, such corrective surgery has an increased chance of success. Therefore, a method capable of detecting the extent and depth of wear of the articulating surfaces of an artificial joint or capable of detecting minute displacement of artificial joint components which are fixed within the bone is of paramount importance both to the patient and the treating physician.
The Spine
The spine is a column of individual vertebrae. Within the spinal column, vertebrae inter-articulate via three joints which form a tripod-like configuration ground the disc occupying the space between the bodies (anteriorly) and the two facet joints (posteriorly).
Degenerative processes of the spine affect all three joints and causes reduction of the disc space in between the vertebrae. Spinal injury may cause instability and loss of bone and may require surgical fusion of the affected vertebrae or vertebral replacement. Fusion is effected by a variety of techniques such as applying bone graft in the damaged disc spaces or by utilizing implanted fixation devices such as screws, cages, plates, rods or hooks.
If fusion is unsuccessful, partial or total lack of union between the vertebrae (non-union) leads to a painful condition which arises from the motion existing between the vertebrae. Such motion, which is oftentimes difficult to detect, often requires additional surgical intervention.
Therefore accurate measurements of implant displacement and of pathological motion during the post operative follow up period as well as subsidence of motion (fusion) is of paramount importance.
Dental Implants
Dental implants are typically composed of a metallic (or other biocompatible material) fixture which is anchored within the maxillary or mandibular bone, a post (e.g., rod or screw) which is attached to the fixture and a prosthetic tooth (typically referred to as a crown, or a cap) which is fitted over the post.
The stability of the implant is essential for longevity thereof and for the preservation of the bone stock. A loose dental implant will cause absorption of bone and further deterioration of the bone stock, often requiring bone reconstruction using various grafting procedures. Thus, it is in the interest of both patient and dental surgeon to detect denial implant loosening prior to bone deterioration.
Bone Fractures
Following traumatic or intentional (osteotomy) bone fractures, natural bone processes unite the fractured or broken bone segments. Oftentimes, the exact time of union remains uncertain and as such, the duration of treatment is oftentimes unnecessarily prolonged.
In addition, when bone segments fail to properly unite, the resulting state of non-union can lead to pain and loss of function in the fractured or broken member.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system and method which enable to monitor relative wear and/or displacement in artificial joints, vertebrae, segments of fractured bones o

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