Prosthesis Instability Research Articles

Murine model of prosthesis failure for the long‐term study of aseptic loosening

We examined a novel mouse model of wear debris-induced prosthesis instability and osteolysis, and its application for the evaluation of therapy. A stainless steel or titanium-alloy pin was implanted into the proximal tibia to form a contiguous surface with the articular cartilage. In some mice, titanium particles were injected into the tibial canal during the surgery, followed by monthly intraarticular injection. MicroCT scans revealed that the implants without particle challenge were stable without bone mineral density changes for 6 months. Histological analysis showed new bone formation around the implant at 6 weeks postsurgery. Periprosthetic soft tissue with inflammatory cells was a ubiquitous finding at the interface between the implant and surrounding bone in samples exposed to titanium particles, and expression of IL-1beta, TNFalpha, and CD68 was common in these joints. Pullout tests indicated that an average 5N load was required to pull out stable implants from surrounding bone. However, particle stimulation dramatically reduced the pullout force to less than 0.4 N. The feasibility of in vivo gene transfer on this model was confirmed by X-gal staining of synovial membrane and periprosthetic tissue after injection of AAV-LacZ in the prosthetic joint. This murine model of weight-bearing knee prosthesis provides an economical, reproducible, and easily obtained means to study joint arthroplasty failure. The ability to evaluate the biomechanical properties of the prosthetic joint, in addition to histological and biochemical examination, results in a useful model to investigate many of the properties of prosthetic joint components during the response to debris-associated osteolysis.

Importance of a radial head component in Sorbie unlinked total elbow arthroplasty.

The effects of a radial head component on total elbow arthroplasty kinematics and stability were evaluated using an anatomic design unlinked total elbow prosthesis. An electromagnetic tracking device recorded motion and varus and valgus displacements under various conditions in 10 cadaveric elbows. The motion patterns of the intact elbows and the Sorbie-Questor total elbow prostheses with a radial head component were similar, as both tended to have a valgus position in extension, varus at midflexion, and more valgus toward full flexion. Under conditions of simulated muscle loading, the maximum valgus and varus laxity of the elbow prosthesis was, on average, 8.6 degrees +/- 4.0 degrees greater than normal. Without the radial head component, however, significant kinematic disturbances and instabilities were seen. The varus and valgus displacements were 13.3 degrees +/- 5.5 degrees greater than the intact elbows. One total elbow arthroplasty without a radial head dislocated during testing. Increasing the muscle loading across the elbow significantly enhanced dynamic stability of the total elbow arthroplasties, especially in the extension half of elbow motion where instability is greatest. However, this dynamic enhancement of stability was seen only in those elbows in which the radial head component had been implanted. The radial head component is an important stabilizer, particularly in extension for this prosthesis, and possibly for other unlinked total elbow prostheses. Although instability of unlinked prostheses depends on the prosthetic design, the use of a radial head replacement may be an important factor in preventing such instability. Perhaps even more importantly, a radial head component balances the load distribution across the articulation, which could decrease stress on the ulnohumeral articulation and therefore possibly reduce polyethylene wear, osteolysis, and loosening.

Malleomyringoplasty using a silicone prosthesis.

Successful replacement of the sound conducting mechanism of the ear has been hampered by infection, perforation, prosthesis instability and extrusion. In this animal study on thirty rats a silicone prosthesis was inserted between two layers of fascia as a total replacement of the tympanic membrane and ossicular chain. After four months the graft was found to be intact without evidence of infection or extrusion in all but one of the 30 rats. These results justify a trial of a similar silicone prosthesis in humans.

Instability, migration and laxity of total hip prostheses. A roentgen stereophotogrammetric study.

Roentgen stereophotogrammetric analysis was used in the evaluation of clinical and/or radiographic problems in 28 total hip replacements without suspicion of infection. Instability of the acetabular and/or the femoral component was revealed in 14 cases. In 21 cases, examined twice, migration of the acetabular component was found in eight cases and migration of the femoral component in 15 cases. The method allows instability and migration of the prosthetic components as well as joint laxity to be determined with a high degree of accuracy.

Instability and wear of total hip prostheses determined with roentgen stereophotogrammetry.

A roentgen stereophotogrammetric analysis of hip prostheses was made in four patients with rheumatoid arthritis during a postoperative period of 2 years. Implanted tantalum balls, prosthetic femoral head, and ends of the wire in the acetabular socket were used as measurement points. The migration of the prosthetic head and the acetabular socket in relation to the pelvic bone was determined. The difference between the cranial migration of the head and the socket is a measure of the postoperative instability of the hip joint and deformation of the prosthetic components. This deformation occurs in the plastic acetabular socket and is mainly due to wear. The roentgen stereophotogrammetric method can be applied to standard hip orostheses with a metal femoral head and a plastic or metal acetabular socket to study migration or loosening of the prosthesis in relation to the supporting bone, prosthesis instability, and deformation of the prosthetic components.

Magnets to Stabilize Dentures

Despite the progress made in prosthodontics, much remains to be done before both dentist and patient are wholly satisfied. Most dentists are constantly investigating new, different and presumably better methods of constructing dentures. And far too many patients gravitate constantly from dental office to dental office in an effort to obtain more satisfactory service. Probably the time will never arrive when all dental prosthetic problems will be solved completely, but in the meantime, the best minds in the profession will be turned toward its solution. Embedding small but powerful magnets in the molar region of dentures is another method de­ vised to overcome prosthesis instability, a problem which Joshua Greenwood at­ tempted to solve with spiral springs. In providing a full upper or lower denture, a dentist is expected to fabricate a structure which is to be placed on a foundation that is neither rigid nor uni­ formly yielding. He must place that den­ ture so exactly that it will mesh precisely with an opposing denture. Moreover, it must be stabilized in the presence of, and despite the interference of, the movable tissue that is continually trying to dis­ lodge it. Not only must the base be firm, it must be seated comfortably on the tissue; the patient must never be con­ scious of this foreign object in his or her mouth. Discomfort to the patient gen­ erally is accompanied by atrophy or pressure which causes the underlying ridge to change more rapidly than it would normally. The difficulty of this problem is indi­ cated by the radical methods some men are adopting to serve the edentulous pa­ tient. Without attempting to evaluate the merits of the procedure, implant dentures must be considered a radical procedure. Men are resorting to it only after the conventional technics fail to produce den­ tures that patients can wear confidently and comfortably. The use of magnetized dentures may be termed a radical pro­ cedure, but it is a procedure that can be evaluated, and its worth can be proved without difficulty to the patient or the dentist.