Jerome J. Klawitter

Long-Term Follow-up of Pyrolytic Carbon Metacarpophalangeal Implants*

BACKGROUND The metacarpophalangeal joint is the most commonly involved joint when rheumatoid arthritis affects the hand. Many prosthetic implants have been designed for the replacement of this joint. Although studies of these implants have shown relief of pain, they have generally demonstrated a poor range of motion, progression of ulnar drift, and bone loss, as well as failure, fracture, and dislocation of the implant. METHODS From December 1979 to February 1987, 151 pyrolytic carbon metacarpophalangeal implants were inserted in fifty-three patients. The implants had an articulating, unconstrained design with a hemispherical head and grooved, offset stems. Forty-four patients had rheumatoid arthritis; five, posttraumatic arthritis; three, osteoarthritis; and one, systemic lupus erythematosus. Three patients (eleven implants) were lost to long-term follow-up, and twenty patients (fifty-one functioning implants) died after the implant had been in situ for an average of 7.2 years. Eighteen implants (12 percent) in eleven patients were revised. Fourteen of the eighteen implants were replaced with a silicone-elastomer or another type of implant, and the remaining four were removed and a pyrolytic carbon implant was reinserted with the addition of bone cement or bone graft, or both. Twenty-six patients (seventy-one implants) were available for long-term review at an average of 11.7 years (range, 10.1 to 16.0 years) after implantation. RESULTS The implants improved the arc of motion of the fingers by an average of 13 degrees and elevated the arc by an average of 16 degrees. As a result, fingers were in a more functional, extended position. A complete set of preoperative, postoperative, and follow-up radiographs was available for fifty-three of the seventy-one implants that were followed long term. There was a high prevalence of joint stability: fifty (94 percent) of the fifty-three implants were in a reduced position postoperatively, and forty-one (82 percent) of those fifty implants were still in the postoperative reduced position at the time of long-term follow-up. Ulnar deviation averaged 20 degrees preoperatively and 19 degrees at the time of follow-up, with only the long finger having an increase in deviation. No adverse remodeling or resorption of bone was seen. Fifty (94 percent) of the fifty-three implants had evidence of osseointegration, with sclerosis around the end and shaft of the prosthetic stems. Radiolucent changes were seen adjacent to twelve implants. There was minimum-to-moderate subsidence (four millimeters or less) of thirty-four implants; most of the subsidence occurred immediately postoperatively. Survivorship analysis demonstrated an average annual failure rate of 2.1 percent and a sixteen-year survival rate of 70.3 percent. The five and ten-year survival rates were 82.3 percent (95 percent confidence interval, 74.6 to 88.2 percent) and 81.4 percent (95 percent confidence interval, 73.0 to 87.8 percent), respectively. None of the revised implants had any visible changes of wear or deformity of the surfaces or stems. Four instances of chronic inflammatory tissue and three instances of proliferative synovitis were noted histologically. Focal pigment deposits were seen in three fingers, one of which had removal of the implant two months after a fracture. No evidence of intracellular particles or particulate synovitis was found. CONCLUSIONS The results of this study demonstrate that pyrolytic carbon is a biologically and biomechanically compatible, wear-resistant, and durable material for arthroplasty of the metacarpophalangeal joint.

Stress Analysis of Porous Rooted Dental Implants

A two-dimensional plane stress finite element analysis of porous rooted dental implants was performed. The results of this analysis were compared to results obtained from mechanical tests performed on actual implanted specimens. The appropriate selection of interface material properties was shown to be highly significant.

An Evaluation of Porous Alumina Ceramic Dental Implants

The fabrication, characterization, and clinical results of porous rooted alumina dental implants in animals are presented. Failures of all implants occurred in less than six months and were attributed to the presence of microporosity on the crown and cervical portion of the implant which prevented the establishment of an effective bialogical seal between the oral cavity and the alveolus.

Pyrolite carbon implants in the metacarpophalangeal joint of baboons.

A nonconstrained uncémented Pyrolite carbon prosthesis was evaluated for replacement of the metacarpophalangeal joint. Six prostheses were inserted into the long finger metacarpophalangeal joint of four baboons. Nine months after insertion, the prostheses and surrounding tissues were removed enbioc and evaluated radiographrca/ly, utilizing histologic and microradiographic analyses. The four Pyrolite carbon implants inserted without cement were well tolerated. Histological evidence of direct appositional bone fixation along the medullary stem was observed in one specimen, and a combination of bone fixation with an interposing fibrous tissue membrane was observed in another. There was no evidence of bone resorption around the implant stems, and functional fixation was obtained with all of the uncemented Pyrolite carbon implants. No foreign body reaction was observed in the soft tissues, and no evidence of intracellular particles was present. Two cemented implants (one Pyrolite carbon and one polyethylene and metal) were also evaluated; both showed evidence of bone resorption and/or gross implant loosening.This study has demonstrated the potential for biological fixation with Pyrolite carbon-stem med implants for prosthetic replacement of the metacarpophalangeal joint, which thus offers significant improvement as a material for joint reconstruction.

Clinical, Radiographical, and Histological Evaluation of Porous Rooted Polymethylmethacrylate Dental Implants

Forty-three porous rooted polymethylmethacrylate (PMMA) dental implants were inserted into twenty-four dogs. Successful implants were maintained for up to three years. Histological sections with the implants in situ of implants revealed a soft tissue-implant interface similar to natural teeth. Bone and fibrous tissue ingrowth into the pores attached the implant to the bone. Failures were attrabuted to mechanical weakness of the implant, thin buccal cortical bone, and excessive implant-gingiva interface.

Compatibility of Bioceramics with the Physiological Environment

When prosthetic materials are placed in the body, consideration must be given to (1) the effect of the physiological environment upon the prosthetic metal, medical polymer, or bioceramic, and (2) the effect of the prosthetic material and its corrosion or degradation products upon the fluids and tissues of the surrounding environment. The interaction which occurs between biomedical materials and the physiological environment is discussed with emphasis on the mechanism of biocorrosion, biodegradation, and wear as well as on the toxicology of implant materials. Since bone and soft tissue invade certain physiologically acceptable porous ceramic materials, there is reason for optimism that ceramics will become very useful materials of construction for orthopedic and oral appliances.

Characterization of Tissue Growth into Pellets and Partial Sections of Porous Porcelain and Titania Implanted in Bone

Porous titania and porous porcelain were selected for this investigation* because of their chemical inertness and ease of fabrication. Titanium metal implants have demonstrated a high degree of tissue tolerance1,2; these are certain to have maintained some oxide layer on the surface. Also, porcelain was shown to be non-toxic when implanted intramuscularly in rabbits3.